초록
The aim of the research is to verify the efficiency of the double-layered bubble sheets method by evaluating the basic properties and temperature history, and analyzing the economics through the field application under the conditions of mass concrete construction during cold weather. In the case of the fresh concrete, all tested properties of slump, air content, and chloride content were satisfied the target values. Furthermore, the compressive strength at 28 days achieved designed compressive strength. From the temperature history of the mass concrete constructed during cold weather, gradual increase of the temperature up to 50.3℃ was observed about 60 hours after the placing. At this time, the top-surface temperature was 32.6℃ which was 17.7℃ difference to the core part and it could restrain the cracking due to the heat of hydration with 0.85 of thermal crack index. It can be analyzed that the combined effect of decreasing the maximum temperature of the concrete at core part by controlling the mix design to decrease the heat of hydration, and further reducing the temperature difference between top and core parts of the mass concrete by keeping the surface temperature by insulating cure using bubble sheets was successful. The measured values of average curing temperature at all measuring points were confirmed higher than 10℃. Additionally, since all measuring points were calculated 66°DD of maturity, 5 MPa of minimum compressive strength of preventing early-age frozen damage was secured. In aspect of economics, comparing with currently used heat-curing method, the suggested double-layered bubble sheet method showed cost reducing effect in all parts of materials, labor, and other costs. Furthermore, the cost could be reduced more as the number of re-using was increased, so it could reduce 85 % of cost to the currently used heat-curing method.
