Development of fly ash and slag based high-strength alkali-activated foam concrete

Foam concrete is a lightweight construction material with excellent thermal and acoustic insulation ability. It is widely used in building envelopes, partitioning walls, sandwich components, etc. However, the foam concrete applied most is made by Portland cement that consumes much energy and emits a large amount of CO2 during its production process. As a green binding material without clinker, the alkali-activated material fully utilizes fly ash, slag and other industrial solid wastes or by-products, which largely reduces CO2 emissions. In this paper, the fly ash and slag based alkali-activated foam concrete with a design density ranging from 200 kg/m3 to 1200 kg/m3 was developed. Based on the bubble dynamics theory, the mechanical behavior and the stability of bubbles in the mixture were analyzed, and a calculation method for judging the stability of bubbles in the mixture was proposed. According to the analysis and performance of prepared bubbles, Sodium dodecyl sulfate was selected as the foaming agent to prepare the foam concrete. The compressive strength of the developed foam concrete ranged from 0.50 MPa to 44.98 MPa while the flexural strength ranged from 0.22 MPa to 13.86 MPa, respectively, with respect to different densities. The results show that the mechanical strengths of alkali-activated foam concrete are higher than that of ordinary Portland cement based foam concrete with the same density. In addition, alkali-resistant glass fibers were used to improve the problem of the brittleness of low-density foam concrete. It was observed that the 0.5% volume fraction of fibers was optimal to improve the mechanical properties.