Improvement on microstructure of concrete by polycarboxylate superplasticizer (PCE) and its influence on durability of concrete

Abstract

In this study, the influence of polycarboxylate superplasticizers (PCEs) on durability of concrete was investigated. Carbonation, water impermeability and rapid chloride permeability of concrete with different types of polycarboxylate superplasticizer and polynaphthalene superplasticizer (PNS) were tested. In order to obtain deeper insights into the influence of PCE on concrete durability, microstructure in the concrete was explored by means of mercury intrusion porosimetry (MIP), thermogravimetry (TG) and nano-indentation technique. Smaller carbonation depth, water penetration depth and better resistance to chloride ion penetration show that concretes with PCE have better durability performances than concretes with PNS. MIP results show that the mortars with PCE have lower porosity than that with PNS. The fraction of pores with diameters larger than 100nm in the mortars with PCE is lower than in the mortar with PNS. According to TG tests, there are more hydration products in the cement pastes with PCE than in the cement pastes with PNS. Nano-indentation tests show a higher ratio of high density C–S–H to low density C–S–H in the cement paste with PCE than in the cement paste with PNS. It can be concluded that PCE leads to denser microstructure in concrete than PNS and, therefore, better durability performances of concrete.