Microstructural and mechanical characterization of foamed concrete reinforced with scrap aluminum engine residue

Foamed concrete (FC) is a lightweight cementitious material made by adding a stable pre-formed foam to a cement paste or mortar to make a homogenized mixture of a controlled low density. The present work aims at evaluating the effect Scrap Aluminum Engine Residue (SAER) has on fresh, mechanical, thermal, and microstructural properties of FC with a water-to-cement ratio of 0.4 at targeted densities of 900 kg/m³ (FC-900) and 1100 kg/m³ (FC-1100). SAER was added at 1.5%, 2.5%, and 5.0% as a weight of cement. After 28 days curing, ASTM standard tests were conducted to analyze the fresh density, spread flow, stability, compressive strength, flexural strength, thermal conductivity along with microstructure characteristics via X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The addition of SAER to the wet mix enhanced fresh density and induced moderately in the early age expansion but compromised workability. The best result was obtained when 2.5% SAER was used, where the gain in compressive strength is 92.8% (FC-900) and 242.9% (FC-1100), and in the flexural strength, 68.8% and 67.8%, respectively. The thermal conductivity was reduced by up to 44% in FC-900 which implies that it is a sign of improved insulation. XRD showed lower crystallinity as the SAER content increased, but the higher density mixes showed sharper diffraction peaks. SEM observations revealed that the most uniform and dense microstructure of a mixture was the FC-900 mix with a 2.5% SAER containing minimum porosity. Such results lead to the conclusion that 2.5% SAER is the most effective dose of the component that can maximize mechanical strength and thermal insulation properties in foamed concrete.