CN114380527B

CN114380527B - Reinforced modifier for concrete admixture and preparation method thereof

Info

Publication number: CN114380527B
Application number: CN202210289392.2A
Authority: CN
Inventors: 李镓睿; 张祖华; 甄彧; 郑伟; 周恩涛; 徐威武
Original assignee: Hunan Ningying New Material Technology Co ltd
Current assignee: Hunan Ningying New Material Technology Co ltd
Priority date: 2022-03-23
Filing date: 2022-03-23
Publication date: 2022-05-24
Anticipated expiration: 2042-03-23
Also published as: CN114380527A

Abstract

The invention provides a strengthening modifier for concrete admixture and a preparation method thereof, wherein the preparation method mainly comprises the steps of carrying out emulsion polymerization on acrylamide, allyl alcohol, acrylic acid, allyl (diisopropylamino) dihydrosilane and four functional monomers under ultrasonic emulsification under an oxidation-reduction initiation system to form a copolymer solution, adding two auxiliary agents of sodium metasilicate and tetrasodium ethylene diamine tetraacetate into the copolymer solution, stirring and dissolving to obtain the strengthening modifier for concrete admixture. The invention can improve the hydration limit of the admixture, improve the hydration speed, simultaneously strengthen the capability of the inactive admixture to be cemented by cement, and promote the cement hydration products, such as C-S-H gel to fully cover the surface and the internal pores of the admixture.

Description

Reinforced modifier for concrete admixture and preparation method thereof

Technical Field

The invention relates to the technical field of building materials, in particular to a strengthening modifier for a concrete admixture and a preparation method thereof.

Background

The concrete admixture is used as a cementing material in concrete. The common concrete admixture for commercial concrete at present comprises fly ash, mineral powder, limestone powder and steel slag powder. The nature of these admixtures in concrete determines that they can make up no more than 45% of the total cementitious material, the amount of single admixtures generally does not exceed 30%, even limestone flour, which is considered as an admixture with no cementitious activity, is strictly limited to 20%. The root cause of the above limitation is due to insufficient activity of the admixture. According to the definition of national standard, the activity of admixture is defined as the ratio of the strength of mortar after curing to the strength of mortar without admixture of cement after mixing with admixture of standard sand. In the above-mentioned conventional admixtures, only the activity of the ore fines can reach more than 95%, and they are called S95 grade ore fines. The activity of other admixtures is often only 70-80%, and the activity of limestone powder is even only 60-70%.

The main reasons for insufficient admixture activity are that they have no or insufficient cementing ability. The insufficient cementing capacity is mainly reflected in the following two aspects: materials (such as steel slag powder, fly ash and the like) which have general hydraulicity or can form hydraulicity together with alkaline substances, and the main reason of low activity is insufficient hydration capability; the low activity of the materials which do not have hydraulic property (such as limestone powder, ground silica sand and the like) is mainly caused by insufficient cementation with the cementing material, and the C-S-H gel generated by the cementing material (mainly cement) is difficult to permeate into the pores of admixture micro-powder particles and cannot be cemented, and the property is even not beneficial to the strength of concrete and is harmful.

The current auxiliary agents for improving the activity of concrete admixtures on the market are generally grinding aids or similar activators (such as triethanolamine), but the related products generally have the functions of chelating calcium ions on the surfaces of gelled materials including the admixtures, increasing the solubility of the calcium ions, enabling the calcium ions to reach complete hydration in advance and further improving the activity index of the admixtures. However, the product can not change the problem of insufficient hydration capability of the admixture, only the hydration process is induced to be completed in advance by increasing the solubility of calcium ions, and compared with the general process of slowly dissolving and hydrating without adding grinding aid, the product has higher hydration degree at 28 days, thereby improving the activity of the admixture. But the problem of insufficient total hydration capacity of the admixture cannot be solved, and the increase difference of the mortar strength is worse than that of the admixture without the grinding aid at 90 days.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a strengthening modifier for a concrete admixture and a preparation method thereof. The invention realizes the improvement of the cementing capacity (or the cemented capacity) of the admixture and the great improvement of the activity of the admixture mainly by changing the surface property and the porosity property of the admixture. According to the invention, the surface activity is improved by combining the composite surface modifier with the composite surfactant and breaking silicon-oxygen tetrahedrons and structures on the surface of the admixture and capturing surface calcium ions. The invention can improve the hydration limit of the admixture, improve the hydration speed, simultaneously strengthen the capability of the inactive admixture to be cemented by cement, and promote the cement hydration products, such as C-S-H gel to fully cover the surface and the internal pores of the admixture.

In order to achieve the purpose, the invention provides a preparation method of a strengthening modifier for a concrete admixture, which comprises the following steps:

firstly, dissolving 15 parts of acrylic acid, 25-35 parts of acrylamide, 25-35 parts of allyl alcohol and 1 part of ferrous sulfate in 240 parts of water, uniformly stirring in a reactor, and heating to 60 ℃ to obtain a base solution;

secondly, taking 5-15 parts of allyl (diisopropylamino) dihydrosilane, 0.2 part of mercaptoethanol, 1 part of ammonium persulfate and 50 parts of water, stirring and mixing, emulsifying by using an ultrasonic emulsifier, and emulsifying to obtain an emulsion A;

thirdly, dripping the emulsion A into the base solution at a constant speed within 120 minutes into a reactor, and keeping the ultrasonic emulsifier working and continuously stirring at 60-75 ℃ in the process; after the dripping is finished, continuously stirring for at least 60 minutes to obtain a polymer B;

and fourthly, adding 1-2 parts of sodium metasilicate and 1-2 parts of ethylene diamine tetraacetic acid tetrasodium salt (EDTA-4 Na for short) into the reactor, and fully stirring and dissolving to obtain the strengthening modifier for the admixture.

Further, in the first step, 30 parts of acrylamide and 30 parts of allyl alcohol are used.

Further, in the second step, allyl (diisopropylamino) dihydrosilane was 10 parts.

Further, the molecular weight of the obtained polymer B is 2 to 5 ten thousand.

The invention also provides a strengthening modifier for the concrete admixture, which is prepared by the preparation method of the strengthening modifier for the concrete admixture.

The invention has the following beneficial effects:

1. the strengthening modifier for the concrete admixture, which is prepared by the invention, realizes the improvement of the cementing capacity (or the cemented capacity) of the admixture and the great improvement of the activity of the admixture by changing the surface property and the pore property of the admixture. The synthesized B Polymer (PAAA) has surface activity, coordination and bonding property (can combine with free oxygen on the surface of silicon dioxide), and plays a key role in improving the activity of the admixture.

Specifically, the B polymer PAAA contains carboxylic acid groups, so that good surface activity is provided, and meanwhile, the B polymer PAAA plays a role in dispersing admixture particles, breaks the flocculation structure of the admixture particles, enables the admixture particles to be fully dispersed in cement-based slurry, enhances the contact area between cement and the admixture particles, and increases the cementing capacity of the cement to the admixture particles.

The carboxylic acid groups and hydroxyl groups in the B polymer PAAA play a grinding-aiding role to a certain extent, negative electricity is provided in the grinding process to neutralize the positive electricity on the surface of the particles, and the particles are adsorbed on the surface to prevent the broken particles from gathering again. In addition, the carboxylic acid groups and hydroxyl groups in the B polymer PAAA can also form hydrogen bonds with OH < - > existing in dicalcium silicate and tricalcium silicate in the hydration process, so that the growth direction of calcium silicate hydrate crystals is promoted to grow along the surface and internal pores of admixture particles. This is because the polymer molecules are adsorbed on the surface of the admixture particles and on the internal pore walls, which has a certain guiding effect on the crystal growth.

The nitrogen atom in the amide group in the B polymer PAAA has lone pair electrons, so that the coordination to calcium ions can be well carried out, and the solubility of the calcium ions on the surface of the admixture is increased. The process is carried out under the participation of EDTA-4Na, calcium ions which are stabilized on the surface of the crystal are captured by the EDTA, the calcium ions are stably chelated, and after the stability of the balance of the surface of the crystal is broken, the allylamine can play a role according to N atoms on residues. The solubility of calcium ions is increased, so that more media in the particles participate in the hydration reaction, and the hydration reaction is performed more quickly and completely.

The silicon atom introduced by allyl (diisopropylamino) dihydrosilane (ADDS) in the B polymer PAAA can form Si-O-Si with the newly generated terminal Si-O free O atom on the surface of silicon oxide (such as silicon dioxide or silicon-oxygen glass body) after the nitrogen atom coordinates with calcium ions, so that polymer molecules are fixed on the surface of admixture particles, the orderliness of Si-O tetrahedron is broken, and stable (CaO) x (SiO) is forced₂) The y crystals react with the base during hydration and contribute to the silicon atoms in the silane groups entering [ SiO ]₄]The tetrahedron is involved in the generation process of the C-S-H gel, changes the properties of the mineral which cannot be hydrated originally, increases the substances involved in the hydration reaction, and ensures that the hydration degree is more thorough. During the milling process, there are a large number of free O atoms on the nascent surface for silicon bonding, as the particles continue to create a nascent surface.

2. After synthesizing the B polymer PAAA, 1-2 parts of sodium metasilicate and 1-2 parts of EDTA-4Na are added for mixing and compounding. Wherein the sodium metasilicate on one hand provides an alkaline environment and on the other hand can temporarily occupy the newly generated surface [ SiO4]Tetrahedrally, preventing it from re-bonding with the newly formed faces of other admixture particles. The main function of EDTA-4Na is to destroy (CaO) x (SiO)₂) The lattice integrity of y, EDTA-4Na has strong chelating ability, can directly extract calcium ions from the solid surface and chelate the calcium ions to form defect sites, and is helpful for the entry and attachment of PAAA molecules.

3. The reinforcing modifier for the concrete admixture is mainly used for improving the cementing capacity (or the cemented capacity) of the admixture and greatly improving the activity of the admixture by changing the surface property and the pore property of the admixture. According to the invention, the surface activity is improved by combining the composite surface modifier with the composite surfactant and breaking silicon-oxygen tetrahedrons and structures on the surface of the admixture and capturing surface calcium ions.

In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is an electron micrograph of a 28d cemented sand test piece after fracturing using a comparative example;

FIG. 2 is an electron micrograph of a blended 28d mortar specimen after fracturing using an embodiment of the present invention;

FIG. 3 is an electron micrograph of a 28d mortar specimen after fracturing using a second blend of the present invention;

FIG. 4 is a schematic diagram of the polymerization equation and the structure of the product in the synthesis of B according to the present invention;

FIG. 5 is a regression plot demonstrating that PAAA molecules adsorb to the surface of admixture particles in a chemisorbed fashion for ICP-OES testing.

Detailed Description

Embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways as defined and covered by the claims.

The first embodiment is as follows:

the first step is that 15 parts of acrylic acid, 30 parts of acrylamide, 30 parts of allyl alcohol and 1 part of ferrous sulfate are taken and dissolved in 240 parts of water, the mixture is stirred evenly in a reactor and heated to 60 ℃ to obtain base liquid.

And secondly, taking 10 parts of ADDS, 0.2 part of mercaptoethanol, 1 part of ammonium persulfate and 50 parts of water, stirring and mixing, emulsifying by using an ultrasonic emulsifier, and emulsifying to obtain the emulsion A. The phacoemulsifier is kept working throughout the manufacturing process to maintain the emulsified state.

And thirdly, dripping the solution A into the base solution at a constant speed in 120 minutes into a reactor, keeping the ultrasonic emulsifier working, keeping the reactor continuously stirred, and keeping the temperature in the reactor to be not lower than 60 ℃ and not higher than 75 ℃.

And fourthly, continuously stirring until no more opacified liquid exists in the reactor after the dropwise addition is finished, and stirring for at least 60 minutes. If the emulsion has a coagulation phenomenon and is aggregated into droplets, the ultrasonic emulsifier is placed in the reactor to continue working, and stirring is kept until the liquid in the reactor is clear, so as to obtain a polymer B (PAAA for short), wherein the specific reaction equation is shown in FIG. 4.

And fifthly, adding 1 part of sodium metasilicate and 1.5 parts of EDTA-4Na into the reactor, and fully stirring and dissolving to obtain the strengthening modifier for the admixture.

Example two:

the first step is that 15 parts of acrylic acid, 35 parts of acrylamide, 30 parts of allyl alcohol and 1 part of ferrous sulfate are taken and dissolved in 240 parts of water, the mixture is stirred evenly in a reactor and heated to 60 ℃ to obtain base liquid.

And secondly, taking 5 parts of ADDS, 0.2 part of mercaptoethanol, 1 part of ammonium persulfate and 50 parts of water, stirring and mixing, emulsifying by using an ultrasonic emulsifier, and emulsifying to obtain the emulsion A. The phacoemulsifier is kept in operation throughout the fabrication process to maintain the emulsified state.

And thirdly, dripping the solution A into the base solution at a constant speed in 120 minutes into a reactor, keeping the ultrasonic emulsifier working during the period, keeping the reactor stirred continuously, and keeping the temperature in the reactor to be not lower than 60 ℃ and not higher than 75 ℃.

And fourthly, continuously stirring until no more opacified liquid exists in the reactor after the dropwise addition is finished, and stirring for at least 60 minutes. If the emulsion has coagulation and is aggregated into droplets, the ultrasonic emulsifier is placed in the reactor to continue working, and the stirring is kept until the liquid in the reactor is clear.

And fifthly, adding 1 part of sodium metasilicate and 2 parts of EDTA-4Na into the reactor, fully stirring and dissolving to obtain the strengthening modifier for the admixture.

Example three:

the first step is that 15 parts of acrylic acid, 30 parts of acrylamide, 35 parts of allyl alcohol and 1 part of ferrous sulfate are taken and dissolved in 240 parts of water, the mixture is stirred evenly in a reactor and heated to 60 ℃ to obtain base liquid.

And secondly, taking 15 parts of ADDS, 0.2 part of mercaptoethanol, 1 part of ammonium persulfate and 50 parts of water, stirring and mixing, emulsifying by using an ultrasonic emulsifier, and emulsifying to obtain the emulsion A. The phacoemulsifier is kept working throughout the manufacturing process to maintain the emulsified state.

And fourthly, continuously stirring until no more opacified liquid exists in the reactor after the dropwise addition is finished, and stirring for at least 60 minutes. If the emulsion has a coagulation phenomenon and is aggregated into droplets, the ultrasonic emulsifier is placed in the reactor to continuously work, and the stirring is kept until the liquid in the reactor is clear.

Comparative example one: 0.03% triethanolamine

According to the China building industry standard JG/T486-2015 composite admixture for concrete, the activity index and the mortar strength growth ratio are tested, 30% of steel slag powder, 60% of limestone powder and 10% of granulated blast furnace slag powder are used as raw materials, and 0.1% of the active index and the mortar strength growth ratio is mixed in the first embodiment, the second embodiment and the first comparative embodiment. The activity indexes of the examples and the comparative examples were tested while keeping the fineness of the admixtures of the examples and the comparative examples between 9 and 10% of the screen residue of the 45 μm square mesh screen. The results are shown in Table 1:

TABLE 1

Case(s)	3d Activity index	7d Activity index	28d Activity index	90d mortar strength growth ratio
					Comparative example 1	58.2%	66.4%	75.1%	0.96
Example one	68.2%	85.7%	102.3%	1.05
					Example two	66.3%	81.2%	97.7%	1.03

From the above data, it can be seen that the activity data of the examples are significantly better than the comparative examples, while example two is slightly better than example one. This is probably because the raw materials in this example are limestone powder and steel slag powder as main raw materials, and the calcium content is higher, and the use of more acrylamide and EDTA-4Na is more helpful to the activity improvement.

The 28d mortar samples of the first example, the second example and the first comparative example were broken and observed under a scanning electron microscope, and magnified 30000 times to obtain the following three figures, as shown in FIGS. 1-3. It can be seen from the figure that the hydration degree of the first and second examples is much higher than that of the first comparative example, the hydration product coverage is obviously higher, the compaction degree is obviously higher, and the porosity is lower. Meanwhile, the growth directions of the calcium silicate hydrate crystals are different from each other, and the crystals are regularly grown on the surface in the embodiment and have main tendencies of horizontal and inward growth; in contrast, in comparative example I it can be seen that the crystals grow randomly, with a large number of dendrites growing outward, affecting the cementation of the calcium silicate hydrate crystals to the admixture particles. This is because PAAA has a guiding effect on crystal growth, and particularly, when PAAA molecules are bonded on the surface of admixture particles, hydroxyl groups of the PAAA molecules can form chemical bonding force such as hydrogen bonds with free Si-OH groups in C-S-H gel on the surface of newly grown crystals, so that the PAAA molecules are promoted to grow along the surface of the admixture particles instead of growing outwards. Therefore, the invention is verified to have the effects of increasing the limit hydration degree and the cementation degree of the inactive admixture. The experimental results of the third embodiment are similar to those of the first and second embodiments, and are not repeated herein.

The reinforcing modifier for the concrete admixture prepared by the invention can improve the hydration limit of the admixture, improve the hydration speed, simultaneously strengthen the capability of the inactive admixture to be cemented by cement, and promote cement hydration products, such as C-S-H gel to fully cover the surface and the internal pores of the admixture. Because, in the grinding process, because the admixture particles are continuously destroyed, new semi-free oxygen atoms are continuously generated on the surface, and silicon atoms in the polymer can be combined with the semi-free oxygen atoms to form silicon-oxygen bonds, so that the polymer is fully attached to the surfaces of the admixture particles. While adhering, the crystal ordered structure of the original silicon-oxygen tetrahedron is destroyed, and stable (CaO) x (SiO2) y crystals are forced to react with alkali in the hydration process and participate in the generation process of the C-S-H gel (playing a role of crystal nucleus or directly reacting with water to form calcium silicate hydrate). In addition, the amide group in the polymer can coordinate calcium ions, so that the solubility of the calcium ions on the surface of the admixture is increased, the interior of the admixture is fully exposed to promote the hydration process of the admixture, and the hydration limit is increased. Since most of the PAAA is bonded to the surface of the powder particles or the inner surface of the pores therein, the above-mentioned effects occur on these surfaces, and the C-S-H products produced by these effects are also concentrated on these surfaces without being diffused without directionality.

In addition, only after polymerization can the function be effectively exerted. This is because, although the groups carried by the respective monomers are functional, they must be bonded to the surface of the admixture particle before they can exert their respective effects, and many of them have no adsorbability by themselves, for example, propenol and acrylamide neither have electronegativity as in acrylic acid nor silicon atoms in ADDS molecules capable of forming Si-O bonds, and are difficult to bond effectively to the surface of the admixture particle. Therefore, after the polymer is formed, carboxyl negative ions can drive the whole molecular chain to be close to the surface of the admixture particle, and silicon atoms can anchor the whole PAAA molecule on the surface of the admixture.

To verify that the PAAA molecules adsorb to the surface of the admixture particles in a chemisorbed form, the following experiment was performed:

preparing a standard solution: preparing the solution of the first embodiment into a standard solution with four concentrations of 0.01%, 0.005%, 0.001% and 0.0005%, adding a small amount of sulfuric acid to make the pH of the standard solution less than 7, precipitating sodium metasilicate, and performing suction filtration to obtain the standard solution.

In the first embodiment, the admixture prepared by grinding the raw materials of 30% of steel slag powder, 60% of limestone powder and 10% of granulated blast furnace slag powder which are mixed in 0.1% is used. Taking 10g of finished admixture, adding 89g of water and 1g of 1M sulfuric acid solution to prepare 10% suspension, carrying out ultrasonic treatment for 10min at 40kHz with 100W power, adding sulfuric acid into the filtered clear liquid to acidify until the pH is =7, and filtering out the precipitate generated by sodium metasilicate to obtain the clear liquid to be tested.

The ICP-OES test was performed on the standard solution and the filtered clear solution, the silicon element was quantitatively analyzed, a standard curve was drawn with the standard solution, linear fitting was performed, and then calculation was performed, and the results are shown in table 2:

TABLE 2

	ExamplesA concentration of	Si atom concentration/ppb
			Standard solution 1	0.0100%	381
Standard solution 2	0.0050%	198
			Standard solution 3	0.0010%	40
Standard solution 4	0.0005%	20
			Solution to be tested	0.00137% (calculated by regression)	38

The regression equation was calculated as: y =3.802 × 10⁶x +2.8348, correlation coefficient R²=0.9996, substantially complete linear correlation (as shown in fig. 5). The Si concentration of the solution to be measured is measured to be 38ppb, and the concentration of the solution dissolved in the solution is calculated to be 0.0009 percent which is equivalent to that of the first embodiment; however, the actual amount added was 0.1%, the total content in the 10% suspension was 0.01%, and the sonication excluded physical adsorption, which still gave a measurable concentration of only 0.00137%, thus confirming that at least 86.3% of the PAAA molecules were chemisorbed to the admixture particles.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The preparation method of the strengthening modifier for the concrete admixture is characterized by comprising the following steps of:

and fourthly, adding 1-2 parts of sodium metasilicate and 1-2 parts of tetrasodium ethylene diamine tetraacetate into the reactor, fully stirring and dissolving to obtain the reinforced modifier for the concrete admixture.

2. The method of claim 1, wherein in the first step, the amount of acrylamide is 30 parts and the amount of allyl alcohol is 30 parts.

3. The method of claim 1, wherein in the second step, the allyl (diisopropylamino) dihydrosilane is present in an amount of 10 parts.

4. The method of claim 1, wherein the molecular weight of the polymer B is from 2 to 5 million.

5. A strengthening modifier for concrete admixture, characterized in that, it is prepared by the method of any one of claims 1 to 4.