Effect of immersion time of glass powder on mechanical properties of concrete contained glass powder as cement replacement

•New mixing method improved the early compressive strength of concrete.•Longer immersion time of glass powder in water improved the compressive strength of concrete up to 145%.•Packing and pozzolanic reaction are responsible on the increase of the compressive strength at early age while the pozzoalnic reactivity is the responsible later. The goal of this work is to investigate the effect of immersion time of glass powder (GP) in water before mixing it with the other concrete ingredients on the fresh and hardened properties of concrete. Six immersion times (0, 1, 2, 3, 6 and 12 h) were investigated with different amount of GP as cement replacement (0, 2.5, 5, 10 and 20%). The dissolution of GP in water leads to form more Na ions than Ca ions, because Na ions have less mobility than Ca ions. The concentration of Na decreased as a function of immersion time as it bonds with the SiO2 on the surface of GP particles. Immediately after putting the glass powder in the water, the workability of concrete decreased with the increase of GP content due to the sorption of water molecules on GP particles. As the immersion time increased the workability of concrete increased with the amount of glass powder due to the bleeding effect of the water from the GP. The optimum compressive strength was obtained at 2.5 and 5% GP mixes and at 3 h and 6 h immersion time. At early age, the higher compressive strength is originated from the double effect of the development of pozzolanic reaction due to the increase of the free ions in the water before mixing with the concrete and the packing filling effect of glass powder. The densification of the transitional zone between the cement paste and the aggregate leads to higher compressive strength of concrete. Later, at long curing time, the increase of the compressive strength is correlated to the progress of the pozzolanic reaction of the GP.