CN108751764B - Modified calcium oxide expanding agent for compensating shrinkage concrete and preparation method thereof - Google Patents
Modified calcium oxide expanding agent for compensating shrinkage concrete and preparation method thereof Download PDFInfo
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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Abstract
The modified calcium oxide expanding agent for the shrinkage-compensating concrete is prepared by mixing and ball-milling 0.1-20 wt% of the modifying agent and 80-99.9 wt% of the calcium oxide expanding agent; the calcium oxide expanding agent is an expanding agent containing free calcium oxide, and the free calcium oxide is used as a stable expansion source for playing a role in expansion; the modifier is composed of one or more of the following substances: sodium sulfate or a crystalline hydrate thereof, ammonium bisulfate or a crystalline hydrate thereof, sodium sulfite or a crystalline hydrate thereof, ammonium sulfite or a crystalline hydrate thereof. The modified expanding agent can reduce the early hydration rate of the expanding agent, reduce the expansion energy loss of the expanding agent in the concrete plasticity stage, improve the expansion rate, reduce the contribution degree of the expanding agent to the temperature rise of the concrete, avoid influencing the setting time of the concrete and avoid reducing the slump and the expansion degree of the concrete. The preparation method is simple, can be used for batch production, and does not use toxic and other dangerous goods as raw materials.
Description
Technical Field
The invention relates to the field of building materials, and particularly provides a preparation method of a modified calcium oxide expanding agent with low early hydration rate and high limited expansion rate for compensating shrinkage concrete.
Background
The early volume change of concrete is an important factor causing the concrete cracking, and mainly comprises chemical shrinkage reduction, autogenous shrinkage, drying shrinkage and cooling shrinkage of a cementing material. The most common way to control the cracking of concrete is to reduce the temperature reduction shrinkage of concrete, such as adding inert admixture, stirring with cooling water, reducing the temperature of raw materials, reducing the reactivity of cementitious materials, etc. The calcium oxide expanding agent used for compensating the shrinkage concrete has an excessively high hydration rate in a hydration process, generates a large amount of heat in a short time, causes the temperature of the concrete to be higher, increases the cracking risk caused by the temperature reduction and shrinkage of the concrete, and reduces the effective expansion energy of the calcium oxide expanding agent. Therefore, the early hydration rate of the calcium oxide expanding agent is reduced, the contribution degree of the calcium oxide expanding agent to the temperature of concrete is reduced, and the effective expansion energy of the calcium oxide expanding agent is improved.
According to the law of conservation of energy, the heat generated by the calcium oxide expanding agent in the hydration process is certain. In order to reduce the contribution degree of the calcium oxide expanding agent to the temperature rise of the concrete, the hydration rate needs to be reduced as much as possible, and the hydration period needs to be prolonged, so that the heat release concentration is reduced, and the effective expansion energy can be improved.
In the current market, most of high-performance concrete expanding agents are calcined by taking limestone as a main raw material to obtain calcium oxide expanding agents taking free calcium oxide as a stable expansion source. However, the early hydration rate of the expanding agent is high, so that most of the expanding energy is consumed in the concrete plasticity stage, the compensation shrinkage capacity in an effective expansion window is insufficient, and the expected compensation shrinkage effect cannot be achieved; in addition, the temperature rise of the concrete can be increased by the concentrated heat release of free calcium oxide in the expanding agent, so that the temperature cracking risk of the concrete is increased; finally, such bulking agents also suffer from poor moisture barrier properties, short shelf life, and the like. Therefore, in order to solve the above problems, it is urgently required to optimize the calcium oxide-based expanding agent.
The expansive agent or the modified expansive agent of the concrete in the prior art mostly influences the setting time of the concrete, reduces the slump and the expansion degree of the concrete and is not beneficial to concrete construction.
Chinese patent CN103964722A discloses a chemical admixture for improving the efficiency of concrete expanding agent under limited conditions, which mentions that the use of sodium phosphate salt as an admixture can improve the limited expansion rate of concrete, but sodium phosphate salt has a retarding effect on the concrete gelling system, and the patent does not provide relevant data on the influence of the setting time of concrete.
Chinese patent CN103435317A is a compound expanding agent for inhibiting temperature rise in early stage and promoting hydration in later stage. The composite expanding agent consists of calcium oxide, sulphoaluminate cement clinker, anhydrite, magnesium oxide, boric acid, zinc sulfate and ICA, and the composite expanding agent comprises the following components in percentage by mass: 10-30% of calcium oxide, 28-43% of sulphoaluminate cement clinker, 25-40% of anhydrite, 5-15% of magnesium oxide, 0.3-0.5% of boric acid, 1-1.5% of zinc sulfate and 0.2-0.5% of ICA. The addition of boric acid, zinc sulfate and other substances in the patent can delay the reaction rate of the expanding agent in the early stage of hydration, weaken the peak value of hydration heat release, delay the occurrence time of the heat release peak, and reduce the hydration temperature rise together with ICA. However, the preparation method of the composite expanding agent in the patent is complex and is not beneficial to scale production.
Chinese patent CN104671689A discloses a modified calcium oxide expanded clinker, its preparation method and its application, wherein it is mentioned that the modified calcium oxide expanded clinker is obtained by reacting sulfur dioxide gas or sulfuric acid with an expanding agent. The invention adopts a mechanism that calcium sulfate is attached to the surface of the calcium oxide expanding agent to achieve the effect of improving the expansion performance and the moisture resistance of the calcium oxide expanding agent. The reaction rate of the sulfur dioxide and the calcium oxide expanding agent is inconvenient to control, the expanded clinker powder needs to be flatly laid in a reaction container to ensure that the expanded clinker powder is fully contacted with the sulfur dioxide, the large-scale production of the modified expanding agent is not facilitated, and the calcium oxide expanded powder is easy to form agglomeration during the heating reaction in a heat preservation furnace, so that the specific surface area of the calcium oxide expanded powder is reduced, and the activity of the calcium oxide expanded powder is influenced. When the sulfuric acid impregnation method is used, the reaction rate is not convenient to control, a solvent is required to be added, and the solvent is required to be filtered, dried and removed in the later period; the calcium oxide expansion powder is easy to agglomerate in the process of dipping and drying, and the temperature is easy to be too high due to the too fast addition of the sulfuric acid, so that the reaction speed is influenced, and the later expansion performance is also influenced. And sulfur dioxide gas and sulfuric acid have toxicity and strong corrosivity, so that great safety risk exists, and large-scale popularization is not facilitated.
The above-mentioned patent technologies are all actively exploring the modification of the expanding agent to achieve better performance for compensating the shrinkage of the concrete. However, the methods have limitations, and better methods for improving the performance of the calcium oxide-based expanding agent need to be researched.
Disclosure of Invention
Aiming at the technical defects, the invention aims to provide a modified calcium oxide expanding agent for compensating shrinkage concrete and a preparation method thereof. The preparation method is simple, can realize batch production, and does not use toxic or strong corrosive raw materials.
The modified calcium oxide expanding agent for the shrinkage-compensating concrete is prepared by mixing and ball-milling 0.1-20 wt% of the modifying agent and 80-99.9 wt% of the calcium oxide expanding agent; the calcium oxide expanding agent is an expanding agent containing free calcium oxide, and the free calcium oxide is used as a stable expansion source for playing a role in expansion; the modifier consists of one or more of the following substances: sodium sulfate or a crystalline hydrate thereof, ammonium bisulfate or a crystalline hydrate thereof, sodium sulfite or a crystalline hydrate thereof, ammonium sulfite or a crystalline hydrate thereof.
The preparation method of the modified calcium oxide expanding agent for the compensation shrinkage concrete comprises the following steps: putting the modifier and the calcium oxide expanding agent into a ball mill, performing ball milling for 30-60 min, reacting the modifier with calcium oxide on the surfaces of calcium oxide expanding agent particles under the combined action of mechanical force and heat generated by the ball mill, generating calcium sulfate or calcium sulfite which is difficult to dissolve in water on the surfaces of the calcium oxide expanding agent particles, and sieving the calcium sulfate or the calcium sulfite through a 80-micron square-hole sieve to prepare the modified calcium oxide expanding agent for the compensation shrinkage concrete.
The preparation method of the modified calcium oxide expanding agent is simple and practical. By adopting a direct ball milling mode, under the combined action of mechanical force and heat generated by a grinding ball, the modifier is in solid-phase reaction with calcium oxide on the surfaces of calcium oxide type expanding agent particles, so that agglomeration among the calcium oxide type expanding agent particles can be prevented in the ball milling process, the activity of the modified calcium oxide type expanding agent is ensured, the calcium oxide and the modifier can be fully mixed, and the surface of the calcium oxide and the modifier are favorably generated into substances (such as calcium sulfate and calcium sulfite) which are difficult to dissolve in water and are attached to the surfaces of the expanding agent particles. Because free calcium oxide is isolated from water, the loss of the calcium oxide expanding agent in the concrete plasticity stage can be reduced, the hydration reaction rate is reduced, the free calcium oxide inside reacts with water to generate effective volume expansion along with the reaction and dissolution of calcium sulfate and calcium sulfite in a concrete cementing material system, and the expansion rate of the concrete is finally improved.
The modifier can be any one of sodium sulfate or a crystal hydrate thereof, ammonium bisulfate or a crystal hydrate thereof, sodium sulfite or a crystal hydrate thereof, and ammonium sulfite or a crystal hydrate thereof, or a mixture of several of the above in any proportion; compared with the sulfur dioxide or sulfuric acid modifier mentioned in the patent, the modifier is nontoxic and noncorrosive, is convenient for safe production, can be produced in batch, has controllable reaction rate in the ball milling process, and can form the modified calcium oxide expanding agent with uniform and compact surface, large specific surface area and high activity.
The modified calcium oxide expanding agent prepared by the invention forms a layer of compact calcium sulfate or calcium sulfite sediment which is difficult to dissolve in water on the surface after modification, so that the moisture resistance of the calcium oxide expanding agent can be improved. The fluidity and the slump of the concrete can be increased to a certain extent, the influence on the setting time of the concrete is small, and the construction of the concrete is facilitated.
Preferably, the specific surface area of the calcium oxide expanding agent is 150-400 m2Per kg, wherein the content of free calcium oxide (f-CaO) is 20-85 wt%. The calcium oxide expanding agent optimized in the scheme can react with the modifier more quickly to prepare the modified calcium oxide expanding agent with higher activity, so that the expansion rate is higher.
Preferably, the material is prepared by mixing and ball-milling 1-10% of modifier and 90-99% of calcium oxide expanding agent by mass percentage. The modifier and the calcium oxide expanding agent in the proportion not only can ensure better mixing reaction of the modifier and the calcium oxide expanding agent, but also can ensure that the modified calcium oxide expanding agent has high expansion rate, has less influence on the gelation time of concrete, can improve the slump and the expansion degree to a certain extent, and is more favorable for concrete construction.
Preferably, the modifier consists of sodium sulfate and ammonium bisulfate in a mass ratio of 0.5-2: 1. The ammonium sulfate and the ammonium bisulfate in the preferred proportion are used for modifying the calcium oxide expanding agent, so that the reaction rate is more suitable, and the uniform and compact calcium sulfate is more favorably formed on the surface of the calcium oxide; the moisture resistance of the calcium oxide expanding agent is improved.
More preferably, the modifier is prepared by mixing and ball-milling 5% of modifier and 95% of calcium oxide expanding agent by mass, and the mass ratio of sodium sulfate to ammonium bisulfate in the modifier is 1: 1. The preferable scheme can ensure that the reaction speed and the reaction degree are more proper, and the free modifier in the modified calcium oxide expanding agent product is proper, so that the modified calcium oxide expanding agent has less influence on the setting time of the concrete, and the slump and the expansion degree of the concrete are not influenced.
Compared with the prior art, the invention has the beneficial effects that:
(1) the modified calcium oxide expanding agent disclosed by the invention can reduce the early hydration rate of the calcium oxide expanding agent, reduce the expansion energy loss of the calcium oxide expanding agent in the concrete plasticity stage and improve the expansion rate of the calcium oxide expanding agent;
(2) the preparation method of the modified calcium oxide expanding agent is simple and practical and is convenient for industrialization, the ball milling not only generates mechanical force and heat, but also can improve the dispersibility, enable the reaction to be faster and more uniform, and also can improve the specific surface area of the product and the expansion rate;
(3) the modifier used in the invention is nontoxic and non-corrosive, is convenient for safe production, has proper reaction rate, and can form uniform and compact sediments on the surface of calcium oxide; the influence on the setting time of the concrete is small, the fluidity and the slump of the concrete can be increased to a certain extent, and the construction of the concrete is facilitated.
Drawings
FIG. 1 shows the temperature rise curve of hydration heat of the swelling agent of the examples and comparative examples.
Detailed Description
The modified calcium oxide expanding agent for the compensation shrinkage concrete is characterized by being prepared by mixing and ball-milling 0.1-20% by mass of a modifier and 80-99.9% by mass of a calcium oxide expanding agent; the calcium oxide expanding agent is an expanding agent containing free calcium oxide, and the free calcium oxide is used as a stable expansion source for playing a role in expansion; the modifier consists of one or more of the following substances: sodium sulfate or a crystalline hydrate thereof, ammonium bisulfate or a crystalline hydrate thereof, sodium sulfite or a crystalline hydrate thereof, ammonium sulfite or a crystalline hydrate thereof.
For better comparison to illustrate the experimental effect, the modified calcium oxide expansion agent for compensating the shrinkage concrete in the following examples adopts the same preparation method: putting the modifier and the calcium oxide expanding agent into a ball mill, carrying out ball milling for 30min, reacting the modifier with calcium oxide on the surfaces of calcium oxide expanding agent particles under the combined action of mechanical force and heat generated by the ball mill, generating calcium sulfate or calcium sulfite which is difficult to dissolve in water on the surfaces of the calcium oxide expanding agent particles, and sieving the calcium sulfate or the calcium sulfite through a 80-micron square-hole sieve to prepare the modified calcium oxide expanding agent for the compensation shrinkage concrete.
For better comparison and illustration of experimental effects, FQY high-performance calcium oxide expansion agents manufactured by Wuhan's Sanyuan Special building materials Co., Ltd are used as the calcium oxide expansion agents in the following examples, and the chemical analysis thereof is shown in Table 1 below.
Table 1: chemical analysis of calcium oxide-based swelling agent/%)
| Loss | SO3 | SiO2 | Fe2O3 | Al2O3 | CaO | MgO | f-CaO |
| 2.10 | 19.72 | 2.00 | 1.19 | 4.39 | 68.62 | 1.74 | 47.72 |
The cement in the invention adopts special standard cement for testing concrete additives produced by Shandong Lucheng cement Co.
The fly ash in the invention is national standard II produced by a Qingshan power plant.
The mineral powder in the invention is ordinary S95 grade mineral powder produced by Wangda building materials company Limited.
The water reducing agent is a Ujoin-PC polycarboxylic acid water reducing agent produced by Wuhan-sourced brocade building material science and technology Limited company.
The technical solutions of the present invention are described in detail and fully below with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention. Equivalent changes or substitutions of method, process route, function and the like by those skilled in the art according to the following embodiments are within the scope of the present invention.
Example 1
Putting 1 percent of sodium sulfate and 99 percent of calcium oxide expanding agent in percentage by mass into a ball mill for ball milling for 30min, and then sieving the mixture by a 80 mu m square-hole sieve to prepare the modified calcium oxide expanding agent.
Example 2
Putting 5 percent of sodium sulfate and 95 percent of calcium oxide expanding agent in percentage by mass into a ball mill for ball milling for 30min, and then sieving the mixture by a 80 mu m square-hole sieve to prepare the modified calcium oxide expanding agent.
Example 3
Putting 10% of sodium sulfate and 90% of calcium oxide expanding agent in percentage by mass into a ball mill for ball milling for 30min, and then sieving through a 80-micron square-hole sieve to prepare the modified calcium oxide expanding agent.
Example 4
5 percent of ammonium sulfate and 95 percent of calcium oxide expanding agent by mass percent are put into a ball mill together for ball milling for 30min, and then the mixture is sieved by a square-hole sieve with the size of 80 mu m to prepare the modified calcium oxide expanding agent.
Example 5
5 percent of ammonium sulfite and 95 percent of calcium oxide expanding agent by mass are put into a ball mill together for ball milling for 30min, and then are sieved by a square-hole sieve with the diameter of 80 mu m to prepare the modified calcium oxide expanding agent.
Example 6
20 percent of sodium sulfate decahydrate and 80 percent of calcium oxide expanding agent by mass percent are put into a ball mill together for ball milling for 30min, and then the mixture is sieved by a square-hole sieve with the size of 80 mu m to prepare the modified calcium oxide expanding agent.
Example 7
Putting 0.1 percent of sodium sulfate and 99.9 percent of calcium oxide expanding agent in percentage by mass into a ball mill together for ball milling for 30min, and then sieving the mixture by a square-hole sieve with the diameter of 80 mu m to prepare the modified calcium oxide expanding agent.
Example 8
Putting 2.5 percent of sodium sulfate, 2.5 percent of ammonium bisulfate and 95 percent of calcium oxide expanding agent in percentage by mass into a ball mill for ball milling for 30min, and then sieving by a square-hole sieve with the diameter of 80 mu m to prepare the modified calcium oxide expanding agent.
Comparative example 1
And (3) directly stirring and uniformly mixing 5% of sodium sulfate and 95% of calcium oxide expanding agent by mass percent to prepare the modifier-doped calcium oxide expanding agent of the comparative example.
Comparative example 2
5 percent of ammonium sulfate and 95 percent of calcium oxide expanding agent are directly stirred and mixed evenly to prepare the calcium oxide expanding agent doped with the modifier in the comparative example.
Comparative example 3
5 percent of ammonium sulfate and 95 percent of calcium oxide expanding agent are directly stirred and mixed evenly to prepare the calcium oxide expanding agent doped with the modifier in the comparative example.
Comparative example 4
This comparative example used an unmodified calcium oxide based expansion agent.
Comparative example 5
120.0g of a calcium oxide-based swelling agent was weighed into a 500ml three-necked round-bottomed flask containing anhydrous ethanol. The middle opening of the three-opening round-bottom flask is provided with a polytetrafluoroethylene stirrer. 10g of 98% H2SO4The dropper is plugged into one side opening of the three-mouth flask. Stirring by a stirrer at 150 r/min; simultaneously the concentration H in the dropper2SO4Slowly titrating into absolute ethyl alcohol dispersed with calcium oxide swelling agent.
However, in this process, an irritating odor emanates, probably due to the high concentration of H2SO4The strong oxidizing property of the alcohol reacts with the absolute ethyl alcohol. Looking up the related data to obtain the dense H2SO4Can react with ethanol at normal temperature to generate the ethyl bisulfate, and the speed is generally higher.
Filtering the calcium oxide expanding agent, and drying at 105 ℃ to obtain the sulfuric acid modified calcium oxide expanding agent.
The temperature rise curve of the pure slurry hydration heat of the expanding agent of the sample is tested, the container adopted in the experiment is a 200ml paper cup, the temperature is measured by adopting a TP700 multi-channel data recorder manufactured by Shenzhen Tuotui electronic Limited company, and the formula comprises 100g of the expanding agent and 50g of water. The test results are shown in fig. 1. The curve temperature peaks of comparative example 4, comparative example 1, comparative example 2, example 2 and example 4 appear in the figure from left to right, and experimental data show that the temperature peak of the unmodified calcium oxide type expanding agent of the comparative example 4 is sharp, and the maximum temperature reaches 100 ℃; the maximum temperature peaks of the modified calcium oxide expanding agents in the embodiment of the invention are not more than 40 ℃, the temperature peak occurrence time is greatly prolonged and exceeds 1h, the inconsistent performance of the calcium oxide expanding agents doped with the modifier in the comparative example is related to the self performance of the modifier, the temperature rise of the comparative example 1 is still higher, the temperature rise of the comparative example 2 is greatly reduced, and the temperature rise time is more than 0.5h, but is still worse than that of the embodiment.
The influence of the modified expanding agent on the setting time of the cementing material is evaluated by adopting a net slurry experiment, wherein the net slurry setting time experiment method is executed according to the corresponding regulation in GB/T1346-2011 'detection method for water consumption, setting time and stability of standard consistency of cement'; the experimental method for limiting the expansion rate of the mortar and the concrete is carried out according to the corresponding regulation in GB23439-2009 concrete expanding agent; the concrete slump and slump expansion test method is executed according to corresponding regulations in GB/T50080-2002 Standard of Performance test methods of common concrete mixtures; the cement mortar strength test method is carried out according to the corresponding regulation of GB/T17671-1999 cement mortar strength detection method.
TABLE 2 Net slurry setting times for the examples and comparative examples
Table 2 the experimental results show that: the modified calcium oxide expanding agent of the embodiment of the invention has little influence on the setting time of the cement paste, particularly the modified calcium oxide expanding agent of the embodiment 8 has no influence basically, and the setting time of the comparative example added with the modifying agent by a direct external mixing method is shortened or prolonged. The modifier of the embodiment is shown to have solid-phase reaction with calcium oxide on the surfaces of the expansion agent particles in the ball milling process, and generate substances (such as calcium sulfate and calcium sulfite) which are difficult to dissolve in water, and the substances are attached to the surfaces of the expansion agent particles instead of acting on the whole cement paste. In the comparative example, the modifier is directly mixed with the expanding agent, so that no surface solid phase reaction occurs, the modifier directly participates in the hydration reaction process of the cement slurry in the form of an additive, and the whole cement hydration process is influenced.
TABLE 3 limiting expansion ratio and compressive strength of cement mortar of examples and comparative examples
Table 3 the results of the experiments show that: the expansion limiting rate of the modified expanding agent in the embodiment of the invention is obviously improved by 7d in water of the mortar and 21d in air. The direct external addition of the modifier influences the whole gelling system, and the influence law of limiting the expansion rate of 7d in water and 21d in air of the mortar is different along with the influence of the modifier on the setting time of the cement paste. The modified calcium oxide-based swelling agent prepared by the concentrated sulfuric acid impregnation method of comparative example 5 restricted the swelling rate to be not substantially increased as compared with comparative example 4. Probably because the concentrated sulfuric acid and the absolute ethyl alcohol have esterification reaction in the comparative example 5, the concentrated sulfuric acid can not play the role of the modified calcium oxide expanding agent, and compact sediments are not formed on the surface of the calcium oxide expanding agent. By combining the experimental data in fig. 1 and table 3, it can be found that the calcium oxide expanding agent of the present embodiment, after being modified, can achieve the effects of inhibiting the early hydration heat release of the expanding agent and improving the expansion limiting rate of 7d and 21 d.
Application example 1
230kg/m cement370kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent3
Application example 2
230kg/m cement335kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent335kg/m of modified calcium oxide-based expanding agent obtained in example 23。
Application example 3
230kg/m cement335kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent335kg/m of modified calcium oxide-based expansive agent prepared in example 83。
Application example 4
230kg/m cement335kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent3Comparative example 1 modified calcium oxide-based expanding agent 35kg/m3
Application example 5
230kg/m cement335kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent3Comparative example 4 calcium oxide-based swelling agent 35kg/m3。
Application example 6
230kg/m cement335kg/m of fly ash345kg/m of mineral powder3783kg/m of sand31082kg/m pebbles3157kg/m of water34.75kg/m of water reducing agent3Comparative example 5 modified calcium oxide-based expansive agent 35kg/m3。
TABLE 4 concrete slump and limiting expansion ratio of application examples
Table 4 the results of the experiments show that: the modified expansive agents of examples 2 and 8 have little influence on the concrete slump and the slump expansion, while the modified expansive agent of comparative example 1 has a great influence on the concrete slump and the slump expansion. This is because the modifier forms a layer of compact insoluble deposit on the surface of the expanding agent in the embodiment, which can improve the moisture resistance of the expanding agent. The fluidity and the slump of the concrete can be increased to a certain extent, and the construction of the concrete is facilitated. The concrete limited expansion rates of application examples 2 and 3 are higher than those of application examples 5 and 6, which shows that as the sediments such as calcium sulfate and the like are dissolved in the concrete cementing material system through reaction, the internal free calcium oxide reacts with water to generate effective volume expansion, and finally the concrete expansion rate is improved.
Having shown and described the basic principles, essential features and advantages of the invention, while embodiments of the invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (4)
1. The modified calcium oxide expanding agent for the compensation shrinkage concrete is characterized by being prepared by mixing and ball-milling 1-10 mass percent of a modifying agent and 90-99 mass percent of a calcium oxide expanding agent; the calcium oxide expanding agent is an expanding agent containing free calcium oxide, and the free calcium oxide is used as a stable expansion source for playing a role in expansion; the modifier consists of sodium sulfate and ammonium bisulfate in a mass ratio of 0.5-2: 1.
2. The modified calcium oxide-based expansive agent for shrinkage-compensating concrete according to claim 1, wherein the specific surface area of the calcium oxide-based expansive agent is 150 to 400m2Per kg, wherein the content of free calcium oxide (f-CaO) is 20-85 wt%.
3. The modified calcium oxide expanding agent for the shrinkage-compensating concrete as claimed in claim 1, wherein the modified calcium oxide expanding agent is prepared by mixing and ball-milling 5% by mass of a modifying agent and 95% by mass of a calcium oxide expanding agent, and the mass ratio of sodium sulfate to ammonium bisulfate in the modifying agent is 1: 1.
4. The preparation method of the modified calcium oxide expanding agent for the shrinkage-compensating concrete according to any one of claims 1 to 3, wherein the modifying agent and the calcium oxide expanding agent are put into a ball mill together, the ball milling is carried out for 30 to 60 minutes, the modifying agent reacts with calcium oxide on the surfaces of calcium oxide expanding agent particles under the combined action of mechanical force and heat generated by the ball mill, calcium sulfate or calcium sulfite which is difficult to dissolve in water is generated on the surfaces of the calcium oxide expanding agent particles, and the calcium oxide expanding agent passes through a 80-micron square-hole sieve, so that the modified calcium oxide expanding agent for the shrinkage-compensating concrete is prepared.
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| CN108751764A (en) | 2018-11-06 |
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