EARLY AGE THERMAL CRACKING CONTROL IN MASS CONCRETE SHEARWALLS USING HIGH STRENGTH SELFCONSOLIDATING CONCRETE

摘要

Major shearwalls for a 56-storey mixed-use concrete tower in Surrey, Canada, were designed withrnarchitectural features on the exterior surfaces. They required massive concrete pours and use of high-strengthrnconcrete with high flowability. Some concrete placement was to take place in hot weather. All of these factorsrncould potentially produce high temperatures in concrete and early-age thermal cracking. Thermal crackingrncontrol was recognized as a need during the structural design stage. The shearwall design based on thernanticipated seismic and wind induced loads meets the minimal reinforcement requirement for thermal crackrncontrol. Maximum temperature and maximum temperature differential in the massive concrete structures shouldrnbe evaluated and controlled to prevent disorders due to Delayed Ettringite Formation (DEF) and to minimizernearly-age thermal cracking.rnA high strength self-consolidating concrete (SCC) mix was selected for achieving the desired architecturalrnappearance. A large volume of supplementary cementitious materials (SCM) was used to partially replacernPortland limestone cement for reduced heat of hydration. A wall mockup with actual wall thickness and actualrnformwork was constructed to evaluate the temperature rise of the SCC mix and the effectiveness of the insulationrnprovided by the formwork. Temperatures were closely monitored and controlled in the mass concrete shearwall.rnStaged formwork “cracking” and removal approaches were used in concrete temperature control for the purposernof efficient use of the concrete formworks.rnThe study found that the shearwall mockup with actual formwork provided useful information of therntemperature rise and temperature differential characteristics in the mass concrete using high strength SCC.rnProperly-developed concrete temperature control and management plans may be more practical and economicalrnin controlling the temperatures of mass concrete to minimize early age cracking and to increase formworkrnproductivity.