Hydration versus strength in a portland cement developed from domestic mineral wastes — a comparative study

Early age hydration studies on fresh pastes of a Type I cement produced from local mineral tailings have been conducted by using thermal techniques such as DTA and TGA and degrees of hydration at varying time intervals have been estimated in terms of nonevaporable water and free calcium hydroxide incorporated in the hydration products. The results are subjected to an earlier proposed expression which gives a direct correlation between strength and degree of hydration for a given hydrating cement paste except for the period of low reactivity, commonly referred to as the dormant period exhibiting very low heat evolution in a calorimetric plot, when cement remains plastic while still undergoing a certain degree of hydration. It is noticed that the critical degree of hydration at which strength starts developing is a function of hydration time and theoretically corresponds to the termination of the acceleration period when tricalcium silicates and dicalcium silicates in the cement have hydrated to produce enough hydration products to intermesh and initiate early strength. The experimental data are compared with those of a commercially available Type I cement and are interpreted in terms of strength development as a function of hydration.