In this paper, a multi-scale analysis of the effect of foam on chemo-mineralogical and microstructural features of the soil-cement-water system is presented. Time-dependent mineralogical and microstructural changes induced by foam weremonitored at increasing curing times by means of X-ray diffraction, thermogravimetric analysis, scanning electronmicroscopy and mercury intrusion porosimetry. Addition of foam does not alter chemo-physical evolution of the soil-cement-water system in terms of either cement hydration or pozzolanic reactions. Large voids are present in the samples asfootprints of air bubbles upon mixing, increasing the porosity of samples but not altering their matrix microstructure.Macroscopic behaviour of treated samples was investigated by direct shear tests. Chemo-physical evolution induced byadding cement is the main factor responsible for mechanical improvement shown by the treated samples. Sample porosityinduced by adding foam plays a key role in the mechanical response of lightweight cemented samples, inducing a transitionof stress-strain behaviour from brittle and dilative to ductile and contractile as foam content is increased.