PSI - Issue 64

Abbas S.A. Al-Hedad et al. / Procedia Structural Integrity 64 (2024) 1386–1393 Abbas S. A. Al-Hedad and Muhammad N. S. Hadi/ Structural Integrity Procedia 00 (2019) 000 – 000

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high range water reducer at 2950 ml/m 3 and accelerator at 78 ml/m 3 were used. Shrinkage limiter was added at 1160 ml/m 3 . The slump of the concrete mixture was 150 mm leading to flowability of the concrete to be appropriate to flow through the openings of the geogrid layers. The specimens of Groups ST and CY were cast using plywood molds having the inside dimensions of 150 mm × 150 mm × 550 mm, as shown in Fig. 2. The concrete mixture with the geogrid reinforcement were vibrated for 3 minutes using a Syntron vibrating table, Model VP-65B (Syntron Packer, 2017). The compressive strength of concrete was determined at the age of 28 days by testing three concrete cylinders with 100 mm diameter and 200 mm height. The average compressive strength of three concrete cylinders was 40.0 MPa. The flexural strength of concrete was determined by testing two concrete prisms having the dimensions of 150 mm × 150 mm × 550 mm. The average flexural strength of concrete was 4.7 MPa.

Moulds for Specimens Gs and GC

Geogrid layers

Fig. 2. Plywood molds for casting the specimens of Groups ST and CY.

2.3. Testing Specimens The specimens of Groups ST and CY were tested between the ages of 150 days and 350 days. The specimens of Group ST were tested under static four-point bending loads up to failure, as shown in Fig. 3(a). The static four-point bending loads were applied at a rate of 1 MPa/min. The specimens of Group CY were tested under cyclic four-point bending loads at a frequency of 7 Hz under various flexural stress levels (Fig. 3(a)). The specimens of Group CY were tested at the first flexural stress level of 3.0 MPa. Afterwards, the specimens of Group CY were tested with following flexural stress levels of 3.1 MP, 3.4 MPa, 3.6 MPa, 3.8 MPa, 4.1 MPa, 4.3 MPa, 4.6 MPa and 4.8 MPa, as shown in Table (3). At each stress level, the load was cycled at 7 Hz to cause a maximum flexural stress at the above stated values and a minimum of 15% of the adopted flexural stress. For each flexural stress level, the specimens of Group CY were subjected to 50000 cycles. Table 3. Details of tested specimens under cyclic four-point bending loads (Group CY). Type of group Property Frequency of cyclic loads 7 Hz Ranges of cyclic stress levels 3.0 MPa 3.1 MPa 3.4 MPa 3.6 MPa 3.8 MPa 3.6 MPa The width of crack at the tip of the notch of the specimens of Groups ST and CY were measured using a linear variable displacement transducer (LVDT), called LVDTH, Type LCD500A (Hanson and Ballinger (1992). The LVDTH had a range of measurement of 50 mm, as shown in Fig. 3(a). The LVDTH was held by a steel holder. The steel holder was fixed at the supporting steel frame behind the specimen. The arm of the LVDTH was supported by a steel bracket. The steel bracket was fabricated and firmly fixed to the specimen using steel bolts having 7 mm diameter and 25 mm length. The steel bolts of the steel bracket were fixed through a square aluminum plate with a 3 mm thickness and a 25 mm side length (Fig. 3(a)). The aluminum plate was glued on both sides of the specimens using epoxy, Type Araldite, Parts A and B (Bunnings Group Limited, 2015). The location of LVDTH ( D LVDTH ) was 20 mm from the bottom of the specimens of Group ST and 36 mm from the bottom of the specimens of Group CY, as shown in Fig. 3(b). The width of crack at the tip of notch of the specimens ( w tip ) was determined using the expression of { w tip = [(110 / ( D LVDTH + 150)) × w LVDTH ]} in millimeters. The w LVDTH represents the width of crack at the location of LVDTH (Fig. 3(b)). The calculation of the width of crack