Waste glasses were finely grind to use as ordinary Portland cement (OPC) replacement in concrete. Its pozzolanic reactivity was evaluated at different replacement levels, including 5%, 10%, 15% by mass. The particle size distribution for glass powder is almost the same as that of OPC. It was found that the total hydration heat was greatly reduced due to the dilution effect of OPC, which results in a lower strength at early age. However, the pozzolanic reaction of glass powder became obvious with longer curing period, supported by the much improved strength for concrete with 15% glass powder. Calcium hydroxide content was determined at different ages for paste with various amount of glass powder and the results revealed that the calcium hydroxide drastically dropped with age, consumed by the pozzolanic reaction of glass powder. At 28 days, almost no calcium hydroxide was found in the paste with glass powder, implying that the optimum replacement level should be less than 45%.