PSI - Issue 68

Rami Hawileh et al. / Procedia Structural Integrity 68 (2025) 259–265 R. Hawileh et al./ Structural Integrity Procedia 00 (2025) 000–000

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2. Experimental program The primary objective of this study is to understand how exposure to different temperatures impacts the mechanical properties of high-strength concrete with and without the addition of synthetic fibers. The experimental approach, including mix design details, test matrix, and testing procedure is described in this section. 2.1. Mix Design In consultation with Emirates Beton Ready-mix, a local concrete producer, a mix design was proposed with a design compressive strength ( f’ c ) of 90 MPA and a flow value of 740 mm. The mix design had a composition of 63% OPC, 26% ground granulated blast furnace slag (GGBFS), 11% Micro Silica (MS) and a water/binder (w/b) ratio of 0.25. The maximum aggregate size utilized was 20 mm with a well graded aggregates distribution. A 50 mm steel fibre dosage of 1% by volume was added to increase the durability and ductility of the concrete. Based on literature findings, a PP fibre dosage of 0.1% was shown to prevent the effect of explosive spalling without affecting the strength or workability of the concrete. Therefore, another mix design was proposed with 0.1% fibre dosage by volume. Table 1 presents the concrete mix design utilized for the two mixes: HSC-ST with only steel fibres, and HSC-(ST+PP) with steel and PP fibres. The properties of the supplied fibres are shown in Table 2.

Table 1: Mix design properties Ingredient

HSC-ST

HSC-(ST+PP)

Comments

Coarse Aggregate (kg) Fine Aggregate (kg)

825 990 347 143 135 60

825 990 347 143 135 60

Ordinary Portland Cement (kg)

63% of Binder 11% of Binder 26% of Binder 1% of Volume 0.1 % of Volume

Silica Fumes (kg) GGBFS (kg)

Water (kg)

50mm Steel Fibers (kg) PP Fibers (kg) Unit Weight (kg/m 3 )

60

60

0.00 2560

0.91 2561

Table 2: Fiber Material Properties Property

Steel fibres

PP fibres

Tensile strength (MPa) Young Modulus (GPa)

2300

500

210 6%

10

Strain at ultimate Length (mm) Diameter (mm)

-

60

56

0.9

1

Aspect ratio

65

56

Density (kg/m 3 ) Melting Point (°C)

7850

910

1400- 1450

160-165

2.2. Test matrix and testing procedure Standard cylindrical samples of 300×150 mm dimensions were cast to investigate the residual compressive strength of concrete after being exposed to elevated temperatures up to 600 °C. Samples were heated for two hours in a high temperature Muffle Furnace. In addition, three specimens were tested for each exposed temperature and compared to specimens tested at room temperature (25 °C). The details of the tested specimens and exposure temperature are presented in Table 3. The compressive strength was tested in accordance with ASTM C39/C39M-21 standards (ASTM, 2021) using SANS compressive testing machine at a stress control rate of 0.25 MPa/sec after being cooled for 24 hours. The furnace was carefully controlled to achieve a heating rate of 10 °C per minute, followed by a holding period of 150 minutes at the target temperature. This protocol ensured that the samples were uniformly exposed to the desired temperature. The mass of each sample was recorded before and after exposure to high temperatures to allow for the calculation of mass loss percentages.