Superplasticizer Synthesis And Its Application In Recycled Aggregate Concrete

Polycarboxylate superplasticizer, which is a high performance water-reducing agent developed in recent years, has the features of high water-reducing rate, good slump retention, low shrinkage, good enhancement effect and no environmental pollution, representing the future direction of the development of concrete admixtures.This paper adopted the active monomer copolymerization method to synthesis polycarboxylate superplasticizer. Firstly, the macromonomer, methoxy polyethylene glycol methacrylate ester (MPEGMA) was prepared, which was then used to synthesis target product with methacrylic acid (MAA) and sodium methallyl sulfonate (SMAS) using ammonium persulfate (APS) as initiator. The esterification ratio reached95.37%under the optimum experiment conditions that n(MAA) n(MPEG1000) was2.5:1, the amount of catalyst (p-toluene sulfonic acid) was3%according to the mass of MAA and MPEG, the amount of inhibitor (phenothiazine) was2%according to the mass of MAA, the esterification temperature was120℃and the esterification time was6h, through single factor experiment and orthogonal test. The molecular structure of the macromonomer was characterized, and then the storage condition was discussed.The synthesis conditions of polycarboxylate superplasticizer were as follows: the molar ratio of MAA to MPEGMA was3:1,14%of SMAS of the mass of MAA and MPEGMA,5%of APS of all the monomers, at reaction temperature of85℃, the reaction time3h and homogenous dropping time1～2h. The uniformity indexes of polycarboxylate superplasticizer and concrete application performance were tested. The results showed that polycarboxylate superplasticizer had well dispersion and dispersion retentivity at the dosage of0.5%and0.29of W/C, the concrete admixed with polycarboxylate superplasticizer displayed good workability and remarkable strengthening action at later stage.Compared with natural concrete aggregate (NCA), recycled concrete aggregate (RCA) has the characteristics of low apparent density, high water absorption, high crushing index, etc. As is large in water consumption, low hardening strength and low elastic modulus, recycled concrete (RC) can only be applied to some non-load bearing and bearing components.To expand the application area of RC, it is necessary to be modified and strengthened for RCA.This paper adopted four kinds of chemical grout to modify and strengthen recycled coarse aggregate, which were simple cement grout, cement slurry mixed with silicon powder, cement slurry mixed with ultra-fine fly ash, cement slurry mixed with polycarboxylate superplasticizer. The test results showed that apparent density of RC was somewhat increased and the crushing index was also improved by strengthening treatment. Compared to the other three kinds of chemical grout, cement slurry doped with polycarboxylate superplasticizer had higher enhancement effect. The RC prepared by modified recycled coarse aggregate had better slump controlling ability, higher compressive strength and elastic modulus than the RC prepared by original recycled coarse aggregate at the same strength level and replacement, satisfying the requirements for construction and application of RC. The results indicated the application of polycarboxylate superplasticizer in RC is beneficial to broaden the application range of RC and relief the resources and environment problems, which is of significance for the sustainable development of concrete industry.