Calcined Clay Research Articles

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.

Hydration behaviour of limestone-calcined clay and limestone-slag blends in ternary cement

The effect of kaolinitic calcined clay and slag on the hydration of limestone-containing ternary blended cements was investigated. The effect of alumina from different sources of SCMs was considered to activate the formation of carboaluminates. Ternary blends with 50% ordinary portland cement clinker, 45% blends of limestone calcined clay (LC2) in 1:2 blend and slag limestone blend (SLS) in 2:1 mix proportion with 5% of gypsum were studied. The hydration behaviour was analysed based on cement mortar compressive strength, heat of hydration using an isothermal calorimeter and bound water measured using thermal gravimetric analysis (TGA). In addition, the degree of hydration of clinker phases and the composition of calcium - alumino - silicate - hydrate (C-A-S-H) gels forming in two different systems were compared on 90 days hydrated samples analysed using X-Ray diffractometry (XRD) and scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDX) respectively. The results show a rapid early strength development in limestone calcined clay cement blend (LC3) but a lower clinker hydration in comparison with slag limestone cement blend (SLSC) at later ages. In both the cement blends the formation of hemicarboaluminate (Hc) and monocarboaluminate (Mc) was confirmed at 90 days, but the conversion of Hc to Mc was higher in SLSC. Results further confirmed a lower degree of hydration and higher alumina incorporation in the C-A-S-H gel in the LC3 comparison to SLSC. The presence of calcium hydroxide was also confirmed in the SLSC blend due to the hydraulic nature of slag that supported the later age conversion of Hc to Mc as not seen in LC3.

Enhancement of pozzolanic activity of calcined clays by limestone powder addition

The influence of limestone powder addition on pozzolanic reactivity of calcined clays were investigated. Two clays containing kaolinite and halloysite in their compositions were obtained from different deposits in Turkey and physical, mineralogical, and morphological properties of the raw and calcined clay were characterized. Pozzolanic reactivity of calcined clays with and without limestone powder addition was then examined by means of lime consumption in lime-calcined clay pastes and their isothermal calorimetry as well as strength activity index test. Limestone powder addition enhanced the pozzolanic reactivity of calcined clays by increasing lime consumption and presenting higher heat of reaction released during pozzolanic activity. Limestone addition also provided benefits of reduced water requirement and increased strength activity for calcined clays. Improvements in pozzolanic reactivity and strength activity of calcined clays with limestone powder addition were attributed to nucleation effect provided by limestone particles and also formation of carboaluminate phases during pozzolanic reaction.

Use of kaolinite clays in development of a low carbon MgO-clay binder system

Magnesium oxide based cements may provide a promising alternative to the conventional Portland cement in many applications. This study investigates the feasibility of using calcined kaolinitic clay to produce an MgO binder. The MgO-based binder were prepared using a low kaolinite content clay and metakaolin and were compared with a silica fume system. Implications of the addition of magnesium carbonate in the binder were also investigated. Isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were used to study the hydration characteristics of the binder system whereas compressive strength and porosity were measured to determine mechanical and durability attributes. The economic and environmental aspects of the binder system is also discussed. Hydrotalcite like phases were clearly produced on hydration in the clay mixes containing carbonate additions. The compressive strength of clay mixes was at par or better compared to systems containing silica fume, and the clay systems had significantly lower porosity levels. The presence of magnesium carbonate further enhanced the physical properties of the clay mixes.

On the use of limestone calcined clay cement (LC3) in high-strength strain-hardening cement-based composites (HS-SHCC)

High-strength strain-hardening cement-based composites (HS-SHCC) demonstrate excellent mechanical and durability properties. However, high cement content typical to HS-SHCC results not only in high carbon footprint, but also in excessive hydration heat and severe autogenous shrinkage. In this investigation, Limestone Calcined Clay Cement (LC3) was used to produce sustainable HS-SHCC. The LC3 substitution resulted in higher energy consumption during mixing and in shorter setting times of the fresh, plain matrices. Although the LC3 substitution slightly reduced the compressive strength, the formation of highly polymerized C-A-S-H gel and abundant ettringite benefited the flexural strength of the plain matrices. Additionally, single-fiber pullout experiments showed that the use of LC3 led to increased fiber-matrix bond strength and pullout energy. Finally, the replacement of Portland cement by LC3 resulted in HS-SHCC with similar mechanical performance to the reference composite, indicating a high potential for using LC3 in high-performance cement-based composites.

Effects of an Illite Clay Substitution on Geopolymer Synthesis as an Alternative to Metakaolin

AbstractIn this study, a calcined illite clay from Bailen, Jaen, Spain, was valorized as a substitute of metakaolin in the synthesis of new geopolymeric materials. The raw materials, raw clay and c...

Pore Analysis and the Behaviour of the Unreacted Metakaolin Particles in the Networks of Geopolymer Cements Using Metakaolins From Kaolinitic and Halloysitic Clays

This work aims to study the pore analysis and the behaviour of the unreacted metakaolin particles in the geopolymer cements from halloysitic and kaolinitic clays. The XRD patterns of the geopolymer cements show the unreacted metakaolin particles at about 21 °(2θ). The micrography images of the specimen from calcined kaolinitic clay confirm the presence of the unreacted metakaolin particles except the one using calcined kaolinitic clay from Bangoua. Whereas those from calcined halloysitic clay are compacts, homogeneous and denser microstructure. The compressive strength of the specimen from calcined halloysitic clay (88.50 ± 2.08 MPa) is higher compared to those from calcined kaolinitic clays (between 45.43 ± 1.84 and 57.20 ± 1.09 MPa). The pore analysis shows that the pore size diameters of the specimen from calcined halloysitic clay are in the range 7.4–16.2 nm while those from calcined kaolinitic clays are ranging from 5.5 to 12.3 nm. It was found that although the geopolymer cement from calcined halloysitic clay contains more unreacted metakaolin particles, it possesses the mesopores due to the inclusion of these fine unreacted metakaolin particles in its structure.

Bone ash reinforced geopolymer composites

AbstractPotassium‐based, geopolymer composites were made with BASF®metakaolin and Mymensingh clay‐derived metakaolin from Bangladesh. Since the natural Mymensingh clay contained 40 wt.% quartz, this same amount of quartz particulates was added to the BASF®metakaolin to make a synthetic analog of the natural calcined clay. By analogy with bone china, bone ash or calcined hydroxyapatite (5CaO•3P2O5or “HA”) particles, having a Ca: P ratio of 3.3:1, were added to make the three types of geopolymer‐based composites described above. For less refractory particulate additions, dicalcium phosphate (DCP) (2CaO•P2O5or “DCP”) particles, having a Ca: P ratio of 2:1, were also added to another set of geopolymers. The ambient temperature compressive and flexural strengths were measured for all of the geopolymer composites. The HA or DCP reinforced geopolymer composites were fabricated and heat‐treated to 1150°C/1 h, after which they were converted to their mineralogical analogs. Their mechanical properties of compressive and 3‐point flexural strengths were again measured. Flexural strengths of 22.42 ± 11.0 MPa and 31.97 ± 8.3 MPa were measured in 1 × 1 × 10 cm3heat‐treated geopolymer bars reinforced with 10 wt.% of DCP and in geopolymer reinforced with 10 wt.% DCP +40 wt.% quartz additions, respectively. Significant improvements to ambient temperature properties were observed due to the self‐healing effect of the flowing amorphous DCP, whose presence was verified by SEM. The geopolymer samples exhibited reduced water absorption (WA) (on a percentage dry weight basis) of within 0.03‐0.5% after being heated at 1100℃/1 h and 1125℃/1 h, as compared with those at room temperature, which varied between 2.56% and 7.89%.

Role of calcination on geopolymerization of lateritic clay by alkali treatment

In the present study, the role of calcination of a low iron lateritic clay sample was investigated to synthesize the geopolymer. The analyses like X-ray fluorescence (XRF) spectroscopy for chemical composition, X-ray diffractometry (XRD) for mineral composition, and Fourier transform infrared (FT-IR) spectroscopy & scanning electron microscopy (SEM) for structural changes upon calcination at 500, 700 and, 900 °C were used to assess the suitability of selected lateritic clay sample for geopolymer. The drop in electrical conductivity and greater consumption of calcium hydroxide by CS-900 confirmed its potential reactivity than CS-700, CS-500, and CS-Control. The quality of geopolymer derived from un-calcined and calcined lateritic clay samples by alkali activation was evaluated by comparing results of compressive strength, water absorption test, and stability in the aggressive environment of chloride, FT-IR, XRD, and SEM analyses. The experimental results reveal that the quality of geopolymer enhances as the calcination temperature of the lateritic clay sample increases, However, calcination of the lateritic clay sample at 900 °C gives significant results and yield good quality geopolymer with 24.8 MPa of compressive strength, 7.07% of water absorption and 2.22% loss in mass in an aggressive environment.

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Alkali-activated calcined clays are promising candidates for playing a prominent role in the future construction industry. These binders may achieve excellent mechanical performance, but one issue deserving attention is the proneness to plastic shrinkage and surface cracking. Tackling this issue requires the deployment of laboratory techniques that allow shrinkage-inducing mechanisms to be quantitatively assessed. Here, we demonstrate that time-lapse X-ray imaging can be used to quantify shrinkage immediately after mixing, when the binder is still in its fresh state, with excellent time and space resolution. The numeric quantification of strain is complemented by the real time visual inspection of the displacing sample interface and of the bleed aqueous solution layer that may form. Implementation of this method to a set of alkali-activated cement pastes, prepared by combining calcined clays having different mineralogical composition with sodium silicate activating solutions having different hbox {SiO}_2/hbox {Na}_2hbox {O} ratios, suggests that two main mechanisms control the early dimensional stability of alkali-activated calcined clays. These mechanisms are: (a) volumetric contraction occurring in response to capillary stress arising from water evaporation and (b) segregation by particle settling, favoured in the water-saturated regime.

Calcined clay – Limestone cements: Hydration processes with high and low-grade kaolinite clays

The development of ternary binders based on limestone and calcined clays appear as a promising way to increase the substitution of clinker. Their production is likely to remain limited if highly kaolinitic clays are required, but calcined clays with low metakaolin content are less reactive in a binary binder, as shown in many previous studies. This study focused on the difference, regarding hydration degree and products, between several binders containing calcined clay and limestone filler. Two calcined clays were studied, coming from two very different raw clays. The first calcined clay contained more metakaolin than the second one. In addition to ordinary Portland cement, four binders were analysed: two binary blends with 25% of cement substitution by the two calcined clays. Two ternary binders, composed of 30% of calcined clay and 15% of limestone filler, were also studied, using both calcined clays. Binary binders showed strong differences between the two calcined clays. However, this work showed that in a ternary binder, significant pozzolanic activity and synergy between calcined clay and limestone filler were observed even for the composite calcined clay with minor metakaolinite content. From this comprehensive study on hydration, it can be concluded that calcined clay with low metakaolin content is likely to result in the same degree of hydration and products at long-term as high metakaolin calcined clay in a ternary system.

Comparative studies on LC3 based concrete with OPC & PPC based concretes

Abstract Now a day’s utilization of sustainable cement based materials are increased in construction industry to enhance the performance of concrete in from strength and durability point on one side and the other side to decrease the emission of CO2 into atmosphere. The availability of supplementary cementitious materials (SCM) is not that much of production of cement due to implementation of sustainable development strategies in every industry. However, SCM‘s may not be available in many countries. Due to this cement clinker can be partially replaced with limestone + calcined clay to an extent of 50%, which can show promising results as per strength and durability point of view. Present study is focused on comparison of Limestone Calcined Clay Cement (LC3) based concrete with Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) based concretes. M 40 grade concrete is considered for strength and durability aspects. From this investigation, it is found that replacement of clinker with LC3-50% is beneficial in terms of strength and durability.

Effects of Calcination Temperature and Time on the Physical-Chemical Efficiency of Thermally Activated Clays in Cement Systems

Introduction of finely disperse mineral additives of natural and man-made origin to Portland cement in order to improve the indicators of its physical-mechanical properties and partially replace clinker is one of the urgent directions for solving the resource and energy saving problems, as well as environmental protection problems in the production and application of building materials. The expansion of the raw material base of mineral additives can be achieved by using calcined polymineral clays, which are common in many regions of the Russian Federation, including the Republic of Mordovia. The article presents the results of research on the effects of calcination temperature and time of thermally activated polymineral clays of the Republic of Mordovia on their physical-chemical efficiency in cement systems. According to the study results of dehydration processes of clay minerals using the synchronous thermal analysis, it is established that the optimum calcination temperature for clays of Nikitsky and Staroshaigovsky deposits located in the area of 500–800 °C. This temperature range corresponds to the processes of the initial crystal structure restructuring of clay minerals of the kaolinite and illite groups, associated with their dehydroxylation, which contributes to the transition of these phases to the active form. The optimization of calcination parameters of polymineral clays based on the study results of influence of their additives on the mixed cement binder activity confirmed the thermal analysis data. It was found that the production of mineral additives with the highest values of the activity index is facilitated by 2-hour heat treatment of clays at 700 °C. At the specified calcination parameters, the replacement of 10% of Portland cement with the additive of thermally activated Nikitsky clay allows achieving the mixed binder activity that exceeds by 3 % the same indicator of mixed binder based on Portland cement and high-quality metakaolin.

A Case Study of Limestone Calcined Clay and Limestone Calcined Laterite for Blended Cement Concrete

A Case Study of Limestone Calcined Clay and Limestone Calcined Laterite for Blended Cement Concrete

Adsorption-desorption of phenolic compounds from olive mills wastewater using Tunisian natural clay

Olive mills wastewater (OMW) exhibit substantial contaminated properties due to their content of phenolic constituents and organic substances. The purpose of this work was the investigation of the efficiency of clay materials for the adsorption of phenolic compounds, which are contained in OMW. Furthermore, thermal activation of the clay took place in order to improve phenolic compounds uptake and afterwards, desorption process was studied. The adsorbent was characterized using XRD, XRF and BET surface area analyses. The adsorption efficiency of phenolic compounds by raw and calcined clay at 600 °C was 77.61% and 84.21%, respectively at acidic pH. The values of Gibbs free energy indicated that adsorption process is spontaneous and beneficial at higher temperatures. Alkaline medium was propitious for phenolic compounds desorption. The obtained results showed that natural clay could be used as a low-cost adsorbent for OMW treatment.

Effectiveness of PCE superplasticizers in calcined clay blended cements

The impact of a calcined clay (CC) rich in meta kaolin (~50 wt%) present in composite cements at 0–40% substitution rate for the clinker was studied relative to the dispersing force of different PCE superplasticizers. It was found that CC increases the water demand of the blended cements considerably (+85% for the 60:40 blend vs. neat OPC). Furthermore, PCEs which fluidize OPC best also provide optimal performance in CC blended cements, but require much higher dosages (in OPC/CC 60:40, 4–6 times as compared to neat OPC). In all systems, HPEG-PCE produced superior dispersing performance over anionic MPEG-PCEs. A mechanistic study involving zeta potential measurements revealed that the initially negatively charged calcined clay surface adsorbs huge amounts of Ca2+ ions from the pore solution, thus facilitating adsorption of anionic PCE superplasticizers. The results signify that commercially available PCE products can effectively fluidize OPC/CC blended cements.

Physicochemical Characterization of Moroccan Natural Clays and the Study of their Adsorption Capacity for the Methyl Orange and Methylene

The objective of this work was the physicochemical characterization of a Moroccan natural clay from the Jorf Arfoud region (Lampert Coodinates: x = 595610, y = 101578) and its valorization in the elimination of organic pollutants (methyl orange MO and methylene blue MB) from aqueous solutions, with the adsorption technique on raw and calcined clay at 500°C. The clay was characterized by chemical analysis such as X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy (SEM). Crude and purified clays, consisting essentially of silica and alumina, are a characteristic property of phyllosilicates and also contain amounts of quartz, kaolinite and calcite as associated minerals. The experiments were performed after optimization of the parameters influencing the system, such as pH, adsorbent mass, initial dye concentration and temperature. The clays used absorb better the MB than MO, for an initial concentration of 10 mg/L and 20 mg/L respectively. Langmuir and Freundlich models of adsorption isotherms were applied to fit experimental equilibrium data. Results have showed that the adsorption of MB and MO followed very well the second order kinetic model on raw clay. The adsorption process was found to be exothermic in the case of MB. However, the adsorption of MO was endothermic.

Use of calcined clay as cementitious addition in mortars to immobilize heavy metals

Abstract The aim of this study was to examine the use of calcined clay (CC), which is a pozzolanic material, as a substitute for 10% by weight of the amount of cement, for the stabilization/solidification (S/S) of hazardous waste using a hydraulic binder. For comparison, an ordinary Portland cement was used. The standard toxicity characteristic leaching procedure (TCLP) test showed that the average concentrations of heavy metals in the raw hazardous waste far exceeded those of the required standards. Leaching of heavy metals from the mortar was evaluated by the monolithic leaching test (MLT) under dynamic leaching conditions for 64 days in sulfated and neutral media. Tests of compressive strength, setting times, and X-ray diffraction were carried out. The addition of CC considerably improved the strength of the mortar specimens containing hazardous waste. Following the MLT test, CC cement-made mortar was more efficient in the S/S of heavy metals than mortar made without CC.

Overview of the lightweight oil-well cement mechanical properties for shallow wells

Lightweight oil-well cement eliminates the need for the much expensive and problematic multi-stage cementing approach for isolating shallow intervals. However, the generally low compressive strength of lightweight cement in comparison to the neat cement recipes has been a major concern for operators who consider compressive strength the most important parameter.lightweight cement exhibit other desirable mechanical properties that affect the long-term integrity of the cement sheath. The objective of this review is to present laboratory and field investigations on the performance of different lightweight systems.According to field and laboratory investigations, a high compressive strength should not be of much concern, especially for shallow and weak formations where compressive strength higher than the formation can be deleterious. A minimum compressive strength of 50 psi is sufficient to support the casing. About 250–1000 psi is adequate to meet the requirement of many operations. Besides, foamed, perlite, zeolite, gilsonite, and microsphere-based cement exhibit adequate early age compressive strength and more important mechanical properties such as high tensile strength, low Young modulus, and high Poisson ratio which increase cement elasticity.With the enhancement in the mechanical performance of lightweight cement containing metakaolin and vermiculite, both calcined clays, it is recommend to inverstigate the use of calcined bentonite clay as supplementary cementitious material.

Influence of alkali activator type and proportion on strength performance of calcined clay geopolymer mortar

The global abundance of low purity kaolin clay and the low embodied energy associated with its calcination makes it a promising aluminosilicate source that will extend the application of geopolymers. In this paper, the compressive strength and microstructure of iron rich, calcined clay based geopolymer mortars activated by two forms of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solutions were studied and reported. The samples were cured either in the air or under sealed conditions. The result shows that the 28 days strength of the mortars achieved by reacting the calcined clay with hydrous sodium silicate powder, dissolved under normal atmospheric conditions and sodium silicate solution produced in a pressure reactor vessel are 0.5 MPa and 28.8 MPa respectively. The former produced a non-geopolymer mortar that has a discrete, undensified and uncompacted structure with heavy presence of residual particles, thus, achieving a strength that is 1.7% of the latter. The functional group analysis reveals that the binding phase of the peak strength mortar is ferro sialate (Fe-Si-O-Al).