Effect of untreated and thermoactivated construction spoil on microstructure and properties of low-carbon foam concrete

This study proposes to develop low-carbon foam concrete by replacing cement with construction spoil (CS). The influences of CS content, thermoactivated treatment and particle size on the microstructure and macro-properties of foam concrete were systematically studied. Key parameters analyzed included the fluidity, rheology, setting time and defoaming rate of fresh slurry, as well as the pore structure, phase composition, compressive strength, drying shrinkage and water transport of hardened concrete. Furthermore, life cycle assessment and cost analysis were employed to quantify the carbon footprint and cost of the material. The results showed that using untreated CS resulted in reduced fluidity, prolonged setting time, increased yield stress and plastic viscosity, and increased defoaming rate of fresh mixture, as well decreased hydration products, and reduced interconnected pores and average pore size, which weakened the strength, shrinkage and transport performance of hardened concrete. The heat treatment of CS effectively enhanced the early stability of foam concrete with CS, decreased the pore size and increased the pore sphericity due to the generated metakaolin components. With further use of finer-grained heat-treated CS, the induced hydration products increased, the interconnected pores decreased, and the proportion of small-sized spherical pores increased. These microstructural refinements significantly enhanced various macroscopic properties of the material. The use of either untreated or thermal-activated CS reduced the carbon emission and cost of foam concrete by up to about 28.2 % and 13.2 %, respectively. • A low-carbon foam concrete was developed by partially replacing cement with construction spoil (CS). • The influences of CS content, treatment, and particle size on the microstructure and properties of foam concrete were studied. • The impact mechanisms of untreated and heat-treated CS on the performance of foam concrete were revealed.