## 2 Materials and Methods
The temperature sensors were inserted in the middle of the 2 cylindrical samples and 2 boxes and logged every 30 min for 28 days (Figure 1). Along with internal temperature, two more sensors were recording the ambient temperature and ambient relative humidity at the same time, by analogy with [23]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Age, Hours** & \multicolumn{2}{c}{\(i\)**Parameters**} & \multicolumn{2}{c}{**Compressive Strength in Cylinders, MPa**} \\ \hline
**t** & **IT** & **AT** & **ARH** & **CS** \\ \hline
0.5 & 21.44 & 23.9 & 29.7 & 0 \\ \hline
1 & 21.56 & 23.4 & 30.6 & 0 \\ \hline
1.5 & 21.94 & 23.3 & 33.8 & 0 \\ \hline \(\ldots\) & \(\ldots\) & \(\ldots\) & \(\ldots\) & \(\ldots\) \\ \hline
672 & 11.88 & 13.8 & 40.9 & 30.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Laboratory testing log template to retrieve the complex maturity–strength relationship. Figure 1: Testing set for estimating the concrete strength. Compression tests were conducted with a TMC-3224 hydraulic compression testing machine, according to [13] for cylindrical and [14] for cubic samples, in order to determine their average value of strength on the 1 st, 3 rd, 7 th, 14 th and 28 th days (Figure 2). Intermediate values of the compressive strength of cylinders in Tables 1 and 2 are retrieved from the trend line equation from the strength-age relationship in Figure 3.  
Correlation coefficients and weights for each of these parameters were calculated for every day in Table 2, and the mean value of the weight for the 28-day period is used in Equation (2). To determine the complex maturity-strength relationship, the trend line with the most fitting equation was drawn between the compressive strength of cylindrical samples and the complex maturity calculated by Equation (2). The resulting trend line corresponds to the logarithmic dependence \(S=a\cdot ln(M)+b\) in Figure 3, where \(S\) is strength, and \(M\) is the maturity of the concrete. The obtained complex maturity-strength relationship is used later to determine the current strength of the concrete by monitoring internal and ambient temperature and ambient relative humidity. As mentioned above, the internal and ambient temperature and ambient relative humidity were also tracked for the 2 boxes (Table 3), representing the concrete structures curing on the site. The recorded data made it possible to calculate their complex maturity by  
Figure 3: Relationship between complex maturity and strength of the concrete. Figure 2: Compression test of cylindrical and cubic samples on the 1 st, 3 rd, 7 th, 14 th and 28 th days. Equations (2)-(7) at each time interval of testing (Table 4). According to the equation defined in Figure 3, corresponding to the trend line, it became possible to estimate the current strength of concrete in the boxes for each period by establishing the complex maturity-strength relationship for this particular type of concrete and to determine the stage of curing matching to 70% of the designed concrete strength, allowing for further construction. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Age, Days** & \multicolumn{3}{c}{**Maturity of \(i\) Parameter**} & \multicolumn{3}{c}{**Complex Maturity, \({}^{\circ}\)C-Days**} & \multicolumn{2}{c}{**Estimated Strength in Boxes, MPa**} \\ \hline \(t\) & \(M_{TT}\) & \(M_{AT}\) & \(M_{ARHI}\) & \(M_{e}\) & \(CS\) \\ \hline
1 & 41.76 & 39.72  
To compare the estimated and actual compressive strengths, the strength of concrete in boxes was measured by the IPS-MG 4.01 sclerometer (Figure 4). It has a nonvolatile memory, a data transfer mode to a computer via a COM port and a function for entering individual calibration dependencies into the software device, set by the user. Measuring the strength of the concrete consists of applying a series of up to 15 blows to the controlled area of the product.