Granite Sludge Research Articles

Preparation, pore structure and properties of uniformly porous glass-ceramics sintered from granite powder using SiC@SiO2 foaming agent

Granite sludge produced during the processing of granite blocks should be efficiently recycled for environmental protection and as a sustainable resource. In this work, porous glass-ceramics were prepared by stepwise sintering of granite powder using core-shell SiC@SiO2 foaming agent. The SiC and SiC@SiO2 foaming agents were compared in terms of the sintering and foaming behaviors of the powder compacts by thermal expansion, thermogravimetry and mass spectroscopy. The foaming agent and foaming temperature were investigated to study their effects on the pore structure and properties of the porous glass-ceramics. The SiO2 shells of the SiC@SiO2 particles inhibited the oxidation of the SiC cores and the release of CO2 at the early stage of the sintering process, thus preventing pore coalescence and increasing the densification and specific strength of the sintered glass-ceramics. As the foaming temperature increased, the porous glass-ceramics exhibited a linear relationship between pore size and foaming temperature, and the specific strength first increased and then decreased due to pore coalescence and reduced crystallinity. Furthermore, the linear relationship between thermal conductivity and porosity indicates a closed pore structure, as demonstrated by computed tomography. At a foaming temperature of 1220 °C, the porous glass-ceramic has a porosity of 50.1 %, a specific strength of 16.6 kN⋅m/kg and a thermal conductivity of 0.747 W/(m⋅K). Numerical simulation confirms that lightweight glazed glass-ceramics have potential applications in energy-efficient building tiles.

Effect of MgO addition on the structural evolution, crystallization and properties of self-glazed ceramics sintered from granite sludge

Recycling of granite sludge has both economic and environmental benefits. In this paper, high glossiness self-glazed ceramics were prepared from granite sludge with the addition of TiO2, Ca(OH)2 and MgO by combining two-step sintering and low-temperature crystallization. The effect of MgO addition on the phase evolution, crystallization and properties of the glazed ceramics was studied to reveal its role in the diopside precipitation. With increasing MgO content, the reduced glass viscosity accelerates the dissolution of quartz and anorthite into the liquid glass phase, resulting in a decrease in flexural strength above 1 % MgO. Meanwhile, the addition of MgO increases the non-bridging oxygen to lower the glass transition temperature. The increase in the Al/Si ratio of the glass phase and the mixed alkaline earth effect contribute to an increase in the crystallization temperature. After thermal treatment at 950 °C, the precipitated diopside increases the crystallinity of the glazed glass-ceramic from 6.4 % to 19.3 % at 3 % MgO, resulting in a surface glossiness of 99.7 GU and a flexural strength of 64.1 MPa. High glossiness self-glazed ceramics with an aesthetic appearance could be used in decorative building tiles for scalable utilization of granite sludge.

Influence of Ca(OH)2 modification on the pore structure and properties of porous glass-ceramics stepwise sintered from granite sludge

The utilization of granite sludge offers significant economic and environmental advantages. This study focuses on preparing porous glass-ceramics from Ca(OH)2-modified granite sludge through a two-step sintering process comprising dense sintering and high-temperature foaming, with the addition of 1 % SiC powder as a foaming agent. The impact of foaming temperature and Ca(OH)2 addition on the structure, compressive strength, specific strength, and thermal conductivity of the porous glass-ceramics is examined. Incorporating the Ca(OH)2 modifier reduces the glass's viscosity and effectively eliminates micropores on the pore walls. The former promotes foaming and increases porosity, while the latter increases the specific strength of porous glass-ceramics. Increasing both the foaming temperature and the Ca(OH)2 concentration reduces glass viscosity and promotes mineral dissolution, facilitating the foaming process. However, the specific strength of the porous glass-ceramics initially increases before decreasing due to pore coalescence and excessive mineral dissolution. Theoretical evaluations of compressive strength and thermal conductivity indicate that porous glass-ceramics possess a closed-cell pore structure. Porous glass-ceramic made from granite powder containing 3.5 % Ca(OH)2 and foamed at 1240 °C exhibits an apparent density and porosity of 0.73 g/cm3 and 67.1 %, respectively. The compressive strength and thermal conductivity are 14.2 MPa and 0.422 W/(m·K) respectively, with a peak specific strength of 19.4 kN·m/kg. This innovative process enables the scalable recycling of granite sludge into energy-saving building materials.

Recycling of granite sludge for the preparation of high‐strength glazed glass‐ceramics using stepwise sintering

AbstractThe reutilization of granite sludge generated in granite cutting and processing possesses economic and ecological benefits. In this study, high‐strength glazed glass‐ceramics were prepared entirely from granite powder using dense sintering and instantaneous glaze firing. The densification and glaze formation are clarified in terms of phase evolution to study their effects on the flexural strength and surface glossiness of the glass‐ceramics. The milling process promotes particle refinement and the removal of colored minerals, thus increasing the powder whiteness and sinterability. After dense sintering at 1100°C, instantaneous glaze firing at high temperatures decreases the flexural strength while greatly increases the surface glossiness of the glass‐ceramics due to the dissolution of quartz and feldspars in the liquid phase. After the acid‐leached powder was densely sintered and fired with a rapid heating of 50°C/min to 1300°C, the pinhole‐free glazed glass‐ceramic has a flexural strength of 112.5 MPa and a surface glossiness of 54.7 GU (glossiness unit), meeting the quality requirements of the bright glazed tiles in the market. The stepwise sintering process provides a simple processing route for recycling granite sludge into decorative construction tiles and high‐temperature glazes, promising the scalable and value‐added utilization of granite sludge.

Manufacturing ceramic foams from granite sludge

Manufacturing ceramic foams from granite sludge

Laboratory investigation on the fracture toughness (Mode I) and durability properties of eco-friendly cement emulsified asphalt mortar (CRTS II) exposed to acid attack

Cement Emulsified Asphalt Mortar (CEAM) has gained prominence as a vital material for its energy and noise damping properties between the concrete roadbed and track slab in a high-speed railway system. Therefore, it is evident that CEAM properties need to be better understood and optimized. Since cracking caused by traffic loading and atmospheric conditions is one of the primary causes of failure in CEAM, addressing this issue is of great importance. Furthermore, there is a growing need for more environmentally friendly and durable CEAM due to the environmental impact of cement production in the form of greenhouse effect. The objective of this study is to assess the impact of partially replacing cement content in CEAM Type II (CRTS II) specimens with pozzolanic materials such as silica fume, metakaolin, and granite sludge to investigate how these pozzolans affect the fracture toughness (Mode I) performance under both normal (water curing) and sulfuric acid exposure conditions with the main focus on evaluating the pozzolans ability to resist acid attack from a fracture toughness perspective as the research novelty. For this purpose, specimens containing pozzolans at 5 %, 10 %, and 15 % substitution level (by weight of cement) were subjected to Semi-Circular Bending (SCB) test both under normal and exposure to 5 % sulfuric acid solution conditions. Moreover, water absorption test was conducted on specimens in normal condition as a durability index. The test results of this study revealed that substitution of these pozzolanic materials enhanced the fracture toughness in normal condition. Specifically, at a 10 % substitution as the optimal level, silica fume and metakaolin resulted in 18 % and 15 % increase in fracture toughness performance compared to the control specimen in normal condition. However, granite sludge exhibited almost the same performance as the control specimen at 5% substitution as its optimal level. In acid exposure condition, the detrimental effect of acid on the fracture toughness performance of specimens was reduced by 61 %, 55 % and 13 % for samples containing silica fume, metakaolin and granite sludge at 15% substitution level, respectively. Furthermore, water absorption test results showed that inclusion of silica fume and metakaolin at a substitution level of 15 % results in 56 % and 47 % reduction in water absorption compared to the control specimen, respectively, while for granite sludge, it was almost the same as control specimen. These results were also confirmed by SEM studies. Since the use of these pozzolans as cement substitution not only improves the fracture toughness in normal condition but also provides protection against acid-induced degradation, this study contributes to the development of a more durable and environmentally friendly CEAM.

Evaluation of Properties for Making of Bricks by Using Granite Sludge Powder

Numerous issues arise from the discharge of waste materials. The primary issues are the spot involved by locales of capacity, significance of expenses and the natural effect. The primary objective of this preliminary work is to investigate the possibility of using stone waste as a substitute for raw materials in the production of granite sludge bricks. The exhibition of the Rock ooze block's compressive strength and a correlation of it with the ordinary dirt blocks. Clay,water,sand ,fly ash,cement, and other components make up granite sludge brick. Due to its lower cost and higher compressive strength in comparison to other bricks, its wides preaduse may become an important criterion for evaluation. Granite sludge bricks have been the subject of numerous experiments, and the results indicate that they lack compressive strength. As a result, numerous tests on the granite sludge brick's strength using various additional materials were carried out.These various additions might include fly ash, clay, cement, s and, and soon, the alterations ingranitesl udge bricks' compressive strength caused by these various additional materials.The granite bricks have a moisture content of 20% and measure 22 cm by 10 cm by 7 cm. Hence we involved a modest material for the streng thin rock ooze block. Where they have extra pieces in development, so we involved them in mud blocks. Granites ludge bricks performed better than conventional bricks, as demonstrated by the findings. Clay was added to the mixture in weight amounts of 10%,20%,30%,40%, and 50%.Test for water absorption and compressive strength.

Viability of bulk utilization of granite sludge powder (GSP) to enhance the geotechnical behavior of expansive soil

Granite blocks are cut, ground, and polished in the processing industries to achieve the desired dimension and texture. As a by-product of this process, finely powdered granite sludge powder (GSP) is generated. Over the last few decades, extensive research has been conducted in the field of using various industrial by-products to enhance the geotechnical characteristics of poor soils, thereby benefiting both the environment and the economy. The current study seeks to determine whether granite sludge powder can improve the geotechnical properties of expansive soils and be reused in pavement applications. Thus, the effect of different concentrations of granite sludge powder (0%, 5%, 10%, 20%, 30%, and 40% of the dry weight of soil) on the index and engineering properties of black cotton (BC) soil is evaluated. The study reveals that, with addition of up to 40% granite sludge powder to untreated natural expansive soil reduced free swell, Atterberg limits, and optimum moisture content. Whereas the engineering properties such as UCS, dry density, and CBR improved with the addition of GSP up to 30% and reduced thereafter. The maximum CBR value of 19.8 was obtained at 30% GSP concentration relative to the weight of dry soil. According to the test results obtained, granite sludge powder up to 30% can improve expansive soils geotechnical properties and could be used in subgrade applications for low volume roads.

Technical, Environmental, and Cost Assessment of Granite Sludge Valorisation

The granite sludge (GS) produced during block sawing can be exploited as alternative raw material in ceramic and concrete industries. Based on the case study of a Portuguese granite processing plant, this work analysed, by experimental tests and Environmental and Cost Life Cycle analyses, the feasibility of GS valorisation as a substitute (i) for feldspar in a ceramic paste and (ii) fine–medium inert filler in structural concrete. The results demonstrated that both the valorisation pathways are more advantageous than GS landfilling. Due to granulometric, mineralogical composition and shrinkage, GS can substitute feldspar in sandstone tiles or tableware products, although its tinting effect can limit noble whitish ceramic applications. In structural concrete mixes, 5% w/w GS instead of fine inert filler reduces the compressive strength and increases the water:cement ratio. The GS generates lower environmental impacts as a substitute for inert filler than as a substitute for feldspar in most of the impact categories analysed, even though the latter valorisation pathway provides higher benefits in Climate Change and the Depletion of Fossil resources, Water, and Ozone. If no monetary value is recognised for GS valorisation by the market, the sustainability of GS life cycle cost decreases when compared to its landfilling.

Low-cost, highly-performance fired clay bodies incorporating natural stone sludge: Microstructure and engineering properties

The industry of ornamental stones results in an accumulation of huge amounts in millions of tons of low-cost stone wastes in a very fine state. These stone wastes, particularly granite wastes, are considered a source of feldspar and quartz minerals, that are the essential components for ceramic bodies industry. The current study aims at studying the potential use of granite stone wastes (GSW), as a source of quartz, feldspars, in addition to some clay minerals, in preparing low cost, highly performance fired clay bodies in regard with engineering properties and microstructure investigation. To achieve this goal, the chemical, mineralogical, thermal, and physical characterization of the raw materials using XRF, XRD, TG/DSC, and BET were carried out. Six formulated batches (B0, B1, B2, B3, B4, B5) using different proportions of granite waste (0, 10, 20, 30, 40, 50%) were prepared and fired at different temperatures (1000, 1050, 1100, 1150, 1200, 1250 ºC). The green and fired granite – modified clay bodies were measured for linear shrinkage (DLS, FLS), density, absorption, porosity, compressive strength, and microstructure features (SEM/EDAX). The results showed that the granite wastes are composed mainly of feldspar (albite) and quartz and revealed high percentages of fluxing oxides (CaO, Fe 2 O 3 , Na 2 O, K 2 O). An improvement in the engineering properties of the fired granite - modified clay bodies up to 50% replacement and 1200 ºC firing temperature. The maximum compressive strength and density values were achieved at 40% granite addition for (B4) by 311.92 MPa and 2.48 g/cm 3 ; respectively, with 1.7% water absorption and 8.68% firing linear shrinkage values. The fired clay bodies incorporating granite sludge wastes fulfilled the acceptable ranges for the medium water absorption values (3-10%) as recommended by the international standard (ISO 13006) for use as ceramic tiles. • Manufacturing of low- cost fired clay bodies using granite sludge wastes. • An observable reduction in drying linear shrinkage up to 50% granite sludge wastes • A remarkable enhancement in engineering properties using up to 50% granite sludge wastes replacement. • A significant reduction in the firing linear shrinkage up to 50% wastes addition and 1200 ºC firing temperature • A remarkable increase in compressive strength up to 1200 ºC firing temperature and 40% waste addition

The feasibility of recycling marble & granite sludge in the polymer-modified cementitious mortars Part A: In polymer-modified cementitious adhesive mortar

In the present scientific article, a potential assessment and feasibility study of the recycling process of marble and granite sludge into the system of pre-packed polymer-modified cementitious mortar products has been investigated instead of being disposed of or landfilled. Therefore, several polymer-modified mortar formulations were designed to explore the inclusion effect of marble and granite sludge waste on the overall performance of the prepared mortar formulations in the application area of the polymer-modified cementitious adhesive. In this work, starting raw materials and hardened mortar specimens (28 days) of the prepared mortar formulations were well-characterized by different scientific techniques, including X-ray fluorescence for chemical oxides composition, X-ray diffraction for mineral phases composition Fourier-transform infrared (FTIR). To achieve the study's goals, different percentages of marble and granite sludge were incorporated into the prepared mortar formulations in the range of 0%, 5%, 10%, 15%, 20%, 25%, and 30% to replace the used silica sand in each formulation. The results showed that the marble and granite sludge waste is mainly composed of calcite and quartz minerals, with an average particle size of 4.86 µm. The results also showed an improvement in the workability, performance, and adhesion strength of the prepared polymer-modified cementitious adhesive mortar formulation upon using the optimum sludge addition percentage. Moreover, the experimental results show that the compressive and flexural strength of the prepared mortar formulations were also enhanced by increasing the sludge content.

Synthesis and Grafted NH2-Al/MCM-41 with Amine Functional Groups as Humidity Control Material from Silicon Carbide Sludge and Granite Sludge

Mesoporous Al/MCM-41 was synthesized by extracting silicon carbide sludge and granite sludge as the sources of silicon and aluminum. Different concentrations of aminosilane (2.5, 5, 7.5 vol.%) were used to reflux the grafted NH2-Al/MCM-41 with amine functional groups (NH2-Al/MCM-41). The physical and chemical characteristics were analyzed. The results confirmed that silicon carbide sludge and granite sludge can effectively synthesize Al/MCM-41 with low cost and environmental protection. Reflow grafted amine functional groups can effectively improve the surface properties of NH2-Al/MCM-41. The moisture adsorption and desorption capacity of grafted NH2-Al/MCM-41 with amine functional groups was also studied. Based on moisture adsorption and desorption capacity, the surface properties of NH2-Al/MCM-41 were studied. When 5 vol.% of NH2-Al/MCM-41 amine functional groups is added, the moisture adsorption and desorption capacity is best. When the relative humidity = 95%, the equilibrium moisture content is 39.4 kg/kg, which complies with the standard of Japanese Industrial Standard (JIS A 1475). Therefore, the use of waste derived from the industry to replace expensive commercial materials was simple and environmentally friendly, and the grafted NH2-Al/MCM-41 with amine functional groups can be utilized in multiple applications, particularly as moisture regulation materials in building engineering.

Utilization of granite sludge for production of cordierite ceramics by direct coagulation casting

In this work, an attempt to produce cordierite ceramics from granite sludge waste, talc and alumina was performed by direct coagulation casting process. To optimize the conditions for cordierite formation, three mix-compositions were firstly prepared by processing the starting materials in different conditions. The first mix was prepared by firing the mix of granite sludge, talc and alumina up to 1300 °C while the second and third mixes were fabricated by firing alumina and talc at 1300 °C or 1350 °C, respectively, then the granite sludge was added. Both batches were fired at different temperatures. According to the percentage of formed cordierite, the third mix was selected to be solidified by direct coagulation casting method followed by sintering at different temperatures. The casted cordierite was examined by thermal analysis while the sintered bodies were tested for their physical, mechanical and electrical properties. The results indicated that the pre-heating of alumina and talc at 1350 °C (third mix) enhanced the formation of cordierite and some amounts of spinel. For the casted sintered specimens, the porosity was decreased with increasing the sintering temperature. Also, there was an increase in compressive strength for the samples sintered up to 1250 °C. The dielectric constant values were varied between 4.5 and 5.89 while the dielectric loss was varied between 2 × 10−3 and 7 × 10−3, at room temperature.

The effect of sintering on the properties of magnesia-granite sludge ceramics shaped by temperature-induced forming

Recycling waste materials have attracted considerable attention owing to the increased interest in depressing the negative impact on the environment. The present work investigates the effect of increasing the granite sludge-waste materials from granite manufacture-on the physical, mechanical and electrical properties of magnesia ceramics. The temperature-induced forming (TIF) method is used to shape magnesia-granite sludge ceramics. The sintered ceramics are characterized by XRD and SEM, in addition to measuring the bulk density, apparent porosity, linear shrinkage, microhardness, and electrical resistivity. Sintering of magnesia-granite bodies resulted in the formation of periclase-forsterite ceramics. The XRD results show that the forsterite phase increases reaching 78% at 40 wt% granite. The increase in granite sludge from 10 to 40 wt% increases the bulk density from 1.86 to 2.69 g/cm3 and the apparent porosity decreases from 40 to 15%, respectively. Microhardness is improved by increasing the granite sludge wt% reaching 7.9 GPa. The microstructure of the formed periclase-forsterite is versatile with a rhombohedral structure for periclase and a flower structure for forsterite. The forsterite phase is formed by the diffusion of granite sludge into the formed periclase.

Investigation of using granite sludge waste and silica fume in clay bricks at different firing temperatures

ABSTRACT A large amount of granite sludge waste (GSW) is produced during the granite quarry processing that has a negative impact on the environment. The main aim of this study to investigate the possibility of partial replacement of brick clay by GSW and silica fume (SF) due to the similarity of the mineralogical composition of GSW and clay. Five different series of clay to SF to GSW proportions were tried, which were (70:5:25), (70:10:20), (70:15:15), (70:20:10), (70:25:5) by weight. These bricks were mixed and molded in the dimensions of 50 x 50 x 50 mm3 and then fired at three different temperatures (700°C, 750°C and 800°C). The properties of green and fired bricks were studied as a function of waste percent. The vitrification parameters, such as compressive strength, water absorption, saturation coefficient, apparent porosity and bulk density, were determined and compared with ASTM standards. The results showed that the water absorption and compressive strength is very sensitive to the temperature changes than waste addition. It is possible to produce bricks with the highest compressive strength of 18.5 MPa at firing temperature 700°C using 70% clay, 25% SF and 5% granite sludge waste with water absorption of 18.2% and saturation coefficient 0.9 to meet the standard specification ASTM C216 grade for moderate weathering that are recommended for environmental and economic benefits.

Sulfate Resistance in Cements Bearing Ornamental Granite Industry Sludge.

This study explores the effect on sulfate resistance of the use of ornamental granite industry waste as a supplementary cementitious material (at replacement ratios of 10% and 20%) in cement manufacture. The present paucity of scientific knowledge of the behaviour of these new cements when exposed to an external source of sulfates justifies the need for, and the originality of, this research. After characterising the waste chemically and mineralogically, cement paste specimens were prepared in order to determine the durability of the newly designed eco-cements using Köch–Steinegger corrosion indices. The new hydration products, which might induce microstructural, mineralogical, or morphological decay in the specimens, were also analysed by comparing the samples before and after soaking in a sodium sulfate solution for different test periods. Respect to the results, the damage to pastes bearing 10% granite sludge (GS) is the same as observed in OPC, whilst the former exhibit a higher Köch-Steinegger corrosion rate (1.61) than both OPC and OPC+20GS. Soaking the pastes in sodium sulfate induces matrix densification due to ettringite formation and gypsum precipitation in the pores. Further to those results, at an optimal replacement ratio of 10%, these alternative, eco-friendlier materials can be used in the design and construction of non-structural cement-based (mortar or concrete) members exposed to an external source of sulfate.

Behaviour of fresh and hardened concrete incorporating marble and granite sludge as cement replacement

The present article aims to study the effect of using marble and granite sludge, resulting from ornamental stone industry, as cement replacement on the properties of fresh and hardened concrete mixes. The chemical analysis, mineralogical composition, and physical properties of marble and granite sludge as well as OPC were measured using XRF, XRD, BET, and BT techniques. The experimental work has been conducted through two steps, the first step included preparation of nine mixes of blended cement pastes, and the second step included preparation of nine concrete mixes. The two steps were prepared using different proportions of marble and granite sludge substituting for cement binder by 10%, 20%, 30%, and 40% in addition to the control mixture with 0% sludge. The initial and final setting times of the blended cement pastes were determined using Vicat test. The workability of the fresh concrete mixes was determined using slump test. The physico-mechanical properties of all hardened concrete mixes such as water absorption, porosity, density, compressive, flexural, and splitting tensile strengths were measured at different curing ages starting with 7 days passing through 28 days and ending with 56 days. Regarding the durability performance of the hardened concrete mixes, various tests such as water penetration depth and chloride ion penetration were measured at 28 days of curing, and the acid attack test was determined at 7, 28, and 90 days of exposure after normal curing at 28 days.The results clearly revealed that there is an improvement towards the water penetration depth and sulphuric acid attack resistance at all replacement levels more than the control mixture. Regarding the other properties such as water absorption, density, strengths, and chloride penetration, there is insignificance decline up to 20% marble and granite sludge compared with the control mixes. It is recommended to utilize both marble and granite separately up to 20% as cement replacement in concrete making without adversely impact on its the mechanical or durability performance. The results of all hardened concrete mixes are in compatible with the requirements of concrete bricks and concrete paving units in terms of water absorption and compressive strength.

Performance of self-compacting mortars with granite sludge as aggregate

Waste produced in the extraction and processing of granite stone severely damages the environment when it is deposited in landfills. This research aims to use granite sludge as an alternative to conventional aggregates (natural sand and siliceous filler) in self-compacting mortars production. In a previous stage, the granite sludge was characterised by chemical and mineralogical composition, specific gravity, scanning electron microscopy, particle size distribution and environmental evaluation by leaching test. Subsequently, three replacement percentages (0%, 20% and 40%) by volume of conventional aggregate with granite sludge were evaluated for their self-compactability properties. Compressive and flexural strength at 7, 28 and 91 curing days were measured. The mineralogical phases using X-ray diffraction techniques, microstructure by mercury intrusion porosimetry, shrinkage and mass loss, water absorption by capillarity, water absorption capacity, bulk and skeletal density, open porosity for water and wettability of hardened mortar specimens were all studied. The granite sludge incorporation did not affect the cement hydration phases, although the microstructure of the self-compacting mortars was slightly modified. The morphology of the granite sludge particles reduced the filling effect of pores and required a slight increase in the w/c ratio to maintain the self-compacting parameter. This fact justifies the slight increase in porosity, the lower bulk density and the slight decrease in the mechanical strength of mortars with granite sludge. The durability properties were also slightly affected compared to the self-compacting reference mortar. From an engineering point of view, the results show the feasibility of incorporating up to 40% of granite sludge in self-compacting mortar. This study explores a sustainable alternative to conventional aggregates in the manufacture of self-compacting mortar by reducing the consumption of raw materials and avoiding granite sludge landfill.

Energy performance and calorimetric behaviour of cements bearing granite sludge

Blending supplementary cementitious materials with portland cement is one of the current strategies for producing more eco-efficient binders by lowering the energy consumption and CO2 emissions intrinsic to OPC manufacture. The effect of such additions on heat of hydration and energy performance is a subject of particular interest, for higher heat may reduce the service life of a concrete structure, whilst energy consumption per tonne of binder or megapascal may prove not to be energy-efficient. This paper explores the energy performance of granite sludge (GS) as an active addition to clinker and the effect of this by-product on heat of hydration and eco-efficiency. The findings show that maximum heating and total heat released are lower in the additioned than in the conventional material, with the difference widening at higher replacement ratios. At 35% GS, maximum heating was 36% lower than in OPC and total heat released 24% lower. Optimal energy performance is observed at ratios of 15% to 30% (both inclusive), with the experimental materials requiring less energy (−1.6 kW·h·t−1/MPa – 0.8 kW·h·t−1/MPa) than ordinary cement per megapascal (MPa) of strength. Cements with 15% to 30% granite sludge are consequently eco-efficient. With 15% GS they can be classified as ordinary (>270 J/g at 41 h), with 20% to 30% as low heat cements (<270 J/g at 41 h) and with 35% as very low heat cements (<220 J/g at 41 h).

Activation temperature-mediated mineralogical transformations in slate quarry sludge: Pozzolanic properties

Ornamental stone quarries generate huge volumes of waste. The valorisation of such waste as possible additions (supplementary cementitious materials) to cement would contribute to the implementation of circular economy criteria in the construction industry. The study reported here constitutes a first-time analysis of the pozzolanicity and morphological and microstructural changes induced in slate quarry sludge by thermal activation. The findings showed that thermal activation enhanced waste pozzolanicity, which at later ages was slightly higher than found in granite sludge and lower than in silica fume and fired clay-based materials. According to the Frattini test, the materials resulting from blending 20% or less of this waste cannot be regarded as CEM IV pozzolanic cements. A microstructural study revealed the surface formation of C-S-H gels in the slate sludge/Ca(OH)2 system, which was more intense when the waste was activated. According to the statistical analysis performed, three factors -time, activation temperature and replacement ratio-, significantly affected slate sludge pozzolanicity.