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Abstract:
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A large amount of heat can be liberated during cement hydration , causing very large temperature increases in mass concrete members . The non -uniform temperature field produced by the cement during curing can cause very high internal stresses that may crack the concrete . Concrete thermal cracking in very large structures is a well -known phenomenon and was studied extensively during the height of dam construction in the United States . In recent years concrete bridge member sizes have increased for structural and aesthetic reasons . Recent problems in San Antonio and Houston , Texas with thermal cracking and very high internal temperatures in mass concrete bridge members has renewed interest in studying early -age thermal cracking and its mechanisms . In order to predict the early -age thermal cracking risk of a concrete member , the temperature history , autogenous shrinkage , modulus development , tensile strength development , coefficient of thermal expansion development , creep behavior , and external restraint conditions must be known . A testing procedure has been developed to measure concrete heat of hydration , mechanical property development , and free shrinkage response at different curing temperatures . The concrete free shrinkage includes thermal and autogenous shrinkage components and is measured using a newly developed free shrinkage testing apparatus . The early age concrete creep is calculated from rigid cracking frame tests performed at different varying temperatures . Trends in early age creep behavior for different concrete mixtures common in mass concrete have been found and are used to develop a statistical model relating concrete mixture proportions and constituent material properties for use in mass concrete thermal stress modeling . The results from the test methods described are used in a new concrete early -age cracking risk and durability software package called ConcreteWorks . |