Effect of nano-alumina modified foaming agents on properties of foamed concrete

This paper presents a novel method for preparing an ultra-stable foam based on SOCl2 treatment and nano-alumina (NA) modification by comparing the properties of foams fabricated by different nanomodified foaming agents. Meanwhile, the effect of nano-modified foaming agent on the mechanical strength, drying shrinkage, water absorption, and uniformity of the corresponding foamed concrete is also investigated. Experimental results reveal that the stability, density, and viscosity of foams fabricated by plant protein-based surfactants (PS), animal protein-based surfactants (AS), and synthetic surfactants (SS) with similar functional groups, density, and stability could be enhanced with the addition of NA. When NA was used as a stabilizer, the drainage of SS, AS, and PS at 5 min was decreased by 11%, 5%, and 4% respectively. The mechanical strength, drying shrinkage, and uniformity of foamed concrete with SS, AS, and PS could be enhanced with the addition of NA. The properties of foamed concrete with nanomodified SS (NA-SS) was better than those having nano-modified AS (NA-AS) and nano-modified PS (NAPS) which may be due to the uniform distribution of NA in NA-SS foam and discrete distribution of NA in NA-AS and NA-PS foam. The carboxyl group on the SS surface after SOCl2 treatment reacts with the hydroxyl group on the nano-alumina surface resulting in uniform NA adhesion to the air-water interface. The hydration product layer produced by the pozzolanic reaction between Ca(OH)(2) and the uniformly distributed NA can fill the pores of cell wall homogeneously, improving the strength of the cell wall and increasing the performance of the foamed concrete. (C) 2020 Elsevier Ltd. All rights reserved.