Investigation of phase composition and microstructure of foamed cement paste with different supplementary cementing materials

Foamed concrete is highly porous, and the pores inside the material improve the insulation performance. However, the material strength decreases with increasing pores (porosity). To enhance the mechanical properties of the material without reducing porosity, the solid matrix of foamed concrete can be adjusted. For this purpose, several foamed cementitious specimens with various supplementary cementing materials (SCMs) and compositions were produced and investigated to evaluate the effect of SCMs on the microstructures of foamed cement paste. In addition to the specimen with cement only, SCMs such as fly ash and silica fume were used to produce foamed cementitious specimens with increased strength. To compare the effect of the water/binder ratio on the microstructure characteristics, a set of specimens was prepared with varying water/binder ratios. The microstructures of the foamed cementitious specimens with the various SCMs were analyzed using three different approaches: X-ray diffraction, scanning electron microscopy, and X-ray micro-computed tomography. The results from those approaches as complementary tools demonstrated that pozzolanic SCMs can improve the material strength of foamed cement paste by increasing the amount of C–S–H or Si phases. In addition, the microstructural investigation also confirmed that the water/binder ratio affects the degree of hydration.