Effect of Drying Temperature on the Physical and Mechanical Properties of Starch-Gelled Lightweight Concretes

Abstract

Lightweight starch gelled concretes constitute an innovative class of cement based composites obtained by direct gelatinization of starch in the cement slurry, allowing a highly porous matrix (porosity often exceeding 60%) with low density and enhanced thermal insulation. This work focuses on the influence of drying temperature on the physical and mechanical performance of such composites, aiming to mitigate shrinkage related cracking and optimize production parameters. Six starch gelled concrete mixtures were prepared with cement content varying from 400 to 600 g per 1 dm3, including four variants with 70 g per 1 dm3 of hydrated lime and all containing 35 g per 1 dm3 of starch. After 28 day curing at high relative humidity and about 20°C, the specimens were dried at 70, 105, 120, and 150°C to evaluate the effect of temperature on density, compressive and flexural strength, thermal properties and crack formation. The study shows that drying at 105°C is most favourable for starch gelled mixes containing hydrated lime, providing higher strength while limiting cracks, whereas 70°C proves optimal for lime free variants, minimizing shrinkage and preserving surface integrity. The addition of lime improves flexural and compressive strength, reduces settlement and bleeding, and drastically decreases surface cracking after drying. All composites exhibit low thermal conductivity, confirming their suitability as thermal insulation materials, while higher binder (cement and lime) content increases density, strength, and thermal conductivity, without a corresponding increase in shrinkage related damage when drying conditions are properly controlled. However, further comprehensive research is necessary to better understand their long-term durability and to optimize production parameters for widespread industrial use.