Numerical Approach towards Aging Management of Concrete Structures: Material Strength Evaluation in a Massive Concrete Structure under One-Sided Heating
Numerical Approach towards Aging Management of Concrete Structures: Material Strength Evaluation in a Massive Concrete Structure under One-Sided Heating
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DOI：
10.3151/jact.13.500
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发表时间：
2015-11
影响因子：
2
通讯作者：
I. Maruyama;G. Igarashi
中科院分区：
文献类型：
--
作者：
I. Maruyama;G. Igarashi
为了对既有钢筋混凝土构件进行性能评估，提出了一种预测构件中混凝土物理性能时空变化的化学-热-湿模型--计算水泥基材料模型（CCBM）。所提出的模拟模型包括水泥矿物的水化速率、相组成和水泥浆体的合成性质（即，压缩强度、杨氏模量、泊松比、热膨胀系数、自生收缩、干燥收缩、热容、传热系数、水蒸气吸附等温线和水传递系数）。此外，混凝土的抗压强度模型考虑了水泥浆体强度的变化，由于其胶体特性，以及由于加热和干燥时骨料和砂浆之间的体积差异而在骨料周围产生的微观缺陷。通过将这些模式与热量和水分传输耦合，评估了空间分布和时间变化的具体特性。这些模型的验证是通过使用现有的实验数据。使用此CCBM，一个厚的混凝土墙与中等波特兰水泥与水灰比为0.55下单侧加热进行了模拟和潜在的问题，可能会出现在完整性评估进行了讨论。如果在放置91天内评估的所需抗压强度保持不变，则额外的水化过程可以建立足够的强度裕度，以克服由于加热和干燥导致的强度降低的风险。然而，在由于重新评估的风险（例如地震的震级）而增加所需强度的情况下，性能评估并不是微不足道的，因为从可以执行采样的一侧获取的芯样可以表现出比目标混凝土构件的平均强度更大的强度。因此，在这种情况下，数值评估可能会有所帮助。
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.