There is a burgeoning interest in the development of geopolymers as sustainable construction materials and incombustible inorganic polymers. However, geopolymers show high quasi-brittle behavior. To overcome such weakness, hundreds of research have been focused on development, characterization, and implementation of fiber reinforced geopolymers for a wide range of applications. This paper discusses the rapidly developing state-of-the-art of fiber-reinforced geopolymer composites, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states, mechanical properties, toughening mechanisms, thermal characteristics, and environmental durability. It is intended to build a strong conceptual and technical background for what is currently understood on fiber reinforced geopolymers by tying the subject together with knowns for other similar cementitious composites rather than a historical report of literature.

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The utilization of recycled tyre polymer fibre (RTPF) into concrete production is feasible to promote sustainable development and mitigate environmental pollution of global landfilled waste tyres. This paper for the first time presents an experimental study on flexural fatigue behaviour of concrete reinforced with mixed RTPF considering different fibre dosages (i.e., 1.2, 2.4, 4.8 and 9.6 kg/m 3). Results indicate that with the presence of RTPF, the flexural strength of concrete was increased by 3.6-9.6%. The fatigue life of all mixtures followed the two-parameter Weibull distribution and can be accurately predicted using the developed double-logarithm fatigue equations. Concrete reinforced with 4.8 kg/m 3 of RTPF presented the longest fatigue life under different failure probabilities. RTPF and polypropylene fibre (PPF) reinforced concrete exhibited similar fatigue failure mechanisms. 0.2-0.4% Vf of RTPF could substitute around 0.1% Vf of PPF in concrete considering overall static, dynamic and fatigue performance.

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The effect of recycled tyre polymer fibre (RTPF) on mechanical and durability performance of concrete has been increasingly studied in recent years, primarily because of the economic and sustainable feasibility of RTPF's application in construction industry. This paper presents an experimental study on workability, static compressive strength and dynamic compressive properties of concrete reinforced with RTPF with various fibre dosages (i.e. 1.2, 2.4, 4.8 and 9.6 kg/m 3 ) that have not been extensively investigated. Results indicate that the dynamic compressive properties including dynamic compressive strength, energy absorption capacity, ultimate strain and dynamic increase factor of all mixtures were highly sensitive to the strain rate. The optimal RTPF content was found to be 2.4 kg/m 3 (i.e. 0.2% fibre volume fraction (Vf)) considering fresh and hardened properties, as adding this content into concrete induced the most development in dynamic compressive strength (with the highest increase of 12.9%), fracture energy (with the highest improvement of 54.4%) and total energy absorption (with the largest enhancement of 26.4%). It was found from scanning electron microscope (SEM) image analysis that RTPF exhibits bridging performance with no obvious fracture on its surface, and 0.1% Vf of PPF could be replaced by 0.2% Vf of RTPF for concrete.

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