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
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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.