Development and Characteristics of Ultra-Lightweight Concrete Mixed with Polyvinyl Alcohol Solution and Perlite

Polyvinyl alcohol (PVA) is a nontoxic, biodegradable, water-soluble polymer used in various fields. The use of PVA in concrete has been limited due to problems such as initial setting delay, early age strength reduction, and decreased mechanical and durability performance caused by the generation of microbubbles. This study aims to verify the performance and effectiveness of PVA as a foaming agent by reversely utilizing the microbubble generation phenomenon of PVA, which has been recognized as a problem. In addition, the production and characteristics of ultra-light foamed concrete were evaluated using perlite (PL). PVA solutions with concentrations of 2.5% and 5.0% were considered. PL ratios of 10% (P1), 20% (P2), 30% (P3), and 40% (P4) were applied to the mass of the PVA solution. The mass of PVA solution (s), OPC (c), and PL considered in the experiment were classified into s/c, s/PL, PL/c, and s/(c + PL), respectively, and the optimal mixing ratio was presented based on the experimental results. In addition, a new high-temperature-curing method was applied that combines high-temperature wet curing (60 °C, relative humidity 90% or higher) and high-temperature dry curing (105 ± 5 °C) to improve the strength reduction problem at the early age and to increase the pore expansion effect. In addition, thermal analysis (TG/DTA), X-ray diffeaction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were applied to analyze the hydration reaction products. The formed pores were imaged from the cross-section of each sample using an optical microscope, and the pore size was measured using image-processing software. The experimental results proved that PVA is a sufficiently effective material as a foaming agent for manufacturing foamed concrete in a high-temperature-curing environment. PVA showed a synergistic effect in expanding pores and increasing porosity, and PL improved insulation and lightweight. The manufactured ultralight foam concrete had a density of less than 1.0 g/cm3, a strength of 1–6 MPa, and a thermal conductivity of 0.13–0.19 W/m∙K. The appropriate mixing ratios within the range considered in this study were s/PL ratio of 5–3.33, PL/c ratio of 0.2–0.45, and s/(c + PL) ratio of 0.77–1.25.