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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.

Traditionally, the construction industry has predominantly used Portland cement (PC) to manufacture bricks, as it is one of the most-commonly available building materials. However, the employment of waste industrial material for brick production can lead to a significant improvement in terms of sustainability within the construction sector. Geopolymer bricks made from brown coal fly ash, a promising industrial waste by-product, serve as a potential alternative. Conducting a life cycle assessment (LCA), this study thoroughly evaluated the entire manufacturing process’s environmental impact, from source material acquisition and transportation to brick manufacturing, distribution, usage, and end-of-life, for brown coal bricks as compared to PC bricks. The LCA of the brown coal bricks revealed that their primary environmental impacts stemmed from the raw material manufacturing and usage, while exhibiting substantial reductions in ozone depletion, water depletion, and metal depletion. These findings highlighted the environmental advantages of the brown coal bricks and their potential to revolutionize sustainable construction practices.

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 deta...

The deposition of textile waste into landfill has reached an unsustainable level and raises serious environmental issues across the world. Transforming textile waste into fiber reinforcement in cem...

This article reports the results of an investigation into the efficiency of mechanical activation to increase the reactivity in alkali activated mortar synthesized from low-grade clay. Mechanical a...

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.

The construction of conventional concrete structures produces a significant quantity of CO2 released into the environment which can directly impact human health and contribute to global warming. Geopolymer foam concrete is a low carbon eco-friendly concrete in which CO2 releasing cement is replaced with industrial waste materials. However, the durability of geopolymer foam concrete under needs to be investigated over a range of corrosive environments to enable application as a construction material. Therefore, determining the influence of these corrosive factors on the reinforcing steel in geopolymer foam concrete is the objective of the current research. A detailed multi-variable experimental programme was conducted, and models were derived to quantifying the factors influencing the corrosion and mechanical behaviour of reinforced geopolymer foam concrete (RGFC) under exposure to varying chloride, temperature and humidity. Specimens were cast with three chloride percentages, i.e., 1%, 3% and 5% for accelerated corrosion, and exposed to temperatures of 35 and 24 Celsius, and humidity levels of 50% and 90%, respectively. Gravimetric weight loss measurements of the corroded reinforcing steel were undertaken at three designated time intervals. Following corrosion monitoring, the corroded reinforcing steel was tested under tension to observe the influence of the environmental exposure on their mechanical properties, specifically ductility and strength. Utilizing the test results, analytical expression and Multilayer Perception (MLP) neural network computations were executed to accurately quantify the influence of the various environmental exposure conditions on corrosion in RGFC. The findings of the modelling suggested temperature as the most dominant factor in inducing corrosion followed by humidity. Furthermore, the relationships for the prediction of loss of ductility and tensile strength of the reinforcing steel in RGFC as the function of chloride, temperature and humidity were derived. Finally, to conclude, the outcomes of the current research enhance the knowledge on the durability of GFC as a construction material and practically contribute to its service life determination.

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 pap...

This paper evaluates the long-term mechanical properties (up to 1 year) of alkali-activated slag concrete produced with recycled coarse aggregate (AAS-RA) and natural coarse aggregate (AAS-...

A comprehensive experimental study has been conducted to investigate the geopolymerisation and compressive strength development of mortar made from brown coal fly ash from two separate locations in...

When freshly cast concrete is exposed to water this can result in an increase in the pH of the water, which in turn can have an adverse effect on the local flora and fauna. The use of repla...

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.

This study investigates the corrosion of reinforcement in geopolymer concrete manufactured from three different low calcium fly ashes from Australian power plants. The long term corrosion condition of embedded rebar in fly ash geopolymer concretes containing cast in chlorides (0–5%) subjected to wet-dry cycles, together with specimens exposed to ponding in 3% NaCl were examined. Half-cell potential and linear polarisation resistance techniques were used to measure corrosion up to 540 days of age, and compared with results of a similar binder content PC concrete. Increased levels of corrosion were observed in the cast-in chloride geopolymer specimens compared with the equivalent PC concretes. However, in the case of the ponded specimens the reinforcement in the geopolymer concrete specimens displayed lower corrosion levels than the PC concrete. The higher corrosion rate in the cast-in specimens is attributed to a lower pH in the geopolymer specimens resulting in a higher Cl−/OH− ratio. In the ponded specimens the formation of three-dimensional N-A-S-H and C-A-S-H cross linking in the gel matrix reduces chloride diffusion to rebar depth, resulting in a lower corrosion rate being observed for ponded geopolymer specimens compared to the PC concrete.

The widespread industry adoption of geopolymer concrete has the potential to positively contribute to environmental sustainability in both the industrial and construction sectors, through the recycling of waste materials, and the reduction in carbon emissions. Extensive research has been conducted into geopolymers during the past two decades, demonstrating the potential for the alkali-activated cement to replace ordinary Portland cement. However, there are a number of challenges facing the adoption of geopolymers. Much of the research into geopolymers uses sodium silicate solution as the alkali activator. Studies have noted that sodium silicate solutions are highly corrosive, and, as such, can be defined as user-hostile systems. Alternative alkali activators, such as potassium silicate solutions, have been proposed as more user-friendly and therefore more favourable for industry adoption. The highly variable nature of waste materials needs to be a focus of future research, with mix designs that focus on locally available waste materials with minimal processing. Much research has focused on heat-cured geopolymers; however, this increases the embodied energy while reducing the environmental benefit, which also acts as a limiting factor for in situ applications. Research into ambient temperature curing, addressing the issues of compressive strength, the rate of strength development, and curing time is required. Durability issues need to be addressed with studies finding the compressive strength of geopolymers being reduced after relatively short time periods of immersion in water, and potential problems relating to chloride induced corrosion of reinforcing steel. Further research is recommended for developing standardized leachate analysis for geopolymers containing recycled waste materials. The objective of this paper is to review the research into waste-incorporated geopolymers and highlight the barriers to industry adoption with a view to pointing the way forward for future research.

Replacing virgin materials with recycled or sustainable materials to reduce energy consumptions and emissions is the focus of contemporary research to reduce building related emissions. Geopolymer concrete produced using 100% fly ash is a similar sustainable construction material capable of replacing Portland Cement (PC) concrete. As a replacement for PC, fly ash seems to be a sustainable solution, however the benefits from the production process of fly ash geopolymer (FAGP) concrete is the subject of considerable debate. In addition, factors such as local availability and transportation issues could potentially increase the emission profile of FAGP concrete. Thus, this study aims to evaluate the emission profiles for different types of fly ash in Australia considering availability and transportation. A case study and a scenario analysis are also presented to demonstrate the factors that affect the Green House Gas (GHG) emission profile of FAGP manufacture. The results indicate that to the GHG emission profile for FAGP concrete changes considerably based on the material availability, transportation and mix design. Alkali activators and elevated heat curing processes also significantly contribute the total GHG emissions of FAGP concrete production. The results further signify that the case study location could influence the employment of FAGP concrete in terms of GHG emissions. Further studies are encouraged on optimising the cost, GHG emissions, availability and strength characteristics to strike a balance between in sustainability for selecting the best FAGP type for construction. The results also provide the initial factors to be considered in developing a guideline for employing sustainable materials in the building industry.

Steel fiber reinforced concrete (SFRC) is developed traditionally from ordinary concreteadmixed with randomly distributed steel fibers. The matrix of SFRC is always formed by adjustingthe mix proportion used for the ordinary concrete, which plays the role of controlling the properties ofSFRC. In this paper, the mix proportion of self-compacting concrete (SCC) compared with vibrationcompacted concrete (VCC) is statistically analyzed. A predictive formula for water-binder ratio isproposed in relation to the designed compressive strength of SCC and the cement strength affected bymineral admixtures. It is expected to provide reference for the mix proportion design for flowing andhigh-flowing SFRC.

The effect of pre-treatment of low grade waste clay on the disposition of the water in clay based geopolymer has been investigated. The condition of the clay was untreated, calcined, and mechanically activated. Two different curing conditions were applied: ambient curing over 24 ​h and 120 ​°C over a 6 ​h. Time-domain NMR, FTIR, and EDS were used to study the water disposition in the clay-based geopolymer. Geopolymers cured under ambient conditions demonstrated no discernible change in the water interactions due to insufficient heat during curing to trigger the polycondensation. Time-domain NMR revealed that for the geopolymers heat-cured at 120 ​°C, the water component becomes more strongly bound with increasing curing time. The mechanically-activated system showed the strongest water bond compared to the calcined and untreated systems. FTIR results indicate that the intensity of the vibrational band arising from the structural water at 3620 ​cm-1 increases with increasing curing.

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.

Due to environmental concerns regarding the use of Portland cement as the principal binder material in concrete and mortar it is imperative to identify alternative materials that could reduce the carbon footprint of the construction industry. One alternative to address these issues is the use of alkali activated materials, in particular, when based on waste streams that currently have no or only limited industrial application. This paper reports a preliminary study into the synthesis of geopolymer mortar utilizing Brown Coal Fly Ash. The ash had a CaO content of ~39%, indicating that synthesis at ambient or low temperature may be feasible. The paper reports initial trials on the effect of curing temperature, ambient to 120 °C, on the mechanical properties of the mortars produced. The results showed that ambient cured mortar achieved a compressive strength of 6.5 MPa at 3 days. A curing temperature of 60 °C gave the optimum results with a compressive strength of almost 20 MPa and a flexural strength of 3.5 MPa obtained.

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.

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.

Production of alternative aggregates is an area of study that is contributing to achieve the goal of producing sustainable concrete. However, a thorough understanding of the material is required prior to its application in construction for sustainable practice. While laboratory experiments can facilitate the understanding of new material, it is always challenging to use lab tests for damaged response evaluation and in particular failure assessment of its applications. State-of-art numerical modeling approaches with advanced material modeling can facilitate minimizing those challenges when they are calibrated/benchmarked using measured data. This study investigates for a suitable modeling approach to capture the damage response of a new material (i.e. Geopolymer) based coarse aggregate (GPA) concrete. Modeling was conducted by adopting the standard continuum modelling method. Unconfined strength test was simulated by considering Concrete Damage Plasticity (CDP) model in an explicit platform. Laboratory experiments such as stress-strain tests and compressive strength tests were also performed to calibrate and benchmark the results from the numerical model. The effect of mesh sensitivity has been identified in the outcome of damage prediction for GPA concrete. Results from the verified numerical models have been related to assess the permeability degradation of GPA. Outcomes from the study are important to predict structural/damage response using the new Geopolymer based aggregate concrete and facilitate the evaluation of structural response under loading.

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&ndash, 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.

So far, the alkali activated concrete has primarily focused on the effect of source material properties and ratio of mix proportions on the compressive strength development. A little research has focused on developing a standard mix design procedure for alkali activated concrete for a range of compressive strength grades. This study developed a standard mix design procedure for alkali activated slag‒fly ash (low calcium, class F) blended concrete using two machine learning techniques, Artificial Neural Networks (ANN) and Multivariate Adaptive Regression Spline (MARS). The algorithm for the predictive model for concrete mix design was developed using MATLAB programming environment by considering the five key input parameters; water/solid ratio, alkaline activator/binder ratio, Na-Silicate /NaOH ratio, fly ash/slag ratio and NaOH molarity. The targeted compressive strengths ranging from 25–45 MPa (3.63–6.53 ksi) at 28 days were achieved with laboratory testing, using the proposed machine learning mix design procedure. Thus, this tool has the capability to provide a novel approach for the design of slag-fly ash blended alkali activated concrete grades matching to the requirements of in-situ field constructions.

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, Na2SiO3/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.

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/m2. 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.