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Blast furnace slag (SL) is an amorphous calcium aluminosilicate material that exhibits both pozzolanic and latent hydraulic activities. It has been successfully used to reduce the heat of hydration in mass concrete. However, SL currently available in the market generally experiences pre-treatment to increase its reactivity to be closer to that of portland cement. Therefore, using such pre-treated SL may not be applicable for reducing the heat of hydration in mass concrete. In this work, the adiabatic and semi-adiabatic temperature rise of concretes with 20% and 40% SL (mass replacement of cement) containing calcium sulfate were investigated. Isothermal calorimetry and thermal analysis (TGA) were used to study the hydration kinetics of cement paste at 23 and 50 °C. Results were compared with those with control cement and 20% replacements of silica fume, fly ash, and metakaolin. Results obtained from adiabatic calorimetry and isothermal calorimetry testing showed that the concrete with SL had somewhat higher maximum temperature rise and heat release compared to other materials, regardless of SL replacement levels. However, there was a delay in time to reach maximum temperature with increasing SL replacement level. At 50 °C, a significant acceleration was observed for SL, which is more likely related to the pozzolanic reaction than the hydraulic reaction. Semi-adiabatic calorimetry did not show a greater temperature rise for the SL compared to other materials; the differences in results between semi-adiabatic and adiabatic calorimetry are important and should be noted. Based on these results, it is concluded that the use of blast furnace slag should be carefully considered if used for mass concrete applications.

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Set time of shotcrete is mainly driven by the use of a highly reactive set accelerator. The control of set time is very important for providing successful application of shotcrete in the construction site, because it determines key parameters such as capability to increase layer thickness and loss of the material caused by rebound of shotcrete. However, there is no standard test procedure available to determine the set and stiffening process of shotcrete. In this research, the stiffening process of shotcrete mortar was measured using the penetration resistance test in the American Society for Testing and Materials (ASTM) C403, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance. Various types of shotcrete accelerators and three different sources of portland cement have been used to investigate the set and stiffening process of shotcrete mortar. According to the experimental results, calcium aluminate type accelerators worked most effectively in controlling set and stiffening of shotcrete mortar. It was found that the penetration resistance test can be used to evaluate compatibility issues between the cement and the shotcrete accelerator. The set time of shotcrete can be determined using best fitted function using current set time criteria of 3.5 and 27.6 MPa for initial and final set.