Effect of formwork removal time reduction on construction productivity improvement by mix design of early strength concrete

In this study, we examined the effects of cement fineness, SO₃ content, an accelerating agent, and chemical admixtures mixed with unit weights of cement on concrete early strength using concrete mixtures. C24 (characteristic value of concrete, 24 MPa) was used in the experiment conducted. Ordinary Portland cement (OPC), high fineness and SO₃ OPC (HFS_OPC), and Early Portland cement (EPC) were selected as the study materials. The unit weights of cement were set to OPC 330, 350, and 380. Further, a concrete mixture was prepared with a triethanolamine (TEA)-based chemical admixture to HFS. A raw material analysis was conducted, and the compressive strength, temperature history, and maturity (D·h) were examined. Then, the vertical formwork removal time was evaluated according to the criterion of each country. Finally, the time required to develop concrete strength of 5 MPa was estimated. Results showed that the early strength of concrete mixed with HFS and EPC was greater than that exhibited by concrete with an increased unit weight of cement with OPC. In addition, when HFS was used with EPC, its strength developed early, similar to the trend exhibited by EPC, even at low temperatures.