Properties of Steel Fiber-Reinforced Alkali-Activated Slag Concrete Made with Recycled Concrete Aggregates and Dune Sand

Reutilizing industrial by-products and recycled concrete aggregates (RCA) to replace cement and natural aggregates (NA) in concrete is becoming increasingly important for sustainable development. Yet, experimental evidence is needed prior to the widespread use of this sustainable concrete by the construction industry. This study examines the performance of alkali-activated slag concrete made with RCA and reinforced with steel fibers. Natural coarse aggregates were replaced with RCA. Steel fibers were added to mixes incorporating RCA at different volume fractions. Desert dune sand was used as fine aggregate. The mechanical and durability properties of plain and steel fiber-reinforced concrete made with RCA were experimentally examined. The results showed that the compressive strength did not decrease in plain concrete mixes with 30 and 70% RCA replacement. However, full replacement of NA with RCA resulted in a 20% reduction in the compressive strength of the plain mix. In fact, 100% RCA mixes could only be produced with compressive strength comparable to that of an NA-based control mix in conjunction with 2% steel fiber, by volume. In turn, at least 1% steel fiber, by volume, was required to maintain comparable splitting tensile strength. Furthermore, RCA replacement led to higher water absorption and sorptivity and lower bulk resistivity, ultrasonic pulse velocity, and abrasion resistance. Steel fiber incorporation in RCA-based mixes densified the concrete and improved its resistance to abrasion, water permeation, and transport, thereby enhancing its mechanical properties to exceed that of the NA-based counterpart. The hardened properties were correlated to 28-day cylinder compressive strength through analytical regression models.

Automated summary

The study found that replacing 30% and 70% of natural aggregates with RCA in concrete did not decrease compressive strength, while full replacement of NA with RCA resulted in a 20% decrease in compressive strength. In order to achieve compressive strength comparable to that of an NA-based mix, 100% RCA mixes required 2% volume of steel fibers. Overall, incorporating steel fibers in RCA-based mixes improved mechanical properties and resistance to abrasion, water permeation, and transport compared to NA-based mixes.