The effect of water to cement ratio and age on the mechanical properties of cement mortar and concrete made of micro‐nano bubbles without adding any admixtures

The effect of using water containing micro‐nano bubbles (WMNB) without adding any admixtures and normal water (NW) on the mechanical properties of cement mortar and concrete samples were investigated. Four various water to cement ratios equal to 0.6, 0.5, 0.4, and 0.35 (ranging from conventional concrete to high strength concrete), and three different curing ages of 7, 28, and 90 days were considered. The experimental results showed that the initial and final setting time of cement paste, the flow of hydraulic cement mortar and the slump of concrete samples made with WMNB were lower than that of made with NW. However, the compressive strength of cement mortar in using WMNB indicated an increase up to 16 and 7% in at 7 and 28 days, respectively. We also concluded that the optimum percentage of water to cement ratio was 0.35, which in that ratio the compressive strength enhancement of concrete made of WMNB reached the peak of 6, 18.3, and 16.3% at 7, 28, and 90 days age, respectively. Whereas increasing water to cement ratio, resulted in reducing the compressive strength of concrete. Besides, the high‐resolution scanning electron microscopy images with Energy Dispersive X‐Ray analysis were briefly conducted to explore the morphological change.