Numerical Approach towards Aging Management of Concrete Structures: Material Strength Evaluation in a Massive Concrete Structure under One-Sided Heating

Ippei Maruyama, Go Igarashi

Journal of Advanced Concrete Technology, 13, 500-527, 2015

For the purpose of performance evaluation of an existing reinforced concrete member, a computational simulation model to predict the spatial and temporal changes of physical properties of concrete in the member, named the “Computational Cement-Based Material Model (CCBM)”, was proposed. This proposed simulation model includes models of rate of hydration of cement minerals, phase composition, and resultant hygro-thermo-mechanical properties of cement paste (i.e., compressive strength, Young’s modulus, Poisson’s ratio, thermal expansion coefficient, autogenous shrinkage, drying shrinkage, heat capacity, heat transfer coefficient, water vapor sorption isotherms, and water transfer coefficient). Furthermore, the model for compressive strength of concrete considered the variation in cement paste strength due to its colloidal features as well as micro-defects produced around aggregate due to differences in volume between aggregates and mortar upon heating and drying. The concrete properties of spatial distribution and temporal changes were evaluated by coupling these models with heat and water transport. Validation of these models was achieved by using existing experimental data. Using this CCBM, a thick concrete wall made with moderate Portland cement with a water-to-cement ratio of 0.55 under one-sided heating was simulated and potential problems that can arise during an integrity evaluation were discussed. If the required compressive strength, which was assessed within 91 days of placement, remains unchanged, an additional hydration process can build an adequate strength margin to overcome the risk of strength reduction due to heat and drying. However, in the case that the required strength is increased due to a re-evaluated risk, such as the magnitude of an earthquake, performance evaluation is not trivial as the core sample taken from the side where the execution of sampling is possible could exhibit a greater strength than the average strength of the target concrete member. Therefore, numerical evaluation might aid in this kind of situation.

In this paper, a computational model predicting spatial and temporal changes of physical properties of concrete was proposed. Hydration rate of cement minerals, phase composition, as well as those resultant physical and mechanical properties such as strength, Young's modulus, thermal expansion coefficient, autogenous and drying shrinkage and so on, were simulated in the model. Finally, the model was used to evaluate the physical and mechanical properties of a concrete wall with one-sided heating. The reviewer regards that the model has high originality and technical quality. The simulated results as well as the experiment data used for the verification are reliable. The results were carefully obtained and substantially discussed, and the discussion is clear logically. This paper provides a helpful approach to predict and evaluate the performance and safety of those concrete structures that usually are difficult to monitor.
(Reviewer A)