Abstract:

This study proposed a preparation technique for magnesium oxysulfate cement-based ultra-lightweight foam concrete （MOS-ULFC）， in which pressure is applied during the prefabricated foaming and slurry mixing stages， followed by pressure release during molding. The pressure differential induced bubble expansion， thereby increasing porosity and achieving ultra-lightweight characteristics. The effects of different foaming pressures on the density， mechanical properties， thermal conductivity， and pore structure of MOS-ULFC were systematically analyzed. Results show that， within the range of 101~160 kPa， increasing the foaming pressure markedly reduces the density and thermal conductivity of MOS-ULFC. When the foaming pressure increases from 101 kPa to 130 kPa， the dry density decreases from 157.81 kg/m³ to 49.22 kg/m³， with a reduction of 68.81%， while the thermal conductivity decreases from 0.069 8 W/（m·K） to 0.037 1 W/（m·K）， with a reduction of 46.85%. At 160 kPa， both density and thermal conductivity of MOS-ULFC increase slightly but remaine lower than those of the atmospheric-pressure group （101 kPa）. Applying pressure during prefabricated foaming and slurry mixing stages significantly increases the internal pressure of bubbles. Upon returning to atmospheric pressure after molding， the trapped air rapidly expands， leading to a substantial increase in bubble size， and consequently， in average pore size and porosity. Specifically， when the foaming pressure increases from 101 kPa to 130 kPa， the average pore size increases from 78.53 μm to 113.49 μm （an increase of 44.52%）， while the total porosity increases from 91.94% to 96.21%. This work provides a new approach for the ultra-lightweight design and preparation of foam concrete.

Key words: foam concrete, foaming pressure, density, thermal conductivity, pore structure, ultra-lightweight