Post-cracking Behaviour of Glass Fibre Reinforced Concrete with Recycled Aggregates

In the past two decades, numerous studies have demonstrated the benefit of adding fibres in structural concrete. The addition of fibres in concrete limits the crack opening after concrete cracking. For conventional concrete with natural aggregates, the post-cracking behaviour is mainly determined by the type and amount of the fibres. Due to the increased shortage of raw materials, the use of recycled aggregates (RAs) in structural concrete has gained more and more interests recently. Nevertheless, the influence of fibres on the post-cracking behaviour of concrete with RAs has not well been understood. This paper presents an extensive experimental study on the behaviour of concrete with RAs reinforced with alkali resistant (AR) glass fibres. To better understand the effect of the quality of the RAs, three types of RAs were used in the present work, which include a high grade recycled concrete aggregate (RCA+), a normal quality RCA (nRCA) as well as a mixed recycled aggregate (MA). In addition, a natural aggregate (limestone) is also used as the reference aggregate. A total of 24 fibre reinforced notched beams are tested under three-point bending load according to EN 14651. In all fibre reinforced concrete mixtures, the CEM-FIL MinibarsTM was used with a fibre content of 0.75 V%. The test results indicate that the quality of the RAs can have a significant influence on the post-cracking behaviour of the beams, especially in the Crack Mouth Opening Displacement (CMOD) range of 0.5–1.2 mm.status: publishe

A Comprehensive Study of the Polypropylene Fiber Reinforced Fly Ash Based Geopolymer

As a cementitious material, geopolymers show a high quasi-brittle behavior and a relatively low fracture energy. To overcome such a weakness, incorporation of fibers to a brittle matrix is a well-known technique to enhance the flexural properties. This study comprehensively evaluates the short and long term impacts of different volume percentages of polypropylene fiber (PPF) reinforcement on fly ash based geopolymer composites. Different characteristics of the composite were compared at fresh state by flow measurement and hardened state by variation of shrinkage over time to assess the response of composites under flexural and compressive load conditions. The fiber-matrix interface, fiber surface and toughening mechanisms were assessed using field emission scan electron microscopy (FESEM) and atomic force microscopy (AFM). The results show that incorporation of PPF up to 3 wt % into the geopolymer paste reduces the shrinkage and enhances the energy absorption of the composites. While, it might reduce the ultimate flexural and compressive strength of the material depending on fiber content