Prediction of temperature rise in concrete due to heat of hydration of cement

Abstract

Temperature rise due to heat of hydration in concrete depends on many factors such as geometry of the concrete element, chemical, physical and thermal properties of concrete materials, mix proportion, initial temperature during concrete batching, and thermal boundary conditions during concrete hardening etc. The multicomponent cement hydration model developed by Maekawa et al., predicts the heat generation due to cement hydration based on cement contents, water contents, reference heat generation rate of main mineral components in cement, i.e. alite (C3S), belite (C2S), aluminate (C3A), ferrite (C4AF), and gypsum (CS2H), mineral of cement, fineness of cement, thermal activity and interdependences of mineral components, and effects of consumption of free water during the hydration process etc. This cement hydration model was incorporated in the transient heat conduction analysis. The transient heat conduction analysis was carried out with ANSYS, finite element analysis software using Advance Parametric Design Language (APDL) computer programming to predict the temperature ruse due to heat of hydration of cement in concrete element for a given thermal boundary conditions. Since the heat of hydration of cement is highly temperature dependent, variation of thermal properties of concrete at early ages is essential to predict the temperature response due to heat of hydration of cement in concrete. Experimental investigations were carried out to develop a model to estimate the variation of thermal conductivity of concrete from fresh to hardened state. The specific heat capacity of concrete (ϲ) was estimated based on the specific heat capacities of cement powder and hydration products using Dulong – Petit Rule (DPR), Neumann – Kopp Rule (NKR), and mixing theory. Thermal conductivity of concrete (λ) was determined by fitting temperature rise curve at center of cube with temperature rise curve predicted by transient heat conduction analysis. Estimated specific heat capacity of concrete was applied in iv transient heat conduction analysis program, to predict temperature rise curve from 1hrs to 1day for several mix proportions. A mathematical model was developed to predict the variation of thermal conductivity based on experimentally investigated thermal conductivity data, mix proportions, thermal conductivity of concrete material found in literature, cement and water contents, formation, shapes, and saturation of gel and capillary pores of cement paste , degrees of hydration, surface saturation of aggregates by applying into general and effective medium theories used in estimation of effective thermal conductivity of a multicomponent material. The developed model was calibrated and verified with experimental data of concrete cube samples for several mix proportions. A computer program was developed using APDL coding of ANSYS software to predict the thermal properties of concrete once mix proportion, chemical, physical and thermal properties of concrete materials are known. This model was coupled with the multicomponent heat of hydration model to improve the program’s ability to predict temperature rise with effects of variation of thermal properties with degree of hydration of cement. The developed multicomponent heat of hydration model was calibrated and verified with temperature rise data detained from several field tests which were carried out in several construction projects in Sri Lanka. Measured and predicted temperature response are in good agreement, and therefore the proposed model can be used to predict temperature rise when chemical composition, mix proportions, and thermal boundary conditions are known. Furthermore, the developed hydration model was used to obtain appropriate values for T1 (i.e. temperature drop between hydration peak and ambient temperature under local conditions which are required in design of water retaining structures.