Substitution Of Metakaolin Research Articles

Study on the mechanical properties and microstructure of fiber reinforced metakaolin-based recycled aggregate concrete

The paper aimed to study the compound effect of metakaolin (MK) and fiber, including polyvinyl alcohol (PVA) fiber (PF)and basalt fiber (BF) on the recycled aggregate concrete (RAC). Eighteen kinds of RAC were prepared and divided into three groups, namely the RAC mixed with MK (RM) group replacing cement rate of 0%, 5%, 10%, 15%, 20% and 25%, the RM-BF group mixed with 1.3% BF (percentage of cementitious material) based on the RM group, and the RM-PF group mixed with 1.3% PF based on the RM group. The mechanical properties such as compressive strength, splitting tensile strength, flexural strength, and bending toughness were studied, and the pore structure was analyzed by nuclear magnetic resonance (NMR). In addition, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the crystal composition and micro morphology. The results showed that MK had a positive effect on the improvement of the mechanical properties and the improvement of microstructure of RAC, and this positive effect first increased and then decreased with the increase of MK substitution rate. For the RM-PF group and RM-BF group, the study indicated that the mechanical properties and microstructure of RAC under the combined effect of fiber and MK were further improved. Especially in terms of mechanical properties, the splitting tensile strength and flexural strength enhancement was more significant. The internal pores of RAC with MK substitution rate of 15% and fibers were significantly reduced, and a large amount of calcium silicate hydrate (C-S-H) gel was generated inside RAC, which had the best adhesion to the fiber. It was believed that RAC with PF and 15% MK had the most significantly enhanced performance.

Manufacturing of Low-Carbon Binders Using Waste Glass and Dredged Sediments: Formulation and Performance Assessment at Laboratory Scale

Few studies focus on the co-valorization of river dredging sediments (DS) and residual waste glass (RWG) in alkali-activated binders. This study investigates the use of DS as an aluminosilicate source by substituting a natural resource (metakaolin (MK)), while using RWG as an activator (sodium silicate source). Suitable treatments are selected to increase the potential reactivity of each residue. The DS is thermally treated at 750 °C to promote limestone and aluminosilicate clays’ activation. The RWG (amorphous, rich in silicon, and containing sodium) is used as an alkaline activator after treatment in 10 M NaOH. Structural monitoring using nuclear magnetic resonance (29NMR and 27NMR), X-ray diffraction, and leaching is conducted to achieve processing optimization. In the second stage, mortars were prepared and characterized by determining compressive strength, water absorption, mercury porosimetry and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). Results obtained show the great advantage of combining RWG and DS in an alkali-activation binder. The treated RWG offers advantages when used as sodium silicate activating solution, while the substitution of MK by calcined sediments (DS-750 °C) at 10%, 20%, and 30% leads to improvements in the properties of the matrix such as an increase in compressive strength and a refinement and reduction of the pore size within the matrix.

Insights to the sulfate resistance and microstructures of alkali-activated metakaolin/slag pastes

In this work, the effects of slag addition on the geopolymerization process and sulfate resistance of alkali-activated cement were studied. The substitution of metakaolin by slag increased the reactivity of precursors, contributing to a higher reaction rate and accelerating geopolymerization process. The mechanical properties and sulfate resistance were significantly improved with the incorporation of slag. The results show that the transformation of gel phases and development of pore structures were the vital reasons for improvement of sulfate resistance. The quantity of C-A-S-H generation increased with the slag content and consequently to a more compact microstructure. The refinement of pore structures came from the higher space-filling capacity of C-A-S-H phase and the filling effect of slag particles. The optimum replacement level of metakaolin was 30 wt%, in terms of sulfate resistance development and the potential damage of ettringite. This work provides a reference for the utilization of granulated blast furnace slag in metakaolin based geopolymer, which is of great value in urging geopolymer towards practical application in harsh environment.

The influence of Metakaolin on the copper slag substituted concrete with the fine aggregate of Beas river

Shortage of natural aggregates boosts the usage of alternate materials, therefore for enhancing the characteristics of the concrete made by alternative materials the influence Metakaolin on the characteristics of concrete was investigated. The present analysis shows the consequences of Metakaolin on the mechanical and durability characteristics of Copper Slag (CS) concrete as a substitute for Beas river fine aggregates in which CS substitution levels were retained at 0%, 20%, 40%, & 60% and its characteristics were improved with Metakaolin (MK). We added MK to the mixes in which 40% & 60% were the substitution amounts. The effects of the mechanical characteristics were investigated based on the compressive strength and split tensile strength, while the durability characteristics were tested on the basis of initial surface water absorption for the cube and water absorption values. For the 40% substitution of fine aggregates with Copper Slag (CS) and 10% substitution of Metakaolin with Cement, the best results for mechanical and the attributes of the durability of the concrete were observed.

Mine wastes based geopolymers: A critical review

Abstract The quantities of waste rocks and tailings generated by the mining industry have been increased in the last decades. The accumulation and the surface storage of these mine wastes represents a real challenge in terms of environmental and health issues. Thus, the recycling and valorization of these mine wastes is one of the most effective ways of reducing their volume and mitigating their negative environmental impact. Among the recent and sustainable management strategies, geopolymerization technology offers many advantages, (i) the stabilization of polluted/inert mine wastes in the geopolymer matrix, (ii) valorization of a large volume of wastes in the construction sector and consequently minimization of environmental impacts, and finally (iii) the significant reduction of greenhouse gas emissions generated by the use of ordinary Portland cement (OPC) in the construction sector. This paper is intended to present an updated and critical review of the existing literature about mine wastes based geopolymers, by focusing mainly on the mechanical performances of each type of waste. The fundamentals of geopolymers synthesis and the effect of metakaolin substitution by mine wastes are investigated. The influence of the chemical composition of mine wastes was linked to the compressive strength. Results of recent studies showed that geopolymeric materials elaborated using mine wastes presented similar or better mechanical, physical, and durability properties compared to OPC.

Valorisation of soil contaminated by petroleum hydrocarbons and toxic metals in geopolymer mortar formation

Until the complete transition to a renewable energy sources based economy, the potential environmental hazards associated with petroleum refinery industries affecting water, air and soil seek sustainable solutions. In the present study contaminated soil from a refinery is used as an alternative source for producing useful building materials by geopolymerization. To this end, soil remediation by thermal desorption was initially applied. Thermal treatment was performed between 60 and 250 °C for short time intervals (10–30 min) in order to remove organic pollutants (Total Petroleum Hydrocarbons, TPHs and Polycyclic Aromatic Hydrocarbons, PAHs). Physical, chemical analyses, mineral phase composition, as well as thermogravimetric analysis were employed to characterize the sample. Moreover, removal efficiency of TPHs and PAHs was evaluated. Subsequently, the treated soil presenting the maximum elimination of TPH and PAHs was used in geopolymer mortar formation aiming to stabilize the toxic metals (TMs) and produce a possible profitable material. For geopolymer synthesis the substitution of metakaolin (MT) by treated soil at 0, 50, 70 and 100% was tested. The produced specimens were evaluated based on the 28 day compressive strength and metals leaching. Results showed that the geopolymer constructed by 50% MT-50% remediated soil at 250 °C for 30 min, had negligible content of organic pollutants, TMs were immobilized and exhibited increased strength thus giving significant recycling benefits. Valorisation of industrial residues to produce building materials is a promising solution for sustainable waste management.

Performance-based evaluation of flash-metakaolin as cement replacement in marine structures – Case of chloride migration and corrosion

In order to increase the durability of concrete in maritime environments, it is often recommended to use supplementary cementing materials such as silica fume or blast furnace slag. Metakaolin, even of low purity, also allows a significant improvement of the chloride diffusion. The aim of this work was to evaluate the characteristics of concretes based on flash metakaolin when exposed to a marine environment. Concretes based on CEM I cement (more than 95% of clinker) or CEM II/A cement and metakaolin were compared to a cement often used in a marine context (SR cement). The results show that a substitution of metakaolin for CEM I or CEM II/A allowed a reduction of the coefficient of chloride migration into the cementitious paste on the one hand and, on the other hand, gave results similar to those of sulfate resistant cements with a low C3A content. Then, tests of accelerated corrosion confirmed the beneficial effect of metakaolin in a marine context. Finally, a predictive model was used to estimate the lifespan of the mixtures exposed to chloride ions. The model showed that the substitution of metakaolin for cement could significantly increase the lifespan of the structures.

KAJIAN KARBONASI PADA BETON MUTU TINGGI MEMADAT MANDIRI DENGAN VARIASI KOMPOSISI METAKAOLIN

<p class="Abstract"><em>The construction industry is an important thing to support the development of a country. In concrete construction, quality, strength, and durability of concrete are the main requirements of all. In urban tropical countries, carbonation is one of the essential factors that affect the durability of concrete, and it may cause corrosion of reinforced steel in concrete. Therefore, high strength self-compacting concrete may be expected as the solution, improved by pozzolanic additions, metakaolin with substitution dosage at 10%; 12,5%; 15%; 17,5%; and 20%. This study purposed to determine the effect of metakaolin and its optimum dosage to improve high strength self-compacting concrete quality on its carbonation rates. This study was done by using experimental methods. It needs a plain cylindrical concrete with 75 mm diameter and 150 mm height, and testing by SNI 03-6468-2000, EFNARC 2002, and SEM-PUPR 25-2015. The carbonation test is done using accelerated laboratory carbonation </em><em>in Structures and Materials Laboratory, Faculty of Engineering, Universitas Sebelas Maret </em><em>by soaking the specimens in a 4% carbonate solution for 15 days, 37 days, and 51 days, proceeded by splitting using CTM, and spray it using a 1% phenolphthalein indicator to determine its carbonation depth. Based on the results, metakaolin might improve concrete quality by reducing its carbonation rates by 15% substitution dosage of cement content, with a nominal atmospheric carbonation coefficient 3,71 mm/year<sup>½</sup>, reduced 44,41% from HSSCC without metakaolin substitution. Metakaolin addition might reduce fresh concrete's workability and fulfill self-compacting concrete requirements specified by EFNARC 2002.</em></p>

Hydration and mechanical properties of UHPC matrix containing limestone and different levels of metakaolin

In this paper, the hydration process and mechanical properties of UHPC matrix incorporated with limestone (LS) and different substitution rates of metakaolin (MK) were investigated. MK was added with five levels of substitution (0, 5%, 10%, 15% and 20%) and LS was kept at 30% of the total binder mass. Mechanical properties, hydration heat, hydration products and pore structure measurements were carried out for every mixture. The results show that the hydration rate as well as the hydration heat peak of UHPC pastes decrease with MK level in the first 24 h possibly due to the higher superplasticizer usage, but the hydration process is accelerated with the incorporation of MK after 24 h. The pozzolanic reaction of MK and synergistic effect with LS consumes portlandite and induces the formation of more CSH gels with the improved microstructure of UHPC matrix. The trace of calcium monocarboaluminate (Mc) phase can be observed in UHPC paste samples with a low MK substitution (5%), and becomes weaker with the higher MK dosage. The pozzolanic reaction of MK with replacement level of 15% results in the best long-term compressive strength of UHPC mortars. Therefore, the incorporation of both MK and LS at an optimal level is favorable to manufacture UHPC with improved mechanical properties.

Improving the Properties of Self-compacted Concrete with Using Combined Silica Fume and Metakaolin

The viscosity is the main property of self- compacted concrete (SCC) and using of pozzolan material such as metakaolin (MK) and Silica fume (SF) can help to achieve that goal. The effect of simultaneous substitution of MK and SF instead of cement on the rheological and mechanical properties of self-compacted concrete was experimentally investigated in this paper. Seventeen mix designs were cast with a substitution weight percentage (5, 10, 15, 20 %) in water to adhesive material ratio equal 0.32. All mixes were examined by compressive, tensile strengths and water absorption tests with an appropriate fluidity, without having signs of segregation or instability. The test results were indicated that the SCC mixes containing MK and SF had higher compressive and tensile strengths in comparison with no-pozzolan concrete. The comparison of linear multiple regression techniques (LMRT) and nonlinear multiple regression technique outputs with experimental results showed an appropriate similarity.

Comparative Study on Geopolymer Binders Based on Two Alkaline Solutions (NaOH and KOH)

This study specifically investigated the influence of the composition of aluminosilicate material i.e. the substitution of metakaolin by rice husk ash and the nature of alkaline activators (Na+/K+) on mineralogical, structural, physical and mechanical properties of geopolymer binders. This influence was evaluated based on X-ray diffraction (XRD), Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscope (SEM analyses, apparent density, water accessible porosity, compressive strength and thermal properties. Two types of geopolymer binder were synthesized according to the type of alkali activator used, the NaOH-based geopolymer and the KOH-based geopolymer. The results of characterization performed after 14 days of curing of geopolymer samples showed that the activation of the aluminosilicate powder using alkaline solution led to change in their microstructure. The highest compressive strength was obtained with the NaOH-based geopolymer.

Reactivity and Microstructure of Metakaolin Based Geopolymers: Effect of Fly Ash and Liquid/Solid Contents.

Geopolymers are inorganic binders based on mixtures of an aluminosilicate powder with an alkali-silicate solution. Properties of geopolymers are strongly determined by the type of reactive solid, the liquid/solid ratio of paste and, amongst others, the Si/Al ratio of the formed geopolymer network. In this study, fly ash blended metakaolin based geopolymers with varying liquid/solid ratios (l/s), activated by potassium silicate solution, are investigated. Reactivity of metakaolin and fly ash was investigated by powder X-ray diffraction (XRD) and dissolution tests. Reactivity, mechanical properties and microstructure of hardened pastes were analyzed by setting and compressive strength tests, mercury intrusion porosimetry (MIP), capillary water absorption tests, thermogravimetric analysis-differential scanning calorimeter (TGA-DSC), isothermal calorimetry and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The results show that substitution of metakaolin by fly ash as well as variation of l/s brings advantages up to a certain degree, but also has a considerable influence on the pore size distribution, mechanical properties, Si/Al ratio of the geopolymer network and the content of bound water.

Mitigating alkali-silica reaction induced concrete degradation through cement substitution by metakaolin and bentonite

This paper reports the results of an investigation on the efficiency of cement modification with clay minerals in preventing deteriorations of concrete due to alkali-aggregate reactions. Coupled substitution of metakaolin and bentonite in Portland cement was studied for a synergistic effect to mitigate alkali-silica reactivity (ASR). The expansion and cracking behavior of mortar bars were investigated. Hydration products of cement blends in two environments, immersion in saturated lime water and “mortar bar test” environment (i.e., in 1 N sodium hydroxide solution at 80 °C), were characterized. The role of the clay-based minerals in mitigating ASR was also evaluated by monitoring the strength development and characterizing the microstructural defects of the cement blends. The results indicate that cement modification with a combination of metakaolin and bentonite can effectively mitigate ASR-induced concrete deteriorations. By replacing 10% and 30% cement, expansion of mortar was decreased from deleterious to innocuous level. With 50% cement substitution, no ASR expansion was observed, and accordingly, no crack could be detected. The incorporated aluminum originating from the minerals slowed down the SiO2 dissolution, and formation of gel and its swelling potential. In addition, the decreased alkalinity and consumption of calcium in the modified cement matrix also contributed to the suppressed ASR. This paper demonstrates a low-cost approach to mitigating ASR; and metakaolin, bentonite, or both can effectively replace other supplementary cementitious materials used for the same purpose (e.g., fly ash) which may not be available or cost effective.

Performance of lightweight cement-based and alkali-activated mortars exposed to high-temperature

The behavior of lightweight cement-based and alkali-activated mortars after exposure to temperatures of 500, 750, and 1000 °C was compared. In cement-based mortars, cement was partially replaced (40 vol%) by several refractory fillers (coal fly-ash, biomass fly-ash, cocciopesto, metakaolin). In alkali-activated mortars, metakaolin was partially substituted (0, 25, 50 wt%) by coal fly-ash. The substitution of cement by 40% metakaolin and the substitution of metakaolin by 50% fly ash enhances the resistance to high temperatures of cement-based and alkali-activated mortars, respectively. After exposure to 1000 °C, the high residual compressive strength of cement-based mortars with metakaolin is due to the formation of new crystalline species, whereas in alkali-activated mortars is due to their high densification.

The Effect of Substituting Metakaolin for Sand on the Thermomechanical Behaviour of Reactive Powder Concrete (RPC)

The weakening of the behavior of reactive powder concrete (RPC) under high temperature is a major drawback; therefore, it is necessary to find an ingredient that improves their resistance under rising temperatures. The present work involves the use of metakaolin as a substitute for sand in a reactive powder concrete (RPC) in order to assess its effect on the mechanical strength at high temperatures. The test specimens are preheated up to 100°, 300°, 500°, 700° and 900°C, respectively following a well-defined cycle, thereafter subjected to a three-point bending followed by compression tests. Samples of the tested specimens were used for thermal, mineralogical and microstructural analyses using the thermogravimetric and differential thermal analysis (TG / DTA), the X-ray diffraction (XRD) and the scanning electron microscopic Analysis (SEM).The heating tests revealed that all the specimens exploded before reaching 500°C. However, they can withstand 300°C before exploding for different exposure durations depending on the metakaolin substitution ratio. Therefore, the mechanical tests were applied only on unheated specimens and those heated up to 100°C. The results showed that the use of metakaolin improves the mechanical strength of the RPC, both at room temperature (25°C±1°C) and at 100°C. This result is confirmed by the microstructure analysis, which revealed the absence of portlandite. The latter did react with the metakaolin silica to form new calcium silicate hydrates (CSH) enhancing the mechanical strength.

Influence of Metakaolin on Chemical Resistance of Low Calcium Fly Ash Based Geopolymer Concrete

The study on cementless concrete is one of the most trending topics in the construction industry. This paper will give an inclusive on the effect of metakaolin on developing a low calcium fly ash (FA) based geopolymer concrete (GPC). Nine mixes were prepared with 30% and 50% replacement of low calcium FA with metakaolin, and molarity (8M, 12M and 16M) of alkaline activator (NaOH). Experiments were conducted on weight loss, residual compressive strength and Ultrasonic pulse velocity (UPV) of the GPC mixes. The experimental results indicated that workability of the mixes reduces with increasing percentage of metakaolin in comparison to the controlled GPC mix (100% low calcium FA). The compressive and tensile strength of geopolymer concrete mix with increasing molarity of NaOH solution and 30 - 50% replacement of fly ash with metakaolin was observed to be enhanced by 10 - 12% and 28 - 34% at 28 and 90 days respectively. The acid resistance values in terms of weight loss, compressive strength and quality of the specimens with 50% metakaolin substitution cured in H2SO4 solution for 56 days with different molarity was higher as compare to the control mixes. Thus, presence of metakaolin in the low calcium based GPC helps in resisting the aggressive chemical ingress in the concrete.

Valorization of mussel and oyster shells toward metakaolin-based alkaline activated material

Abstract The valorization of oyster or mussel shells toward metakaolin-based geomaterials was investigated. The aim is to better understand the feasibility and the reaction involved during the incorporation of shells (natural or calcined) into a metakaolin-based alkaline solution for potential building or contaminants sorbents applications. Mixtures are realized by (i) the substitution of metakaolin (MK) source by shells raw material (from 0 to 100% mass) or (ii) addition up to 50% mass. Substitution of MK by shells was conducted without material structure loss up to 40% and 30% addition, whether the type and treatment of shells used. In each addition or substitution, the results highlight the duality between both reactions i.e. polycondensation versus hydration. (i) using natural shells, only polycondensation reaction occurs due to the unreactivity of shells (interaction of shells with matrix by surface binding: role of aggregates or fillers); (ii) using calcined shells, coexistence of polycondensation in first followed (or stopped) by hydration reaction: presence of portlandite and C(A)SH. Then the results traduce the role of MK (Al and Si source) reactivity and calcium form (carbonate versus lime; reactivity) in MK-based alkali activated materials. The geochemical leaching approach can be used as a sensitive probe of the structural network.

Admixture compatibility in metakaolin–portland-limestone cement blends

Despite potential benefits including enhanced mechanical properties, reduced permeability, and decreased environmental impact, higher rates of metakaolin substitution for cement (> 10% MK by mass of cement) have been limited practically because of lower workability in such mixtures. When metakaolin is combined with portland-limestone cement (PLC), potential synergies further enhance hardened concrete performance and decrease environmental impact, but the greater surface area of PLCs suggests even greater challenges for workability in such blends. This study evaluates four water-reducing admixture chemistries-polycarboxylate ether (PCE), calcium lignosulfonate (LS), naphthalene formaldehyde condensate (PNS) and polymelamine sulfonate (PMS)—to assess their effectiveness in metakaolin-PLC combinations at up to 30% MK. At that upper bound, only PCE and PMS impart adequate workability within their recommended dosage limits. While PMS delays tricalcium silicate hydration and LS shows significant incompatibilities at higher MK contents, PCE has the least effect on hydration and can be used at a consistent dosage rate up to 30% MK.

Rheological study of cement paste with metakaolin and/or limestone filler using Mixture Design of Experiments

Several cement pastes with different amounts of metakaolin (MK) and/or limestone filler (LF) were prepared. The water/cementitious materials ratio was maintained constant at 0.3, with addition of 0.5%wt/wt of poly-carboxylate ether (PCE) superplasticizer admixture. The following parameters of the fresh cement pastes were evaluated: the slump and spread, the Marsh funnel time, the plastic viscosity, yield stress, viscoelastic properties and thixotropy. After the curing of 7day old pastes, compressive strength tests were performed according to the Brazilian standard using 50×100mm cylinder specimens. We conclude that LF alone is not able to avoid segregation or bleeding, and there is no difference between cement pastes mixed with LF and pure OPC pastes, in terms of rheology. On the other hand, if one needs low slump and low spread, the use of MK is recommended because this material creates a strong, thixotropic interconnected net inside of the paste, increasing the yield stress and the thixotropy of the cement paste. By adding 5–10%wt/wt MK, the average increase of compressive strength is approximately 45% at 7days, compared to the control (only OPC, water and PCE). The maximum recommended amount of LF or MK substitution in our case was 10%wt.

The influence of metakaolin substitution by slag in alkali-activated inorganic binders for civil engineering

In this study the effect of metakaolin replacement by milled blast furnace slag in alkali-activated geopolymeric binder was investigated in accordance to their rheological and mechanical properties. It was demonstrated that slag addition into the metakaolin binder can improve mechanical properties of final products. Our investigation was focused on broad interval of metakaolin substitution in the range from 100 to 40 volume per cents of metakaolin so that the volume content of solids in final binder was maintained constant. Prepared binders were activated by alkaline solution of potassium silicate with silicate module of 1.61. The particle size analyses were performed for determination of particle size distribution. The rheological properties were determined in accordance to flow properties by measurements on Ford viscosity cup and by oscillatory measurements of hardening process. For the investigation of hardening process, the strain controlled small amplitude oscillatory rheometry was used in plane-plate geometry. For determination of applied mechanical properties were binders filled by ceramic grog in the granularity range 0-1 mm. The filling was maintained constant at 275 volume per cents in accordance to ratio of solids in dry binder. The mechanical properties were investigated after 1, 7 and 28 days and microstructure was documented by scanning electron microscopy. The results indicate that slag addition have beneficial effect not only on mechanical properties of hardened binder but also on flow properties of fresh geopolymer paste and subsequent hardening kinetics of alkali-activated binders.