PSI - Issue 42

Jamal A. Abdalla et al. / Procedia Structural Integrity 42 (2022) 1231–1238 Abdalla et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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2.3. Material properties Two self-consolidating concrete (SCC) mixes were prepared in a ready-mix plant, one mix contained 100% natural aggregates and the other mix contained 100% recycled aggregates. Two sizes of course aggregates were sieved: 0-5 mm and 10-20 mm. The fine aggregates were natural sand from the river. The physical and mechanical properties of the recycled aggregates used in this study are tabulated in Table 1. It should be noted that all tested properties comply with the accepted values according to each standard. The target compressive strength of the concrete mixtures was 30 MPa. The mixture proportions of the fresh concrete mixes are provided in Table 2. Owing to the high absorption of RAC, an additional amount of water was added to the RC mix to ensure better workability. This amount was calculated based on the water absorption and predetermined absorption capacity of RAC (coarse aggregates + fine aggregates + dry sand) at 24 hours.

Table 1. Properties of the recycled aggregates

Apparent specific gravity

Water absorption at 24 hrs (%)

Fines content * (%)

Soundness weighted average loss (%)

Los Angeles Abrasion

Chloride content (%)

Sulphate content (%)

Grain size

0-5 mm

2.69 2.73

7.5 4.6

5.2 0.2

1 1

-

0.01 0.01

0.08 0.02

10-20 mm Testing Standard

25

ASTMC127 -2007

ASTM C127 2007

BS EN933-1 97

BS812 1988

BS EN1744-1

ASTM C131 01

ASTM C88-05

* Percentage passing 75µm

Table 2. Concrete mix design

Glenim Sky 502 (ml/ m 3 )

Water (L/ m 3 )

Extra water (L/ m 3 )

20mm Cr. Agg (kg/ m 3 )

0-5mm Fin Agg (kg/ m 3 )

River Sand (kg/ m 3 )

Water cement ratio

Slump Test (mm)

Concrete mix

Cement (kg/ m 3 )

NC RC

400 437

154 175

-

680 704

360 560

240 550

5000 4236

0.385 0.481

200 200

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Concrete cylinders of dimensions 300 mm (height) x 150 mm (diameter) were cast and cured with the beams to determine the compressive strength of concrete. The cylinders were tested after 28 days and the average obtained compressive strength was 37 and 36 MPa for the NC and RC mixes, respectively. As for the steel reinforcement, tensile tests were conducted on 8- and 12-mm diameter rebars. The obtained average yield strength was 550 MPa with an elastic modulus of 200 GPa. The CFRP laminates used in this study had design thickness, tensile strength, elastic modulus, and rupture strain of 0.5 mm, 1492 MPa, 83.8 GPa, and 1.7%, as specified by the manufacturer, respectively. In addition, the two-part epoxy adhesive that was used to bond the CFRP sheets onto the concrete had tensile strength, elastic modulus, and rupture strain of 28 MPa, 1 GPa, and 3.4%, respectively. 2.4. Test setup The beams were simply supported and tested under two-point loading as shown in Fig. 3. A universal testing machine with 2000 kN capacity was used to apply the load at a displacement-controlled rate of 1 mm/min. The load was applied at the center on a spreader beam that divided the load into two equal parts to form a constant moment region of 620 mm, as shown in Fig. 3. The shear span and overhang lengths were 615 and 75 mm, respectively. Strain gauges are placed onto the center of the U-wraps on both sides to monitor the strain in the CFRP laminates, as shown in Fig. 3. In addition, one concrete strain gauge was mounted at the top center of the beam ’s midspan to record the strain in the concrete. To measure the mid-span deflection, a linear differential variable transducer (LVDT) was placed mid-span at the bottom of the beam specimens, as illustrated in Fig. 3.