Effect of Fly Ash and Reactive MgO on the Engineering Properties and Durability of High-Performance Concrete Produced with Alkali-Activated Slag and Recycled Aggregate

Abstract

This study investigated the engineering properties and durability of high-performance recycled aggregate concrete (HPRAC) specimens. The specimens were prepared using alkali-activated slag with varying proportions of fly ash (FA) (Category 1) and reactive MgO (Category 2). The first category included specimens in four subcategories in which FA replaced ground granulated blast furnace slag (GGBFS) in the binder at ratios of 0%, 15%, 30%, and 45% by weight. The second category included specimens in three categories in which a group mixture containing 15% FA and 85% GGBFS was modified by 2.5%, 5%, and 7.5% reactive MgO (based on the total weight of FA and GGBFS). The engineering properties of HPRAC specimens were assessed using tests for slump, compressive strength, splitting tensile strength, water absorption test, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), thermal conductivity, and rapid chloride ion penetration (RCPT). All the HPRAC specimens exhibited good strength and durability at 91 days of curing. However, the engineering properties of the concrete samples were significantly affected by the levels of added FA and MgO. Although the CF15M5 mixture exhibited the highest compressive strength and best attributes of the HPRAC specimens, its performance in terms of the tested variables still was inferior to that of natural aggregate concrete.