Laboratory investigation of foamed concrete prepared by recycled waste concrete powder and ground granulated blast furnace slag

Foamed concrete is a primary choice for building envelopes due to its good thermal inertia, controllable density and excellent fire resistance. Because of the high carbon emissions and energy consumption, it has become an increasingly urgent need to find a material that can replace cement. In particular, how to effectively use solid waste is an important trend and a significant challenge. In this study, foamed concrete was prepared by recycled waste concrete powder (RP) and ground granulated blast furnace slag (GGBS) using wet foam mixing method. By measuring the stability time of preformed foam and setting process of paste, as well as the compressive strength, dry density, porosity and thermal conductivity of specimen, the effects of alkali activator dosage, CaCl2·6H2O dosage and foam content on the properties of foamed concrete were discussed. The pore structure and reaction mechanism were analyzed by means of image analysis and X-ray diffraction. The results indicate that the compressive strength of specimen increased and then decreased with the increase of alkali content, and reached the maximum value at 5% of alkali activator. But the porosity and dry density were less affected by the amount of alkali activator. The addition of CaCl2·6H2O significantly shortened the setting process of paste, which made the paste and preformed foam achieve a better matching state. Thus the compressive strength and thermal inertia were markedly improved, and the pores were effectively refined. Foamed concrete with different density grades can be prepared by changing preformed foam content. With the increase of foam content, compressive strength and thermal inertia were obviously decreased, and the pore distribution was gradually coarsening. Furthermore, the thermal conductivity and porosity conformed to ME2 model. The activity of both RP and GGBS can be effectively activated, the two played a coordinating and complementary role to achieve the effect of synergistic utilization of solid waste.