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

Abstract

For the purpose of performance evaluation of an existing reinforced concrete member, a chemo-thermo-hygro 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 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.

Determination of Thermal Properties of Hardening Concrete for Massive Nuclear Shielding Structures

“…Since most of concrete shielding structures are usually massive structures the limits are imposed on the temperature development in the hardening concrete in order to prevent the early age cracking, [Tia 2010], [Maruyama 2015]. The contractor is required to plan the concrete work so as that large temperature differences between different parts of the structure do not arise.…”

Review of the Current State of Knowledge on the Effects of Radiation on Concrete

“…Simultaneously, the prolonged moderate temperature exposure (<65°C by design) and strong internal moisture content gradient (Oxfall 2013) affect the degree of hydration of concrete, and thus, its mechanical properties. In particular, it leads to the development of lower strengths toward the reactor cavity (Maruyama and Igarashi 2015). The dissipation of the RIVE-induced elastic stresses implies a potential relaxation in the cement paste, but, more significantly, the development of cracking (Giorla, Le Pape, and Dunant 2016).…”

Feedback System of Ion Transfer through Cracks During Deterioration of Mortar Due to Sulfate Attack Evaluated by RBSM-Truss Network Model

“…Indeed, gel porosity was defined as the difference between molecular volume of C 1.7 SH 2.5 and C 1.7 SH 4.0 . The details of the physical properties can be found in Maruyama et al (2015).…”

“…CCBM is one of the cement hydration model proposed by Maruyama et al (2015). This model has been constructed by physical and chemical properties that can influence to the hydration process of cementitious material under different relative humidity and temperature based on many experimental data.…”

“…In this paper, the numerical analytical system, which can reconstruct hydration process, transformation of solid phase and manifestation and propagation behavior of expansion crack, is proposed based on previous model (Miura et al 2016). This analytical system is composed of a hydration model using Computational CementBased Material model (CCBM) (Maruyama 2015) that can predict the change in solid phase, porosity, and mechanical behaviors due to hydration; a diffusion-reaction model that can predict transportation of sulfate ion and transformation of solid phase due to sulfate attack; and RBSM which can evaluate expansion cracking behavior.…”