Integral waterproof concrete : a comprehensive review

The ingress of water and aggressive substances is the primary reason for the chemical and physical degradation of concrete infrastructure, leading to a reduction in durability and a shortening of life span. In practice, different integral waterproofing admixtures and surface coatings have been widely used to prevent or mitigate this problem. Compared with surface protection, the incorporation of integral waterproofing admixtures (such as densifiers, water repellents, and crystalline admixtures) in concrete has several benefits, such as ease of application, elimination of regular maintenance, and little or no deterioration over time. So far, there is no comprehensive review on integral waterproofing admixtures and their effects on various properties of concrete. This review examines existing literature on integral waterproof concrete containing various commercial and laboratory-made waterproofing admixtures. This comprehensive review highlights that the use of integral waterproofing admixtures has the potential to increase the service life and improve the durability of concrete structures and infrastructure. However, the admixtures may have a negative impact on some concrete properties, such as workability and strength. Whilst many hydrophobic and crystalline admixtures can reduce the water absorption rate of concrete by up to 80%, they often have a negative impact on the concrete compressive strength, causing a strength reduction of about 10% or more. Their influence on some durability properties (e.g., reinforcement corrosion, microbial-induced concrete corrosion) is inconclusive, indicating the need for further research. There is also a need to develop proper guidelines to determine the efficacy of integral waterproofing admixtures. More research is also required to assess the long-term performance of integral waterproof concrete and its benefits based on life cycle assessment

Clayey soil stabilization using alkali-activated volcanic ash and slag

Lime and Portland cement are the most widely used binders in soil stabilization projects. However, due to the high carbon emission in cement production, research on soil stabilization by the use of more environmentally-friendly binders with lower carbon footprint has attracted much attention in recent years. This research investigated the potential of using alkali-activated ground granulated blast furnace slag (GGBS) and volcanic ash (VA) as green binders in clayey soil stabilization projects, which has not been studied before. The effects of different combinations of VA with GGBS, various liquid/solid ratios, different curing conditions, and different curing periods (i.e. 7 d, 28 d and 90 d) were investigated. Compressive strength and durability of specimens against wet-dry and freeze-thaw cycles were then studied through the use of mechanical and microstructural tests. The results demonstrated that the coexistence of GGBS and VA in geopolymerization process was more effective due to the synergic formation of N-A-S-H and C-(A)-S-H gels. Moreover, although VA needs heat curing to become activated and develop strength, its partial replacement with GGBS made the binder suitable for application at ambient temperature and resulted in a remarkably superior resistance against wet-dry and freeze-thaw cycles. The carbon embodied of the mixtures was also evaluated, and the results confirmed the low carbon footprints of the alkali-activated mixtures. Finally, it was concluded that the alkali-activated GGBS/VA could be promisingly used in clayey soil stabilization projects instead of conventional binders

Properties of fly ash-based spray-applied fire resistive materials

Spray-applied fire-resistive materials (SFRMs) are one of the most commonly used passive fire protection materials due to their low thermal conductivity, lightweight, cost-effectiveness, and ease of application. Gypsum and Portland cement are commonly used in SFRMs to bind lightweight fillers and fibres. Due to the wide application of SFRMs, their production consumes large amounts of natural and non-renewable resources and contributes significantly to greenhouse gas emissions. This paper investigates the feasibility of using industrial by-products (e.g., fly ash) and waste materials (e.g., waste glass) to manufacture SFRMs with the aim of reducing the environmental impact. Accordingly, three SFRMs with different densities were developed utilising fly ash blended cement (FAC) and expanded glass. The use of FAC significantly reduced the use of Portland cement by 81% and achieved a 28-day compressive strength of 33.8–46.3 MPa for the binder. The developed SFRMs had average densities of 345 kg/m3, 560 kg/m3, and 698 kg/m3 for low-, medium-, and high-density groups, respectively. The compressive strengths of the SFRMs ranged from 747 kPa to 888 kPa, 6188 kPa to 7314 kPa, and 2343 kPa to 3535 kPa for the corresponding three groups, respectively. Additionally, the bond strengths of the corresponding SFRMs are 14.4 kPa–19.3 kPa (low-density), 34 kPa–40.9 kPa (medium-density), and 51.5 kPa–85.1 kPa (high-density), respectively. All the tested SFRMs met the requirements for density, compressive strength, bond strength, and non-combustibility. The thermal properties of the developed SFRMs were comparable to those of commercially available cementitious-based SFRMs in the same density group. In addition, using FAC instead of Portland cement could reduce carbon emissions by 68.4% and save costs by 38.4% in the Australian context

Coal tailings as a soil conditioner : evaluation of tailing properties and effect on tomato plants

The global coal industry yields a vast amount of tailings waste, and the utilisation of these tailings necessitates innovative eforts contributing to the United Nations Sustainable Development Goals. One of such novel initiatives is to reuse coal tailings (CT) safely, ecofriendly, and cost-efectively in agroecosystems as a soil conditioner to enhance the productivity of lands. This study aimed to evaluate the potential utilisation of coal tailings waste in the soil amelioration to improve plant performance. The physico–chemical characteristics of coal tailings from two Australian mining sites (CT1 and CT2) showed that the tailings samples are alkaline with loamy and loamy sand textures, respectively. The tailings have ~ 3% of macronutrients, high carbon (C), and low heavy metals and metalloids (As, Cd, Se, Cu, Zn, and Pb). The germination rate of tomato seeds was improved in the low-rate CT treatment. Greenhouse tomato plants exhibited an increase in leaf’s K, Ca, and Mg contents in CT1 and CT2 treatments. More importantly, the CT treatment-induced accumulation of heavy metals in plants was mostly insignifcant in both CT treatments. Therefore, we highlight the potential application of coal tailings as a soil conditioner because of the benefcial efect of improved carbon and nutrients (N, P, K, Mg, and Ca) in tomato leaves. Further amendment of the coal tailings should focus on the adjustment of pH and the addition of other benefcial materials for the improvement of soil properties for crops in both the greenhouse and the feld

Refined finite element modelling of concrete-filled steel stub columns

A wide range of experimental data is collected in this paper and used to develop refined FE models to simulate concrete-filled steel tubular (CFST) stub columns under axial compression. The simulation is based on the concrete damaged plasticity material model, where a new strain hardening/softening function is developed for confined concrete and new models are introduced for a few material parameters used in the concrete model. The prediction accuracy from the current model is compared with that of an existing FE model, which has been well established and widely used by many researchers. The comparison indicates that the new model is more versatile and accurate to be used in modelling CFST stub columns, even when high-strength concrete and/or thin-walled tubes are used

Stress-strain curves of prestressing steel after exposure to elevated temperatures

To evaluate the damage to a structure after fire exposure, the residual mechanical properties of structural materials need to be evaluated first. A literature review is conducted to analyse the major factors influencing the post-fire properties of prestressing steel. Existing test data are collected from an extensive survey of the available literature. A simplified stress-strain model is developed for prestressing steel in residual conditions (i.e. after heating and cooling to room temperature). Measured stress-strain curves are used to verify the accuracy of the proposed model

Mechanical properties of prestressing steel after fire exposure

Prestressed concrete structures have been widely used all over the world, and there is a growing need to study the postfire repairability that is relevant whenever a fire occurs and no collapse happens after cooling. To evaluate the damage to the structure after fire exposure, the residual mechanical properties of structural materials need to be evaluated first. A literature review is conducted to analyse the major factors influencing the post-fire properties of prestressing steel. Existing test data are collected from an extensive survey of the available literature. Based on statistical analysis, the effects of heat exposure on the modulus of elasticity, yield strength and tensile strength, as well as ultimate strain, are analysed. A simplified stress–strain model is developed for prestressing steel in residual conditions (i.e. after heating and cooling to room temperature). Measured stress–strain curves are used to verify the accuracy of the proposed model

Stress-strain model for ferritic stainless steels

Compared with austenitic or duplex stainless steels, ferritic stainless steels have no or very low nickel content. Therefore, their cost is lower and more stable than those of austenitic and duplex stainless steels, providing a more viable alternative for structural applications. They are also less affected by gradual yielding than their austenitic and duplex counterparts and thus retain elastic stiffness at relatively high stress levels more like their ordinary carbon steel counterparts. Existing stress-strain models, however, are less accurate in predicting stress-strain curves for ferritic stainless steels than for austenitic and duplex stainless steels. The paper collects a wide range of tensile test data for ferritic stainless steel coupons cut either from steel sheets or cold-formed hollow sections. Using the three basic Ramberg–Osgood parameters, stress-strain models are developed for both flat and corner ferritic stainless steels. The accuracy of the proposed models is verified by comparing their predictions with experimental stress-strain curves

Residual bond strength in steel reinforced concrete columns after fire exposure

Steel reinforced concrete columns have been widely used in many countries. The effect of fire exposure on the residual bond strength between the encased steel section and concrete is investigated in this paper. A total of 11 specimens, including 3 unheated specimens and 8 specimens which had been exposed to ISO 834 standard fire for 90 min or 180 min, were tested to investigate the influence of the following parameters: (a) fire exposure time, (b) thickness of concrete cover, (c) concrete strength, and (d) tie arrangement. A comparison is made between the measured bond stressslip curves and predictions of an existing model