Strength and leaching behavior of tailing-based paste backfill at high water content amended with lime activated ground granulated blast furnace slag and flocculant.

Flocculent is commonly used in mining activities to improve the concentration of tailing slurry by enhancing the sedimentation process of small tailings particles. The presence of flocculent in thickened tailings is unavoidable, and it affects the heavy metal leaching performances and mechanical and rheological characteristics of tailing-based cemented paste backfill (CPB). This study is carried out to investigate the physicochemical and leachability of CPB amended with flocculants and lime-activated ground granulated blast-furnace slag (GGBS). The stabilized samples were subjected to a series of model tests, including toxicity characteristics leaching procedure (TCLP) and pH, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction. Moreover, the CPB amended with anionic polyacrylamide (APAM) demonstrated better performance in terms of a decrease in heavy metal leachability besides higher mechanical strength than poly aluminum chloride (PAC) and poly ferric chloride (PFC) samples. Furthermore, the UCS results showed that increasing binder content up to 15% negatively influences strength improvement of all stabilized samples because of weak connections between soil particles and cementitious material, resulting in high leachability of heavy metals. The analysis of XRD and SEM showed that anionic polyacrylamide (APAM) cases exhibited more voluminous hydration products, resulting in a compact stabilized matrix and substantially reduced heavy metal leachability.

Preliminary investigation of high-water content dredged sediment treated with chemical-physical combined method at low cement content.

Land reclamation projects are increasingly incorporating dredged sediment from waterways. The high water content of dredged sediment is a major issue, making the dewatering process difficult and time-consuming. The chemical-physical combined method (CP) is therefore used in this study, which simultaneously uses vacuum dewatering by utilising vacuum pressure (VP) in conjunction with prefabricated horizontal drain (PHD) and Portland cement (PC)-based solidification/stabilisation (SS), thereby significantly reducing the duration of treatment of DS with high water content. The effectiveness and feasibility of the chemical-physical combined method with Portland cement (PC) as a binder are evaluated and compared with the traditional PC-based solidification/stabilisation (SS) method. A number of experimental tests were performed to accomplish the objectives of the study, such as unconfined compressive strength (USS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results indicated that the CP method showed better performance compared to the traditional SS method in treating high water content DS at low cement content. The water content of DS treated with the chemical-physical combined method was reduced by half in just about 3 days, and the final rate of settlement was 2.9 times higher than with SS-treated DS. The USC results showed that the strength of CP cases was 4.8 times higher than SS-treated DS after 56 days of curing age. The microstructural tests revealed the development of CSH and CASH as major hydration products of both CP and SS cases. Moreover, CP cases exhibited a densely stabilised matrix compared to SS cases.

Environmental assessment and mechanical properties of Polypropylene fibres reinforced ternary binder foamed concrete.

Rapid urbanization and 'concretization' have increased the use of concrete as the preferred building material. However, the production of cement and other concrete-related activities, contribute significantly to both the carbon dioxide emissions and climate change. Agro-industrial wastes such as Palm Oil Fuel Ash (POFA) and Eggshell Powder (ESP) have been utilized in concrete as supplementary cementitious materials, to reduce the cement content, in order to minimize the carbon footprint and the environmental pollution associated with the dumping of waste. Both POFA and ESP have been utilized in ternary binder foamed concrete; however, higher content of cement replacement tends to reduce the concrete's strength significantly. Therefore, this research was conducted to study the influence of ternary binder foamed concrete, incorporating 30% POFA and 5-15% ESP by weight of the total binder, when reinforced with polypropylene (PP) fibres. Based on the results, the ternary binder foamed concrete showed better strength than the control foamed concrete due to the pozzolanic reaction and the addition of PP fibres slightly improved the strength. Furthermore, ternary binder foamed concrete can reduce up to 33.79% of the total CO2 emissions. In terms of cost, all ternary binder foamed concrete mixes reduced the overall cost of the mix. The lowest cost per 1 MPa was achieved by ternary binder foamed concrete mix which incorporated 30% POFA, 5% ESP and 0.20% PP fibres. However, the optimum S5 ternary binder foamed concrete mix, which incorporated 30% POFA, 10% ESP and 0.20% PP fibres, exhibited a cost of $3.74 per 1 MPa strength, which was $1.1 lower than the control foamed concrete. PP reinforced ternary binder foamed concrete is an eco-efficient and cost-effective concrete that can be used in numerous civil engineering applications, mitigating the environmental and the emissions generated by agro-industrial waste.

Assessing long-term performance of stabilized Zn-contaminated dredged sediment slurry treated with the PHDVPSS method.

Solidification/stabilization (S/S) has been widely used for effective treatment of dredged sediment (DS) for many years, with the objective of improving the mechanical properties of DS through the addition of inorganic cementitious materials. Most previous studies have reported the short-term performance of S/S. However, long-term effectiveness is critical, as contaminants remain underground and are subjected to a variety of environmental stresses that can degrade S/S materials. In this regard, this experimental work investigated the long-term efficacy of solidification/stabilization of dredged contaminated sediments (DCS) treated with a new integrated method, namely PHDVPSS, which uses a prefabricated horizontal drain (PHD) assisted by vacuum pressure (VP) as well as solidification/stabilization. The DCS were treated with Portland cement (PC) as binder in the PHDVPSS method (abbreviated as VP-PC) at different zinc (Zn) concentration levels and compared with the traditional cement-based solidification/stabilization method (abbreviated as SS-PC). A series of experimental tests such as unconfined compressive strength (UCS), toxicity characteristics leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy in conjunction with energy-dispersive spectroscopy (SEM-EDS) were performed to assess the long-term strength, leaching and microstructural characteristics of high-water-content DCS, respectively. The UCS test results indicated that the strength of VP-PC mixes increased significantly with curing time compared to the limited strength development of SS-PC mixes. After 180-day curing, VP-PC mixes exhibited 3.5-5.5 times higher UCS values than the SS-PC mixes. Furthermore, when compared to the SS-PC mixes, the VP-PC mixes had 14.7-36.4% lower leached Zn concentrations at different Zn levels. This is attributed to an increase in the least reactive F4 (residual) fraction and a decrease in the most mobile F1 (acid-soluble) fraction as confirmed by the BCR method. Microstructural tests including XRD and SEM-EDS revealed that calcium silicate hydrate-like compounds were identified as the main hydration products of both the VP-PC and SS-PC mixes. However, portlandite, a major hydration product of PC, was not detected in either case, which is attributed to the retardant effect of Zn on cement hydration. Overall, the experimental results showed that the PHDVPSS method, when compared to the conventional solidification/stabilization method, is a viable choice for treating high-water-content DCS at different Zn concentration levels with low cement content.

Strength and Leaching Behavior of Contaminated Mining Sludge at High Water Content Stabilized with Lime Activated GGBS.

Sludge management is one of the major challenges in mining activities. The direct disposal of contaminated mining sludge can bring severe damages to the environment and community. Solidification/stabilization (S/S) is a very efficient technology for the treatment of contaminated mining sludge because it improves the stability of sludge dumping sites and reduces the leachability of contaminants. Very few studies investigate the S/S of mining sludge, especially with high water content. This paper investigated the effectiveness of S/S for the treatment of mining sludge at high water content by using quick lime (CaO) activated ground granulated blast furnace slag (GGBS) in comparison to ordinary Portland cement (OPC). To evaluate the mechanical, leaching, and microstructural behavior of CMS at high water content stabilized by lime-activated GGBS and OPC, a series of laboratory experimental tests were performed. Experimental results indicated that increasing the dosage of binder led to increased strength and decreased leachability of the heavy metal. In contrast, an increase in the water content of the mixture resulted in a decrease in compressive strength and an increase in the leachability of heavy metals. On the other hand, lime-activated GGBS mixes had substantially better performance than OPC mixes in the aspect of strength development of treated mining sludge and showed comparable capability of heavy metal stabilization compared to OPC. The microstructural tests revealed the formation of different hydration products such as calcium silicate hydrate, calcium aluminum silicate hydrate, ettringite, hydrotalcite, and heavy metal complexes in CG and OPC mixes.

Physico-mechanical and microstructural behaviour of high-water content zinc-contaminated dredged sediment treated with integrated approach PHDVPSS.

This paper uses a new integrated method, namely PHDVPSS, which utilizes vacuum pressure (VP) coupled with prefabricated horizontal drain along with solidification/stabilization (SS) for the effective treatment of high-water content dredged contaminated sediment (DCS). This study sought to evaluate the physico-mechanical and microstructural behaviour of high-water content DCS treated with MgO-GGBS (MG) and Portland cement (PC) as PHDVPSS binders and compared to the traditional Portland cement solidification/stabilization (SS-PC) method. Physico-mechanical and microstructural characteristics of the DCS treated with the PHDVPSS method were evaluated by performing a number of tests such as unconfined compressive strength (UCS), toxicity characteristics of the leaching process (TCLP), pH, X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS). Treatment results showed that the DCS treated with the MG binder in the PHDVPSS method showed superior performance in terms of a significant reduction in the water content and leachability of zinc (Zn) along with higher mechanical strength and dry density of the samples compared to the traditional SS-PC method. After 56-day curing time, VP-MG cases showed 17.6 % and 50 % higher dry density values, resulting in 2.5 and 17.3 times higher UCS values than VP-PC and SS-PC cases, respectively. In contrast, VP-MG cases showed lower pH values than those of VP-PC and SS-PC cases. Moreover, VP-MG cases exhibited 37.5 % and 44.3 % lower leached Zn concentration during a TCLP test than VP-PC cases and SS-PC cases, respectively. XRD and SEM-EDS tests showed that more voluminous hydration products were produced in the VP-MG cases, which in turn produced a dense stabilized matrix and significantly reduced the leachability of zinc.

Thermo-mechanical properties and sustainability analysis of newly developed eco-friendly structural foamed concrete by reusing palm oil fuel ash and eggshell powder as supplementary cementitious materials.

The production of cement contributes to 10% of global carbon dioxide (CO2) pollution and 74 to 81% towards the total CO2 pollution by concrete. In addition to that, its low strength-to-weight ratio, high density and thermal conductivity are among the few limitations of heavy weight concrete. Therefore, this study was carried out to provide a solution to these limitations by developing innovative eco-friendly lightweight foamed concrete (LFC) of 1800 kg/m3 density incorporating 20-25% palm oil fuel ash (POFA) and 5-15% eggshell powder (ESP) by weight of total binder as supplementary cementitious material (SCM). The influence of combined utilization of POFA and ESP on the fresh state properties of eco-friendly LFC was determined using the J-ring test. To determine the mechanical properties, a total of 48 cubes and 24 cylinders were prepared for compressive strength, splitting tensile strength and modulus of elasticity each. A total of 24 panels were prepared to determine the thermal properties in terms of surface temperature and thermal conductivity. Furthermore, to assess the environmental impact and eco-friendliness of the developed LFC, the embodied carbon and eco-strength efficiency was calculated. It was determined that the utilization of POFA and ESP reduced the workability slightly but enhanced the mechanical properties of LFC (17.05 to 22.60 MPa compressive strength and 1.43 to 2.61 MPa tensile strength), thus satisfies the ACI213R requirements for structural lightweight concrete and that it can be used for structural applications. Additionally, the thermal conductivity reduced ranging from 0.55 to 0.63 W/mK compared to 0.82 W/mK achieved by control sample. Furthermore, the developed LFC showed a 16.96 to 33.55% reduction in embodied carbon and exhibited higher eco-strength efficiency between 47.82 and 76.97%. Overall, the combined utilization of POFA and ESP as SCMs not only enhanced the thermo-mechanical performance, makes the sustainable LFC as structural lightweight concrete, but also has reduced the environmental impacts caused by the disposal of POFA and ESP in landfills as well as reducing the total CO2 emissions during the production of eco-friendly LFC.