Application of the hydration heat of concrete bored piles when using foundation soils according to Principle II (Active method)

Introduction. The use of bored piles in foundation works is a common construction technology, which has been successfully employed for construction in permafrost zones. However, up to the present time, the heat of hydration released during the hardening of cement mixes has been considered as an adverse event thus not being practically applied, particularly when preparing foundation soils according to Principle II, or the Active method.
Aim: to study the process of cement hydration when hardening and to assess variations in its temperature in order to use the data obtained for thermal and deformation calculations in construction design.
Materials and methods. An analysis of regulatory framework, as well as scientific and technical literature, was carried out. Experimental laboratory studies of different cement mixes were performed. The obtained results were analyzed, the directions for further studies were outlined along with design recommendations.
Results. The experimental study showed the maximum increase in the temperature of cement mixes one day after laying to range between 8.2 and 29.9 °С depending on the composition and initial temperatures of the mixes. Thermal and geotechnical calculations for a particular designed project based on the obtained data proved the efficiency of the considered approach for foundation works. Hence, this allowed the requirements for a minimum temperature of a cement mix and an estimated period of soil thawing under the building foundation to be included in the design documentation.
Conclusions. The conducted experiments and numerical calculations showed that, under a certain set of characteristics of cement mixes for bored pile foundations, the released heat of hydration can be sufficient for thawing permafrost soils and preparing the foundation soils for use in terms of Principle II. This approach ensures time and cost optimization during the construction period.

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