Modelling of the compressive strength development of cement mortar with furnace slag and desulfurization slag from the early strength

Replacing natural resources with renewable materials is a very important research topic for sustainable development. Several recycled materials such as furnace slag (S) and desulfurization slag (D) were widely used and applied in concrete or cement mortar. The compressive strength at the 28th day was usually used as design strength for structure. Thus, an assessment of the compressive strength of cement mortar with furnace slag and desulfurization slag from the early strength is desirable to develop. In this study, desulfurization slag that could pass through a No. 4 sieve and furnace slag with a fineness of approximately 4000 cm2/g were used to replace the fine aggregate (0%, 10%, 20% or 40%) and cement (0%, 10%, 20% or 40%), respectively, through a volumetric method. The cement mortar thus formulated was then put through a series of compressive strength tests in which the samples were cured at a 23-25 °C room temperature and a 75 °C high temperature. According to the test results, the compressive strength decreased as the replacement rate of desulfurization slag increased, but increased as that of the furnace slag increased. Using the test results when the replacement rates of D were 0%, 10% and 20%, a hyperbolic function was used to perform a multivariate non-linear regression analysis, thus establishing a compressive strength prediction model for cement mortars of other ages based on the early strength at the age of 7 days. From the confirmatory analysis, when the replacement rate of desulfurization slag D = 40%, the MAPE (mean absolute percentage error) value of the test sample cured at high temperature was found to be 6.13%, while that for the test sample cured at room temperature was 11.32%. Moreover, when D was 0%, 10% and 20%, the MAPE value for the test sample cured at high temperature was 3.05%-4.47%, respectively, while that for the test sample cured at room temperature was 7.83%-9.17%. Generally speaking, the results delivered by the analytical model established in this study were satisfactory under different conditions. As it is capable of performing a predictive analysis of the compressive strength of cement mortar at other ages based on the early strength at the age of 7 days, this model could contribute to the safety assessment of concrete structures during the construction phase.