Effect of usual water-reducing agents on the rheological and mechanical properties of phosphoaluminate cement

As one new type of cementitious material, phosphoaluminate cement (PAC) has excellent mechanical property and durability, the water-reducing agents as an important type of admixture have significance for the application of PAC. In this paper, the adaptability and interaction mechanism of PAC and usual water-reducing agents were investigated. The experimental results showed that naphthalene (NS) and calcium lignosulfonate (CLS) with an electrostatic repulsion effect, and polycarboxylic acid (PCE) with a steric hindrance effect could improve the fluidity of PAC. Unlike NS and CLS, PCE didn't prohibit the normal hydration of PAC. It was due to the strong (NS, CLS) or weak (PCE) adsorption formed between anionic type NS, CLS, PCE and positively charged aluminate mineral of PAC in a hydration environment. Strong adsorption could prevent PAC particles from contacting with water molecules, which affected hydration. To investigate the influence of element P in the interaction of PAC with water-reducing agents, the comparative analysis was carried out on PAC and aluminate cement (CAC). FTIR and XPS showed that PO4 3- reacted with Ca2+ to form C3P, which reduced the positive charge of the mineral surface, but PAC adsorbed more PCE and formed a thicker adsorption layer than CAC because of higher Ca2+ content in PAC.