Thermal Crack Mitigation in Massive Concrete Structures with Cooling Pipes

This work investigates the thermal and mechanical behaviour of a concrete pilot block, which forms part of a flood prevention polder dam on the Krounka River in the Czech Republic. Particular attention is paid to the early-age behaviour of the structure and the development of cracks as a result of hydration heat. A numerical model is developed using the object-oriented finite element software OOFEM, supported by open-source tools for pre- and post-processing. Cement hydration is simulated using the affinity hydration model, with parameters calibrated from experimental data. The thermal analysis is formulated as a transient heat transfer problem and validated using temperature data from embedded sensors. The nonlinear mechanical analysis is coupled with the thermal simulation results. Concrete is modelled as an ageing viscoelastic material with tensile fracture behaviour. Basic creep and autogenous shrinkage are described by the Microprestress Solidification theory and fracture behaviour is captured using a fixed crack model. Model parameters are derived primarily from experiments, supplemented by literature values where necessary. The results of mechanical analysis are compared with in situ strain data, overall showing good agreement. The evolution of the crack width is also the key objective. The findings indicate that the structure is not prone to early-age cracking under realistic boundary conditions. However, it is highly sensitive to external restraint. When underlying concrete is modelled as axially rigid, significant through-cracks with maximum width of 0.3mm occur. The study highlights the importance of embedded cooling systems in reducing thermal cracks and demonstrates the applicability of numerical modelling as an effective tool for the design and evaluation of the risk of cracking in massive concrete structures.