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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]

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]

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]

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]

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]

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]

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]

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]

• 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]

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]

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]

• 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]

• 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]