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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]

Geopolymer is a sustainable construction material produced by the activation of fly ash using a high concentration alkali to initiate a polymerisation reaction. A key parameter in determining the potential adoption of geopolymer concrete in the construction industry is the long term durability of the material. To determine the durability characteristics a detailed investigation of the permeation properties of four different fly ash geopolymer concretes was carried out up to one year of age. An improvement in the durability properties is observed for all geopolymer concretes with time. This is attributed to an on-going geopolymerization which results in continuing gel formation leading to a more densely packed microstructure, with an associated reduction in meso-pores and macro-pores. The packing density coupled, with the pore size distribution, were observed to determine the permeation and diffusion characteristics of the concrete. The increased in meso-pores represents the increase in the gel of the matrix and in turn this affect the increase of water absorption. On the other hand, a high quantity of macro-pores leads to an increase in the water and air permeability of geopolymer concrete. A large quantity of coarse particles in fly ash results in an uneven gel distribution which reduces pore-filling ability, while the presence of a high quantity of CaO was observed to contribute to a densely packed microstructure. Notably the initial chloride diffusion coefficients are analogous to those observed in Portland and blended cement concretes and also decrease with the age in a similar manner. [ABSTRACT FROM AUTHOR]

When concrete structures--such as pier supports--are placed in water, they can have a detrimental effect on the surrounding environment by causing the pH to rise. This rise in pH can harm and kill animal and plant life. The concentration of hydroxyl ions leached from concrete can be affected by a number of factors, including cement type, shape of structure, ratio of surface area and volume, and the low of the water. This paper presents the results of a research project that investigated three mixtures: 100% ordinary portland cement (OPC), 30% pulverized fly ash (PVA), and 65% ground-granulated blast-furnace slag (GGBS). Tests were conducted in both stagnant and lowing water using a range of specimen geometries and sizes. The results showed that the mixture, volume/surface area, and geometry of the specimen can affect both the rate of leaching and the cumulative number of moles of hydroxyl ions leached. [ABSTRACT FROM AUTHOR]

This paper reports the comparison of engineering properties of alkali activated slag (AAS) and low calcium fly ash geopolymer (FAGP) concretes up to 540 days. The results showed that the AAS concrete had higher compressive and tensile strength, elastic modulus and lower permeation characteristics than FAGP concrete in the initial 90 days. However, a reduction in AAS concrete performance was observed between 90 and 540 days, while an increase was noted in FAGP concrete over the same time period. The microscopy revealed that both reactions progressed beyond 90 days with the slag–alkali producing excess C–S–H gel which was observed to increase the crack propagation and crack width at latter ages, attributed to the combined effect of disjoining pressure and self-desiccation. The fly ash geopolymerization also continued following an initial 24 h heat curing resulting in a crack-free dense microstructure at 540 days. Overall the discrepancy in microstructural development beyond 90 days in the two concretes would explain the contradictory performance over the longer time frame. [ABSTRACT FROM AUTHOR]

• Carbonation products improved durability of RHA-fly ash alkali activated concrete. • Efflorescence products cause deterioration of gel matrix forming a wider crack network. • 10RHA had lower chloride diffusion coefficient and higher maturity factor than 100FA. • Addition of RHA increases chloride absorption/encapsulation capacity in alkali activated concrete. This study evaluates the long term (up to 365 days) durability properties (i.e., absorption and permeability properties) of a blended fly ash-rice husk ash (RHA) AAC and compares the results with 100 % fly ash AAC. The results showed that the addition of RHA adversely affected the durability characteristics. Degradation of the alkali-activated binder through long-term crack propagation (initiated during heat curing) due to the formation of efflorescence products is identified as one of the major factors contributing to the deterioration observed. The combined effect of the degree of crack propagation and the homogeneity within the microstructure are the main factors that influence the long-term durability properties of blended fly ash-RHA AAC. However, the blended fly ash-RHA AAC had a lower chloride diffusion coefficient at both 28 and 365 days and a higher maturity factor than 100 % fly ash AAC, indicating improved resistance to chloride ingress over time. Overall, the crack propagation becomes the dominant mechanism over the longer term (365 days) despite initial ongoing alkali activation. [ABSTRACT FROM AUTHOR]

• HVFA concrete has low early age strengths above 60% cement replacements. • HVFA concrete has a higher sulphate/acid/chloride resistance and a lower shrinkage. • Higher the fineness of fly ash and additives, greater the reactivity and hydration. • Nano silica significantly enhances the properties of HVFA concrete at all ages. • Material combinations could be optimized to develop effective HVFA concretes. Fly ash is commonly used as a partial cement replacement material, but this is limited to replacement levels of 30% or less, with significant quantities of fly ash still not utilized globally. There has been significant recent research into High Volume Fly Ash (HVFA) concrete to enable the utilization of fly ash and to reduce CO 2 emission by reducing cement demand. This comprehensive review summarizes up to date literature on HVFA concrete with more than 50% of cement replacement using ASTM Class F low calcium fly ash. Firstly, the available HVFA literature in which only fly has been used to replace cement, is categorized based on the replacement level and the mechanical and durability property results are summarized. Secondly, the remaining literature is categorized based on the different material additions to modify the HVFA concrete and the results are compared. The summarized results are discussed to elucidate the mechanisms underlying the reported results. The effect of each material addition on the HVFA concrete properties are also discussed to identify potentially more suitable additives for future development. Overall, this paper will provide an understanding of the current state of HVFA concrete research and the gaps in research for the development HVFA concrete containing higher replacement levels and achieving the required performance. Hence, summarised knowledge would significantly be beneficial to design prospective research towards a sustainable cement-free concrete using industrial waste. [ABSTRACT FROM AUTHOR]