Abstract
Prediction of hydration temperature and induced stresses in mass foundation slabs, due to the hydration effects is a difficult task. The complexity of this issue is compounded by transient and non-linear thermo-mechanical phenomena as well by a significant number of contributing technological and material factors that affect the early-age volume changes. This is a probable reason for the limited number of simple analytical methods allowing for the estimation of these effects. This work presents a new proposal in the discussed field. The submitted analytical method for determining the hydration temperature rise, its differentials at a cross-section and induced thermal stresses in mass concrete foundation slabs considers the majority of important technological and material factors, such as the initial temperature of the concrete, the ambient temperature, the thermal properties of the concrete and the heat exchange conditions on the slab surfaces. In stress analysis, both self-balanced and restraint stresses are calculated. Finally, the method is validated in FE analysis conducted for the slabs with various heights and made of different types of cements, as well as by the thermal measurements from the construction site. Due to the limited number of methods allowing for the analytical estimation of the early age thermo-mechanical effects in slabs, this new proposal can be useful in the assessment of these effects.
Highlights
The main feature of a mass concrete foundation slab at an early age is its thermal volume change due to the hydration heat
Many parameters are necessary for the risk in mass foundation slabs presents particular problems both because of the properties of maturing analysis discussed above, such as heat evolved during cement hydration, thermal and mechanical concrete, as well as the conditions of the construction process
It has been noted that the proper estimation of early age stresses induced in the foundation slab is more bothering than estimating temperature changes
Summary
The main feature of a mass concrete foundation slab at an early age is its thermal volume change due to the hydration heat. Many parameters are necessary for the risk in mass foundation slabs presents particular problems both because of the properties of maturing analysis discussed above, such as heat evolved during cement hydration, thermal and mechanical concrete, as well as the conditions of the construction process. The latest version of Japanese standards concerning the process of design and reducing the thermal cracking risk in mass concrete structures presents the simplified method resulting from the comprehensive numerical simulations [9] Following this method, the temperature difference at the slab thickness is not calculated, but the placing temperature, the ambient temperature and the ultimate adiabatic temperature rise are related to the reference values and used in the determination of thermal cracking index. The temperature measurements in the real foundation slabs have been used
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