JP7516385B2 - Process for preparation of concrete equipment, concrete mix, method for preparing concrete mix - Google Patents

Description

CLAIM OF PRIORITY This application claims priority to Provisional Application No. 62/765,597, filed September 1, 2018, which is incorporated by reference in its entirety for all that it teaches without exclusion.

The use of additional cementitious materials in concrete to improve concrete properties, such as water impermeability, compressive strength, and abrasion resistance, is well known. Various types of particulate silica, such as silica fume, have been used in concrete as additional cementitious materials to improve water impermeability and compressive strength. A common problem with silica is that it increases the water demand of the concrete mix, which can result in a higher likelihood of large amounts of bleeding water, thus increasing the likelihood of capillary and void formation during curing. Even when relatively large amounts of silica fume are used to reduce bleeding water, the water is usually kept to a minimum (often 5-10 weight percent of the cementitious material). In many cases, the water is carefully apportioned so that the water:cementitious material ratio is present in a relative amount less than about 0.5. (Design and Control of Concrete Mixtures, 16th Edition, 2nd Printing (Revised), Kosmatka, Steven H.; p. 156). Such small amounts of water, typically less than those recommended by cement manufacturers, can significantly impair the rheology of the concrete mix, making it difficult to pour or work with. At such low water contents, materials such as superplasticizers may be required.

In a prior application (Application No. 16/501,232, filed March 8, 2019, incorporated by reference in its entirety for all that it teaches without exclusion), concrete and preparation methods are disclosed that include small particle size, high surface area amorphous silica used in cement at only about 0.1 to about 4 ounces per 100 weight percent of cementitious material, much less than is commonly used in the industry for structural purposes. In another aspect, improved concretes are prepared by process-specific addition of silica. These improved concretes can be prepared using standard amounts of water recommended by the cement manufacturer, or even more than the recommended amount, without significantly compromising compressive strength. Such results are truly surprising. Despite the use of such amounts of water, little or no bleeding water is observed during curing. Capillary and void formation is minimized or essentially completely inhibited, and more water is retained in the concrete during curing, allowing more water to participate in hardening over a longer period of time, resulting in greatly improved compressive strength.

Despite their relatively high water tolerance, the low-silica concretes described above have, among other improved properties, improved compressive strength and abrasion resistance. The improvement in compressive strength is surprising given the low amount of silica used, whereas known methods sometimes use very high amounts to achieve very little gain. Furthermore, significant improvements in the abrasion resistance of concrete have not generally been observed using silica, e.g., silica fume, even in greater amounts than typically used (id, p. 159). The low-silica concretes described in the aforementioned application (U.S. Provisional Patent Application No. 62/761,064) significantly improve abrasion resistance as measured by the test ASTM C944 (with respect to the aforementioned standard, it should be noted that the version using the 22 pd, 98 kg load was used herein with all reference to that standard). Standard concretes (i.e., not containing the high surface area amorphous silica described below) may have values ranging from about 2.5 to about 4.0 grams loss. The low silica concrete described herein may have an ASTM C944 value of 1.1 grams loss or less.

Surprisingly, in the present case, as disclosed below, it has been found that the use of both 1) amorphous silica as disclosed in the above application, and 2) counterintuitively, admixtures with a mixture containing a concrete re-emulsifier (cutting agent), can improve the abrasion resistance even for cements prepared with only amorphous silica, not to mention for typical cements (i.e., cements prepared without amorphous silica or cutting agents). It has been found that the abrasion resistance can be improved so that the ASTM C944 loss can be as low as 0.6 grams or less. Furthermore, the concrete of the present invention has been observed to generally have a significantly reduced water absorption both during and after curing (finishing water absorption during curing, and water absorption during use, i.e., after curing, are primarily the result of capillary formation during curing, as water migrates to the surface during curing). In some cases, water absorption during and/or after curing can be completely eliminated. Such results are unexpected in that the admixtures include compounds commonly used to re-emulsify concrete. Concrete cutting agents have been used in the concrete industry to dissolve hardened (i.e. cured) concrete deposits from equipment used in the manufacture and processing of concrete, such as ready mixes, power trowels, etc. It was expected that the presence of a re-emulsifier, which has the ability to destroy the structure of hardened concrete (the C-S-H matrix), would thin the concrete mix, impede hardening, or otherwise adversely affect the hardened structure of the concrete by allowing water migration during curing. However, when used in combination with silica as described below, not only does the concrete harden, but little or no bleeding water is typically observed during the curing of the concrete of the present invention. Additionally, as noted above, the hardened concrete has superior abrasion resistance to conventional concrete as well as concrete prepared with silica admixtures alone.

Surprisingly, concrete can achieve a high degree of water impermeability without undergoing a finishing step (see, for example, Example 2, which describes the production of footings that exhibit density and impermeability). Thus, the concrete of the present invention is particularly suitable for exterior concrete applications. Generally, exterior concrete, e.g., sidewalks, curbs, parking lots, do not require extensive finishing, although some degree of troweling may be performed. Small surface defects can usually be left as they are, and eventually the surface weathers away, leaving the defect problem unresolved. However, water damage during the life of the concrete is a problem for exterior concrete. One measure taken is the application of hardeners and sealants. The protection provided by these chemicals is generally short-lived. Another measure is the use of air-entrained concrete to minimize damage from absorbed water during freezing. In practice, neither measure is a long-term solution to the problem of freeze damage. However, the hardened concrete of the present invention usually absorbs very little or no water at all. Neither separate finish nor sealant application is required. Furthermore, the concrete therefore does not typically require air entrainment to resist freeze-thaw damage.

Standard water absorption for outdoor cement by the Rilum test is about 1.5 to 3 ml in 20 minutes. The surface of the concrete of the present invention essentially did not absorb water, despite the absence of a finishing step. For example, the Rilum test is expected to provide a 20 minute absorption of about 0 to about 1.0 ml in 20 minutes. Without wishing to be bound by theory, it is speculated that the concrete of the present invention may not develop surface defects and capillaries that are problematic in other concretes, or that the concrete of the present invention may significantly reduce their development.

More notably, when the concrete of the present invention is finished, the surface that develops can be plastic-like (the extent of which can be controlled by the details of the finishing process, as described below) that significantly reduces the amount of friction against the finishing blade when compared to standard concrete finishes. Increasing the finishing speed relative to standard concrete finishing speeds generally further facilitates achieving a glossy surface with a plastic-like consistency.

Generally, the finish of concrete prepared with existing methods and formulations improves surface smoothness and planarity, and to some extent improves with increased finishing time. Such concretes can be finished by hand or with a riding power trowel, with the use of a riding power trowel generally providing a faster, more uniform, and higher quality finish than a hand trowel. Regardless of the finishing method selected, however, the concretes of the present invention generally finish faster (i.e., require less time to reach a given degree of gloss) and have higher gloss potential (e.g., as measured by a gloss meter) with respect to the finishing process. With respect to the latter, it can be expected that the use of faster speeds than conventional (especially once the surface reaches a point where gloss enhancement essentially stops at lower speeds) will result in glosses that exceed those possible with existing concretes.

Such faster finishing speeds are generally easier to use with the concrete of the present invention because of reduced friction. Additionally, the admixtures provided herein generally provide concrete that requires less finishing effort throughout the finishing process to obtain a finished surface. Whether the finisher is working with a hand trowel or a riding power trowel, the finisher can typically feel the difference in friction between the trowel or finishing blade, and the friction of the floor surface is generally significantly less than a floor surface without the admixture of the present invention. Generally, the time required to finish a floor surface to a given gloss with a finisher is reduced for a given finisher speed (rpm). Additionally, a faster finishing speed (about 190-210 rpm) may be required than would normally be used for finishing speeds (about 180-about 190 rpm), but the surface can be finished to a higher gloss than a conventional concrete surface. Newer finishers may have slower top speeds (180 or 190 rpm) than older machines (200 or 210 rpm) because it is apparently believed within the industry that fast finishing speeds are not necessary. Therefore, it may be necessary to use older model machines to get the excellent surface that is obtained with the concrete of this invention.

While not wishing to be bound by theory, it is believed that the heat of curing promotes a reaction between the high surface area amorphous silica and the components of the "re-emulsified" admixture to form a plastic-like component throughout the concrete. Finishing at high speeds promotes this reaction at the surface and may prevent some of that reaction from occurring within the bulk of the concrete due to heat dissipation at the surface. While not wishing to be bound by theory, it is believed that the formation of a plastic-like material promoted by the heat generated by finishing at high finishing speeds (i.e., typically 200 rpm or greater) results in a surface with an improved gloss compared to that possible with conventional concrete.

It is noted in the art that the finishing of the concrete surface can affect the water impermeability of the slab. "Closing the slab," i.e., finishing the slab using techniques that involve the repetitive, directional application of finishing machinery known in the art, is a finishing method that can reduce water permeability. While such methods can be applied to the concrete of the present invention, the concrete of the present invention exhibits surprisingly high water impermeability, or complete water impermeability even without further finishing steps.

It should also be noted that the surface of the concrete of the present invention is generally harder than concrete of conventional methods and formulations. Generally, most concretes increase in hardness with curing time. For example, most concretes prepared according to existing methods have a hardness in the range of about 4 to about 5 on the Mohs Hardness Scratch Test about 28 days after pouring. It is not uncommon for the concrete of the present invention to achieve such hardness after a length of time in the range of about 3 to about 8 days (about 72 to about 192 hours) after pouring. After about 28 days, it is not uncommon for the concrete of the present invention to have a hardness in the range of about 6 to about 9, or in many cases, a hardness in the range of about 7 to about 8.

The method of the present invention is preferably used as an admixture with concrete mixes containing amorphous silica (such as those prepared as described in the section below entitled "Novel Compositions for Improving Concrete Performance"). Admixtures for use with the compositions of the foregoing section are described herein, and methods for their use in these mixes are fully described. Without wishing to be bound by theory, it is believed that the use of silicas not described herein, e.g., having particle sizes larger than those described herein, may provide some limited benefit of the invention, but will likely be more difficult to pour, process, and finish than concretes prepared with low particle size, high surface area amorphous silica.

Shown is a concrete slab containing 4 ounces of E5 Internal Cure per 100 weight percent. E5 Finish is typically used on surfaces as a finish at a rate of 1000 square feet per gallon. The burnishing process was started immediately after the finishing step was completed. Figure 1 shows an undamaged surface despite a 27 inch burnisher operating at 2500 rpm. The photo is of topically applied E5 Finish, but as shown, an admixture application of E5 Finish will produce the same results. It shows the surface changed from about Grade 1 to about Grade 2. The photo is of E5 Finish applied topically, but as shown, an admixture application of E5 Finish would achieve the same results.

The following is a detailed description of the admixture formulations that can be used in the present invention. Although the invention disclosed in this provisional application refers to Korkay Concrete Dissolver ("Korkay"), a formulation available on March 20, 2017 from Tate's Soaps and Surfactants, those skilled in the art will recognize that Korkay and its aqueous dilutions are chemical formulations, and that such chemical formulations can be prepared by a variety of different ingredients and/or methods and are suitable for use in the present invention to obtain the benefits of the present invention. In one embodiment, the admixture composition comprises or consists essentially of an aqueous dilution of Korkay.

It should be recognized that formulations containing the same chemical components of Korkay or aqueous dilutions thereof may be useful in the present invention in which the concentration of one or more components not including water therein deviates from the concentration relative to Korkay or aqueous dilutions by less than 50, 40, 30, 20, 10 or 5 weight percent, respectively, based on the weight of Korkay or aqueous dilutions thereof. Such chemical compositions may be used in the amounts and proportions recommended above.

In another embodiment, the admixture comprises water, or comprises or consists essentially of water, an alpha-hydroxy acid, a glycol alkyl ether, and a polyethylene glycol having an average molecular weight in the range of about 500 to about 1500 mw. In a further embodiment, the alpha-hydroxy acid contains in the range of about 5 to about 1 carbon, with glycolic acid being preferred. Glycolic acid is commercially available from Chemsolv. The glycol alkyl ether is preferably polypropylene methyl ether, with dipropylene glycol methyl ether being preferred. Dipropylene glycol methyl ether is commercially available from a number of sources, e.g., Dow Chemical, Lyondell Bassell, Shell. The polyethylene glycol having an average molecular weight in the range of about 500 to about 1500 molecular weight is preferably polyethylene glycol having an average molecular weight in the range of about 750 to about 1250 molecular weight, with a molecular weight range of about 950 to about 1050 being even more preferred. One example of a suitable polyethylene glycol is PEG(1000).

In another embodiment, the alpha-hydroxy acid is preferably present in the admixture in a range of about 5 to about 20 weight percent, with a weight percent in the range of about 10 to about 15 weight percent being more preferred. The weight percent of the glycol alkyl ether is preferably in a range of about 5 to about 20 weight percent, with a weight percent in the range of about 10 to about 15 weight percent being more preferred. The weight percent of the polyethylene glycol is preferably in a range of about 1 to about 15 weight percent, with a ratio in the range of about 1 to about 9 weight percent being more preferred. Water is present in a range of about 70 to about 80 weight percent, with a weight percent in the range of about 71 to about 77 weight percent being more preferred.

In a further embodiment, the admixture comprises the following four parts:
1) 74% water,
2) 13% glycolic acid;
3) 8% dipropylene glycol methyl ether (DPM glycol ether);
4) 5% polyethylene glycol (PEG 1000 type);
Preferably, the dilution comprises, consists of, or consists essentially of 1 part mixture to about 4 to about 20 parts water, with a dilution of about 5 to about 12 parts water being more preferred, a dilution of about 6 to about 8 parts water being even more preferred, with a range of about 6.5 to about 7.5, or even about 6.8 to about 7.2 being especially preferred. By components equivalent to such dilutions, or "component equivalents," it is meant that the admixture comprises, consists of, or consists essentially of the same components and relative proportions as set forth above, but that the admixture was not prepared by the specified dilution.

In other embodiments, the admixture added to the concrete mix (e.g., prepared with the amount of amorphous silica described in U.S. Provisional Application No. 62/765,597 or recited herein and added to the ready mix containing the concrete mix) comprises, consists of, or consists essentially of about 4 to about 20 parts by weight of Korkay to 1 part by weight of water, with about 5 to about 12 parts by weight of water being more preferred, and about 6 to about 8 parts by weight of water being even more preferred. (The E5 Finish formulation can be formed by producing a mixture containing about 7 parts by weight of water to about 1 part by weight of Korkay). In some embodiments, the admixture comprises the E5 Finish formulation. In other embodiments, the admixture comprises a water-diluted or water-removed concentrate of E5 Finish or a chemically identical preparation as described above. In other embodiments, the admixture comprises, or consists essentially of E5 Finish. In further embodiments, the aforementioned admixtures are added to the ready mix in an amount ranging from about 0.5 to about 8 ounces per 100 pounds of cement, with about 2 to about 5 ounces per 100 pounds of cement being preferred, with about 2.5 to about 3.5 ounces per 100 pounds of cement being even more preferred, and with about 2.8 to about 3.2 ounces per 100 pounds of cement being most preferred.

For amounts of E5 Finish above about 5 ounces per 100 weight of cementitious material, or for amounts of amorphous silica above about 5 ounces per 100 weight of cementitious material, the observed benefits of the present invention may begin to diminish in that, in some cases, increased brittleness and decreased compressive strength may be observed. For a given content of amorphous silica (or E5 Internal Cure) and Korkay (or E5 Finish) within the preferred (or broadest) ranges set forth herein, generally, some decrease in abrasion resistance, water impermeability, and compressive strength may be expected when varying the amount of amorphous silica from about 4 ounces per 100 weight, or the amount of E5 Finish from about 3 ounces per 100 weight.

It should be noted that the formulations are generally used as admixtures, and therefore they are prepared in a predetermined ratio and added to the bulk concrete mix, e.g., small particle size amorphous silica, e.g., ready mixes, including concrete mixes described below. Such addition of the admixture is most preferred. However, it may be acceptable to add the components of the admixture separately. For example, it may be acceptable to add part or all of one or more of the water, glycolic acid, dipropylene glycol methyl ether, or polyethylene glycol components to the concrete mix, especially after the mix has been thoroughly mixed and before adding the remainder of the admixture. For example, the concrete mix can be prepared with at least a portion of the water allocated to the admixture. In such a situation, it should be understood that in ascertaining the amount of water in the concrete mix and the admixture, the total amount of water should be considered as the sum of two partial amounts, one of which is within the total amount of water permitted for the concrete mix and the other is within the total amount of water permitted for the admixture. Such separate addition of the components may provide some of the benefits of the invention. However, for optimal results, it is highly preferred to use an embodiment of the admixture as described herein. A mixture of its components, namely, a mixture containing alpha-hydroxy acid, glycol alkyl ether, polyethylene glycol and water, is added to a ready mix containing a mixed concrete mixture containing amorphous silica, as described below.

Without wishing to be bound by theory, it is believed that the heat generated during concrete curing (as a result of the admixtures used in preparing the concrete) aids in the formation of a tough, plastic-like matrix throughout the concrete during curing as a result of the admixture's components interacting with the amorphous silica in the concrete. Such a result is demonstrated by experiments in which E5 Internal Cure was mixed directly with E5 Finish under heat in a container, resulting in a tough, translucent or transparent material believed to be a matrix material.

The admixture is mixed into the concrete mix, optionally including amorphous silica, which can be added as E5 Internal cure. Typically, the concrete mix includes amorphous silica having particles with an average particle size of less than about 55 nm, and in some embodiments less than about 7.8 nm, or in other embodiments from about 5 to about 55 nm or from about 5 to about 7.9 nm, and having a surface area in the range of about 430 to about 900 ^m2 /g, and present in the concrete in a weight ratio of about 0.1 to about 4 ounces of amorphous silica per 100 pounds of cement (i.e., not including water, aggregate, sand, or other additives).

Amorphous silica from other sources may be suitable as long as it is characterized by the particle size parameters above. Non-limiting examples of suitable amorphous silica include colloidal silica, precipitated silica, silica gel, and fumed silica, with colloidal silica or silica gel being preferred. It is more preferred to use particles having an average particle size of less than about 25 nm, and even more preferred to have an average particle size of less than about 7.9 nm. A more preferred weight ratio in concrete is about 0.1 to about 3 ounces of amorphous silica per 100 pounds of cement (not including water, aggregate, sand, or other additives). An even more preferred weight ratio in concrete is about 0.1 to about 1 ounce of amorphous silica per 100 pounds of cement (again not including water, aggregate, sand, or other additives).

In yet another embodiment, amorphous silicas having a surface area in the range of about 50 to about 900 ^m2 /gram are preferred, with about 150 to about 900 ^m2 /gram being more preferred, and about 400 to about 900 ^m2 /gram being even more preferred. Amorphous silicas having an alkaline pH are preferred, with a pH in the range of 8 to 11 being more preferred.

In yet another embodiment, the amorphous silica is provided by using E5 INTERNAL CURE, an additive commercially available from Specification Products LLC. In one embodiment, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 20 ounces of E5 INTERNAL CURE to 100 pounds of cement (not including water, sand, aggregate, or other additives). More preferably, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 10 ounces of E5 INTERNAL CURE to about 100 pounds of cement (not including water, sand, aggregate, or other additives). Even more preferably, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 5 ounces of E5 INTERNAL CURE to about 100 pounds of cement (not including water, sand, aggregates, or other additives). The ideal value is in the range of about 3 to 5, or about 4 ounces per 100 pounds by weight.

Surprisingly, using more than about 20 ounces of E5 INTERNAL CURE per about 100 pounds of cement (not including water, sand, aggregates, or other additives) or more than about 5 ounces of amorphous silica per about 100 pounds of cement (not including water, sand, aggregates, or other additives) may result in no benefit in that no or only minimal beneficial water or compressive strength benefits may be observed.

The order of addition of the amorphous silica and admixtures (non-limiting examples include E5 Internal Cure and E5 Finish, respectively) is important to realize maximum benefit from the process, composition, and concrete of the present invention. For example, it is highly preferred to add the amorphous silica to the cement mix before adding the cutting agent-containing admixture.

The amorphous silica is preferably mixed with the cement mixture in accordance with the section below entitled "Novel Compositions for Improving Concrete Performance."

Concrete mix is made from ingredients including certain amounts of a) dry cement mix, b) water, c) amorphous silica, d) aggregates and/or sand.

Dry concrete mixes generally have a recommended water content that provides a water/cement ratio that provides the concrete mix with a combination of desirable pouring and hardening properties. In some cases, the recommended water content spans a wide range of water contents. As shown below, the initial water content of the concrete mix before pouring can cause problems during curing and finishing that reduce the quality of the resulting concrete installation (slab, footing, etc.). To reduce water-borne structural defects in the hardened concrete, water-reducing measures, such as "water reducers" and superplasticizers, are typically used. Although the advantages of the present invention should be apparent in situations where the water content is reduced from that recommended by the manufacturer, it should be noted that the present invention can be used to provide a concrete of the present invention in situations where the water included in the concrete mix is equal to or greater than that specified by the manufacturer of the dry cement mix. Water reducers in the concrete mix are generally not required.

Thus, in broad aspects, the cement mix and water are present in the concrete mix in the following proportions:
The amount of water and the amount of dry cement mix, said cement mix comprising:
i) a water/cement ratio value recommended by the manufacturer; wherein the recommended ratio is in the range of about 0.35 to about 0.65, and when mixed with an amount of water, the water/cement ratio is greater than a value corresponding to about 10% less than the recommended value, but less than a value corresponding to about 30% more than the recommended value;
or
ii) a range of water/cement ratios recommended by the manufacturer, having upper and lower limits, which, when mixed with an amount of water, will result in a water/cement ratio greater than a value corresponding to about 10% less than the lower limit and less than or equal to a value corresponding to about 30% more than the upper limit;
or
iii) an amount such that when mixed with the amount of water, the water/cement ratio is in the range of about 0.35 to 0.65;
It is characterized by:

The advantages of the present invention are expected to be apparent generally through the use of commercially available types of Portland cement. The cement mix may be one or more types commonly used in construction, e.g., Types I, II, III, IV and V Portland cement.

The amount of water mentioned above is added to the cement mix. This amount includes all water mixed with the concrete mix including at least the cement mix, except for water introduced with silica in the case of water-containing formulations of silica, such as colloids, dispersions, emulsions, etc., as well as water introduced with cutting agent-containing admixtures. As described in more detail below, water can be mixed with the concrete mix including at least the cement mix in multiple portions, for example, a first portion of water is mixed with the concrete mix and stirred for a period of time, followed by the addition of a second portion of water (e.g., "tail water") to mix with the concrete mix including at least the cement mix. It should be noted that after the concrete has partially set, water may be applied to the surface of the concrete to prevent premature drying of the surface, which may cause shrinkage, and subsequent processing and finishing difficulties. This "finishing" water is not included in the amount of water. In other embodiments, the water/cement ratio is in the range of about 0.38 to 0.55, or in more specific embodiments, in the range of about 0.48 to about 0.52, or in the range of about 0.38 to about 0.42.

In relation to i), ii) and iii) above, in a more preferred embodiment, the water and cement mix are present in the concrete mix in a ratio at the time of mixing of the amount of dry cement mix to the amount of water, the water/cement ratio being:
At least the recommended value, but not exceeding the value equivalent to 30% more than the recommended value, or
The preferred range is equal to or greater than the upper limit, but equal to or less than a value equivalent to more than about 30% above the upper limit, or at least 0.35 and 0.65.

The particle size of the amorphous silica is particularly important. Larger particle sizes, such as those found in micronized silica, generally do not reduce the formation of capillaries and voids to the extent seen when amorphous silica of the size specified herein is used in the specified amounts. The concrete mix of the present invention preferably comprises an amount of amorphous nanosilica present in an amount ranging from about 0.1 to about 7.0 ounces per 100 weight (cwt) of cement of a) and has a particle size such that the average silica particle size is in the range of about 1 to about 55 nanometers, and/or the surface area of the silica particles is in the range of about 300 to about 900 m ² /g, or in other embodiments, in the range of about 450 to about 900 m ² /g.

Amorphous silica from a variety of sources is generally suitable, so long as it is characterized by the particle size and surface area parameters described above. Non-limiting examples of suitable amorphous silica include colloidal silica, precipitated silica, silica gel, and fumed silica. However, colloidal amorphous silica and silica gel are preferred, with colloidal amorphous silica being most preferred.

In further embodiments, the silica particle size is in the range of about 5 to about 55 nm. Particles having an average particle size of less than about 25 nm are preferred, particles having an average particle size of less than about 10 nm are more preferred, and particles having an average particle size of less than about 7.9 nm are even more preferred. A preferred weight ratio in concrete is about 0.1 to about 3 ounces of amorphous silica per 100 pounds of cement (without water, aggregate, sand, or other additives). A more preferred weight ratio in concrete is about 0.1 to about 1 ounce of amorphous silica per 100 pounds of cement (again without water, aggregate, sand, or other additives). Even more preferred is about 0.45 to about 0.75 ounces of amorphous silica per 100 pounds of cement (again without water, aggregate, sand, or other additives). Surprisingly, above about 3 to about 4 ounces of amorphous nano-silica per 100 pounds of cement mix, the concrete mix may become difficult to pour or process, and compressive strength may be significantly reduced, even relative to non-silica controls. Otherwise, amounts above about 1 ounce per 100 pounds of cement generally reduce the increase in compressive strength relative to the preferred range of about 0.45 to about 0.75 ounces of amorphous silica per 100 pounds of cement. The given preferred range is the most economically feasible range, i.e., beyond which the increase in compressive strength per additional unit of silica becomes less, and the cost of silica per unit of increase in compressive strength may make the cost of concrete prohibitive.

Amorphous silicas having a surface area in the range of about 50 to about 900 ^m2 /gram are preferred, with about 150 to about 900 ^m2 /gram being more preferred, with about 400 to about 900 ^m2 /gram being even more preferred, with 450 to 700 ^m2 /gram or 500 to 600 ^m2 /gram being even more preferred. Amorphous silicas having an alkaline pH (above about pH 7) are preferred, with a pH in the range of 8 to 11 being more preferred.

In yet another embodiment, the amorphous silica is provided by using E5 INTERNAL CURE, an additive available from Specification Products LLC, which contains about 15% amorphous silica by weight in about 85% water by weight. The silica particles are characterized by an average particle size of less than about 10 nm (as measured by the BET method) and a surface area of about 550 ^m2 /g. In one embodiment, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 20 ounces of E5 INTERNAL CURE to 100 pounds of cement (without water, sand, aggregate, or other additives). More preferably, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 10 ounces of E5 INTERNAL CURE to about 100 pounds of cement (without water, sand, aggregate, or other additives). More preferably, the weight ratio of E5 INTERNAL CURE to cement ranges from about 1 to about 5 ounces of E5 INTERNAL CURE to about 100 pounds of cement, and even more preferably, from about 3 to about 5 ounces of E5 INTERNAL CURE to about 100 pounds of cement (without water, sand, aggregates, or other additives). Surprisingly, using more than about 20 ounces of E5 to about 100 pounds of cement (again without water, sand, aggregates, or other additives) can be beneficial in that no, or only minimal, additional beneficial water or compressive strength benefits may be observed. The resulting concrete mix may be difficult to pour, and the resulting concrete may be of poor quality. It is noted that while the quality of the concrete decreases as one moves away from the preferred range of about 3 to about 5 ounces per 100 pounds of cement, the compressive strength may still be improved over that without the E5 INTERNAL CURE colloidal amorphous silica. In a preferred embodiment, the colloidal silica added to the concrete mix ranges from about 40 to about 98% silica by weight, with 60-95% being preferred, 70-92% being more preferred, and 75-90% being even more preferred.

Aggregates and sand can be used in the concrete of the present invention in amounts generally known in the art for construction purposes. In one embodiment, the amount of aggregate and/or the amount of sand are used such that they total in amounts ranging from about 400 to about 700% bwoc by weight. Generally, the concrete mix is prepared with ingredients including a cement mix, water, and preferably an amount of aggregate and sand (sometimes referred to in the art as "coarse aggregate" and "fine aggregate", respectively). It is acceptable for the concrete mix to contain only one of the two, e.g., only sand or only aggregate, although it is preferred that the mix contains at least an amount of each. Sand and aggregate can contribute to the silica content of the cement mix and therefore affect (i.e., somewhat increase) the water requirement of the concrete mix. Generally, most types of aggregates suitable for the application in which the concrete is to be used can be used. Coarse aggregates include coarse, crushed limestone gravel, larger size clean crushed stone, etc., as well as fine aggregates, smaller size clean crushed stone, fine limestone gravel, etc. Similarly, many types of sand can be used, such as mountain (coarse) sand, river sand, etc. In general, for concrete applications, "coarse sand" is preferred over "free-flowing sand" which is known to be suitable for use in mortars. However, free-flowing sand is generally expected to have a different water requirement than coarse sand when used in the preparation of concrete. As is known in the art, weight-bearing applications may require coarse aggregates, such as coarse, crushed limestone. Such coarse aggregates are preferred for poured concrete applications, particularly for use in poured building slabs, such as coarse crushed limestone gravel and larger size clean crushed stone, as well as mountain sand.

The aggregate to sand ratio based on weight of cement (bwoc) is preferably in the range of about 2000 to about 4000 pounds per yard of dry cement mix (more preferably about 520 to about 610 pounds per yard, or about 560 to about 570 pounds per yard, and even more preferably about 564 pounds per yard). More preferably, the aggregate to sand mix ratio is in the range of about 2700 to about 3300 pounds per yard of dry cement mix. More preferably, the aggregate to sand mix ratio is in the range of about 2900 to about 3100 pounds per yard of dry cement mix. In another embodiment, the aggregate and sand weight is 50 to 90% by weight based on the weight of the concrete, with a range of about 70 to about 85% by weight being preferred. The relative amounts of aggregate and sand are not critical, but a range of about 20% to about 70% by weight sand based on the weight of the sand and aggregate mix is preferred, with a range of about 40% to about 50% by weight sand being preferred.

It has been found that even the small amounts of amorphous nanosilica necessary to provide the disclosed benefits, especially in commercial scale injections, can be detrimental to the injectability of the concrete mix and to the quality of the resulting concrete, even rendering the concrete unsuitable, if added to the cement mix before the water. The process of the present invention generally includes situations in which at least a portion of the amount of water is added before the amount of amorphous nanosilica is added, with at least a period of stirring between additions to distribute the water before the addition of the amorphous silica. In practice, water can be added later in the preparation process, if desired. For example, it is known practice to add water in two (or more) portions, e.g., one portion as "tail water" after the addition and stirring of the first portion. In one embodiment, the amorphous silica is added as colloidal silica with the second portion of water. In a preferred embodiment, the colloidal silica is added after the addition of water, which is added in two portions, with stirring after the addition of each portion.

Thus, more generally, the amount of water can be added in its entirety or in portions including an initial portion including a range of about 20% to about 95% by weight of the amount of water and a tail water portion including the remainder, the initial portion of water being mixed with the amount of cement mix and aggregate/sand component to form a first mix, and the amorphous silica being added to the mix including the cement mix, aggregate/sand component, and the initial portion of water amount to form a second mix. Even more preferably, the initial portion includes a range of 35 to about 60% by weight of the amount of water.

(The following three situations (i.e., "Situation 1", "Situation 2" and "Situation 3") correspond to i) adding silica after adding tail water, ii) adding silica before adding tail water, and iii) adding silica and tail water simultaneously, respectively.)

In the embodiment where split water is added, the tail water is 1) added to the first mix, or 2) added to the second mix, or 3) added to the first mix with the amorphous silica, the amorphous silica and the tail water being mixed together as necessary, and 1) the first mix is stirred for a time _t11 before the addition of the tail water, for a time _t12 after the addition of the tail water but before the addition of the amorphous silica, and for a time _t13 after the addition of the amorphous silica but before the addition of the admixture, or 2) the second mix is stirred for a time _t21 before the addition of the amorphous silica, for a time _t22 after the addition of the amorphous silica but before the addition of the tail water, and for a time _t23 after the addition of the tail water but before the addition of the admixture, or 3) the second mix is stirred for a time t21 before the simultaneous addition of the amorphous silica and the tail water. ₃₁ and then after addition of the silica but before addition of the admixtures, the concrete mix is stirred for a time t ₃₂ .

In situation 1), the second portion of water (tail water) is added to a concrete mix containing the first portion of water, cement mix, and sand/aggregate components, preferably at a mixing speed (e.g., in a ready mix) ranging from about 2 to about 5 rpm, with t ₁₁ preferably ranging from about 2 to about 8 minutes, more preferably from about 3 to about 6 minutes. Time t ₁₂ preferably ranging from about 0.5 to about 4 minutes, more preferably ranging from about 1 to about 2 minutes, with a mixing speed ranging from about 2 to about 5 rpm. Time t ₁₃ preferably ranging from about 2 to about 10 minutes, more preferably ranging from about 5 to about 10 minutes, with a relatively high mixing speed at a speed ranging from about 12 to about 15 rpm before adding the admixtures. After adding the admixtures and mixing as described below, the speed can be reduced to a speed ranging from about 2 to about 5 rpm for a period such as, for example, transport time to the injection site. Delivery time standards are set by the American Concrete Institute: for example, concrete must be poured within 60 minutes of the end of high speed mixing if the temperature is 90 F or above, and within 90 minutes if the temperature is below 90 F.

In situation 2), the second portion of water (tail water) is added to a concrete mix containing the first portion of water, the amount of cement mix and sand/aggregate components, and amorphous silica, preferably at a mixing speed (e.g., in a ready mix) ranging from about 2 to about 5 rpm, with t ₂₁ preferably ranging from about 2 to about 8 minutes, more preferably from about 3 to about 6 minutes. Time t ₂₂ preferably ranging from about 0.5 to about 2 minutes, more preferably from about 0.5 to 1 minute, with a mixing speed ranging from about 2 to about 5 rpm. Time t ₂₃ , the time immediately prior to adding the admixture, preferably ranging from about 2 to about 10 minutes, more preferably from about 5 to about 10 minutes, with a relatively fast mixing speed at a speed ranging from about 12 to about 15 rpm. After adding the admixture and mixing as described below, the speed can be reduced to a speed ranging from about 2 to about 5 rpm for a period such as, for example, transport time to the injection site. As noted above, shipping time standards are set by the American Concrete Institute.

In situation 3), the tail water is added to the first mix together with the amorphous silica, and the amorphous silica and tail water are mixed together as necessary, preferably at a mixing speed (e.g., in the ready mix) ranging from about 2 to about 5 rpm, with t ₃₁ preferably ranging from about 2 minutes to about 8 minutes, more preferably from about 3 to about 6 minutes. Time t ₃₂ , the time immediately prior to adding the admixture, is at a relatively high mixing speed at a speed ranging from about 12 to about 15 rpm, preferably ranging from about 2 to about 10 minutes, more preferably ranging from about 5 to about 10 minutes. After adding the admixture and mixing as described below, the speed can be reduced to a speed ranging from about 2 to about 5 rpm for a period such as, for example, transport time to the injection site. As noted above, transport time standards are set by the American Concrete Institute.

In another embodiment, once the entire amount of water has been added to the cement mix and aggregate/sand component amounts to form a mix, the mix is stirred for a time t _a before adding the amorphous silica, and the concrete mix is stirred for a time t _b before adding the admixtures. For wet batch processes, it is convenient to add the entire amount of water at once. Time t _a is preferably in the range of about 2 minutes to about 8 minutes, more preferably about 3 minutes to about 6 minutes, with a mixing speed (e.g., in a ready mix) in the range of about 2 to about 5 rpm. Time t _b is preferably in the range of about 2 minutes to about 10 minutes, more preferably about 5 minutes to about 10 minutes, with a relatively fast mixing speed in the range of about 12 to about 15 rpm. After adding and mixing the admixtures as described below, the speed can be reduced to a speed in the range of about 2 to about 5 rpm for a period such as, for example, transport time to the injection site. As mentioned above, standards for transport times are set by the American Concrete Institute. The advantages of the invention are generally observed in the case of a single addition of water, but in practice, splitting the water into two parts is generally adhered to. After mixing of the concrete mix containing the first part, the use of the second part has the advantage of washing out the poorly mixed cement mix from near the mouth of the barrel into the remainder of the ready mix.

The admixture is preferably added at the point where the mixture contains silica, and the silica-containing mixture is thoroughly mixed before the addition of the admixture. Thus, in addition to the above recommendations regarding silica addition, there are similar recommendations before and after the addition of the cutting agent-containing admixture, but before injection. These conditions are consistent with those described above. In a preferred embodiment, the silica-containing mixture is mixed at one or more speeds in the range of about 6 RPM and above for a total time of at least 3 minutes. In a more preferred embodiment, the silica-containing mixture is mixed at one or more speeds in the range of about 7 RPM to about 15 RPM, and more preferably in the range of about 12 to about 15 RPM, for a time in the range of about 5 minutes to about 15 minutes, more preferably in the range of about 5 minutes to about 10 minutes. After the aforementioned mixing step, the cutting agent-containing admixture is added. In a preferred embodiment, the mixture including the cutting agent-containing mixture is mixed at one or more speeds in the range of about 6 RPM and above for a total time of at least 3 minutes. In a more preferred embodiment, the cutting agent-containing mixture is mixed at one or more speeds in the range of about 7 RPM to about 15 RPM, and more preferably in the range of about 12 to about 15 RPM, for a time period in the range of about 5 minutes to about 15 minutes, and more preferably in the range of about 5 minutes to about 10 minutes.

Concrete mixes can be prepared in wet ("central mix") or dry ("transit mix") batch situations. In the wet batch mode, the dry ingredients are mixed with the amount of water in one of the ways described above, followed by mixing with the amorphous silica to obtain the concrete mix. The mix is stirred as described above, or introduced into the ready mix and stirred therein as described above. In essence, the wet batch and dry batch situations are similar, except that some of the wet batch procedures are performed outside the ready mix (e.g., at the plant). The dry batch process ("transit mix") is somewhat preferred. For example, 40±20%, or in a further embodiment, ±10%, of the total amount of water utilized in the preparation of the concrete mix, sand and coarse aggregate used in the batch is placed in the ready mix. The cement mix, coarse aggregate, and sand are mixed together and placed in the ready mix. The remaining water is then placed in the ready mix. Once the dry ingredients and water are thoroughly mixed, the amorphous silica is added and the mixture is mixed for 5 to 10 minutes. Mixing is preferably done at a relatively high drum rotation speed, for example, in the range of about 12 to about 15 rpm. Once the faster mixing is done, the batch can then be poured. However, it is acceptable to have a time between high speed mixing and pouring, for example, transportation time to the pouring section. Generally, as long as the concrete is mixed at a low speed, for example, about 3 to about 5 rpm, a time between high speed mixing and pouring in the range of about 1 to about 60 minutes is acceptable.

In one embodiment, it is particularly convenient to add silica to the ready mix, which includes water, cement, and other dry ingredients, once the ready mix arrives at the injection site. It has further been found that after the amorphous silica has been added, the concrete/silica mixture should be mixed for a period of time, most preferably at least about 5 to about 10 minutes, before injection. However, other periods may be acceptable with respect to at least partially obtaining the benefits of the present invention.

The benefits of the present invention can be expected in commercially used variations of the aforementioned process so long as the amorphous silica is added last after blending the dry ingredients with the first and second portions of water (or with the second portion of water) and the mixture with added silica is blended for the times specified herein before injection.

In a preferred embodiment, it is particularly convenient to add the silica to the ready mix, which includes water, cement, and other dry ingredients, once the ready mix has arrived at the injection site. Furthermore, it has been found that after the amorphous silica has been added, the concrete/silica mixture should be mixed, for example with a ready mix mixer, for a period of time, most preferably at least about 5 to about 10 minutes, preferably at high speed, for example 12 to 15 rpm. However, other periods and other speeds may be acceptable with respect to at least partially obtaining the benefits of the present invention.

The concrete mix can be prepared in wet or dry batch conditions, as desired. For example, 40±15%, or in another embodiment ±10%, of the water required to fully wet the cement, sand, and coarse aggregates used in the batch is placed in a ready mix. The cement mix, coarse aggregates, and sand are mixed together and placed in the ready mix. The remaining water is then placed in the ready mix.

Once the dry ingredients and water are mixed, the amorphous silica is added and the mixture is mixed for a time ranging from about 3 to about 15 minutes, more preferably from about 5 to about 10 minutes, preferably at a relatively fast drum rotation speed, e.g., from about 8 to about 20 rpm, more preferably from about 12 to about 15 rpm. It is acceptable to have a time from high speed mixing to silica addition, e.g., transportation time to the injection site. Generally, a time from high speed mixing to silica addition ranging from about 1 to about 60 minutes is acceptable, as long as the concrete is mixed at a low speed, e.g., from about 3 to about 5 rpm. In one embodiment, the cement mixture containing silica is preferably thoroughly mixed before adding the admixture. Once the high speed mixing has been performed, the admixture can then be added, e.g., to the ready mix. Once the silica has been added to the mix and thoroughly mixed, it is preferable to add the admixture to the batch within 30 minutes, more preferably within 20 minutes, and even more preferably within 10 minutes. Once the admixture is added to the concrete mixture containing the mixed amorphous silica component, the admixture containing the admixture can then be mixed at a speed ranging from about 1 to about 18 rpm for a time ranging from about 2 to about 20 minutes.

As indicated above, concrete is generally mixed with split water addition, i.e., one portion of water is added before the addition of the dry ingredients, and the portion added after the first portion and the dry ingredients are mixed together for a period of time. The benefits of the present invention can be expected in all commercially used variants, as long as the process is as follows:
1) After the dry ingredients and water have been mixed together, and within about 60 minutes of batching (i.e., thoroughly mixing) the water and other concrete ingredients, the amorphous silica is added (whether the water is added in one addition or in two or more additions).
2) The silica-containing mixture is mixed at a relatively high drum rotation speed (eg, one or more speeds ranging from about 8 to about 20 rpm for a time ranging from about 3 to about 15 minutes).
3) Adding the admixture to the silica-containing mixture and kneading the resulting mixture at one or more speeds in the range of greater than about 1 rpm for a time in the range of about 2 to about 20 minutes, preferably greater than about 10 rpm, more preferably in the range of about 12 rpm to about 15 rpm, for a time period of at least 1 minute, but as long as 18 minutes or more.
4) The concrete mixture is poured within approximately 60 minutes of mixing in 3).

The abrasion resistance of concrete formed from the compositions and methods of the present invention is generally increased compared to concrete formed from standard methods and compositions (i.e., prepared without the addition of amorphous silica and admixtures). Subjecting the concrete of the present invention to the abrasion resistance test ASTM C944 generally results in less weight loss than standard concrete prepared in substantially the same manner, but without the amorphous silica and admixtures. For example, as shown in Examples 1 and 3, the standard concrete has a higher abrasion loss than the concrete of the present invention. The standard concrete of Example 3 exhibits an abrasion loss of 1.1 grams, while the concrete formed from the compositions and methods of the present invention results in a loss of 0.6 grams. Generally, the concrete of the present invention may result in an abrasion loss that is reduced by 50 percent or even more relative to the standard concrete. By standard concrete, it is meant concrete prepared by the same method, ingredients, and ratios of ingredients, but without the addition of the disclosed amorphous silica and the disclosed admixtures.

Below is a detailed description of the steps of the finishing process in which the advantages of the present invention are evident. Accompanying the detailed step descriptions are visual illustrations of the changes in the surface as the process progresses, with emphasis on the differences due to the method and formulation of the present invention. Finishing concrete for indoor use generally involves three successive steps after the poured slab begins to harden: troweling, mixing, and a final finishing step. Each is performed at a specific stage of hardening, and the determination of when to begin each step is within the skilled judgment of the builder. Since many or most slabs are often the first elements of a new construction, external factors such as temperature, relative humidity, and wind speed influence the decision. As explained in the section entitled "Novel Compositions for Improving Concrete Performance," the use of certain types of amorphous silica in certain processes for preparing concrete minimizes many of the effects of external elements on hardening. Thus, the standard three-step finishing process is very simple, often requires less energy at each step, and there is less risk of damage to the concrete during finishing. For example, all three are generally required to obtain a standard finish for concrete in the construction slabs that underpin most residential and commercial construction. Troweling in the present invention is generally easier than standard concrete due to the excellent water retention properties of concrete described below. Troweling can be done by methods known in the art, such as a hand trowel, a push trowel, a riding power trowel, or using a 36, 48, or 60 inch pan or float shoe. Generally, less effort is required for smoothing compared to the effort required to smooth conventional concrete due to reduced friction between the blade and the surface, and therefore machine speeds can be significantly slower than those required to smooth concrete made by existing methods, minimizing the potential for damage to the concrete surface.

And the mixing step is typically performed as known in the art, for example with a riding power trowel or a push trowel with a combination blade. It is during this step that the plastic-like nature of the surface typically becomes more evident and noticeable. This surface is typically distinctly different from the surface developed during mixing by concrete that does not include both 1) the inventive amorphous silica amount, particle size, and surface area disclosed herein, and 2) the inventive admixture formulation disclosed herein. This effect is described by the inventors as "plastic-like." The surface develops a smoother appearance, which typically increases somewhat with mixing time, when compared to commonly used concrete formulations at a similar stage of finishing that do not utilize the inventive recipe and process details disclosed herein, and the surface exhibits a reduced incidence of large pores as well as improved flatness. By "plastic-like" it is meant that the surface has at least the appearance of a coating, said coating generally being somewhat occluded, to the extent that the brightness is not high during mixing, but can decrease with the progress of mixing and/or with increasing combination blade speed. Later during mixing, a glass-like texture and even better brightness may or may not be obtained, as may subsequent finishing steps. Using faster mixing speeds (about 190 rpm or higher) than those used with conventional concrete may, but does not necessarily, result in an improved finish in terms of brightness and gloss (note that mixing may not be performed or may be deemed unnecessary). Again, the greater the amount of moisture retained on the concrete's surface, the less friction there is between the surface and the combination blade, which in turn requires less energy for the machine to maintain a given speed. The risk of machine damage to the surface is generally greatly reduced.

Finishing can then be performed. Methods known in the art, such as a riding power trowel with a finishing blade, or a hand trowel, can be used. People who have worked with the concrete of the present invention have noted that the finishing process causes the surface to acquire increasingly vitreous characteristics, e.g., more vibrant than concretes known in the art and prepared in the same manner, but generally not as vibrant as that obtained with a burnishing process. While not wishing to be bound by theory, it is believed that the increased vibrant is the result of moisture retention at the concrete surface due to the inclusion of the silica of the present invention as disclosed herein. The vibrant, gloss, and flatness achievable after the finishing process is generally sufficient to qualify as a "Grade 1" finish. In conventional concretes (i.e., without the formulated mix and disclosed use of amorphous silica in the disclosed surface or admixtures), the finishing process does not necessarily impart this vitreous, i.e., enhanced vibrant and/or gloss, at conventional maximum finishing speeds of about 190 rpm.

Most available finishers are limited to a maximum speed of about 190 rpm, although some older machines can achieve a maximum speed of about 220 rpm. One feature often observed in the use of either the admixtures or surfaces of the formulations of the present invention is that the use of faster finishing blade speeds (e.g., 200-220 rpm) than previously used speeds (e.g., 180-200 rpm) can improve the finish beyond that achievable at the previous speeds, with the surface taking on a greater luster and brightness than achievable at the lower speeds. The resulting surface is often still a "Grade 1" finish, but at such increased speeds has increased brightness and luster compared to unfinished surfaces of the present invention. To the inventor's knowledge, such improved brightness at higher speeds is unique to the concrete surfaces of the present invention.

The finishing time is until the surface has the desired appearance. For example, two passes may be required to observe a finish with excellent vibrancy, gloss, and flatness. Note that the finish may take on a more matte appearance during the blending process. This can be preserved, if desired, by not performing a final finishing step. To obtain a finish with a more glassy appearance and texture, it is generally necessary to proceed to the final finishing stage.

Finishing can be done in various grades based on the desired gloss and brightness of the concrete surface. As mentioned above and as practiced in the industry, finishing using a finishing machine at a maximum speed of 190 rpm generally results in a "Grade 1" finish, as is known in the art. Further improvements in surface quality, i.e., improved gloss and brightness, can generally be obtained by using a burnishing machine, also known in the art, to develop a "Grade 2" or "Grade 3" finish. Those skilled in the art can generally ascertain the grade of the finish by visual inspection of the finished surface (approximate RA (roughness average) readings corresponding to the various grades: Grade 1 generally corresponds to an RA of 50-20, Grade 2 generally corresponds to an RA of 19-11, and Grade 3 generally corresponds to an RA of 5-0). It should be noted that the quality of the finish when burnished depends on the quality of the finish obtained by the finishing process, which typically results in a Grade 1 surface. Higher grade finishes obtained by burnishing generally have a polished appearance to them. Note that unlike traditional concrete, the shine of the polished floors of the present invention is achieved without the use of protectants or sealants.

Because floor burnishing machines operate at much higher speeds (rpm) than finishing machines, it has traditionally been necessary to wait at least about 3-4 days after finishing, and up to 28 days or even longer, before using the burnishing machine on a finished surface. Early use is known in the art to generally expose the finished surface to significant damage, such as scratches (which can be very deep: 2-4 mm) and risk of aggregate exposure. Notably, as disclosed and described herein, concrete prepared with amorphous silica and admixtures or surface finishes of the formulations disclosed and described herein can be polished immediately after finishing, if desired, without damage to the concrete surface.

More specifically, concrete prepared with amorphous silica as described herein or in U.S. Provisional Application No. 62/761,064, incorporated herein by reference, and further prepared with admixtures using Korkay or E5 Finish-containing formulations as described herein, can be polished immediately after the finishing step without damaging the surface of the concrete.

For example, Figure 1 shows a concrete slab containing 4 ounces of E5 Internal Cure per 100 weight percent. E5 Finish is used topically as a finish at a rate of 1000 square feet per gallon. The burnishing process was started immediately after the finishing step was completed. Figure 1 shows an undamaged surface despite a 27 inch burnisher operating at 2500 rpm. Figure 2 shows that the surface has changed from nearly Grade 1 to nearly Grade 2. Although both figures correspond to the use of cutting agents on the surface, the effect is visually indistinguishable from the effect seen with an admixture with cutting agents.

Burnishing machines generally come in three sizes (17, 20, and 27 inch diameter), with the larger diameter machines reaching speeds as high as 2500 rpm. Generally, the faster the speed, the better the brightness and gloss. One notable feature of the present invention is that concrete prepared by conventional methods generally requires the application of a guard or sealer prior to burnishing to achieve a grade 2 or grade 3 gloss quality, often with a 28 day wait before burnishing can begin. The concrete of the present invention can be burnished immediately after finishing without the application of a guard or sealer, without damaging the concrete surface. Without being bound to a particular theory, it is believed that the finishing and burnishing process causes the amorphous silica to react with the surfacing or admixture formulation to produce a glassy material or phase, with a more complete reaction associated with higher finisher and burnisher rpm. It has also been observed that, as with the finishing process, less friction exists between the machine and the floor, resulting in a lower RA (roughness average) number and a longer burnishing pad life.

The number of burnishing passes used is generally simply the number required to achieve the brightness and gloss. The number of passes required to transform a Grade 1 finish into a Grade 2 finish may be as low as 3-4, or as high as 4-20. Transforming a Grade 1 into a Grade 2 may require approximately 20 minutes of high speed burnishing for every 1000 square feet of surface. It has been found that if a floor does not develop a gloss during finishing, it is difficult to polish. Experience has shown that waiting some time after finishing, for example 1-24 hours or more, before beginning burnishing can improve the brightness of the burnishing in some circumstances.

Other benefits resulting from the use of admixture-free silica in the methods of the present invention (Application No. 16/501,232, filed March 8, 2019, is incorporated by reference without exclusion for all it teaches) are generally not diminished by the use of admixtures. In a preferred embodiment, the concrete mix is formed and mixed in an industrial scale pour, such as for preparing a footing or slab. In another embodiment, the concrete mix is made using and in an apparatus that holds the mix as it is being made and also has the ability to mix the mix, e.g., ready mix.

An advantage of the process of the present invention is that the water in concrete structures, e.g., slabs, formulated according to the present invention, appears to be immobilized within the structure, rather than being lost through evaporation. The expected result of this much water is that it will participate in hydration over an extended period of time, rather than forming capillaries and voids. Thus, regardless of thickness, concrete slabs, walls, and other structures are expected to exhibit reduced or absent voids and capillaries, and a correlated increase in compressive strength. Using the concrete of the present invention, concrete structures up to about 20 feet thick can be formed with improved structure and compressive strength.

An advantage of the process of the present invention is that the poured concrete is less damaged by drying caused by environmental conditions such as temperature, relative humidity, and air movement such as wind. For example, high quality concrete can be produced with wind speeds of up to 50 mph, temperatures of up to 120°F, and temperatures as low as 10°F, with relative humidity as low as 5% and as high as 85% or higher.

The compressive strength of concrete formed by the method of the present invention is generally increased relative to concrete formed by a similar or preferably the same method, except for the addition of silica after mixing of water, cement mix, and filler (aggregate, sand, etc.). "Similar" or "same" refers to the environmental conditions, such as wind speed, relative humidity, temperature profile, and other environmental factors, such as shading and thermal radiation, with respect to the evaluation of the increase in compressive strength. Factors that the pourer can control, such as mixing time and parameters, pouring parameters (i.e., slab dimensions), are more easily explained. The increase in compressive strength is preferably evaluated from pours that are identical except for the addition of amorphous silica. In a preferred embodiment, the evaluation is performed by pouring from the same components in the same amounts, prepared at the same time but in separate ready mixes, and poured side-by-side, at the same time but using separate ready mixes. Such pours are "substantially identical".

The increase in compressive strength can range from about 5 to about 40%, or even more, based on the compressive strength of a pair of substantially identical injections that do not contain silica. In more commonly observed embodiments, the increase in compressive strength evaluated from substantially identical injections ranges from about 10 to about 30%.

The concrete of the present invention can be used generally in applications requiring poured concrete, e.g., slabs, footings, etc. An advantage of the present invention is that the concrete prepared therefrom generally has high resistance to water penetration and therefore can be used in pouring applications that are particularly susceptible to exposure to moisture and associated damage, e.g., footings.

As shown below, the present invention involves the discovery that when nanosilica is added to a concrete mix, preferably as colloidal silica, after the addition of at least a portion of water, a cement having improved properties, such as improved compressive strength, among other properties, such as wear resistance and water permeability, is obtained.

The sizes of additive concrete components, such as sand and aggregates, used in the art can generally be used in the concretes of the present invention without detracting from the benefits provided by the present invention.

Thus, in preparing concrete that is generally free of defects otherwise associated with concretes containing large amounts of mobile water, it is possible to utilize concrete that contains sufficient water for hydration, pouring, and working. The compositions of the present invention result in concrete that retains water such that the exposed surface is less likely to dry out quickly than concrete without the addition of amorphous silica. The relative water retention effect is observed even under ambient conditions where surfaces would normally tend to dry out. Thus, the concrete can be poured under a wider range of environmental conditions than standard concrete. Thus, the surface can be finished with reduced amounts of surface water, or in some cases, without the addition of surface water.

Shrinkage is generally reduced compared to concretes containing the same amount of water. Even more surprising is the increase in compressive strength. This result is generally obtained even when the concrete contains a quantity of mobile water that, in the absence of amorphous silica, risks the formation of capillaries and voids.

Without wishing to be bound by theory, it is speculated that the amorphous silica may immobilize water during curing, preventing it from migrating and retarding evaporation, as well as the formation of capillaries and voids. Surprisingly, the immobilization does not prevent the water from participating in long-term, prolonged hydration, which results in an unexpected increase in compressive strength.

An overarching advantage of the present invention is the ability to avoid using excess water in the setting reaction (hydration) as water is typically lost through evaporation. Such advantages can be obtained with less water than is theoretically required for full hydration of the concrete, and even in the case of concrete that is poured with more water than is theoretically required for hydration.

A problem with existing concrete preparation and pouring processes is the risk that occurs when pouring is performed under less than optimal conditions. As shown below, relative humidity, wind speed, and temperature, among other environmental factors, affect the amount of water at various locations on and in the concrete, thus constantly compromising standard pouring. This can occur even when the amount of water contained complies with the recommended amount of water specified by the cement mix manufacturer, whether it is a recommended range of values or a single specified optimum value. The present invention reduces the risk of water-related problems and allows operation at the water content recommended by the cement manufacturer. These recommended values generally correspond to the amount of water required to allow the hydration reaction to proceed to an acceptable extent, or in some cases to completion. In the practice of the present invention, the use of the amount of water specified by the cement manufacturer is preferred. However, the present invention also reduces the risk of water problems with other processes, even when the water content deviates from that specified by the manufacturer. Thus, in some embodiments, the water content is within the range of about -30% of the minimum value specified by the manufacturer's specifications to +30% of the maximum value specified by the manufacturer's specifications, based on the weight of water added to the cement prior to adding the colloidal amorphous silica or other silicas described herein.

Yet another advantage of the present invention is derived from the ability of its formulations to retain water for the benefit of extended hydration without forming capillaries and void vessels. It is known in the art that the addition of aggregates, sand and other commonly contained bulking and reinforcing materials to cement to form concrete generally requires additional water to accommodate them in the concrete, which may actually promote the formation of capillaries, particularly void vessels. Such vessels are associated with and located in relation to the surface of the contained material. Generally, the most preferred aggregates and materials are of a quality such that they are intimately associated with the concrete over their surface area, and during hydration, vessel formation is minimized, as well as the associated loss of compressive strength. However, such high quality contained materials are generally uneconomical. Surprisingly, the inclusion of amorphous silica particles can reduce or prevent the formation of void vessels and the formation of capillaries, even in the presence of aggregates. Without wishing to be bound by theory, the reduction in such defects, particularly void vessels, and the associated increase in compressive strength tend to indicate that the high surface area of amorphous silica particles is involved in a direct association with the contained material, even though the material quality is not optimal. This association may help exclude water and strengthen the adhesion of the concrete to the materials it contains.

Yet another advantage of the present invention is that the concrete mix prepared therefrom can be pourable and/or workable without the use of so-called "superplasticizers". Non-limiting examples of such superplasticizers include lignin sulfonates, sulfonated naphthalene formaldehyde polycondensates, sulfonated melamine formaldehyde polycondensates, polycarboxylic acid ethers and other superplasticizer components, whether in emulsion, dispersion, powder, or other chemical form. In one embodiment, the concrete mix of the present invention is pourable without superplasticizers, free of superplasticizers, or essentially free of superplasticizers. "Essentially free of superplasticizers" means that the content of superplasticizers is a trace amount, less than about 0.1%, based on the weight of the cement.

The following is a non-limiting list of admixtures that may be used in the present invention. Alternatively, the concrete mix of the present invention may not contain any or all of the following additives or other additives. The list below is organized according to ASTM C494 categories. Admixtures that are and are not certified by ASTM C-494 are included.

The admixtures can be added as powders or liquids.
- Conventional water reducers and retarders (Types A, B, D)
Nominal injection amount range: 0.5 to 6 OZ/C
Superplasticizer: Normal setting and retardation (Types F, G)
Nominal injection amount range: 2 to 40 OZ/C
- Hardening accelerator: Water-reducing or non-water-reducing (Types C and E)
Nominal injection volume range: 2 to 45 OZ/C
Type S admixture as defined by ASTM C494:
・Mid-range water reducer and retarder ・Nominal injection rate range: 2 to 45 OZ/C
・Rust inhibitor ・Nominal injection amount range: 0.25 to 5 GAL/YD
・MVRA (water vapor reducing admixture)
Nominal injection volume range: 5 to 24 OZ/C
・SRA (shrinkage reducing admixture)
Nominal injection amount range: 0.25 to 5 GAL/YD
- Hydration stabilizer - Nominal injection amount range: 0.5 to 24 OZ/C
・Viscosity adjuster ・Nominal injection amount range: 0.25 to 8 OZ/C
- air entraining admixtures;
Nominal injection range: OZ required to entrain air: 0.1 to 36 OZ/C
Colorants; liquid and solid Nominal injection range: 0.1-20 LB/YD

Example 1
Preparation of interior slab with admixtures Abrasion resistance measured by ASTM-C944 Pour size: 400 sq. ft. Weather conditions: 52-78 degrees, approximately 60% humidity, sunny. Pour started around 7am and finishing was completed by 1pm.

The concrete was poured using normal practice (ACI 302). The mix design was standardized (i.e., the standard 6 bag mix described in step 1 was used). The amorphous silica used was introduced as E5 Internal Cure. The admixtures used were introduced as E5 Finish. The slabs were prepared as shown in steps 1-8 below.

1-A 4-inch thick interior concrete slab was poured with non-air-entrained concrete using a conventional Class A concrete design of 6 bags (564 lbs) of cement (total of 9 cubic yards) to 31 gallons of water per cubic yard (SSD-saturated surface dry). Approximately 12 gallons of water per cubic yard were added to the ready-mix concrete, followed by the dry cement mix (564 lbs per yard), aggregates and sand (1250 lbs sand per yard, 1750 lbs stone per yard). The water and dry ingredients were mixed for 1-2 minutes, and approximately 19 gallons of additional water per yard were added to the ready-mix. The mixture was mixed (in a concrete drum with a high speed of 12-15 RPM for mixing the concrete) for an additional time of 5-10 minutes. The concrete barrel was slowed to 3-5 RPM when the driver was ready to transport the concrete to the job site.

2- Next, a total of 203 ounces of E5 Internal Cure (4 ounces/100 lbs of cement) was added after the 9 yards were poured and batched. Again, 564 lbs of cement and 31 gallons of water per cubic yard.

3- Teams allowed the ready mix driver to mix the batch for 5 minutes at a speed of 12-15 rpm.

4- E5 Finish was then added to the Ready Mix truck (3 oz per 100 wt. of cement) and mixed for approximately 12-15 minutes. Mixing began with the truck at idle drum speed (3-5 RPM) for 2 minutes. Then the drum speed was increased to 12-15 RPM for the remainder of the time.

5- The slab was poured (injected) and after a 3 hour waiting period the finishing process started.

6- A concrete hand trowel was used to perform the panning process. The panning speed for the troweling process was 80-130 revolutions per minute. This process took 1.5 hours, at which point the surface texture of the slab indicated it was ready for the next ride-on power trowel.

7- Push Trowel A combination blade was attached to the power trowel and the mixing process was started. After about the first two passes of the slab, the surface had a plastic-like appearance. Blade speed was about 100-165 revolutions per minute. Note that the surface was more easily finished than in situations where E5 Finish was applied topically after pouring, which is itself another discovery by the same inventor as in this application. The surface showed greatly reduced friction against the combination blade. A finisher with extensive experience pouring and finishing concrete noted the reduced friction and commented that "there was practically very little resistance to the machine and it felt like I was finishing on a ball bearing surface." A dull, non-shiny condition identifiable to the skilled artisan indicated readiness for the finishing process, as known and identifiable by those skilled in the art.

8- A finishing blade was attached to a push trowel and the surface was finished at a speed of approximately 165 rpm. The finisher stated that "the surface was beginning to look a little like glass" and that "the more finishing was done, the clearer the finish became." The finished surface appeared to have a somewhat glass-like coating, although the brightness was not as bright as glass. The slab appeared to be denser and more reinforced throughout the matrix than normal concrete. Abrasion resistance was measured according to ASTM-C944 and a loss of 0.6 grams was observed. Experience showed that the burnishing step could be done without waiting and it was expected that the burnishing would greatly improve the brightness of the surface coat.

Example 2
Preparation of Footings with Admixtures Footings are a common use of poured concrete in the construction industry. Poured concrete is generally exposed to constant moisture due to soil contact during curing. Such constant contact may also provide a source of moisture for hardened concrete. Footings were poured to observe the properties of poured concrete under such conditions. The objectives were to ascertain the density of the concrete obtained in the footings (i.e., absence of capillaries and voids) and to determine if the strength of the concrete was affected.

Pour size: 50 feet long, 2 feet wide, 30 inches thick Conditions: 60 degrees Pour began at 11:00 AM and was completed at 1:00 PM.

Five bags (475 lbs) of cement were used with 31 gallons of water (SSD - surface dry saturated) per cubic yard (7.5 cubic yards total). Approximately 12 gallons of water per cubic yard were added to the ready mix concrete, followed by dry cement mix (564 lbs per yard), coarse (stone) and fine aggregates (sand), 1250 lbs of sand and 1750 lbs of stone per yard of concrete. The water and dry ingredients were mixed for 1-2 minutes and approximately 19 gallons of additional water per yard was added to the ready mix. All of the above was done with a drum speed of 3-5 RPM. Next, E5 Internal Cure was added to the ready mix truck at 3 oz per 100 weight of cement. The mixture was then mixed for an additional time of 5-10 minutes at a high speed of 12-15 RPM. The driver then slowed the concrete barrel to 3-5 RPM and drove for 5-10 minutes to the test pour. E5 Finish was then added to the ready mix truck at a rate of 3 ounces per 100 weight percent cement. The drum speed was then increased to approximately 12-15 RPM for approximately 5-10 minutes and the mixture was poured.

Approximately 35-45 minutes after pouring, a plastic-like surface was observed. No bleeding channels were evident. After 24 hours, the footing showed no evidence of shrinkage as no stress cracks were observed. The absence of shrinkage is believed to be due to closure or clogging of the channels. Thus, the surface was observed to be very dense, which was confirmed by the compression failure of the cylinder. Such results tended to indicate that the concrete could be used both indoors and outdoors.

Compressive failure results for ASTM C39\Cl23l cylinders showed that the compressive strength reached over 30,000 psi in 28 days, 25% more than that achieved in 7 days.

Example 3
Slab Preparation Without Admixtures Abrasion Resistance Measured by ASTM-C944 Location: Shelby Materials Redmix Plant, Shelbyville, Indiana Environmental Conditions: Start time of pour was 7:30 AM with a start temperature of approximately 60°F. Ambient temperatures peaked during the day with highs in the 80s. Relative humidity ranged from 18% to 67%. Wind speeds ranged from 3 to 18 mph.

Process and Results:
1 - A 4-inch thick interior concrete slab was poured with non-air-entrained concrete using a conventional Class A concrete design of 6 bags (564 lbs) of cement (total of 9 yards) to 31 gallons of water per cubic yard (SSD - surface dry saturated). Approximately 12 gallons of water per cubic yard was added to the ready-mix concrete, followed by the dry cement mix (564 lbs per yard), fine aggregate (sand) and coarse aggregate (stone) (1250 lbs sand, and 1750 lbs stone per yard of coarse aggregate). The water and dry ingredients were mixed for 1-2 minutes, and approximately 19 gallons of additional water per yard was added to the ready-mix. The mixture was mixed in the concrete drum for an additional time of 5-10 minutes at 12-15 RPM. When the driver was ready to transport the concrete to the job site, the concrete barrel was slowed to 3-5 RPM. Transport time to the pour was approximately 5-10 minutes.

2- Next, after the 9 yards were loaded and batched, a total of 380.7 ounces of E5 Internal CURE (7.5 ounces/100 lbs of cement) was added. Again, 564 lbs of cement per cubic yard and 31 gallons of water.

3 - Teams allowed the ready mix driver to mix the batch for 5 minutes at 12-15 rpm.

4-Then concrete was poured into the slab form.

5- After pouring, the slab was level and the surface was closed using a bull float. Once the surface was hard enough to start the mechanical finishing process, finishing was completed using a preferred method.

6-It is noted that during the bull-floating process to close the surface, the concrete was able to close much easier than that prepared by the conventional ready-mix process.

7- During the finishing process where bleeding water is typically present, no bleeding water occurred in this process. However, the surface remained wet. Surprisingly, unlike concrete prepared from a conventional Readymix product, water was retained within the concrete surface under conditions where the surface would have been much drier using Readymix without E5 INTERNAL CURE.

8 - The team then spent 4 hours completing the concrete finishing process. Unlike concrete prepared from traditional ready mixes, the finishing process could be done with machines running at half throttle as moisture still remains on the concrete surface. This makes the finishing process much easier than concrete without E5 INTERNAL CURE. Traditional concrete requires machines to run at 100% throttle, a more labor-intensive process that increases the risk of surface damage during finishing.

9- Wear resistance was measured by subjecting the relevant cylinders to ASTM-C944 and a loss of 1.1 grams was observed.

Claims (19)

A process for the preparation of a concrete facility, the process comprising the steps of:
A) preparing a concrete mix from the following components: a) an amount of dry cement mix, said cement mix comprising:
i) a water/cement ratio value recommended by the manufacturer, said recommended ratio being in the range of 0.35 to 0.65, and when mixed with b), said water/cement ratio is greater than a value corresponding to 10% less than said recommended value and less than or equal to a value corresponding to 30% more than said recommended value;
or
ii) a range of water/cement ratios recommended by the manufacturer, having upper and lower limits, which, when mixed with b) below, results in a water/cement ratio greater than a value corresponding to 10% less than the lower limit and less than a value corresponding to 30% more than the upper limit;
or
iii) in an amount such that, when mixed with b) below, the water/cement ratio is in the range of 0.35 to 0.65;
A quantity of dry cement mix,
b) the amount of water; and
c) an amount of amorphous silica in the range of 2.8 to 198.4 grams (0.1 to 7.0 ounces) per 100 weight percent of the cement of a), wherein the average silica particle size is in the range of 1 to 55 nanometers and/or the surface area of said silica particles is in the range of 300 to 900 m ² /g;
d) an amount of aggregate and/or an amount of sand in the range of 400-700 wt% bwoc;
preparing a concrete mix comprising each of
B) the water of b) is added in its entirety or in portions including an initial portion including at least 20% by weight of the amount of water and a tail water portion, and the initial portion of the water is mixed with the components of a) and d) to form a first mix, and the amorphous silica is added to the mix including the initial portion of a), d) and b) to form a second mix;
And,
the tail water is 1) added to the first mix, or 2) added to the second mix, or 3) added to the first mix with the amorphous silica, the amorphous silica and the tail water are added and mixed together, and 1) the first mix is stirred for a time _t11 before the addition of the tail water, for a time _t12 after the addition of the tail water, and for a time _t13 after the addition of the amorphous silica, or 2) the second mix is stirred for a time _t21 before the addition of the amorphous silica, for a time _t22 after the addition of the amorphous silica but before the addition of the tail water, and for a time _t23 after the addition of the tail water, or 3) the second mix is stirred for a time _t31 before the simultaneous addition of the amorphous silica and the tail water, and then the concrete mix is stirred for a time _t32 ;
or,
C) the amount of water is added to the components of a) and d) to form a mix, then the mix is stirred for a time t _a prior to the addition of the amorphous silica, and the concrete mix is stirred for a time t _b ;
If the constraints of B) or C) are met, the silica-containing mixture results from B) or C), said silica-containing mixture is mixed for a time period longer than 5 minutes at a mixing speed of at least 7 RPM;
D) an admixture comprising an alpha-hydroxy acid is added after step B) or step C) to form an admixture-containing mixture, said admixture-containing mixture being mixed at one or more speeds greater than 6 RPM for a total time of at least 3 minutes;
E) pouring the concrete mix of D) to form a concrete facility;
A process including the steps of: The process of claim 1, wherein the first portion of water comprises at least 30, 40, 50, 60, 70, 80, 90, or 99 wt% of the amount of water. When the dry cement mix of a) is mixed with the water of b), the water/cement ratio becomes:
i) equal to or greater than the recommended value, but less than a value equivalent to 30% more than the recommended value; or
ii) equal to or greater than the upper limit of the recommended range, but equal to or less than a value equivalent to 30% greater than the upper limit; or
3. The process of claim 1, wherein for iii) it is at least 0.35 but not more than 0.65. The process of claim 1, wherein the amorphous silica is introduced into the first mix as a colloidal silica solution, the solution comprising 50-95% by weight silica and 5-50% by weight water. The process of claim 4, wherein the silica comprises 75-90% by weight silica and 10-25% by weight water. The process of claim 5, wherein the amorphous silica is added in an amount ranging from 70.8 to 155.9 grams (2.5 to 5.5 ounces) per 100 weight percent cement. The process of claim 6, wherein the amorphous silica is added in an amount ranging from 99.2 to 127.5 grams (3.5 to 4.5 ounces) per 100 weight percent cement. The process of claim 4, wherein the colloidal silica is added after the tail water. The process of claim 1, wherein the concrete is poured into a slab or footing. The process of claim 1, wherein the process is carried out in a ready mix, the tail water is added to the first mix after the first mix has been stirred at a speed ranging from 2 rpm to 18 rpm for a time ranging from 15 seconds to 5 minutes, and after the tail water addition, the mix is stirred at a speed ranging from 5 rpm to 18 rpm for a time ranging from 1 minute to 18 minutes, and then the silica is added to the ready mix as colloidal silica, and the mix is stirred at a speed ranging from 2 to 18 rpm for a time ranging from 1 to 15 minutes. The process of claim 1, wherein the process is carried out in a ready mix, the tail water is added to the first mix after the first mix has been stirred at a speed ranging from 2 rpm to 18 rpm for a time ranging from 15 seconds to 5 minutes, and after the tail water addition, the mix is stirred at a speed ranging from 5 rpm to 18 rpm for a time ranging from 1 minute to 18 minutes, and then the silica is added to the ready mix as colloidal silica, and the mix is stirred at a speed ranging from 2 to 18 rpm for a time ranging from 1 minute to 15 minutes, and the process of claim 4. The process of claim 1, wherein the admixture containing the admixture is mixed at a speed ranging from 7 RPM to 15 RPM for a time ranging from 5 minutes to 15 minutes. The process of claim 12, wherein the admixture containing the admixture is mixed for a period ranging from 5 minutes to 10 minutes. The process of claim 13, wherein the admixture containing the admixture is mixed at one or more speeds ranging from 7 RPM to 15 RPM. The process of claim 14, wherein the admixture containing the admixture is mixed at one or more speeds ranging from 12 to 15 RPM. The process of claim 15, wherein the silica-containing mixture is mixed for a total time ranging from 5 minutes to 15 minutes. The process of claim 16, wherein the silica-containing mixture is mixed for a total time ranging from 5 minutes to 10 minutes. The process of claim 17, wherein the silica-containing mixture is mixed at one or more speeds ranging from 7 RPM to 15 RPM. The process of claim 18, wherein the silica-containing mixture is mixed at one or more speeds ranging from 12 to 15 RPM.

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