Seven-day test result assessment of the developed strength in composite cement mortar with slag

An important research topic for sustainable development is the replacement of natural resources with renewable materials. Several recycled materials, such as furnace slag and steel slag, were used and applied in concrete or cement mortar. The design strength of the concrete or cement mortar normally represents its 28th day strength. Thus, an assessment of the compressive strength of cement mortar with furnace slag powder and steel slag from the early strength is desirable. In this study, Baosteel Slag Short-Flow (BSSF) slag and furnace slag powder were used to replace fine aggregate (0%, 25%, 50%, 75% and 100%) and cement (20%), respectively, through a volumetric method, and three water-binder ratios of 0.45, 0.50, and 0.55 were used to produce composite cement mortar. According to the test results, the compressive strength increased as the replacement rate of BSSF slag increased. Using the test results for the water-binder ratio (W/B) values of 0.45 and 0.55, 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, at the water-binder ratio W/B = 0.50, the MAPE (mean absolute percentage error) value of the test specimens was found to be 8.12%. Moreover, when the W/B was 0.45 and 0.55, the MAPE value for the test specimens was 9.38% and 5.29%, respectively. All of the MAPE values were less than 10%; thus, the analytical model results established in this study were satisfactory under different conditions. Therefore, the proposed model can be used as a reliable tool for assessing the design strength of cement mortar from early age test results, and it could contribute to the safety assessment of cement mortar structures during the construction phase.