Effects of Coal Metakaolin on the Mechanical Properties and Microstructure of High-belite Sulphoaluminate Cement

The effects of coal metakaolin on the mechanical properties of high-belite sulphoaluminate cement under compressive loading were investigated.The composition and microstructure of hydration products at different hydration times were analyzed by X-ray diffraction and scanning electronic microscopy.The hydration process of blended cement was studied via electrochemical impedance spectroscopy.In particular,replacing a part of cement with CMK(10%,20%,and 30%)was found to promote the hydration process,to refine the pore size,and to improve the compressive strength of the composite.The best compressive strength of the cement was achieved at a CMK content of 30%after 28 days hydration,being improved by 20.13 MPa,or1.44 times relative to that of undoped specimens.Furthermore,the compressive strength is shown to correlate with the impedance parameter R_(CCP),which allows the latter to be used for nondestructive assessment of the compressive strength of blended cement materials.

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.

Stabilization of a Lateric Clay from Burkina Faso with Cement-Metakaolin for an Application in Road Construction

The objective of this work is to obtain a composite of clay-cement-metakaolin having good mechanical properties and geotechnical. To do this, a lateritic clay from Burkina Faso referenced ALK was characterized by various methods (X-ray diffraction, infrared spectrometry, thermal analysis and Inductively Coupled Plasma, Atomic Emission Spectrometry) in order to be used as a base course after adding cement and metakaolin. The results of the mineralogical characterization of this clay showed that it is composed of kaolinite (65.7 wt.%), quartz (19.3 wt.%) and goethite (10.8 wt.%). The geotechnical tests carried out showed that ALK is moderately plastic with a plasticity index Ip = 22%. The optimum moisture content and the maximum dry density are respectively 15.9% and 1.76 g∙cm-3. Simple compressive strength and splitting tensile strength are Rc = 1.59 MPa and ft = 0.149 MPa respectively. The California Bearing Ratio (CBR) index at 95% is 40% and above the minimum value of 30% shows that ALK can be used as a sub-base course in road construction. The addition of cement and metakaolin in various proportions improved the CBR index and the mechanical strength of the composites produced. This improvement is due to the formation of hydrated calcium silicate (CSH) resulting from the pozzolanic reaction between the portlandite of the cement and the amorphous silica of the metakaolin. Thus the 2 wt.% metakaolin and 6 wt.% cement formulation with a 95%CBR index of 81% is suitable for the development of a base course in road construction.

The Early Hydration and Strength Development of High-strength Precast Concrete with Cement/Metakaolin Systems

To study the relationship between material composition, curing conditions and strength development, the study simulated high-strength precast concrete pile production, and a high-strength mortar up to 90 MPa was designed and a hot-water pool was built for concrete curing. The major point of the study was to achieve a high early strength by using cement/metakaolin systems without autoclave curing with high-pressure steam. By means of XRD and thermal analysis, the progress of the hydration of the cement pastes blended with metakaolin was characterized. The main results indicate that high strength can be obtained at early age by the use of metakaolin and thermal treatment （hot-water curing）. The improvement in strength of mortars with metakaolin can be explained by an increase in the amount of C-S-H and C-S-A-H hydrated phases and a decrease in the amount of calcium hydration（CH）. Further more, a decrease in Ca/Si ratio of the matrix was observed from the results of EDX analysis, which also leaded to an improvement of the compressive strength. These results are of great importance for the high-strength precast concrete manufacturing industry.

Replacement of alkali silicate solution with silica fume in metakaolin-based geopolymers

A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5% , 10% and 20% metakaolin were prepared at a water / cementitious material ratio ( W/C) of 0. 30. In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison. The specimens were cured in water at 27℃ for 3 to 90 days. The results show that at the early age of curing (3 days and 7 days), metakaolin replacements increase the compressive strength, but silica fume replacement slightly reduces the compressive strength. At the age of and after 28 days , the compressive strength of the concrete with metakaolin and silica fume replacement increases. A strong reduction in the total porosity and average pore diameter were observed in the concrete with MK 20% and 10% in the first 7 days.

Effect of Epoxy Resin on Mechanical Properties of Metakaolin based Geopolymer and Microscopic Analysis

By using NaOH and Na2SiO3 as the activator,the mechanical properties and shrinkage of the geopolymer after incorporation of 0%,10%,20%,and 30% epoxy resin were investigated.The mechanism of epoxy resin toughening metakaolin based geopolymer was analyzed by X-ray diffraction,scanning electron microscopy and Fourier transform infrared spectroscopy.It was shown that with the increases of epoxy resin,the shrinkage performance was obviously improved and the flexural strength increased by 53.5%.The compressive strength of EGP10,EGP20,and EGP30 increased by 49.12%,57.04%,and 65.34% after curing for 28 days,respectively.There were five obvious vibration peaks of 811 cm^-1,1 000 cm^-1,1 050 cm^-1,1 590cm^-1,and 3 400 cm^-1 in the geopolymer and the undisturbed metakaolin.More geopolymer gels were formed in the material and the microstructure was more compact.

Dominant Factors on the Early Hydration of Metakaolin-Cement Paste

The dominant factors during early hydration process of cement paste containing 10% metakaolin replacement （MK10） and 10% kaolin replacement （K10） are investigated in comparison to neat cement paste （NCP）, and X-ray Diffraction （XRD） analysis is employed to identify the crystalline phases of all specimens. Thermogravimetric （TG） and Differential Scanning Calorimetry （DSC） are used to identify the phase constituents. The amount of acid-insoluble residue （AIR） of all specimens is used to evaluate the unreacted materials. The results indicate that, after the first day, MK act as nuclei for the formation of C-S-H during hydration of C3S and C2S, densifying the microstructure of cement paste. Its contribution is mainly due to the fine nature of the MK. From 3 days to 7 days, more and more MK reacts with CH to form C-S-H, making the microstructure denser. The strength contribution is mainly due to the chemical activity of MK.

Metakaolin-Based Geopolymers for Targeted Adsorbents to Heavy Metal Ion Separation

Geopolymer adsorbents were prepared from silica and metakaolin in different Al and Si components and applied for removal of metal ions, Cs+ and Pb2+, from other heavy metal ions mixture. The geopolymer was optimized at Si/Al = 2 as adsorbent, targeting to Cs+ and Pb2+ separation. The binding behavior was well fitted to Langmuir model, which proved that the metakaolin-based geopolymer had multibinding to adsorb ions. The effective adsorption was also observed independent of NaCl concentration for the Cs+ and Pb2+. This meant that the ion adsorption of geopolymers occurred under non-electrostatic mechanism.

Synthesis of SAPO-34 using metakaolin in the presence of β-cyclodextrin

SAPO-34 molecular sieves were synthesized by the addition of β-cyclodextrin（β-CD） as crystal growth inhibitor using metakaolin as silicon and aluminum sources. Properties of the obtained samples were characterized by XRD,SEM,N2adsorption–desorption,FTIR,XRF,EDX,NH293-TPD andSi MAS NMR. When β-CD was added,crystal size of the SAPO-34 crystals decreased. Variation of Si content from the crystal center to surface decreased while total Si content hardly changed.29 Si MAS NMR results showed that β-CD contributed to better Si dispersion and decreased the size of Si（4Si） patches. Moreover,the MTO（methanol-to-olefin） process was conducted to investigate the influence of β-CD on catalytic performance. The synthesized sample with molar ratio of β-CD/Al2O3 equaling 0.055 remained active for 610 min while the sample synthesized without β-CD for only 280 min,which indicates that the lifetime of catalyst synthesized with β-CD is greatly prolonged.

Crystallization behavior of zeolite beta from acid-leached metakaolin

Well-crystallized zeolite beta was synthesized by using acid-leached metakaolin as the silica-alumina source and tetraethylammonium hydroxide structure-directing agent.The influence of the composition of the reaction mixture on product crystallinity was investigated,and the crystallization process was studied by examining solid samples obtained at different synthesis times.Results showed that the acid-leached metakaolin was fully converted into soluble aluminum and silicon species,which is crucial for the formation of well-crystallized zeolite beta.At the beginning of the crystallization process,these soluble aluminum and silicon species formed a aluminum-rich intermediate structure with layer morphology.With the crystallization proceeding,more silicon species were incorporated into the zeolite beta framework and the layered structure was changed into spherical particles of zeolite beta with high SiO 2 /Al 2 O 3 ratio and crystallinity.

Compressive Strength of Metakaolin-Based Geopolymers: Influence of KOH Concentration, Temperature, Time and Relative Humidity

The influence of KOH concentration (8 and 12 M) and curing conditions as temperature (40℃ and 60℃), time (7 and 28 days) and relative humidity (85% and 95% RH), on compressive strength of metakaolin-based geopolymers (MK-based GP) was evaluated. Derived from the experimental design technique, and using a factorial design 2K with two replications in the center point, eighteen experiments were conducted. The results reveal that the best performance conditions of geopolymerization to develop a higher compressive strength of 20 MPa are 12 M KOH to 60℃ and 85% RH at 28 curing days. With these conditions, the value of relative humidity of 85%, promotes high strength compact samples, and a maximum of 42 MPa at 90 days. The results of significant, compressive design of GP showed that KOH concentration and curing relative humidity were the most important factors, followed by curing time and temperature. The GP were characterized by XRD, and their evolution on compression strength was followed by SEM.

Properties of High Volume Fly Ash Concrete Compensated by Metakaolin or Silica Fume

The compressive strength and dynamic modulus of high volume fly ash concrete with incorporation of either metakaolin or silica fume were investigated. The water to cementitious materials ratio was kept at 0.4 for all mixtures. The use of high volume fly ash in concrete greatly reduces the strength and dynamic modulus during the first 28 days. The decreased properties during the short term of high volume fly ash concrete is effectively compensated by the incorporation of metakaolin or silica fume. The DTA results confirmed that metakaolin or silica fume increase the amount of the hydration products. An empirical relationship between dynamic modulus and compressive strength of concrete has been obtained. This relation provides a nondestructive evaluation for estimating the strength of concrete by use of the dynamic modulus.

CO_(2)and Cost-Based Optimum Design of Sustainable Metakaolin-Modified Concrete

Metakaolin is a highly reactive pozzolanic material that is widely utilized for enhancing the performance of concrete.This study offers a framework for the mixture design of sustainable metakaolin-modified concrete with low CO_(2)emissions and low costs.Different design strengths after 28 days are first formulated,with values such as 30,40,50,and 60 MPa.A genetic algorithm is then used to determine the optimal mixtures.Minimized CO_(2)and cost are set as the aims of the genetic algorithm.The strength of the concrete,its workability(slump),and carbonation service life with climate change are set as constraints of the genetic algorithm.Five design cases are considered:1)low-CO_(2)concrete with no carbonation,2)low-CO_(2)concrete with carbonation,3)low-material cost concrete with carbonation,4)low-total cost concrete with carbonation,and 5)low-total cost concrete with climate change.Based on the analysis,the following results are found:1)When the design’s strength is 30 MPa,to satisfy the requirement of carbonation durability,the concrete real strength should exceed 30 MPa.Moreover,after considering climate change,the concrete real strength should be further improved.2)When the design strength is 40,50,or 60 MPa for low-total-cost concrete,climate change has no impact on the optimal design because the concrete has sufficient carbonation resistance.3)Low-material-cost concrete has the same mixture as low-total-cost concrete because compared with the material cost,the CO_(2)emission cost is much lower.Moreover,for low-material-cost or low-total-cost concrete,the metakaolin content is at the lower limit because the price of metakaolin is much higher than that of cement.Summarily,the proposed model covered different aspects of sustainable concrete,such as cost and CO_(2)emissions,clarified various decisive factors of mix design,such as strength and carbon durability,and considered different conditions of climate change,such as no climate change and Representative Concentration Pathways(RCP)8.5.The proposed method is valuable for designing sustainable metakaolin-modified concrete with low CO_(2)emissions and costs.

Influences of Multi-Component Supplementary Cementitious Materials on the Performance of Metakaolin Based Geopolymer

In this study,the workability and reaction mechanism of metakaolin(MK)based geopolymer blended with rice husk ash(RHA)and silica fume(SF)was investigated.The prepared samples were subjected to tests including compressive strength and fluidity tests.X-ray diffraction(XRD)and Scanning electron microscope(SEM)were employed to explore the phase composition and microstructure of geopolymers.The molecular bonding information of geopolymer was provided by Fourier transform infrared spectroscopy(FTIR).Meanwhile,the porosity of geopolymer was obtained by Mercury intrusion porosimeter(MIP)analysis.The high-activity RHA obtained after calcination at 600℃ was used as a supplementary cementitious material to prepare geopolymer.The properties of preventing morphology cracking and compressive strength are improved.The addition of RHA and SF changes the working performance of MK based geopolymer and provided a theoretical basis for future practical applications.Meanwhile,the high chemical activity of SF and RHA contributes to the healing of microcracks.

Metakaolin as an Active Pozzolan for Cement That Improves Its Properties and Reduces Its Pollution Hazard

Prepared metakaolin produced by calcination of a kaolin sample at 750&degC after soaking for 5 hrs was tested as an active pozzolan for locally produced cement. Blended pastes of partially replaced ordinary Portland cement with different metakaolin amounts 5%, 10% and 15% were prepared, then they were hydrated with water for various time intervals of 1, 3, 7, 14 and 28 days. At each time interval, the hydrated paste specimens were tested for compressive strength, hydration kinetics and followed up using differential scanning calorimetry, X-ray diffractometry analyses and scanning electron microscopy techniques. Results showed that the blended pastes OPC-MK10 recorded the highest compressive strength values at all the hydration times reaching 33.10, 86.40, 101.20, 112, and 122 MPa with increasing the age of hydration as compared with the neat samples which recorded 31.70, 65.20, 72.6, 82 and 101.30 MPa respectively. Meanwhile, the OPC-MK10 blend showed a decrease in the free CaO content reaching 4.07%, 4.27%, 4.23%, 4.19%, and 4.11% CaO with increasing age of hydration compared with the neat samples which recorded 4.27%, 5.15%, 5.42%, 5.61%, and 5.96% CaO respectively. The DSC thermograms results for the hardened neat and OPC-Mk10 pastes at the 14 and 28 hydration days showed the formation of hydrated materials mainly calcium silicate hydrates, calcium sulphoaluminate hydrates and calcium aluminates hydrates. The X-ray diffractometry analyses of both hardened neat and OPC- MK10 showed that, the intensity of calcium hydroxide peaks of OPC-MK10 was lower than in case of neat OPC, while the peak of the hydration products of calcium silicate hydrates and calcium aluminates silicate hydrates of OPC- MK10 samples were of higher intensity than in case of neat OPC. Scanning electron microscopy micrographs indicated the formation of denser micro- structure for the hardened OPC-MK10 paste as compared to neat OPC pastes after the 28 days age of hydration.

Geopolymers Using Rice Husk Silica and Metakaolin Derivatives;Preparation and Their Characteristics

The effect of the amorphous silica derived from biomass rice husk (RH) in the alkaline activating solution on the properties was investigated in geopolymerization process, when metakaolin was used as the aluminum source from metakaolin (MK). With changing a molar ratio of SiO2/Al2O3 = 3.0 and 10, the curing in the preparation of geopolymers was carried out at 85&#176C, 100&#176C and 200&#176C. Viscoelastic properties of the geopolymer pastes including SiO2 and Al2O3 components suggested that the alkaline activation was found in higher RH silica source. The mineralogical and microstructural characteristics of the cured products were evaluated to be amorphous aluminosilicate.

Effect of the Formulation of Sodium Activation Solutions on the Setting Time of Metakaolin Based Geopolymers

Geopolymer materials today represent innovative products,used frequently as a substitute for cementitious traditional materials.They are obtained by the action of an alkaline activation solution(composed of mainly of silicon dioxide(SiO2)and sodium hydroxide(NaOH)and water)on a powder natural or synthetic aluminosilicates.In this work,we seek to highlight the effect of the percentage of sodium dioxide firstly,on the evolution of the viscosity of the alkali-activated solution and secondly,on the evolution of the viscosity of geopolymeric solution.Another aspect of this work is the determination of the effect of this percentage on the kinetics that characterize the start of the percolation phenomenon(transition from the fresh state to the hardened state).At last result concerns the impact of temperature on this transition.This contribution consolidates the control protocols for the formulation of geopolymers and allows the optimization of the processes of their exploitation.

Hydration of Portland Cement in the Presence of Highly Reactive Metakaolin

The degree of conversion of highly reactive metakaolin in Portland cement metakaolin paste at different ages as well as the influence of metakaolin on the degree of hydration of Portland cement and composition of C-S-H is investigated by?27Al- and 29Si-MAS NMR spectroscopy. At the age of 7 days, in the paste with 10% of metakaolin, the additive is completely consumed. In the 30% substituted cement paste, the content of metakaolin remains quite high (about 40% of the initial amount) even after 3 months of hydration. At the age of 1 - 3 months, the degree of Portland cement hydration in the presence of metakaolin is of 15% - 20% less than without it, probably, due to deficit of water or spatial restrictions. After 7 days of hydration, about half of C-S-H consists of material derived from metakaolin. Metakaolin mainly contributes to Q2 and Q2 (1Al) species, whereas PC does to Q1. After 1 day of hydration, an amount of ettringite in cement paste with high dosage of metakaolin is higher than in pure PC paste.

Structural and Thermomechanical Study of Plastic Films Made from Cassava-Starch Reinforced with Kaolin and Metakaolin

The structural and thermomechanical properties of starch-based plastic films reinforced with kaolin and metakaolin have been studied by various techniques (X-ray diffraction, IR-TF spectroscopy, scanning electron microscopy, tensile tests, and thermal resistance). The results obtained showed that kaolin, an inert material, prevents the starch from losing its granular structure and to solubilize during the heating, generating plastic films of low Young’s modulus (7 MPa). On the other hand, metakaolin, an amorphous and dehydroxylated material obtained after heating of kaolin at 700°C for 1 hour, substantially improves the thermomechanical properties of the plastic films. The Young’s modulus increases from 19 MPa to 25 MPa while the thermal resistance increases from 90°C to 120°C. This was attributed to good dispersion of the metakaolin in the polymer matrix after the loss of the granular structure of the starch during heating.