Ultra-high performance concrete admixture as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of chemical building materials, and particularly relates to an ultra-high performance concrete admixture as well as a preparation method and application thereof. The admixture is in a dry powder state and comprises an auxiliary material and a solid polycarboxylate superplasticizer in a mass ratio of (5-20): (80-95), and the auxiliary material comprises the following components in parts by mass: 5-10 parts of a co-dispersant, 1-5 parts of silicon dioxide, 0.5-1 part of inorganic carbonate, 1-5 parts of inorganic silicate and 0.05-0.5 part of a defoaming agent. The admixture has the characteristics of low mixing amount, viscosity reduction, high early strength and the like, is mixed into an ultra-high performance concrete premix in a powder state, not only can obviously reduce the viscosity of the ultra-high performance concrete, but also can obviously improve the early strength of the ultra-high performance concrete, and has no negative influence on the later mechanical properties of the ultra-high performance concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical building materials, and specifically relates to an admixture for ultra-high performance concrete and a preparation method and application thereof. Background Art

[0002] Ultra-high performance concrete (UHPC) is a new type of cement-based material with ultra-high strength, high toughness and high durability. It is increasingly widely used in engineering fields such as bridges, buildings, nuclear power, municipal engineering, and oceans. The characteristics of low water-cement ratio, large amount of adhesive, and high steel fiber content cause the UHPC mixture to have high viscosity and low fluidity, and it is necessary to add a higher dose of water reducer than ordinary concrete to ensure its construction performance. The polycarboxylate water reducer used in ordinary concrete has limited water-reducing performance. Even if the dosage is increased, it is impossible to fully disperse the UHPC adhesive under low water-cement ratio conditions, resulting in a series of problems such as high viscosity, long setting time, and slow early strength development in the produced UHPC.

[0003] Zhang Haijiao et al. conducted a comparative study on ordinary polycarboxylate water reducers and UHPC-specific polycarboxylate water reducers, indicating that the ordinary polycarboxylate water reducer not only increased the dosage by 43%, significantly prolonged the setting time, but also significantly reduced the compressive strength (Reference: Research on the Application of Ordinary Polycarboxylate Water Reducer in Ultra-High Performance Concrete, New Building Materials, 2023).

[0004] Gao Yujun et al. studied the effects of molecular structure changes of polycarboxylic acid water-reducing agents on the workability and strength of UHPC from the perspective of water-reducing agent synthesis, and obtained the optimal process control parameters. However, liquid water-reducing agents have a high water content and are not suitable for direct application in UHPC premixes (Reference: Effects of Polycarboxylic Acid Water-Reducing Agents with Different Structures on the Performance of Ultra-High Performance Concrete, Chemical Research and Applications, 2023). Summary of the invention

[0005] In view of the problems of high viscosity and slow early strength development of ultra-high performance concrete, the present invention provides an admixture for ultra-high performance concrete and its preparation method and application. The admixture has the characteristics of low dosage, viscosity reduction and high early strength. It is directly added to the premix in powder state, which can significantly improve the flow rate and 24-hour strength of UHPC at room temperature.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] An admixture for ultra-high performance concrete, the admixture is in a dry powder state, comprising auxiliary materials and a solid polycarboxylate water reducer in a mass ratio of (5-20):(80-95), wherein the auxiliary materials comprise the following components in parts by mass: 5-10 parts of a co-dispersant, 1-5 parts of silicon dioxide, 0.4-1 parts of an inorganic carbonate, 1-5 parts of an inorganic silicate, and 0.05-0.5 parts of a defoamer.

[0008] Preferably, the co-dispersant has a structure shown in general formula I:

[0009]

[0010] Wherein, R represents -CH3 or -CH2CH3;

[0011] a=1-10.

[0012] Studies have found that the above-mentioned co-dispersant is particularly suitable for the admixture system of the present invention, has more excellent synergistic dispersion and efficient lubrication effect at a low water-binder ratio, and promotes the improvement of the mechanical strength of concrete to a certain extent.

[0013] Preferably, the silicon dioxide is fumed silicon dioxide with a particle size of less than 100 nm, and the type may be hydrophilic or hydrophobic.

[0014] Preferably, the inorganic carbonate is selected from one of sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate, and magnesium carbonate, or a mixture of any proportions thereof. The soluble carbonate is added to the concrete to react chemically with calcium ions dissolved in the cement clinker, and nanometer-sized calcium carbonate particles are generated under the combined action of the polycarboxylate water reducer and the co-dispersant, which can further promote the compactness and strength of the concrete.

[0015] Preferably, the inorganic silicate is selected from one or a mixture of hydrated calcium silicate, sodium silicate, potassium silicate, calcium silicate crystal nucleus in any proportion.

[0016] Preferably, the solid polycarboxylate water-reducing agent is prepared by vacuum freeze-drying and grinding a liquid polycarboxylate water-reducing agent mother liquid; the water-reducing rate of the base mortar of the solid polycarboxylate water-reducing agent is ≥60%, and the chloride ion content is ≤0.1wt%. The "base mortar water-reducing rate" is the water-reducing rate measured by the experimental method specified in the "Technical Requirements for Ultra-High Performance Concrete Water-Reducing Agents" issued by the China Building Materials Federation and the China Concrete and Cement Products Association.

[0017] Further preferably, the liquid polycarboxylate water-reducing agent mother liquor is selected from one of VPEG type polycarboxylate water-reducing agent mother liquor, TPEG type polycarboxylate water-reducing agent mother liquor, HPEG type polycarboxylate water-reducing agent mother liquor, or a mixture of several of them in any proportion. The molecular weight of the raw material polyether macromonomer used in preparing the liquid polycarboxylate water-reducing agent mother liquor is ≥3000, and preferably the molecular weight of the polyether macromonomer is 4000 or 5000.

[0018] The present invention also provides a method for preparing the above-mentioned ultra-high performance concrete admixture, comprising the following steps:

[0019] 1) uniformly mixing the co-dispersant, inorganic carbonate, inorganic silicate and defoamer to obtain a composite premix S1;

[0020] 2) mixing the solid polycarboxylate water-reducing agent and silicon dioxide uniformly, and crushing them by a pulverizer to obtain a composite premix S2;

[0021] 3) The composite premix S1 and the composite premix S2 are mixed evenly, and then ultrasonically crushed and sieved to obtain the concrete admixture.

[0022] In the preparation method provided by the present invention, the solid polycarboxylate water-reducing agent and silicon dioxide are separately premixed and crushed in step 2) to avoid agglomeration and moisture absorption of the polycarboxylate water-reducing agent powder. Silicon dioxide can act as an isolating agent to prolong its storage stability.

[0023] In a preferred embodiment, in step 2), the solid polycarboxylate water-reducing agent and silicon dioxide are uniformly mixed by first stirring and then ultrasonic vibration.

[0024] In a preferred embodiment, in step 3), the composite premix S1 and the composite premix S2 are mixed uniformly by ultrasonic vibration.

[0025] The present invention also provides application of the ultra-high performance concrete admixture in ultra-high performance concrete.

[0026] The beneficial effects of the present invention are at least:

[0027] 1) The ultra-high performance concrete admixture provided by the present invention can effectively reduce the viscosity of ultra-high performance concrete and improve its fluidity. In particular, after the viscosity is reduced, bubbles are more easily discharged, the air content of ultra-high performance concrete is reduced, and the strength performance of ultra-high performance concrete is improved;

[0028] 2) The ultra-high performance concrete admixture provided by the present invention introduces reactive inorganic silicates and inorganic carbonates, which can reduce the inhibitory effect of the water reducer on cement hydration, promote the early hydration of ultra-high performance concrete, shorten the setting time and improve the early strength;

[0029] 3) The ultra-high performance concrete admixture provided by the present invention is in a dry powder state when not in use, and can be added when producing ultra-high performance concrete premix, which is more convenient to use than liquid water reducer;

[0030] 4) The ultra-high performance concrete admixture provided by the present invention has excellent water-reducing performance, excellent dispersibility in the water-binder ratio range of 0.12-0.20, low dosage and long-lasting flowability. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention is described clearly and completely below. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product instructions are used.

[0032] In the following examples, the co-dispersants used are from Wanhua Chemical (a is 1, R is -CH3) and Huntsman Company products (a is 3, R is -CH3).

[0033] The fumed silica is derived from Evonik Degussa (hydrophilic type) and Deshan Chemical (hydrophobic type).

[0034] The VPEG solid polycarboxylate water reducer used is prepared by vacuum freeze drying and grinding the mother liquor of VPEG liquid polycarboxylate water reducer produced and sold by China Construction Western Construction New Materials Technology Co., Ltd.;

[0035] The TPEG solid polycarboxylate water reducer used is prepared by vacuum freeze drying and grinding the mother liquor of TPEG liquid polycarboxylate water reducer produced and sold by China Construction Western Construction New Materials Technology Co., Ltd.;

[0036] The HPEG solid polycarboxylate water reducer used is prepared by vacuum freeze drying and grinding the HPEG liquid polycarboxylate water reducer mother liquor produced and sold by China Construction Western Construction New Materials Technology Co., Ltd.;

[0037] The defoaming agent used is a powder defoaming agent with modified polyether as the main ingredient, which comes from Nanjing Qinghai Chemical. Powder defoaming agents of other brands can also be used.

[0038] Example 1

[0039] An admixture for ultra-high performance concrete, the raw material components of which mainly include, by weight: 10 parts of a co-dispersant, 3 parts of hydrophilic fumed silica with a particle size of less than 100 nm, 0.5 parts of sodium carbonate, 5 parts of hydrated calcium silicate, 0.05 parts of a defoamer, and 80 parts of a VPEG type solid polycarboxylate water reducer. The co-dispersant is Jeffamin D-230, which has the following structure:

[0040]

[0041] Wherein a is 3 and R is -CH3.

[0042] Prepare according to the following steps:

[0043] (1) The co-dispersant, sodium carbonate, calcium silicate hydrate and defoamer are uniformly mixed according to their weight proportions to form a composite premix S1.

[0044] (2) 80 parts of VPEG solid polycarboxylate water-reducing agent (polyether macromonomer molecular weight = 3000, water reduction rate 41%, chloride ion content 0.01%) and 3 parts of fumed silica were weighed and mixed, and then pulverized in a pulverizer for 20 minutes to obtain a powder polycarboxylate water-reducing agent mixture S2 containing silica.

[0045] (3) Add the mixture S2 obtained in step (2) to S1, mix thoroughly and evenly, and then ultrasonically crush, sieve (80 mesh sieve, the same below) and package to obtain the ultra-high performance concrete admixture.

[0046] Example 2

[0047] An admixture for ultra-high performance concrete, the raw material components of which are mainly composed of: 5 parts of co-dispersant, 1 part of hydrophilic fumed silica with a particle size of less than 100 nm, 0.7 parts of potassium carbonate, 4 parts of hydrated calcium silicate, 1 part of sodium silicate, 0.05 parts of defoamer, and 90 parts of HPEG type solid polycarboxylate water reducer, by weight. The co-dispersant has the following structure:

[0048]

[0049] Wherein a is 1 and R is -CH3.

[0050] Prepare according to the following steps:

[0051] (1) The co-dispersant, potassium carbonate, hydrated calcium silicate, sodium silicate and defoamer are uniformly mixed according to their weight proportions to form a composite premix S1.

[0052] (2) 90 parts of HPEG-type solid polycarboxylate water-reducing agent (polyether macromonomer molecular weight = 4000, water reduction rate 45%, chloride ion content 0.03%) and 1 part of fumed silica were weighed and mixed, and then pulverized in a pulverizer for 20 minutes to obtain a powder polycarboxylate water-reducing agent mixture S2 containing silica.

[0053] (3) Add the mixture S2 obtained in step (2) into S1, mix thoroughly and evenly, and then ultrasonically crush, sieve and package to obtain an ultra-high performance concrete admixture.

[0054] Example 3

[0055] An admixture for ultra-high performance concrete, the raw material components of which mainly include, by weight: 5 parts of a co-dispersant, 3 parts of hydrophobic fumed silica with a particle size of less than 100 nm, 0.3 parts of lithium carbonate, 0.7 parts of magnesium carbonate, 5 parts of hydrated calcium silicate, 0.1 parts of a defoamer, and 95 parts of an HPEG-type solid polycarboxylate water reducer. The co-dispersant has the following structure:

[0056]

[0057] Wherein a is 1 and R is -CH3.

[0058] Prepare according to the following steps:

[0059] (1) The co-dispersant, lithium carbonate, magnesium carbonate, calcium silicate hydrate and defoamer are uniformly mixed according to their weight proportions to form a composite premix S1.

[0060] (2) 95 parts of HPEG solid polycarboxylate water-reducing agent (polyether macromonomer molecular weight = 5000, water reduction rate 40%, chloride ion content 0.01%) and 3 parts of hydrophobic fumed silica were weighed and mixed, and then pulverized in a pulverizer for 20 minutes to obtain a silica-containing powder polycarboxylate water-reducing agent mixture S2.

[0061] (3) Add the mixture S2 obtained in step (2) into S1, mix thoroughly and evenly, and then ultrasonically crush, sieve and package to obtain an ultra-high performance concrete admixture.

[0062] Example 4

[0063] An admixture for ultra-high performance concrete, the raw material components of which are mainly composed of: 5 parts of co-dispersant, 5 parts of hydrophilic fumed silica with a particle size of less than 100 nm, 0.3 parts of lithium carbonate, 0.1 parts of ammonium carbonate, 5 parts of calcium silicate crystal nuclei, 0.1 parts of defoamer, and 80 parts of VPEG type solid polycarboxylate water reducer, by weight. The co-dispersant has the following structure:

[0064]

[0065] Wherein a is 1 and R is -CH3.

[0066] Prepare according to the following steps:

[0067] (1) The co-dispersant, lithium carbonate, ammonium carbonate, calcium silicate crystal nuclei and defoaming agent are uniformly mixed according to their weight proportions to form a composite premix S1.

[0068] (2) 80 parts of VPEG solid polycarboxylate water-reducing agent (polyether macromonomer molecular weight = 5000, water reduction rate 40%, chloride ion content 0.01%) and 5 parts of hydrophilic fumed silica were weighed and mixed, and then pulverized in a pulverizer for 20 minutes to obtain a silica-containing powder polycarboxylate water-reducing agent mixture S2.

[0069] (3) Add the mixture S2 obtained in step (2) into S1, mix thoroughly and evenly, and then ultrasonically crush, sieve and package to obtain an ultra-high performance concrete admixture.

[0070] Example 5

[0071] An admixture for ultra-high performance concrete, the raw material components of which mainly include, by weight: 10 parts of a co-dispersant, 5 parts of hydrophilic fumed silica with a particle size of less than 100 nm, 0.3 parts of lithium carbonate, 0.1 parts of potassium carbonate, 4 parts of calcium silicate crystal nuclei, 1 part of potassium silicate, 0.1 parts of a defoamer, and 80 parts of a TPEG-type solid polycarboxylate water reducer. The co-dispersant is Jeffamin D-230, which has the following structure:

[0072]

[0073] Wherein a is 3 and R is -CH3.

[0074] Prepare according to the following steps:

[0075] (1) The co-dispersant, lithium carbonate, potassium carbonate, calcium silicate crystal nuclei, potassium silicate and defoaming agent are uniformly mixed according to their weight proportions to form a composite premix S1.

[0076] (2) 80 parts of TPEG-type solid polycarboxylate water-reducing agent (polyether macromonomer molecular weight = 3000, water reduction rate 45%, chloride ion content 0.01%) and 5 parts of hydrophilic fumed silica were weighed and mixed, and then pulverized in a pulverizer for 20 minutes to obtain a silica-containing powder polycarboxylate water-reducing agent mixture S2.

[0077] (3) Add the mixture S2 obtained in step (2) into S1, mix thoroughly and evenly, and then ultrasonically crush, sieve and package to obtain an ultra-high performance concrete admixture.

[0078] Control group

[0079] The control group used ordinary powdered polycarboxylate water reducer, which was prepared according to the method described in the literature “Effects of modified polysiloxane on the properties of synthetic solid polycarboxylate water reducer, New Building Materials, 2021”.

[0080] Application Examples

[0081] The performance of the ultra-high performance concrete prepared in Examples 1-5 of the present invention and the ordinary powder polycarboxylate water-reducing agent in the control group were tested. The concrete mix ratio used in the test is: 450kg cement, 100kg fly ash, 55kg silica fume, 760kg sand, 990kg gravel, appropriate amount of fiber, and 110kg water; the amount of the admixture of the embodiment or the ordinary powder polycarboxylate water-reducing agent in the control group in the concrete is 5.5kg. The test method refers to the "Standard for Test Methods for Performance of Ordinary Concrete Mixtures" (GB / T 50080-2016) to test its performance.

[0082] Table 1 Ultra-high performance concrete performance test results

[0083]

[0084] As shown in Table 1, the concrete prepared in the control group has a high viscosity, a collapse flow rate time of 15s, and is not completely hardened after 16h of curing at room temperature. However, the concrete mixture prepared using Examples 1 to 5 of the present invention has a flow rate of less than 5s, a low viscosity, and is easy to flow. The strength reaches more than 30MPa after 16h of curing under the same conditions, and the 28d strength is more than 120MPa, which is significantly higher than the control group.

[0085] In summary, the admixture of the present invention can not only significantly reduce the viscosity of ultra-high performance concrete, but also significantly improve the early strength of ultra-high performance concrete, and has no negative impact on the later mechanical properties of ultra-high performance concrete.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An admixture for ultra-high performance concrete, characterized in that: The admixture is in a dry powder state, including auxiliary materials and solid polycarboxylic acid water reducer in a mass ratio of (5-20): (80-95), wherein the auxiliary materials include the following components in parts by mass: 5-10 parts of a co-dispersant, 1-5 parts of silicon dioxide, 0.4-1 parts of an inorganic carbonate, 1-5 parts of an inorganic silicate, and 0.05-0.5 parts of a defoaming agent.

2. The ultra-high performance concrete admixture according to claim 1, characterized in that: The co-dispersant has a structure shown in general formula I: Wherein, R represents -CH3 or -CH2CH3; a＝1-10。 3. The ultra-high performance concrete admixture according to claim 1 or 2, characterized in that: The silicon dioxide is fumed silicon dioxide with a particle size less than 100 nm.

4. The ultra-high performance concrete admixture according to claim 1 or 2, characterized in that: The inorganic carbonate is selected from one of sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate and magnesium carbonate or a mixture of the two or more of the two or more in any proportion.

5. The ultra-high performance concrete admixture according to claim 1 or 2, characterized in that: The inorganic silicate is selected from one of hydrated calcium silicate, sodium silicate, potassium silicate, calcium silicate crystal nucleus or a mixture of several of them in any proportion.

6. The ultra-high performance concrete admixture according to claim 1 or 2, characterized in that: The solid polycarboxylate water reducer is prepared by sequentially vacuum freeze drying and grinding a liquid polycarboxylate water reducer mother solution; the base mortar water reduction rate of the solid polycarboxylate water reducer is ≥60%, and the chloride ion content is ≤0.1wt%.

7. The ultra-high performance concrete admixture according to claim 6, characterized in that: The liquid polycarboxylate water-reducing agent mother liquor is selected from one of VPEG type polycarboxylate water-reducing agent mother liquor, TPEG type polycarboxylate water-reducing agent mother liquor, and HPEG type polycarboxylate water-reducing agent mother liquor, or a mixture of several of them in any proportion.

8. The method for preparing the admixture for ultra-high performance concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) uniformly mixing the co-dispersant, inorganic carbonate, inorganic silicate and defoamer to obtain a composite premix S1; 2) mixing the solid polycarboxylate water-reducing agent and silicon dioxide uniformly, and crushing them by a pulverizer to obtain a composite premix S2; 3) The composite premix S1 and the composite premix S2 are mixed evenly, and then ultrasonically crushed and sieved to obtain the concrete admixture.

9. Use of the ultra-high performance concrete admixture according to any one of claims 1 to 7 in ultra-high performance concrete.

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