No abstract

No abstract

No abstract

In this paper, a brief overview of the current literature on the dispersion mechanism of polycarboxylate-type superplasticisers (PCEs) is first presented. Then, the available free water amount and fluidity of cement paste with various water-to-cement ratios (w/c) and PCE dosages are measured. The phase and particle size distribution of early cement hydrates are analysed by X-ray diffraction and laser particle size analysis, respectively. As a result, a surprising tendency is observed: the increase rate of fluidity increases with decreasing w/c ratio when the dosage of PCE gradually increases. This phenomenon cannot be explained by the steric effect. The authors also conclude that not less than 2·0% of solids volume of ‘AFt–PCE’ structures (early hydrates of ettringite (AFt) coated with PCE, < 200 nm) are dispersed well in the interstitial pore space along with non-adsorbed PCE. Based on these results, the authors present a possible dispersion mechanism in the PCE–cement system studied here based on the repulsion originating from the exclusion of free polymers (non-adsorbed PCE, ‘AFt–PCE’ structure and some other fine matters coated with PCE) from the gap between cement particles.

Influences of phosphorus slag from 10% to 50% (by mass) on the setting time and the water requirement of the normal consistency of cement pastes, flowability, resistance to carbonation, and the compressive strength of cement mortars were investigated. The physical activation by improving fineness and the chemical activation by adding the chemical activator were evaluated by the compressive strength of cement mortars with 30% by mass of phosphorus slag. Hydration heat, X-ray diffraction, and scanning electron microscopy were used to study the microstructure of cement pastes and mortars with 30% by mass of phosphorus slag and the chemical activator. Results showed that the setting time of cement pastes was delayed by phosphorus slag from 10% to 50%. Phosphorus slag had nearly no effects on the water requirement of the normal consistency of cement pastes and the flowability of cement mortars. The resistance to carbonation of cement mortars was decreased by phosphorus slag from 10% to 50% according to the acceleration carbonation. The compressive strength of cement mortars was also decreased by phosphorus slag from 10% to 50% and the low activity of phosphorus slag was concluded based on compressive strength of cement mortars. The effect of the chemical activator on the compressive strength of cement mortars with 30% by mass of phosphorus slag was better than improving fineness of phosphorus slag from 300 m2/kg to 450 m2/kg. Both hydration heat and cement hydrates were inhibited by phosphorus slag and could be partly compensated by the chemical activator. Loose morphology and propagations of microcracks were found in cement pastes and mortars with 30% by mass of phosphorus slag.