Properties of Ultralight EPS Concrete Prepared Using a Powder Precoating Process

To address the issues of low strength, uneven particle distribution, and weak interfacial bonding in ultralight expanded polystyrene (EPS) concrete, this study proposes a powder precoating process. This process involves precoating the surface of EPS particles with a layer of powder material. The differences in the effects of this process and the ordinary process on the properties of ultralight EPS concrete were systematically compared. The results showed that the precoating process increases the compressive strength by 21.4%–25.6% for ultralight EPS concrete with a low density grade of 200 – 400 kg / m 3 , and the flexural strength is increased by up to 40.6% for the concrete with a density grade of 600 kg / m 3 . Additionally, it can effectively alleviate the phenomenon of reduced concrete strength caused by the incorporation of fly ash. The uniformity index of ultralight EPS concrete prepared by the precoating process reached 0.78, whereas that of the ordinary process was 0.59. Cross-section observations confirmed that the EPS particles are more evenly distributed, the number of pores is reduced, and the delamination phenomenon is basically eliminated. The slope of the thermal conductivity of the precoating process with increasing density decreases from 1.64 × 10 − 6 (of the ordinary process) to 1.57 × 10 − 6 , indicating that the precoating process provides better thermal insulation performance at the same density. Microscopic analysis revealed that the precoating process improves compactness by optimizing the structure of the interfacial transition zone, promoting the formation of calcium silicate hydrate (C─S─H), and reducing the residual calcium hydroxide ( Ca ( OH ) 2 ), without introducing new chemical bonds. This process provides technical support for the application of ultralight EPS concrete in energy-efficient buildings.