*7.2. Web and Top Slab (Stage II)*

Another regular case is the web (40 cm) and the top slab (56 cm), i.e., medium-weight elements, monitored during the second stage of bridge investigations [11]. The recorded temperature history in the concrete web and the top plate are presented in Figure 24. The initial temperature of the mix, which was used to concrete the web was 29.1 ◦C, and in the case of the top plate it was 28.5 ◦C. The maximum concrete temperature of both the web and the top plate was recorded after 17.5 h. At point p4 and p12 its value was equal to 57.8 and 59.6 ◦C. Thus, the maximum temperature of self-heating caused by the cement hydration recorded in the web and the top plate was 28.7 and 31.1 ◦C.

In both monitored elements, boundary conditions had a strong influence on the temperature distribution. The concrete temperature of the web, 40 cm thick, surrounded on both sides with formwork, was very similar at all measurement points (Figure 24a). The top slab was on the one hand uncovered, and on the other protected with shuttering, which was the reason of temperature difference (e.g., Δp9-p12 = 5.2 ◦C; Figure 24b). Due to the high air temperature, these differences were not significant.

**Figure 24.** Temperature development of the concrete during 240 h: (**a**) Web and (**b**) top slab.

During concreting of overhanging section of the bridge span, the average ambient temperature of 10 days was 20.1 ◦C. The average wind speed in this period reached 8 km/h = 2.22 m/s [39]. Calculations, as before, for constant and variable air temperature were made. Thermophysical parameters were adopted in accordance with Tables 2, 6 and 7. The temperature measurements in the web and the top plate in six points were carried out, while the graph presents results from three characteristic points (due to the readability of the graph). Better convergence of numerical and experimental data was obtained in the case of using a variable ambient temperature (Figure 25, Figure 26). According to Figure 25b the relative error for points p1, p3 and p4 was equal to 0.8%, 0.3% and 1.1% (max. temperature) and 5.8%, 0.9% and 2.7% (time occurrence of max. temperature). Based on Figure 26b the relative error for points p9, p10 and p12 was equal to 3.6%, 0.5% and 0.7% (max. temperature) and 1.9%, 1.0% and 0.8% (time occurrence of max. temperature). Good results have also been achieved for the temperature distribution in the cross-section of the web and the top plate, where the measured values were marked with dots (Figure 27, Figure 28). For the web the symmetry condition of the temperature distribution was met. Conducted research confirmed correctness of model assumptions and emphasized the importance of ambient temperature.


**Table 6.** Thermophysical parameters—web, 40 cm thick, stage II.


**Figure 25.** The concrete temperature of web, 40 cm thick (stage II): (**a**) Constant ambient temperature and (**b**) variable, measured ambient temperature.

**Figure 26.** The concrete temperature of top slab, 56 cm thick (stage II): (**a**) Constant ambient temperature and (**b**) variable, measured ambient temperature.

**Figure 27.** (**a**) Space variation of the web temperature field at different curing time and (**b**) concrete temperature distribution map (in both cases variable, measured ambient temperature).

**Figure 28.** (**a**) Space variation of the top slab temperature field at different curing time and (**b**) concrete temperature distribution map (in both cases variable, measured ambient temperature).
