Increase In Metakaolin Content Research Articles

Integration of monitoring indicators for self-sensing alkali activated cementitious materials: From electrical signals - resistivity to autogenous shrinkage

The chemical shrinkage and autogenous shrinkage of alkali-activated materials (AAMs) are usually more significant than that of ordinary Portland cement (OPC). Therefore, both searching for efficient methods to reduce shrinkage and exploring the shrinkage mechanism of AAMs are of great significance in promoting the application of AAMs. In this paper, metakaolin is used to reduce the chemical shrinkage and autogenous shrinkage of AAMs, while an innovative resistivity measurement is used to concretize the electrical signal of AAMs and the relationship between autogenous shrinkage and resistivity was explored. The early resistivity and heat of hydration curves of AAMs can be divided into five stages with high similarity, demonstrating the feasibility of indirectly quantifying the autogenous shrinkage and chemical shrinkage by resistivity. The results of TG-IR, MIP, and heat of hydration prove that the early reaction rate of AAMs decreases with the increase of metakaolin content, which further leads to the decrease of early chemical shrinkage and autogenous shrinkage. The reduction of autogenous shrinkage reached the maximum (49%) when the metakaolin content was 50%. A mathematical model between autogenous shrinkage and resistivity was established, which means that the resistivity of self-sensing materials can be used as an index to evaluate the early autogenous shrinkage of AAMs.

Effect of Metakaolin on the Water Resistance of Magnesium Phosphate Cement Mortar

In order to study the effect of metakaolin on the water resistance of magnesium phosphate cement mortar, we took four factors as research objects: the setting time, fluidity, compressive strength, and water resistance of magnesium phosphate cement mortar. These were studied after adding equal gradations of metakaolin, and we then carried out SEM microcosmic experiments on the best group. The results showed that with the increase in metakaolin content, the setting time of magnesium phosphate cement decreased gradually, and the fluidity of the mortar decreased as a whole. The effect of metakaolin on the fluidity of the magnesium phosphate cement mortar was not significant when the content of metakaolin was less than 8%. Metakaolin was able to improve the pore structure of magnesium phosphate cement mortar; for example, it improved its compressive strength and water resistance due to both chemical and physical interactions. The water resistance of mortar samples in the same timeframe increased first and then decreased with the increase in metakaolin content. When the content of metakaolin was 12%, the water resistance of magnesium phosphate cement mortar achieved the optimal results. A 50.32% improvement of the 56 d strength retention rate and a 54.89% improvement of the 90 d strength retention rate proves its effective long-term water resistance.

Strength behavior of metakaolin and fly ash treated dredged clay at high water content

This study investigated the strength behaviors of dredged clays treated with metakaolin (MK) and fly ash (FA). A series of laboratory tests including direct shear and unconfined compressive strength tests were performed on MK and FA-treated dredged clay at various MK contents and different curing times. The direct shear test results showed that the shear stress and displacement curves for all specimens tested are strain-softening types and influenced by MK content and curing time. The variation curve at a higher MK content or higher curing time is always higher than that at a lower one. The shear strength from the direct shear test at a given vertical stress consistently increases linearly with the increase of MK content while increasing parabolically with curing time. This indicates both curing time and MK content contribute to the development of the shear strength. Both strength parameters c and φ grow with increasing MK content and curing time. Unconfined compressive strength test results show the strain-softening behavior for all tested specimens. Compared with adding FA alone or MK alone, adding both fly ash and MK exhibited a better treatment effect in the unconfined compressive strength, which increases with increasing MK content and curing time.

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.

Strength damage mechanism and pore structure evolution of modified Pisha sandstone cement soil with metakaolin

To fully understand the solidification effect of metakaolin (MK) on Pisha sandstone cement soil, unconfined compressive strength (UCS), ultradepth 3D microscopy (U3DM), nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were carried out on the solidified soil. The solidification mechanism of MK was comprehensively analysed from the perspectives of macromechanics, mesostructure and micromechanisms. From the perspective of macromechanics, the damage variable V tended to decrease with increase in MK content, which indicates that the addition of MK helps improve the ability of the solidified soil to resist damage. From a mesoscopic perspective, the addition of MK reduced the average height difference of the surface of the solidified soil. The complexity of the size, number, distribution and shape of pores in the solidified soil was comprehensively analysed based on NMR experiments. With increase in MK content, the proportion of pores with a pore radius >1 µm decreased, whereas the fractal dimensions D T and D 2 increased. XRD and SEM experiments show that the hydration products (calcium aluminate hydrate and calcium silicate hydrate) formed after the incorporation of MK were tightly combined with the soil particles and filled the pores. A grey entropy correlation analysis carried out to analyse the correlation effect of different pore structures on the strength of the solidified soil showed that pore sizes of 0–0.1 µm had a large influence on the UCS. This is a valuable finding on the link between the microstructure and macromechanics of solidified soils.

Effect of Metakaolin on Strength Properties of Lateritic Soil Intended for Use as Road Construction Material

An excellent all-weather road is essential in providing reliable transportation services that comprise social and economic development elements. However, in most cases, the road has to be constructed on a soft foundation soil where large deformations usually occur, which causes increases in maintenance costs and leads to interruption of traffic service, especially during the wet season. It is necessary to stabilize or improve the in-situ soils. This study explores the potential of using metakaolin to improve the geotechnical properties of lateritic soil for road construction materials. The soil classifies as A-6(4) and CL according to the American Association of State Highway and Transport Officials and the Unified Soil Classification System. The soil was treated with 5, 17.5 and 30 % concentrations of metakaolin by dry weight and was compacted using three compaction energies: British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were carried out to evaluate the effect of metakaolin on the soil investigated. Results showed a general improvement in the engineering properties of the soil with an increase in metakaolin content, particularly when compacted at the BSH energy level. However, the results did not meet the 1500-3000 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification for road base courses. However, 30 % lateritic soil/metakaolin blended soil compacted using WAS and BSH energy levels suffice for use as sub-base in road construction, having met the 750-1500 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification. The Peak CBR value for the treated soil, compacted using the three energy levels of BSL, WAS, and BSH, occurred at 30 % metakaolin concentration with corresponding soaked CBR values of 17, 23 and 31 %. The Nigerian General Specification recommends a nominal strength criterion of a soaked CBR value of 30 and 80 % to be attained by material to be used as sub-base and base course in road construction. Based on the above criterion, only the 30 % metakaolin treated blend compacted at the BSH energy level met the 30 % requirement for sub-base materials.

Effects of metakaolin and sodium silicate solution on workability and compressive strength of sustainable Geopolymer mortar

In this study, the Geopolymer mortar had been examined under flowability and compressive strength using metakaolin. The binder content of 50% fly ash and 30% Ground Granulated Blast Furnace Slag (GGBFS) has been kept constant. The remaining 20% of binder is partially replaced by metakaolin to fly ash such as 5%, 10% 15% and 20%. The sodium silicate (Na2SiO3) solution molarity has been varied from 1.5 M to 2 M. The test results indicate that, the fine particles of metakaolin (up to 15%) improves the flowability and also act as a filler material and another hand, increase in molarity of the solution leads to decrease in flowability but increase in compressive strength had observed. The compressive strength of the Geopolymer mortar had been increased with increase in metakaolin content. The optimum proportion of 15% metakaolin with 1.5 M Na2SiO3 solution is suggested in terms of workability and compressive strength of Geopolymer mortar under ambient curing.

Preparation, characterization and rheological analysis of eco-friendly road geopolymer grouting materials based on volcanic ash and metakaolin

Geopolymer has been applied in road engineering as an environmentally friendly material. This study prepared geopolymer road grouting pastes in different mixture ratios of volcanic ash (VA) and metakaolin (MK). The mechanical properties, setting time, bleeding and expansion ratio, fluidity and expansion ratio, time-dependent rheological analysis were systematically evaluated. Finally, the microscopic experiments, including X-Ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy with Energy Dispersive Spectrometer (SEM-EDS), were conducted to investigate the mechanism of geopolymerization based on VA and MK. The results showed that the mechanical strength increased with the content of MK. The flow curve of all pastes fitted the Bingham model. With the increase of MK content, the yield stress and plastic viscosity coefficient increased, which is because the stacked multilayer gullies microstructure aggravated the internal friction of paste particles, which led to decreased expansibility and pumpability. When the mass ratio of VA/MK was 1:0.33, the paste achieved the balance of mechanical strength and rheological properties with superior water retention and deformation resistance. The microscopic experiments showed that MK's mechanism enhanced the mechanical strength of geopolymer due to its high content of amorphous phases, smaller average particle size, and rich content of Al element. The SEM-EDS indicated that the MK improved the mechanical strength also by the improvement of nucleation effect. VA and MK complement each other in mechanical strength development under room temperature and fluidity, which are expected to be an alternative for cement as an eco-friendly road grouting material.

The effect of metakaolin on the hardening process of alkali activated slag by using electrochemical impedance spectroscopy

The purpose of this research work is to study the hardening behavior of the alkali activated slag-metakaolin (AASM) material from a new electrochemical perspective. The measurements of the compressive strength and the electrochemical impedance spectroscopy (EIS) were conducted. The results demonstrated that the strength of AASM paste decreases with the increase of metakaolin content. In addition, a suitable electrochemical equivalent model has been used in order to analyse of the relationship between the microstructure of the AASM paste and the EIS data. And found that the resistance of ion transport process Rct1 show an increasing trend over the testing period and the compressive strength and the Rct1 of AASM has similar growth trend and strong correlation, which means that the EIS may be used to predict the strength development of the AASM paste.

Effect of Nano-CuO on Engineering and Microstructure Properties of Fibre-Reinforced Mortars Incorporating Metakaolin: Experimental and Numerical Studies.

In this study, the effects of nano-CuO (NC) on engineering properties of fibre-reinforced mortars incorporating metakaolin (MK) were investigated. The effects of polypropylene fibre (PP) were also examined. A total of twenty-six mixtures were prepared. The experimental results were compared with numerical results obtained by adaptive neuro-fuzzy inference system (ANFIS) and Primal Estimated sub-GrAdient Solver for SVM (Pegasos) algorithm. Scanning Electron Microscope (SEM) was also employed to investigate the microstructure of the cement matrix. The mechanical test results showed that both compressive and flexural strengths of cement mortars decreased with the increase of MK content, however the strength values increased significantly with increasing NC content in the mixture. The water absorption of samples decreased remarkably with increasing NC particles in the mixture. When PP fibres were added, the strengths of cement mortars were further enhanced accompanied with lower water absorption values. The addition of 2 wt % and 3 wt % nanoparticles in cement mortar led to a positive contribution to strength and resistance to water absorption. Mixture of PP-MK10NC3 indicated the best results for both compressive and flexural strengths at 28 and 90 days. SEM images illustrated that the morphology of cement matrix became more porous with increasing MK content, but the porosity reduced with the inclusion of NC. In addition, it is evident from the SEM images that more cement hydration products adhered onto the surface of fibres, which would improve the fibre–matrix interface. The numerical results obtained by ANFIS and Pegasos were close to the experimental results. The value of R2 obtained for each data set (validate, test and train) was higher than 0.90 and the values of mean absolute percentage error (MAPE) and the relative root mean squared error (PRMSE) were near zero. The ANFIS and Pegasos models can be used to predict the mechanical properties and water absorptions of fibre-reinforced mortars with MK and NC.

Composition design and performance of alkali-activated cements

In the present work, the relationship between the composition of the SiO2–Al2O3–CaO precursor system and the setting time, microstructure and mechanical properties of the resulting alkali-activated cement (AAC) were investigated. The results showed that with the increase of metakaolin content and the modulus of activator solution, setting time of alkali-activated cements was prolonged. The compressive strength increased with the increase of CaO content to a certain extent, but had different trends as Si/Al ratio varied. Microstructural analyses revealed that CaO content had remarkable effects on the microstructure of AAC. In calcium-free system, the strength was dependent on the three-dimensional structure of N–A–S–H gels. As the CaO content increased gradually, the main activation product changed from N–A–S–H to C–(A)–S–H gel, resulting in a more compact structure. This investigation helps to build up a practical approach for the composition design of alkali-activated cements.

Improvement for the strength of salt-rich soft soil reinforced by cement

ABSTRACTThe corrosive ions in salt-rich soft soil have negative effects on soil–cement when the soft soil ground is reinforced by cement. To improve the strength of salt-rich soil–cement, a series of laboratory tests on metakaolin were performed, and the effects of metakaolin content and different ions on the mechanical characteristic of salt-rich soil–cement were explored as well. It was found that the strength of salt-rich soil–cement increased with an increase in metakaolin content, and then no further increase in strength was found when the metakaolin content exceeds a certain value. Therefore, salt-rich soil–cements with different ions have its optimal metakaolin content. Orthogonal test results show that three ions Cl−, Mg2+, and have different effects on the strength of salt-rich soil–cement improved by metakaolin, Cl− has the most important influence on the strength but is minor. Metakaolin has the characteristics of accelerating hydration reaction of salt-rich soil–cement, filling effect, and volcanic ash effect, which can reduce the negative effects of corrosive ions on the strength of salt-rich soil–cement.

Hydration Products, Microstructure and Durability of Concrete with Metakaolin Addition

The durability, microstructure and hydration products of concrete containing 0-6wt% metakaolin (MK) were studied by analytical techniques. The hydration products were calcium hydroxide (CH), ettringite and calcium silicate hydrate gels in the control concrete, and additional monocarboaluminate and hemicarboaluminate were identified in concrete containing MK. CH content decreased by 28 days hydration in concrete containing MK, due to the pozzolanic reaction between MK and CH. Chloride diffusion coefficient decreased with the increase of MK content. By addition of 6wt% MK, chloride diffusion coefficient decreased by 60%.

Effect of metakaolin addition and seawater mixing on the properties and hydration of concrete

The effect of metakaolin (MK) and seawater mixing on the properties and hydration products of concrete was studied by analytical techniques. MK improved compressive strength by refining pore structure without altering porosity. Seawater increased compressive strength at early age without altering pore structure. The combination of MK and seawater improved both early and later age strength. Hydration products in pastes containing MK were Portlandite, ettringite, hemicarboaluminate, monocarboaluminate and C-S-H gels. In pastes with seawater, instead of hemicarboaluminate and monocarboaluminate, hydrocalumite was identified. MK promoted hydrocalumite formation. MK decreased CH content with increase of MK content and age. Seawater increased CH content at early age with MK content. The combination increased CH content at early age and decreased later. At 28days, most chloride in seawater was immobilized by hydrocalumite. The combination improved properties of concrete at both early and later age.

Effect of metakaolin and foundry sand on the near surface characteristics of concrete

This paper deals with the effect of foundry sand (FS) and metakaolin (MK) on the near surface characteristics of concrete. A control concrete having cement content 450 kg/m 3 and w/c of 0.45 was designed. Cement was replaced with three percentages (5%, 10%, and 15%) of metakaolin weight, and fine aggregates were replaced with 20% foundry sand. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days. Test results indicated that with the increase in MK content from 5% to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics. Inclusion of foundry sand resulted in reduction in compressive strength. This aspect cements the findings that addition of FS causes permeability of concrete to increase causing in an increase in sorptivity and water absorption of concrete.

Effect of metakaolin on the near surface characteristics of concrete

Results on an investigation dealing with the effect of metakaolin (MK) on the near surface characteristics of concrete are presented in this paper. A control concrete having cement content 450 kg/m3 and w/c of 0.45 was designed. Cement was replaced with three percentages (5, 10, and 15%) of metakaolin weight. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days. Test results indicated that with the increase in MK content from 5 to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics.

Metakaolin concrete at a low water to binder ratio

This paper investigates the performance of concrete containing metakaolin (MK) at a low water to binder ratio of 0.3. Portland cement (PC) was partially replaced with 0–20% MK. Testing included, compressive strength, ultrasonic pulse velocity ( V), dynamic modulus of elasticity ( E d) and length change. Specimens were either cured in water or in air at 20 °C. The results indicate that the performance of MK concrete at low water to binder ratio is not different from that at higher water to binder ratios reported in a previous investigation. The maximum contribution of MK to strength occurs at 14 days of curing in that the relative strength of MK concrete shows a maximum value at that curing time as found in a previous investigation. The optimum replacement level of cement with MK is about 15%. Linear relationship exists between V and E d for air cured and water cured specimens. A systematic increase in MK content of up to at least 20% leads to a decrease in shrinkage and an increase in expansion after 56 days of curing. Correlation between the various properties is also conducted.

Absorption characteristics of metakaolin concrete

The water absorption (WA) by total immersion and by capillary rise of concrete containing metakaolin (MK) is investigated. Cement was partially replaced with up to 20% MK. The results show that the presence of MK is greatly beneficial in reducing the WA by capillary action. There is a systematic reduction in absorption by capillary action with the increase in MK content in concrete. This reduction is further supported by visual examination of specimens. The absorption by total immersion, however, tends to increase slightly with the increase in MK content. Between 14 and 28 days curing, there is a slight increase in absorption by total immersion and by capillary rise for all MK concretes. Correlation between the absorption characteristics, dynamic modulus of elasticity ( E d), strength and pore size distribution was conducted.

Sulphate Resistance of Metakaolin Mortar

The partial substitution of cement (both high C 3A and intermediate C 3A) with metakaolin (MK) is investigated in terms of resistance of MK mortar to sodium sulphate (Na 2SO 4) solution. Results on strength, porosity, pore size distribution, and calcium hydroxide (CH) contents are also reported. The sulphate expansion results demonstrate that the sulphate resistance is increased as the replacement level of cement with MK increases, up to at least 25% replacement. Refinement in pore structure and reduction in CH content increase with increase in MK content (for moist-cured mortar), and these two factors are considered to be the principal factors affecting improvement in sulphate resistance. Also, although after prolonged periods of exposure to Na 2SO 4 solution, there is (relative to water-cured specimens) significant strength loss of PC mortars and mortars with low levels of MK (5 and 10%); for mortars with high levels of MK (15, 20 and 25%), there is consistent strength gain.

Pore size distribution of metakaolin paste

The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Pastes containing 0,5,10 and 15% metakaolin were prepared at a constant water/binder (wb) ratio of 0.55. Specimens were moist cured for periods from 3 to 365 days. The intruded pore volume and the pore structure were determined by mercury intrusion porosimetry. The proportion of large pores (radius > 0.02) in the paste decreases with both increase in metakaolin content and increase in curing time. Although the total intruded pore volume generally decreases with increase in curing time it is found to increase with increase in metakaolin content. Also an increase in pore volume is observed between the curing times of 14 and 28 days for pastes containing metakaolin. This latter observation is explained in terms of two possible mechanisms.