Method for Evaluation of In-place concrete Strength using Concrete Temperature History.

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It becomes more important to obtain information about the in-place strength of concrete as it exists in a structure especially for the use of high-strength concrete. As carried out in accordance with standard procedures, the test on cylinders only r13EA\ : epresents the potential strength of concrete as delivered to a site. A system for evaluation of in-place strength of concrete is proposed based on the methods developed in this research.(1) Evaluation on strength development accelerated by the hydration heat accumulation. The temperature in the high-strength concrete member rises about 40 degrees due to hydration heat. Various experiments were performed to clarify the effect of the13EA\ : high temperature histories during early age on accelerated strength development in early age and strength degradation in later age. On the basis of these test results, the practical method for evaluation of strength development was derived.(2) Analysis for temperature rise in concrete due to hydration heat. The examination on the temperature distribution in the concrete member obtained from tests shows that the dependency of hydration rate on temperature exists and it can be expressed13EA\ : by using Arrhenius equation. An analytical method considering this dependency was developed.(3) Application of pull-out tests for very high strength concrete. Pull-out tests on very high strength concrete were performed using specially improved test devices. The strength-predicting equation applicable for whole range of concrete strength w13EA\ : as derived.(4) Proposed method for evaluation of in-place strength. A method for determination of target strength at mix design is proposed based on the combination of the strength method and the analysis of temperature rise described in this study. A recommen13EA\ : ded method for evaluation of in-place strength is shown by applying the strength development theory and the pull-out test on concrete during construction.