Round Determinate Panel Test

Round determinate panel test (RDPT) is another effective test that reflects the post-cracking behaviour of fibre reinforced concrete. The panel-based performance assessment is desirable, because panels fail through a combination of stress actions that reflect in situ behaviour of concrete more closely than other mechanical tests in the laboratory (Cengiz and Turanli 2004; Parmentier et al. 2008). This test has a significantly lower variability in the post-cracking performance than other tests. Energy absorption by the fibre reinforced concrete specimen is considered in

RDPT, making it one of the most reliable test methods for post-cracking performance assessment (Bernard 2002).

The RDPT specimens were tested in flexure according to ASTM C1550-12 (ASTM 2012). Production of the round panels began with the circular metal ring forms, which were mounted on a wood pallet. The forms had a diameter and height of 800 mm and 75 mm, respectively, per ASTM C1550 specifications (Fig. 4.5). The ring forms, and the wooden pallets on which they were mounted, were coated in form oil to allow easy extraction of the shotcrete panel. After casting, the panels were covered with plastic and left in the lab for a week. After that, the panels were sent to K&H Geotechnical Services Pty Ltd., Australia, and placed in their curing room. The temperature of the curing room was maintained around 21 °C, with 95% relative humidity.

Before they were tested, the panels were removed from the curing room and placed in the testing apparatus with a hand-operated forklift. A panel was removed from the curing room only when it was time for the panel to be tested. As can be seen in Fig. 2.16, a central point load was applied on the round panel supported on three symmetrically arranged hinged supports. The three pivoted supports ensured that load distribution was always determinate in the round panel specimens. A hydraulic universal testing machine with a capacity of 250 kN was used for

Fig. 4.5 Preparation of the round panels

applying the load. As specified in the standard, the load piston advanced at a constant rate of 4.0 ± 1.0 mm/min up to a central displacement of at least 45. 0 mm. The deflection was recorded by a Linear Variable Deflection Transducer (LVDT) placed under the centre of the specimen. The tests (Fig. 4.6) were carried out at K&H Geotechnical Services Pty Ltd., Australia.

Three panels for each type were produced for testing, two of which must test correctly. To test correctly, a panel must break into three pieces and be within certain size specifications. The data were plotted as a load-net deflection curve, with a maximum centre point deflection value of 40 mm. The area under the curve represented the energy absorption of a panel. Its value was entered into a formula and corrected to account for any deviation from ASTM C1550 specifications in thickness or diameter by using the following equation:

where:

w the corrected energy absorption, w' the measured energy absorption,

Test apparatus for the RDPT d the specified central deflection at which the capacity to absorb energy is measured, mm

Fig. 4.6 Test apparatus for the RDPT d the specified central deflection at which the capacity to absorb energy is measured, mm,

t the measured average thickness, mm, t0 the nominal thickness of 75 mm, d the measured average diameter, mm, and d0 the nominal diameter of 800 mm

 
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