Effect of BaO on mineral structure and hydration behavior of phosphoaluminate cement

Abstract

Phosphoaluminate cement (PAC) clinker was one new type of special cement, which exhibits good mechanical properties and durability. In this paper, the effect of BaO on the mineral structure and hydration behavior of PAC clinker were investigated. The experimental results showed that the mineral structure of PAC clinker was modified by the addition of barium oxide (BaO). The optimal content of BaO in PAC clinker was 10.5 mol% (the substitution mole ratio of BaO for CaO, calcium oxide). Compared with reference specimen, the rate of strength growth of hardened paste for PAC clinker with 10.5% BaO cured for 1, 3, 7 and 28 days was 50.8, 21.0, 27.0 and 49.9%, respectively. The possible reason was that the addition of BaO could activate crystal structure of calcium phosphoalumniate (8CaO·6Al2O3·P2O5, C8A6P, C8A6P) and improve its hydration activity, which has been proven by the XRD and hydration heat analysis. The addition of BaO also affected the ratio of hydration products of PAC clinker, which were illustrated by XRD and DSC analysis. The MIP analysis showed that the addition of BaO could optimize the pore structure of hardened paste for PAC clinker, which was accordance with the discussion of compressive strength of hardened paste for PAC clinker. In conclusion, the addition of BaO dramatically improved the compressive strength of hardened paste for PAC clinker and changed remarkably its ratio of hydration products.