CN107311497B

CN107311497B - Concrete internal curing type expanding agent and preparation method thereof

Info

Publication number: CN107311497B
Application number: CN201611216596.4A
Authority: CN
Inventors: 李明; 刘加平; 田倩; 王育江; 徐文; 姚婷; 陆安群
Original assignee: Sobute New Materials Co Ltd; Nanjing Bote New Materials Co Ltd
Current assignee: Sobute New Materials Co Ltd; Nanjing Bote New Materials Co Ltd
Priority date: 2016-12-26
Filing date: 2016-12-26
Publication date: 2020-03-27
Anticipated expiration: 2036-12-26
Also published as: CN107311497A

Abstract

The invention discloses a concrete internal curing type expanding agent and a preparation method thereof. The concrete internal curing type expanding agent consists of an expanding clinker and a porous micro-medium, wherein the expanding agent plays a role in compensating shrinkage, and the porous micro-medium achieves the effects of internal curing shrinkage reduction and optimizing the hydration process of the expanding agent through humidity regulation and control and simultaneously serves as a dispersing carrier of the expanding clinker. The prepared concrete internal curing type expanding agent fully utilizes the synergistic effect of the two, can effectively reduce the self-shrinkage and drying shrinkage of concrete, reduces the temperature shrinkage in the temperature reduction stage after the temperature of the concrete is raised, can improve the hydration degree of the concrete, and overcomes the defect of strength reduction caused by the internally doped expanding agent.

Description

Concrete internal curing type expanding agent and preparation method thereof

Technical Field

The invention belongs to the field of building materials, and particularly relates to a concrete internal curing type expanding agent and a preparation method thereof.

Background

In fact, a concrete structure formed by pouring is in an environment with hydration-temperature-humidity-constraint multi-field coupling effect, under the multi-field coupling effect, the concrete can generate shrinkage deformation and internal stress, and when the tensile strength of the concrete is not enough to resist the compressive stress of the concrete, the concrete can crack. The cracking phenomenon is more serious along with the improvement of the fineness and early hydration rate of cement, and is commonly existed in structures such as a continuous side wall structure, a bottom plate, a middle plate, a top plate and the like. The generation of cracks poses threats and challenges to durability and structural safety service, and the subsequent crack repair also brings great cost. Therefore, it is necessary to take appropriate measures to control the cracks.

The concrete is caused to generate early shrinkage deformation cracking mainly due to two reasons: (1) moisture deformation, mainly embodied as self-shrinkage and drying shrinkage; (2) the temperature deformation is mainly reflected by the hydration temperature rise of the concrete and the expansion and contraction caused by the heat exchange with the surrounding environment. Therefore, besides the heat preservation and moisture preservation maintenance in the construction period, the concrete structure cracking risk, especially the cracking risk in the temperature reduction stage, can be reduced by compensating the volume deformation of the concrete or reducing the shrinkage deformation of the concrete through the humidity regulation in a mode of adding functional materials.

The publication numbers CN101774777B, CN102219422B, and CN102745933B disclose a calcium oxide-related expanding agent, which has a relatively fast expansion efficiency, often exerts its effect substantially before the temperature reduction stage of the actual concrete casting, cannot generate effective compensation shrinkage at the temperature reduction stage, and has a relatively poor expansion process regulation and control performance, so that the improvement effect on the cracking degree is limited, and the internal admixture often reduces the concrete strength.

Publication No. CN104671688A discloses a modified calcium oxide expansion clinker, a preparation method and application thereof. The reaction between carbon dioxide and the expansion clinker is utilized to form compact calcium carbonate on the surface of the expansion clinker, and the compact calcium carbonate is mixed with the dispersive carrier to prepare the modified calcium oxide expanding agent. After the expansion agent is modified, although the expansion amount and the expansion process are improved optimally, the compensation shrinkage capacity in the temperature reduction stage is still limited, and the strength of the concrete can still be reduced when the expansion agent is doped.

The publication No. CN103342494B discloses a hydration heat inhibition type concrete expansion material and a preparation method and application thereof, the expansion material is compounded with an expansion agent, a hydration heat inhibitor and an internal curing agent, and the risk of cracking of concrete is reduced by utilizing the compensation shrinkage effect of the expansion agent, the optimized regulation and control effect of the hydration heat inhibitor on the temperature history and the internal curing effect of super absorbent resin. In fact, the used internally-cured super absorbent resin still has problems in actual engineering application, the super absorbent resin does not absorb water in advance when the expansion material is internally doped, the internal curing effect is limited, and the super absorbent resin additionally absorbs water to form colloid when the expansion material is externally doped, so that the colloid is not uniformly distributed when a mixing plant is used for production and stirring, and the defect of holes in concrete is easily formed, and the strength is reduced. In addition, the hydration heat regulation and control effect is possibly influenced by the fluctuation of concrete raw materials, construction factors and seasonal factors (the construction season influences the concrete mold-entering temperature), and a large number of system tests need to be carried out before actual use, so that the expansion material has high application cost and low universality.

Publication No. CN102674738B discloses a multifunctional anti-cracking additive and a preparation method thereof, wherein the anti-cracking additive prepared by mixing and grinding the expansion amount of calcium oxide, dextrin and fly ash is utilized to realize the regulation and control of the temperature field and the expansion process of a concrete structure so as to reduce the anti-cracking risk to the maximum extent. However, the anti-cracking admixture still has the problems of high expansion efficiency, limited adjustability of expansion process and strength reduction.

The publication number CN105130335A discloses low-shrinkage crack-resistant C60-grade self-compacting bridge tower concrete based on internal curing, shrinkage compensation and toughening and a preparation method thereof, and the concrete is mainly used for the C60-grade self-compacting bridge tower concrete and is not suitable for urban rail transit engineering and basement wallboard structure concrete.

In the technology, the expansion clinker, the internal curing agent and the hydration heat regulation material are involved, and the expansion clinker, the internal curing agent and the hydration heat regulation material respectively play roles in compensating shrinkage, regulating and reducing internal humidity and regulating hydration heat. At present, the actual engineering application is more, the risk of concrete cracking is reduced by the compensation shrinkage effect brought by adding the expanding agent, the compensation shrinkage effect of the concrete at the temperature reduction stage is limited, the generation of cracks cannot be effectively controlled, and meanwhile, the concrete strength is reduced due to the fact that partial cementing materials are replaced. Therefore, in order to solve the above problems, it is necessary to prepare a novel multifunctional expanding agent in consideration of convenience of construction and effectiveness of crack resistance and shrinkage reduction.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a concrete internal curing type expanding agent, which takes a porous micro-medium with an internal curing effect as a dispersing carrier of an expansion clinker, the expanding agent plays a role in compensating shrinkage, the porous micro-medium plays a role in internal curing shrinkage reduction and optimizing the hydration course of the expanding agent through humidity regulation, the purposes of compensating shrinkage in the temperature reduction stage of concrete and later-period continuous internal curing humidity regulation shrinkage reduction are achieved, the cracking risk in the whole construction and concrete service period is further reduced, the cement hydration degree is improved, and the defect that the strength of the concrete is reduced by internally doping the expanding agent is overcome.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

a concrete internal curing type expanding agent comprises an expanding clinker and a porous micro-medium, wherein the expanding clinker accounts for 20-60% by mass, and the porous micro-medium accounts for 40-80% by mass;

the expansion clinker is calcium oxide expansion clinker which comprises free calcium oxide, sulphoaluminate, anhydrous gypsum and a mixture thereof;

the porous micro-medium is any one or a mixture of two of rice hull ash and ground porous light aggregate compounded in any proportion;

the average grain diameter of the rice hull ash is 5-80 mu m, and the grain diameter of the ground porous light aggregate is 5-160 mu m.

The levigated porous light aggregate is prepared by levigating porous light aggregate, and the water absorption rate is 8-25% 24h before levigating.

Preferably, the ground porous lightweight aggregate can be shale lightweight aggregate of 700-900 grades.

The preparation method of the concrete internal curing type expanding agent comprises the following steps:

(1) preparing expanded clinker powder: grinding the expanded clinker until the specific surface area is 200-400 m²Per kg, obtaining expanded clinker powder;

(2) preparing a porous micro-medium: treating and screening rice hull ash or ground porous light aggregate or a mixture of the rice hull ash and the ground porous light aggregate in any proportion, wherein the particle size of the rice hull ash or the ground porous light aggregate meets the requirement;

(3) and mixing the expanded clinker powder with the porous micro-medium according to the amount to obtain the concrete internal curing type expanding agent.

The invention also provides an application method of the concrete internal curing type expanding agent, and the concrete internal curing type expanding agent can be used in a mode of replacing the internal mixing of the cementing material and can also be used in a mode of external mixing; the concrete is recommended to be doped in an internal doping mode, the doping amount is calculated according to the mass percentage of the total concrete cementing materials, the optimal doping amount is recommended to be 4-6% for the plate structure, and the optimal doping amount is recommended to be 8-10% for the side wall structure.

When the concrete internal curing type expanding agent is used, the single water consumption of concrete is adjusted, and the additional water consumption for 24 hours is calculated according to the using amount of the single concrete porous micro-medium and the water absorption for 24 hours, so that the additionally increased water consumption of the concrete is 0.8 times of the additional water consumption for 24 hours.

The invention has the beneficial effects that:

(1) the concrete internal curing type expanding agent prepared based on the invention can play a role in reducing shrinkage at a temperature reduction stage with a larger cracking risk of a concrete structure, effectively reduce the cracking risk, continuously play a role in regulating and reducing internal curing humidity, reduce the shrinkage deformation of concrete, improve the hydration degree and make up for the defect that the strength of the concrete is reduced by internally doping the expanding agent.

(2) The concrete internal curing type expanding agent provided by the invention is simple in preparation and use methods, convenient to construct and low in comprehensive crack resistance cost.

Drawings

FIG. 1 is a temperature history after concrete pouring of an underground side wall of an urban rail transit project.

FIG. 2 shows the results of the self-contraction test under normal temperature conditions in example 1.

FIG. 3 shows the results of the volume deformation test under variable temperature conditions in example 1.

FIG. 4 shows the results of the self-contraction test under normal temperature conditions in example 2.

FIG. 5 shows the results of the volume deformation test under variable temperature conditions in example 2.

FIG. 6 shows the results of the self-contraction test under normal temperature conditions in example 3.

FIG. 7 shows the results of the volume deformation test under the temperature-varying conditions in example 3.

Detailed Description

In order to better understand the present invention, the following examples are further illustrative, but the present invention is not limited to the following examples, and all the percentages are by mass unless otherwise specified.

Example 1

Crushing the commercial calcium oxide expansion clinker into 200m of specific surface area²The curing expanding agent IEA-I10 kg in concrete is prepared by fully mixing rice hull ash with the average grain diameter of 20 mu m and 40 percent of calcium oxide clinker with 60 percent of rice hull ash.

The concrete is prepared according to the mixing proportion of the concrete on the side wall of a subway station of a certain rail transit engineering shown in the table 1, wherein a reference group is that no expanding agent is added, an EA group is that a commercially available calcium oxide expanding agent is added, an IEA-I group is that an internal curing type expanding agent IEA-I prepared by the invention is added, two expanding materials are added into the concrete in a mode of internally doping to replace a cementing material, the doping amount is 8%, wherein the water absorption rate of rice hull ash for 24 hours is 11%, and the increase of the water consumption of a single component is calculated to be 1.6 kg. The compression strength of the concrete is tested according to the standard GB/T50081-2002 of the test method for the mechanical property of the common concrete, the self-contraction deformation of the concrete is tested according to the standard GB/T50082-2009 of the test method for the long-term property and the durability of the common concrete, and the limited expansion rate of EA and IEA-I is tested according to the GB23439-2009 of the concrete expanding agent. In order to further evaluate the effect of compensating shrinkage of the internal curing type expanding agent in the concrete temperature drop stage, according to an entity temperature monitoring curve of the concrete of the side wall of the station (as shown in fig. 1, a temperature changing program is conveniently set, and the entity monitoring curve is subjected to smoothing treatment), as can be seen from an entity monitoring result shown in fig. 1, the mold entering temperature of the concrete is 35 ℃, the concrete temperature rises to 71 ℃ within 1.5d, and then the temperature is reduced at a rate of about 6.5 ℃/d, so that a large temperature drop shrinkage stress is generated when the potential ratio of the concrete temperature reduction rate is too fast, and a vertical temperature crack is easily generated under the constraint of a foundation and the like. Setting a temperature change course of a temperature change box, carrying out deformation test under the temperature change condition, pouring concrete into a PVC pipe before the test, embedding a differential strain gauge, and sealing the whole test piece by using aluminum foil paper.

TABLE 1 concrete mix proportion (kg/m)³)

The test results of the concrete compressive strength and the limited expansion rate are shown in the table 2, and the results show that the calcium oxide expansive agent EA in the market and the concrete internal curing expansive agent IEA-I prepared by the invention meet the type II requirement, after the EA with the mass ratio of 8% is added, the strength of the concrete at different ages is reduced by about 8% -10%, after the IEA-I is added, the strength of the concrete at the early age is basically not influenced, and the later strength is improved.

TABLE 2 mechanical Properties and limiting expansion Rate test results

The result of the self-contraction test of the concrete under the indoor normal temperature condition specified by the standard is shown in fig. 2, and the result shows that the self-contraction of the concrete can be effectively eliminated and considerable expansion is brought, and it is pointed out that after the EA is added, the expansion efficiency of the concrete is completely exhausted after the age of 20d, then the contraction trend begins to appear, and after the IEA-I is added, the concrete still continuously expands at the later stage, which shows that the comprehensive expansion efficiency is superior to that of the EA.

The deformation test under the temperature-changing course based on the entity monitoring is shown in fig. 3, and the result shows that the expansion amount brought by IEA-I is slightly higher than EA in the temperature-rising stage, only 5 mu epsilon is compensated after the EA is doped in the temperature-reducing stage compared with the benchmark, and 36 mu epsilon is compensated by the doped IEA-I, so that the compensation and shrinkage-reducing effects of the IEA-I in the whole temperature course change range of the concrete are better than that of the EA, and particularly the compensation and shrinkage effects in the temperature-reducing stage can effectively reduce the cracking risk of the concrete.

Example 2

Crushing the commercial calcium oxide expansion clinker into 400m of specific surface area²A powder of the formula (I)/kg,the 700-grade shale lightweight aggregate is selected and crushed to the particle size range of 5-80 mu m, the 24-hour absorption rate is 23.5%, and the concrete internal curing expanding agent IEA-II 10kg is prepared after fully mixing according to the proportion of 40% of calcium oxide clinker and 60% of ground lightweight aggregate.

The concrete is prepared according to the mixing proportion of the concrete on the side wall of a subway station of a certain rail transit engineering shown in the table 3, wherein a reference group is that no expanding agent is added, an EA group is that a commercially available calcium oxide expanding agent is added, an IEA-II group is that an internal curing type expanding agent IEA-II prepared by the invention is added, and both expanding materials are added into the concrete in a mode of internally adding the expanding material instead of the cementing material, and the adding amount is 9%. Wherein, the single water consumption is increased by 3.8kg by calculation according to the 24h water absorption of the lightweight aggregate of 23.5 percent. The compression strength of the concrete is tested according to the standard GB/T50081-2002 of the test method for the mechanical property of the common concrete, the self-contraction deformation of the concrete is tested according to the standard GB/T50082-2009 of the test method for the long-term property and the durability of the common concrete, and the limited expansion rate of EA and IEA-II is tested according to the GB23439-2009 of the concrete expanding agent. Meanwhile, deformation test under variable temperature condition is carried out according to the temperature history shown in figure 1.

TABLE 3 concrete mix ratio (kg/m)³)

The test results of the concrete compressive strength and the limited expansion rate are shown in the table 4, and the results show that the calcium oxide expansive agent EA sold in the market and the concrete internal curing expansive agent IEA-II prepared by the invention meet the type II requirement, after the EA with the mass ratio of 9 percent is added, the strength of the concrete at different ages is reduced by about 10 to 12 percent, after the IEA-II is added, the strength of the concrete at the early age is basically not influenced, and the later strength is improved.

TABLE 4 mechanical Properties and limiting expansion Rate test results

The self-contraction test result of the concrete under the indoor normal temperature condition specified by the standard is shown in figure 4, and the result shows that after the IEA-II is added, the early expansion efficiency is equivalent to that of EA, the concrete still shows continuous expansion at the later stage and brings larger expansion amount, and the comprehensive expansion efficiency is superior to that of EA.

The deformation test based on the temperature change process of the entity monitoring is shown in fig. 5, and the result shows that the expansion amount brought by IEA-II is obviously higher than EA in the temperature rise stage, so that the expansion pressure stress is formed in the reinforced concrete. In the temperature reduction stage, compared with the benchmark, the doped EA only compensates for 5 mu epsilon, the compensation effect in the temperature reduction stage is limited, and the doped IEA-II compensates for 53 mu epsilon, so that the compensation shrinkage reduction effect of the IEA-II in the whole temperature course change range of the concrete is better than that of the EA, and particularly the compensation shrinkage effect in the temperature reduction stage can effectively reduce the cracking risk of the concrete.

Example 3

Crushing the commercial calcium oxide expansion clinker into 300m of specific surface area²Selecting 900-grade shale light aggregate as powder, crushing the shale light aggregate until the particle size range is 80-160 mu m, fully mixing the shale light aggregate with the absorption rate of 15.6 percent for 24 hours according to the proportion of 30 percent of calcium oxide clinker and 70 percent of ground light aggregate, and preparing the concrete internal curing expanding agent IEA-III10 kg.

The concrete is prepared according to the mixing proportion of the concrete of the subway station floor of the rail transit engineering shown in the table 5, wherein the reference group is that no expanding agent is added, the EA group is that a commercial calcium oxide expanding agent is added, the IEA-III group is that a concrete internal curing type expanding agent IEA-III prepared according to the invention is added, and both expanding materials are added into the concrete in a mode of internally mixing and replacing a cementing material, and the mixing proportion by mass is 6%. Wherein, the single water consumption is increased by 2.0kg by calculation according to the 24h water absorption of the lightweight aggregate of 15.6 percent. The compression strength of the concrete is tested according to the standard GB/T50081-2002 of the test method for the mechanical property of the common concrete, the self-contraction deformation of the concrete is tested according to the standard GB/T50082-2009 of the test method for the long-term property and the durability of the common concrete, and the limited expansion rate of EA and IEA-III is tested according to the GB23439-2009 of the concrete expanding agent. And simultaneously carrying out deformation test under the condition of variable temperature.

TABLE 5 concrete mix ratio (kg/m)³)

The test results of the concrete compressive strength and the limited expansion rate are shown in the table 6, and the results show that the calcium oxide expansive agent EA sold in the market and the concrete internal curing expansive agent IEA-III prepared by the invention meet the type II requirement, after the EA with the mass ratio of 6% is added, the strength of the concrete at different ages is reduced by about 8-10%, after the IEA-III is added, the strength of the concrete at the early age is basically not influenced, and the later strength is improved.

TABLE 6 mechanical Properties and limiting expansion Rate test results

The results of the self-contraction test of the concrete under the indoor normal temperature conditions specified by the standard are shown in fig. 6, and the results show that after the incorporation of EA, the expansion efficiency of the concrete is almost exhausted after the 10d age, and then the contraction trend begins to appear, after the incorporation of IEA-III, the early expansion efficiency is equivalent to that of EA, and the concrete still shows continuous expansion at the later stage, and brings larger expansion amount, and show that the comprehensive expansion efficiency is superior to that of EA.

The deformation test based on the entity monitoring temperature change process is shown in fig. 7, and the result shows that the expansion amount brought by IEA-III is obviously higher than EA in the temperature rise stage, so that expansion compression stress is formed in reinforced concrete, in the temperature drop stage, EA is added to compensate only 4 mu epsilon, compared with the benchmark, the compensation effect in the temperature drop stage is limited, and IEA-III is added to compensate 38 mu epsilon, so that the compensation and shrinkage reduction effects of IEA-III in the whole concrete temperature process change range are better than EA, and particularly the compensation and shrinkage effects in the temperature drop stage can effectively reduce the cracking risk of concrete.

It is apparent that the above embodiments are only examples for clearly illustrating and do not limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications are therefore intended to be included within the scope of the invention as claimed.

Claims

1. The concrete internal curing type expanding agent is characterized in that: the expanded clinker aggregate porous medium comprises 20-60% of expanded clinker aggregate and 40-80% of porous micro medium;

the expansion clinker is calcium oxide expansion clinker which comprises free calcium oxide, sulphoaluminate, anhydrous gypsum and a mixture thereof; the porous micro-medium is any one or a mixture of two of rice hull ash and ground porous light aggregate compounded in any proportion;

the average grain size of the rice hull ash is 5-80 mu m, and the grain size of the ground porous light aggregate is 5-160 mu m.

2. The concrete internal curing type expanding agent as claimed in claim 1, wherein the ground porous light aggregate is prepared by grinding porous light aggregate, and the water absorption rate is 8% -25% 24h before grinding.

3. The concrete internal curing expanding agent as claimed in claim 2, wherein the ground porous lightweight aggregate is shale lightweight aggregate of 700-900 grade.

4. The method for preparing the concrete internal curing type expanding agent as claimed in any one of claims 1 to 3, which is characterized by comprising the following steps:

5. The method for applying the concrete internal curing type expanding agent as claimed in any one of claims 1 to 3, wherein the expanding agent can be used in an internal mixing mode or an external mixing mode; the concrete is doped in an internal doping mode, the doping amount is calculated by the mass percent of the total concrete cementing material, and for a plate structure, the doping amount is 4-6%, and for a side wall structure, the doping amount is 8-10%.

6. The method for applying the concrete internal curing type expanding agent as claimed in claim 5, wherein the expanding agent is used for adjusting the single water consumption of the concrete, and the additional water consumption for 24 hours is calculated according to the single concrete porous micro-medium consumption and the water absorption for 24 hours, so that the additional water consumption of the concrete is 0.8 times of the additional water consumption for 24 hours.