Metakaolin Research Articles

Analysis of the Strength of Different Minerals-Modified MPC Based on Mathematical Models

The study discussed the effects of different mineral incorporations and the curing time on the strength of modified magnesium phosphate cement (MPC) mortars through mechanical tests, mathematical model analysis and microstructure characterization. Fly ash (FA), silica fume (SF), and metakaolin (MK), which exhibit excellent durability and bonding properties, were used to modify the MPC. A quantitative relationship was established between the strength of modified MPC mortars and the mineral incorporation and curing time. First, the strength of each mineral-modified MPC mortar cured in air with different mineral incorporations and curing durations was evaluated. The strengths of MPC mortars containing 10% fly ash, 15% silica fume, and 10% metakaolin—which perform best in their incorporations—were compared to analyze the function of the three minerals. To establish the relationship between strength and mineral incorporation and curing time, three mathematical models, linear model, general nonlinear model, and data distribution shape nonlinear model (DDSNM), are commonly used for material property analysis based on statistics. DDSNM best describes the trend of strength change among the three models and the error is small for three minerals. Based on DDSNM, the influence of various minerals on the strength of MPC mortar was quantitatively evaluated by calculating the variable partial derivatives, and verified by scanning electron microscopy and X-ray diffraction. MK performs the best in improving the flexural strength performance of MPC, while SF performs the best in the compressive strength. FA-MPC has low sensitivity to dosage fluctuations and is easy to prepare.

Durability prediction of geopolymer mortar reinforced with nanoparticles and PVA fiber using particle swarm optimized BP neural network

Abstract In this study, polyvinyl alcohol (PVA) fibers and nanoparticles were incorporated to enhance the durability of geopolymer mortar (GM) with metakaolin (MK) and fly ash (FA). The dosage of nano-SiO2 (NS) was 0–2.5% and that of PVA fiber was 0–1.2%. The durability of GM includes resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion. Compared with the single BP neural network (BPNN) model, a particle swarm optimized BPNN (PSO-BPNN) model was utilized to predict the resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion of GMs with different dosages of nanoparticles and PVA fibers. In the model, the dosage of NS, PVA fiber, FA, and MK were used as input layers, and the durability parameters of electric flux, mass loss, and compressive strength loss of GMs were used as output layers. The result exhibits that the root mean square errors (RMSEs) of BPNN for resistance to chloride ion penetration, freeze–thaw cycles, and sulfate erosion of GM mixed with nanoparticles and PVA fibers are 145.39, 6.43, and 2.19, whereas RMSEs obtained from PSO-BPNN are 76.33, 2.87, and 1.03, respectively. The NN optimized by particle swarm algorithm has better prediction accuracy. The PSO-BPNN can be utilized for estimating durability of GM reinforced by NS and PVA fiber, which can provide a guide for the proportion design of GM with PVA fiber and NS as well as for the engineering practice in the future.

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.

Production, characterization and performance of green geopolymer modified with industrial by-products

Industrial by-products; have received a lot of attention as a possible precursor for cement and/or concrete production for a more environmentally and economically sound use of raw materials and energy sources. Geopolymer is a potentially useful porous material for OPC binder applications. The use of industrial wastes to produce a greener geopolymer is one area of fascinating research. In this work, geopolymer pastes were developed using alkali liquid as an activator and metakaolin (MK), alumina powder (AP), silica fume (SF), and cement kin dust (CKD) as industrial by-products. Several geopolymer samples have been developed. Research has been carried out on its processing and related physical and mechanical properties through deep microstructure investigation. The samples were cured in water by immersion with relative humidity (95 ± 5%), and at room temperature (~ 19–23 °C) prior to being tested for its workability and durability. The effect of the different composition of precursors on water absorption, density, porosity, and the compressive strength of the prepared geopolymers have been investigated. The results showed that the compressive strength of geopolymers at 28 days of curing is directly proportional to the ratio of the alkali liquid. Ultimately, the best geopolymer paste mixture (GPD1 and GPD2), was confirmed to contain (15% of CKD + 85% MK and Alumina solution (55 wt%)) and (25% of CKD + 75% MK + Alumina solution (55 wt%)) respectively, with 73% desirability for maximum water absorption (~ 44%) and compressive strength (4.9 MPa).

M100 concrete probing on quinary cementitious matrix incorporated with industrial ferrochrome slag sand

The potential exploration of micro (10−6) and nano (10−9) sized binders and Ferrochrome slag sand (FSS) is supplanted and discussed in the M100 concrete. Supplementary Cementitious Materials (SCM) and FSS are supplanted in concrete to sustain and minimize the exploitation of resources. The clinker products are diminished by replacing SCM like Metakaolin (MK) of 8, 10, and 12% and Nanosilica (NS) of 0.5, 1 and 1.5%. Besides, the FSS (10, 20, 30, 40, 50, and 100%) is incorporated in the place of crushed sand (Csand). The in-depth material characterization demonstrates the shape, micro texture, and elemental analysis. The optimum mix (F4) has a compressive strength of 126.08 N/mm2 at 28 days. The densely hydrated cluster (CSH(H&L)) in the F4 mix are an intellectual cause of strength gain. The microstructure with Hadley grain (Peeling bark) in the F10 mix is a root for the strength degradation. The MgO in slag escalates the strength at 365 days. The Packing action of SCM and FSS are schematized. The TGA plot of the F4 mix has a significant (−9.34%) silicate hydrate peak than referral concrete (RC). The Global warming potential (GWP) of the F4 mix saves 12.96% emission of CO2 than RC.

Effects of Waste Plastic and Glass Aggregates on the Strength Properties of Ambient-Cured One-Part Metakaolin-Based Geopolymer Concrete

The production of Portland cement (PC) is associated with carbon emissions. One-part geopolymer “just add water” is a user- and environmentally-friendly binder that can potentially substitute PC. However, there is limited research on the setting time, fresh, and strength properties of one-part metakaolin (MK)-based geopolymer concrete (OMGPC) incorporating recycled aggregates. Hence, the study explored the fresh, mechanical (compressive, flexural, splitting tensile, and E-modulus) and microstructural properties of ambient cured (7-, 28-, and 90-day) OMGPC containing recycled waste plastics (RESIN8) and recycled fine waste glass aggregate (FWG) at 5% and 10% by volume of the sand. The study result shows that 2% trisodium phosphate by wt. of the binder retard the initial and final setting times of OMGPC. At the same time, the incorporation of RESIN8 and FWG aggregates improved the workability of geopolymer concrete. The lightweight properties of RESIN8 aggregate reduce the hardened density of OMGPC, while the FWG specimens show a similar density to the control. The compressive strength of RESIN8 and FWG OMGPC range from 19.8 to 24.6 MPa and 26.9 to 30 MPa, respectively, compared to the control (26 to 28.9 MPa) at all curing ages. The flexural and splitting tensile strength of the OMGPC range from 2.2 to 4.5 MPa and 1.7 to 2.8 MPa, respectively. OMGPC is a viable alternative to Portland cement, and FWG can substitute sand in structural concrete by up to 10% and RESIN8 aggregate at 5% by volume of the natural sand.

Hydration properties of magnesium phosphate cement paste mixed with metakaolin and silica fume

AbstractMagnesium phosphate cement (MPC) exhibits a faster setting time and higher early strength, making it suitable for crack repair. However, its application in civil engineering is hindered by its fast initial hydration rate and poor water resistance. To address these limitations, metakaolin (MK) and silica fume (SF) were utilized to enhance the properties of MPC. The effects of MK and SF on the setting time, compressive strength, water resistance, hydration process, and microstructure of MPC were investigated. The results demonstrate that both MK and SF significantly prolong the setting time of MPC and improve its water resistance. The main hydration products of MPC, after incorporating MK and SF, are k‐struvite (MgKPO4·6H2O) and unreacted MgO. The presence of MgSiO3 and AlPO4 also contributes to the enhancement of compressive strength and water resistance. The incorporation of MK and SF actively participates in the hydration reaction of the MPC system. Furthermore, MgSiO3 and AlPO4 intertwine with MKP, resulting in a denser internal structure of the cured MPC, thereby improving its water resistance.

Effect of sand–precursor ratio on mechanical properties and durability of geopolymer mortar with manufactured sand

Abstract The geopolymer mortar (GPM) prepared from industrial by-products and alkali activation solution (AAS) is one of the hot spots of current building materials. As a feasible alternative to natural river sand, manufactured sand (MS) alleviates the global ecological pressure. In this study, MS was used for fine aggregate. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution were used as AAS. Metakaolin (MK) and fly ash (FA) were used as the precursor to prepare MK-FA-based GPM with MS (MS-GPM), which was of great significance for saving non-renewable resources, mitigating the greenhouse effect, and recycling waste. Numerous studies were conducted to explore the effect of sand–precursor ratio (r sp) on mechanical and durability characteristics of MS-GPM. Relationships between compressive strength and tensile or flexural strength were established by linear fitting equation. Finally, analysis of variance (ANOVA) was used to systematically calculate the effect of r sp on performance. The results indicated that the mechanical strength and impermeability of MS-GPM decreased and crack resistance increased with r sp from 1 to 5. The strength of MS-GPM was the best when r sp was 1. With the increase of r sp, the proportion of MS in MS-GPM increases, and the relative cementitious material decreases, which has an adverse impact on mechanical properties and impermeability. Linear fitting revealed that the compressive strength of MS-GPM was closely related to tensile strength and flexural strength. ANOVA results indicated that r sp in the range of 1–5 had great effects on the performance of MS-GPM. The aim of this article is to further promote the possibility of applying MS-GPM in practical engineering by designing reasonable r sp.

The use of machine learning techniques to investigate the properties of metakaolin-based geopolymer concrete

The construction industry significantly contributes to global greenhouse gas emissions, highlighting the imperative for developing environmentally friendly construction materials. Geopolymers, particularly those utilizing metakaolin (MK), have emerged as a promising green alternative to conventional concrete. However, the acquisition of MK-based geopolymer concrete with optimal mechanical properties poses challenges due to numerous influential factors, disagreement over various findings, and the lack of a reliable predictive model. This study aimed to address this gap by employing a wide range of machine learning methods, namely gradient boosting machine, random forest, decision tree, artificial neural network, and support vector machine. Different optimization and regularization techniques were used to comprehensively understand the factors affecting the compressive strength of MK-based geopolymer concrete, including mixture design, chemical characteristics of the initial binder and activators, and different curing regimes. The results demonstrated the exceptional performance of the gradient boosting machine in predicting the compressive strength of MK-based geopolymer concrete, achieving a coefficient of determination of 0.983 and a mean absolute error of 1.615 MPa. Additionally, the study employed partial dependence plots, feature importance analysis, and SHapley Additive exPlanations (SHAP) to elucidate the proposed models. The coarse-to-fine aggregate ratio, H2O/Na2O molar ratio, extra water content, and sodium hydroxide concentration were identified as the most critical parameters affecting the compressive strength of MK-based geopolymer concrete. This research contributes to advancing the development of sustainable construction materials, streamlining experimental tasks, minimizing the need for labor and materials, improving time efficiency, and providing valuable insights for optimizing the design of MK-based geopolymer concrete.

Mechanical Strength and Microstructure of Soft Soil Stabilized with Cement, Lime, and Metakaolin-Based Geopolymer Stabilizers

Soft soils require particular consideration when designing civil engineering structures due to their high compressibility, low shear strength, and permeability. Using chemical additives and geopolymers to stabilize soft soils is a practical approach to improve their engineering properties. The objective of the study was to explore the use of conventional stabilizers alongside metakaolin-based geopolymers. This study also aimed to investigate the compaction characteristics, mechanical strength, shear behavior, and microstructure of stabilized soft soil. The compaction test was carried out using various amounts of cement (6%, 8%, and 10%) and metakaolin (3%, 5%, and 7%) based on the dry weight of the soil. Cement, lime, and geopolymer were added to the soft soil at 15% of the dry weight of the soil for triaxial shear tests. The compaction test results indicated that the stabilized soil exhibited the highest maximum dry density at 8% cement content. Adding metakaolin (MK) to the cement-modified soil decreased the maximum dry density, smoothed the compaction curve, and increased the optimum moisture content. The unconfined compressive strength (UCS) test revealed that cement-stabilized soil had the highest yield stress, while adding MK to the cement-modified soil reduced the yield stress after 7 days of curing. Compared to untreated soft soil, there was a significant increase in shear strength parameters for cement-, metakaolin-, and lime-stabilized soil. This study demonstrates that adding chemical additives and geopolymers can improve the soft soil’s compaction characteristics, mechanical strength, and shear strength parameters.

Microstructure and mechanical properties of geopolymers utilizing excavated soils, metakaolin and slags

This paper presents a study on the potential of geopolymer (GP) as a substitute for ordinary Portland cement (OPC) in construction applications. OPC is widely used in construction due to its high strength and durability. However, manufacturing is extremely energy-intensive and produces large amounts of carbon dioxide (CO2) emissions. Also, In France, 130 million tons of excavated soils are generated each year [1] and classified as waste material without proper disposal methods. Therefore, the use of excavated clays coming from construction projects in GP formulations will have a positive impact on decreasing waste materials. Moreover, flash calcination used as heat thermal technique eliminate the organic matter and enhance the geopolymerization reaction with the alkaline reagent used in GP. On the other hand, GP are a type of alternative material made from industrial by-products such slags. This study used various methods to optimize GP mix design by evaluating the fresh and hardened properties. The results has shown that GP has a higher compressive strength than OPC in short term (between +5% and 76% at 1 day) and present a comparable strength in long term. The analysis of the microstructure throughout nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) has shown the GP designed has a stable reticulated polymeric structure. Mercury porosity has shown a finer nonometric porosity that corresponds to a compacted and fitted micelle structure. This study provides a solid contribution to the sustainability of the construction industry by developing a GP binder composed of flash-calcined excavated clay (FCC), metakaolin (MK), and slag (GBFS) that can achieve better results than OPC binder.

Potential of Carica Papaya Stem Activated Carbon in Removal of Undesired Compounds from Metakaolin

Metakaolin (MK) is a pozzolan exhibiting additional cementitious tendency and is made by dehydroxylating Kaolin Clay (KC). In this study,potential of Carica papaya Stem Activated Carbon (CPSAC) in removal of undesired compounds or impurities from MK was examined.Carica papaya Stem (CPS) was processed into powder and chemically activated using hydrochloric (HCl) acid, while MK was produced from KC through calcination process.Five conical flasks contained 5 to 25 % CPSAC at 5 % weight intervals. Two hundredg of MK or KC was added and well mixed to achieve homogeneity.The KC+CPSAC samples were subjected to calcination inside a muffle furnace at 700 °C and removed after 1 to 2 h then allowed to cool; while the MK+CPSAC samples were soaked in water (125 mL for each sample) for 24 h, thereafter oven-dried at 105 °C. Subsequently, the samples obtained were subjected to Scanning Electron Microscopy (SEM) analysis to investigate their surface morphology, while X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) techniques were employed to ascertain their chemical and mineralogical compositions, respectively.The data obtained from chemical composition analyses were thereafter subjected to optimization studies.The SEM plates showed thatthe sizes of all thesamples were within ranges of 2 and 50 nm, and their intensity pinnacles from XRD plots ranged between 200 and 4000 cps. CPSAC (21.42%) eliminated the unwanted compounds in the MK andincreasethe amount of its major oxides (Al2O3, CaO, SiO2 and Fe2O3by 43.76,16.89, 12.76, 6.51 %, respectively). In conclusion, CPSAC showed potential as a viable industrial treatment material for MK. HIGHLIGHTS Remediation of unwanted compounds from MK CPSAC’s efficacies in soil (MK) remediation Treatment effects of calcination process and agricultural adsorbent on MK Optimization studies of MK compounds GRAPHICAL ABSTRACT

Pozzolanic Metakaolin Reactions: Stoichiometric and Kinetic Modeling

In the pursue of environmentally-friendly binders for the construction industry, metakaolin (MK) has emerged as promising material, with its hardening performance primarily driven by pozzolanic reactions. However, in systems containing MK and calcium hydroxide (CH), transformation reactions from metastable to stable phases, particularly in excessive CH conditions, can adversely affect material properties. To anticipate these processes, this study introduces a stoichiometry-based reaction modeling approach for pozzolanic MK reactions, encompassing both short-term kinetics and long-term transformation processes. The primary pozzolanic reactions of MK are briefly outlined, highlighting two sequential, partially overlapping reactions forming C4AH13 and C2ASH8. Short-term reaction kinetics are modeled using isothermal calorimetry measurements and deconvoluting the two reaction peaks. The model is in good agreement with experimental quantitative X–ray diffraction (qXRD), thermogravimetric analysis (TGA) and helium pycnometer (density, i.e. solid volume) results. Model limitations are discussed based on qualitative scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis. Leveraging the proposed model, the temperature dependency of pozzolanic MK reactions is analyzed, revealing an activation energy for the primary reaction of 84 kJ/mol. The model is intended to lay a foundation for designing innovative binder systems based on metakaolin, while paving the way for sustainable construction in the future.

Synergistic effect of recycling waste coconut shell ash, metakaolin, and calcined clay as supplementary cementitious material on hardened properties and embodied carbon of high strength concrete

Researchers are investigating eco-friendly binders like coconut shell ash (CSA), metakaolin (MK), and calcined clay (CC) as supplementary cementitious materials (SCM) in high-strength concrete (HSC). Abundantly available as industrial or agricultural waste, these materials, when combined with Portland cement (PC), offer synergistic benefits. This not only improves concrete performance but also addresses waste disposal issues, presenting a sustainable and environmentally friendly solution for long-term use in HSC production. However, this study performed on fresh and mechanical characteristics of HSC blended with CSA, MK, and CCA alone and together as SCM after 28 days of curing. A total of 504 samples of standard concrete were cast and the cubical samples were tested to achieve the targeted compressive strength about 80 MPa after 28 days. The experimental results indicated that the rise in tensile, flexural and compressive strengths of 9.62%, 8.27%, and 10.71% at 9% of CSA, MK, and CC as SCM after 28 days of curing. As SCM content increases, the density, porosity and water absorption of concrete decrease. Moreover, the workability of fresh concrete is getting reduced when the concentration of SCMs increases in HSC. In addition, the concrete's sustainability assessment revealed that employing 18% MK, CC, and CSA as SCM reduced carbon emissions by approximately 11.78%. It is suggested that using 9% CC, MK and CSA together in HSC yields the best results for practical applications in civil engineering.

Analysis of the Rheological Properties of Natural Hydraulic Lime-Based Suspensions for Sustainable Construction and Heritage Conservation.

Natural hydraulic lime (NHL)-based binders play a crucial role in preserving cultural heritage structures, ensuring integrity and longevity. Beyond traditional uses, these binders exhibit potential for integration into both non-structural and structural components, being compatible with innovative manufacturing processes such as digital fabrication. Meticulously designed grouts, with applicability in their fresh and hardened states, are essential for heritage stability. This study explores the relationships between mineral additions, chemical admixtures, and lime for grout formulations, aiming to advance our understanding and inform the optimization of materials for heritage restoration. Key questions include the influence of natural volcanic pozzolan (NVP) and metakaolin (MK) on rheology and the impact of varying ratios of superplasticizer on NHL-based grout's rheological behavior. This systematic evaluation of rheological parameters aims to innovate mix designs, expanding NHL-based binders' applicability in construction and science. Our hypotheses suggest that well-designed lime grout formulations, incorporating NVP and MK, can enhance rheological properties, addressing challenges in sustainable construction and heritage conservation. This research provides valuable insights for optimizing lime-based materials, fostering advancements in heritage restoration, and promoting wider NHL-based binder adoption in diverse construction applications.

Study of Reinforced Concrete with the Addition of Pozzolanic against the Penetration of Chlorides through Electrochemical Impedance Spectroscopy

The present work analyzes the behavior in terms of corrosion resistance of three reinforced concrete formulations over a period of 1 year. The samples were subject to a monitoring methodology using the Electrochemical Impedance Spectroscopy (EIE) technique, working only with the real component over time. Three mixtures were used, one conventional without pozzolanic addition (REF) and two others with pozzolanic additions, rice husk ash (RHA) and metakaolin (MK). Prototypes were created and exposed to the action of a 165 g/L NaCl sodium chloride solution. The characterization of the materials was carried out by determining the chloride diffusion profile (ASTM 1556), analyzing images using tomography and with the support of analytical techniques such as X-ray fluorescence and X-ray diffraction. The monitoring methodology using EIE demonstrated the positive effect of the insertion of pozzolans, rice husk ash (RHA) and metakaolin (MK) in delaying the process of chloride diffusion in the concrete, resulting in greater resistance to corrosion. The EIE also showed that the active mineral addition in concrete, resulting in aluminum-silicic composition (MK), had a predominant protective effect on the steel/concrete interface against the attack of chloride ions.

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.

تطوير القوة وتوصيف البنية المجهرية للملاط القلوي المنشط الثلاثي المخلوط تحت ظروف معالجة مختلفة

This article reports the contribution of diverse oxides existent inraw materials such as ultrafine palm oil fuel ash (UPOFA), ground granulated blast furnace slag (GGBFS), and metakaolin (MK) on the performance of alkaline activated mortars (AAMs). The strength and microstructure development of ternary-blended alkali-activated mortar (AATMs) under various curing conditions, namely temperature, ambient, water, and steam were investigated. Themixturewas prepared with the same content of binder, aggregate and alkaline activator (AA) and cured at 75 ⁰C for 24 hours. The mixture was characterized in terms of compressive strength (CS) as a main property, and confirmed by XRD, and FTIR analyses. The findings indicated that ternary blended AAMs cured at steam temperatures exhibited higher strengths, accompanied by better compacted and homogeneous microstructure, compared to other curing conditions applied. The results showed that due to the high geopolymerization reactivity of ternary blended alkali-activated mortars which is sensitive to the curing conditions and curing at steam temperature was beneficial to the development of geopolymer CS. The XRD and FTIR analyses showed that the total content of Al2O3 and SiO2 plays an important role in CS development

Evaluation of Chloride Ion Attack in Self-Compacting Concrete Using Recycled Construction and Demolition Waste Aggregates

Construction and demolition waste (CDW) destined for recycling companies has great potential for use in civil construction, since it gives rise to recycled aggregates of different particle sizes that can be used in concrete. However, there is a lack of studies on the durability of concrete produced with recycled aggregates from CDW. This study analyzed the influence of incorporating recycled aggregates from CDW, sand, and gravel on the durability parameters of SCC mixtures, with and without the addition of metakaolin (MK), when subjected to two exposure conditions: outdoors and in cycles of attack by chloride ions. Five mixtures were produced: reference SCC, with natural sand and gravel; SCC with recycled sand and gravel; SCC with recycled sand and gravel and the addition of 10% MK; SAC with recycled sand, natural gravel, and the addition of 10% MK; and SCC with natural sand, recycled gravel and the addition of 10% MK. The water/binder ratio was kept constant for all mixtures and the additive dosage was adjusted according to the variation in the use of aggregates. The mechanical and durability properties were assessed using axial compressive strength, ultrasonic pulse velocity, chloride penetration, chloride ion diffusion, and electrical resistivity tests. The results showed the feasibility of using recycled aggregates from CDW in SCC. The addition of MK significantly improved the performance of SCC using these aggregates. The mixtures with added MK showed a low risk of corrosion and high resistance to chloride ion penetration, and, under highly aggressive attack conditions, it was observed that the chloride ions did not exceed the minimum cover thickness recommended for reinforced concrete structures. The addition of MK to the mix with recycled aggregates caused an 84.6% reduction in the Cl− diffusion coefficient, there was also a 40.3% reduction in Cl− penetration and an increase of up to 156.14% in electrical resistivity compared to the mix with recycled aggregates without the addition of MK. The SCC mix with recycled sand and metakaolin stood out positively compared to the others, achieving an axial compressive strength similar to the reference mix (55.10 MPa). We, therefore, conclude that it is possible to produce such a mix with acceptable performance and ensure good behavior under aggressive environmental conditions.

Development and evaluation of basaltic volcanic ash based high performance concrete incorporating metakaolin, micro and nano-silica

High-performance concrete is an excellent choice for modern engineering structures due to its superior performance, low maintenance costs, and long service life. Therefore, this study was aimed to produce high-performance concrete by incorporating a high volume of basaltic volcanic ash along with metakaolin (MK), micro-silica (MS), and nano-silica (NS). An investigation was performed in regard to the mechanical and durability properties, autogenous and drying shrinkage, and microstructural and pore-structure properties. A control mix, binary mixes, and ternary mixes were examined. The binary mixes contained fine (VA) and ultra-fine (VAF) volcanic ashes, and the ternary mixes contained combinations of VA with MK, MS, and NS. Test results show that ternary mixes with 30% and 40% cement substitution demonstrated better strength development and higher resistance to chloride penetration and water absorption. All binary and ternary mixes displayed lower autogenous shrinkage, as well as lower or comparable drying shrinkage than the control mix. Moreover, the combination of VA with MK, MS, and NS up to 40% resulted in micro and pore structure refinement by forming high-density gels. The findings indicate that VA in combination with MK, MS, and NS, can effectively substitute cement at up to 40% for the production of sustainable high-performance concrete.