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