Lightweight fired clay brick production for archeological heritage site maintenance application

In this paper, azodicarbonamide (AC), a thermo-sensitive chemical blowing agent, was applied to produce the lightweight fired clay brick with low thermal conductivity and suitable mechanical property. Rice husk was also added to induce the ancient brick texture and brick reinforcement for the archeological site maintenance purpose. Prior to production, thermal decomposition of AC was estimated to design the firing condition, and it was added from 0 to 3.0 pph. AC exhibited suitable thermal sensitivity that could begin pore formation via gas releasing process at the firing temperature of 300 °C. X-ray fluorescence (XRF) indicated that the chemical compositions of the clay bricks before and after firing were the same excepted for Cl, which was possibly liberated under firing process. X-ray diffraction (XRD) analysis showed some structural changes and the crystal transformation after firing. In comparison, all chemical-blown bricks showed the significant decrease of bulk density, indicating the capability of AC to lighten the brick by generating the porous structure. The compressive strength values were higher than the requirement value of the severe weathering grade of the clay brick, which was specified by ASTM C62-12. In summary, the optimal use of AC blowing agent of 2.0 pph with the assistance of rice husk provided the bricks with lower bulk density, higher specific compressive strength, higher porosity and lower thermal insulation properties than neat fired clay brick.