Carbonaceous inserts from lignocellulosic and non-lignocellulosic sources in cement mortar: Preparation conditions and its effect on hydration kinetics and physical properties

Landfilling and open burning of biomass wastes lead to adverse environmental impacts. A potential means to valorize such wastes can be achieved through thermal conversion to biochar, and applying the produced biochar as admixture in cementitious construction materials. This article aims to investigate the influence of biochar from different lignocellulsic wastes, including sorghum, cotton stalk, wood and dairy manure, and non-lignocellulosic algae waste on hydration, mechanical and permeability properties of cement mortar. Performance of biochar-mortar composites were compared with mortar prepared with three different commercial biochar with relatively high carbon content and surface area. The findings suggest that biochar with higher surace area and pore volume, for instance, wood biochar, tend to increase hydration, while biochar with high ash content, for instance dairy manure biochar in this case, reduce peak hydration heat and negatively affect the overall hydration over 7-day monitoring period. Strength results suggest that depending on elemental carbon content and surface area, addition of biochar from different lignocellulosic biomass increases compressive strength, elastic modulus and fracture toughness by 10-12%, 16-20% and 30-40% respectively at 2 years compared to control. Among lignocellulosic biochars, only wood biochar prepared at 500 degrees C led to slight increase (7%) in 28-day strength compared to control, while non-lignocellulosic algae biochar reduced strength of mortar by 15%. Depending on feedstock and production condition, addition of lignocellulosic and non-lignocellulosic biochar led to 10-50% reduction in permeability at 28-day age, measured by water absorption through capillary action. The findings suggest that addition of biochar from horticultural, agricultural and forest waste may be a sustainable means to improve physical properties of construction materials while reducing the need for incineration and landfilling. (C) 2020 Published by Elsevier Ltd.