Phase composition changes due to ammonium-sulphate: attack on Portland and Portland fly ash cements

The behaviour of Portland cement and Portland cement with 30% fly ash in 10% ammonium-sulphate solution was studied within a comprehensive research program. All materials have been chemically analysed and their physico-chemical and mechanical properties have been investigated. X-ray diffraction was used for following changes into microstructure after storage of samples in ammonium-sulphate solution, and phase composition changes were identified. Based on XRD analysis of the phase composition changes it could be concluded that the main product of the ammonium-sulphate attack on cements is gypsum, followed by ettringite. The presence of gypsum is increased with the time of exposing of samples in the solution for both types of cement, but it has occurred that the increase of this phase is higher in the PCBP samples containing fly ash. Compressive strengths of PCB and PCBP samples after curing in water for 14 days and exposed in ammonium-sulphate solution for 3, 7, 14, 21 and 28 days are investigated. PCBP samples containing fly ash have better behaviour in ammonium-sulphate solution. Addition of fly ash to Portland cement makes this cement become more resistant to the sulphate aggressive environment. (C) 1999 Elsevier Science Ltd. All rights reserved.