Pore topology, volume expansion and pressure development in chemically-induced foam cements

Foam cement is an engineered lightweight material relevant to a broad range of engineering applications. This study explores the effects of aluminum chips on cement-bentonite slurry expansion, pressure development, and the evolution of pore topology. The terminal volume expansion under free-boundary conditions or the pressure build up under volume-controlled conditions are a function of the aluminum mass ratio, bentonite mass ratio, and aluminum chip size. X-ray CT images show that finer aluminum chips create smaller pores but result in a larger volume expansion than when larger sized chips are used; on the other hand, large chip sizes result in unreacted residual aluminum. Time-lapse CT images clearly show the sequence of processes which lead to the development of foam cement: gas bubble nucleation, bubble growth, capillary-driven grain displacement enhanced by the presence of bentonite, coalescence, percolation, gas leakage and pore collapse. These results illustrate the potential to customize the mixture composition of chemically-induced gassy cement to control expansion and pressure build up, and to minimize percolating discontinuities and gas release.