## 3 Results  
Internal temperature monitoring of the concrete samples in vertical cylinder molds and its average values are presented in Figure 5a for 28 days of curing. Daily fluctuations in daytime and nighttime represent a spiky graph within certain limits; nevertheless, it is possible to trace the exothermic reaction that takes place during the curing of the concrete. The ambient temperature was positive during the concrete curing and varied between 3 and 25 \({}^{\circ}\)C within 8-18 \({}^{\circ}\)C prevailing fluctuation. The ambient relative humidity generally showed a rather dry environment of 40-60%, with two time jumps over four weeks of curing (Figure 5b). The strength gain of concrete after the seventh day for specimens in cylindrical molds slows down a little, but then resumes a gradual growth, while the concrete in the boxes stabilizes and forms a gently sloping curve. The results for strength on the 1 st, 3 rd, 7 th, 14 th and 28 th days are presented in Figure 6a. Since compression tests were only carried out on certain days, for the remaining days, the compressive strength was determined using the trend line shown in Figure 6a. The most fitting trend line and the corresponding formula, expressing the dependence of compressive strength on age for the concrete cylinders, is presented in natural logarithmic approximation. Further, Figure 6b shows the maturity-strength relationship according to the [13] standard in accordance with Equation (1), based on only one parameter--internal temperature. Figure 4: Determination of the strength of concrete in boxes obtained by the IPS-MG 4.01 sclerometer. In Figure 7, the complex maturity values calculated by Equations (2)-(7), and including the impact of IT, AT and ARH parameters, were presented in relation to the compressive strength cylinders, determined in Figure 6a. The corresponding trend line in natural logarithm approximation and a coefficient of determination R\({}^{2}\) = 0.9987 confirm the high convergence. Knowledge of the relationship between the compressive strength and the complex maturity, determined for a given concrete mixture, enables estimation of the strength at any value of complex maturity on the site. For the concrete class B25, the necessary value to continue the construction is 22.4 MPa, which corresponds to 70% of standard strength of 32.0 MPa on the 28 th day. The internal temperature history of concrete boxes chases a similar pattern of internal temperature in cylindrical samples, due to the simultaneous testing and identical ambient environment, although with less influence of daily fluctuation due to the higher volume of heat capacity of large concrete samples in the boxes (Figure 8). Figure 5: Temperature and humidity monitoring for concrete cylindrical samples over time: (**a**) Internal temperature fluctuation (average value); (**b**) Ambient temperature and ambient relative humidity. Figure 6: Concrete strength gained over time: (**a**) Compressive strength on the 1 st, 3 rd, 7 th, 14 th and 28 th days; (**b**) Maturity–strength relationship according to [13]. Using the maturity-strength relationships from Figures 6b and 7, the internal temperature history from Figure 8, ambient temperature and relative humidity history from Figure 5b, and Equations (1)-(4), the current strength values in boxes were estimated for the Nurse-Saul and the proposed methods. The maturity values at each period were calculated using the average values of internal temperature in boxes. Figure 9 shows the values of concrete strength measured by non-destructive testing with IPS-MG 4.01 sclerometer in both boxes and their average. The results obtained by various strength methods on the 1 st, 3 rd, 7 th, 14 th and 28 th days of concrete curing are presented in Table 5, where strength in boxes, representing the construction on the site was measured by the IPS-MG 4.01 sclerometer, as well as estimated by [13] and the proposed method of complex maturity. Figure 8: Internal temperature in the boxes (average value).