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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]

Geopolymer aggregate (GPA) is a novel coarse aggregate synthesized from low-calcium fly ash with a highly alkaline activator. It is also classified as a lightweight aggregate, having a density of 1709 kg/m³ (106.7 lb/ft3). This paper reports the findings of the detailed investigation of mechanical properties of GPA concrete, which was observed up to a period of 1 year. The characteristics of GPA concrete were benchmarked against conventional basalt aggregate concrete. Compressive, flexural, and splitting tensile strengths, elastic modulus, and Poisson's ratio of GPA concrete ranged from 42.1 to 50.81 MPa (6.1 to 7.37 ksi), 4.75 to 5.27 MPa (0.69 to 0.76 ksi), 3.02 to 3.66 MPa (0.44 to 0.53 ksi), 20 to 20.5 GPa (2900 to 2973 ksi), and 0.13 to 0.11, respectively within a 90- to 365-day period. The correlations between existing concrete standards and major mechanical properties of GPA concrete are discussed. Relationships are developed between compressive strength and mechanical properties including flexural strength, splitting tensile strength, and elastic modulus using statistical regression analysis. The suitability of using the existing relationships in Australian standards and American Concrete Institute codes for GPA concrete are critically examined. In addition, the microstructure of GPA concrete was examined using scanning electron microscopy (SEM) imaging and microhardness testing. The thickness of the interfacial transition zone (ITZ) is estimated to be 55, 50, and 45 µm (21.65 x 10-4, 19.68 x 10-4, and 17.72 x 10-4 in.) at 28, 90, and 365 days, respectively. Overall, the observations of this study verify the potential of using GPA concrete in various structural applications, making it a viable and sustainable alternative to conventional aggregate concrete. [ABSTRACT FROM AUTHOR]

Quarry aggregate reserves are depleting rapidly within Australia and the rest of the world due to an increasing demand for aggregates driven by expansion in construction. The annual production of premix concrete in Australia is approximately 30 million cubic meters, while 3–5% of concrete delivered to site remains unused and is disposed of in landfill or crushing plants. The production of coarse aggregates using this waste concrete is potentially a sustainable approach to reduce environmental and economic impact. A testing program has been conducted to investigate mechanical performance and permeation characteristics of concrete produced using a novel manufactured coarse aggregate recycled directly from fresh premix concrete. The recycled coarse aggregate (RCA) concrete satisfied the specified 28-day design strength of 25 MPa and 40 MPa at 28 days and a mean compressive strength of 60 MPa at 90 days. Aggregate grading was observed to determine strength development, while low water absorption, low drying shrinkage, and higher packing density indicate that the RCA concrete is a high-quality material with a dense pore structure. The rough fracture surface of the aggregate increased the bond between C-S-H gel matrix and RCA at the interfacial transition zone. Furthermore, a good correlation was observed between compressive strength and all other mechanical properties displayed by the quarried aggregate concrete. The application of design equations as stated in Australian standards were observed to provide a conservative design for RCA concrete structures based on the mechanical properties. [ABSTRACT FROM AUTHOR]

This study investigates low cement quaternary blend HVFA concrete mixes utilizing up to 80% cement replacement using fly ash, hydrated lime and nano-silica. The optimized concrete mixes achieved a compressive strength of 55 MPa and 48 MPa, for HVFA-65 and HVFA-80 concretes, respectively. Additional fly ash and hydrated lime dosage in HVFA concrete increased the rate of hydration of the C3A and C4AF phases but decreased the hydration of the C3S phase. This resulted in lower early age strength development in the HVFA concrete than occurs in PC concrete but significantly higher than for fly ash and hydrated lime alone. The addition of the nano-silica resulted in an increase in C–S–H gel incorporation of tetrahedrally coordinated aluminium (AlIV) into the HVFA concrete and the substitution of Si by Al in the C–S–H gel, leading to an increase in compressive strength in the HVFA concrete. Early age carbonation was increased with a higher of fly ash percentage. However, the reaction products dissolved in the pore water to form calcium bicarbonate with time. [ABSTRACT FROM AUTHOR]

Highlights • A total of 7 out of 72 beams had steel potentials that remained above −150 mV (Ag/AgCl) following CP. • A total of 48 out of 72 beams displayed residual protection based on the potential decay following CP. • There is a good correlation between charge delivered and the duration of the residual protection. • The saturation of the concrete due to tidal action appears to depress the open circuit potential. • Greater residual protection was observed in concrete elements in less aggressive environments. Abstract Impressed Current Cathodic Protection (ICCP) is an established technique for the remediation of steel reinforced concrete structures. There have been examples of residual protection being afforded to structures where the ICCP system has been de-activated but to date no detailed investigation over the duration of the de-activation period has been undertaken. This study reports the findings of a systematic study in which an ICCP system was suspended for a period of 106 days. The results showed that based on the absolute passive potential criterion of maintaining a potential more positive than −150 mV with respect to a silver silver chloride reference electrode, 10% of the elements studied displayed residual protection. However, analysing the data based on the movement of the instant off potential to more positive values with time showed that 85% displayed evidence of residual protection. The data displayed a good correlation between charge passed and the duration of residual protection. [ABSTRACT FROM AUTHOR]

The properties and microstructure of a novel manufactured geopolymer coarse aggregate have been investigated. The analysis has included compressive and tensile strengths of concretes made with the manufactured geopolymer coarse aggregate and a comparative natural crushed coarse aggregate. In addition, the microstructure and pore structure development of both concretes at the interfacial transition zone (ITZ) and bulk cement matrix were studied though scanning electron microscopy and X-ray computed tomography. The data showed that the novel geopolymer coarse aggregate satisfied the requirements of Australian Standard AS 2758.1 and is comparable to the natural aggregate. The dry density of the geopolymer aggregate concrete was less than that of the natural aggregate being just over 2000 kg/m3 (124.9 lb/ft3), with a mean 7-day strength in excess of 30 MPa (4.44 ksi) and a mean 28-day compressive strength in excess of 40 MPa (5.8 ksi). Moreover, it showed a 60% reduction in porosity between 7 and 28 days with a wellcompacted and dense ITZ observed at 28 days. In addition, the flexural strength demonstrated a good correlation with compressive strength, comparable to that of the natural aggregate concrete. Overall, the geopolymer investigated in this research shows potential as a lightweight coarse aggregate for concrete, with the additional benefit of reducing the environmental impact of fly ash from coal-fired power generation. [ABSTRACT FROM AUTHOR]

• Both HVFA-65 and HVFA-80 concretes provided enhanced durability compared to a comparable Portland cement concrete. • HVFA-65 concrete gave superior performance in sulphate media and HVFA-80 gave superior performance when subject to acid media. • XRD, TGA and NMR analysis showed evidence of gypsum formation and reduction of Calcium Hydroxide content with time. • A lower Calcium Hydroxide content in HVFA-80 compared to HVFA-65 accounts for the enhanced sulfuric acid resistance in HVFA-80 concrete. High Volume Fly Ash (HVFA) concrete has been shown to be a viable alternative construction material to Portland cement concrete to improve sustainability and durability. In addition, nano silica been found to be a significant contributor towards increasing the early age strength and the durability properties of HVFA concrete. This study reports an investigating of the resistance of HVFA concrete with 65% and 80% replacement of cement, with nano silica and hydrated lime, exposed to acid and sulphate solutions over a 2-year period. The change in physical appearance, mass and length was monitored, together with detailed mechanical, chemical and microscopy analysis at 12 and 24 months. The results indicate that the HVFA concrete mixes provided enhanced resistance compared to Portland cement concrete. The HVFA 80% cement replacement performed better in acid media while, the HVFA concrete mix with 65% cement replacement was superior in sulphate media. [ABSTRACT FROM AUTHOR]

Summary: A terrestrial laser scanner (TLS) assessment of corrosion and deterioration on an accelerated laboratory specimen, together with a 40‐year‐old seawall, has been undertaken. The assessment studied the potential of a commercial TLS to detect crack initiation and growth and to monitor long‐term deterioration. In concrete structures with ongoing deterioration, the TLS data were able to identify indicators of delaminated concrete, via surface movement over time, as well as concrete loss. Thus, TLS provides a possible technique to monitor deterioration of concrete structures over time without the need for close access. In the accelerated laboratory specimen, the data showed an apparent correlation between measurement uncertainty and crack growth, though no clear evidence of the exact time of crack initiation or crack width could be determined. [ABSTRACT FROM AUTHOR]

This paper examines the variation in bond strength in corroding specimens, before surface cracks are visible. Reinforced concrete specimens containing 16 mm and 12 mm diameter bars at covers of 1, 2 and 3 times bar diameter, with and without confinement, were subjected to accelerated corrosion. Bond strength is seen to increase during the early stages of corrosion (pre external cracking) for confined bars at all covers and unconfined bars at 3 times cover. However, while 16 mm bars, 1 and 2 times cover showed similar behaviour the 12 mm bars displayed a decrease in bond once corrosion was initiated. [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]

Alkali-activated concretes have been shown to be an environmentally advantageous construction material as they utilize waste or by-products as precursors, such as fly ash and ground blast furnace slag. These concretes also have the ability to achieve strengths suitable for structural applications. However, each mix design of an alkali-activated concretes is unique and requires a detailed life cycle analysis to determine the environmental impact and cost viability. This study evaluates the feasibility of alkali-activated fly ash or fly ash geopolymer and alkali-activated slag concrete developed for application in Australia currently subject to long term site performance studies. This paper reports a detailed life cycle assessment analysis of these concretes to assess their environmental footprint. The paper considers three distinct allocation methods: baseline, mass, and economic allocation, with two system boundaries: manufacture and construction. The study shows AAS concrete has a lower environmental impact than an equivalent strength PC concrete in two impact categories, global warming potential and eutrophication, while acidification and human toxicity depend on the allocation method applied in the manufacturing stage. The global warming potential (100-years) of AAS is 5.25–35% less than PC concrete. The FAGP concrete has more negative impacts on the environment than PC-based concrete, regardless of which allocation method is applied. The report highlights alkaline activators and transportation of raw materials as the main environmental impact contributors to concrete manufacture. The global warming potential of FAGP is 22–34% higher than the equivalent PC concrete in the baseline method. For the construction stage boundary, machinery appliances for handling concrete and transportation only contributes a small environmental impact (<4%) compared with concrete manufacturing. Cost estimation for concrete production suggests that the cost of the alkali-activated concrete is competitive with the conventional concrete market, dependant on the proximity of the feedstocks and the cost of sodium silicate. Neglecting the transportation cost of feedstocks, the cost of AAS concrete can be 4.8% cheaper, whereas the cost of FAGP concrete is 2.7% more expensive than PC concrete. • AAS concrete has a lower environmental impact than PC concrete. • FAGP concrete production has a greater environmental impact compared to PC concrete. • The most significant contributors to the environmental impact are transportation and the alkaline activators. • The cost of FAGP and AAS concrete are comparable with the conventional concrete. • The primary cost factors are transportation and price of Na 2 SiO 3. [ABSTRACT FROM AUTHOR]

The deterioration of structures due to reinforcement corrosion is a major problem both in Australia and globally. The corrosion of the reinforcement can lead to rust staining, cracking spalling, and eventually structural failure if no remedial action is taken. In order to assess the condition of a structure a visual inspection is often the first step, with any defects noted. Further visual inspection or installation of monitoring equipment may then be made to identify any subsequent deterioration that occurs. These activities can often be time consuming and expensive, both in the undertaking and in the analysis of the data. This paper reports the use of laser scanning technology to monitor the condition and deterioration of reinforced concrete specimens and relate the level and rate of crack growth with a standard visual inspection. [ABSTRACT FROM AUTHOR]

Despite extensive in-depth research into high calcium fly ash geopolymer concretes and a number of proposed methods to calculate the mix proportions, no universally applicable method to determine the mix proportions has been developed. This paper uses an artificial neural network (ANN) machine learning toolbox in a MATLAB programming environment together with a Bayesian regularization algorithm, the Levenberg-Marquardt algorithm and a scaled conjugate gradient algorithm to attain a specified target compressive strength at 28 days. The relationship between the four key parameters, namely water/solid ratio, alkaline activator/binder ratio, Na2SiO3/NaOH ratio and NaOH molarity, and the compressive strength of geopolymer concrete is determined. The geopolymer concrete mix proportions based on the ANN algorithm model and contour plots developed were experimentally validated. Thus, the proposed method can be used to determine mix designs for high calcium fly ash geopolymer concrete in the range 25–45 MPa at 28 days. In addition, the design equations developed using the statistical regression model provide an insight to predict tensile strength and elastic modulus for a given compressive strength. [ABSTRACT FROM AUTHOR]

Textile fibre-reinforced concrete based reviews have explored various engineering properties, such as strengthening of concrete, enhancing strain capacity, crack control, durability, and energy absorption. An essential missing component is a comprehensive analysis of the thermal and acoustic insulation performance of textile fibre-reinforced concrete. The paper provides a large-scale analytical database by analysing prior literature on the thermal and acoustic performance of textile fibre-reinforced concrete. It further reviews the microstructural and pore-structural aspects of concrete to provide an overview of the underlying mechanisms driving these properties. This review explores the impact of textile fibre inclusion from 0–20 as a mass percentage (wt%) and 0–40 as a volume percentage (v%). The key findings of the review are that jute fibre-reinforced mortar demonstrated superior thermal conductivity, achieving 0.068 W/mK at 20 wt% inclusion, followed by 0.08 W/mK of basalt fibres at 20 v% inclusion, demonstrating that fibres possess commendable insulation qualities. Notably, inclusion of 30 v% of 2–4 mm miscanthus fibre in concrete showed outstanding dual performance, achieving optimal thermal conductivity of 0.09 W/mK and 90% acoustic absorption at 841 Hz. Finally, the study suggests directions to address identified gaps that can be utilised in the design of future research focusing end-user applications. • Textile fibres of 20 w% and 40 v% increase thermal & acoustic performance in concrete. • Upto 88% reduction in thermal conductivity can be achieved using plant-based textiles. • Textile fibre concrete achieves peak sound absorption in 1500–2500 Hz frequency range. • 2-6 mm fibre length improves thermal insulation more effectively. • Analytical database reported can be utilised in design of end-user applications. [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]

Shrinkage cracks pose significant challenges to the long-term durability of concrete structures, and it can be effectively address by incorporating various types of fibres. Synthetic textile fibres show a significant 10–50 % shrinkage reduction, while natural cellulosic fibres achieve a comparable 5–30 % reduction. This improvement is attributed to the bridging and anchorage effects between fibres and the cement matrix, enhancing overall concrete performance. However, the factors such as fibre length, diameter, volume fraction and characteristics have significant effect on shrinkage performance. This paper aims to present a comprehensive analysis of these critical mechanisms and factors that impact the shrinkage behaviour in both synthetic textile and natural cellulosic fibre-reinforced concrete. The inclusion of fibres creates a three-dimensional fibre matrix within the concrete that provide an internal effect to restrain the absorb water and it reduce the shrinkage of the concrete. Moreover, the presence of fibres introduces a secondary reinforcing mechanism to release tension during the drying process, thereby preventing crack propagation. The highly porous nature of the cellulose structure enhances the porosity of the concrete, creating cross-linked pathways for water evaporation. However, pre wetted cellulose fibre mitigates drying shrinkage by providing internal curing of the concrete. Furthermore, various physical, chemical, and combined surface modification methods have been used to improve the properties of natural fibres. • Shrinkage, cracks in synthetic and natural cellulosic fibre concrete were discussed. • Synthetic fibres show 10–50 % shrinkage reduction while cellulose give 5–30 %. • Bridging and anchorage effect between fibres and matrix cause shrinkage reduction. • Fibre volume fraction is a key factor for shrinkage and crack behaviour in concrete. • Fibre dimensions, strength, modulus, water interaction impact shrinkage and cracks. [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]

• AAS–RA concrete attained 90% compressive strength produced by AAS–RA concrete. • AAS–RA concrete showed lower chloride permeability and sorptivity in long term. • Extending water curing upto 28 days reduces drying shrinkage of AAS-RA concrete. • Porous external surface is attributed to initial water absorption in AAS-RA concrete. • AAS-RA concrete displayed 52% carbon emission reduction than PC concrete. Adaption of reclaimed resources within the construction industry, in order to move towards environmental sustainability and a carbon neutral society is essential. To address this issue this study focused on the investigation of the long term performance, carbon emissions and coast savings of Alkali-activated slag (AAS) concrete incorporating recycled coarse aggregate (AAS-RA) up to one year of age. The performance and sustainability aspect of AAS-RA concrete was then compared with AAS concrete incorporated with natural quarry aggregate (AAS-NA) and PC concrete, respectively. Both AAS concretes achieved similar compressive strength of approx. 40 MPa and tensile strength of approx. 3.3 MPa after one year. Hence, full replacement of quarried coarse aggregate using recycled aggregate in AAS concrete did not display any evidence of an adverse impact to the strength characteristics. However, the 7-day and 28-day water cured AAS concretes demonstrated 32% and 16% higher drying shrinkage at one year in excess of the maximum permissible limit specified in AS3600. Both AAS concretes displayed high water absorption but low chloride permeability and sorptivity. A highly porous external surface layer interconnected with numerous capillaries and microcracks is hypothesised to be the reason for the high water absorption. Gel formation densified the microstructure and filled the capillaries in the bulk matrix, which in turn resulted in the lower permeability and secondary sorptivity. The AAS-NA and AAS-RA concretes displayed 43.5% and 52% carbon emission reduction compared to an equivalent strength of PC concrete having similar binder content. [ABSTRACT FROM AUTHOR]