Modification And Characterization Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer is a high-performance water-reducing agent.It is highly demanded in world’s concrete market for the merits of low content, good dispersion, strong designability and etc. With the advancement of urban extension and infrastructure construction, the Chinese market has also put forward new requirements for polycarboxylate water-reducing agent. It is our advancing direction to explore new water-reducing agents and new synthetic methods.In this paper, the experimental content relies on the construction of Chinese high-speed railway. We find several problems with concrete application such as poor fluidity, poor slump retention and lack of strength. In order to improve the performance of polycarboxylate superplasticizer, we introduce a number of hydroxyl groups,carboxyl groups, sulfonic acid groups into the main chain of the polycarboxylate superplasticizer molecules through the molecular design route. The main research work is listed as follow:1. The itaconic acid is grafted into the main chain of the polycarboxylate superplasticizer molecule by chemical grafting. The effects of temperature, time,molar ratio and initiator dosage on the product were investigated. The optimum synthesis condition was established by the fluidity of cement paste. The concrete performance of itaconic acid modified water-reducing agent, commercially water-reducing agent and non-modified water-reducing agent were also determined.We found that the cement dispersibility is significantly better than the non-modified water-reducing because of the polycarboxyl structure. Concrete strength test show that with the addition of itaconic acid modified water-reducing agent, the strength of concrete was higher than that of non-modified water-reducing agent. Therefore,itaconic acid modified water-reducing agent has the market potential.2. 2-acrylamido-2-propanesulfonic acid was successfully grafted into the main chain of the polycarboxylate superplasticizer by chemical grafting. The optimum synthesis condition was determined by the orthogonal experiment design. The mechanism of the preservation of water reducing agent was explored through the cement hydration heat test and zeta potential analysis-the cement particle could be preferentially adsorbed on the surface of the water-reducing agent, which effectively shields the active sites of cement hydration and maintains excellent dispersion maintainability. It is found that the strength of the concrete with AMPS modified water-reducing agent can reach 80% in 7d and 120% in 28d respectively, which is better than that of unmodified water-reducing agent and commercially water-reducing agent. This indicats that AMPS modified water-reducing agent can not only improve the dispersion and retention of concrete, but also can guarantee the mechanical properties of concrete.3. A new monomer sucrose ester was introduced into the backbone of the polycarboxylate water-reducing agent by chemical grafting. was determined. The best synthesis condition is achieved by determining the effect of each reaction factor on the performance of the water-reducing agent. By the zeta potential analysis, it was found that the modified water-reducing agent molecules could adsorb more cement particle on the surface,which can improve water-reducing performance. The concrete slump analysis shows that modified concrete slab is better. By the test of SEM, it was found that the incorporation of the water-reducing agent was beneficial to the growth of needle-like calcium hydroxide and resulted in the high-strength concrete.