Metakaolin Content Research Articles

Performance of recycled aggregate concrete with supplementary cementitious materials (fly ash, GBFS, silica fume, and metakaolin): Mechanical properties, pore structure, and water absorption

Recycled aggregate concrete (RAC) is an eco-friendly material that is increasingly being used in new constructions. Nowadays, the application of RAC is mainly limited by lower mechanical properties and durability performance. This paper outlines the mechanical properties (i.e., compressive strength, splitting tensile strength, and flexural strength), pore structure, and water absorption of RAC with supplementary cementitious materials (SCMs). In addition, to improve the properties and more sustainability of RAC, utilization of SCMs such as fly ash (FA), granulated blast furnace slag (GBFS), silica fume(SF), and metakaolin(MK) were used as cement replacement materials. Thirty-two mixtures were designed with five volume ratios of recycled concrete aggregates (RCA) replacing natural aggregate and containing FA, GBFS, SF, and MK contents as cement replacement (by weight), respectively. The results show that up to 20% FA or 20% SF in binary blends, or 15% SF in ternary blends, the RAC had higher compressive and splitting tensile strength and, thereafter, a gradual reduction in strength with an increase in FA or SF. MK significantly increasingly improved the strengths of RAC with binary or ternary blends, with the rise in the replacement ratio of MK. By characterization of the mineral composition and its relative weight, and the pore structure of RAC with SCMs, the critical influential factors on mechanical properties and water absorption of RAC with binary or ternary blends were the pozzolanic action and filling action of SCMs; however, those of RAC with quaternary or multi- blends was the filling action. It was also found that the water absorptions of RAC with SCMs were positive relative to the total intrusion volume and porosity. A regression model of predicted compressive strength was established.

Synergistic effects of the use of metakaolin, sand and water on the properties of cementitious composites for 3D printing

3D concrete printing (3DCP) is a construction technique based on the deposition of successive layers of a cementitious composite without the need for conventional formwork. For the technique to be applied it is necessary that the cementitious composite used allows the passage in continuous flow in a 3D printing nozzle (extrusion capacity) and presents low deformation of the printed layers (buildability). In this perspective, the aim of this study was to understand the influence of Metakaolin (MK), sand and water incorporation on the extrusion capabilities and buildability of cementitious composites for 3D printing. The analysis was designed in a simplex lattice mixture statistical experimental planning. Extrusion ability was evaluated using an experimental flow rate by extruder mill and slump flow. Buildability was analyzed by the maximum number of printed layers, shape retention index, layer thickness variation, and squareness deviation in printed blocks. The squeeze flow test was carried out as a parameter for both printing properties. The water/binder ratio was the most determinant variable in extrusion capacity for its responsibility to fluidize the mixture. Increasing the sand content improves buildability but reduces the application time. On the other hand, MK presented the advantage of controlling viscosity and maintaining good fluidity over time, due to a slower setting. There was a significant interaction between sand and MK in the packing of grains, increasing the properties related to extrusion. It was possible to print with a 30% MK content by adjusting the water. The yield stress was directly related to the flow rate, validating the experimental methodology created. Thus, it was possible to understand the effect of each component, as well as their interactions.

Performance Improved of a Lime and Hemp-Based Concrete through the Addition of Metakaolin

This work describes in detail the experimental investigation of the physico-mechanical properties of nonstructural hemp concrete (usually used as insulating wall material) when the Air-lime based Tradial PF70 binder is partially replaced using Metakaolin. The objective is to reduce the amount of free Ca2+ ions in the binder as these are responsible for the degradation of vegetables particles and can therefore induce a loss of mechanical performances. In order to assess the effectiveness of pozzolanic reaction, amounts of 0%, 10%, and 20% vol. of Air-lime binder were replaced by the Metakaolin material, while testing the mechanical properties of concrete specimens containing 200% and 300% of hemp particles. Through SEM and EDX analysis, a tight relationship has been found to exist between the Metakaolin content and physical-mechanical properties of specimen. The pozzolanic reaction consumes calcium hydroxide from binder to produce Hydrated Calcium Silicates (C-S-H) and in turn, this leads to a decrease in the pH-value of the pore solution which is the main factor responsible for hemp particle degradation.

A comparative cradle-to-gate life cycle assessment of geopolymer concrete produced from industrial side streams in comparison with traditional concrete

Traditional concrete production is a major contributor to global warming. Industrially produced geopolymer concrete is a viable substitute to limit the negative impacts of concrete production. Thus, this study developed novel geopolymer concrete mix designs using industrial side streams, such as bark boiler ash, construction and demolition waste (CDW), fibre waste, and mine tailings. A cradle-to-gate life cycle assessment (LCA) methodology was conducted to evaluate the potential impacts of these different geopolymer concrete (GPC) mix designs in comparison with traditional concrete. The results showed that industrial-based geopolymer concrete with lower amounts of sodium silicate and metakaolin exhibited better environmental performance. Specifically, a 10 % reduction in metakaolin content reduces the global warming impact by 16 % compared with traditional concrete. The processing and curing of industrial waste for concrete formulations has an environmental impact of less than 1 %. From a sustainability perspective, the environmental performance of geopolymer concrete produced from industrial side streams can be further improved by increasing the concentration of recycled waste in the concrete mixes. In addition, the effective use of industrial side streams can improve the waste management, sustainability, and strength of concrete.

Mechanical properties of an eco-friendly one-part alkali-activated binder: Influence of metakaolin and water content

Alkali-activated binder (AAB) is a product with lower carbon footprint and has great potential to be an alternative to Portland cement in civil construction. In this study, one-part AAB has been synthesized by mixing alternative sodium silicate powder, obtained from rice husk ash (RHA) and metakaolin (MK). The main objective was to verify the effect of MK (two types were used with different reactivity characteristics) and water content on the mechanical properties of pastes and mortars produced with the one-part AAB. Some tests were conducted (e.g. setting times, flexural and compressive strengths, elastic modulus) and the results indicated that the MK type and the water content directly affect different properties. As expected, the decrease in water content decreased the workability of the mortars and improved the mechanical strength. A more reactive MK provided an increase in compressive strength higher than 60%. The results confirm the possibility of producing an alternative sodium silicate powder from RHA dissolution, that when mixed with MK, results in AAB with acceptable compressive strength. This paper reveals that with the correct materials and a good mix design, the properties of this eco-friendly AAB can be considerably improved.

Gray correlation analysis of factors influencing compressive strength and durability of nano-SiO2and PVA fiber reinforced geopolymer mortar

AbstractTo investigate the mechanical properties and durability of nano-SiO2, polyvinyl alcohol (PVA) fiber-modified fly ash (FA), and metakaolin (MK)-based geopolymer mortar (FMGM), tests of compressive strength, electrical flux, freeze–thaw cycles, and sulfate dry and wet cycles were conducted. Based on the experimental results, combined with Dunn’s gray correlation theory analysis method, a mathematical analysis of the effect sensitivity of the contents of the four mixtures on the mechanical properties and durability of FMGM was carried out. The method of gray correlation analysis can solve the mathematical problem with partial unclear and uncertain information, and the method requires less data and less computation compared with other mathematical analysis method. The results showed that the gray correlation degree between the content of MK and the electric flux value is higher than the that of other comparison sequence and each reference sequence, while the gray correlation degree between the PVA fiber dosage and the loss rate of compressive strength is lower than that of other comparison sequence and each reference sequence. The influence of the four mixture contents on the compressive strength and mass loss rate was in the following decreasing order: MK and FA, PVA fiber, and nano-SiO2. In addition, the influence of the four material mixture contents on the electric flux value and compressive strength loss rate was consistent in the following decreasing order: MK and FA, nano-SiO2, and PVA fiber. Furthermore, the mechanical properties and durability reached the optimum when the PVA fiber content was 0.6% and the dosage of nano-SiO2was 1.0%. The results of this study can provide a new method for the analysis and evaluation of mechanical properties and durability of nano-SiO2and PVA fiber-reinforced FMGM in future.

Prediction of Rapid Chloride Penetration Resistance to Assess the Influence of Affecting Variables on Metakaolin-Based Concrete Using Gene Expression Programming.

The useful life of a concrete structure is highly dependent upon its durability, which enables it to withstand the harsh environmental conditions. Resistance of a concrete specimen to rapid chloride ion penetration (RCP) is one of the tests to indirectly measure its durability. The central aim of this study was to investigate the influence of different variables, such as, age, amount of binder, fine aggregate, coarse aggregate, water to binder ratio, metakaolin content and the compressive strength of concrete on the RCP resistance using a genetic programming approach. The number of chromosomes (Nc), genes (Ng) and, the head size (Hs) of the gene expression programming (GEP) model were varied to study their influence on the predicted RCP values. The performance of all the GEP models was assessed using a variety of performance indices, i.e., R2, RMSE and comparison of regression slopes. The optimal GEP model (Model T3) was obtained when the Nc = 100, Hs = 8 and Ng = 3. This model exhibits an R2 of 0.89 and 0.92 in the training and testing phases, respectively. The regression slope analysis revealed that the predicted values are in good agreement with the experimental values, as evident from their higher R2 values. Similarly, parametric analysis was also conducted for the best performing Model T3. The analysis showed that the amount of binder, compressive strength and age of the sample enhanced the RCP resistance of the concrete specimens. Among the different input variables, the RCP resistance sharply increased during initial stages of curing (28-d), thus validating the model results.

Effects of water to binder ratio on the chloride binding behaviour of artificial seawater cement paste blended with metakaolin and silica fume

• Effects of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on chloride binding behaviour of seawater cement paste (SCP) are investigated. • Influence of water to binder (w/b) ratios (0.2 and 0.4) and SCMs (silica fume and metakaolin) on the porosity and pore size distribution of SCP is revealed by the 1 H Nuclear magnetic resonance (NMR) measurement. • The risk of steel corrosion in SCP with different w/b ratios is evaluated by the [Cl − ]/[OH − ] ratio. • The relationship between chloride binding ratio, porosity and [Cl − ]/[OH − ] ratio has been explored. This work investigates the effects of water-to-binder (w/b) ratio and supplementary cementitious materials (SCMs) including silica fume (SF) and metakaolin (MK) on chloride binding of seawater cement paste (SCP) by using a water extraction method. The chloride binding capacity, contents of chloride bound in Friedel’s salt and chloride adsorbed by C S H gel are quantified. The resistance to steel corrosion is evaluated by [Cl − ]/[OH − ] ratio. The results show that the chloride binding ratio (content of bound to free chloride) gradually increases with the w/b ratio decreasing from 0.4 to 0.2. In addition, the chloride ions adsorbed by C S H gel in SCP with w/b ratio 0.2 contributes more largely to chloride binding capacity than SCP with w/b ratio 0.4. Moreover, the incorporation of MK improves the chloride binding capacity of SCP while the utilization of SF doesn’t make much difference. In addition, the [Cl − ]/[OH − ] ratio in SCP keeps at a very low level during the whole experimental process, and decreases with the reduction of w/b ratio, the increase of content of MK and curing ages. The correlation of chloride binding ratio with [Cl − ]/[OH − ] ratio can be described by an exponential decay model while a linear relationship is observed between chloride binding ratio and the volume of macropores larger than 200 nm in diameter.

CHARACTERIZATION OF METAKAOLIN PREPARED FROM UN-TAPPED KAOLIN DEPOSIT AS ALTERNATIVE TO CEMENT IN CONSTRUCTION INDUSTRY

In this work, the production and characterization of metakaolin from un-tapped kaolins deposit were carried out and their pozzalanic reactivity in cement replacement were evaluated between 28days and 56days accompanied by a steep decrease of Ca(OH)¬¬¬2 content. The physiochemical properties of the two kaolins and metakaolins were studied by X-ray fluorescence (XRF), thermogravimetry analysis (TGA) and X-ray diffraction (XRD) analysis. The properties of cements containing metakaolin were monitored for period up to 56days. Two metakaolins derived from indigeneous Ahoko and Aloji Kaolins were used. Cement mortars and concretes with 0%, 5%,10%, 15%, 20%,30% and 35% metakaolin’s were studied. Water demand and setting time were determined in all samples. The blended cements of the metakaolins demand significantly more water than the relatively pure cement. 10% replacement has the highest water demand percentage .it is concluded that a 10% metakaolin content of Ahoko and 10% metakaolin content of Aloji seems to be generally favorable than the other replacement percentages. The produced metakaolins derived from indigenous kaolins are good pozzolans with respect to setting time and water demand. Keyword: cement; metakaolin; dehydroxylation; pozzolan; setting time

Composition design and characterization of alkali-activated Slag–Metakaolin materials

This study explores the effects of the interactions among Na2O content, metakaolin content and activator modulus on the compressive strength and autogenous shrinkage of alkali-activated slag–metakaolin (AASM) materials. The Box–Behnken RSM design was used to create an experimental scheme, establish a model, and optimize the mix proportions. Fourier transform infrared spectroscopy, scanning electron microscopy, and Mercury intrusion experiments were used to analyze the compositions, microstructures, and pore structures of the hydration products of the AASM, respectively. Results showed that the interactions between the activator modulus and metakaolin content, as well as Na2O content and metakaolin content, are the key factors affecting the compressive strength and autogenous shrinkage, respectively, of the AASM. Under the optimal conditions of Na2O content of 6%, sodium silicate modulus of 1.5, and metakaolin/slag ratio of 1: 3, the relative errors in the model verification test for compressive strength and autogenous shrinkage are 0% and 0.18%, respectively. In the water glass modulus and metakaolin content interaction, Ca2+, A13+, and Si4+ ions in the composite system react with several [SiO4]4− groups to form C-A-S-H and N-A-S-H gels, which fill each other to make the composite structure denser. When Na2O interacts with metakaolin, the OH− and Na+ in the solution react with A13+ and Si4+ to generate additional N-A-S-H, thereby reducing the compressive strength of the composite system, mitigating autogenous shrinkage, and increasing volume stability.

Effect of Metakaolin Content and Water/Binder Ratio on Strength and Durability Properties of Modified Cement Mortar

Abstract The aim of this research was to examine the effects of metakaolin (MK) content and low water/binder (w/b) ratio on the basic performance and durability properties of cement mortar. The effects of various mix proportions on the flowability, consistency, water absorption, and mechanical properties of modified cement mortar were investigated. Also analyzed were the effects of MK content on the impermeability, frost resistance, and sulfate corrosion resistance of modified cement mortar when the w/b ratio was 0.31, according to the basic physical properties that were comprehensively considered. The internal microstructure of the modified cement mortar was analyzed by scanning electron microscopy. According to the results, 10 replacement levels were the optimum level of MK content in terms of strength and durability properties at a w/b ratio equaling 0.31. Compared with the control cement mortar, the modified cement mortar containing MK showed better development in strength and durability properties.

Durability of Repair Metakaolin Geopolymeric Cement under Different Factors

Nowadays, energy saving, and green sustainability are influencing the development of all industries, including the construction industry. In recent years, geopolymeric cement and concrete have become hot topic materials as a replacement for traditional OPC; this work carried out orthogonal experiments to identify four potential factors affecting the basic properties of the metakaolin-geopolymeric cement specimens. The results showed that the metakaolin and activator contents were the two primary influencing factors. Given the importance of studying the durability of building restoration materials in harsh environments, this experiment focused on testing the bond strength, permeability resistance, sulphate corrosion resistance, and freeze-thaw resistance of metakaolin geopolymer pastes with different proportions of metakaolin dopant and alkali activator content. The findings are that durability of the formed specimens significantly improved when suitable metakaolin and activator contents were incorporated, and bond strength was also improved. Moreover, the microscopic tests, including SEM and FT-IR experiments, were used to better reflect the changing durability of pattern. The experiments showed that the best durability of the metakaolin geopolymeric cement was achieved when the ratio of metakaolin to cement was 1.5 and the ratio of activator to cementitious material was 0.3. It can be concluded that the appropriate content of metakaolin and activator can give the geopolymer excellent performance under harsh conditions, which will contribute to the wide application of geopolymer.

Utilization of crushed recycled glass and metakaolin for development of self-compacting concrete

• Crushed recycled glass and metakaolin were used for developing self-compacting concrete. • Crushed recycled glass has capability to improve the flow-ability of SCC. • The use of metakaolin offers improved strength properties at all glass replacement levels. • A relation between compressive strength, glass replacement and metakaolin content was developed. • Microstructural investigation of SCC was done through SEM, EDS and XRD analysis. Hypothetically, all the glass is recyclable, despite of which, only a small fraction of it is recovered globally. Furthermore, decomposition rate of waste glass is lowest when compared to conventional waste such as paper, rubber and plastic. So a gainful utilisation of waste glass in production of self-compacting concrete (SCC) would be fascinating. To this goal, a greener SCC incorporating crushed recycled glass (CRG) has been developed in this study. Alongside, the influence of metakaolin (MK) on fresh, strength and microstructural properties of CRG incorporated SCC was studied. To achieve this purpose, a total of 24 different SCC mixtures were prepared in which MK was used as a cement substitute; cement was partially replaced with 0%, 4%, 8%, and 12% MK and CRG was used to replace fine aggregate at the level of 0, 10, 20, 30, 40 and 50 % by volume. Slump flow, V-funnel, l -box and U-box test relates to passing and flowing ability of SCC, were improved as the CRG content increased in the mix. However, mechanical properties were decreased with increase in CRG content. Incorporating MK in CRG incorporated SCC mixtures improved the strength properties corresponding to all the glass replacement levels. The results showed that a greener SCC can be made using crushed recycled glass as sand replacement material and metakaolin as cement substitute.

Hybrid MARS-, MEP-, and ANN-based prediction for modeling the compressive strength of cement mortar with various sand size and clay mineral metakaolin content

Hybrid MARS-, MEP-, and ANN-based prediction for modeling the compressive strength of cement mortar with various sand size and clay mineral metakaolin content

Simultaneous stabilization/solidification of arsenic in acidic wastewater and tin mine tailings with synthetic multiple solid waste base geopolymer

Stabilization/Solidification (S/S) is considered as a feasible technology for the treatment of arsenic (As) in acidic wastewater (AW) and tin mine tailings (TMTs); however, high cost, high carbon footprint, and strict reaction conditions are the main limitations. Herein, a novel alkali-activated geopolymer material (AAGM) for S/S As was synthesized by combining AW, TMT, gypsum (GP), and metakaolin (MK). At room temperature, an initial As concentration of 3914 mg/L, a NaOH content of 4.98%, and an MK content of 20% decreased the As leaching concentration to 1.55 mg/L (<5 mg/L). The main S/S mechanisms of As included physical encapsulation of C-(A)-S-H and geopolymer structures, ion exchange of ettringite, and formation of Fe–As and Ca–As precipitates. Further studies showed that increasing initial As concentration and MK content facilitated the formation of Ca–As precipitates and C–(A)–S–H gels. The semi-dynamic leaching tests revealed that the leaching mechanism of As was surface wash-off. The effective diffusion coefficients of the samples were less than 10−13 cm2/s, and the respective leachability indexes were greater than 9, indicating that AAGM was effective in preventing the leaching of As. Therefore, this study provides a green and low cost solution for the synergistic utilization of AW, TMT, GP, and MK.

Evaluating the properties of hot asphalt mixtures modified by Metakaolin

The mineral filler has an important role in filling the voids between aggregates inside the asphalt matrix. This study investigates the effect of using Metakaolin (MK) as a modifier on the mechanical properties of hot mix asphalt. MK was added to the mixtures as a part of the filler used. As known, the hot mix asphalt (HMA) consists of coarse aggregate, fine aggregate, filler material, and asphalt binder with or without existing modifiers. The components of the HMA were subjected to validation tests to check the validity of the materials for producing HMA The asphalt binder used was bitumen 60/70. Tests performed on bitumen were penetration test, softening point test, flash and firing point test. The optimum asphalt content based on the designed control mix was 5.2%. the control mix has no content of MK. MK was added as a partial replacement of filler used (limestone powder). Mk was added to the HMA by replacing 20%, 40%, 60%, 80%, and 100% of the filler. A comparative study was performed to evaluate the effects of HMA modification by MK. Marshall quotient (MQ) increases by 10.37% for the mix modified by 40% MK. MK has significant effects on the indirect tensile strength (ITS).

Prediction of Rapid Chloride Penetration Resistance of Metakaolin Based Concrete Using Multi-Expression Programming

This study investigates the resistance of concrete to Rapid Chloride ions Penetration (RCP) as an indirect measure of the concrete’s durability. The RCP resistance of concrete is modelled in multi-expression programming approach using different input variables, such as, age of concrete, amount of binder, fine aggregate, coarse aggregate, water to binder ratio, metakaolin content and the compressive strength (CS) of concrete. The parametric investigation was carried out by varying the hyperparameters, i.e., number of subpopulations Nsub, subpopulation size Ssize, crossover probability Cprob, mutation probability Mprob, tournament size Tsize, code length Cleng, and number of generations Ngener to get an optimum model. The performance of all the 29 number of trained models were assessed by comparing mean absolute error (MAE) values. The optimum model was obtained for Nsub = 50, Ssize = 100, Cprob = 0.9, Mprob = 0.01, Tsize = 9, Cleng = 100, and Ngener = 300 with MAE of 279.17 in case of training (TR) phase, whereas 301.66 for testing (TS) phase. The regression slope analysis revealed that the predicted values are in good agreement with the experimental values, as evident from their higher R and R2 values equaling 0.96 and 0.93 (for the TR phase), and 0.92 and 0.90 (for the TS phase), respectively. Similarly, parametric and sensitivity analyses revealed that the RCP resistance is governed by the age of concrete, amount of binder, concrete CS, and aggregate quantity in the concrete mix. Among all the input variables, the RCP resistance sharply increased within the first 28 days age of the concrete specimen and similarly plummeted with increasing the quantity of fine aggregate, thus validating the model results.

A State-of-the-Art Review on the Incorporation of Recycled Concrete Aggregates in Geopolymer Concrete

Geopolymer concrete (GC) has the potential to incorporate recycled concrete aggregates (RCA) obtained from construction and demolition waste. This research aims to review the current state-of-the-art knowledge of the RCA in GC and identify the existing knowledge gaps for future research direction. This paper highlights the essential factors that impact the GC’s mechanical and durability properties. Moreover, the influence of various percentages of coarse and fine RCA and the pattern of their replacement will be assessed. The effect of aluminosilicate material, alkaline activators, and curing regime also will be evaluated. Besides, the durability-related characteristics of this concrete will be analysed. The impact of exposure to a higher temperature, freeze–thaw cycles, marine environment, and acid and alkali attack will be comprehensively reviewed. A literature review revealed that increasing alumina silicate content, such as slag and metakaolin, and increasing the Na2SiO3/NaOH ratio and alkali-activator-to-binder ratio improve the hardened GC. However, increasing slag and metakaolin content and the Na2SiO3/NaOH ratio has an adverse impact on its workability. Therefore, finding the optimum mix design for using RCA in GC is vital. Moreover, there is a scope for developing a self-compacting GC cured at ambient temperature using RCA.

Experimental Study on the Mechanical Properties and Microstructure of Metakaolin-Based Geopolymer Modified Clay.

Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering.

Impact of metakaolin content and fineness on the behavior of calcined clay blended cements admixed with HPEG PCE superplasticizer

In this study, three calcined clays (CCs) possessing different metakaolin contents (23; 51 and 86 wt%) were investigated with respect to their pozzolanic reactivity, water demand and workability in the presence of an HPEG PCE superplasticizer. Furthermore, mixed CC samples were prepared by blending a specific CC of low metakaolin content (23 wt%) with pure metakaolin to achieve metakaolin contents of 30, 40 and 51 wt% in the final CC. Results on pozzolanic reactivity from the R3 test evidenced that increased metakaolin contents result in higher pozzolanic reactivity and improve 1d compressive strength. Whereas, higher metakaolin contents increased water demand significantly. Moreover, PCE dosages of up to 12 times were recorded. Furthermore, it was found that also fineness of the CC influences workability. Fineness mainly affects the water demand, while the metakaolin content plays a dominant role regarding PCE dosage. A mechanistic investigation revealed that in cement pore solution calcined clays initially exhibit a negative surface charge, but then sorb huge quantities of Ca2+ which enables PCE to adsorb onto the surfaces of CCs, as was evidenced by zeta potential measurements and from adsorption isotherms.