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The corrosion of steel due to chloride ingress is one of the major causes of deterioration of reinforced concrete structures. In order to ensure a structure achieves the design life specified, predictive modelling is employed. To undertake this modelling, details are required on a number of variables; however, each of these variables has a level of uncertainty which can affect the reliability of the model. To address these issues, this paper reports the analysis of data taken from four distinct elements on a port structure, in Australia, constructed in three phases between 1926 and 1985, using both pre-cast and cast in situ techniques. The cover depth, surface chloride concentration and chloride diffusion coefficient were determined for different elements on the structure, with a total of 244 data points obtained. The data was analysed to identify the statistical distributions and probability density functions produced. A novel analytical model was developed based on the solutions to Fick's equation. The results showed that both surface chloride and the diffusion coefficient were positively skewed with no significant variation in the sensitivity. It was also found that controlling the diffusion coefficient has a more influential effect than increasing the cover. [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]

• 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]

This study presents the development and validation of a mix design determination procedure for geopolymer concrete to achieve the desired compressive strength. The procedure integrates artificial neural network (ANN) model developed based on a comprehensive data base from literature, data clustering, and parameter optimization techniques to enhance accuracy and reliability. Experimental validation is undertaken to demonstrate the mix design determination procedure’s capability to accurately predict mix designs for geopolymer concrete based on the target compressive strength, validating its efficacy for mix proportion determination. The integration of chemical oxide content in fly ash, curing time, curing temperature, and activator properties results in a 15.9% improvement in prediction accuracy for the training dataset and a 68.3% enhancement for the testing dataset, compared to the base ANN model that includes only the weight of fly ash and activator properties. Employing data clustering techniques enables the identification of prior estimates for the mix design parameters related to specific fly ash types and target compressive strength, streamlining the mix design process by analyzing pertinent data subsets. Parameter optimization ensures refined mix proportions, achieving the desired target strength economically while minimizing material waste and cost. The development of a user interface facilitates easy manipulation of mix designs, catering to users of varying expertise levels. Additional options for deeper insights into geopolymer concrete characteristics can be integrated into the mix design determination procedure. To assess the mix design determination procedure's ability to generalize effectively, a variety of fly ash samples with distinct chemical compositions were utilized, differing from those already present in the database. This approach allows for a thorough evaluation of the mix design determination procedure's performance when presented with fly ash compositions it has not encountered before. By doing so, this provides insights into the adaptability of the mix design determination procedure beyond the limitations of the training and testing datasets. [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]

Recent studies have shown that when the operation of steel reinforced concrete impressed current cathodic protection systems is halted the steel can remain passive for a period of time. This paper reports a systematic study using both laboratory specimens and a small scale site trial to investigate the factors influencing the occurrence and duration of residual protection using charge densities of 20, 60, 180 and 540 mA/m 2 . Both the laboratory and site specimens demonstrated short term residual protection. The results indicated that the residual protection was dependant on both the duration and charge passed, with longer periods of protection observed on site following a second application of current. [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]

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]

The development and modification of high volume fly ash (HVFA) concrete using nanomaterials to enhance the strength has advanced significantly of late. However, the long-term behavior of HVFA concrete with nanomaterials, including permeation and durability characteristics, have yet to be studied in detail. This study reports the long-term permeation and diffusion characteristics and the carbonation of nanoengineered HVFA concretes utilizing up to 80% cement replacement with fly ash, hydrated lime, and nanosilica. The 450-day compressive strength of the HVFA concrete was 73 MPa. The air and water permeability indices of HVFA-65 and HVFA-80 concretes (65% and 80% cement replaced) decreased from 0.058 to 0.039 Ln(mbar)/min and 0.3–0.1(×10−7 m3/min0.5) between 28 and 450 days, and 0.078–0.043 Ln(mbar)/min and 0.5–0.2(×10−7 m3/min0.5) , respectively. These permeation values were significantly lower than the specified indices for low permeability concretes. The presence of pores, ranging from 30 μm to 1 mm, was observed to be the principal influence on the permeability properties. The pore size and the quantity of pores decreased significantly in the HVFA composites over time. The C─ A─ S─ H gel products formed [ Ca/Si=0.43 and Ca/(Si+Al)=0.25 ] increased both pore discontinuity and the strength of the interfacial transmission zone (ITZ). This increased the packing density in the gel matrix correlated with enhanced durability. The chloride diffusion coefficients of HVFA-65 and HVFA-80 decreased from 3.88 to 0.60(×10−12 m2/s) and from 4.06 to 1.61(×10−12 m2/s) , respectively, between 28 and 450 days. Furthermore, both HVFA-65 and HVFA-80 composites displayed low carbonation coefficients, 2.93 and 4.73 mm/month0.5 , respectively. Calcite was observed at 28 days and was attributed to the carbonation of the hydrated lime. Calcite intensity in the HVFA concretes was observed to decrease up to 90 days; this was attributed to dissolution in pore water to form the more soluble calcium bicarbonate. However, from 90 to 450 days, carbonation led to the accumulating of additional undissolved calcite (calcium carbonate) within the HVFA composites over the long term. [ABSTRACT FROM AUTHOR]

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]

Buried steel infrastructure can be a source of iron ions for bacterial species, leading to microbiologically influenced corrosion (MIC). Localized corrosion of pipelines due to MIC is one of the key failure mechanisms of buried steel pipelines. In order to better understand the mechanisms of localized corrosion in soil, semisolid agar has been developed as an analogue for soil. Here, Pseudomonas fluorescens has been introduced to the system to understand how bacteria interact with steel. Through electrochemical testing including open circuit potentials, potentiodynamic scans, anodic potential holds, and electrochemical impedance spectroscopy it has been shown that P. fluorescens increases the rate of corrosion. Time for oxide and biofilms to develop was shown to not impact on the rate of corrosion but did alter the consistency of biofilm present and the viability of P. fluorescens following electrochemical testing. The proposed mechanism for increased corrosion rates of carbon steel involves the interactions of pyoverdine with the steel, preventing the formation of a cohesive passive layer, after initial cell attachment, followed by the formation of a metal concentration gradient on the steel surface. [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]

Carpet fibres have demonstrated the potential to mitigate early-age cracking and improve tensile properties in concrete. However, a detailed analysis of the varied types of standard carpet fibres in reinforced concrete has been lacking. This study aims to bridge this gap by investigating the performance of concrete reinforced with widely used waste carpet fibres, namely Nylon, Polypropylene, Polytrimethylene terephthalate, and Polyester. The study employs fibres at 0.3 % and 0.5 % volume fractions with a 12 mm length. The research examines mechanical properties, shrinkage and cracking behaviour, pore structure, microstructure, and the ITZ. Results show that 0.3 % fibre volume yielded optimal performance based on GRA analysis. All fibre types reduced shrinkage compared to the control with no fibres. Nylon T1 at 0.3 % achieved a 22.3 % reduction at 90 days. Furthermore, fibre inclusion enhanced flexural and splitting tensile strengths up to 12 % and 39 % respectively due to fibre bridging, pore refinement, and reduced porosity. Notably, individual fibre mechanical properties influenced concrete performance significantly. Hydrophilic fibres exhibited a thinner 10 µm ITZ compared to 15 µm for hydrophobic fibres, contributing to denser interfacial regions and improved bonding. This study demonstrates the potential of carpet fibre-reinforced concrete as a sustainable solution, offering enhanced mechanical properties, shrinkage mitigation, and effective utilization of carpet waste, addressing critical issues in construction and waste management sectors. • PTT T1 (0.5 %) had highest flexural strength, 11.8 % higher at 28 days, than control. • Compressive strength and shrinkage reduction were optimum with 0.3 % fibre volume. • Nylon T1 fibres (0.3 %) reduced shrinkage by 22.3 % at 90 days compared to the control. • Nylon T1(0.3 %) had the lowest porosity, 81.12 % lower than the control at 28 days. • Hydrophobic fibres had an ITZ of 15 µm, while hydrophilic fibres had an ITZ of 10 µm. [ABSTRACT FROM AUTHOR]

A major challenge in the specification of geopolymer mix designs is the variability in the fly ash used and the impact of that variability on the performance of the geopolymer produced. The factors affecting the performance of geopolymers made from a total of five chemically and physically distinct fly ashes are reported. The key factor identified as influencing the strength was the workability, with a flow in the range between 110 ± 5% and 140 ± 5% required for optimal performance. In this flow range, the strength of geopolymer is governed by the specific surface area of precursor fly ash coupled with the quantity of the 10 μm and 20 μm particles. In addition a negative zeta potential of the fly ash was identified as assisting gel formation with the smaller the negative zeta potential of the geopolymer product the more gel formation and high compressive strength observed. [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]

This study investigates the influence of the chemical and physical properties of two abundantly available waste by-products in Sri Lanka, fly ash and rice husk ash (RHA) as precursor materials for the synthesis of alkali-activated binders. The suitability of the two types of fly ash and the replacement of fly ash by RHA (10% and 20% by weight of the binder content) were assessed. The study reports the development of compressive strength together with an in-depth analysis of the reaction mechanism of the blended RHA alkali-activated binders. The 100% fly ash mortar achieved the optimum compressive strength of 38.9 MPa at 28 days. Replacement of the fly ash with 10% and 20% RHA reduced the compressive strength by approximately 14% and 43%, respectively. The higher specific surface area of RHA and relatively higher unburnt carbon content in RHA were identified as the major factors influencing the low compressive strength obtained. Furthermore, the addition of RHA increases the reactive silica in the gel matrix and leads to an increase in the Si/Al ratio (3.70–3.89), which has a negative effect on the compressive strength. The difference in solubility rate of precursor fly ash and RHA negatively affect the formation of the gel matrix which is hypothesized as a further reason for the lower compressive strength observed in the RHA mixes. [ABSTRACT FROM AUTHOR]

The pollution of water through release of hydroxyl ions from freshly cast concrete exposed to water can have a detrimental effect on aquatic life by causing a rise in pH. The concentration of hydroxyl ions leached from concrete can be affected by a number of factors. A detailed study has been undertaken to ascertain the effect of parameters such as flow rate, age of concrete after exposure, air quality, cement type, surface area and the volume of concrete. This paper presents the results of the experimental programme and a predictive model for change of pH of water after exposure to freshly cast concrete. Analysis of the results showed that the flow rate was the most significant factor in both the peak pH observed and the time to the peak pH. The volume of the sample was also identified as being a significant factor in the peak pH. [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]

The long-term impact on creep, drying shrinkage, and permeation characteristics of an innovative concrete produced with manufactured geopolymer coarse aggregate (GPA) has been investigated and compared with quarried Basalt aggregate concrete. Microstructure and pore-structure development up to 1 year were examined through scanning electron microscopy, nanoindentation, and X-ray computed tomography. Compressive strength and elastic modulus of GPA concrete varied from 34.6 to 50.8 and 18.5 to 20.5 GPa, respectively, between 28 and 365 days. The 1-year creep strain of GPA concrete was 747 microstrain while the calculated creep coefficient was 0.97, which is significantly lower than the creep coefficient predicted by AS 3600 and CEB-FIP models. Moreover, the 365-day drying shrinkage is 570 microstrain, which is also lower than the maximum permissible limit specified by AS3600. The GPA concrete displayed high water absorption, but lower air and water permeability compared to Basalt aggregate concrete. This is attributed to a porous surface layer with large number of capillaries increasing the water absorption of GPA concrete through capillary suction. The discontinuity in the pore network coupled with a condensed interfacial transition zone formed in GPA concrete could be the reason for lower permeability. Overall, the long-term performance of the GPA demonstrates a potential as a lightweight coarse aggregate for concrete, with the added advantage of reducing the environmental impact utilizing fly ash from coal-fired power generation. [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]

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]

• 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]

Developments of binary, ternary, and even quaternary cementitious binder materials have been widely recognised in research and practices to elevate the sustainability of modern construction industry. To this end, a robust method to predict the hydration of novel binder systems is essential to facilitate informed material designs, yet extremely lacking. In this study, focusing on fly ash cement binders, a unified hydration model, applicable to multi-blend systems that further incorporate hydrated lime and/or nano silica, is freshly established. The proposed method features kinetic models to predict reaction degree for each binder component that are further coupled with a thermodynamic model to evaluate phase assemblage during hydration. The proposed model is carefully calibrated and verified against separate sets of experimental data. It is demonstrated to be applicable to binders incorporating up to 80 % of total cement replacement, and capable of robustly assessing the influence of multi-blend compositions on the hydrating systems. • A kinetic hydration model under unified theory for multi-blend binder is developed. • A numerical framework is proposed to enable coupled kinetic-thermodynamic analysis. • Hydration analyses on binary, ternary, and quaternary binder systems are performed. • Model effectiveness is verified for binders with up to 80 % of cement replacement. • Influence of quaternary blend compositions on hydrating binder system is discussed. [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]

Production of alkali-activated binders is a developing research field that utilizes industrial/agricultural by-products and solid waste for the development of sustainable concrete. This paper comprehensively reviews the literature relating to rice husk ash (RHA)–based alkali-activated binders incorporating fly ash (low/high calcium) and blast furnace slag. The literature demonstrates that the properties of raw material significantly influence the formation of the alkali-activated gel matrix. Every precursor (low/high calcium fly ash and slag) that is used to develop alkali-activated binders with RHA have their own reaction mechanism dependant on their specific chemical composition. Hence the incorporation of RHA influences each binder in a unique way depending upon the alkali activation process and reaction mechanisms. The incorporation of RHA, in the range 5%–15%, with blended slag alkali activated binders, yields better compressive strength, when compared with RHA blended with fly ash (low/high calcium). The review presented in this paper is very useful to understand the behavior of alkali-activated binders incorporating RHA and in advancing the research into the successful application of RHA as a binder for alkali-activated materials. [ABSTRACT FROM AUTHOR]

Geopolymer concrete is a sustainable replacement to the Ordinary Portland Cement (OPC) concrete as it mitigates some of the associated problems of OPC manufacturing such as greenhouse gas emission and natural resource depletion. There has been significant recent research in the design of fly ash-based geopolymer concrete using advanced machine learning techniques which can address some of the problems with classical mix design approaches. However, practical application of geopolymer concrete is limited due to lack of standard mix design procedure. This comprehensive review summarizes the current literature on machine learning methodologies to predict the compressive strength of fly ash-based geopolymer concrete. Firstly, the input parameters used for the machine learning model development are categorized based on feature selection or feature extraction. Secondly, available machine learning approaches are categorized based on analysis methods namely, nonlinear regression, ensemble learning, and evolutionary programming. The effect of hyperparameters on the individual model performance, and model comparison based on the prediction performance are also discussed to identify potentially more suitable model type and hyper parameter ranges. Further, the paper discusses the input variable's sensitivity towards the model performance which provides guidance towards future model developments. Overall, this paper will provide an understanding of the current state of machine learning approaches to predict the compressive strength of geopolymer concrete and the gaps in research for the development of models and achieving the required performance. Hence, the summarized knowledge will be highly beneficial to design prospective research towards sustainable cement-free concrete using fly ash. • Artificial neural networks (ANN) predict geopolymer concrete strength well, offering reliable forecasts for new data. • Support vector machines and random forests offer ANN- like performance, serving as alternatives in machine learning (ML). • The success of ML model relies on proper selection of inputs and tuning hyperparameters for optimal performance. • The chemical, physical, and mineralogical characteristics of fly ash emerge as pivotal input variables in ML models. • Validating models through laboratory experiments is imperative, ensuring generalization for real-world applications. [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]

The utilization of industrial and agricultural by-products for the production of alkali activated concrete (AAC) has the potential to yield significant benefits towards sustainability goals. To be a viable material, the construction industry requires a construction material that achieves the requisite strength and the other property requirements as specified in codes and standards while demonstrating improved sustainability criteria. Fly ash and Rice Husk Ash (RHA) are abundantly available waste products, principally located in Asian countries. Currently, a significant proportion of these materials are disposed of in landfills, lagoons and rivers but offer potential to utilize in AAC. Hence, the identification of variables associated with fly ash and fly ah-RHA blended AAC by utilizing fly ash and RHA is vital. This study quantifies the environmental and economic factors by assessing the Greenhouse gas (GHG) emission, environmental impacts and benefits, and cost analysis of utilizing fly ash and RHA in AAC compared to Portland Cement (PC) concrete. Alkaline activator is a key component responsible for the highest GHG emission, cost and environmental impact amounts obtained for fly ash geopolymer and blended alkali-activated concrete compared with PC concrete. Alkali activators contribute to 74% of the total GHG emission, while heat curing contributed only 9% to the total GHG emission. The addition of 10% RHA to alkali-activated concrete showed a slight benefit for the analysis. Utilization of waste fly ash and RHA is responsible for providing significant benefits in terms of fresh and marine water ecotoxicity by avoiding waste disposal at the dumpsites, rivers, and storage lagoons. • 12% & 48% increment in GHG emission and initial cost was observed, respectively, for blended alkali-activated concrete. • Alkali activators contributed 74% to the total GHG emission of blended alkali-activated concrete. • Addition of 10% RHA leads to a reduction of 1 kgCO 2 -eq/m3 of GHG emission. • Sodium silicate and sodium hydroxide are responsible upto 97% of the total impact for all categories except marine water ecotoxicity. • Utilization of waste fly ash & RHA provides environmental credits in terms of fresh and marine water ecotoxicity. [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]

Many research studies have been conducted during recent years on the topic of geopolymer materials based on the engineering performance of the concrete. What has been missing is the combination of this research in a way that would provide a simple to use design tool for geopolymer concrete as a replacement to concrete based on Portland Cement. This research paper addresses this requirement for developing a standard mix design method for Class F, low calcium fly ash based geopolymer concrete using Multivariate Adaptive Regression Spline (MARS) model. Published geopolymer concrete research data was combined into a database and analysed to give the ratios of water/solid, alkaline activator/fly ash, Na 2 SiO 3 /NaOH, and NaOH molarity. Targeted compressive strengths ranging from 30 MPa to 55 MPa at 28 days were achieved with laboratory experiments, using the proposed MARS mix design methodology. Thus, this tool has the capability to provide a novel approach for the design of geopolymer concrete mixes to achieve the desired compressive strength appropriate for the construction requirement. [ABSTRACT FROM AUTHOR]

• A coupled hydration-thermodynamic model is developed for predicting hydration products and porosity of high-volume fly ash (HVFA) blended cement. • Compressive strength of HVFA binder is computed by multi-scale model using predicted hydration products and porosity. • Porosity of the blended cement increases with fly ash replacement percentage for specific water/binder ratio. • The reaction degree of fly ash and compressive strength show decreasing trend with fly ash replacement percentage. Partial replacement of cement using fly ash, as an environmentally friendly approach, has gained increased attention in construction practice. The realistic prediction of microstructure and mechanical properties of fly ash blended cement paste is therefore noteworthy for many practical applications including selection of construction material and their appraisal of design. In this research work, an integrated framework is proposed and demonstrated for predicting the hydration products and compressive strength of high-volume fly ash binders. The prediction framework is designed to have multiple stages. For computing the hydrates of blended cement paste, a coupled hydration model with thermodynamic modelling is developed. A hierarchical model that captures the development of the paste via multiple levels (from C-S-H globules to blended cement paste) is used subsequently to predict the compressive strength as a function of hydration period. Here, unlike previous works, the formation of C–S–H is realistically modelled by distinguishing it into low- and high-density C–S–H. A series of experiments (including XRD Rietveld analysis, thermo gravimetric analysis, selective dissolution, mercury intrusion porosimetry and compression tests) are performed; hence the predictability of the developed work is assessed by comparing the predicted results with experimental data. A very good agreement is seen between the predicted results (hydration products, pore volume and compressive strength) and experimental results, indicating that the proposed model can be applicable to the high-volume fly ash cement paste to reliably capture the hydrates and compressive strength. It is further noted that with an increase in fly ash replacement ratio, the capillary porosity increases, while the reaction rate and compressive strength decrease. [ABSTRACT FROM AUTHOR]

The attack of concrete owing to sulfate present in sewage is a major problem, both in Australia and worldwide. The prediction of the expected long-term performance of concrete exposed to sewerage and similar environments can be difficult as it is affected by a large number of parameters. In addition the deterioration process in concrete takes a long time to reach a significant level. Whereas considerable research has been undertaken in flowing sewage systems in pipes, little research has been undertaken on static systems contained in septic tanks. A research project conducted at RMIT University has investigated the deterioration of concrete septic tanks located in rural Victoria. A comprehensive set of laboratory experiments was established to measure the accelerated deterioration of concrete under exposure to sulfuric acid. The specimens were manufactured using the same mix design and ingredients used in septic tank production in rural Victoria prior to 1990. The mass changes in the concrete specimens have been recorded and based on the data, a statistical model has been developed to predict the mass change of concrete with time as a function of the cement content and acid concentration observed in sewage. [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]

• 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]

• Two HVFA concrete mixes utilizing 65% and 80% cement replacement, were developed. • Nano-silica & Hydrated lime increased early age hydration involving C 3 A and C 4 AF phases. • Formation of Monosulfoaluminate contribute to early age compressive strength gain. • HVFA concrete displayed 51–60% carbon savings and a reduced Global Warming Impact. • HVFA concrete shows a 10% cost reduction compared with Portland Cement concrete. This study investigates strength development, reactivity and environmental/economic benefits of blended High Volume Fly Ash (HVFA) concrete mixes utilizing 65% and 80% cement replacement utilizing a combination of fly ash and hydrated lime, with and without nano-silica. The carbon and non-carbon emissions are considered as environmental impacts while life cycle costs from cradle-to-gate, which is from material extraction to production, are considered for comparison of the economic benefits. The compressive strength of the HVFA mixes increased with the addition of nano-silica. The HVFA–65 and HVFA–80, without nano-silica, achieved 25.0 MPa and 14.5 MPa at 7 days, respectively, and 42.7 MPa and 29.5 MPa at 28 days. With the addition of nano-silica the HVFA–65 ns and HVFA–80 ns concrete had compressive strengths of 37.5 MPa and 28.8 MPa at 7 days and increased to 47.1 MPa and 40.1 MPa at 28 days. Incorporating 3% nano-silica into HVFA concrete increased the early age hydration reaction. This is attributed to the reaction of the C 3 A and C 4 AF phases and the formation of monosulfoaluminate, which contributed to the early age strength gain. The majority of Ca2+ ions were consumed during the initial hydration, with few Ca2+ ions remaining for the subsequent hydration reaction with the C 3 S phase. The HVFA concrete mixes displayed between 51 and 60 % carbon savings and a reduced Global Warming Impact. The non-Greenhouse Gas emissions, i.e. SO 2 and NO x , reflects minor savings in the Acidification Impact (AI) and Photochemical Oxidant Formation Impact (POFI) environmental impact indicators. Further, HVFA concrete incorporated with hydrated lime shows a 10% cost reduction compared with Portland Cement concrete. [ABSTRACT FROM AUTHOR]