Drying shrinkage, durability and microstructure of foamed concrete containing high volume lime mud-fly ash

This paper aims to study the drying shrinkage, durability and microstructure of foamed concrete containing high volume lime mud (LM) and fly ash (FA). The effects of wet density (600 kg/m3, 700 kg/m3, 800 kg/m3 and 900 kg/m3) and LM-FA dosage (0 wt%, 50 wt%, 60 wt%, 70 wt% and 80 wt%) on flowability, compressive strength, drying shrinkage, dry-wet resistance, freeze–thaw resistance, and microstructures were investigated. X-ray diffractometer (XRD) and thermo gravimetric (TG) were used to study the hydration products. Environmental scanning electron microscopy (ESEM) and image analysis method were combined to analyze the characteristics of air voids, including aspect ratio, average pore diameter, and size distribution. The results show that wet density and LM-FA dosage had significant on foamed concrete properties. When the wet density increased or LM-FA dosage decreased, the compressive strength and the drying shrinkage increased. The compressive strength ranged from 1.31 to 2.52 MPa. The drying shrinkage was between 0.34% and 0.44%. For all specimens, after 30 freeze–thaw or 50 dry-wet cycles, the compressive strength was still higher than the specification required strength of 0.8 MPa. For air voids, the equivalent diameter, ranging from 149 μm to 202 μm, and the volume of pores larger than 200 μm decreased as the wet density and LM-FA dosage increased. However, the aspect ratio was between 1.15 and 1.20 for all specimens. TG and XDR results show that the lime mud accelerated the hydration of FA.