**7. Concrete Temperature Evolution of the Bridge Deck**

The one-dimensional model (1D) was used to predict the temperature development of regular concrete slabs. In case of any irregularities such as the proximity of the protruding reinforcement or the influence of the temperature of earlier concreted parts of element, previously determined model parameters are no longer valid. Therefore, the calculations were performed for elements with clearly defined boundary conditions. This applies to the B-B section of the bottom plate of stage I, the web and the top plate (stage II) and the web monitored during III stage of research on the bridge.

Numerical simulations were carried out relying on experimentally determined constants for each research stage. The selected model parameters and heat transfer coefficients were adopted from the own propositions dedicated to the analyzed high-performance concrete and element thickness up to 100 cm. In this kind of structure, semi-adiabatic conditions of concrete hardening might be assumed. The prediction of concrete temperature for compressive strength assessment is the most useful for the medium-weight structure, which constitute the building contractor's interest. The proposed relationships are not intended for massive or thin-walled concrete elements. On the basis of laboratory and field tests, the coefficient κ/*n*<sup>0</sup> as a function of ambient temperature (Figure 19a), and the parameter *n* versus the thickness of the element (Figure 19b) was expressed. In both cases a linear function was used, and the accuracy of the approximated data (black dots) describes the determination coefficient R2. As shown in Figure 18c, the parameter *A*0/κ is mainly responsible for the time of extreme temperature occurrence, so for elements with thicknesses higher than 60 cm (80 and 93 cm) the value 1·10−<sup>5</sup> was assumed, and for elements thinner than 60 cm (35, 40 and 56 cm) *<sup>A</sup>*0/<sup>κ</sup> equals 1·10<sup>−</sup>4.

**Figure 19.** The proposition of determination model parameters: (**a**) κ/*n*<sup>0</sup> and (**b**) *n*.

Literature propositions for heat transfer coefficients for forced convection or for insulation layer are often the result of specific experimental investigations and are only relevant in this particular case. In this study, the convective heat transfer coefficient on the concrete surface protected by the formwork layer α*f orm <sup>s</sup>* depended on the difference between the initial temperature of the mixture *T*<sup>0</sup> and the ambient one *Tenv* (Figure 20a). In Figure 20 dots corresponded to the experimental data, which came from the three stages of field tests and the existing atmospheric conditions. For the heat transfer coefficient for the free surface of the slab α*f c*, the formula as a function of wind speed was proposed. The comparison with the suggestion of other researchers is illustrated in Figure 20b.

**Figure 20.** The own suggestion of connective heat transfer coefficient: (**a**) α*f orm <sup>s</sup>* and (**b**) α*f c*.

In the future, to determine reliable nomograms (such as Figures 19 and 20), a series of concrete tests should be performed for different storage conditions and different concrete volumes. This approach would be justified in the case of repetitive elements, manufactured e.g., in a prefabrication plant. However, for individual constructions, at least measurements of the temperature of concrete cubes hardening in an adiabatic calorimeter or isothermal and semi-adiabatic conditions are required. Additionally, the measurement system should be installed in one regular section on the object, e.g., the start segment.
