Biochar as internal curing material to prepare foamed concrete

Abstract

Biochar is one of the by-products of biomass pyrolysis, which has the characteristics of water absorption and low thermal conductivity, etc. This study produced foamed concrete incorporated rice husk biochar (RHBC) produced at 300℃, 500℃ & 700℃ pyrolysis (B300, B500, B700) with replacement rates of 1%, 3%, 5% and 7 %. The experimental results show that B700 has the highest mechanical properties of 11.3 MPa compressive strength and 2.82 MPa bending strength under its optimal addition rate (5% B700), which are much higher than the control group (5.6 MPa compressive strength and 1.23 MPa bending strength). Meanwhile, the resistance to humid environment and shrinkage resistance were shrinkage resistance improved the most. Instrumental analysis (TGA, XRD, heat flow, CT and SEM) revealed that the porous RHBC enhanced and extended the hydration processes, resulting in the formation of additional cementitious materials, and filled in the cracks, forming more homogeneous pore structure. In addition, the impact of RHBC on the foam’s and cement paste’s stability were studied. It can be concluded that the addition of RHBC enhances the bubble restraint force (Fc) by increasing the yield cement paste’s stress, thus reducing the bubble diameter size and bubble buoyancy (Fb), ultimately leading to higher stability of foam and better mechanical properties of foamed concrete.