Mitigating Efflorescence and Enhancing Compressive Strength of Clay Bricks through Partial Replacement with Quarry Dust, Marble Dust, and Fly Ash: An Experimental Study

Clay masonry units remain a dominant construction material across the Indian subcontinent owing to their availability, thermal comfort, and comparatively low embodied cost, yet two persistent defects — surface efflorescence and inadequate compressive strength — continue to limit their long-term performance. Efflorescence, the crystallisation of soluble salts drawn to the brick surface by capillary moisture movement, degrades appearance and signals an underlying pore structure that can also compromise durability, while insufficient compressive strength restricts the load class for which a unit may be specified. This study experimentally examines whether partially substituting the clay matrix with three locally available by-products — quarry dust, marble dust, and fly ash — can address both defects simultaneously. Four brick mixes (an unmodified control and one mix per additive) were prepared under identical moulding, drying, and firing conditions and evaluated in triplicate for compressive strength and 24-hour water absorption, the latter interpreted as an indirect indicator of the capillary porosity that drives efflorescence. Quarry dust produced the largest strength gain (17.6% above control) while leaving water absorption essentially unchanged; fly ash gave a smaller strength gain (9.2%) but the lowest absorption of all four mixes (a 2.9% reduction relative to control); marble dust improved strength only marginally (1.7%) while increasing water absorption by 34.5%, to the edge of the 15% threshold conventionally applied to load-bearing units. The results indicate that quarry dust and fly ash are the most promising of the three by-products for jointly reducing efflorescence risk and raising strength, while marble dust requires further dosage optimisation before it can be recommended on the same basis.黏土砌筑单元（clay masonry units）在印度次大陆地区仍是主流建筑材料，这得益于其取材便捷、热舒适性能优异且隐含成本相对较低。然而两类长期存在的缺陷——表面泛霜（efflorescence）与抗压强度不足——始终制约其长期服役性能。泛霜是指可溶性盐随毛细水分迁移至砖体表面后结晶析出的现象，不仅会破坏外观，还暗示砌体内部孔隙结构存在缺陷，进而削弱结构耐久性；而抗压强度不足则会限制该砌块可适用的荷载等级。本研究通过实验探究，采用三种当地易得的工业副产物——采石场粉尘、大理石粉尘以及粉煤灰——部分替代黏土基体，能否同时解决上述两类缺陷。研究制备了四组砖体配合料（一组为未改性对照组，其余三组分别添加上述一种副产物），所有组均在一致的成型、干燥与焙烧条件下制备，并分别进行三次重复实验以测试抗压强度与24小时吸水率；其中吸水率被视为驱动泛霜的毛细孔隙率的间接表征指标。测试结果显示：采石场粉尘可实现最大的强度提升（较对照组提升17.6%），且吸水率基本无变化；粉煤灰的强度提升幅度较小（9.2%），但四组配合料中吸水率最低（较对照组降低2.9%）；大理石粉尘仅小幅提升强度（1.7%），却使吸水率升高34.5%，接近承重砖体通用的15%吸水率阈值上限。实验结果表明，在三种副产物中，采石场粉尘与粉煤灰在同时降低泛霜风险与提升抗压强度两方面表现最优；而大理石粉尘则需进一步优化掺量，方可在同等标准下推广应用。