Cement Replacement and Improved Hydration in Ultra-High Performance Concrete Using Biochar

Abstract

This study demonstrates the efficacy of biochar in a dual role of internal curing agent as well as a viable candidate for cement replacement in ultra-high performance concrete (UHPC). Bio-char (BC), a product of pyrolysis of mixed wood saw dust, was prepared by pyrolytic conversion at 500 °C. Biochar produced was manually grinded into micron-sized particles. It was then pre-soaked for 24 h to achieve saturation, which was then mixed to replace 2%, 5% and 8% of cement by wt. in UHPC. Isothermal calorimetry (ITC) tests showed that the presence of BC improved the hydration in BC-UHPC mix compared to reference. This is further confirmed from the bound-water measurements using thermo-gravimetric analysis (TGA), where a substantial improvement in BC-UHPC mix compared to reference was observed. Scanning electron microscope (SEM) images revealed that pores of BC serve as nucleation sites for hydration products. The drop in compressive strength in BC-UHPC mix were limited to 10% of the reference mix, and comparable strength was achieved at 5% replacement level. Overall, the results indicate that bio-char from wood waste can be a potential mineral admixture in UHPC, which might be effective to reduce cement demand and create novel avenue for waste valorisation.