Effects of Calcium Chloride, Ocher, and PP Fibers on the Mechanical Properties of Low Cement High-Performance Concrete with Ca(OH)2-Activated Slag Binder: A Novel Approach.

The high amount of carbon dioxide produced by using cement as a component in concrete has led to environmental issues. Additionally, the amount of cement used in high-performance concrete (HPC) is considerable. As an alternative, slag is being used to reduce cement consumption. This study presents the development of HPC with minimal use of cement without significant strength reduction. The cementitious materials comprise 85% slag, 5% hydrated lime, and 10% ordinary Portland cement (OPC). Replacing cement with slag at high percentages always reduces the strength of concrete. Therefore, appropriate additives were used to achieve the strength of conventional concrete made of OPC. Calcium chloride was used as the most well-known accelerator of hydration, as well as ocher (red clay) due to its Fe2O3 content. Compressive strength and four-point flexural tests at the ages of 7 and 28 days, and Thermogravimetric Analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were performed. The results showed that the mixture which included 2% calcium chloride with 2% ocher, provided the highest compressive and flexural strengths of 93.2 and 8.1 MPa, respectively. These values were 99% of the compressive strength and 96% of the flexural strength of the concrete sample made of OPC only. The microstructural analysis showed that this mixing design had the highest content of calcium-silicate-hydrate (C–S–H) and other vital phases. Also, due to the role of chloride ions in steel corrosion, the electrical resistance test was performed on the sample that contained 2% calcium chloride and the sample with OPC only. The results showed that calcium chloride used as an accelerator will not cause corrosion of steel bars in the concrete. [ABSTRACT FROM AUTHOR]