Issue 78

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

Fraction [mm]

Aggregate crushing, loss of mass [%]

Type of aggregate

N/gravel N/gravel G/granite G/granite

4–8

6.4

8–16

10.0 14.5

4–8

8–16 17.0 Table 3: Aggregate crushing value – test results. The obtained mean values of aggregate crushing for fraction compositions were: • for gravel aggregate of fraction composition 4-16 mm – 8.2%, • for granite aggregate of fraction composition 4-16mm – 15.8%.

It can be seen from the presented data that lower crushing values were obtained for gravel samples than for granite samples of the same fraction or of the same fraction composition (4-16 mm). This confirmed that aggregate type significantly influenced the mean crushing value and, consequently, its mechanical strength. These findings further demonstrated that the crushed granite aggregate, characterised by a higher crushing value, has lower strength than the gravel aggregate due to its more irregular and sharper grain edges. Concrete splitting tensile strength testing The Brazilian method was applied to test the tensile splitting strength of concrete according to the European standard [2]. The bearing strips made of plywood with the cross section 15 mm × 4 mm were used in accordance with the code [2] to ensure the equal distribution of force on the specimen length. The tested specimens were grouped into four series according to the strength parameters of the concrete matrix and the aggregate, as presented in Tab. 4. The splitting test was performed on cylindrical specimens. The specimens of two different lengths were tested in each series: 300 mm and 150 mm. The experimental results of splitting tensile strength are juxtaposed in Tab. 5 separately for short-length cylinders and standard cylinders.

Flexural strength of the cement mortar – mean value [MPa]

Type of aggregate

Aggregate crushing – mean value [%]

Series

w/c

H16N L16N H16G L16G

gravel gravel granite granite

0.38 0.55 0.38 0.55

8.79 6.86 8.79 6.86

8.20 8.20

15.80

15.80 Table 4: Juxtaposition of cement mortar and aggregate properties for the specimens’ series.

Cylinders 150 × 300 mm

Cylinders 150 × 150 mm

Tensile splitting strength – f ct,15/30

Tensile splitting strength – f ct,15/15

Number of tested specimens

Number of tested specimens

Series

Mean value [MPa]

Standard deviation [MPa]

Mean value [MPa]

Standard deviation [MPa]

H16N L16N H16G L16G

8 8 8 8

3.54 2.68 3.78 3.40

0.22 0.26 0.47 0.14

8 8 8 8

3.77 3.11 4.22 3.49

0.29 0.22 0.38 0.33

Table 5: Tensile splitting strength - test results.

Significant differences were observed when comparing results obtained from cylinders with lengths of 150 mm and 300 mm (standard specimens). It was found that the results from short and standard-length cylinders cannot be directly evaluated within a single dataset. Consequently, it was necessary to apply a conversion to the results obtained from shorter specimens

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