Experimental Study and Application of a Novel Foamed Concrete to Yield Airtight Walls in Coal Mines

Airtight walls are vital to prevent spontaneous combustion of residual coal as caused by air leakage. A new type of foamed concrete (FC) was developed to control air leakage. FC specimens of four densities (250, 450, 650, and 850 kg/m(3)) were prepared for use in a series of physical and mechanical tests. A thickener was used to control the FC shrinkage and collapse. The permeability of the FC decreased approximately exponentially with an increasing density. On the contrary, the compressive strength (sigma) and elastic modulus (E) increased in exponential and linear relationship separately with the increase in density, under uniaxial compression conditions. Under triaxial compression, the compressive strength of the FC increased with an increase in confining pressure and appeared slight plastic. The impact experiment showed that the dynamic compressive strength of the FC appeared to be strain-rate dependent, and it increased with an increase in the strain rate and pressure under a confining pressure. Without a confining pressure, the variation in compressive strength exhibited a slow decrease. Applied FC resulted in a 5 M Pa 28-day compressive strength of the airtight wall with no remaining fissures and with air leakage suppression to the gob.