Effects of Desert Sands on the Fresh and Hardened Properties of Cement-Based Materials

The use of desert sands as an alternative to river sand in concrete may be limited by the presence of internally sourced sulfate and chloride ions, which may affect hydration and long-term performance. This study investigates the influence of naturally contaminated desert sands on the fresh and hardened properties of cement-based materials. Mortar mixtures produced with sands from three sites of the Atacama Desert were compared with mixtures containing artificially contaminated sands designed to reproduce equivalent ionic release during mixing. Hydration kinetics by isothermal calorimetry, strength development, and susceptibility to internal sulfate attack (ISA) were evaluated using isothermal calorimetry, compressive strength testing, and length change measurements. Results show that chloride contents up to 1.0% by mass of dry sand accelerated early hydration and increased 7-day compressive strength by up to 15% relative to the reference mixture. Conversely, sulfate contents of 0.24% reduced 28-day compressive strength by up to 18% and promoted long-term expansion associated with ISA. Mixtures containing combined moderate sulfate and high chloride levels exhibited enhanced early hydration without significant strength loss at later ages. The novelty of this study lies in linking ion release from natural desert sands to equivalent artificial contamination, enabling a systematic evaluation of internal sulfate-chloride interactions in cement-based materials.