Slate Waste Research Articles

Enhancing mechanical performance in SLS-printed PA12-slate composites through amino-silane treatment of mineral waste

The SLS additive manufacturing industry enables the development of products for diverse applications with distinct properties due to its excellent surface finish and ability to create varied part geometries, but it consumes high-performance materials with high acquisition costs. An extensive quarrying of stone leads to the accumulation of mineral residues, posing environmental hazards by contaminating soil and water when disposed of in landfills. The primary objective of the study was to incorporate mineral waste into the SLS technique and investigate the influence of its addition, along with a silane-based chemical treatment, on the mechanical performance of polymer-mineral composites (PA12-slate). Additionally, the feasibility of producing a highly loaded printed prototype, employing 50 wt% of mineral waste, was examined. Samples of PA12, PA12 blended with 50 wt% slate waste, and slate waste treated with silane underwent fabrication via selective laser sintering (SLS) and subsequent mechanical characterization, including tensile, flexural, and compressive tests. Additionally, the samples underwent accelerated aging using a QUV weathering tester, followed by mechanical characterization. The geometric accuracy, stability, and processing feasibility of these formulations were evaluated through SLS-printed composite prototypes utilizing PA12_50Sla_Si. It was found that the addition of 50% of slate to the PA12 presented mechanical properties decreasing compared to the printed PA12 only. However, an increase was verified when using silane-induced mineral bonding. The incorporation of mineral agents and silane enhanced the resistance of PA12 to aging. However, after aging, both tensile and flexural strength decreased across all printed samples. Nonetheless, this study showcased the feasibility of producing complex PA12-slate waste specimens containing up to 50 wt% of mineral waste using the SLS printing technique. Therefore, SLS presents itself as a viable means of adding value to this mineral waste.

Environmental and technical assessment on the application of slate waste in Portland-composite cement CEM II

Large volumes of waste are generated from the manufacture of slabs, roofing, and tiles using slate stone. The use of waste in the construction industry is prevalent due to the environmental advantages associated with the implementation of circular economy standards. This paper examines the production of Portland cement CEM II using heat-treated slate waste. The fineness index results were 10.95 % for the 75-μm sieve and 23.53 % for the 45-μm sieve. Assessment of reactivity using mechanical methods showed that mortars produced with 20 % slate waste (SW) achieved a strength of 42.35 MPa and a mechanical index of 84.93 %. Direct measurement (FTIR), along with chemical methods (Frattini Test and Saturated lime test), confirm the pozzolanic activity of the slate waste. The environmental impact assessment demonstrated a reduction in the carbon dioxide emission rate by 21.49 % (6.54E+02 kgCO2-eq/t) with the use of Portland cement CEM II/CSW. The valorization of slate waste can contribute to the availability of an alternative source of raw material and the reduction of natural resource consumption. However, further studies on mechanical performance and durability are necessary for this waste to be applied in structural cementitious matrices.

The Mechanical Performance of Recycled Slate Waste Fiber Composites Based on Unsaturated Polyester Resins.

In the last few decades, there has been increasing social awareness for environmental conservation, which is driving the development of composite materials based on natural fibers. These new materials have interesting properties that allow for their use in a variety of applications. This study deals with the development of composite materials based on unsaturated polyester resins reinforced with recycled mineral fibers, such as slate fibers obtained from slate production waste, which have similar properties to glass fiber. The mechanical properties of these composites have been determined by tensile and flexural/bending tests. The influence of various variables such as matrix composition (flexible polyester content) and the weight percentage of fiber added to mechanical properties were evaluated. The flexible/rigid polyester content varied from 0 to 40% and the fiber one from 0 to 30 wt%. Composites with ≥20 wt% of slate fiber reinforcement are shown to have tensile (35 MPa) and flexural (57 MPa) strengths that can compete with materials reinforced with artificial fibers.

Study of the influence of thermo-mechanical treatment on the properties of slate waste

RESUMO Este trabalho estuda o efeito da forma de tratamento termomecânico (calcinação e moagem) do resíduo de ardósia com foco na ativação das propriedades pozolânicas. O programa experimental consistiu em avaliar as propriedades físicas, químicas, minerais e morfológicas do resíduo. O material foi cominuído por 1 hora e 45 minutos, peneirado e, em seguida, as amostras passantes em 45 µm foram submetidas ao tratamento térmico, as quais foram expostas a temperatura 1000ºC, mantendo-se constante por um período de até 5 horas e foram moídas novamente. As análises cristalográficas demonstraram que processo de calcinação gerou uma redução da cristalinidade pela diminuição dos picos e formação de um possível halo de amorfização. Os resíduos de ardósia após tratamento térmico, aumentaram o tamanho médio devido ao efeito de aglomeração pela fusão das partículas o que interferiu no efeito da ativação pozolânicas, sendo que uma maior moagem garantiu um ótimo resultado de ativação, comprovando que a granulometria mais elevada interfere na reatividade do material. Ficou evidenciado que para ativação do resíduo de ardósia se faz necessária a utilização de moagem antes do processo de aquecimento (partículas menores de 45 µm) e após (partículas menores de 38 µm).

Analysis of the Resilient Modulus and California Bearing Ratio in mixtures containing slate waste and clayey soil

The use of slate waste can help to reduce the impacts caused to the environment due to the decrease of the appropriate disposal areas and the disordered consumption of raw material. This article presents an analysis of the Resilient Modulus (RM) and the California Bearing Ratio (CBR) of this waste in mixtures with clayey soil. To analyze variations in RM and CBR due to the increase in the slate waste content, tests were carried out on reference mixtures (REF) and mixtures containing slate waste (SLT). The tests were carried out for mixtures of granular material (gneiss for REF and slate waste for SLT) and clay soil, containing different levels of granular materials (50%, 60%, 70%, 80% and 90%) It was observed that the values of Resilient Modulus and California Bearing Ratio of the SLT mixtures increased 62.8% and 127.0% with the addition of the slate waste between the SLT 50/50 and SLT 90/10 mixtures, respectively. This behavior was similar to that presented by the REF mixtures, which increased 125.0% in RM and 60.1% in CBR for the same addition of granular material. The results obtained indicate that the mixtures containing slate waste presented RM and CBR similar to those of conventional materials (such as the REF mixtures) used in layers of sub-base and the base of pavements. Finally, it was concluded that the relationship between RM and CBR is non-linear for both mixtures (REF and SLT) in function of granular material addition.

Sustainable material manufacturing from hazardous bauxite red mud in composites with clay slate waste and lime production waste

The primary purpose of this study was to experimentally validate the possibility of using hazardous red mud (RM) from bauxite ore treatment and clay slate mining wastes (SW)—scraps of slabs and polishing sludge—as the main raw components in composites with poorly burned limestone as lime production wastes (LPW) here used as a binding additive. Mixtures of these components were homogenized, hydrated, and compacted with a compressive strength of 10 MPa. The incorporation of 15–30% LPW led to axial strength values of 4.7–12.8 MPa on the 28th curing day and 10.6–23.7 MPa on the 365th day. The results of XRF, XRD, AAS, and SEM with EDS, DTA-TGA, and LAMMA analyses showed that all mechanical properties of the developed materials were enhanced due to the synthesis of new formations, mainly amorphous and partly crystalline, during the microstructural densification of the composites. The developed materials can be used as road base and airfield runways, levee cores, industrial and municipal waste dumps, building foundations, and production of tiles, bricks, and blocks. The most important contribution of this study is the convincing experimental evidence of an efficient engineering solution to the ecological problems of three types of industrial enterprise, without the use of expensive traditional market materials such as Portland cement or commercial lime, preventing the accumulation of large amounts of these wastes in industrial dumps. Furthermore, it would significantly reduce nature’s irreversible destruction by quarries of natural raw material like clay, sand, and crushed stone.

Avaliação do efeito da adição de resíduo de ardósia no módulo de resiliência de misturas com solo argiloso

A extração de ardósia gera grandes volumes de resíduo que poderiam ser aplicados em pavimentação. O ensaio dinâmico para determinação do Módulo de Resiliência (MR) fornece dados importantes para a análise estrutural dos pavimentos. Embora haja diversos estudos de MR para aplicações em pavimentos, poucos se referem à análise dos efeitos do aumento percentual de resíduos em misturas. Neste artigo foi possível constatar, por meio de caracterização físico-mecânica e ensaios de MR de misturas com solo argiloso contendo porcentagens (60, 70 e 80% em massa) de resíduos de ardósia (SLT) e agregado de gnaisse (REF), que há comportamento físico similar das misturas SLT e REF. Observou-se que os valores de Índice de Suporte Califórnia (ISC) e MR da mistura SLT aumentaram 16,1% e 40,9%, respectivamente, com a adição do resíduo de ardósia entre as misturas SLT 60/40 e SLT 80/20. Os resultados de MR obtidos estão dentro da faixa relatada nas referências bibliográficas para materiais reciclados e naturais utilizados em pavimentação. Por fim, o software de dimensionamento MeDiNa foi utilizado para comprovar a possibilidade da utilização das misturas SLT em camada de base e sub-base em pavimentação. Desse modo, constata-se a importância de se desenvolver estudos que permitam melhor análise da aplicabilidade de resíduos em substituição aos materiais convencionais na pavimentação.

Aproveitamento do rejeito de lavra de ardósia para a produção de carga mineral

A exploração da ardósia gera uma grande quantidade de resíduos, principalmente nas suas fases de extração e de beneficiamento, dando origem a passivos ambientais. No intuito de minimizar esse impacto, este trabalho teve como objetivo aproveitar o rejeito de ardósia para produzir cargas minerais, que são amplamente utilizadas na fabricação de materiais compósitos. Com este propósito, o resíduo de ardósia foi coletado da pilha de rejeito de uma mineradora próxima a cidade de Pompéu/MG, sendo caracterizado tecnologicamente e também por processos de cominuição para adequação de granulometria. Analisando os resultados, constatou-se que este rejeito satisfaz as especificações para ser utilizado como potencial carga mineral, devido à alta porcentagem de sílica e alumina e enquadramento abaixo de 0,045mm após moagem, características estas semelhantes à de cargas já utilizadas no mercado. Desta maneira, essa possível reutilização pode contribuir de forma significativa para a gestão dos resíduos sólidos na mineração e minimização dos impactos ambientais.

Manufacturing of Ultra-light Ceramsite from Slate Wastes in Shangri-la, China

Manufacturing of Ultra-light Ceramsite from Slate Wastes in Shangri-la, China

Study of Compaction Characteristics of Soil with the Addition of Slate Mining Waste

Objectives: This paper brings out the results of an experimental programme carried out at National Institute of Technology, Hamirpur to evaluate the effectiveness of using slate quarry waste for soil stabilization by studying the compaction characteristics of various proportions of slate waste in native soil, as a pre-requirement to reach at soil-slate mix for shear strength and settlement testing for use as a sub grade material for foundations of structures and pavements. Methods/Statistical Analysis: Disturbed sampling of soil was done and was classified according to Indian Standard Soil Classification System (ISSCS), using Liquid limit and Plasticity index. Slate waste was sampled and Sieve analysis was performed. Light compaction tests were performed in order to get the Maximum Dry Density and Optimum Moisture content of soil with slate mining waste in various proportions. Findings: The soil was found to have liquid limit and plastic limit of 46.0833% and 26.1570 % respectively. According to ISSCS, Soil was found to be clay of medium compressibility. Slate waste with cu and ccof9.04 and 0.67 respectively was utilized for the study. The Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) was found to be 24.989% and 1.497 g/cc, 32% and 1.95g/cc for soil and slate waste respectively. Variation of OMC and MDD with slate waste (%) added was analysed. The results show that the addition of waste material has increased the OMC as well as the MDD. An increase in MDD depicts a stable soil. The increase in OMC is due to the water absorption of slate waste. Application/Improvements: These results can be further used for study of strength, settlement behaviour, and slope stability of the soil-slate waste mix. It can be utilized for economics in pavements and improvement of Sub grade of pavements and buildings.

Simplified greywater treatment systems: Slow filters of sand and slate waste followed by granular activated carbon

One of the main actions of sustainability that is applicable to residential, commercial, and public buildings is the rational use of water that contemplates the reuse of greywater as one of the main options for reducing the consumption of drinking water. Therefore, this research aimed to study the efficiencies of simplified treatments for greywater reuse using slow sand and slow slate waste filtration, both followed by granular activated carbon filters. The system monitoring was conducted over 28 weeks, using analyses of the following parameters: pH, turbidity, apparent color, biochemical oxygen demand (BOD), chemical oxygen demand (COD), surfactants, total coliforms, and thermotolerant coliforms. The system was run at two different filtration rates: 6 and 2 m3/m2/day. Statistical analyses showed no significant differences in the majority of the results when filtration rate changed from 6 to 2 m3/m2/day. The average removal efficiencies with regard to the turbidity, apparent color, COD and BOD were 61, 54, 56, and 56%, respectively, for the sand filter, and 66, 61, 60, and 51%, respectively, for the slate waste filter. Both systems showed good efficiencies in removing surfactants, around 70%, while the pH reached values of around 7.80. The average removal efficiencies of the total and thermotolerant coliforms were of 61 and 90%, respectively, for the sand filter, and 67 and 80%, respectively, for the slate waste filter. The statistical analysis found no significant differences between the responses of the two systems, which attest to the fact that the slate waste can be a substitute for sand. The maximum levels of efficiency were high, indicating the potential of the systems, and suggesting their optimization in order to achieve much higher average efficiencies.

Scientific and technical aspects of blended cement matrices containing activated slate wastes

The extraction of slate for use as a construction material generates large quantities of waste (between 75% and 90% in weight), which are dumped on landfill sites, with the ensuing technical, economic, environmental, and social problems. One possible way of reusing this raw waste is through its thermal activation to produce a new cementitious material for the manufacture of eco-efficient cements.An assessment is presented in this study of the chemical, mineralogical and pozzolanic properties of ash waste, activated at 1000°C over 2h, as well as a study of the main technical properties of blended cements prepared with 10% and 20% slate ash. The results show the high pozzolanic activity of the slate ash, principally over the seven first days, forming CSH gels as a principal hydrated phase of the pozzolanic reaction, followed by randomly interstratified chlorite/smectite phases and monosulfoaluminate [C3A·SO4Ca·12H2O]. These blended cements prepared with 10% and 20% activated slate waste comply with both the physical and the mechanical requirements of current European standards.

The Influence of Slate Waste Activation Conditions on Mineralogical Changes and Pozzolanic Behavior

The transformation process of clay minerals into pozzolanic products for use as active additives in cement matrixes has been closely studied by both the scientific community and the cement industry. Sourcing these additions from recycled waste products is widely prioritized in environmental policies, because of their associated environmental benefits. This article reports an exhaustive analysis of slate waste in Spain, for its eventual use as an alternative source of pozzolans, based on activated phyllosilicates. The analysis examines the effect of activation conditions on mineralogy and the formation and evolution of the hydrated phases that form during the pozzolanic reaction at 28 days. The results show good pozzolanic activity in the starting slate wastes activated between 800°C and 1100°C of temperature for 2 h of retention, on which basis 1000°C and 2 h were recommended as the more suitable activation conditions for these activated slate wastes (ASW), as total destruction of all phyllosilicates is ensured under those conditions. The hydrated phases formed during the pozzolanic reaction in theASW/Ca(\OH)2system were calcium silicate hydrate gels (CSH), randomly interstratified chlorite (Cl) /smectite with variables containing chlorite/smectite ratios 30% chlorite, 40% chlorite, 50% chlorite, 60% chlorite, respectively, and monosulfoaluminate (C3A·SO4Ca·12H2O) directly related to the activation process used in this article. All of these findings support the viability of slate waste for use as a pozzolanic addition.

Alleviation of Both Water and Nutrient Limitations is Necessary to Accelerate Ecological Restoration of Waste Rock Tips

Hard rock quarries are commonly located close to national parks and special areas of conservation and are generally regarded as visually intrusive. Consequently, restoration strategies that effectively accelerate natural plant regeneration processes are required. Slate waste tips present extreme conditions for plant establishment with multiple potential limiting factors (e.g., lack of organic matter, nutrients, and poor water retention). In this study, we investigated ecological strategies to accelerate natural regeneration at the largest slate quarry in Europe. A field experiment was conducted to assess ecosystem restoration using a contrasting set of native woody species. Treatments included amendments of waste tips with: polyacrylamide gel to increase water-holding capacity; mineral fertilizer to increase nutrient supply; and two treatments that increased both (organic waste or boulder clay addition). Ecosystem recovery was evaluated through above- and below-ground productivity (plant and microbial, respectively) and soil analyses. Neither increasing nutrient supply (with mineral fertilizer) nor water-holding capacity (with polyacrylamide gel) was sufficient, alone, to improve plant establishment. However, both boulder clay and organic waste amendment significantly enhanced plant growth. There was a marked positive interaction in the effects on tree growth of the amendment with organic waste and boulder clay. Large interactions occurred between tree species and substrate amendments. The growth of N(2)-fixing species was strongly favored over non-fixers where there was no addition of material increasing soil nitrogen supply, whereas the growth advantage of pioneer species over non-pioneers was greatest with fertilizer, organic waste, or clay additions. Organic waste addition had the greatest positive impact on soil processes.

Engineering properties of concrete made with slate waste

This paper reports on the engineering properties and microstructure of concrete incorporating slate waste aggregates generated from roofing slate production in the UK. Various concrete mixtures were designed using different sizes of slate waste as aggregate replacement. Concrete produced with limestone aggregate was used as control. The results showed that concrete produced with limestone aggregate tended to fail predominantly through the interfacial zone between the aggregate surface and the cement paste and mortar, without any observed aggregate fragmentation. In contrast, the concrete made with slate waste aggregate showed signs of failure emanating from both the interfacial zone as well as from the cracking and subsequent fragmentation of the aggregates. The findings show that the concrete made with slate waste aggregates attained compressive strength of 25–30 N/mm2, splitting strength of 2–3 N/mm2 and elastic modulus of 25–32 kN/mm2 thus indicating potential for using slate waste as a replacement for limestone aggregate in most low- to medium-strength engineering applications.

Recycling of metamorphic rock waste in ecological cement

Metamorphic waste can cause much damage to the environment and so the partial substitution of Portland cement with metamorphic rock waste to produce environmentally-friendly cement/concrete has been suggested. In the present study, the pozzolanic reactivity of metamorphic rock waste was investigated and the possibility of the partial replacement of Portland cement blended with rock waste powder was analysed. The results indicate that the compressive strengths of mortar containing slate waste at both early age and after 28 days were generally increased as the slate ratio increased up to at least 15% replacement. The dry shrinkage of mortar with or without rock powder was measured from 3 days up to 56 days. The results show that the replacement of Portland cement with 15% rock waste yielded high pozzolannic reactivity, cost advantages and environmental benefits as a green material.

Marchlyn Mawr additional stored energy project

Marchlyn Mawr is located in North Wales and serves as the upper storage reservoir for the Dinorwig Power Station, which operates a 1728 MW pumped storage scheme. Owing to increasing demands on the existing power generation capabilities within the UK, MWH was commissioned by First Hydro Company to provide a detailed engineering solution that would enable the reservoir level to be raised and provide an additional 1·1 GWh of stored energy within the hydro-electric system. The initial scope of work provided by the Client required raising the reservoir level by 2·5 m. However, detailed flood studies carried out during the feasibility stage demonstrated that by raising the crest by 2·5 m and enlarging the overflow could enable a 3·3 m increase in the operating top water level, thereby increasing the available head for power generation. An insight into the measures taken to satisfy the environmental conditions imposed by the planning application is given, as well as the results of full-scale preconstruction trials that were carried out on site, which resulted in modifications to the final design and construction sequence. The engineering solution involved the construction of a 620 m long retaining wall, raising of the dam crest level using rockfill derived from slate waste, enlargement of the existing overflow structure as well as modifications to appurtenant structures and the extension of the original grout curtain.

Applications of slate waste material in the UK

The potential of using slate waste generated from roofing slate production in the UK in various applications is reviewed and the environmental impact of the stockpile of slate waste is also assessed. The findings suggest that there is potential for using slate waste in many situations, including engineering applications. In order to reduce the environmental impact arising from the quarrying of conventional construction materials, the abundance of slate waste in Wales in particular and the UK in general could be exploited. With associated economic advantages despite reported transportation difficulties, utilisation of this waste stream for most practical and low- to medium-strength engineering applications is feasible and would maximise the use of surplus regional and national industrial wastes and minimise the environmental impact of their disposal.

Unfired clay masonry bricks incorporating slate waste

This paper discusses the potential of using slate waste generated from roofing slate production in the UK in the manufacture of unfired clay masonry bricks. Ground granulated blast-furnace slag activated by lime and Portland cement were used to stabilise Lower Oxford Clay incorporating slate waste in the preparation of laboratory cylindrical test specimens. The specimens were moist cured at room temperature (20±2°C) for between 3 and 90 days before testing for compressive strength. The drying and linear expansion behaviours of the test samples were assessed by means of moisture content measurement (at the age of testing) and linear expansion measurement after soaking the samples in deionised water. The strength of the cement-activated blended mixture was lower than that of the lime-activated mixtures. An environmental comparison of the unfired clay masonry bricks with mainstream construction (fired) bricks shows that the unfired clay bricks have good environmental characteristics over a range of important criteria. These results suggest that there is potential for using activated slag mixtures in the manufacture of bricks for low-cost environmentally friendly housing and energy-efficient masonry wall construction within the UK.

New Ceramic Products from Slate and Aluminium Sludge Wastes

Previous studies had shown that a promising material could be obtained by mixing aluminium-rich sludge with slate powder (with Al2O3:SiO2 molar proportion of 2:1), shaping by uniaxial pressing and sintering at 1300oC, in order both to detoxify the sludge by fixing the metals in a leach-resistant ceramic matrix and to yield a new material from the reactions of the above compounds at high temperature. In view of potential applications, since this material was also found to be inert after leaching tests, a further systematic study, reported in the present paper, was carried out, in order to determine its mechanical properties and discuss them in function of the microstructure. The average values of Vickers hardness HV3 (683), bend strength (126 MPa), Young's modulus (161GPa) and fracture toughness (3.35 MPa.m1/2) are significantly higher than those found for the as sintered slate powders, which is attributed to the increased fraction of α- alumina and reduced content of glassy phase in the microstructure of the material with sludge addition.