Preparation And Properties Of Nanosilica-doped Polycarboxylate Superplasticizer

Nanoparticles and polycarboxylate superplasticizer can improve the mechanical properties and workability of cement-based materials,respectively,and if they can be combined,they are expected to complement each other.Nevertheless,the current combination of nanoparticles and polycarboxylate superplasticizer is mainly simple physical blending,and the synergistic effect of the two is extremely limited.In this study,nano-silica modified polycarboxylate superplasticizer(NS/PCE)was synthesized by one-step method,and the composition,structure and properties of NS/PCE were studied.The results show that NS can be grafted onto the PCE molecular chain by Si-O~-chemical bond,and appropriate content of NS can promote the transformation of TPEG monomer,thus promoting the polymerization reaction.With the augment of NS,the grafting rate of NS in NS/PCE was stable after firstly increase.When the NS content was 20%,the grafting amount reached saturation.Electrostatic repulsion and steric hindrance together promote the dispersion of NS particles in NS/PCE solution.NS/PCE can improve the workability and adsorption properties of fresh cement pastes.In addition,adding NS/PCE makes the yield stress and the apparent viscosity of fresh cement pastes decreases.With the increase of grafting amount of NS,the fluidity of cement paste containing NS/PCE raises firstly and then decreases,and the adsorption quantity of cement particles to NS/PCE reaches the maximum at the NS content of 10%.NS/PCE can reduce the delay effect of traditional polycarboxylate superplasticizer on the early hydration of cement.The NS release gradually from NS/PCE and exert its pozzolanic effect in the process of cement hydration,so that the strength of cement mortars and concretes can be obviously enhanced.The incorporation of NS/PCE promotes the densification of hardened cement matrix,in which the crystal content and orientation coefficient of calcium hydroxide decrease significantly.