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In accordance with global estimations, approx. 15 million tons of residues are yearly generated from paper and pulp industry, which are traditionally used as biofuels or just disposed in landfills. However, residues composition and laws in force urge producers to search for new waste management strategies. From another point of view, the construction industry uses more than 33% of total natural resources, worldwide which has led several governments to limit the use of natural raw materials for building. In particular, fired brick industry produces yearly approx. 1600 billion bricks which represents millions of tons of natural resources consumption. Therefore, the goal is to contribute to reduce the amount of used clay. Thus, this paper explores the mineral and technological properties of brick made by using different percentages of paper pulp residues and fired at 900 °C. Results indicate that by increasing the replacement ratio, blend requires larger amounts of water which leads to a proportional increasing of shrinkage during drying. In spite of mineral transformations are not influenced by paper pulp residue, the porosity is linearly increased which leads to reduce compressive strength and thermal conductivity up to 30% for 20% of replacement ratio, in both cases. Thus, it is concluded that series made by replacing up to 10% show compressive strength above 5 MPa, water absorption beyond 20% and toxicity indexes meet the mandatory requirements. [ABSTRACT FROM AUTHOR]

The use of waste-based materials in the construction industry has received significant attention in recent years to develop environmentally-friendly construction materials. This paper presents an experimental study on the properties of bricks containing clay, fly ash (FA), and bottom ash (BA). A total of 12 batches of bricks were manufactured and experimental tests were conducted at two firing temperature of 950 and 1050 °C to determine the apparent porosity, water absorption, apparent specific gravity, bulk density, compressive strength, and thermal conductivity. Microstructural analysis was undertaken to describe the reasons for the obtained experimental results. The results show that the bricks fired at 1050 °C exhibit slightly lower apparent porosity and water absorption but slightly higher bulk density and thermal conductivity than those fired at 950 °C. The results also show that an increase in the FA content leads to an increase in the apparent porosity and water absorption but a decrease in bulk density and thermal conductivity of the bricks. BA content does not have any significant influence of the properties of the bricks. It is also shown that bricks containing 5% FA, 5% BA, and 10% BA exhibit a similar compressive strength to those containing only clay. The leaching results show that the leaching of heavy metals from fired bricks is significantly lower than that of the limit concentrations. The leaching concentrations of the samples show that the heavy metals were immobilized in the ceramic structures of all fired bricks. These highly promising findings suggest that up to 30% replacement of wastes with ashes can provide bricks to reduce the environmental impact of abundant waste products and conserve non-renewable natural resources. [ABSTRACT FROM AUTHOR]

Large clayey sedimentary layers are extracted as waste rock material to reach the phosphate ores. Considered as mining wastes intimately mixed with other silicated and carbonated lithologies, they are stored as coarse waste rocks in large dumps nearby the phosphate mines; as it is the case of Gantour mine of OCP group (Morocco). These clay occurrences have been investigated as a raw material for the production of ceramics, especially fired clay bricks. In this paper, pressed and fired briquettes made of the isolated clayey lithology were manufactured. The clay material mineralogy include dolomite, quartz, palygorskite, and montmorillonite. The as-formed briquettes were oven dried at 105 °C then fired in the range 900–1100 °C. Both raw and sintered samples (at various temperature) were investigated by differential thermal and thermogravimetric analysis (TG-DTA), X-ray diffraction (XRD), optical and scanning electron microscope (OM-SEM) and Fourier Transform Infra-Red (FTIR). Main physical and mechanical properties were assessed and correlated to the microstructural changes. The obtained results revealed that sintering temperature increase led to dehydroxylation of clay minerals, persistence of quartz and neo-formation of diopside, anorthite, hematite and magnetite. SEM secondary electron images showed bricks vitrification together with micro-porosity formation during firing, which greatly influenced the mechanical properties. The elaborated bricks displayed acceptable water absorption capacity and firing shrinkage rate with good flexural strength, showing that they could be used in the bricks manufacturing. This clay lithology from phosphate mines should then be considered as a raw material to be valorized and reused. • Thermal behavior of clay lithology from the Moroccan phosphate series. • Physico-chemical characteristics of fired eco-friendly bricks. • Mechanical performances of the clay lithology based materials. • Use of response surface methodology (RSM) for the correlation of the physical properties with the processing factors. [ABSTRACT FROM AUTHOR]

The disposal of waste rock fine (WRF) from the manufacturing process of crushed aggregates is attracting more and more attention due to the thorny issues related to clay particles. This paper investigated the use of WRF as a substitute for fine aggregate that solidified by phosphogypsum (PG), groundgranulated blast-furnace slag (GGBS), and ordinary Portland cement (OPC) system in manufacturing of baking-free brick. Three kinds of WRF with different clay fraction (i.e., natural WRF, silty WRF, and clayey WRF) were prepared via slurry settlement methods. Thereafter, their mechanical behaviors were compared by unconfined compressive strength (UCS), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests. The results show that natural WRF contains 81.9% silt and 18.1% clay, after settling-based separation process, the strength of solidified silty and clayey WRF samples decreased by 4.1% and 16.5% at 28 days curing period. Micromorphology, compositional, and microstructural analyses indicate that the strength of solidified WRF is governed by both bonding and filling effect, therein, the strength of solidified silty and clayey WRF samples were lower as compared with natural WRF-based modified samples due to the gradation effect. In addition, it was noticed that although clay particles may participate in the secondary pozzolanic reaction to contribute bonding strength, they also possess superior adsorption capability owing to the large specific surface area, which will adsorb on the surface of cementitious materials and thus hinder the hydration reaction. Moreover, water stability, environmental leaching, economic, and greenhouse gas emission results further confirmed the advantage of reusing WRF and industrial by product resources. [Display omitted] • The combination of industrial by products and waste rock fine is applicable and effective in manufacturing of baking-free brick. • Clay fraction is a sensitive indicator of mechanical behaviors for WRF-based brick. • The behavioral difference of solidified WRFs was attributed to the different coupled contribution of bonding and filling within solidified matrix. • The proposed framework for WRF-based brick can meet both the environmental and engineering requirements. [ABSTRACT FROM AUTHOR]

Earth pressure balance shield (EPBS) has become the mainstream construction method for metro tunnels in China, which inevitably generates a large amount of discharged soil, putting enormous pressure on the environment and the cost. In order to realize the resource utilization of shield dregs, this paper explored the feasibility of recycling the waste silty clay as a soil conditioner in EPBS tunnel construction. Mixtures of bentonite, wasted silty clay, carboxymethyl cellulose (CMC), and tap water in different ratios were prepared. Defining the substituted ratio as the mass ratio of silty clay to (bentonite + silty clay), the effect of the substituted ratio on the apparent viscosity, flow curve, rheological model and physical stability of bentonite-silty clay composite slurry were investigated. Furthermore, the relationship between slurry microstructures and macroscopic rheological properties was revealed by scanning electron microscopy (SEM). The results show that the constitutive relationship of bentonite slurry (0% substituted ratio) can be well described by Herschel-Bulkley model. The silty clay has a deteriorating effect on the rheological behavior and physical stability, and changes the flow pattern of the composite slurry. Microscopically, CMC makes the clay particles in slurries form agglomerates with larger particle sizes, and can absorb excess free water from the slurry, thus significantly increasing the yield stress and apparent viscosity. The recycling scheme proposed in this study can not only greatly reduce the procurement cost of raw materials, but also eliminate the transportation and disposal costs of discharged soil, which has significant environmental benefits and promising application prospects. [ABSTRACT FROM AUTHOR]

This paper presents the comprehensive evaluation results of physical and environmental performances for a novel wet-white (chrome-free) leather manufacturing. The tanning process is optimized as 15 wt% tannic acid (TA) combination with 4 wt% Laponite nanoclay, giving the leather with shrinkage temperature ( T s ) above 86 °C. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements indicate that Laponite can be evenly and tightly bound within the leather matrix, which is further confirmed by scanning electron microscopy and energy dispersive X-ray (SEM-EDX) spectroscopy analysis. The resultant wet-white leathers have reasonable good physical properties that can meet the standard requirements for furniture leather without containing hazardous Cr(VI) and formaldehyde. Further life cycle assessment (LCA) studies shows that tanning process is the main contributor to environmental impact categories in the wet-white tanning process, and tannic acid is the most significant substance factor. Compared to conventional chrome tanning, the wet-white tanning process exhibits much lower abiotic depletion potential (ADP), and reduced global warming potential (GWP) and human toxicity potential (HTP) impacts due to the nature of vegetable tanning; whereas, GWP excluding biogenic carbon and energy consumption are higher owing to prolonged run time. [ABSTRACT FROM AUTHOR]

This paper provides an efficient alternative way to conserve natural clays and to reduce both fired bricks costs production and wastes amounts generation. It aims to substitute natural clay by treated calamine processing wastes (TCPMT) to manufacture value added fired bricks. Different mixes containing up to 40% of TCPMT were pressed, dried and fired at various temperatures: 900, 950, 1000 and 1050 °C. The fired bricks were characterized for their physical, mechanical, mineralogical, microstructural, environmental and durability properties. The results show that the increase of temperature allows the enhancement of mechanical strength, the reduction of water absorption due to the decrease of accessible pores amount and the enhancement of potential contaminants immobilization. The mechanical strength of bricks decreases with the addition of TCPMT due to the increased formation of pores and the apparition of some coarse grains which are considered as regions of weakness of the studied bricks. The leaching behavior of reference and selected optimum bricks, assessed according to a tank leaching test, shows that almost toxic elements; Pb, Zn, As, Cr, Mo, Ba, Cd and Cu are immobilized in the sintered bricks. Finally, the experimental approach outcomes show the possibility to produce bricks containing up to 30 wt% of TCPMT with the required engineering and environmental properties when fired at 1050 °C. [ABSTRACT FROM AUTHOR]

The use of traditional binders such as cement or lime has induced critical resource consumption, carbon emission, and environmental issues. Recycling biomass/industrial solid wastes as a novel eco-friendly binder is a promising alternative. This paper explores the critical problems of effectively stimulating the activity of waste RHA and the environmental compatibility of the developed waste-based binder. A series of unconfined compression, chemical, and leaching toxicity tests were conducted to evaluate the feasibility of the waste-based binder for waste clay stabilization in road engineering. The results show that the pozzolanic activity of waste RHA was strongly activated by CS with strong alkalinity. The most significant performance improvement for stabilizing waste clay was achieved at 6% RHA with adding 6% CS as an alkalinity activator and 3% MK as a supplement of aluminum phase composition. The 7d soaked compressive strength q iu of stabilizing waste clay reached 1.4 MPa, which met the requirements of the road base for freeway/first-class highway. There was a positive promotion for the reuse and elimination of massive waste RHA and CS. Moreover, many hazardous elements existing in raw materials RHA, CS, and clay were rarely detected in leaching solutions and satisfied groundwater safety. The utilization of RHA, CS, clay wastes in road engineering did not cause marked environmental risks. Finally, abundant newly generated hydration products can be observed due to the carbonization reaction and pozzolanic reaction, thus exhibiting excellent mechanical properties and environmental compatibility. This study presents a promising recycling and reuse way of biomass/industrial solid wastes as an alternative to cement/lime for soil stabilization in road engineering, contributing to carbon neutralization/carbon peak and sustaining economics. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic not only poses an unprecedented threat to global health but also severely disrupts the natural environment and ecosystems. Mitigating the adverse impacts of plastic-based personal protective equipment (PPE) waste requires the cooperation of professionals from various fields. This paper discusses a novel, cleaner approach to soil stabilisation by repurposing the nitrile gloves into a sustainable road material to improve the mechanical properties of expansive clay soil as pavement subgrade. For the first time, extensive geotechnical testings, including standard compaction, unconfined compressive strength (UCS), unsoaked California bearing ratio (CBR), repeated load triaxial (RLT), and swelling-shrinkage tests, were carried out to investigate the engineering performance of different proportions of the shredded nitrile gloves (SNG) (e.g., 1%, 1.5%, 2%) were blended with expansive clay (EC). In addition, surface roughness, scanning electron microscopy (SEM), and X-ray micro-CT analyses were conducted, and images were obtained to study the microstructural modification of the EC-SNG mixtures. The experimental results indicated that the blend of expansive clay with SNG helped in increasing the compressive strength, resilient modulus, and CBR and assisted in reducing the swelling and shrinkage of the soil. SEM and surface roughness analyses indicated the interaction between the soil matrix interface and the rough surface of the SNG. The main reasons for increasing the strength and stability of clay soil could be attributed to the high tensile strength of the SNG and the formation of the three-dimensional grid, and friction between the soil particles and SNG. According to the X-ray micro-CT test results, the incorporation of SNG led to an increase in closed porosity. [Display omitted] • An innovative approach to mitigate the problem of medical waste generation associated with COVID-19 is presented. • A cleaner and sustainable subgrade was developed by using discarded nitrile gloves. • The addition of 1.5% SNG to the soil provided the highest strength properties. • SNG reduced the swelling and shrinkage of the expansive clay subgrade. [ABSTRACT FROM AUTHOR]

Expansive clays are problematic soils as they contain minerals that swell when wetted and shrink during drying. Highway construction on expansive soils requires some form of chemical stabilisation or other treatments to improve pavement performance. Many commercial and waste by-products, such as cement, lime, fly ash and slag, are used as chemical stabilisers to treat expansive clays. Municipal solid waste incineration (MSWI) fly ash is a product obtained from waste-to-energy plants which have attracted increasing attention to prevent land contamination and to reduce landfill costs. This paper investigates the stabilisation mechanism and hydro-mechanical performance of MSWI fly ash-stabilised high plasticity expansive clays. In this study, compressive strength, California bearing ratio (CBR), dynamic cone penetration, shrinkage and swelling, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) tests were conducted to understand the performance of MSWI fly ash for the treatment of high-plasticity expansive clay. The study found that MSWI fly ash reduces swelling potential and increases the ten-day soaked CBR to about 80%. Microlevel analysis showed that hydration reaction, cationic exchange, flocculation, and agglomeration between clay sheets are the key phases in MSWI fly ash stabilisation. In addition, the porosity of the clay reduced from 3.43% to 0.18% after stabilisation with 20% MSWI fly ash. The outcomes from the study provide guidance on using MSWI ash for improving problematic soils while enabling an efficient way to manage municipal solid wastes. [Display omitted] • Application of municipal solid waste incineration ash (MSWI fly ash) to stabilise high plasticity clay was investigated. • MSWI fly ash stabilised samples exhibit negligible swelling and shrinkage. • Even for extreme rainfall cases, MSWI fly ash stabilised samples perform well. • Cationic exchange and hydration are the main stabilisation mechanisms. • Porosity of clay reduced from 3.43% to 0.18% after stabilisation with 20% MSWI fly ash. [ABSTRACT FROM AUTHOR]

In this paper, synthesis of geopolymer from bagasse bottom ash and naturally available china clay was studied in order to effectively utilize both these low cost and easily available materials. The ash and china clay activated at 900 °C were grinded in three different proportions as a source material for the synthesis of geopolymers to get SiO 2 /Al 2 O 3 as 2.5, 3.0 and 3.5. Sodium silicate (Na 2 SiO 3 ) and sodium hydroxide (NaOH) were used as alkaline medium. XRD revealed that clay activated at 900 °C become highly amorphous and disordered material which resulted good quality geopolymer. Different types of mortars ranging in ratio of polymer to sand were made and the compressive strength was measured. The raw material, geopolymer composites and mortars were characterized by using different analytical techniques including X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy (SEM). Highest compressive strength of geopolymer composite was recorded as 2487 with silica to alumina ratio of 2.5 and for mortar 1947 PSI with geopolymer to sand ratio of 1:1 respectively. [ABSTRACT FROM AUTHOR]

Cement is the most produced material around the world. Developing countries face a growth of population involving an increasing need of infrastructures. Due to this situation, the cement industry needs to find the best comprise between increasing the cement production and without increasing the negative environmental impact. A promising solution has been found in the use of supplementary cementitious materials (SCM), these materials are used to replace clinker in cement because of their pozzolanic reactivity. In this paper, a method was developed to assess the details of the economic and environmental potential of the specific Limestone Calcined Clays Cement LC 3 technology in the Cuban context. A comparison with traditional Portland cement and the current commercial blended cement with zeolite (PPC) sold in Cuba was made. The results provide evidenced based data for the development of a strategy to adopt the LC 3 technology by the Cuban market. This assessment method can then be easily extended to markets in other developing countries. [ABSTRACT FROM AUTHOR]

A broader utilization of calcined gypsum in external applications remains limited mainly due to its high solubility in water. This drawback can be improved by combining it with supplementary cementitious materials and an activator of pozzolanic reactions (cement or lime). This paper aims to explore the feasibility of utilizing non-conventionally used fired clay brick waste, a by-product from brick production, to design gypsum-based binders with improved water resistance. A comprehensive study of the system consisting of calcined gypsum, fired clay brick waste, and lime was done from a microscopic (mineral composition, porosity development, and morphology) to macroscopic (basic physical and mechanical properties) point of view up to 90 days of age. Additionally, a simplified environmental study was conducted using the Life Cycle Assessment method. Amorphous phase and ettringite were the main hydration products. The mechanical tests revealed that the pozzolanic reactions caused by the addition of fired clay brick waste were delayed, which was reflected by a slow increase in strength within the studied period. Contrary to the reference binders, the compressive strength of the samples containing the lowest percentage of fired clay brick waste provided the most promising results even after 90 days of water curing. Considering that the newly designed ternary binders are prepared from low-cost and eco-friendly pozzolana active waste, the results presented in this study could help eliminate the disposal of fired clay brick waste and convert it into useful binder material suitable for green building rendering and restoration work of historical buildings. [Display omitted] • Brick waste was utilized to manufacture green and low-cost gypsum-based binders. • Ternary binders showed improved water resistance via increasing strength in time. • A high ceramics/gypsum ratio accelerated the formation of amorph and ettringite. • Oven drying of binders speeded up the transformation of portlandite into calcite. • Oven drying at 40 °C enhanced the compressive strength of binders by 17–23%. [ABSTRACT FROM AUTHOR]

In this paper the main mechanical properties of concrete produced with recycled aggregates obtained from crushing both structural and non-structural lightweight concrete are characterized. Various concrete mixes with replacement ratios of 20%, 50% and 100% of two types of coarse lightweight aggregates (LWA) by recycled lightweight concrete aggregates (RLCA) were studied in terms of their compressive strength, tensile strength, modulus of elasticity and abrasion resistance. Generally the experimental results show that all the studied properties are improved with the introduction of RLCA. In particular, concrete with RLCA has higher structural efficiency than the reference concrete, with LWA alone. It is thus concluded that more cost-effective structural lightweight concrete (LWC) can be produced with the introduction of RLCA. Moreover, it is shown that the RLCA obtained from non-structural lightweight concrete can be used to produce structural LWC. There is a slight reduction of the concrete's mechanical properties when the stronger LWA is replaced with the more porous RLCA obtained from non-structural lightweight concrete. [ABSTRACT FROM AUTHOR]

In sedimentary phosphates mining operations, clayey layers are removed as mine wastes. The main objective of this paper was to investigate the feasibility to valorize these mine wastes as Lightweight aggregates (LWAs) by mixing them with organic wastes (sawdust and coffee grounds) which act as pore-forming agents. Thermal transformations and microstructural changes during heating were investigated using X-ray diffraction, thermal analysis, scanning electron microscope and Fourier-transform infrared spectroscopy. The bulk density, compressive strength and water absorption of LWAs were also determined. Neoformed mineral phases was characterized and correlated to the LWA microstructure. The results demonstrated that original aluminosilicated minerals, dolomite and part of quartz were involved in the mineralization process and melt abundance respectively. SEM observations displayed a tangled microstructure that results from merged particles and different pores sizes. The addition of pore-forming agent to clays waste enhanced the macro-pore formation process in comparison to the reference samples. LWAs with good performances (density 0.8–0.95 g/cm3 and compressive strength ∼77 MPa) were successfully manufactured by mixing 25 wt% of coffee grounds or sawdusts with clayey phosphate waste. Image 1 • Recycling of clayey phosphate mine wastes as raw material for lightweight aggregates (LWAs) manufacture. • Use of organic wastes (coffee grounds and sawdusts) as pore-forming agent. • LWAs with good performances (density 0.8–0.95 g/cm3 and compressive strength ∼77 MPa) were successfully manufactured. • The produced LWAs using 25 wt.% of pore-forming agent provide environmental and economic advantages. [ABSTRACT FROM AUTHOR]

This study presents a comparison of the life cycle carbon emission (LCCO 2) and embodied energy calculation between two kinds of bricks, sun-dried and fired clay, as means of evaluating the energy and climate impact of each brick type and the economics of production. Focus is paid to the differences across the whole production chain between sun-dried clay bricks, which represent the traditional norm, and fired clay bricks, which are the most widely-used walling materials in conventional buildings. A case study was carried out in Dakhla Oasis in the Western Desert of Egypt. The results of this study show that if sun-dried bricks are used instead of fired bricks, a reduction of up to 5907 kg CO₂e (in CO₂ emissions) and 5305 MJ of embodied energy for every1000 bricks produced could be achieved. The paper concludes by offering alternative scenarios for brick-making and suggestions for improving sun-dried brick production. The methodology used in this study contributes to the development of an investigative-comparative way to assess choices between building materials. It also intends to help inform local homeowners and building practitioners not only in Egypt, but also globally, about resource depletion, energy consumption, and harmful emissions from fired industrial bricks as a common building construction material. • Sun dried clay bricks are a nearly zero carbon building material with low embodied energy. • For every 1000 sun-dried bricks, a reduction in CO₂ by 5907 kg CO2e and 5305 MJ EE is achieved. • Social and cultural norms can affect the choice of different building materials. [ABSTRACT FROM AUTHOR]

Waste marine clay, a commonly found natural deposit in coastal regions, can serve as partial cement alternative in mortar after thermal treatment, thus facilitate sustainable urban development without polluting the environment. This paper studied the influence of calcination temperature, fineness of grounded particles and cement replacement ratio on the pozzolanic activity of the thermally treated marine clay. TG results reveal that dehydroxylation of waste marine clay with low kaolinite mainly occurs between 500 and 600 °C and completes at 700 °C. Calcined marine clay accelerates cement hydration and causes higher total heat. From the microscopic analysis, it can be found that the calcined marine clay favours the consumption of portlandite accompanied by the formation of the C–S–H, C-A-H, AFm and strätlingite. MIP results show that calcined marine clay can refine the pore system with declines in the threshold pore size, critical pore size and average pore size, while the total pore volume and porosity are increased with higher replacement ratio. Mortar incorporating 15% fine calcined marine clay as cement substitute exhibits comparable strength with the reference mortar. However, beyond 45% cement replacement ratio, mortar strength substantially drops as a result of cement dilution effect, porous structure and agglomeration of marine clay. [ABSTRACT FROM AUTHOR]

The objective of this paper was to compare the following four alternative management methods of phosphogypsum (PG) waste using Life Cycle Analysis (LCA) and select the one with the lowest environmental footprint: (1) use of PG in brick production, (2) use of PG as soil amendment, (3) use of PG in road construction and (4) disposal of PG in a stack. The results showed that the use of PG waste as soil amendment has a lower environmental footprint than the respective use of conventional gypsum with commercial fertilizers. Similarly, PG waste has a lower environmental footprint when replacing conventional clay in road construction. In contrast, use of PG waste in brick production has a higher footprint than the respective use of clay and sand. Comparison of the four alternative management methods using LCA showed that the use of PG as a soil amendment had the lowest environmental footprint. Disposal of PG waste in stacks, which is currently the most common management method, was ranked as the least preferred one. As an example, using Ecoindicator 99 and the egalitarian perspective total scores were 12.807, −5.334, −0.064 and 15.484 Points (Pt) for brick production, soil amendment, road construction and stack disposal, respectively. Among indicative impact categories, carcinogen scores were 7.643, −0.228, 0.0001 and 0 Pt, respectively. Respiratory inorganics scores were −0.192, −4.540, −0.0383 and 0 Pt, respectively. The ranking based on cost is stack disposal

Engineered Cementitious Composites (ECC) showing multiple-cracking and strain-hardening under tension are appealing for the construction industry, but the high cement content in conventional ECC leads to high environmental impacts. Recently, the limestone and calcined clay (LCC) blend has been proposed as a promising alternative of Supplementary Cementing Materials (SCM) to address the inadequacy of common SCM such as fly ash and blast furnace slag, which have been widely-used in ECC. This paper reports a feasibility study for the first time on using ultrahigh-volume LCC blend (HVLCC, 70% and 80% by weight of binder) to produce sustainable medium-strength ECC. Three water/binder ratios (0.30, 0.35 and 0.40) and two sand/binder ratios (0.2 and 0.4) were explored. HVLCC-ECC can achieve a tensile strain capacity of 0.57–1.58%, tensile strength of 3.24–5.19 MPa and compressive strength of 33–65 MPa at 28 days. HVLCC-ECC also have sufficient early strength at 3 days (22-38 MPa), and similar fresh properties and bulk densities under surface-dry condition (1900-2100 kg/m3), as compared to conventional ECC. Additionally, HVLCC-ECC show about 1/6 higher embodied energy and about 1/6 lower embodied carbon than a typical ECC mix with 55% fly ash in the binder, and ECC with fly ash perform much better than ECC with LCC blend in terms of embodied energy and embodied carbon per unit strength or strain capacity. Nevertheless, this new version of HVLCC-ECC with adequate mechanical performance are still attractive from the perspective of shortage of fly ash in the future due to the reduced consumption of coal. • Medium-strength ECC with Limestone-Calcined Clay (LCC) blend are reported for the first time. • Sustainable PVA-ECC with ultrahigh-volume LCC blend (70–80 wt% of binder) were explored. • Sufficient workability, early strength and 28-day compressive strength of 33–65 MPa were obtained. • 28-day tensile strength of 3.24–5.19 MPa and tensile strain capacity of 0.57–1.58% were achieved. • These ECC are attractive from the perspective of shortage of fly ash due to reduced consumption of coal. [ABSTRACT FROM AUTHOR]

Yellow clays from Moroccan phosphate mines are extracted with other waste rocks lithologies and stored in large dumps within the mine site. The present paper investigates the use of this by-product as a new aluminosilicate source for geopolymers elaboration at the laboratory scale. Yellow clays studied are mainly composed of montmorillonite, dolomite and quartz as major phases. The Toxicity Characteristic Leaching Procedure (TCLP) showed no existence of contaminant. In order to reach thermal activation, the raw clays were first calcined at different temperatures between 500 and 900 °C. Raw and calcined clays were characterized using thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. For the synthesis of geopolymers, calcined powder was mixed with an alkaline solution presenting different NaOH/Na 2 SiO 3 ratios. The compressive strength was measured at 7, 14 and 28 days and material porosity was determined using Mercury Intrusion Porosimetry method in order to explain the mechanical behavior. XRD, 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy, Fourier transformed infrared and TGA have been used to investigate the gel structure. The thermal treatment at 900 °C allowed the destruction of crystalline structure of montmorillonite clays, as well as the formation of new phases such as periclase (MgO) and gehlenite (Ca 2 Al 2 SiO 7). Furthermore, the 27Al - 29Si MAS-NMR and the XRD analysis of the elaborated materials confirmed the formation of two cementitious gels C-A-S-H (Calcium aluminum silicate hydrate) and N-A-S-H (Sodium aluminum silicate hydrate). The compressive strength was around 25 MPa at 28 days. The obtained results are promising; they have shown that elaborated materials can be adapted for construction applications. In this case, it is recommended that economic and commercial study be developed. Image 1 • Yellow clays by-products from Moroccan phosphate mines were studied as a precursor for the synthesis of geopolymers. • The temperature of activation of yellow clay was 900 °C. • Formation of two type of gels after alkali activation. • The compressive strength reached 25 MPa after 28 days of curing at ambient temperature. [ABSTRACT FROM AUTHOR]