GB2105744A - Sulfur-aggragate compositions - Google Patents

Abstract

Sulfur cement-aggregate compositions, such as sulfur concretes and sulfur mortars, comprising an admixture of a sulfur cement and an aggregate which is contaminated with an expansive clay, have the aggregate pretreate wit a water-soluble salt, for example potassium chloride or calcium chloride, either in solid form or in the form of a solution, in order to reduce the water expandibility of the expansive clay contaminant and thereby substantially improve the water stability of the final sulfur cement and aggregate product.

Description

SPECIFICATION Sulfur-aggregate compositions This invention relates to sulfur cement and aggregate compositions and is concerned with sulfur mortars and concretes which contain an aggregate which is contaminated with a water-expansive clay.

Sulfur mortars and concretes generally refer to a mixture of sulfur and aggregate wherein the sulfur functions as the cement or binder. Generally, whether a composition is classed as a mortar or concrete is based on the particle size of the predominate aggregate. Thus, compositions containing larger sized aggregates are generally referred as concretes whereas compositions containing smaller sized aggregate are referred to as mortars. In either case, the compositions can also contain very fine particle size aggregates, such as fly ash, etc., as fillers. Sulfur mortars and concretes are prepared by heating sulfur with an aggregate at a sufficient temperature to render the sulfur molten and then allowing the mixture to cool to solidify the sulfur.Not infrequently, the sulfur also contains a plasticizer which desirably increases the cold plasticity crystallization time of the sulfur, probably by reacting with at least a portion of the sulfur. Such sulfur is referred to as plasticized sulfur.

Sulfur mortars and concretes can be broadly classified as sulfur cement products. Sulfur cement is similar to Portland cement in forming concretes or mortars. In the latter case, the mixture of Portland cement and aggregate is solidified into a final solid product by treatment with water. In the sulfur cement case, heat is used.

Sulfur cement concretes can be used for many of the same purposes as conventionally formed Portland cement concretes. For example, sulfur concretes can be used for structural members, roads, slabs, curbings, gutters, and can be precast or cast at the job site. Sulfur concrete affords a significant advantage over Portland cement concrete, especially in the case of preformed articles, in that the sulfur cement concrete can be remelted and recast. Thus, when defective or surplus articles are prepared, the sulfur-aggregate composition can be reused by merely melting down the article and recasting the composition. Sulfur cement mortars can be used for similar purposes as Portland cement mortars, such as, for example, bonding structural members together. Sulfur cement mortars and concretes also generally have good corrosion resistance to acids and other chemicals.

Sulfur cement, mortars and concretes are well known to the art and various modifications are, for example, described in the patent literature, for example, U.S. Patent Nos. 2,135,747,3,954,480, 4,025,352,4,058,500, and 4,118,230.

One of the disadvantages of sulfur cement mortars and concretes is that the presence of even small amounts of water-expansive clay (for example, 1 percent by weight or more) in the aggregate causes the solidified sulfur cement mortars and concretes to disintegrate when exposed to water. This problem is particularly serious since, because of transportation costs, economic necessity usually requires the use of aggregate sources close to the casting or job site, regardless of the presence of expansive clay. The expansive clay can be removed from the aggregate by washing procedures but such procedures are also generally inconvenient and uneconomical. Thus, if the local sources of aggregate contain expansive clay, the use of sulfur cement mortar concretes is pragmatically severely restricted.

U.S. Patent No. 4,188,230 teaches that this problem may be obviated by the incorporation of petroleum or polyol additives. Such procedures have not, in fact, proved entirely satisfactory. The problem of water-expansive clays was also considered in an article by Shrive, Gillott, Jordaan and Loov, appearing at Page 484 of the Journal of Testing and Evaluation (1977). In this article, the results of certain experiments with water-expansive clays are described. In these experiments, a mixture containing 3 parts, by volume, fly ash, and 2 parts bentonite clay was slurried with water. Batches of this slurry were, respectively, mixed with aqueous solutions containing 1 percent and 5 percent by weight calcium hydroxide or potassium chloride and allowed to stand overnight.Sulfur cement samples were prepared by slowly adding the slurries (to evaporate water) to molten sulfur. The final compositions contained 75:15:10 parts by volume of sulfur:fly ash:bentonite clay. Samp!es of the treated and untreated compositions were immersed in water after setting for 1 day and 7 days. Both the treated and untreated samples disintegrated within 3 or 4 hours of immersion and accordingly the authors discontinued the investigation.

It has now been discovered that by first treating the aggregate with a salt solution or by incorporating a dry water-soluble salt with the aggregate, that aggregate, containing up to about 5 percent by weight expansive clay, can be successfully used to afford sulfur cement-aggregate compositions having excellent resistance to water. This treatment is relatively simple and convenient and has broad applicability, because most aggregate contains less than 5 percent by weight expansive clay and most generally contain less than about 3 percent by weight expansive clay. Thus, the present invention is very significant to the commercialization of concretes.

In one embodiment, the invention comprises a sulfur cement and aggregate composition, comprising a sulfur cement and an aggregate, containing up to about 5 percent by weight and preferably less than 4 percent by weight, based on the aggregate, of an expansive clay, which has been pretreated with a salt solution to substantially improve the resistance of said composition to water deterioration.

In a further embodiment, the invention provides a process for preparing a sulfur cement concrete using an aggregate containing up to 5 percent by weight, based on the aggregate, of expansive clay comprising the improvement of contacting said aggregate with an amount of a solution of a salt, effective to substantially reduce the water expandability of said expansive clay, and substantially drying said aggregate prior to admixture with the sulfur binder.

In another embodiment, the invention comprises a sulfur cement-aggregate composition, comprising sulfur cement and an aggregate, containing up to about 5 percent by weight and preferably less than 4 percent by weight, based on the aggregate, of an expansive clay and in admixture with said aggregate an amount of a water-soluble salt effective to substantially reduce the water expandability of said expansive clay, and wherein said salt is dispersed through said aggregate as discrete particles.

In still another embodiment, the invention provides a process for preparing a sulfur cement and aggregate composition containing an aggregate having up to 5 percent by weight, based on the aggregate, of expansive clay which comprises the improvement of adding to said aggregate an amount of a dry particulate water-soluble salt effective to substantially reduce the water expandability of said expansive clay, prior to admixing said aggregate with said sulfur cement.

The invention will be further described hereinbelow.

The theory or mechanism of the present invention is not clearly understood. Initially, it was conjectured that the improved stability afforded by the present invention was caused by the ion exchange replacement of the sodium ions in the expansive clay with other ions. It was then discovered that improved stability was also obtained using sodium salt (e.g., sodium chloride) solution and that improved stability was also obtained by merely mixing solid salts with the expansive clay-containing aggregate. Thus, the ion exchange theory is not consistent and no other theory is readily apparent.

Nonetheless, the present invention affords a very substantial improvement in water stability which permits the use of locally available aggregates, containing up to about 5 percent expansive clay, in sulfur cement-aggregate compositions.

In accordance with one embodiment of the present invention, aggregate containing up to about 5 percent by weight expansive clay is contacted with a salt solution prior to being mixed with the sulfur cement. Such contact can be conveniently accomplished by washing or slurrying the aggregate with the salt solution or by simply spraying the salt solution on the aggregate. It is important to note, however, that the treatment must be effected prior to combining the aggregate with the sulfur binder, because we have found that contacting the finish sulfur cement-aggregate product with the salt solution is ineffective to afford any significant improvement in water stdbility. Also, it is very much preferred to dry the treated aggregate prior to admixture with the sulfur cement.This generally poses no inconvenience, since typically the aggregate is, in any event, preheated prior to admixture with the sulfur cement to remove entrained moisture, eliminate cold spots and generally improve sulfur cement bonding to the aggregate. Thus, the conventional pre-heating step used to prepare sulfur cementaggregate mixtures can also be used to dry the aggregate.

Suitable salts which can be used include both inorganic salts and organic salts. Mixtures of different salts can also be used. The salt must, of course, be soluble in the solvent used. In general, from pure cost economics, the solvent will be water and thus generally water-soluble salts will be used.

The term "water-soluble salts" refers to salts having solubilities in water of at least 5 g per liter of water at 300 C. Preferably, the water-soluble salts used in the present invention have water solubilities of at least 10 g per liter of water, at 300 C.

In terms of the cation, suitable salts which can be used include, for example. salts having the cations of Groups I, II and Ill of the Periodic Table as well as ammonium, iron, and the like. Preferred cations include potassium, the alkaline earth metals, iron, aluminum, and copper. In terms of the anion, suitable salts include, for example, salts having anions such as halides, nitrates, nitrites, sulfates, carbonates, acetates, oxalates, and the like. Specific examples of suitable salts include potassium chloride, potassium nitrite, calcium chloride, calcium nitrite, ferric chloride, aluminum sulfate, sodium carbonate, potassium bicarbonate, ammonium chloride, tetraethylammonium chloride, calcium bromide, cupric chloride, sodium nitrate, sodium nitrite, potassium sulfate, and the like, and mixtures thereof.Because of their wide availability, high water solubility and low cost, chloride salts are preferred. Potassium and calcium salts are especially preferred because they are relatively inexpensive and afford excellent results. Best results are generally obtained using a potassium salt, and especially using potassium chloride. Also, although sodium chloride is not one of the preferred salts in terms of performance, it affords the advantage of low cost, particularly if a local commercial or natural source (e.g., sea water, salt lakes) of salt water is available. Depending on the concentration of such commercial or natural salt water, it can be used directly or can be first fortified with additional quantities of sodium chloride or other water-soluble salts.

Typically, the salt solution will have a salt concentration in the range of about from 2 to 20 percent by weight, preferably about from 4 to 1 8 percent by weight and most preferably about from 8 to 1 2 percent by weight, though higher salt concentrations could also be used depending upon the solubility of the salt in the particular solvent (e.g., water). Typically, best results are obtained using molar concentrations in the range of about from 0.5 to 2 mols of salt(s) per liter of solution. Generally, about from 1 .25x x10-4 to 1.25 g-mols of the salt (or mixtures of salts) is used per gram of expansive clay contained in the aggregate.In terms of a more convenient commercial weight basis, typically, about from 0.003 to 0.05, preferably about from 0.005 to 0.02 parts by weight of salt(s) is used per part by weight of expansive clay contained in the aggregate.

In a preferred mode of this embodiment of the invention, a water solution of the salt, preferably potassium chloride or calcium chloride, is simply sprayed onto the aggregate. The aggregate is then heated and dried and admixed with the molten sulfur cement. The molten mixture is then formed into shape and allowed to solidify by cooling. The final product is sulfur concrete or mortar having excellent resistance to breakup upon exposure to water. This mode is conveniently attractive because of its convenience.

In another mode of this embodiment, the expansive clay-contaminated aggregate can be immersed or slurried in the salt solution. Preferably, sufficient solution is used to thoroughly wet the aggregate. Contact time is generally not critical and typically, the wetted aggregate can be simply allowed to air dry and/or can be dried by preheating the aggregate. As before noted, preheating generally does not require an additional step since it is generally conventional to preheat the aggregate prior to mixture with the molten sulfur cement to avoid cold spots.

In the second primary embodiment of the invention, a water-soluble salt is merely dry mixed with the aggregate and is thus only loosely distributed with the aggregate. One normally would not expect the resulting composition to have improved water stability because necessarily the clay is free to directly contact water. Surprising, however, the composition also has improved water stability and further is very easy to prepare, since the workmen at the job site need only dump the dry particulate salt in with the aggregate prior to mixing with the sulfur cement.

The composition of this embodiment can be prepared by simply adding the particulate salt to aggregate containing up to 5 percent expansive clay, based on the weight of the aggregate, and then mixing the aggregate with the sulfur cement. As well as mixing the aggregate with the sulfur cement, - this mixing also mixes the salt throughout the aggregate. If desired, the salt can be better distributed throughout the aggregate by a separate mixing step prior to admixing the sulfur cement.

In accordance with the practice of this embodiment of the invention, about from 0.05 to 0.5 gmol, preferably about from 0.10 to 0.30 g-mol, of salt is typically used per kilogram of expansive claycontaining aggregate. In terms of a more convenient weight-to-weight basis, generally about from 0.004 to 0.04 parts by weight, preferably about from 0.008 to 0.030 parts by weight of the salt are used per part of weight of expansive clay-containing aggregate.

Suitable salts which can be used include both water-soluble inorganic and organic salts which are stable at the temperatures used in mixing the aggregate with the sulfur cement. The term "water soluble" refers to salts which have a solubility of at least 5 g per liter of water measured at 30or.

Preferably, the water-soluble salts used in this embodiment have water solubilities of at least 10 g per liter measured at 3O0C. In terms of the cation, suitable salts include, for example, salts having the cations of Groups I, II and Ill of the Periodic Table, iron, and the like. Preferred salts include the salts of potassium, alkali earth metals, iron, aluminum, and copper. In terms of the anion, suitable salts include, for example, salts having the anions halides, nitrates, sulfates, carbonates (where soluble).Species of suitable salts include, for example, potassium chloride, calcium chloride, calcium nitrite, ferric chloride, aluminum sulfate, sodium carbonate, potassium bicarbonate, ammonium chloride, tetraethylammonium chloride, calcium bromide, cupric chloride, sodium nitrate, sodium nitrite, potassium sulfate, and the like, and mixtures thereof.

Again because of their wide availability, high water solubility and low cost, chloride salts are preferred. Potassium and calcium salts are similarly preferred for economic reasons also because such salts generally afford excellent results, especially potassium salts and especially potassium chloride.

Also against as in the use of the solution treatment described above, sodium chloride may also be preferred in certain instances because of its very low cost and high availability, even though it is not preferred in terms of increased stability per unit of salt.

The salt is distributed throughout the aggregate as discrete particles typically having a particle size in the range of about from No. 1 6 to 325 mesh, preferably about from 100 to 200 mesh (U.S.A.

Standard Testing Sieves).

The sulfur cement can be substantially sulfur and/or unaltered plasticized sulfur and, if desired, can contain minor amounts of various fillers and other compatible additives (e.g., flame retardants, ductilating agents, etc.). Best results are obtained using plasticized sulfur or mixture of sulfur and plasticized sulfur.

The term "plasticized sulfur" refers to the reaction product of sulfur with a plasticizer andior mixtures of sulfur and plasticizers and/or the reaction product of sulfur with a plasticizer. Sulfur content (or total sulfur) as used herein includes both unreacted sulfur and the sulfur content of such reaction products. Although it is not wholly necessary to use plasticized sulfur as the sulfur cement in the present invention, we have found that the compositions of invention containing plasticized sulfur generally have much superior water stability to the corresponding composition using sulfur as the cement without a sulfur plasticizer. Where a plasticizer is used, the amount of the plasticizer(s) will vary with the particular plasticizer and the properties desired in the cement.The cement can contain about from 0.1 to 10 percent of the plasticizer and typically will contain about from 2 to 7, preferably about 2-1/2 to 5 percent by weight, based on the total weight of sulfur in the composition.

The term "sulfur plasticizer" or "plasticizer" refers to materials or mixtures of materials which, when added to sulfur, lower its melting point and increase its crystallization time. One convenient way to measure the rate of crystallization is as follows: the test material (0.040 g) is melted on a microscope slide at 1 300C and is then covered with a square microscope slide cover slip. The slide is transferred to a hot plate and is kept at a temperature of 700+20C, as measured on the glass slide using a surface pyrometer. One corner of the melt is seeded with a crystal of test material. The time required for complete crystallization is measured.Plasticized sulfur, then, is sulfur containing an additive which increases the crystallization time within experimental error, i.e., the average crystallization time of the plasticized sulfur is greater than the average crystallization time of the elemental sulfur feedstock. For the present application, plasticizers are those substances which, when added to molten elemental sulfur, cause an increase in crystallization time in reference to the elemental sulfur itself.

Inorganic plasticizers include, for example, the sulfides of iron, arsenic and phosphorus, etc.

Generally, the preferred plasticizers are organic compounds which react with sulfur to give sulfurcontaining materials.

Suitable sulfur plasticizers which can be used include, for example, aliphatic polysulfides, aromatic polysulfides, styrene, dicyclopentadiene, dioctylphthalate, acrylic acid, epoxidized soybean oil, triglycerides, and tall oil fatty acids, and the like, and compatible mixtures thereof.

One class of preferred plasticizers are aliphatic polysulfides, especially those that will not form cross-linking. Thus, butadiene is not a preferred constituent to form the aliphatic polysulfide, as it may form cross-linking sulfur bonds, whereas dicyclopentadiene is a preferred compound for forming the aliphatic polysulfide useful as the sulfur plasticizer. With molten sulfur, dicyclopentadiene forms an extremely satisfactory aliphatic polysulfide.

Another class of preferred plasticizers for use in the composition of the present invention are aromatic polysulfides formed by reacting 1 mol of an aromatic carbocyclic or heterocyclic compound, substituted by at least one functional group of the class -OH or -NHR in which R is H or lower alkyl with at least 2 mols of sulfur.

Suitable organic compounds of this type include: phenol, aniline, N-methyl aniline, 3-hydroxy thiophene, 4-hydroxy pyridine, p-aminophenol, hydroquinone, resorcinol, meta-cresol, thymol, 4,4'- dihydroxy biphenyl, 2,2-di(p-hydroxyphenol) propane, di(p-hydroxyphenyl) methane, etc., p-phenylene diamine, methylene dianiline. Phenol is an especially preferred aromatic compound to form the aromatic polysulfide.

The aromatic polysulfides are generally prepared by heating sulfur and the aromatic compound at a temperature in the range of 1200 to 1 700C for 1 to 12 hours, usually in the presence of a base catalyst such as sodium hydroxide. (See for example, Angew, Chem. Vol. 70, No. 12, Pages 351-67 (1958), the polysulfide product made in this way has a mol ratio of aromatic compound:sulfur of the 1:2 to 1 :10, preferably from 1:3 to 1:7. Upon completion of the reaction, the caustic catalyst is neutralized with an acid such as phosphoric or sulfuric acid. Organic acids may also be used for this purpose. The resulting aromatic polysulfide may be used immediately or it may be cooled and stored for future use.

Another type of aliphatic polysulfide useful as a plasticizer for this invention are the linear aliphatic polysulfides. Although these polysulfides may be used alone as the sulfur plasticizer, it is preferred to use them in combination with either (a) dicyclopentadiene or (b) the aromatic polysulfides described above, especially with the phenol-sulfur adduct. In this connection, the preferred plasticizer mixtures contain from 5 to 60 percent by weight linear aliphatic polysulfide, based on total plasticizer, preferably about 20 to 50 percent by weight.

These aliphatic polysulfides may have branching indicated as follows:

wherein xis an integer of from 2 to 6 and wherein B is H, alkyl, aryl, halogen, nitrile, ester or amide group. Thus, in this connection the aliphatic polysulfide is preferably a linear polysulfide. The chain with the sulfur preferably is linear, but it can have side groups as indicated by B above. Also, this side group B may be aromatic. Thus, styrene can be used to form a phenyl-substituted linear aliphatic polysulfide.

The preferred aliphatic polysulfides of this type are both linear and nonbranched.

Unbranched linear aliphatic polysulfides include those such as Thiokol LP-3 which contains an ether linkage and has the recurring unit: SxCH2CH2OCH2OCH2CH2Sx wherein x has an average value of about 12. The ether constituent of this aliphatic polysulfide is relatively inert to reaction. Other suitable aliphatic polysulfides have the following recurring units: SX+CH2AvSxfrom reaction of alpha, omega-dihaloalkanes and sodium polysulfide; Sx4CH2CH2SCH2CH2#Sx from reaction of alpha, omega-dihalosulfides and sodium polysulfide; and -S#CH2CH2-O-CH2CH2#S-ftom reaction of alpha, omega-dihaloesters and sodium polysulfide wherein x is an integer of 2 to 5; and y is an integer of 2 to 10.

In some instances, it is preferred to use mixtures of materials having different reactivities with sulfur as the plasticizer. For example, very good results can be obtained using a mixture of cyclopentadiene and/or dicyclopentadiene with oligomers of cyclopentadiene. Various plasticizers are also described in the art, for example, see U.S. Patent Nos. 4,058,500 and 4,190,460.

The sulfur cement can also contain very fine particle sized fillers such as, for example, fly ash, talc, mica, silicas, graphite, carbon black, pumice, insoluble salts (e.g., barium carbonate, barium sulfate, calcium carbonate, calcium sulfate, magnesium carbonate, etc.), magnesium oxide, and mixtures thereof. Such fillers typically have a particle size less than 100 mesh (U.S.A. Standard Testing Sieves) and preferably, less than 200 mesh. Such fillers generally act as thickening agents and generally improve the hardness or strength of the sulfur cement product. Where fillers are used, the sulfur cement typically contains about from 1 to 1 5 percent, and more generally, about from 5 to 10 percent of the filler, based on the weight of total sulfur.

Various other additives can be added as desired to alter various properties of the sulfur cement, as is well known to the art; see, for example, U.S. Patent Nos. 4,188,230 (durability altered by the addition of certain petroleum products); and 4,210,458 (viscosity altered by the addition of polyhydric alcohols).

With the exception that the aggregate must be treated with the salt solution prior to being mixed with the molten sulfur cement, the order of addition of the various ingredients is not critical. Similarly, where dry salt is used, the dry salt should be added to the aggregate prior to the sulfur cement, whereas the order of the addition of the remaining ingredients is not critical. Also, it is generally preferred, where plasticizers are used, to add the plasticizer to the sulfur before adding the aggregate.

The ingredients are finally mixed together at temperatures above the melting point of sulfur or plasticized sulfur and below the decomposition or boiling point of the materials. Typically, mixing is affected at temperatures in the range of about from 1100 to 1 800C and preferably, about from 1250 to 1 600 C. In a preferred mode, the sulfur is combined in molten form with the plasticizer and then mixed with preheated aggregate. It is preferred to preheat the aggregate to prevent random cold spots in the mix and ensure good bonding between the sulfur cement and aggregate.

Typically, in the case of the sulfur cement mortars, the mortar contains about from 10 to 50 percent by weight, preferably about from 1 5 to 25 percent by weight, of sulfur cement and about from 50 to 90 percent by weight, preferably about from 75 to 85 percent by weight, of fine-size aggregate.

The fine-size aggregate generally has a particle size less than No. 8 mesh (U.S.A. Standard Testing Sieves), and in the case of the salt solution embodiment, preferably less than No. 1 6 mesh, and preferably, generally greater than 40 mesh and in the case of the dry salt embodiment preferably 50 to 100 percent of the fine-size aggregate is less than 1 6 mesh. Fine-size aggregates which can be used include, for example, plaster sand, Kaiser top sand, Monterey sands, Vulcan sands, and the like, and mixtures thereof.

In the case of sulfur cement concretes, larger-sized aggregate is used in place of all or a portion of the smaller-sized aggregate used for mortars. Typically, the larger-sized aggregate has a particle size of about from No. 4 to 1-1/2 inches, preferably, about from 3/8 to 3/4 inches. The sulfur concrete also preferably contains a lesser amount of smaller-sized aggregate particulate material similar to that used in mortars. Such small-sized aggregate or particulate material includes, for example, the various aggregate previously described herein with respect to the present sulfur cement mortar and typically have a particle size in the range of less than No. 8 mesh and preferably less than 1 6 mesh (U.S.A.

Standard Testing Sieves) but preferably predominantly greater than 40 mesh. Typically, the sulfur cement concrete comprises, by weight, about from 10 to 50 percent total sulfur cement (preferably containing 2-1/2 to 7 percent plasticizer in the case of the salt solution embodiment and 2 to 7 percent plasticizer in the case of the dry salt embodiment); 20 to 60 percent large-sized aggregate; and 30 to 70 percent small-sized aggregate.

As used herein, the term "mesh" is measured in and refers to the "U.S.A. Standard Testing Sieves" system also known as the "U.S. Sieve Series".

A further understanding of the invention can be had from the following non-limiting examples.

Example 1 This example illustrates the improved stability of the sulfur-aggregate compositions of the present invention as compared with the identical sulfur-aggregate compositions prepared without the salt treatment of the present invention.

Control mortars containing 25 percent by weight plasticized sulfur (95 percent by weight sulfur, 2.5 percent by weight dicyclopentadiene and 2.5 percent by weight cyclopentadiene oligomer), 0, 0.5, 1.0, or 3.0 percent bentonite clay and the remainder Kaiser top sand having a mesh size in the range of No. 4 to 100, were prepared. The control mortars were prepared by oven drying the bentonite clay and then mixing the requisite amount of clay with the sand. The clay-sand (1,500 g) mixture was preheated to about 1300C and then mixed with molten plasticized sulfur (500 g) at about 1300C and cast into three 2"x4" cylinders (per composition) and aged at room temperature overnight. A representative cylinder was selected for each composition and immersed in tap water and periodically visually inspected for fractures, cracks, etc., as failure.The days to failure of the respective samples are given in Table 1, hereinbelow.

The above procedure was repeated for 1 percent or 3 percent bentonite clay composition but in this case, the clay was immersed in 1 molar aqueous salt solution and aged overnight in the solution at room temperature. The clay was then removed by filtration, dried and ground back to size. The clay was then mixed with sand as above, mixed with molten sulfur and cast into three 2"x4" cylinders and aged overnight at room temperature. A control sample was also run using water in place of the aqueous salt solution. A representative cylinder for each composition was immersed in tap water and examined for fractures, cracks, etc., as above. The particular salt used and the time to failure of the cylinder for each composition are set forth in Table 1 below.

Table 1 % Wt. clay % Wt. based on Days to Salt clay aggregate* failure Control 0 17*' Control 0.5 0.67 11 Control 1.0 1.33 5 Control 3.0 4.0 0.25 Water 1.0 1.33 5 Water 3.0 4.0 0.125*' KCI 1.0 1.33 30 KCI 3.0 4.0 6 CaCI2 1.0 1.33 26 CaCI2 3.0 4.0 3 MgCI2 1.0 1.33 26 MgCI2 3.0 4.0 3 NH4CI 1.0 1.33 16 NH4CI 3.0 4.0 3 AI2(SO4)3 3.0 4.0 7 FeCI3 3.0 4.0 7 *Aggregate=sand+clay *1All three cylinders tested and average value given.

As can be seen from the above Table 1, where the control sample contained 1 percent bentonite, its life was 5 days whereas the life of the compositions, treated in accordance with the present invention, ranged from 1 6 days for ammonium chloride to 30 days for potassium chloride. In the case where the sample contained 3 percent bentonite, the average life increased from 6 hours for the control to from 3 days for ammonium chloride and magnesium chloride to 7 days for aluminum sulfate and ferric chloride and 6 days for potassium chloride. In each case where water was used alone, the average life was actually reduced as compared with the control.

Example 2 In this example, the same procedure was followed as in Example 1, except that a sulfur plasticizer was not used and the clay (bentonite) was mixed with the aggregate (Kaiser top sand) and then lightly sprayed with a 1 molar aqueous salt solution using about 120 to 1 50 ml of solution per 1,500 g of clay aggregate. After spraying the clay-aggregate mixture, the mixture was dried and mixed with the molten sulfur at 1250 to 1 350C and cast into three cylinders (per composition) as in Example 1. In certain instances, two trials were run for a given composition (i.e., six cylinders).A representative cylinder for each composition (or one for each trial where duplicate trials were run) was then immersed in tap water and visually inspected for cracks, crumbling, etc., every 2 hours for the first 8 hours and then inspected daily thereafter.

The particular salt used and the life of the cylinders using that salt are set forth in Table 2 hereinbelow. (Where two trials were run, average values are given).

As can be seen from Table 2, substantially poorer results were obtained than were obtained in Example 1, where the clay was immersed in the salt solution, but still substantially superior to a control sample wherein the clay-aggregate was sprayed with pure water. The poorer results can be attributed to the poorer salt solution contact with the clay-aggregate mixture and significantly the absence of sulfur plasticizer. (The significance of the plasticizer can be seen by comparing the water controls in Examples 1 and 2. In Example 1, using the plasticizer, the water control had a llfe of 3 hours whereas in the present example, the water control only had a life of 1 5 minutes).

Table 2 %Wt. % Clay in Days to Salt clay aggregate failure KCI 3 4 7 days CaCI2 3 4 2 days FeCI3 3 4 3 hours Al2(SO4)3 3 4 3 hours Water 3 4 1 5 minutes Example 3 In this example, the same procedure was followed as in Example 2, but in this instance, instead of being merely lightly sprayed with the salt solution, the clay-aggregate mixture was thoroughly wetted with a 1 molar salt solution. Also, instead of pure sulfur, the same sulfur binder (95 percent sulfur, 2.5 percent dicyclopentadiene and 2.5 percent cyclopentadiene oligomer) was used as used in Example 1.

The molten compositions were cast into three cylinders and aged overnight as in Example 1 and then a representative cylinder for each composition was immersed in water and examined visually for fractures, cracks, crumbling, etc. (In some instances, trials were repeated for certain compositions and average values reported). The observed life for each composition and the salt used are set forth in Table 3 hereinbelow.

As can be seen from Table 3, the compositions of the present invention exhibited very good stabilities, especially where 1 percent potassium chloride or calcium chloride was used.

Table 3 %wit. Days to Salt clay failure KCI 1 98+ KCI 5 41 CaCI2 1 98+ CaCI2 3 12 CaCI2 5 9 Example 4 In this example, the same procedure as used in Example 3 was followed with the exception that a 100 percent sulfur cement was used in place of the sulfur and plasticizer cement of Example 3. Also, for experimental purposes, a number of higher clay content samples were used. The results of the tests are summarized in Table 4 hereinbelow. The poorer results shown at the 3 percent clay level in Table 4, as compared with Table 3, demonstrates the importance of the plasticizer and also that pragmatically, that the treatment was ineffective in aggregate having an expansive-clay concentration above 7.5 percent by weight.

Table 4 % Wt. % Clay in Days to Salt clay aggregate failure CaCI2 3 4 2 days CaCI2 5 6.7 1-1/2 hours CaCI2 7.5 10 1/2 hour CaCI2 10 13.3 15 minutes Example 5 In this example, the effect of altering the concentration of the salt solution used in the spray treatment of Example 3 was examined. The same procedure and sulfur cement as used in Example 3 was followed with the exception that the concentration of the clay in the aggregate was fixed at 3 percent and the concentration of calcium chloride in the aqueous solution was varied instead.

The results of these tests are summarized in Table 5 hereinbelow. As can be seen from Table 5, the stability of the final product improved as the ratio of salt to clay was increased from 0.0125 mol per 100 g of clay to 0.25 g-mol per 100 g of clay.

Table 5 Salt G-Mols of concentration % Clay in salts per Days to Salt G-Mols/liter % Clay aggregate 100 G clay failure CaCI2 0.05 3 4 0.0125 2 CaCI2 0.5 3 4 0.125 7 CaCI2 1.0 3 4 0.25 12 Example 6 This example illustrates the dry salt composition and process embodiment of the invention, and the improved water stability afforded thereby.

Control sulfur cement-aggregate compositions containing 25 percent by weight plasticized sulfur (95 percent by weight sulfur, 2.5 percent by weight dicyclopentadiene and 2.5 percent by weight cyclopentadiene oligomer); 0, 0.5, 1.0, or 3.0 percent by weight bentonite clay (0, 0.67, 1.33, and 4.0 percent based on aggregate) and the remainder Kaiser top sand having a U.S.A. Standard Testing Sieves mesh size range of No. 4 to 100 were prepared by oven drying the bentonite clay and then mixing the requisite amount of clay with the sand. The clay-sand (1,500 g) mixture was then preheated to about 1 3000 and then mixed with the molten plasticized sulfur (500 g) at about 1 300 C. Each composition was cast into three 2"x4" cylinders and aged overnight at room temperature (about 200C).

Test samples illustrating the present invention were prepared following the same general procedure and using the same components and relative concentrations but in this instance the salt, and the amount thereof, indicated in Table 1 hereinbelow, was admixed with the Kaiser top sand and bentonite clay mixture. The aggregate-salt mixture was allowed to stand overnight and was then heated to 1400C and admixed with molten plasticized sulfur (95 percent sulfur, 2.5 percent dicyclopentadiene, 2.5 percent cyclopentadiene oligomer) at 1300C and cast into three 2"x4" (5.08 cmxl 0.16 cm) cylinders and aged overnight in the same manner as the control composition.Each test composition sample was prepared using 500 g of the sulfur cement, 1,440 g of sand and 60 g of bentonite clay plus varying amounts of either potassium chloride or calcium chloride.

A representative cylinder was selected for each of the control and test compositions. The selected cylinders were immersed in tap water at room temperature (about 200 C). The immersed cylinders were visually inspected daily for fractures, cracks, crumbling, etc. At the first evidence of any of these, the cylinder was considered to have failed. The days to failure of the respective cylinders is reported hereinbelow in Table 6.

As can be seen from Table 6, the compositions of the present invention had greatly superior water stabilities as compared to the corresponding control composition. The control composition containing 4 percent bentonite clay in the aggregate only had a life of about 6 hours in water, whereas the test compositions of the present invention, using the 4 percent bentonite clay-contaminated aggregate, exhibited lives of 5 days where the composition contained only 0.05 g-mol of calcium chloride per kg of aggregate, and upwards of 1 50 days where the test composition contained 0.1 gmol of calcium chloride or potassium chloride per kg of aggregate.

Table 6 Grams salt G-Mol salt Grams per 1000 G per 1000 G % Wt. clay Salt salt aggregate* aggregate in aggregate* Days to failure Control O - - 0 1 7*1 Control 0 0.67 11 Control 0 - - 1.33 5 Control 0 - - 4.0 about 6 hours CaCI2 8.3 5.53 0.05 4 5 CaCI2 16.6 11.07 0.1 4 150+ CaCI2 33.2 22.13 0.2 4 150+ KCI 5.6 3.73 0.05 4 14 KCI 11.2 7.47 0.1 4 150t KCI 22.4 13.93 0.2 4 150+ *Aggregate=sand+clay *1Average value of three cylinders.

Claims (23)

Claims

1. A sulfur cement-aggregate composition comprising an admixture of a sulfur cement and an aggregate which is contaminated with up to 5 percent by weight of an expansive clay, the aggregate being in association with a water-soluble salt effective to substantially reduce the water expandability of the expansive clay contaminant.

2. A composition as claimed in Claim 1, wherein discrete particles of said water-soluble salt are dispersed throughout said aggregate.

3. A composition as claimed in Claim 1, wherein the aggregate is contacted by a solution of said water-soluble salt and then allowed to dry prior to its admixture with the sulfur cement.

4. A composition as claimed in Claim 1,2 or 3, wherein the water-soluble salt has a water solubility at 300C of at least 10 g per litre.

5. A composition as claimed in Claim 1, 2, 3 or 4, wherein said salt is selected from potassium salts, alkaline earth metal salts, aluminum salts, and mixtures of two or more thereof.

6. A composition as claimed in Claim 5, wherein said salt is selected from potassium salts and calcium salts, and mixtures thereof.

7. A composition as claimed in Claim 6, wherein said salt is potassium chloride or calcium chloride.

8. A composition as claimed in Claim 2 or in any one of Claims 4 to 7 as appendant to Claim 2, wherein said composition comprises from 0.05 to 0.5 g-mol of said salt per kg of the expansive claycontaminated aggregate.

9. A composition as claimed in Claim 3 or in any one of Claims 4 to 7 as appendant to Claim 3, wherein said salt solution is an aqueous salt solution.

10. A composition as claimed in Claim 9, wherein said aqueous salt solution has a salt concentration in the range from 4 to 1 8 percent by weight

11. A composition as claimed in Claim 9, wherein said aqueous salt solution has a salt concentration in the range from 0.5 to 2 mols per litre.

12. A composition as claimed in Claim 9, wherein sufficient of said salt solution is contacted with said contaminated aggregate to provide from 0.003 to 0.05 parts by weight of said salt per part by weight of said expansive clay contaminant.

13. A composition as claimed in Claim 9, 10, 11 or 12, wherein said contacting is effected by slurrying the aggregate with said salt solution.

14. A composition as claimed in Claim 9, 10, 11 or 12, wherein said contacting is effected by spraying the aggregate with said salt solution.

1 5. A composition as claimed in any preceding claim, wherein said sulfur cement comprises plasticized sulfur.

1 6. A composition as claimed in Claim 15, wherein said plasticized sulfur is plasticized with a mixture of dicyclopentadiene and oligomers of cyclopentadiene.

1 7. A composition as claimed in any preceding claim, wherein said composition comprises from 1 5 to 25 percent by weight of said sulfur cement and about from 75 to 85 percent by weight of said aggregate.

18. A composition as claimed in any preceding claim, wherein said sulfur cement includes a powdered filler material.

19. A composition as claimed in any preceding claim, wherein a major portion of said aggregate has an average particle size in the range from 8 to 1 6 mesh.

20. A composition as claimed in any one of Claims 1 to 18, wherein a major portion of said aggregate has an average particle size in the range from 8 mesh to 3/4 inch diameter.

21. A composition as claimed in Claim 2 or in any one of Claims 4 to 20 as appendant to Claim 2, wherein said salt has an average particle size in the range from 100 to 200 mesh.

22. A composition as claimed in any preceding claim, wherein said aggregate is contaminated with less than 4 percent by weight of said expansive clay.

23. A sulfur cement-aggregate composition in accordance with Claim 1, substantially as described in any one of the foregoing Examples.