EFFECT OF EPEZITE ON THE PROPERTIES OF CEMENT

摘要

Two samples of ordinary portland cement were investigated. Clinkers were interground with gypsum in laboratory They came from the same plant but were sampled at two-day interval. Standard mortars were cast with those cements referred as C1 and C2. They presented different 2-day and 7-day compressive strengths : 1. 28.5 MPa (2 days) and 47.6 MPa (7 days) for C1, 2. 25.1 MPa (2 days) and 41.4 (7 days) for C2. The measurement of the electrical conductivity carried out on suspensions of cement (water to cement ratio = 4) showed a very high initial value and a particularly short dormant period, for cement C2 The analysis of solutions obtained from filtered suspensions pointed out very high contents in calcium and hydroxyl ions, for cement C2 Scanning electron microscopy examinations, associated with energy-dispersive X-ray analysis, showed the presence of cauliflowerlike crystals of calcium hydroxide, called epezite,originating by air-slaking of free lime. The growth of epezite is thought to be responsible for clinker disintegration in open storage due to the 97-percent volume change when free lime combines with atmospheric moisture. The presence of epezite in cement C2 may explain the lower mechanical performances of the mortar.