Issue 78

M. S ł owik et alii, Fracture and Structural Integrity, 78 (2026) 393-408; DOI: 10.3221/IGF-ESIS.78.23

× 160 mm in the three-point bend tests (see Fig. 4), following the procedure specified in code [35]. A total of 24 specimens were tested: 12 for mortar with w/c = 0.38 and 12 for mortar with w/c = 0.55. The statistical analysis of the gathered experimental data included Grubbs' test for outlier detection (significance level α = 0.05), the mean flexural strength of cement mortar (f ct,cm ), and the standard deviation ( σ ). No statistically significant outliers were detected; therefore, all measured values were retained for further statistical analysis. Test results are presented in Tab. 2.

(a) (b) Figure 4: Configuration of the test setup used for determining the flexural strength of cement mortar in accordance with EN 196-1 [34]: specimen prior to loading (a) and after failure (b).

Flexural strength of the specimen [MPa] 6.93; 6.05; 6.35 7.70; 6.83; 6.99 6.90; 6.90; 7.10 8.98; 9.64; 9.49 8.80; 8.60; 7.90

Flexural strength– mean value [MPa]

Standard deviation σ [MPa]

Symbol of the specimen

w/c

ZL-1; ZL-2; ZL-3

ZL16N-1; ZL16N-2; ZL16N-3 ZL16G-1; ZL16G-2; ZL16G-3

0.55

6.86

0.47

ZH-1; ZH-2; ZH-3

0.38

8.79

0.56

ZH16N-1; ZH16N-2; ZH16N-3 ZH16G-1; ZH16G-2; ZH16G-3

8.50; 8.30; 8.80 Table 2: Flexural strength of cement mortar - test results. The mean flexural strength of the mortar characterised by w/c = 0.38 (stronger matrix) was 28.1% higher than the flexural strength of the mortar of w/c = 0.55 (weaker matrix). Aggregate testing Two categories of coarse aggregate were incorporated into the concrete mixes: natural gravel and crushed granite. Both types of aggregates were subjected to the crushing test according to the Polish recommendations [36]. Prior to testing, the aggregates were oven-dried and separated into size fractions of 4.0–8.0 mm and 8.0–16.0 mm to obtain standardised samples, which were subjected to uniaxial compression in a steel mould (see Fig. 5). The aggregate samples were then sieved to determine the aggregate crushing value, expressed as the percentage loss of mass for each fraction. The outcomes of the crushing tests are summarised in Tab. 3.

(a) (c) Figure 5: The setup for testing the aggregate crushing (a), natural gravel aggregate sample 8-16 mm (b), crushed granite aggregate sample 8-16 mm (c). (b)

398