Design, fabrication, and characterization of distinguished lightweight and sustainable building materials

Abstract

As one of the eco-friendly building materials, autoclaved aerated concrete (AAC) has received considerable attention in industrial and academic research groups over the last few years. Herein, new AAC composites with different ratios of fine sand, lime, cement, and gypsum plaster were prepared in an autoclave at a pressure of 10 bar for 8 h. The effects of adding a polymelamine sulfonate (PMS) superplasticizer to the prepared AAC composites on workability were investigated according to their physical and mechanical properties. The binding phase of calcium silicate hydrate was fully characterized via Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The effect of AAC slurry foaming agent and water to solid ratio (W/S) was reported in detail. Furthermore, we studied the effect of ultrafine sand (<63 μm) reinforcement on the properties of AAC products.Under the specified curing conditions, the results showed that a strength value of 3.8 MPa with a low bulk density of 0.60 g/cm3 (600 kg/m3) was obtained from an AAC composite with 65 wt% fine sand, 15 wt% lime, 15 wt% cement, and 5 wt% gypsum plasters, containing 0.12 wt% Al powder and 45% water to solid ratio (W/S) mixtures. The strength value of the AAC composite can increase to 4.8 MPa, maintaining a low bulk density of 0.60 g/cm3 when the AAC slurry composite included 1% PMS at a W/S of 56% and 0.08% Al powder. In particular, the production of ultra low-density building materials can be efficiently controlled by mixing superplasticized AAC slurries with 0.16 wt% Al powder (at W/S = 56%), reaching a low bulk density of 0.39 g/cm3 (390 kg/m3) with a reasonable strength of 1.70 MPa for AAC samples. Interestingly, 50 wt% of fine sand with a particle size of about 90 μm is sufficient for tobermorite formation from the sand-lime reaction at designated hydrothermal conditions. However, replacing the large particles with ultrafine sand (<63μ) reduced the AAC strength characteristics. Besides, the compressive strength was improved by forming long tobermorite needles, lath structures, or both. In contrast, the gel-like material (poorly crystallized tobermorite) provides the lowest strength properties for AAC (about 3 MPa).