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Three types of textile fabric waste, namely Kevlar, Nomex, and Cordura Nylon, were investigated in this study. The effects of the fiber parameters: volume fraction (0.1%, 0.3%, and 0.5%), length (6, 12, and 24 mm), and use of 1D fiber (width of 0) versus 2D woven fabric fiber (width of 3 and 6 mm) on strength properties, flowability, and shrinkage were studied to determine the optimum textile parameters. The pore structure, microstructure, and fiber-matrix interfacial properties of the optimised mixtures were then characterized by means of X-ray micro-CT, SEM, and nanoindentation at 7, 28, and 90 days. Results showed that the optimized parameters for three types of fabric fibers are 1D fiber (width of 0), length of 12 mm, and volume fraction of 0.3%. This optimized design provided an enhancement of strength and shrinkage resistance. Pore refinement was pronounced in the case of hydrophilic Kevlar and Nomex fibers. However, this also correlates to inferior performance in shrinkage resistance of mortar compared to hydrophobic Cordura Nylon. The fiber-matrix ITZ thickness was dependent on fiber size, while the wettability of fibers (i.e., hydrophobicity or hydrophilicity) was observed to affect the phase distribution in the vicinity of the fiber surface. Furthermore, a large volumetric proportion of the structure is porous in nature (more than 50%) in the region of the fiber-matrix interface after 7 days. With the increment of curing age, the microstructure at the fiber interface becomes denser due to the hydration of the clinker phase facilitating the growth of CSH and CH phases. [ABSTRACT FROM AUTHOR]

The long-term creep and shrinkage behaviour of two High-Volume Fly Ash (HVFA) concretes incorporating nano silica with 65% and 80% replacement of cement has been investigated. This comprised a detailed analysis of the microstructure, pore structure and chemistry of the two HVFA systems up to a period of 450 days. The compressive strength and modulus of elasticity of HVFA-65 concrete increased from 32 to 73 MPa and 30.3 to 40.5 GPa, respectively between 7 and 450 days. The HVFA-80 concrete achieved compressive strength values of 22 and 71 MPa and elastic modulus values of 28.9 and 37 GPa. After a total loading period of 450 days, HVFA-65 and HVFA-80 concretes displayed creep parameters, which were significantly below the values predicted by AS 3600, ACI 209 and CEB-FIP standard model equations. After a total drying period of 450 days 28-day cured specimens showed significantly reduced shrinkage compared to 7-day cured specimens. On the other hand, HVFA-80 concrete displayed higher shrinkage compared to the HVFA-65 specimens throughout the period. All specimens except for 7-day cured HVFA-80 concrete were within the maximum permissible shrinkage of 800 microns recommended for Australian construction practices. HVFA-65 concrete showed a denser microstructure and a stronger, better packed interfacial transition zone (ITZ) compared to HVFA-80 at all ages. The XRD and FTIR analysis data identified the formation of hydration products including C-S-H and C-A-S-H which contributed towards both the strength gain as well as the creep and shrinkage properties displayed by the HVFA concrete by minimizing the total porosity and pore size. [ABSTRACT FROM AUTHOR]

An investigation has been conducted to identify the reaction mechanism and compressive strength of geopolymer made from brown coal fly ash from two locations at Yallourn power station in Australia. The Yallourn-1 (Y1) ash has completed the storage period within the pond, whereas Yallourn-2 (Y2) ash has been stored in the pond for a short period of time. Compressive strength of Y1 geopolymer increased from 12.63 MPa (1.83 ksi) at 7 days to 13.62 MPa (1.98 ksi) at 28 days and 15.90 MPa (2.31 ksi) by 90 days, whereas Y2 achieved 13.26 MPa (1.92 ksi) at 7 days but reduced in strength to 8.55 MPa (1.24 ksi) by 28 days, followed by an increase in strength to 14.00 MPa (2.03 ksi) by 90 days. The low strengths observed is attributed to the low of alumina content of the Yallourn ash, coupled with the higher unburnt carbon content. [ABSTRACT FROM AUTHOR]

This study reports the effect of heat curing at 120 °C on the geopolymeric reaction and strength evolution in brown coal fly ash based geopolymer mortar and concrete. Moreover, an examination of this temperature profile of large size geopolymer concrete specimens is also reported. The specimen temperature and size were observed to influence the conversion from the glassy (amorphous) phases to the crystalline phases and the microstructure development of the geopolymer. The temperature profile could be divided into three principal stages which correlated well with the proposed reaction mechanism for class F fly ash geopolymers. The geopolymerisation progressed more rapidly for the mortar specimens than the concrete specimens with 12 to 14 h providing an optimum curing time for the 50 mm mortar cubes and 24 h being the optimum time for the 100 mm concrete cubes. The 50 mm and 100 mm concrete specimens' compressive strengths in excess of 30 MPa could be obtained at 7 days. The structural integrity was not achieved at the center of 200 mm and 300 mm concrete specimens following 24 h curing at 120 °C. Hence, the optimal curing time required to achieve the best compressive strength for brown coal geopolymer was identified as being dependent on the specimen size. [ABSTRACT FROM AUTHOR]

Controlled Permeability Formwork (CPF) has been shown to improve the durability of concrete by reducing the porosity of the cover concrete. However, research to date has focused on laboratory and short-term trials. This paper reports a long-term project in which specimens have been placed on exposure sites at three coastal locations in Australia for 5 years. The specimens include three materials, 100% Portland cement, 30% Pulverised Fly Ash and 65% Ground Granulated Blastfurnace Slag. Specimens were cured using traditional plywood formwork under wet hessian for 1 and 14 days and with CPF for 1, 7 and 14 days. The performance of the concrete was monitored at six monthly intervals by means of visual inspection, Ultrasonic Pulse velocity, resistivity and surface strength using Schmidt Hammer. At the conclusion of the 5 years, chloride ingress and the apparent chloride diffusion coefficient were determined from sample cores. The results showed that the CPF improved surface appearance and surface hardness of the concrete. In addition, chloride ingress was reduced by the application of CPF, with lifetime modelling indicating that service life expectancy could be improved by up to five times when compared to one day curing under hessian. [ABSTRACT FROM AUTHOR]

This study evaluates the influence of the elemental distribution in the fly ash particles and their impact on phase formation and compressive strength of five low-calcium fly ash geopolymers. The degree of geopolymerization in each geopolymer system was assessed by FT-IR and solid state 27Al MAS-NMR analysis. The corresponding pore volume changes were investigated by mercury intrusion porosimetry (MIP). The uniformity of the distribution of SiO2 and Al2O3 in the fly ash was observed to directly influence the dissolution of the amorphous surface layer in the initial geopolymerization process and control aluminosilicate gel precipitation and gel-phase creation. The results showed that the higher the uniformity of distribution (coupled with the stable conversion of aluminium from octahedral to tetrahedral coordination), the higher the aluminium amalgamation with silicates. The result of this is the production of a three-dimensional (3-D) polysialatesiloxo (Si-O-Al-O-Si) polymeric gel structure with high rigidity and stability, which in turn results in higher compressive strength. It was also observed that an increase of meso-porosity in geopolymer phase formation coupled with a cumulative pore volume below 1000 nm (3.937 x 10-5 in.) is a good indicator of the degree of geopolymerization. [ABSTRACT FROM AUTHOR]

• Hydrophilic fabric fibres refine the pore structure of cementitious matrices. • Hybrid hydrophobic and hydrophilic fibres counterbalance the pore-refining effects. • Fabric waste fibres suppress the crack propagation and mitigate the quantity of cracks. • Hybrid fabric fibres significantly reduces the shrinkage of cementitious composites. • Blended fabric waste fibres can improve strength properties of cement-based materials. In this study, the strength properties, shrinkage and microstructures of mortar incorporating blended fabric fibres were characterised via X-ray micro CT and nanoindentation. Three different hybrid recycled fabric fibres, namely Kevlar/Nomex, Kevlar/Nylon and Nomex/Nylon fibres were investigated at three different blend ratios (2:1, 1:1, and 1:2). The fibre content was maintained at 0.3 % for all mixes. The findings indicated that the optimum blend ratio for hybrid fabric fibres is 1:1. At this optimum fibre blend ratio, an enhancement by 2.7 %, 4.8 % and 5.9 % in compressive strength, together with 9.8 %, 12 % and 13.4 % in flexural strength of mortar are recorded, corresponding to the inclusion of hybrid Nomex/Nylon, Kevlar/Nomex and Kevlar/Nylon fibres respectively. Kevlar/Nomex fibres display no effect in drying shrinkage mitigation, irrespective of blend ratios. In contrast, Kevlar/Nylon and Nomex/Nylon fibres result in reducing 180-day shrinkage rates by up to 13.9 % and 11 % respectively. The hybrid fabric fibres were found to refine the pore network, especially the highly hydrophilic Kevlar/Nomex fibres. Also, an increase in curing days from 7 to 90 days densifies the microstructure near the fibre-matrix interface due to the growth of hydration products (LD/HD C S H and CH). These research findings can open the pathway for utilising textile waste in landfill as reinforcing members for cementitious matrices toward sustainable building and construction. [ABSTRACT FROM AUTHOR]

• The inclusion of PP, PE, and PVA fibres increases total porosity of cementitious matrices. • Hydrophilic fibres tend to reduce the average pore size of cementitious matrices. • Pore refinement effect is pronounced with the inclusion of microfibres. • Thermal expansion of fibres initiates cracks and releases pressure at elevated temperatures. • High melting viscosity of HDPE inhibits vapour transport and show less spalling mitigation. Synthetic fibres such as polypropylene (PP), polyvinyl alcohol (PVA), and polyethylene (PE) in both virgin and recycled forms have been widely employed in cementitious composites. Apart from providing bridging action for absorbing stress-induced energy, the addition of polymeric fibres also changes the pore systems in the microstructure of cementitious materials. This paper reviews the microstructure changes of cementitious composite incorporating these three polymeric fibres under both ambient and high-temperature condition. The microstructure of polymeric fibre reinforced concrete is characterised by higher porosity than plain concrete. The use of hydrophilic PVA fibres with microfibres induces pore-refining effects. At elevated temperature PP, PVA and low-density PE (LDPE) exhibit good spalling resistance in concrete due to the formation of microcracks and empty channels left by melted fibre. However, high-density PE (HDPE) fibre is ineffective in mitigating the increased vapour pressure in concrete due to a low coefficient of thermal expansion and high viscosity. Furthermore, to achieve well-balanced interfacial properties, physical/chemical surface modification is necessitated. The introduction of reactive functional groups into the polymer chain of hydrophobic PP and PE fibre significantly enhance fibre-matrix interaction in strengthening interfacial properties with cement paste. Whereas, neutralising hydroxyl functional groups in the PVA polymer chain counteracts extreme delamination or fibrillation of polar PVA fibre when they interact with the cement matrix. With surface modification, the possibility of premature rupture of PVA fibre can be minimised, while improving the transfer of stress-induced energy between the cement matrix and the fibre. [ABSTRACT FROM AUTHOR]