PSI - Issue 64

Said Debbakh et al. / Procedia Structural Integrity 64 (2024) 130–136 S. DEBBAKH and al. / Structural Integrity Procedia 00 (2024) 000 – 000

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Table 3. Estimated characteristic strength of RCC-1 and RCC2, core diameter D = 103 mm, SR = 2 (Benidir and al., 2023) Reinforced concrete columns RCC-1 Reinforced concrete columns RCC-2 Mean compressive strength of cores ( ), ( =103 , =2) 20.29 23.13 Standard deviation 3.27 1.50 Estimated characteristic strength , ( = 103 , =2) 13.29 16.13 4.2. Pull-off test In this test, the pull-off test (direct tensile strength) was measured by direct dolly pull-off. A dolly bonded to the RCC surface after having been defined by coring through the surface. Table 3 shows the results of direct tensile strength of both columns. From table 3, the results of direct tensile strength of RCC-1 and RCC-2, according to upper, medium and lower zones are 1.52 MPa, 1.62 MPa, 1.92 MPa and 1.55 MPa, 1.77 MPa, 1.93 MPa respectively. It could be observed that the direct tensile strength decreases progressively from the bottom (lower zones) to the top (upper zones) of the columns. In fact, the mean direct tensile strength of RCC-1 and RCC-2 of the lower zones are usually higher than the direct tensile strength of medium and upper zones in each column. For instance, the mean direct tensile strength of RCC-1 and RCC-2 to the lower and upper zones are 1.92 MPa, 1.93 MPa and 1.52 MPa, 1.55 MPa respectively. Moreover, the mean direct tensile strength of RCC-1 is 1.69 MPa and 1.75 MPa for RCC-2, with the same standard deviation (std) of the direct tensile strength of 0.2 MPa. It is important to pinpoint that the direct tensile strength is almost similar for each column. According to the American Concrete Institute (ACI-318, 2005), there is a relationship between the tensile and compressive strength of concrete. The direct tensile strength could be more than five time square root of its compressive strength (Akinpelu and al., 2019; Chhorn and al., 2018). According to the ACI code (ACI 318-2005), which had specified the modulus of rupture MOR as 0.517* fc 0.5 , the mean compressive strength derived from tensile strength of RCC-1 and RCC-2 are 10.68 MPa and 11.45 MPa respectively. The mean compressive strength derived from tensile strength is closer to the estimated characteristic strength of concrete better than the mean compressive strength derived from rebound hammer test. Accordingly, the direct tensile strength test can provide an idea about the zone effect. For this reason, and for better representativeness of the results, three zones should be tested on a structural reinforced concrete column to assess the direct tensile strength, in order to prevent the assessment of the strength from being compromised by a zone effect.

Table 4. Results of direct tensile strength of RCC-1 and RCC-2 Reinforced concrete column RCC-2 Tensile strength (MPa) Tensile strength (MPa)

Left side 1.00 1.83 1.72 1.66 1.76 2.12 2.02 1.67 2.33

Right side

Mean tensile strength (MPa)

Left side 2.11 1.52 1.55 1.80 1.80 1.80 2.09 1.81 1.92

Righ t side 1.35 1.64 1.12 1.85 1.31 2.04 1.90 1.74 2.10

Mean tensile strength (MPa)

*D fc-2 (MPa)

*Dfc-1 (MPa)

1.49 1.59 1.48 1.40 1.32 1.48 1.77 1.53 2.23

Upper

1.52

8.64

1.55

8.98

Medium

1.62

9.81

1.77

11.72

Lower

1.92

13.79

1.93

13.93

Mean

1.69

10.68

1.75

11.45

Standard deviation (std)

0.2

2.7

0.2

2.5

* Dfc: Derived compressive strength from tensile strength according to ACI-318.

5. Conclusions In this paper, the assessment of the in-place concrete quality has been studied using rebound Hammer and pull off tests. Two reinforced concrete columns have been subjected to non-destructive (Rebound Hammer test) and