Influence of moisture states of recycled sand from construction sites on mechanical strengths of cement-based mortar

Abstract

This study focuses on investigating the influence of moisture states of recycled sand (RS) from construction sites on properties of cement-based mortars. The major goal of this study was to utilize the amount of RS as a waste at the construction sites, as well as to reduce the burden on natural sand extraction and to save the construction cost. The use of RS as a partial replacement for natural river sand (NS) at various percentages (0% and 50% by mass of fine aggregate) was employed. Various investigations of properties including consistency of fresh mortar, compressive and flexural strengths of hardened mortar specimens, were conducted. The two moisture states for both sands were saturated surface dry (SSD) and dry state (DS). When increasing the percentages of RS replacement, regardless of the moisture states of sand, the results indicated that consistency of fresh mortar, compressive and flexural strengths at 28 days tended to decrease by 11.1–20.0%, 7.8–8.9%, and 7.4–13.8%, respectively. When compared with mortar using sand at DS state, the improvement of consistency, compressive and flexural strengths at 28 days of mortar using sand at SSD state was 20.0–33.3%, 72.2–74.3%, and 23.3–32.4%, respectively, depending on the type of sand (NS or RS). Furthermore, the correlation between compressive and flexural strengths of the mortar was linear. In conclusion, the replacement of NS by RS at 50% reduced the consistency and mechanical strengths of the cement-based mortar, while the use of RS in SSD state can be considered as an effective solution for enhancing the strengths of cement-based mortar compared to that in DS state.