Characterizing the foam-shell microstructure of industrial ultra-light foamed concrete cast under different temperatures

Abstract

Ultra-lightweight foamed concrete (ULFC), as the most important component of engineered material arresting system (EMAS) for air plane landing safety, faces challenges in quality controls during materials fabrication. This study focused on the microstructure, penetration strength and foaming mechanisms of ULFC blocks cast at 35 °C, 37 °C and 40 °C based on practical factory fabrications. Multi-scale experiments were used to characterize the thermal evolution, strength, foam and shell structure, micro pores of the ULFC materials. Thermal data showed that increasing the casting temperature greatly shortened the induction period, raised the peak temperature, indicating the accelerated hydration process at the raised temperature. X-ray computed tomography data implied that, while raising the void number, compactness and sphericity, the temperature rises depressed the average pore size. Scanning electron microscopy and Nitrogen gas sorption tests showed that the void shell thickness decreased and the microstructure was more porous at a higher casting temperature. The rises of casting temperature were always harmful to the material strength, but had little effects on the chemical mineral formation of the solid matrix. Overall, the shell thickness and the micro pore structure of cement matrix, together with the porosity and pore geometries, jointly impacted the strength of ULFC. The findings of this work would improve the materials designs and fabrication procedures towards the better manipulation of foam structure to meet the requirements of EMAS buffer material.