Applications of 100% Recycled PP Fibre Reinforced Concretes
To showcase the industrial application of the 100% recycled PP fibre produced in this research, the fibre performance was tested in various real-life applications which included concrete footpaths and precast concrete pits. This Chapter describes the complete process of using recycled PP fibre to replace steel mesh in a concrete footpath, showing the efficiency of using recycled PP fibre. The drying shrinkage cracks in this real application were also assessed. The feasibility of using recycled PP fibre to replace steel mesh in the precast concrete drainage pits was also studied.
A footpath is a type of thoroughfare that is intended for use mainly by pedestrians and cyclists. Footpaths usually include alleys, lanes, steps, bridleways, byways, towpaths and green lanes. Steel reinforcing mesh is typically used to reinforce concrete footpaths (Ibrahim 2011; Shannag and Bin Ziyyad 2007). Steel reinforcing mesh is a prefabricated steel grid consisting of a series of parallel longitudinal wires welded to cross wires at the required spacing (AS 2009; ASTM 2007a, b). Steel mesh improves post-cracking performance of concrete and helps to control plastic and dry shrinkage cracks in concrete footpaths. According to AS 3600-2009 (AS 2009), concrete footpath are typically reinforced with Class L steel mesh such as SL82 steel sheets, which normally come in 6 m x 2.4 m size. SL82 steel mesh consists of 7.6 mm steel bars at 200 mm spacing in both directions (Fig. 7.1).
To demonstrate the application of 100% recycled diamond-indent PP fibre in concrete footpaths, a footpath 100 m long and 1.5 m wide was cast in James Cook University on 5th May 2015. The concrete used was of 32 MPa target strength, and the fibre dosage was 4 kg/m3. Figure 7.2 shows the processes of casing the concrete footpath. A road roller was used to compact the soil base, before form work for the footpath was built (Fig. 7.2a). 4 kg/m3 of 100% recycled diamond-indent PP fibre was mixed with concrete directly in a concrete truck and delivered to the field.
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S. Yin, Development of Recycled Polypropylene Plastic Fibres to Reinforce Concrete, Springer Theses, DOI 10.1007/978-981-10-3719-1_7
Fig. 7.1 Steel reinforcing mesh for concrete footpath
The ready-mixed concrete was poured into the form work directly (Fig. 7.2b). As shown in Fig. 7.2c, the PP fibres were evenly dispersed in the concrete. The footpath surface was smoothed as Fig. 7.2d. The edge of footpath was then smoothed, and the footpath was dummy jointed every 2.5 m to prevent drying shrinkage cracks (Fig. 7.2e). Figure 7.2f shows the finished footpath in the fresh stage. Standard curing procedure using water spraying was carried out to prevent plastic shrinkage cracks (Fig. 7.2g). The footpath was ready to use on the third day of casting (Fig. 7.2h). There were not any challenges in the concrete casting and finishing. Plastic shrinkage cracks did not appear after casting. The footpath has been used for half a year, and no drying shrinking cracks are present.