Metakaolin Mixtures Research Articles

Physical-mechanical assessment to mortars including recycled concrete powder and metakaolin

This study aims to evaluate the mechanical and physical properties of mortars incorporating recycled concrete powder (RCP) and metakaolin (MK), a widely utilized supplementary cementitious material (SCM). The mortars were partially replaced with 30 % of either MK or RCP sourced from three distinct sources: construction, demolition, and laboratory. Various parameters, including workability, compressive strength, splitting tensile strength, elastic modulus, water absorption, capillary water absorption, density, void index, and microstructural characteristics of the mortar, were assessed. The findings indicate that the workability of mortars generally decreased due to the morphology and specific surface area of the particle mixtures of RCP and MK. The incorporation of RCP negatively affected the mechanical properties of the mortar. Conversely, mixtures of MK and RCP were observed to maintain or even enhance the mechanical properties of the mortars across all evaluated time intervals (7, 28, and 91 days). In terms of physical properties, the combination of RCP and MK generally led to a reduction in water absorption and capillary water absorption, as well as a decrease in density and void index. Additionally, the use of MK in combination with RCP resulted in a reduction in the amount of cement required (kg·m−3·MPa−1) compared to the reference mix, demonstrating that this alternative approach is not only technically viable but also sustainable.

Alkali-activated materials containing mine tailings and zeolite for seepage water treatment in a closed nickel mine

AbstractIn the present study, alkali-activated materials were assessed as adsorbents for mine water treatment. The composition of alkali-activated materials, involving mixtures of metakaolin, blast-furnace slag, mine tailings, and zeolite, was optimized based on their leaching behavior and adsorption performance. The most effective adsorbent contained solely blast furnace slag as an aluminosilicate precursor and was selected for a pilot-scale study at a closed nickel mine in Finland. In the pilot, seepage water from a gangue area with an influent flow rate of 0.5 m3/d was treated using a permeable reactive barrier set-up containing 10 kg of slag-based adsorbent prepared by a granulation-alkali activation process. During a one-week experiment, the adsorbent granules were capable of effectively uptaking Ni, Fe, and Mn from the seepage water; the removal percentages of Ni, Fe, and Mn were 82.4%, 81.6%, and 82.5%, respectively. The results indicated the feasibility of blast furnace slag-based adsorbents for toxic element removal in a potentially sustainable approach.

Low-carbon metakaolin precursor for one-part and two-part geopolymer activation of demolition wastes

A critical part of civil engineering infrastructure works is to develop innovative construction materials for a low-carbon future development. This study delved into the feasibility of using metakaolin (MK) as a low-carbon precursor for one-part and two-part geopolymer stabilization of recycled demolition wastes. In this research, the effects of MK precursor were evaluated in combination with construction and demolition (C&D) waste aggregates such as crushed brick (CB), reclaimed asphalt (RAP) and recycled concrete (RCA) using one-part and two-part geopolymer activation. Various geotechnical tests were performed including compaction tests, repeated triaxial loading tests (RLT), unconfined compressive strength tests (UCS) and microstructural analysis. Results from this study indicated significant strength development of MK mixtures for both one-part and two-part geopolymer options. Furthermore, one-part geopolymer also showed better activation than two-part geopolymer under 7 days and 20℃ curing condition. Additionally, 30 % MK mixtures were optimal for road construction applications based on the obtained results. At 28 days or 40 ℃, MK mixtures performed best with RCA and CB as main aggregates, showing strength improvement of up to 250 % compared to 7 days and 20 ℃ curing condition. Resilient modulus (Mr) results indicated that the optimal mixtures experienced good resilient behavior with average Mr values ranging from 150 MPa to 200 MPa. Overall, MK precursor was found to be a suitable material for stabilizing demolition aggregates using geopolymer under various curing conditions.

Effect of reactivity of different metakaolin mixtures on geopolymer extrudability

Additive manufacturing of geopolymers is an innovative technology for research and development This work highlights effect of different metakaolin of mixtures reactivity on geopolymer extrudability. Extrudability tests were carried out on geopolymer pastes from different metakaolin ternaries diagrams using two alkaline (potassium silicates K and sodium silicate KNa) solutions. Extrudable areas were delimited. To understand the differences, the reactivity of the different metakaolin mixtures was evaluated. The results showed that for the extrudable areas, the zeta potential values of the metakaolin mixtures ranged from −50 to −60 mV with K solution and were around −60 mV with the change of solution (KNa). Moreover, the extrudable area corresponds to an energy of oligomer formation (determined by thermal analysis) determined between 1.67 and 1.85 kJ mol−1 with metakaolin ternary diagram M1-MI-M5 and 1.58 and 1.76 kJ mol−1 for metakaolin ternary diagram M1-M2-M5. Whatever the alkaline solution used, the alkaline cation concentration of the extrudable domains is greater than or equal to 2.80 mol. L−1. Mechanical strengths increase around 10 % from solution K to KNa. All these results are confirmed by using other aluminosilicate sources, such as argillite (clay calcined at 650 °C) and mixture of several clays (A65030-M170 and A65050-M150).

Improving the strength of metakaolin-lime based binder

Pozzolanic reaction of low-calcium metakaolin (MK) with calcium hydroxide (CH) at ambient temperature in the presence of water forms a series of hydrated phases such as tetracalcium aluminate hydrate (C4AH13), calcium silicate hydrate (C-S-H) and calcium aluminum silicate hydrate (stratlingite - C2ASH8). Stratlingite is the main crystalline phase and is responsible for the strength of the binder. Tetracalcium aluminate hydrate (C4AH13) is carbonated upon contact with air or converted to hemicarboaluminate and/or monocarboaluminate if the system contains excess carbonate phases (calcite or calcareous aggregates). However, the calcium aluminate hydrates formed after the reaction of MK with lime lose their strength over time due to their instability. Especially in a high humidity environment where there is no carbonation, the presence of both stratlingite and (CH) in the binder creates weak phases called katoite (Ca3Al2(SiO4)(OH)8) and can reduce the mechanical strength and durability. On the other hand, it has been determined that using chemical activators to increase the pozzolanic reactivity is the most feasible method, although it increases the cost of the material. In this study, it is aimed to eliminate the phases that cause katoite formation and improve the performance of the binder by using alkaline hydroxide solution in a mixture of metakaolin and slaked lime, similar to the pore solution caused by hydrated cement. For this aim, the effect of sodium carbonate (N-Na2CO3), quicklime (C-CaO) and calcite (CC-CaCO3) on the (CH-Ca(OH)2) activated metakaolin system is investigated through the experimental campaign. The preparation of the mixtures is done by the novel one-part mixing method.

Microstructure, hydration process, and compressive strength assessment of ternary mixtures containing Portland cement, recycled concrete powder, and metakaolin

The aim of this study is to evaluate the effect of recycled concrete powder (RCP) and metakaolin (MK) on the microstructure, hydration, and compressive strength of ternary mixtures containing Portland. The methodology involved producing cementitious pastes with different combinations of RCP + MK, where Portland cement was substituted by 30 %, and three sources of RCP were considered: construction, demolition, and laboratory. The materials were characterized physically, chemically, and mineralogically. The characterization of the fresh state properties was done using a rotational viscometer. The hydration of the pastes was evaluated by isothermal calorimetry, X-ray diffraction, and thermogravimetry. The compressive strength and elastic modulus were determined for 1, 7, 28, and 120 days. Finally, an analysis of the microstructure of the prepared pastes was conducted by scanning electron microscopy. The results show that RCP and MK have negative influence on the fresh state properties, increasing both the yield stress and plastic viscosity. The additions also promote early hydration of Portland cement (first hours), which decreases due to the dilution effect. The quantity of hydrated products tends to be comparable to the reference, except for calcium hydroxide, which is reduced due to the pozzolanic activity of MK. The compressive strength and elastic modulus of the RCP + MK mixtures can be equal and/or superior the reference, demonstrating a synergistic effect between both materials. The use of RCP + MK mixtures is presented as a technically viable alternative to replace Portland cement without compromising performance.

Characterization and photocatalytic performance of cement mortars with incorporation of TiO2 and mineral admixtures.

As the main components of the building envelope, construction materials have a straight relation with air contaminants from anthropogenic origins. Titanium dioxide has been recently applied in construction industry products since its photocatalytic properties can be used for pollutant degradation purposes. This study evaluated the performance of cement-based mortars with the incorporation of TiO2 nanoparticles and mineral admixtures. Six mortar compositions were defined by considering two reference mixes (with and without TiO2 incorporation), two mineral admixtures (bentonite and metakaolin) as partial cement replacement and one waste from ornamental stone processing in two levels of partial substitution of natural sand. Consistency index, density, and entrained air content of mixtures were investigated at fresh state. Compressive strength, water absorption, sorptivity, and micrographs from scanning electron microscopy were used to characterize mortars at hardened state. It was observed that incorporation of TiO2 does not considerably change mortar's properties at fresh and hardened state, despite a denser microstructure and improved interfacial transition zone. In general, the relation between the water-to-cement ratio and porosity on the performances of TiO2-added mortars was shown, which is strongly related to their photocatalytic efficiency. Metakaolin mixtures were more efficient to NO conversion, and high selectivity was observed for the bentonite mortars.

Long term durability assessment of self-compacting concrete made with crushed recycled glass and metakaolin

Sustainable production in construction industry can only be possible through a proper management and conservation of limited natural resources such as fine aggregates. This challenge can be tackled by efficient utilization of discarded waste material such as glass in production of sustainable concrete. This paper investigates the use of crushed recycled glass (CRG) and metakaolin (MK) in development of durable self-compacting concrete (SCC). Four groups of SCC mixtures were prepared using different proportions of CRG (0–50%), while keeping MK concentration equal to 0%, 4%, 8% and 12%. Durability performance of SCC was accessed using water absorption, sorptivity, chloride ion permeability, drying shrinkage, water penetrability under pressure and alkali-silica reaction (ASR) tests. As the CRG content increased, group 4 (having 12 % MK) was most efficient in improving drying shrinkage and pressurized water penetration results; whereas Group 1 (0% MK mixtures) exhibited a minimal change. Raising CRG content in the mix resulted in decrease of water absorption and chloride ion penetration for all groups with group 4 exhibiting maximum reduction. ASR testing revealed that incorporating glass at a higher concentration (40% and 50%) resulted in excessive expansion (more than prescribed limit of 0.1%), which can be suppressed by partially substituting cement with MK. FE-SEM and TGA analysis were carried out to understand the mechanism behind these changes, which revealed that the secondary hydration products formed by addition of MK in concrete can densify the pore structure and refine CRG particle-cement paste interfacial micro-crack width (was evident from FE-SEM micrographs), thus improving the durability of concrete. Indeed, simultaneous incorporation of CRG and MK proved to be advantageous for development of green SCC.

Impact of different metakaolin mixtures on oligomer formation and geopolymer properties: Impurity effect

The impact of metakaolin mixtures on geopolymer formation and corresponding properties was evaluated by synthesizing geopolymers from mixtures of different metakaolins and 5 M potassium silicate. Mixture reactivity was investigated by viscosity, thermogravimetric (DTA-TGA), and in situ infrared spectroscopy (FTIR) measurements. Furthermore, mechanical strength and porosity measurements were undertaken on consolidated materials. The results have shown that the aluminum molar concentration governs the setting time and oligomer formation energy. Indeed, the high aluminum content associated with the high purity of the metakaolins lead to a low formation energy of oligomer, whereas for the metakaolins containing more impurities, the energy required for oligomer formation was higher. Regardless of the formulation, the mechanical strength and porosity trends were similar. Network characteristics were assessed by amorphous material content and in situ infrared spectroscopy (FTIR) analysis. It was demonstrated that (i) for Si/Al < 1.5, an amorphous network is formed with a constant Si/Al ratio, and for (ii) Si/Al > 1.5, different networks are formed. The zeta potential values of the different metakaolin mixtures corroborated these findings. Zeta potential values of metakaolins are governed by the impurities present in the metakaolins, which limit the release of aluminous species from the metakaolins in solution, emphasizing that knowledge of raw materials is essential to understand the local networks formation.

“Effect of incorporating a molten salt waste from nuclear power plants on the properties of geopolymers and Portland cement wasteforms”

This research studies the effect of incorporating a surrogate molten salt radioactive waste (labelled as MS, composed of a mixture of carbonates, chlorides and sulphates) on the mechanical, mineralogical and microstructural features of two types of cementitious systems: i) Portland cementitious systems and ii) a novel “one-part geopolymer”. As Portland cementitious systems, a CEM I/42.5 SR and a CEM III/B 32.5, were selected. The “one-part” geopolymer was prepared with mixtures of metakaolin and blast furnace slag as precursors, and NaOH and Na2SiO3 powders, as solid activators. Results shown that the MS interacts with both cementitious matrixes, affecting the hydration/activation and promoting the crystallisation of sodium/calcium carbonate hydrated phases. Mechanical strengths substantially declined and the microstructure was clearly affected, especially in samples containing 30% of the MS. Some lines of action are suggested to improve the cementation treatment of MS minimising its effect in the development of the different cementitious materials.

Hierarchically porous bioceramics based on geopolymer-hydroxyapatite composite as a novel biomaterial: Structure, mechanical properties and biocompatibility evaluation

In this study, open-cell porous bioceramics based on geopolymers were synthesized by the replica technique. The composition consisted of a mixture of metakaolin (MK) and hydroxyapatite (HA) that combined are suitable for application in bone tissue engineering. Metakaolin is a cheap natural aluminosilicate known for its mechanical properties, while hydroxyapatite stands out for its biocompatibility due to the chemical structure similar to the bone matrix. After undergoing heat treatment (HT), the geopolymer-hydroxyapatite (GMK-HA) synthesized materials, referred to as GMK-HA-HT, presented pores in the range from 1 to 5 mm. In the compressive strength tests, they exhibited values between 1.18 and 2.9 MPa. These ranges of values signify a proper balance between mechanical strength and porosity. X-ray diffraction analysis showed phosphate and/or calcium crystalline phases in all heat-treated samples, indicating HA's successful incorporation in the geopolymer structure. In vitro tests using human adipose-derived mesenchymal stem cells (ADSCs) were conducted to evaluate the biocompatibility of the synthesized materials. The extracts obtained from the GMK-HA-HT were found to be non-cytotoxic. ADSCs in contact with extracts have no morphological changes and when cultured on the GMK-HA-HT surface, the cells interacted with the scaffold and formed a monolayer. Here, for the first time, we provide insights into this new class of materials as a promising biomaterial candidate which could be associated with ADSCs to promote bone healing.

Synergetic effect of cement kiln flue dust for enhancing physico-mechanical properties of metakaolin-blended cement

As a result of the increasing impact of cement kiln flue dust on human health and the environment. In this study, cement kiln flue dust was used as an alkaline activator for mixed cement made from ordinary Portland cement (OPC) and metakaolin (MK). In the first part of the research, the mechanical properties of mixed cement pastes containing different proportions of metakaolin were studied to obtain the best mixture of metakaolin and cement. Various ratios of metakaolin were substituted for MK (5, 10, 15, 20, and 25 %) to obtain the best ratio between OPC and MK. Incorporation of cement kiln flue dust in 15MK mix by different weight ratios (2, 4, 6, 8, and 10%) as a partial substitution ratio from OPC ratio was investigated to improve the pozzolanic activity of MK especially at early ages of hydration. To realization investigate the effect of cement kiln flue dust on MK cement binder, classical tests of setting times and strength at various ages. The results were analyzed by using advanced devices. The results indicated that the MK has a positive effect on the physicomechanical properties of cement. The 15MK mix exhibited the best results regarding the physicochemical and mechanical properties of hardened cement paste, especially at later ages of hydration. The compressive strength of the 15MK mix increased about 23.53% compared with the neat OPC at 28 days of hydration. Based on the physicochemical and mechanical measurement, incorporation of 6% CKFD with 15 % MK in blended cement paste improved the physico- mechanical properties of the hardened cement.

Comparative study of laterite and metakaolin/hematite-based geopolymers: Effect of iron source and alkalization

The objective of this study is to investigate and characterize geopolymers based on laterite or metakaolin-hematite mixture model. The model has been used to reproduce laterite in areas where laterite is not available. The geopolymers were synthetized using (i) calcined laterite and (ii) a mixture of metakaolin and hematite as solid precursors and two alkaline solutions of SiO2/Na2O and SiO2/K2O equal to 1.3. The obtained results reveal that both laterite and metakaolin/hematite-based geopolymers display efficient mechanical properties, regardless of the alkaline activating solution used. Thermal conductivity and compressive strength vary almost linearly, from 0.7 to 1 W/(m.K) and from 20 to 70 MPa, respectively: Na-activated laterite (NaLc) > Na-activated metakaolin + hematite (NaMF) > K-activated metakaolin + hematite (KMF) > K- activated laterite (KLc). This order can be explained by structural modifications after thermal treatment at 1175 °C. In the case of NaLc and NaMF, the samples display weak porosity due to higher crystallinity of the powder. In contrast, KMF and KLc are more heterogeneous with higher porosity.

Effect of microbially induced calcium carbonate precipitation treatment on the solidification and stabilization of municipal solid waste incineration fly ash (MSWI FA) - Based materials incorporated with metakaolin

Microbially induced calcium carbonate precipitation (MICP) has been considered as a potential treatment method for the solidification and stabilization of municipal solid waste incineration fly ash (MSWI-FA).The main obstacle for MICP treatment of MSWI-FA is the harsh environment which causes the bacteria fail to maintain their urease activity effectively, thus decreases the solidification effect and material properties. Currently, there is no research on blending metakaolin (MK) as a protective carrier for the bacteria into the MSWI-FA. The effect of the MICP process on the curing properties of MSWI FA-based cementing materials in the MK and MSWI-FA reaction system is largely unknown. In this study, different mixing ratios of MK were used to adjust the Ca/Si/Al ratio in the mixture, and the properties of the cementing material (MSWI-FA mixed with MK and water) and the MICP-treated material (MSWI-FA mixed with MK and bacterial solution) were investigated. This study contributes to find suitable additives to promote effect of MICP on the solidification of MSWI-FA and the improvement of material properties. The results showed when the mixing ratio of MSWI FA was 90 wt %, the MICP treatment was able to increase the compressive strength of the samples up to 0.99 Mp, and the compressive strength of samples reached 1.46 MPa, when the mixing ratio of MSWI FA was 80 wt %. Though the metakaolin did not show inhibitory effect on the urease activity, the compressive strength of the MICP-treated samples did not further show a significant increase when the mixture of MK was increased from 20 wt% to 30 wt%. Further investigation suggested that MICP activities of bacteria utilizing calcium sources could have an impact on the formation/deformation of calcium-containing hydration products in the reaction system, thus affecting the mechanical and chemical properties of MSWI based materials. MICP treatment is effective in the immobilization of certain heavy metals of MSWI FA, especially for Pb, Cd and Zn. This research shows the potential of using MICP to treat the MSWI fly ash, meanwhile, it is necessary to find suitable reaction system with the proper additives in order to further improve the properties of the MSWI FA based material in terms of mechanical performance.

Effect of different additives on the compressive strength of concrete powder based geopolymer

The aim of the research is to produce geopolymer using secondary raw materials. In this research work concrete powder has been used as a raw material for the production of geopolymers, which belongs to the group of construction and demolition waste (CDW). Beside this various additives (silica fume, aerosil, calcium –stearate, metakaolin, and lime hydrate) have been used to improve mechanical strength. In the study the compressive strength of geopolymers of different compositions (7, 28 and 90 days) was tested, and the geopolymerization processes were identified by FT-IR apparatus. Based on the measurement results the combined mixture of metakaolin and aerosil succeeded in producing the highest compressive strength (=59,64 MPa) geopolymer paste.

Microstructure and flexural performances of glass fibers reinforced phosphate sludge based geopolymers at elevated temperatures

The focus of this study is the development of innovative and sustainable geopolymer composites with improved elevated temperatures performances. To minimize production related costs and support a circular economy model, phosphate sludge and MK are chosen as precursors for alkaline activation, and glass fibers as reinforcement material. The geopolymer composites were prepared by incorporating glass fibers in a geopolymer matrix based on a mixture of metakaolin and PS in a ratio of 50% and with amounts ranging from 0.25% to 1% of fibers. The developed composites were assessed in terms of physical characteristics, microstructural properties and flexural strength prior to and after introduction to higher temperatures. The findings demonstrated that PS based geopolymer matrix flexural strength decreased in the region of temperature between 25 and 600 °C, but increased progressively at higher temperatures, achieving a gain of 3.2% at 1000 °C. The same trend was followed after glass fiber incorporation, leading to a more significant gain of about 16.5% with a 1% fiber content up to 1000 °C. This behavior was assigned to the decomposition of carbonate content of PS at 600 °C as well as to the crystallization of the geopolymer matrix at higher temperatures.

29Si and 27Al MAS NMR spectroscopic studies of activated metakaolin-slag mixtures

Blending metakaolin with slag in alkali-activated materials represents a promising way to achieve both acceptable engineering properties and durability. Nuclear Magnetic Resonance (NMR) spectroscopy has appeared as a key technique to investigate the structure of alkali-activation products. However, there is not a consensus on the analysis of NMR spectra to identify the phases formed in binary slag-metakaolin mixtures. This paper characterizes the phase composition and the reaction degree of alkali-activated metakaolin-slag blends, with special emphasis on the effect of H2O/Na2O ratio. Different approaches based on the literature are presented and implemented to analyze NMR data. The results suggest the formation of a heterogeneous phase involved in the transformation of 3D network to C-A-S-H. The evaluation of the reaction degree showed that the incorporation of slag in activated metakaolin mixtures resulted in higher reactivity of metakaolin and higher compressive strength.

Experimental Study of Blended Binders with Metakaolin

Three metakaolins are evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins vary in mineralogical composition and in fabrication (traditional and flash calcination), but are quite similar in their surface area (16–19 m2/g), but are quite similar in mineralogical composition. Performance of metakaolin mixtures will be compared to two control mixtures (standard concrete for foundation C40/50 and high performance concrete C60/75). In this study, the properties of fresh concrete and the mechanical and durability properties of hardened concrete will be examined. The rheological behaviour are aimed to determine the effect of metakaolin on mixture workability. Compressive, tensile and flexural strength and elastic modulus will be measured at various concrete ages. The influence of metakaolin on durability is assessed through rapid chloride migration and carbonation measurements. For high performance concrete mixtures, drying and autogenous shrinkage will be monitored and creep measurements are performed and compared.

Development of geopolymer derived from slag waste based composite film on cotton fabric: A preliminary approach for flame retardant behavior

Organic-inorganic hybrid composite films with a geopolymer and organic polymers (sodium polyacrylate, polytetrafluorethylene, and polyurethane) were prepared using a facile method for application as flame retardant coatings. The geopolymer paste was successfully synthesized by adding a mixture of metakaolin and slag into an alkali solution. The structural and morphological properties of the barrier films were investigated using Fourier-transform infrared spectroscopy and scanning electron microscopy. The films showed the Si-O and Si-Al peaks characteristic of the geopolymer. The microstructural examination revealed that the films consisted of irregular particles. With an increase in the geopolymer amount, the flexural and compressive strengths of the samples decreased. The tensile strength, thermogravimetric analysis and flame retardant properties of the composite paste were investigated. The films showed a tensile strength of 0.15–0.30 MPa. The composite film coated onto cotton surface was thermally stable up to 200 °C. The cotton (C) and the mixture of cotton and polyester (M) substrates coated with the barrier film showed the char lengths of 5–8 and 4–7 cm, respectively. The geopolymers synthesized using slag and metakaolin exhibited excellent flame retardant properties on the cotton fabric. Hence, these films were found to be promising candidates for flame retardant applications.

Characteristics of Eco-Friendly Metakaolin Based Geopolymer Concrete Pavement Bricks

The purpose of this work is to investigate the possibility to recycled and reused of waste clay brick and waste plastic as constituents in the production of green Geopolymer concrete paving bricks. Powder of clay brick waste (WBP) was used as a partial replacement of Metakaolin (MK) in Geopolymer binder. Moreover, recycled clay brick waste aggregate (BA) and plastic waste aggregate (PL) were incorporated as coarse aggregate in mixtures of Metakaolin based Geopolymer concrete (MK-GPC) pavement bricks. Six types of mixtures were prepared and cast as pavement bricks with dimensions of 150×150×100 mm. All samples have been tested for compressive strength, water absorption and abrasion resistance at age of 28 days; and compared the results with the requirements of Iraqi specification No.1606-2006. The MK-GPC pavement bricks present a compressive strength of 31-47MPa, water absorption of 3.66% to5.32% and abrasion resistance with groove length between 21.78mm to 18.91 mm. These types of pavement bricks are classified as a medium to light capacity for weight loading, and it is possible to be used in wide range of paving applications, especially in aggressive wearing environment.