Metakaolin Content Research Articles

Improved chloride binding capacity in sustainable metakaolin blended seawater cement mortar: Effect of external alternative electric field

Seawater is a promising substitution of fresh water in concrete production to relieve the resource crisis, especially for the concrete fabricated in harsh environment with less freshwater supply, while the excessive chloride ion (Cl-) in seawater may induce severe durability issue. In this work, metakaolin (MK) was used as supplementary cementitious material to prepare seawater cement mortar (SWCM), and ohmic heating (OH) curing was utilized to fabricate MK-SWCM at -20 °C by creating high temperature curing condition, with conductive carbon fibers (CFs) as electrical reinforcement media. The CFs fraction was numerically and experimentally obtained as 1.0 vol%, the electrical resistivity, electric voltage and curing temperature change during OH process was disclosed. Results showed that MK inclusion and OH curing both contributed to enhancing the Cl- binding capacity with higher hydration degree and denser pore structure. To be specific, OH cured SWCM with 10% MK content endowed the Cl- binding ratio of 35.4%, meeting the increase of 97.8% compared to that of room temperature cured SWCM with no MK addition. Moreover, the mechanical strengths were further proven excellent for winter production in cold environment, which were all above 60 MPa with the aid of OH curing. A systematical analysis was conducted to roundly clarify the benefits for MK-SWCM fabrication in cold region from the aspects of Cl- binding capacity efficiency, environmental benefits and mechanical strength.

Comparative Study on the Properties of Fresh and Hardened Concrete Using Metakaolin as Partial Replacement

This study examines the impact of metakaolin as a partial substitute for concrete, analyzing fresh and hardened concrete characteristics. We integrated metakaolin, a pozzolanic substance known for its ability to enhance strength and durability, at various replacement ratios (0%, 5%, 10%, 15%, and 20%) to assess its impact on workability, compressive strength, tensile strength, flexural strength, and resistance to chemical aggression. The workability of fresh concrete went down as the metakaolin content went up. On the other hand, as the metakaolin content went up, the compressive strength, flexural strength, and resistance to acid and sulphate attacks all went up in hardened concrete, though the tensile strength went down a little. The results demonstrate that an ideal metakaolin substitution of around 10–15% can provide significant durability advantages without markedly diminishing workability or tensile strength. This work provides a fundamental understanding for engineers to improve the designs of concrete mixes, especially in situations where chemicals are present.

Studying the metakaolin content, fiber type, and high-temperature effects on the physico-mechanical properties of fly ash-based geopolymer composites

Studying the metakaolin content, fiber type, and high-temperature effects on the physico-mechanical properties of fly ash-based geopolymer composites

Calcined Clays as Concrete Additive in Structural Concrete: Workability, Mechanical Properties, Durability, and Sustainability Performance.

Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze-thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production.

Microstructural and mechanical characteristics of alkali-activated green concrete using slag from electric arc furnaces as precursor and aggregate

Abstract Alkali-activated materials (AAM) have gained popularity in research because of their lower carbon dioxide emissions than Portland cement. Electric arc furnace slag (EAFS) exceeds landfills. Moreover, electric arc furnaces emit less CO2 than oxygen-blast furnaces. This research is the first to suggest that mixing EAFS and metakaolin (MK) as AAM precursors could compensate for the deficiency of SiO2 and Al2O3 in the EAFS and CaO in the MK, which would produce better AAM properties than using either of them singularly. Furthermore, the utilization of EAFS aggregate instead of natural aggregate in alkali-activated concrete (AAC) reduces waste materials, consumes fewer natural resources, and solves the problem of natural aggregate scarcity. This study’s main objectives were to evaluate the effects of varying ratios of EAFS and MK as precursors and EAFS aggregate to natural aggregate ratios on the AAC’s fresh and hardened properties. The properties under consideration are workability and cube compressive strength. The outcomes showed that increasing EAFS with decreasing MK content increased AAC workability and cube compressive strength while increasing EAFS aggregate over natural aggregate improved AAC workability and decreased cube compressive strength.

Mechanical strength and durability of GBFS geopolymer modified with metakaolin and functionalized beta-silicon carbide whiskers

Durability is crucial for materials development in construction and transportation industries. This paper investigates the mechanical strength and durability of alkali-activated granulated blast-furnace slag (GBFS) and modified geopolymer with varying contents of metakaolin (MK) and functionalized beta-silicon carbide whiskers (β-SiCw). Functionalized β-SiCw were prepared utilizing successful chemical methods. Macroscopic experiments tested mechanical strength, bulk density loss rate after exposure to severe conditions, and durability through sulfate wet-dry and freeze-thaw cycles. Microscopic experiments, including SEM-EDS, XRD, TG-DSC, and BET, revealed the microstructure mechanisms. Results showed that MK and functionalized β-SiCw improved mechanical strength by creating a more reactive phase and denser pore structures. Reduced bulk density loss rates and enhanced durability were observed, with a 71.9 % mass loss and 63.4 % compressive strength loss reduction after 50 freeze-thaw cycles, and a 12.2 % decrease in compressive strength loss after 56 days of sulfate wet-dry cycles, compared to control groups. The modified geopolymer had higher tortuosity and finer porosity due to more gel formation and nucleation sites, and functionalized β-SiCw effectively bridged micro-cracks and micro-pores.

Thermal activation of kaolinite through potassium acetate intercalation: A structural and reactivity study

Calcined clays have emerged as a suitable alternative to partially replace conventional cement due to their high pozzolanic activity. This study explores a novel activation methodology for kaolinite, aiming to obtain metakaolin at lower temperatures than conventional thermal activation. This methodology involves a prior intercalation stage with potassium acetate (KAc) before thermal activation. The effectiveness of KAc intercalation was assessed through X-ray diffraction (XRD), indicating an intercalation ratio of approximately 90%. Several calcined temperatures were tested in accordance with the thermal behaviour analyzed through thermogravimetric analysis (TGA). Once calcined, the intercalated kaolinites exhibited enhanced reactivity compared to conventional calcined clays in the range between 400 °C to 550 °C, as demonstrated by modified Chapelle and Si/Al availability tests. A comprehensive structural characterization was conducted to facilitate a better understanding of the novel KAc-based metakaolin reactivity through various techniques (XRD, 27Al - 1H MAS NMR, and TGA). This focused on the crystalline changes in the kaolinite structure, the evolution of Al atoms conformation, and the OH behaviour at different thermal activation temperatures. Overall, this study highlights the potential of KAc intercalation as a strategy to obtain higher metakaolin content at lower temperatures than through conventional thermal treatments, offering insights into the development of its potential use as supplementary cementitious materials or alternative cementitious materials precursor.

Strongly acidic lead contaminated soil solidification/stabilization using metakaolin-modified fly ash phosphoric-based geopolymer

The existing binders are difficult to be compatible with the acidic environment of acidic heavy metal contaminated soil, it is hard to repair acidic heavy metal contaminated soil. In this study, a modified acid phosphorus-based geopolymer (MAPG) binder suitable for the solidification/stabilization (S/S) treatment of acidic heavy metal Pb2+ contaminated soil was fabricated using aluminum dihydrogen phosphate (ADP) as activator, fly ash and metakaolin (MK) as raw materials. The influences of liquid–solid ratio (L/S), MK content, ADP concentration, curing age and leaching environment on the compressive strength, toxic leaching, resistivity, pH and EC of MAPG stabilized acidic Pb2+ contaminated soil were studied. Meantime, the X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, and mercury intrusion (MIP) experiments were used to study the chemical properties and microscopic performance of MAPG treated acidic Pb2+ contaminated soil. The results showed that the MAPG binder prepared from MK had an excellent S/S effect on the acidic Pb2+ contaminated soil, and the MAPG binders had good compatibility with the acidic environment. The compressive strength of each group of MAPG stabilized soil could meet the strength standard (>350 kPa) for solid waste landfill and Pb2+ leaching concentration is < 5 mg/L for toxicity identification criteria after 7 days of curing. With an increase in curing age, the strength of stabilized acidic contaminated soil decreased slightly, but the strength still met the requirements of landfill strength standard after 28 days of curing. In three different leaching environments, the Pb2+ leaching decreased with an increase in curing age. Microscopic analysis showed that the main crystalline compounds in stabilized contaminated soil were potassium feldspar, Berlinite and lead phosphate compounds, and their contents were related to L/S, MK content, ADP concentration, and curing time. Potassium feldspar, berlinite, and lead phosphate compounds could not only fill pores, but also had physisorption, encapsulation and chemical precipitation effects on Pb2+. The study could provide an economical, environmental friendly and efficient binder for the remediation of acidic Pb2+ contaminated soil, but the further investigation into the long-term effectiveness of the MAPG binder or its applicability to other types of contaminated soil is also needed.

Development of 3D-printed magnesium silicate hydrate cement mixes involving metakaolin as a substitute for silica source

ABSTRACT The printability of MgO-SiO2 cement pastes involving the use of microsilica (MS) and metakaolin (MK) as a SiO2 source was thoroughly investigated. Fresh properties, including rheology and early-age strength, mechanical properties and microstructures of pastes incorporating different contents of MK were presented and analyzed. Amongst samples studied, those containing 5% MK as a substitute for MS exhibited the highest static yield stress, and fastest re-flocculation and structuration rates, resulting in the best buildability. Although the inclusion of 10% MK resulted in enhanced paste strength at 7 and 28 days, increased MK content impeded paste printability due to diminished formation of hydrate phases. Use of 5% MK led to higher M-S-H generation compared to other samples at 28 days, contributing to subsequent strength development. Results demonstrated that optimisation of the MK content in MgO-SiO2 pastes can yield satisfactory mechanical strengths without compromising printability.

Enhancing Hydraulic Lime Mortar with Metakaolin: A Study on Improving Restoration Materials for Historic Buildings.

This study investigates the enhancement of hydraulic lime mortar (HLM) using varying contents of metakaolin (MK) to improve its application in the restoration of historic buildings. Samples from historic structures were analyzed, and the effects of different MK contents on the physical and mechanical properties of HLM were examined. The reaction mechanism and microstructural changes were evaluated using XRD and SEM analysis. The results indicated that increasing MK levels in HLM led to a decrease in fluidity, with fluidity reducing by 4.8% at 12% MK. The addition of MK increased water consumption for standard consistency by 5.4% and shortened the final setting time by 10.2%. MK consumption promoted secondary hydration, enhancing compressive strength by up to 98.1% and flexural strength by up to 55.1%, and increasing bonding strength by 26.9%. The density of HLM improved with MK addition, slightly reducing moisture content by 4.5% and water absorption by 4.6%, while the water vapor transmission properties decreased by 50.9%, indicating reduced porosity. The elastic modulus of the mortar increased significantly from 2.19 GPa to 7.88 GPa with the addition of MK, enhancing rigidity and crack resistance. The optimal blend for restoration materials was found to be 9.0% MK and 25.0% heavy calcium carbonate and was characterized by moderate mechanical strength, enhanced early strength, commendable permeability, minimal risk of cracking, and ease of application. This blend is highly suitable for the rehabilitation of historic structures.

Exploring the hydration feature and microstructure evolution of MK-Q-LS blended cementitious materials with electrochemical techniques

The hydration process of blended cementitious materials is primarily affected by the effect mechanism of supplementary cementitious materials. This study utilizes electrochemical impedance spectroscopy (EIS) method to investigate the hydration kinetics of cementitious materials incorporating metakaolin (MK), quartz (Q) and limestone powder (LS). The experimental results reveal the influence of MK+Q+LS on the hydration kinetics, phase assemblage, and microstructure of the blended systems. Besides, the electrochemical impedance response of blended cement materials exhibits variation based on the MK contents and the curing age. Furthermore, the resistance of the continuously connected micro-pores (Rccp) in the blended cementitious material progressively increases throughout the hydration process. The inclusion of MK reduces the Rccp values at early ages, while contributes to an increase in Rccp values from 7 days onward. Additionally, positive correlations are established between the Rccp value and compressive strength/heat release across different MK contents and curing ages. The combination of Rccp values and other characterization method can effectively reveal the microstructure evolution process. Therefore, as a nondestructive method, EIS can be effectively applied to predict the hydration of cementitious materials and the mechanical properties.

Utilization of municipal solid waste incinerator fly ash under high temperature sintering and alkali excitation for use in cementitious material

It is crucial to have a secure and dependable approach to treat and reuse municipal solid waste incinerator (MSWI) fly ash to prevent potential hazards. High temperature sintering is regarded as an efficient method for solidifying heavy metals, and alkali excitation provides a practicable solution for utilizing MSWI fly ash. In this work, the activation mechanism of MSWI fly ash was figured out under high temperature sintering. Besides, the preparation and optimization of sintered MSWI fly ash with metakaolin for use in alkali–activated cementitious material were explored based on Box–Benhnken design (BBD), considering different modulus and alkali equivalent of alkaline activator, as well as different contents of sintered MSWI fly ash and metakaolin. The mechanical performance and alkali excitation mechanism of the cementitious material were investigated. The results showed that the pozzolanic activity of MSWI fly ash treated by high temperature sintering was increased by 81.7 %, which further was improved by alkali excitation. The optimal mix proportion of alkali–activated sintered MSWI fly ash–metakaolin cement mortar consisted of a modulus of 1.332, an alkali equivalent of 1 %, a sintered MSWI fly ash content of 20 %, and a metakaolin content of 10.5 %, whose flexural and compressive strength were 8.5 and 57.3 MPa, respectively. Moreover, SiO32− and OH− in alkaline activator and Al(OH)4–, SiO2(OH)22−, and SiO(OH)32− in metakaolin promoted Ca2+ in sintered MSWI fly ash to generate C–S–H and C–A–S–H. Finally, the alkali–activated mortar made from sintered MSWI fly ash demonstrated high safety and eco–friendliness, with a synthesis toxicity index (STI) of 25.59.

Effect of metakaolin content and shape design on strength performance of lightweight rubberized geopolymer mortars incorporated slag-waste glass powders

Lightweight rubberized geopolymer (LRGP) has gained attention due to its economic, engineering, and environmental benefits. With the rising human demands, the need for alternative materials to meet the requirements of infrastructural expansion, and global industrialization required. Based on those facts, this study aimed to develop of lightweight geopolymer mortars using wastes rubber as fine aggregate (WRA) to replace the natural aggregates, which metakaolin (MK), wastes bottle glass (WBG) and granulated blast furnace slag (GBFS) used as precursor materials with alkaline activator contained low molarity of sodium hydroxide solution and sodium silicate and cured at ambient temperatures. The effect of WRA on physical, mechanical, and microstructural properties of metakaolin-based rubberized geopolymer has been evaluated by using several tests such as compressive, flexural and tensile strength. As well as morphology and chemical reaction on LRGP by using AFM, FESEM, EDX, FTIR and XRD tests. In addition, a sustainable shape design has been cast and subjected to compressive strength to obtain the strength performance of the proposed LRGP mortar. At optimal mixture, the SEM images exhibited improvement in the interfacial transition zone (ITZ) among WRA and binder, leading rubberized geopolymer with 15% WRA to achieve a strength of 27.47 MPa after 28 days and with a reduction in density by 7.2%. The findings of this study can provide valuable insights on utilizing WRA in the shape design and formulation of geopolymer mortar, a key ingredient in the development of functional environmentally friendly building materials.

Corrosion resistance of cement-based materials with sugarcane bagasse ash-metakaolin-Portland cement binder under carbonic acid water environment

This paper investigated the corrosion process of sugarcane bagasse ash (SCBA)-metakaolin (MK)-Portland cement (PC) system under carbonic acid water environment. The phases of cement paste before and after corrosion and microstructure were analyzed by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscope. The results showed that the addition of SCBA to mortar does not significantly enhance overall strength or reduce corrosion depth, whereas MK exhibits superior strength (up to 13.1% higher than SCBA) and lower corrosion depth (up to 69.6% lower than SCBA after 90 days of corrosion). Furthermore, SCBA is more conducive to maintaining strength over time compared with MK. When both MK and SCBA are used in mortar, particularly with a MK content exceeding 15% and an SCBA content below 5%, the optimal corrosion resistance effectiveness can be achieved. This is attributed to the synergistic pozzolanic effect of MK and the filling effect of SCBA.

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.

A Study on the Shrinkage and Compressive Strength of GGBFS and Metakaolin Base Geopolymer under Different NaOH Concentrations.

Geopolymers (GPs) are gaining prominence due to their low carbon emissions and sustainable attributes. However, one challenge with GPs, particularly those made with ground granulated blast furnace slag (GGBFS), is their significant shrinkage during the geopolymerization process, limiting its practical applicability. This study focuses on how the substitution ratio of metakaolin (MK) and the concentration of sodium hydroxide (NaOH) in the activator can influence the shrinkage and strength of a GGBFS-based GP. The experimental approach employed a 3 × 3 parameter matrix, which varied MK substitution ratios (0%, 50%, and 100%) and adjusted the NaOH concentration (6 M, 10 M, and 14 M). The results revealed that increasing MK substitution, particularly with 6 M NaOH activation, reduced the GP shrinkage but also diminished compressive strength, requiring higher NaOH concentrations for strength improvement. Statistical tools, including analysis of variance (ANOVA) and second-order response surface methodology (RSM), were employed for analysis. ANOVA results indicated the significant impacts of both the MK content and NaOH concentration on compressive strength, with no observable interaction. However, the shrinkage exhibited a clear interaction between MK content and NaOH concentration. The RSM model accurately predicted compressive strength and shrinkage, demonstrating a high predictive accuracy, for which the coefficients of determination (R2) were 0.99 and 0.98, respectively. The model provides a reliable method for determining the necessary compressive strength and shrinkage for GGBFS-based GP based on MK substitution and NaOH concentration. Within the optimization range, the RSM model compared with experimental results showed a 6.04% error in compressive strength and 0.77% error in shrinkage for one interpolated parameter set. This study establishes an optimized parameter range ensuring a GP performance that is comparable to or surpassing OPC, with a parameter set achieving a compressive strength of 34.9 MPa and shrinkage of 0.287% at 28 days.

Characterizing the behavior of blended concrete incorporating metakaolin and quarry dust: an experimental investigation

Purpose This study aims to characterize the behavior of blended concrete, including metakaolin (MK) and quarry dust (QD), as supplementary cementing materials. The study focuses on evaluating the effects of these materials on the fresh and hardened properties of concrete. Design/methodology/approach MK, a pozzolanic material, and QD, a fine aggregate by-product, are potentially sustainable alternatives for enhancing concrete performance and reducing environmental impact. The addition of different percentages of MK enhances the pozzolanic reaction, resulting in improved strength development. Furthermore, the optimum dosage of MK, mixed with QD, and mechanical properties like compressive, flexural and split tensile strength of concrete were evaluated to investigate the synergetic effect of MK and quarry dust for M20-grade concrete. Findings The results reveal the influence of metakaolin and QD on the overall performance of blended concrete. Cost analysis showed that the optimum mix can reduce the 7%–8% overall cost of the materials for M20-grade concrete. Energy analysis showed that the optimum mix can reduce 7%–8% energy consumption. Originality/value The effective utilization is determined with the help of the analytical hierarchy process method to find an optimal solution among the selected criteria. According to the AHP analysis, the optimum content of MK and quarry dust is 12% and 16%, respectively, performing best among all other trial mixes.

The efficiency of hybrid intelligent models to evaluate the effect of the size of sand and clay metakaolin content on various compressive strength ranges of cement mortar

The efficiency of hybrid intelligent models to evaluate the effect of the size of sand and clay metakaolin content on various compressive strength ranges of cement mortar

INVESTIGATION OF CALIFORNIA BEARING RATIO VALUE OF BAMA RIDGE SOIL ADMIXED WITH METAKAOLIN

The study focused on assessing the impact of Metakaolin on the properties of Bama Ridge Soil in the Maiduguri region and its environs. Soil samples, collected using a disturbed sampling method from two distinct locations, were transported to the laboratory in polythene bags to prevent moisture loss. According to the American Association of States Highway and Transport Officials (AASHTO) and the Unified Soil Classification System (USCS), the soil was classified as A-3(0) and CL. The California Bearing Ratio (CBR) values ranged from 19.23% to 26.66% for soaked conditions and 25.01% to 32.46% for un-soaked conditions, indicating its suitability as sub-grade material. The study suggested that a 15% Metakaolin content would suffice for lightly trafficked roads. However, caution was advised against using the soil as sub-base material for roads with heavy traffic density, as CBR values slightly exceeded 30%. This implies that while the soil shows promise for specific construction applications, it may not be optimal for handling the substantial loads associated with high traffic volumes.

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%).