## 3 Results  
### Compressive and Bending Strength  
The compressive strength test was carried out on cubes with side 100 mm in accordance with the standard [45]. The compressive strength of the samples was determined depending on their moisture content. In total, 18 samples were used in the study (9 on the basis of Portland cement designated as SP and aluminous SG). In addition, the samples were divided into three groups. The first group consists \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Determination** & **SG** & **SP** \\ \hline Aluminous cement “Górkal 70” (kg) & 488 & - \\ Portland cement 32.5R (kg) & - & 488 \\ Aggregate 0 \(\div\) 4 mm (kg) & 997.14 & 997.14 \\ Aggregate 4 \(\div\) 8 mm (kg) & 398.86 & 398.86 \\ Water (L) & 199 & 199 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The comparison of the composition of concrete mixtures. Figure 3: Diffractograms of mineral content of ceramic aggregate. of dry samples. The second group of samples was placed in water for 1h prior to strength tests and the third group was immersed in water for 24 h. After samples initial drying the strength test started. Compression strength test of cubic samples according to [45] and bending strength test of beam samples according to [46] were carried out in the Construction Laboratory in Civil Engineering and Architecture Faculty of the Lublin University of Technology with using the advanced system for tests on concrete and mortar Advantest made by Controls company compliant with [47]. Figure 4 shows an example of a beam and cubic sample during the test. The samples were made of SG concrete. The strength machine itself is equipped with three frames:  
* frame with pressure up to 3000 kN for testing the compressive strength of concrete elements with maximum dimensions of 200 \(\times\) 200 \(\times\) 200 mm
* frame with pressure up to 250 kN for testing the strength of mortars for bending (samples 40 \(\times\) 40 \(\times\) 160 mm),
* frame with pressure up to 250 kN for testing the compressive strength of mortars, as well as elements with maximum dimensions of 100 \(\times\) 100 \(\times\) 100 mm (e.g., standard samples of cellular concrete). Additional inserts allow testing the tensile strength of concrete elements, e.g., standard cylindrical or cubic samples, or finished products in the form of paving stones. Obtained results of compressive strength tests are presented in Figure 5. The graph compares the average compressive strength of SP and SG concrete with the standard deviation including the soaking time in water at 20 \({}^{\circ}\)C.  
Figure 4: Example samples used in the research: (**a**) beam sample; (**b**) cubic sample. Figure 5: Compressive strength of cubic samples with standard deviations. The obtained test results showed that greater compressive strength obtained samples made on the basis of aluminous cement. The largest average difference concerns dry samples and those pre-moistened for one hour. The average strength of the samples was greater by about 30%. A much smaller difference occurs in the case of samples that were immersed for 24 h. In this case the average compressive strength of the aluminous cement samples was higher by about 15%. In the case of concrete made on Portland cement, the drop in strength caused by moisture was significantly lower than for aluminous cement. In this case, also the lowest average strength obtained samples that were immersed in water for 24 h. The maximum standard deviation in the SG group was 4.78% and in the SP group 3.26%. The described behaviour of the samples is consistent with the suggestion described in the literature [48] that the loss of strength due to moisturizing the samples is caused by the swelling of the cement gel due to the presence of adsorbed water: the cohesive force of solid particles is then reduced. This is also confirmed by the fact that the drop in strength is affected by the length of the sample saturation in water. The bending strength test was performed according to the standard [46].