Comparative evaluation of short- and extended-duration ground desert sand powders as mineral additions in cement paste

This study compares the cement paste-scale behavior of desert sand powders prepared by short- and extended-duration ball milling under laboratory conditions. The 8 h ground powder, DP1, was compared with a previously reported 12 h ground powder, DP2, used as the extended-duration reference. The powders were characterized by particle size distribution, SEM, XRD, and TGA, and incorporated into cement pastes at 5-20% replacement levels. Semi-adiabatic temperature monitoring, low-field NMR, compressive strength, XRD, TGA, and SEM were used to compare early-age hydration indicators, relative water-state evolution, strength retention, and microstructural features. Compared with DP1, DP2 showed an earlier temperature response and higher early-age paste strength. This difference decreased with curing age, and DP1-10 and DP2-10 reached similar strengths at 112 days. Desert sand powder reduced strength compared with OPC, particularly at 7, 28, and 56 days. Therefore, the strength results should be interpreted as paste-scale strength retention under cement replacement, rather than strength improvement over OPC. Extended grinding also led to a larger apparent particle size by laser diffraction, attributed to possible secondary agglomeration observed by SEM. Because BET surface area, dispersion-state measurements, agglomerate-breakage tests, and direct reactivity tests were not conducted, the relationship between DP2 particle state and early-age response remains tentative. Overall, desert sand powder behavior was mainly governed by cement dilution, particle filling, nucleation-related physical effects, water-state evolution, and ongoing cement hydration. Direct chemical contribution or pozzolanic reactivity was not quantified. The results do not establish a universal optimal grinding duration, mortar/concrete-scale performance, or net environmental benefit