Superplasticizer, as a new generation of concrete admixtures, has many outstanding advantages such as low admixture, high water reduction rate, and good slump protection, which endows concrete with excellent conductivity and durability. Application of polycarboxylate superplasticizer.
1 Adaptation of superplasticizer to cementitious materials
Cement mineral composition is more complicated, together with the application of admixture is especially instability of performance of fly ash, superplasticizer with cement and admixture adaptability problems still exist, this kind of problem is mostly reflected in superplasticizer have difference on the saturation point of different cement, reduce the water reducing rate, loss of concrete slump, concrete "tofu" phenomenon in a lack of pulp, exudation, subsidence segregation, pumping, sensitive to dosage can't open or excessive release of concrete problems.The reason is complicated. The freshness and fineness of cement, the type, and content of admixture in cement, the proportion of several mineral components, especially tricalcium aluminate, the type and content of gypsum, the carbon content of fly ash and the water demand all affect the adaptability of the water-reducing agent to cementing materials.
2.Sensitivity of superplasticizer to mud content
Concrete sand silt content in raw materials on the performance of concrete can cause irreversible influence, will reduce the performance of superplasticizer, the root cause is a lot of superplasticizers was clay adsorption after part used for dispersion of cement particles decreases, dispersion, when sand silt content is higher, there will be water reducing rate of superplasticizer was obviously reduced, the concrete slump loss increase, less liquidity, easy to crack, concrete strength drops become poor durability problem, in light of the problems of the silt content, there are several kinds of conventional solution:(1) increase the content of mixture or the proportion of slow-release slump protection agent, but control the amount to prevent concrete from yellowing, bleeding, segregation, bottom grasping and concrete retarding time too long;(2) adjust the sand rate or increase the air intake dose, reduce the sand rate or increase the air intake to increase the free water and slurry volume of the concrete system on the premise of better workability and strength, so as to adjust the performance of concrete;(3) proper addition or change of its components to solve the problem. The experiment proved that adding the proper amount of sodium metabisulfite, sodium thiosulfate, sodium dexamethasone, and sodium sulfate in the water-reducing agent can reduce the influence of mud content on concrete to a certain extent.Of course, the methods mentioned above cannot solve all the problems of mud content, and the influence of mud content on concrete durability needs to be further studied. So, the fundamental method is to reduce the mud content of raw materials.
3 Compounding of superplasticizer with other components
At present, scientific and reasonable compounding of superplasticizer with suitable materials is the main measure to improve the properties of superplasticizer in China.However, superplasticizer has a strong selectivity when compounded with some components, so it is not suitable to be compounded with a-series water-reducing agent, sulfamic acid water-reducing agent, or mi-ammonia water-reducing agent.Mixed with cellulose of different viscosity will have water-bearing flocculent and precipitation, which will affect the water-holding effect of water reducing agent and the actual production;Compound with retarder sometimes also have peculiar smell flocculent and discoloration;With other inorganic salt admixture compatibility is also general, such as early strength agent, antifreeze, poor solubility, it is difficult to mix, in the process of mixing will form oil floating on the surface.Because of this, it is suggested that when superplasticizer is used for compounding with other components, it is necessary to confirm the effect of compounding and the actual impact on concrete through experiments before determining whether superplasticizer can be combined with other components.Moreover must pay attention to the decisive role of the performance of water-reducing agent, mother liquor should play the synergy of various additives, more to increase the versatility of mother liquor, developed using different raw materials, production with different components, the performance difference, form a series of multi-function products, through the different function of mother liquor distribution to achieve good results.
4 sensitivity of dosage and water consumption of superplasticizer
Because of superplasticizer is more sensitive to the change of raw materials, together with the water reducing agent is high water reducing rate, low gelling material and low water consumption factors such as the use of the mix proportioning of concrete saturation point of water reducing agent and USES special "critical", once excessive, can appear the concrete segregation and bleeding, run pulp, harden and excessive air content on the adverse phenomenon, on the other hand, the concrete will be dry, such as poor workability, slump loss big problem, so Suggestions for this problem: (1) should be back to change after the test with raw materials to adjust the dosage to achieve the best effect;(2) the content of polycarboxylic acid superplasticizer and the water consumption of concrete must be strictly controlled in the process of use;(3) for raw materials in the concrete test of water reducing agent, try to adjust the water reducing agent to "slow" type, so as to achieve the purpose of not being sensitive to raw materials and water consumption.
Superplasticizer is a new generation of concrete water reducing agent have prominent advantages, but in the use process have also exposed many problems, much attention has been paid to this problem so far has been employed workers and research topic, the author expect concrete raw materials in the range of possible fluctuations in order to achieve the purpose of relatively stable, advice on similar problems at the same time, should be careful analysis, system test, department of polycarboxylate superplasticizer use problem can be solved.
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