Recycle of steel slag as cementitious material and fine aggregate in concrete: mechanical, durability property and environmental impact.

Using steel slag (SS) as cementitious material and fine aggregate in concrete is an effective and environmental method for SS consumption and cost reduction. In this paper, SS was recycled in large volumes in concrete as partial cementitious material and fine aggregate. The compressive strength and reaction mechanism of cementitious material with different SS powder contents including 20%, 25%, 30%, and 35% were presented. The results indicated that 20% of SS powder improved the compressive strength by 34.57% and the hydration products were ettringite (AFt) and calcium silica hydrate(C-(A)-S-H). Furthermore, the mechanical and durability performance of concrete with SS as fine aggregate were investigated. When the SS substitution rate was 75%, the compressive strength was increased by 37.83%. The volume shrinkage rate and 28d-carbonation depth were reduced nearly by 64% for 90 days and 2.33 mm, respectively. The chloride ion penetration resistance reached the optimal grade Q-V and abrasion resistance was improved by nearly 24%. Along with the reduced CO2 by 210-294 kg/m3 and the decreased cost by 12.61 USD/m3, it is regarded as an effective method to consume steel slag. As such, this research provided a scientific and systematic basis for the large-scale disposal and utilization of industrial waste residues as well as recycled materials preparation.

Geothermal Nano-SiO2 Waste as a Supplementary Cementitious Material for Concrete Exposed at High Critical Temperatures.

The partial replacement effect of Portland cement by geothermal nano-SiO2 waste (GNSW) for sustainable Portland-cement-based concrete was investigated to improve the properties of concrete exposed at high critical temperatures. Portland cement was partially replaced by 20 and 30 wt.% of GNSW. The partial replacement effect on Portland-cement-based concrete subjected to 350, 550, and 750 °C was evaluated by measuring the weight changes, ultrasonic pulse velocity, thermogravimetric and differential thermal analysis, X-ray diffraction, surface inspection, and scanning electron microscopy under residual conditions. The ultrasonic pulse velocity results showed that the GNSW specimens maintained suitable stability after being heated to 350 °C. The SEM analysis revealed a denser microstructure for the 20 wt.% of partial replacement of Portland cement by GNSW specimen compared to the reference concrete when exposed to temperatures up to 400 °C, maintaining stability in its microstructure. The weight losses were higher for the specimens with partial replacements of GNSW than the reference concrete at 550 °C, which can be attributed to the pozzolanic activity presented by the GNSW, which increases the amounts of CSH gel, leading to a much denser cementitious matrix, causing a higher weight loss compared to the reference concrete. GNSW is a viable supplementary cementitious material, enhancing thermal properties up to 400 °C due to its high pozzolanic activity and filler effect while offering environmental benefits by reducing industrial waste.

A Review of Gene-Property Mapping of Cementitious Materials from the Perspective of Material Genome Approach.

As an important gelling material, cementitious materials are widely used in civil engineering construction. Currently, research on these materials is conducted using experimental and numerical image processing methods, which enable the observation and analysis of structural changes and mechanical properties. These methods are instrumental in designing cementitious materials with specific performance criteria, despite their resource-intensive nature. The material genome approach represents a novel trend in material research and development. The establishment of a material gene database facilitates the rapid and precise determination of relationships between characteristic genes and performance, enabling the bidirectional design of cementitious materials' composition and properties. This paper reviews the characteristic genes of cementitious materials from nano-, micro-, and macro-scale perspectives. It summarizes the characteristic genes, analyzes expression parameters at various scales, and concludes regarding their relationship to mechanical properties. On the nanoscale, calcium hydrated silicate (C-S-H) is identified as the most important characteristic gene, with the calcium-silicon ratio being the key parameter describing its structure. On the microscale, the pore structure and bubble system are key characteristics, with parameters such as porosity, pore size distribution, pore shape, air content, and the bubble spacing coefficient directly affecting properties like frost resistance, permeability, and compressive strength. On the macroscale, the aggregate emerges as the most important component of cementitious materials. Its shape, angularity, surface texture (grain), crushing index, and water absorption are the main characteristics influencing properties such as chloride ion penetration resistance, viscosity, fluidity, and strength. By analyzing and mapping the relationship between these genes and properties across different scales, this paper offers new insights and establishes a reference framework for the targeted design of cementitious material properties.

Optimization of Cementitious Material with Thermal-Activated Lead-Zinc Tailings Based on Response Surface Methodology.

The accumulation of lead-zinc tailings will cause a series of problems, including geological disasters and environmental pollution. Efficient secondary utilization of lead-zinc tailings is crucial. In this study, the activity of lead-zinc tailings was stimulated by thermal activation. The optimal thermal activation parameters are a thermal activation temperature of 900 °C and a holding time of 30 min. Based on the response surface methodology, the effect of raw materials content on cementitious material strength was analyzed, and the relational model between cementitious material strength and experimental variables was established. The results show that the sensitivity order of cementitious material strength at 28 days curing age is sand/cement ratio > water/cement ratio > fly ash content > tailing content. According to the relational model, the optimal materials ratio is as follows: tailing/fly ash/cement = 28.99%:14.58%:56.43%, and the sand/binder ratio and water/binder ratio are 1:1 and 0.47, respectively. The corresponding cost is CNY 290.965 per ton, which is the lowest. The strength of cementitious material with these parameters can reach 20 MPa, which meets the requirements of "Technical specification for application of solid waste cementitious material (T/CECS 689-2020)".

Thermal Reactivation of Hydrated Cement Paste: Properties and Impact on Cement Hydration.

In this research, the properties and cementitious performance of thermally activated cement pastes (referred to as DCPs) are investigated. Hydrated pastes prepared from Portland cement and slag blended cement were subjected to different thermal treatments: 350 °C for 2 h, 550 °C for 2 h, 550 °C for 24 h and 750 °C for 2 h. The properties and the reactivity as SCM of the DCPs were characterised as well as their effect on the mechanical performance and hydration of new blended cements incorporating the DCPs as supplementary cementitious materials (SCMs). It was observed that the temperature and duration of the thermal treatment increased the grindability and BET specific surface area of the DCP, as well as the formation of C2S phases and the reactivity as SCM. In contrast, the mechanical strength results for the blended cements indicated that thermal treatment at 350 °C for 2 h provided better performance. The hydration study results showed that highly reactive DCP interfered with the early hydration of the main clinker phases in Portland cement, leading to early setting and slow strength gain. The effect on blended cement hydration was most marked for binary Portland cement-DCP blends. In contrast, in the case of ternary slag cement-DCP blends the use of reactive DCP as SCM enabled to significantly increase early age strength.

The Preparation and Dust Suppression Performance Evaluation of Iron Ore Tailing-Based Cementitious Composites.

In order to comprehensively utilize iron ore tailings (IOTs), the possibility of using IOTs as raw materials for the preparation of cementitious composites (IOTCCs) was investigated, and IOTCC was further applied to mine interface pollution control. The mechanical properties, hydration products, wind erosion resistance, and freeze-thaw (F-T) cycle resistance of IOTCCs were evaluated rigorously. The activity index of iron tailings increased from 42% to 78% after grinding for 20 s. The IOTCC was prepared by blending 86% IOT, 10% ground granulated blast-furnace slag (GGBS), and 4% cement clinker. Meanwhile, the hydration products mainly comprised ettringite, calcium hydroxide, and C-S-H gel, and they were characterized via XRD, IR, and SEM. It was observed that ettringite and C-S-H gel were principally responsible for the strength development of IOTCC mortars with an increase in curing time. The results show that the kaolinite of the tailings was decomposed largely after mechanical activation, which promoted the cementitious property of IOT.

Effect of high temperature on mechanical properties of lithium slag concrete.

As the main gel material of concrete, cement is used in an astonishing amount every year in the construction industry. However, a large amount of CO2 is emitted into the atmosphere while producing cement. Therefore, it is the general trend to look for substitutes for cement and develop new green concrete. Lithium slag (LS) is the industrial waste discharged from lithium salt plants. Through testing, it is found that the chemical composition of LS has a high degree of coincidence with ordinary Portland cement (OPC) Therefore, LS can be incorporated into concrete as supplementary cementations material (SCM) to prepare lithium slag concrete (LSC). The pollution of the natural environment caused by a large number of piled-up and landfilled LS is immeasurable. Consuming and using LS in large quantities and with high efficiency not only eliminates the pollution of lithium slag to the natural environment, but also helps to reduce the amount of cement used in green concrete and truly reuse waste resources. In order to study the mechanical properties of post-heated LSC, the test were carried out for LSC specimens after high-temperature. The main influence factors were considered, including the temperatures of 20℃, 100 â„ƒ, 300 â„ƒ, 500 â„ƒ and 700 â„ƒ, the contents of lithium slag in LSC of 0%, 10%, 20% and 30%, cooling method of LSC after exposure high temperature. The results showed that the mechanical properties of LS concrete specimens were slightly improved at 100 â„ƒ, and when the temperature was 300 â„ƒ or higher, the damage to the specimens was huge and irreversible. An appropriate amount of LS (20% lithium slag content) could improve the strength of LSC. This paper also studied the relationship between lithium slag content and strengths of LS concrete. The research results show that adding an appropriate amount of LS to concrete improves the mechanical properties of concrete. When the LS replacement rate is 20%, the mass loss rate of LSC after different high temperature treatments was the minimum. The cubic compressive strength, axial compressive strength, and flexural strength of specimens with 20% LS substitution can be increased by 8.16%, 8.33%, and 13.46% after high temperature. The cubic compressive strength, axial compressive strength, and flexural strength of specimens with 20% LS substitution can be increased by 8.16%, 8.33%, and 13.46% after high temperature.

Recycling of mineral wool waste as supplementary cementitious material through thermochemical treatment.

Mineral wool is commonly used in construction as thermal insulation material. After the product's lifetime, it is classified as hazardous waste if no trademark of the European Certification Board for Mineral Wool Products (EUCEB) or the German Institute for Quality Assurance and Labelling (RAL) exists. Mineral Wool Waste (MWW) is typically landfilled in Europe, which is challenging due to its low bulk density and dimensional stability. This circumstance highlights the need for alternative recycling methods that increase the recycling rate of construction and demolition (C&D) waste. This article outlines the recycling opportunities of MWW and focuses on the use of thermochemical treatment of different mixtures of input materials to produce a supplementary cementitious material (SCM). The material characterisation results and investigations on the binder suitability demonstrate that the slag fractions after the thermochemical treatment are well-qualified to be used as reactive binder components. Additionally, a material flow analysis was conducted to estimate the substitution potential of MWW as SCM in the Austrian cement industry.

Valorisation of metallurgical residues via carbothermal reduction: A circular economy approach in the cement and iron and steel industry.

The decarbonisation of the steel and cement industry is of utmost importance in tackling climate change. Hence, steel production in modern integrated steel mills will be shifted towards electric arc furnaces in the future, in turn causing dwindling supplies of blast furnace slag, which is used as a supplementary cementitious material inter alia to reduce the CO2 emissions of cement production. Achieving a sustainable circular steel and building material economy requires the valorisation of currently landfilled steel slags and investigating utilisation options for electric arc furnace slag, which is increasingly being generated. For this purpose, different metallurgical residues and by-products were treated by carbothermal reduction in an inductively heated graphite crucible and then rapidly cooled by wet granulation, yielding a slag fraction similar to granulated blast furnace slag and a metal fraction valuable as a secondary raw material. A spreadsheet-based model was developed to calculate residue combinations to accomplish target compositions of the slag and metal fractions to fulfil previously identified requirements of the targeted cementitious and ferrous products. The results demonstrate the high accuracy of the model in predicting the properties (e.g. main oxide composition) of the generated slag and metal fraction, which fulfil the needed requirements for their use as (i) a supplementary cementitious material and (ii) a secondary raw material in steel production.

Utilization of Recycled Brick Powder as Supplementary Cementitious Materials-A Comprehensive Review.

Over the past two decades, extensive research has been conducted to explore alternative supplementary cementitious materials (SCMs) in order to address the environmental concerns associated with the cement industry. Bricks, which are frequently preferred in the construction sector, generate a lot of waste during the production and demolition of existing buildings, requiring environmentally sustainable recycling practices. Therefore, many studies have been carried out in recent years on the use of brick waste as supplementary cementitious materials (SCMs) in cement mortar and concrete production. This critical review evaluates the impact of waste brick powder (WBP) on the mechanical and durability properties of mortar and concrete when used as a partial replacement for cement. It was observed that the properties of WBP-blended cement mortar or concrete depend on several factors, including WBP particle size, replacement ratio, pozzolanic activity, and mineralogical structure. The findings indicate that WBP with a particle size range of 100 µm to 25 µm, with a maximum cement replacement level of 10-20%, exhibits a positive impact on the compressive strength of both mortars and concretes. However, it is crucial to emphasize that a minimum curing duration of 28 days is imperative to facilitate the development of a pozzolanic reaction. This temporal requirement plays a vital role in realizing the optimal benefits of utilizing waste brick powder as a supplementary cementitious material in mortars and concretes.

Effect of wheat straw ash as cementitious material on the mechanical characteristics and embodied carbon of concrete reinforced with coir fiber.

The use of supplementary cementitious materials has been widely accepted due to increasing global carbon emissions resulting from demand and the consequent production of Portland cement. Moreover, researchers are also working on complementing the strength deficiencies of concrete; fiber reinforcement is one of those techniques. This study aims to assess the influence of recycling wheat straw ash (WSA) as cement replacement material and coir/coconut fibers (CF) as reinforcement ingredients together on the mechanical properties, permeability and embodied carbon of concrete. A total of 255 concrete samples were prepared with 1:1.5:3 mix proportions at 0.52 water-cement ratio and these all-concrete specimens were cured for 28 days. It was revealed that the addition of 10 % WSA and 2 % CF in concrete were recorded the compressive, splitting tensile and flexural strengths by 33 MPa, 3.55 MPa and 5.16 MPa which is greater than control mix concrete at 28 days respectively. Moreover, it was also observed that the permeability of concrete incorporating 4 % of coir fiber and 20 % of WSA was reduced by 63.40 % than that of the control mix after 28 days which can prevent the propagation of major and minor cracks. In addition, the embodied carbon of concrete is getting reduced when the replacement level of cement with WSA along with CF increases in concrete. Furthermore, based on the results obtained, the optimum amount of WSA was suggested to be 10 % and that of coir fiber reinforcement was suggested to be 2 % for improved results.

Characterization and mechanical removal of metallic aluminum (Al) embedded in weathered municipal solid waste incineration (MSWI) bottom ash for application as supplementary cementitious material.

Municipal solid waste incineration (MSWI) bottom ash, due to its high mineral content, presents great potential as supplementary cementitious material (SCM). Weathering, also known as aging, is a treatment process commonly employed in waste management to minimize the risk of heavy metal leaching from MSWI bottom ash. Using weathered MSWI bottom ash to produce blended cement pastes is considered as a high-value-added and sustainable waste disposal solution. However, a critical challenge arises from the metallic aluminum (Al) in weathered MSWI bottom ash, which is known to induce detrimental effects such as volume expansion and strength loss of blended cement pastes. While most metallic Al in weathered MSWI bottom ash can be removed with eddy current separators in metal recovery plants, the residual metallic Al, owing to its small particle size, cannot be removed with the same technique. This study is dedicated to addressing this issue. An in-depth analysis was conducted on residual metallic Al embedded in weathered MSWI bottom ash particles, aiming to guide the removal of this metal. This analysis revealed that mechanical removal was the most suitable method for extracting metallic Al. The specific processes and mechanisms underlying this method were elucidated. After reducing metallic Al content in weathered MSWI bottom ash by 77 %, a significant improvement in the quality of blended cement pastes was observed. This work contributes to the broader adoption of mechanical treatments for removing residual metallic Al from weathered MSWI bottom ash and facilitates the application of treated ash as SCM.

Lithium Slag and Solid Waste-Based Binders for Cemented Lithium Mica Fine Tailings Backfill.

To mitigate the adverse effects of fine-grained lithium mica tailings and other solid wastes generated from the extraction of lithium ore mining, as well as the limitations of traditional cement-based binders for lithium mica fine tailings, this study explores the feasibility of using a binder composed of ordinary Portland cement, lithium slag, fly ash, and desulfurization gypsum to stabilize lithium fine tailings into cemented lithium tailings backfill. Compared with traditional cementitious binders, an extensive array of experiments and analyses were conducted on binders formed by various material proportion combinations, employing uniaxial compressive strength tests, microstructural morphology, grayscale analyses, and flowability tests. The results show the following: (1) In this study, an LSB binder exhibiting superior mechanical properties compared to traditional cementitious binders was identified, with an optimal OPC:LS:FA:DG ratio of 2:1:1:1. (2) In the context of cemented lithium mica fine tailings, the LSB-CLTB material exhibits higher unconfined compressive strength and lower self-weight compared to OPC-CLTB materials. At a binder content of 10 wt%, the UCS values achieved by the LSB-CLTB material at curing periods of 7 days, 14 days, and 28 days are 0.97 MPa, 1.52 MPa, and 2.1 MPa, respectively, representing increases of 40.6%, 34.5%, and 44.8% over the compressive strength of OPC-based materials under the same conditions. (3) The LSB binder not only exhibits enhanced pozzolanic reactivity but also facilitates the infilling of detrimental pores through its inherent particle size and the formation of AFt and C-(A)-S-H gels via hydration reactions, thereby effectively improving the compressive strength performance of fine-grained tailings backfill.

Insight into the Micro Evolution of Backfill Paste Prepared with Modified Gangue as Supplementary Cementitious Material: Dissolution and Hydration Mechanisms.

Gangue-based backfill cementitious materials (BCM) are widely applied due to their low CO2 footprint, while the application is restricted by gangue's low reactivity. In this study, dry chemical modification was developed to modify the gangue, and multiple characterized approaches were used to characterize the dissolution property, mineral composition, and particle size distribution of modified gangue (MCG), as well as the compressive strength and microstructure of BCM. The findings show that the residue weight of MCG stabilized at 2 wt.% of formic acid, and the modification reduces the kaolinite and calcite, resulting in smaller particles. Additionally, the three days compressive strength of the BCM made with MCG was improved from 0.3 MPa to 0.6 MPa. Attributed to the increased reactivity of MCG, it was found that the dissolution weight increased by 2.13%. This study offers a novel method for activating gangue and a new kind of MCG-prepared BCM, which makes a significant contribution towards achieving the UN Sustainable Development Goals.

A systematic study on sustainable low carbon cement - Superplasticizer interaction: Fresh, mechanical, microstructural and durability characteristics.

As governments around the world take on ambitious construction projects, from housing to infrastructure to transportation, the demand for cement is set to rise. It is anticipated that global cement production is set to achieve a compound annual growth rate of ∼5.1% for the years 2022-2025. The negative impact of cement production on the environment, such as carbon emissions and energy consumption, is also well known. This instigates the need to look for alternative and sustainable supplementary cementitious materials (SCMs) such as Fly ash (FA), Limestone (LS), Metakaolin (MK), Ground granulated blast furnace slag (GGBFS) and Silica fume (SF) which when blended with Portland clinker result in lower carbon emissions and better end products. With expanding cement demand, the need for chemical admixtures has also increased. This comprehensive study focuses on the compatibility of commercially available superplasticizers with SCMs blended low carbon cement and their influence on fresh and hardened properties along with microstructural and durability aspects. The chemistry of superplasticizers and how it effects the hydration mechanism of blended cement are also highlighted in detail. Moreover, the effect of different types of superplasticizers, their dosage, water binder ratio, and details of experiments used by other authors are also discussed and listed. As cementitious matrix containing any kind of SCM such as FA showed better environmental performance on the basis of life cycle assessment which was due to carbon emission factor (ξi). For cement, ξi was 311.27 kg CO2-eq/t, whereas for FA it was much lower (8.70 kg CO2-eq/t). Based on this comprehensive literature review, current challenges for the utilisation of waste SCMs incorporating superplasticizers along with research gap have been identified. Apart from this, the ongoing research work on the effect of chemical and mineral admixture on Limestone-calcined clay cement (LC3) using statistical modelling to optimize the mix is also discussed. It was observed that the use of a specific type of mineral admixture with a superplasticizer inversely affected the mechanical properties like compressive strength and modulus of rupture but improved the water-binder ratio, porosity, and water absorption.

A comprehensive assessment of mechanical and environmental properties of green concretes produced using recycled concrete aggregates and supplementary cementitious material.

This study aims to present a multi-perspective evaluation of green concretes produced using supplementary cementitious material and recycled concrete aggregates and to balance the reduction in compressive strength values caused by using recycled concrete aggregates with silica fume. For these purposes, statistical analyses were performed on the response surface method using the data of 9 reference and 27 green concrete series mixtures, and mathematical models were developed to predict the compressive strength with high accuracy. Then, energy consumption, global warming potential, and waste generation were taken into account from the environmental impact categories, and the environmental impact scores obtained were compared in detail to examine the impact of the use of silica fume and recycled concrete aggregates on sustainable development. Significant reductions in energy consumption and global warming potential values with the use of silica fume and waste generation values with the use of recycled concrete aggregates were achieved, and it was seen that supplementary cementitious material and recycled concrete aggregates are of great importance in terms of sustainable development. It was seen that these waste materials could be utilized, especially in regions with high earthquake risk, and that these waste materials are of great importance.

Study on Shrinkage in Alkali-Activated Slag-Fly Ash Cementitious Materials.

Traditional silicate cement materials produce a large amount of CO2 during production, making it urgent to seek alternatives. Alkali-activated slag cement is a good substitute, as its production process has low carbon emissions and energy consumption, and it can comprehensively utilize various types of industrial waste residue while possessing superior physical and chemical properties. However, the shrinkage of alkali-activated concrete can be larger than that of traditional silicate concrete. To address this issue, the present study utilized slag powder as the raw material, sodium silicate (water glass) as the alkaline activator, and incorporated fly ash and fine sand to study the dry shrinkage and autogenous shrinkage values of alkali cementitious material under different content. Furthermore, combined with the change trend of pore structure, the impact of their content on the drying shrinkage and autogenous shrinkage of alkali-activated slag cement was discussed. Based on the author's previous research, it was found that by sacrificing a certain mechanical strength, adding fly ash and fine sand can effectively reduce the drying shrinkage and autogenous shrinkage values of alkali-activated slag cement. The higher the content, the greater the strength loss of the material and the lower the shrinkage value. When the fly ash content was 60%, the drying shrinkage and autogenous shrinkage of the alkali-activated slag cement mortar specimens decreased by about 30% and 24%, respectively. When the fine sand content was 40%, the drying shrinkage and autogenous shrinkage of the alkali-activated slag cement mortar specimens decreased by about 14% and 4%, respectively.

Interfacial Weakness Criterion by Indentation in 3D Printed Concrete.

Three-dimensional (3D) printable concrete requires cementitious material that must have suitable but self-contradictory properties to be printable such as fluidity to facilitate pumping along with stiffness and strength to ensure buildability, both having a great influence on the cohesion of the interfacial zone. A pool of characterization tests was developed over the last decades for layered 3D printed structures to quantify and qualify the interfacial region. Although destructive tests are typically selected to capture actual interfacial bonding strength, nondestructive testings were also used. Indentation tests were preferred in this study to locally determine the mechanical properties of the center part of two consecutive layers, the edge of the layer and the interfacial zone. As results, it was found that the previously deposited layer is harder than the upper one. The hardness of the edges of the printed filament can decrease ∼50% over few hundred microns compared to the core of the material. Moreover, this decrease in hardness is also observed at the interface. From the hardness-distance profile measured perpendicularly to the plan of the interface, we propose an interfacial weakness criterion, which has been successfully applied in various conditions of 3D printed concrete elaboration.

DoE Approach to Setting Input Parameters for Digital 3D Printing of Concrete for Coarse Aggregates up to 8 mm.

This paper is primarily concerned with determining and assessing the properties of a cement-based composite material containing large particles of aggregate in digital manufacturing. The motivation is that mixtures with larger aggregate sizes offer benefits such as increased resistance to cracking, savings in other material components (such as Portland cement), and ultimately cost savings. Consequently, in the context of 3D Construction/Concrete Print technology (3DCP), these materials are environmentally friendly, unlike the fine-grained mixtures previously utilized. Prior to printing, these limits must be established within the virtual environment's process parameters in order to reduce the amount of waste produced. This study extends the existing research in the field of large-scale 3DCP by employing coarse aggregate (crushed coarse river stone) with a maximum particle size of 8 mm. The research focuses on inverse material characterization, with the primary goal of determining the optimal combination of three monitored process parameters-print speed, extrusion height, and extrusion width-that will maximize buildability. Design Of Experiment was used to cover all possible variations and reduce the number of required simulations. In particular, the Box-Behnken method was used for three factors and a central point. As a result, thirteen combinations of process parameters covering the area of interest were determined. Thirteen numerical simulations were conducted using the Abaqus software, and the outcomes were discussed.

Solidification Mechanism of Pb and Cd in S2--Enriched Alkali-Activated Municipal Solid Waste Incineration Fly Ash.

S2--enriched alkali-activator (SEAA) was prepared by modifying the alkali activator through Na2S. The effects of S2--enriched alkali-activated slag (SEAAS) on the solidification performance of Pb and Cd in MSWI fly ash were investigated using SEAAS as the solidification material for MSWI fly ash. Combined with microscopic analysis through scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), the effects of SEAAS on the micro-morphology and molecular composition of MSWI fly ash were studied. The solidification mechanism of Pb and Cd in S2--enriched alkali-activated MSWI fly ash was discussed in detail. The results showed that the solidification performance for Pb and Cd in MSWI fly ash induced by SEAAS was significantly enhanced first and then improved gradually with the increase in dosage of ground granulated blast-furnace slag (GGBS). Under a low GGBS dosage of 25%, SEAAS could eliminate the problem of severely exceeding permitted Pb and Cd in MSWI fly ash, which compensated for the deficiency of alkali-activated slag (AAS) in terms of solidifying Cd in MSWI fly ash. The highly alkaline environment provided by SEAA promoted the massive dissolution of S2- in the solvent, which endowed the SEAAS with a stronger ability to capture Cd. Pb and Cd in MSWI fly ash were efficiently solidified by SEAAS under the synergistic effects of sulfide precipitation and chemical bonding of polymerization products.