Low-grade Clay Research Articles

Use of low-grade kaolinite clays in the production of limestone calcined clay cement

The suitability of two different low-grade kaolinitic clays and limestone locally available in Switzerland to produce a limestone calcined-clay cement at industrial scale was investigated. Firstly, the clays characteristics related to reactivity were presented. Then, the effect of calcined clays on cement performance was explored according to EN 197-5 and EN 197-1 requirements. Finally, the new cement was produced at industrial scale by using a Swiss cement plant equipped with a Lepol kiln for clay calcination and clinker production and used to manufacture 3 different concretes mixes for 3 different environmental exposure classes (EN 206). The concrete mixes were tested for mechanical and durability performance. The results show that the two calcined low-grade clays are suitable to produce a limestone calcined-clay cement classified as CEM II/C-M (Q-LL). Moreover, all the 3 concretes manufactured with the new cement meet the minimum mechanical and durability standard requirements of the corresponding exposure classes.

Performance of limestone calcined clay cement (LC3) incorporating low-grade marine clay

Clay is a globally abundant material and can potentially be used as a cement substitute after calcination. Though kaolinitic clay exhibits notable reactivity, the potential of low-grade clay with relatively low kaolinite content remains underexplored. This study comprehensively analyzed the chemical and mineralogical composition of marine clays at various locations and depths in Singapore, assessing their feasibility for preparing limestone calcined clay cement (LC3). The hydration kinetics and microstructure development of LC3 pastes, incorporating calcined marine clay, were investigated by XRD, isothermal calorimetry, SEM, and MIP. Additionally, a mini-migration test was employed to investigate chloride ion diffusion in LC3 pastes. The results revealed that Singapore marine clays contain relatively low kaolinite content (16–20% by QXRD). Despite a 25% reduction of 28 days compressive strength compared to reference OPC, LC3 samples exhibited outstanding resistance against chloride penetration regardless of kaolinite content (<40%) or replacement level (LC3-70 or LC3-50). The chloride diffusion coefficient (LC3-50) is one order of magnitude lower than the OPC system. Overall, our findings broaden the selection of raw materials for LC3 preparation and underscore the robustness of LC3 to resist chloride penetration, irrespective of variations in the clay's quality or source.

Use of Industrial Waste to Improve the Performance Properties of Ceramic

Industrial waste, with an in-depth study of its resource capacity, physico-chemical and technological properties, is a valuable raw material for construction ceramics. The possibility of replacing high-quality clays in technologies for producing clarified ceramic bricks and effective wall ceramics using high-calcium waste generated during water purification by liming in thermal power engineering, chemical and other enterprises has been established. The obtained physicochemical patterns of formation on their basis of the structure and properties of a ceramic composite provide a scientific basis for the use of typical waste, in these studies, dust from electric precipitators of cement production. The role of aluminum-containing waste generated during the electrolysis of molten aluminum in regulating the technological properties of the masses and firing properties of clinker bricks has been revealed, which allows the use of low-grade clays for its production. Scientific research and recommendations on the use of various industrial wastes not only for the purpose of recycling, but also for the use of their valuable properties associated with the chemical composition, behavior in heat treatment, reactivity, the possibility of strengthening due to the formation of a controlled structure of the material, help slow down the process of decline reserves of high-quality clay raw materials.

Investigation on chloride migration behavior of metakaolin-quartz-limestone blended cementitious materials with electrochemical impedance spectroscopy method

Calcined clay and limestone powder composites offer a viable solution for reducing carbon emissions in building materials by allowing significant cement replacement. However, there is a need for further investigation into their impact on durability, especially for low-grade clays. In this study, different ratios of metakaolin and quartz powder are utilized to simulate various grades of calcined clay, while limestone powder is incorporated as a partial cement substitute. Initially, the influence of metakaolin content on rapid chloride migration was analyzed. Subsequently, various analytical techniques such as free water content, Mercury Intrusion Porosimetry (MIP), X-ray diffraction (XRD)/Rietveld method, and electrochemical impedance spectroscopy (EIS) test were employed to investigate the effects of metakaolin contents on the pore structure, phase assemblage, and electrochemical parameters of the blended cementitious system. The relationship between chloride migration coefficient and free water content, critical pore size, and impedance parameters was established to determine the key indicators for chloride migration. The study revealed that systems with partial metakaolin content demonstrate improved chloride resistance in the blended system, which could be predicted using Rct1 from the EIS test. Furthermore, the inclusion of metakaolin and limestone powder facilitated the formation of Monocarboaluminate (Mc) and Hemicarboaluminate (Hc), leading to the refinement of the pore structure and inhibition of chloride transport within the blended material. This study indicates the potential of low-grade calcined clay to enhance the overall durability of the blended cementitious system while contributing to carbon emissions reduction.

Alkali thermal fusion: A prospective route to enhance the reactivity of low-grade clay and utilize as supplementary cementitious material (SCM)

Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and 29Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction.

Performance of a Single Source of Low-Grade Clay in a Limestone Calcined Clay Cement Mortar

The high kaolinite content of metakaolin makes it valuable to other industries, thereby affecting its availability and affordability for the production of limestone calcined clay cement (LC3). This work presents a study on the potential utilization of low-grade clay in place of pure metakaolin in the preparation of LC3 for mortar formulations. CEM I was partially substituted with calcined clay and limestone by 20, 30, 40, and 50 wt.%. The weight ratio of calcined clay and limestone was maintained at 2:1 for all mixes and the water-to-binder ratio was 0.48. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and isothermal conduction calorimetry were used to study the hydration process and products after 28 days. Mechanical and durability assessments of the LC3 mortar specimens were conducted. LC3 specimens (marked LC20%, LC30%, LC40%, and LC50%) trailed the control sample by 1.2%, 4%, 9.8%, and 18%, respectively, at 28 days and 1.6%, 2.3%, 3.6%, and 5.5%, respectively, at 91 days. The optimum replacement of OPC clinker, calcined clay, and limestone was 20% (LC20%).

Preliminary Study of Low-Grade Clays as Secondary Raw Material for Geopolymer

Preliminary Study of Low-Grade Clays as Secondary Raw Material for Geopolymer

Prioritization of low-grade kaolinite and mixed clays for performance evaluation of Limestone Calcined Clay Cement (LC3): Multi-criteria assessment

Limestone calcined clay cement (LC3) is an emerging ternary binder, while typically only kaolinitic clays have been used or investigated for its production. There is a dire need to scientifically investigate the potential utilization of low-grade kaolinitic and mixed clays. In this study, nineteen different natural clays were examined from various locations in Pakistan, with a focus on clay quarries near cement plants. From the dataset, seven significant criteria were identified: mineral type, and the contents of kaolinite, SiO2, Al2O3, Fe2O3, CaO, and the Al2O3/SiO2 mass ratio. Nineteen clays were characterized using X-ray diffraction, X-ray fluorescence, and thermogravimetric analysis. These clays were then prioritized against the identified criteria using multi-criteria decision-making analysis. After characterizing them, the top ten clays were calcined to evaluate the performance of LC3. A correlation analysis was conducted between the characterization of calcined clays and the compressive strength of LC3. It was revealed that all criteria were positively correlated with compressive strength, except for Fe2O3 and CaO, which showed a negative correlation. The correlation coefficients for Fe2O3 and CaO were − 0.44 and − 0.47, respectively. According to the OPC Type I, incorporating low-grade kaolinite with a composition of 40–55% leads to greater compressive strength gain compared to the standard 42.5 MPa compressive strength of OPC Type I. Even clays with lower grades, ranging from 38 to 41 MPa, can achieve up to 96.5% of the compressive strength of OPC Type I. Therefore, low-grade clays could be incorporated into a ternary binder system to produce carbon-neutral cement.

Initial search for low grade clay in Pakistan for producing LC3 ecofriendly cement

Industrialization has though brought comfort to our daily lives, but it has placed a lot of pressure on the planet’s natural resources, subsequently, it has adversely affected the environment. As the need for cement in the construction sector has grown, it has climbed dramatically globally. Around the world, more than 10 billion cubic meters of concrete are produced each year; it is doubtful that this volume will decrease. A significant expected rise in CO2 emissions is caused by increased cement demand. According to the UN Environment Program, buildings are responsible for up to 41% of global anthropogenic carbon emissions. The primary source of greenhouse gases utilized in the manufacturing of cement is clinker. Due to the unsustainable supply of fly ash, calcined clay appears to be a better Supplemental Cementitious Material (SCMs). Kaolin clay is widely available in Pakistan. The purpose of this investigation is to describe the mineral and thermal characteristics of Pakistani clays by examining their geographic distribution. Clay samples were gathered from 39 different places throughout Pakistan during a field investigation program. X-ray diffraction, X-ray Fluorescence, Reactivity, and thermogravimetric analyses were used to analyze the clay samples’ mineral content and thermal characteristics. This study demonstrates that Pakistan has a substantial amount of kaolin clay reserves close to existing groups of cement plants. Pakistani clays can be utilized as SCM in the production of limestone calcined clay cement (LC3) due to the country’s vast kaolin clay reserves. This study further supports the viability of producing LC3 in the nation by providing a thorough analysis of the cement business, known deposits of qualifying clay, and the country’s cement production process.

Influence of Calcination Temperature and Amount of Low-Grade Clay Replacement on Mitigation of the Alkali-Silica Reaction.

Results of experimental investigation on the mitigation of alkali-silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al2O3 content equal to 26% and SiO2-58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na2Oeq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay.

Production of Supplementary Cementitious Materials (Scm) from Low-Grade Clay Via Alkali Fusion

Production of Supplementary Cementitious Materials (Scm) from Low-Grade Clay Via Alkali Fusion

Influence of calcined medium grade clay on the properties of Portland cement pastes

ABSTRACT In the recent decades, the composition of Portland cements has undergone significant changes related to an increase in the range and content of supplementary cementitious materials following development of composite and multicomposite cements. The development of these binders that meet the requirements of sustainability requires the expansion and adaptation of the mineral resource base of cement industry to the production of low-emission binders with a gradual decrease of resource and energy intensities. Efforts to find the widespread sources of pozzolans providing high reactivity and physical–chemical stability have led to intensive studies on thermally treated clays of various chemical–mineralogical composition and their industrial adoption. Due to scarcity and high cost of kaolin clays, great attention is given to medium- and low-grade clays. This article reports on a study to evaluate the effect of calcined clay with 52% of clay minerals on the properties of fresh and hardened pastes, in particular on the resistance to sodium sulfate and nitric acid attacks. The reaction products assemblage of the blended Portland cement pastes was investigated by XRD and thermal analyses. The hardened Portland cement pastes incorporated with thermally treated clay demonstrated better durability performance compared to reference ones.

Low-carbon cements: Potential for low-grade calcined clays to form supplementary cementitious materials

The use of low-carbon supplementary cementitious materials (SCM), such as calcined clays, to replace cement clinker has been recognized by the Cement Industry to achieve reductions in greenhouse gas emissions. This paper investigates eight low-grade clays, with <20% kaolinite, obtained from different geological formations, that have been calcined to produce potential SCMs. The clays were characterised before and after calcining at 750, 800, 850 and 900 °C, and the mineralogical changes and amorphous phase contents determined. The pozzolanic activity and the strength activity index of the different calcined clays were evaluated. The results show that calcined clays from the Oxford and Ampthill geological formations in the UK can produce SCMs with pozzolanic activity higher than conventional SCMs such as PFA. These clays were rich in illite and smectite and produced ∼60% amorphous phase when calcined at 850 °C. Mortars produced using calcined clays had higher compressive strengths than mortars containing pulverised fuel ash and achieved ∼90% of the compressive strength of 100% Portland cement mortar samples at 28 days. The research demonstrates that low-grade clay resources can be calcined to produce SCMs and that these can be used to form cementitious materials with reduced total associated CO2 emissions.

Study of performances and microstructures of mortar with calcined low-grade clay

This paper studied the effect of calcination temperatures (600–900 °C) on physical characteristics and microstructure changes of low-grade clay containing 14.6% kaolinite and 17.8% 2:1 clay mineral. The pozzolanic activity of calcined low-grade clay as a supplementary cementitious material was evaluated using strength activity index and relative strength index. The results show that the kaolinite transformed from crystalline phase to amorphous metakaolin phase at 600 °C, while the particle size of clay first increases and then decreases. The optimal calcination temperature is found between 700 and 800 °C, whereas the optimal cement replacement level is 10–20 wt%.

A Novel Calcium Oxalate/Sepiolite Composite for Highly Selective Adsorption of Pb(II) from Aqueous Solutions

Synthesizing functional nanomaterials from naturally abundant clay has always been of vital importance for resource utilization, however, the lack of new methods to effectively utilize low-grade clay presents a significant challenge. Herein, a calcium oxalate/sepiolite nanocomposite (SMN-x) was prepared by using the water bath heating method to convert the associated calcium carbonate in low-grade sepiolite into calcium oxalate. The developed composite was subsequently used to remove Pb(II) from the aqueous solutions. The SMN-3 adsorbent prepared by heating in a water bath at 90 °C for 3 h (with a high specific surface area of 234.14 m2·g−1) revealed the maximum Pb(II) adsorption capacity of 504.07 mg·g−1 at pH 5, which was about five times higher than that of sepiolite (105.57 mg·g−1). Further, the SMN-3 adsorbent possessed a much higher selectivity for Pb(II) as compared to the other metal ions. Moreover, the residue was noted to be stable and safe. The adsorption kinetics and isotherms conformed to the quasi-second-order kinetic and Langmuir models. During the adsorption process, ion exchange was noted to the main mechanism, however, it was also accompanied by electrostatic attraction. This study provides a novel strategy for the sustainable development of simple and efficient adsorbents by utilizing low-grade clay minerals.

The effect of pre-treatment and curing temperature on the strength development of alkali-activated clay

This paper reports the strength development in alkali-activated clay (AAC) synthesised from untreated and calcined low grade clays. The effects of clay calcination and the temperature adopted in different curing regimes on the mechanical properties of AAC were studied from a microstructural viewpoint. Solid-state MAS NMR, FTIR, EDS, and TEM imaging were used for the microstructural studies. Calcination of the clay resulted in an increase in the 7-day compressive strength of AAC from 31.7 MPa to 47.8 MPa. 29Si MAS NMR results indicated that ratio of Q4(2Al) percentage to Q4(4Al) percentage correlates positively with the compressive strength. Curing the AAC at higher temperatures resulted in higher strength, but there was a conflict between strength development due to ongoing polymerisation and strength deterioration due to post-curing crack propagation. FTIR results indicated the formation of a more polymerized structure and stronger bonds in the AAC as a result of calcination. In addition, FTIR showed a higher Si–O bond strength in AAC cured at a higher temperature, which positively correlated with the compressive strength of the specimens. EDS and TEM results revealed the presence of a silicon-rich phase in AAC synthesised from the untreated clay. This sodium silicate gel exhibited poor hydrolytic stability which could result in long term durability issues.

Low-Grade Clay as an Alkali-Activated Material

The potential application of alkali-activated material (AAM) as an alternative binder in concrete to reduce the environmental impact of cement production has now been established. However, as the production and availability of the primarily utilized waste materials, such as fly Ash and blast furnace slag, decrease, it is necessary to identify alternative materials. One such material is clay, which contains aluminosilicates and is abundantly available across the world. However, the reactivity of untreated low-grade clay can be low. Calcination can be used to activate clay, but this can consume significant energy. To address this issue, this paper reports the investigation of two calcination methodologies, utilizing low-temperature and high-temperature regimes of different durations, namely 24 h heating at 120 °C and 5 h at 750 °C and, and the results are compared with those of the mechanical performance of the AAM produced with untreated low-grade clay. The investigation used two alkali dosages, 10% and 15%, with an alkali modulus varying from 1.0 to 1.75. An increase in strength was observed with calcination of the clay at both 120 and 750 °C compared to untreated clay. Specimens with a dosage of 10% showed enhanced performance compared to those with 15%, with Alkali Modulus (AM) of 1.0 giving the optimal strength at 28 days for both dosages. The strengths achieved were in the range 10 to 20 MPa, suitable for use as concrete masonry brick. The conversion of Al (IV) is identified as the primary factor for the observed increase in strength.

Alkali activation of mechanically activated low-grade clay

This article reports the results of an investigation into the efficiency of mechanical activation to increase the reactivity in alkali activated mortar synthesized from low-grade clay. Mechanical activation significantly changed the structure of clay, increasing the specific surface area, and decreasing the particle size. The 7-day compressive strength of mortar synthesized from untreated clay was 31.7 MPa, which increased to 35.3 after 4 h milling. A further increase of grinding time to 8 h did not result in any increase in compressive strength which is attributed to a decrease in the workability. However, the extent of reactivity did significantly increase as determined from solid-state MAS NMR, FTIR, and EDS analyses. Solid-state MAS NMR results revealed the increased formation of Q4(2Al) silicon sites, which is correlated with improved reaction. Furthermore, the EDS and FTIR analysis results indicated greater incorporation of aluminium into the matrix structure with increased grinding time.

Calcined Low-grade Clays as Sources for Zeolite Containing Material

The continuous development and expansion of a raw material base in response to increasing environmental and technical requirements for most consumable commodities are crucial for the sustainable development of resource- and energy-intensive materials and technologies. As the sources for alkali-activated cements and zeolites, recent studies have reported the suitability of applying calcined clays with various chemical compositions, percentages, and constituent clay minerals and secondary minerals. In this article, the results of a feasibility study on the alkali activation of low-grade clays with 7.26 % montmorillonite/chlorite and 23.14 % kaolinite/montmorillonite minerals are reported. The 6M NaOH activation of clays thermally treated at 700 °C results in the formation of a hardened paste with a compressive strength of up to 5 MPa, with an N-(A)-S-H binder gel and zeolite Na2Al2Si2.5O9∙6.2H2O being the main reaction products.

Geopolymer synthesis using low-grade clays

Due to the large contribution of cement production towards CO2 emission and rising concerns regarding climate change, substitution with alternative binders has become an established alternative to improve sustainability. Aluminosiliceous polymeric materials, known as geopolymer or alkali activated materials, have been proven to achieve a performance as good as and even superior to ordinary Portland cement (OPC). Various source materials have the potential to be used for the geopolymer synthesis depending on the local availability, among which fly ash, slag, and metakaolin have received most attention. A less established alternative is low grade clay, whether as the natural clay or the waste of construction work. These have the potential for geopolymer production due to their composition and abundance worldwide. However, due to the impurities present in these low-grade clays and slower dissolution rates, the synthesised geopolymers generally display lower mechanical performance. In this research, four different clays collected form construction sites in Melbourne, Australia, were characterised, and the optimum clay selected based on the amorphous content, specific surface area, and fineness. Furthermore, a relatively low energy-demand calcination regime was applied to the chosen clay, 550° C for 1 h. For the untreated clay-based geopolymer, a 7-day compressive strength of nearly 32 MPa was achieved, which increased to approaching 50 MPa after calcination at 550° C. A range of microscopy techniques, EDS, XRD, XRF, zetametry, 27Al MAS NMR, and computerised tomography were applied to characterise the microstructure and reaction kinetics of the synthesised geopolymer.