•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 CO2 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.
•Engineering properties of FAGP concrete improve from 28 to 540days from casting.•Continuing gel production of FAGP concrete densify microstrucre over time.•Mechanical properties of AAS concrete ...decrease between 90 and 540days from casting.•Disjoining pressure & self-desiccation effect propagate cracks in AAS in long term.•FAGP concrete is behaving in a similar manor to PC concrete.
This paper reports the comparison of engineering properties of alkali activated slag (AAS) and low calcium fly ash geopolymer (FAGP) concretes up to 540days. 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 90days. However, a reduction in AAS concrete performance was observed between 90 and 540days, while an increase was noted in FAGP concrete over the same time period. The microscopy revealed that both reactions progressed beyond 90days 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 24h heat curing resulting in a crack-free dense microstructure at 540days. Overall the discrepancy in microstructural development beyond 90days in the two concretes would explain the contradictory performance over the longer time frame.
•Durability properties of geopolymer concretes improve from 28 to 365days.•Chloride diffusion coefficient of geopolymer concretes reduce from 28 to 365days.•Continuing gel production densifies ...microstructure and pore-structure over time.•A high quantity of meso-pores in the gel paste increases water absorption.•A high quantity of macro-pores leads to an increase in water and air permeability.
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.
Combination of natural ventilation approaches is a new trend for free space cooling/heating in buildings. A critical review was then undertaken to provide an overview of the combined technologies ...that hope to initialize new ideas and promote future endeavors. The advantages of the integrated natural ventilation systems can be summarized into several principles, including achieving beyond the existing performance by single system, maintaining indoor temperature stability, realizing heat energy recovery, overcoming the inadequacy of a single system, and providing a more comprehensive and useful energy-saving scheme. Most of the existing studies on combined systems are found based on thermal buoyancy, while only a small amount dealt with the combination of wind-driven and buoyancy-induce due to the complexity. Parametric studies in most previous studies focused on several major ones, so a systematic analysis is critically needed to address the performance of the overall combination to achieve stable and durable performance. A thoughtful investigation is also required to avert unpredictable delivery of air flow, such as through the manipulation of external wind forces. The related research focuses should also be shifted following the trend of multi-storey buildings under the rapidly growing population. No guideline was found that arranges these natural ventilation systems in terms of performance and applicability for their practical selections and usages. Also, the thermal bridge breaking in cold winter and condensation in summer may compromise the natural ventilation performance and durability, and longevity of buildings. The studies on the coupling between different natural ventilation systems are still insufficient, requiring quite a bit of effort in future works.
•Combined natural ventilation systems in single building were reviewed.•Advantages of combined natural ventilation systems were summarized.•Existing systems much reply on thermal buoyancy but not combined buoyancy and wind.•Research focuses should be shifted following the trend of multi-storey buildings.•Studies on coupling different natural ventilation systems are still insufficient.
•The number of articles on concrete healing being generated worldwide is increasing.•Basic mechanical tests are commonly used to prove the efficiency of healing.•Few studies investigate internal ...crack distribution and morphology during healing.•Healing is assessed using novel methods based on X-ray tomography, MIP tests.•Porosity, sphericity, single crack width, and Structure Model Index are discussed.
Researchers have put significant effort into developing various healing agents for micro-crack closure to achieve a more durable structure and various destructive and non-destructive test methods are often used for the evaluation of concrete self-healing. In this paper, the use of the X-ray tomography and Mercury Intrusion Porosimetry is reviewed as the most advanced non-destructive test methodologies for the evaluation of concrete self-healing at the micro-structural level. The capabilities of the two test methods in correlation to self-healing in cementitious materials are presented via the void content, crack width/pore diameter and crack volume measurements. In addition, the paper suggests the geometrical aspect of voids as an alternative type of analysis for evaluating self-healing in cementitious materials.
•A new use of recycled glass was identified, thus creating a market for glass wastes.•A novel technology was investigated to utilize glass wastes for building components.•Optimum mix design of new ...composite was explored through a detailed test plan.•Novel technology has been verified for drainage pit lids following performance tests.•New technology is highly sustainable and adoptable for other engineering applications.
Millions of tonnes of glass wastes are produced worldwide, but only marginal is fed back into recycling with majority ending at stockpiles. Though glass wastes are used in the construction industry since decades, there still exists need to recycle this valuable waste product which otherwise could result environmental concerns from excessive stockpiles. This study investigates for a new technology that utilizes recovered glass wastes to manufacture building components using access covers as example, thus introducing a new market for glass wastes. The new technology is based on fine recycled glass in encapsulation of polymeric thermosetting materials from cross linking reaction of resins. First, a series of laboratory tests (i.e. compressive, flexure and impact resistance tests) were performed on composite samples prepared under different glass-composite formulations, glass particle sizes and curing periods to investigate the behaviour of novel glass recycled composite material. Results of sample tests were analysed to identify an optimised mix design for recycled glass composite material. Having identified the optimum dosages, studies were then extended to identify lab manufacturing process for access cover prototype. A special clamping method was adopted to manufacture the access cover using stagewise manufacturing process under optimum formulations. Performance tests conducted following AS3996 revealed that the lab-based access cover can support an external load of up to 4 tonnes which can be further enhanced using geometric optimization. This study provides detailed description of translating glass wastes to manufacture sustainable building components using a unique glass recycling technology which has potential to utilize in broader civil engineering applications.
•Developed a mix design method for fly ash geopolymer concrete using MARS model.•Key variables are water/solid, activator/fly ash, Na2SiO3/NaOH and NaOH molarity.•Contour plots can be used to design ...fly ash geopolymer concrete mix proportions.•Targeted 28-day strength from 30 MPa to 55 MPa achieved in laboratory experiments.
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.
This study presents a transformative dynamic amplification factor for assessing the resilience of over-river bridges, informed by the real-world conditions of flood events. Through advanced finite ...element analysis, we unveil how the interplay between mass and velocity of floating objects significantly influences bridge pier responses, challenging conventional assessment methods. Our findings reveal potential inadequacies in current design standards, such as AASHTO and AS5100, and introduces a dynamic multiplier that enhances structural health assessment algorithms. The core contribution of this research is a data-driven analysis approach, which is critical for the proactive maintenance and risk assessment of bridge infrastructures in areas prone to flooding. By redefining the parameters for damage-level identification, our work advocates for a shift towards more resilient infrastructure systems in the face of global climate change.
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 C
3
A and C
4
AF phases but decreased the hydration of the C
3
S 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 (Al
IV
) 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 structural safety and serviceability during extreme weather, such as floods and storms, is critical. Due to global warming in the last decades, the increase in the intensity of natural disasters, ...i.e., flood loading and the durability of the road structures and infrastructures, is becoming critical. Bridges and structures lose their capacity because of ageing over time. On the other hand, the load intensity is another reason for the structural damage. Debris loading due to the flooding on bridges is one of the reasons for the increase in flood loading and eventually structural damage. Measuring the level of structural damage under extreme events is vital in determining the vulnerability and resilience of structures during a disaster. A damage index (DI) can be defined as a measurement tool for the levels of structural damage. Oftentimes, damage indices are developed to measure the deterioration of the system under earthquake loading. Little work has been published on damage indices (DIs) under flood loading, where a uniform pressure is applied to a structure. This paper presents a comprehensive review of DIs published in the literature and compares two approaches to assess the system’s damage utilising finite element methodologies. The structure model developed in the ABAQUS software package is used to predict the failure of a concrete component under applied lateral loading. The model is validated using published experimental work. The model is verified, and then it is used to compute the damage indicators using two primary techniques, including a deflection-based method and an energy loss-based approach. Using the two offered DIs, the change in damage levels is displayed underwater flow uniform loading. A comparison of the two methods is conducted. In this paper, differences between the two concepts are analysed and presented.
