Effect Of Polycarboxylate Superplasticizer Modified By Silica Hydrate On Properties Of Cement-based Materials

The mixing water could be effectivly reduced by adding superplasticizer into concrete mixtures to maintain the slump.Meanwhile,the addition of superplasticizer could also improve the workability and reduce the cement usages because of its particle dispersion effect.And it has become the indispensable content in modern concrete with the improvement of engineering quality requirements.Polycarboxylate superplasticizer(PC)is considered to be one of the most ideal superplasticizer because of its lower dosage and higher water reducing rate,which has realized large-scale production and engineering application.However,the water reducing mechanism of PC relay on the physical adsorption of negatively charges of PC molecules and positively charges on surface of cement particles under alkaline hydrolysis conditions.Further,these physical adsorptions would become weaker at high sulphate,elevated temperature and silicate environment,which influenced the stability and limited the application of PC.In addition,the PC will also restrain the early hydration and early strength development of cement base material.In recent years,the rapid development of nanotechnology also caused widespread interest in cement engineering area.Nanoparticles can effectively improve the workability,mechanics performance and durability of cement base material with low dosage range.Nanoscaled Si02,in particular,has a large number of active silicon hydroxyl on its surface,which can promote the polycondensation reaction with other material on the surface.And nanoscaled SiO2 has also possessed the high hydration effect and super volcanic activity.However,nanoparticles often exist in the form of aggregate,which difficult to disperse in the cement base material.Currently,the performance improvement of PC and the nano effect development of nanoparticles have become the focus in research area of cement based materials.Based on the highly active surface characteristics of silica hydrate(nanoscale SiO2),which can promote the polycondensation reaction with hydroxyl groups in PC molecular chains.Thus,the SiO2 could load on the PC molecular chains,which will improve the water reduction and adaptability of PC.The PC could also be adsorbed on the surface of Si02 to effectively disperse nanoparticles,which will induce the hydration effect and super volcanic activity of silica hydrates.Therefore,mutual modification of silica hydrate and PC has been proposed in this study.And the modified products have been used to prepare the cement paste and mortar.The high efficiency water reducing effect of PC has been maintained,which improved the working performance of cement base material.And silica hydrate was introduced into the cement base material in the form of relatively uniform,which improved the physical and mechanical performance of cement pastes and mortars.