Influence of some organic admixtures on the rheological and mechanical properties of cement pastes

Three organic admixtures were used; melamine formaldehyde sulphonate, phenol formaldehyde sulphonate and polycarboxylate. The effects of these polymers on the fluidity and fluidity loss of cement pastes were investigated. The polymers were added by two different methods: either together with mixing water (simultaneous addition) or at a specified time (15 min) after mixing with water (later addition). The mini-slump of these pastes at different time intervals of 30, 60, 90 and 120 min was determined. The 28-day compressive strength and differential scanning calorimetry of hardened cement pastes that had been made by the two addition methods were determined. The results revealed that the organic admixtures reduced the mini-slump loss (by time) of fresh cement pastes, which were prepared by the two methods. The effectiveness of later addition was greater than that of simultaneous addition not only at early ages (30 min) but also at later ages (120 min).