Flexural Tests on the Round Panel
Round determinate panel test (RDPT), according to ASTM C1550, involves a centre point loading of a large circular plate (800 mm in diameter and 75 mm in thickness) supported on three points. The specimen toughness is assessed in terms of the energy absorbed in loading the plate to some selected values of central deflection. This test has become popular for fibre reinforced shotcrete due to its high precision in post-cracking performance evaluation (Wang et al. 2004), and is often used in the mining industry (Decker et al. 2012). Its panel-based performance assessment is desirable because panels fail through a combination of stress actions
Fig. 2.15 Schematic of BS EN 14651
that reflect an in situ behaviour of concrete footpaths more closely than other mechanical tests in the laboratory (Parmentier et al. 2008). This test has a significantly lower variability in post-cracking performance than other tests, and therefore energy absorption in the round determinate panel is considered the most reliable test method of post-cracking performance assessments (Zi et al. 2014). Therefore, in our research the RDPT is another method chosen to assess the reinforcement of recycled plastic fibres in concrete.
As shown in Fig. 2.16, a load is applied to the centre of the panel by a hemispherical-ended steel piston. The load is controlled by a programmable logic controller to maintain a constant deflection rate of 4.0 ± 1.0 mm/min. The panel rests on three pivots, evenly spaced around its circumference, and deflection is carried out until a central displacement of at least 40 mm is achieved. The energy absorbed is recorded at deflections of 10, 20, 30, and 40 mm (de Montaignac et al. 2012).
Fig. 2.16 Side view a and top view b of the RDPT apparatus setup according to ASTM C1550