Durability and Hardened Characteristics with SEM Analysis of Eco-Efficient Self-Compacting Concrete Partially Contained Waste Walnut Shell Particles as Fine Aggregate

Substituting waste materials for natural aggregate in SCC can lead to the discovery of ecological building materials. Walnut shell (WS) is one of the agricultural byproducts that can be substituted for aggregate in SCC. In this study, WS was used as a replacement for fine aggregate in SCC by employing five different volume fractions ranging from 8 to 40% in increments of 8% while maintaining a constant percentage of limestone powder (10% by weight of cement). All SCC mixtures were evaluated for the fresh properties (slump flow, slump flow duration, V-funnel, L-box, and wet density) tests, hardened characteristics (compressive strength, splitting tensile strength, flexural strength, Schmidt rebound hammer, and ultrasonic pulse velocity) tests, scanning electron microscopy (SEM) analysis, and the effect of H2SO4 and MgSO4 solution with 5% concentration for one month period on the density, compressive and splitting tensile strengths. The hardened properties were performed at 28 and 56 curing periods. The results revealed that the workability and hardened properties of SCC mixtures decreased with increasing WS content, but the workability outcomes were within the standard specifications of SCC, except for the L-box test. The lowest compressive strength of 23.7 MPa was recorded for the mix containing 40% of WS, greater than the lower strength required for structural purposes. On the other hand, the density, compressive and splitting tensile strengths of all SCC mixes decreased after exposure period for both sulphate attacks. The investigation with SEM reveals that the increasing amount of WS produced more voids and less dense concrete compared to the control mix.