Replacement Level Of Metakaolin Research Articles

Mix design method for self compacting metakaolin concrete with different properties of coarse aggregate

This study deals with a proposed mix design method for SCC utilizing different properties of coarse aggregate. The work was conducted in three phases, i.e. paste, mortar and concrete to facilitate the mix design process. Initial investigation on cement paste determined the basis for water cement ratio and superplasticizer dosage for the concrete. For the study on mortar, metakaolin (MK) as pozzolan was used at replacement levels of 5%, 10%, 15%, and 20% by weight of cement. Self compactability of mortars was obtained by adding suitable materials such as mineral admixtures and superplasticizer which provided a sufficient balance between flowability and viscosity of the mix. The optimum MK replacement level for cement was 10% from the viewpoint of workability and strength. Flowability of mortar decreased with the use of metakaolin. Moreover, strength of mortar increased when the optimum replacement level of pozzolan was used. Different fresh concrete tests were adopted. The results obtained for fresh concrete properties showed that flowability of concrete increased with increase flowability of mortar. The mixes which contained coarse aggregate with lower volume, small size, and continuous grading affected positively the fresh properties of SCC. Finally, the mix design method used was successful in producing SCC with different coarse aggregate properties.

Corrosion behavior of reinforcing steel embedded in chloride contaminated concretes with and without metakaolin

One of the most remarkable drawbacks of the reinforced concrete structural elements is the corrosion of reinforcement. Especially, in marine structures or in such environments where chloride contamination risk exist this issue gains much importance. In this study, chloride contamination of the concrete was implemented by adding 0%, 1.5%, 3%, and 5% NaCl by weight of the total binder content, into concrete. To assess the influence of high reactivity metakaolin (MK) incorporation on the corrosion resistance of the chloride contaminated concrete, 5% and 15% MK replacement levels by the total weight of the binder were assigned in concrete production. The corrosion behaviors of reinforcing bars embedded in concretes were monitored through accelerated corrosion test, corrosion current density and the corresponding corrosion rate by linear polarization technique (LPR). Moreover, the electrical resistivity of concrete was measured. Analysis of the test results indicated that MK was proved to be effective in inhibiting the active corrosion of concrete even at severe chloride contamination levels.

Influence of Metakaolin on Strength and Microstructure of High-Strength Concrete

Concrete with a compressive strength of 100MPa was produced with metakaolin(MK), and the effect of MK replacement levels on compressive strength of concrete with a water to binder ratio of 0.25 was studied in this paper. XRD, microhardness tests, SEM and MIP were used to investigate the influences of MK on the phase composition, microhardness of interfacial transition zone(ITZ), microstructural morphology and pore structure of the high-strength concrete (HSC). The results showed that the incorporation of MK promoted the hydration process and decreased the amount of Ca(OH)2 crystals. Furthermore, MK increased the ITZ microhardness of HSC, enhanced the hydrates and improved the bond performance of aggregate and paste. The weak zone between aggregate and paste became almost disappeared when 10% MK was blended. Meanwhile, refinement of the concrete pore structure was obtained in the presence of MK. The improvement of strength and microstructure became more obvious as the MK replacement level increased to 15%.

Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes

Using mineral admixtures as cement replacement substance in concrete has a tendency to increase by the future in order to provide greater sustainability in construction industry. This paper investigates the effectiveness of metakaolin (MK) and silica fume (SF) on the mechanical properties, shrinkage, and permeability related to durability of high performance concretes. Mechanical properties were evaluated by means of compressive and splitting tensile strength. Water sorptivity and gas permeability tests were carried out to find out the permeation characteristics of the concretes due to the incorporation of MK and SF. Shrinkage behavior of the concretes with and without mineral admixtures were dealt through measurements of free shrinkage strains and weight loss of the specimens due to drying. Moreover, crack formation and propagation of the restrained specimens were observed to better understanding the effect of MK or SF incorporation on the restrained shrinkage properties. For concrete production, replacement levels of 5% and 15% of MK or SF by the weight of cement were assigned. Water-to-cementitious (w/cm) material ratios of 0.25 and 0.35 were used in production of concrete. The design strength level ranging from75 to 86MPa was achieved. Test results revealed that replacement level of MK and SF had significant effects on the mechanical and especially durability characteristics of high performance concretes.

Influence of Metakaolin on Resistivity of Cement Mortar to Magnesium Chloride Solution

An experimental study for the resistance of mortar paste specimens incorporating 0, 5, 10, 15, 20, 25, and 30% metakaolin (Mk, produced by firing kaolin at 820°C for 2 h) to the magnesium chloride solution was reported. Results confirmed that mortar specimens with a high replacement level of metakaolin showed higher resistance to magnesium solution. The reduction of calcium hydroxide and the increase of secondary calcium silicate hydrate (CSH) in the cement matrix results from the pozzolanic reaction of Mk. The compressive strength values of the blended ordinary portland cement (OPC) mortars specimens improved relative to those containing no Mk, up to 25% by weight OPC substitution, and then decreased up to 30% by weight Mk. Scanning electron microscope microstructures indicate a good improvement for the matrix structure of the blended cement mortars, in which a denser structure was observed.

Increasing mortar strength with the use of activated kaolin by-products from paper industry

Making use of industrial by-product or waste clay to partially replace cement in concrete has greatly contributed to sustainable development of environment. This study investigated the optimal activation condition for producing high reactivity metakaolin (MK) by using kaolin by-products (KB) from paper industry. Initially, the material properties of KB were analyzed in this study and the results indicated its great potential to be treated by calcination to be a very effective pozzolan. Afterwards, MK samples produced from different activation treatments of KB, including different calcining temperature, calcining duration, initial temperature rise rime and grinding particle size, were applied in mortar to determine their pozzolanic effect. Results indicated that the optimal activation condition for KB to high reactivity MK conversion is 2-h calcining duration at 750 °C and with 7 μm grinding particle size. Finally, compressive and flexural strengths of mortar samples produced by replacing cement with 0–25% MK content were tested and the results showed that 15% was the optimal cement replacement level of MK and the mortar so produced exhibited 20% improvement in compressive strength compared to control mortar.

Strength Deterioration of Plain and Metakaolin Concretes in Aggressive Sulfate Environments

This study investigates the effectiveness of metakaolin (MK) on the improvement of durability of concretes to sulfate attack. Experimental parameters of the study were MK replacement levels, water to cementitious materials ratio, initial curing procedure in terms of air curing and water curing, and type of the sulfate exposure regimes such as continuous and drying-immersion cyclic exposures. The degree of sulfate attack was evaluated by the reduction in compressive strength (CS) of concrete. The tests were conducted at specified periods up to 365 days. At the end of initial curing, concrete specimens were divided into three groups such that the first group was transferred into tap water to be used as control in the assessment of CS reduction while the other groups were immersed in 10% Na2SO4 solution for the period of 365 days under continuous or cyclic exposures. The results indicated that inclusion of MK as modifying agent increased the resistance of concrete against sulfate attack depending mainly on the MK replacement level, w/cm ratio, and initial curing procedure adopted.

메타카올린 혼합 시멘트 경화체의 황산마그네슘 침식 및 성능저하 모드

In this study, experimental findings on the resistance to magnesium sulfate attack of portland cement mortar and paste specimens incorporating metakaolin (MK) are presented. Specimens with four replacement levels of metakaolin (0, 5, 10 and 15% of cement by mass) were exposed to solutions with concentrations of 0.424% and 4.24% as MgSO4 at ambient temperature. The resistance of mortar specimens was evaluated through visual examination and linear expansion measurements. Additionally, in order to identify the products formed by magnesium sulfate attack, microstructural analyses such as XRD, DSC and SEM/EDS were also performed on the paste samples incorporating metakaolin. Results confirmed that mortar specimens with a high replacement level of metakaolin exhibited lower resistance to a higher concentration of magnesium sulfate solution. It was found that the negative effect of metakaolin on the magnesium sulfate attack is partially attributed to the formation of gypsum and thaumasite. Conclusively, it is necessary to pay a special attention when using metakaolin in concrete structures, particularly under highly concentrated magnesium sulfate environment.

The performance of mortar containing added metakaolin regarding sulfate action

This paper evaluates the performance of adding Colombian metakaolin (MK) to mortar when these are submitted to sulphate action. Four proportions of MK were used as cement replacement in this study: 10%, 20%, 35% and 50% by weight of cement; cement having 11% tricalcium aluminate was used. Mortar specimens were immersed in 5% sodium sulphate solution for a total period of 280 days after the specified initial moist curing period, the degree of sulphate attack was evaluated by measuring the mortar’s cylindrical expansion, mortar cubes’ compressive strength reduction and visual inspection of mortar specimens. An additional study using X-ray diffraction was conducted to determine the products formed in the cement pastes due to the sulphate attack. The results showed that MK mortar sulphate resistance increased when increasing MK replacement level. An MK proportion greater than 20% is recommended for obtaining better performance against sulphate attack.

Improving strength, drying shrinkage, and pore structure of concrete using metakaolin

This paper presents the results of an investigation on the use of metakaolin (MK) as a supplementary cementing material to improve the performance of concrete. Two MK replacement levels were employed in the study: 10% and 20% by weight of the Portland cement used. Plain and PC-MK concretes were designed at two water–cementitious materials (w/cm) ratios of 0.35 and 0.55. The performance characteristics of the concretes were evaluated by measuring compressive and splitting tensile strengths, water absorption, drying shrinkage, and weight loss due to the corresponding drying. The porosity and pore size distribution of the concretes were also examined by using mercury intrusion porosimetry (MIP). Tests were conducted at different ages up to 120 days. The results revealed that the inclusion of MK remarkably reduced the drying shrinkage strain, but increased the strengths of the concretes in varying magnitudes, depending mainly on the replacement level of MK, w/cm ratio, and age of testing. It was also found that the ultrafine MK enhanced substantially the pore structure of the concretes and reduced the content of the harmful large pores, hence made concrete more impervious, especially at a replacement level of 20%.

Comparative study on strength, sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin

This paper reports an investigation in which the performance of plain and metakaolin (MK)-modified concretes were studied under two different curing regimes. The purpose of this study is to evaluate the effectiveness of MK in enhancing the strength and permeation properties of concrete. MK was used to replace 0–20% of Portland cement by weight in concrete with two water-binder (w/b) ratios of 0.35 and 0.55. The change in compressive strength, sorptivity, and chloride ingress with age at all cement replacement levels under both air and water curing are compared with those of the control concrete. The results indicated that the inclusion of MK greatly reduced sorptivity and chloride permeability of concrete in varying magnitudes, depending mainly on replacement level of MK, w/b ratio, curing condition, and chloride exposure period. It was found that under the inadequate or poor curing, MK-modified concretes suffered a more severe loss of compressive strength and permeability-related durability than the plain concretes.

Durability of metakaolin concrete to sulfate attack

This study investigates the effect of metakaolin (MK) replacement of cement on the durability of concrete to sulfate attack. Three MK replacement levels were considered in the study: 5%, 10%, and 15% by weight of cement. The other experimental parameters investigated in the study were: water to binder ratio (0.5 and 0.6), initial moist curing period (3, 7, and 28 days), curing type (moist and autoclaving), and air content (1.5% and 5%). After the specified initial moist curing period, concrete specimens were immersed in 5% sodium sulfate solution for a total period of 18 month. The degree of sulfate attack was evaluated by measuring expansion of concrete prisms, compressive strength reduction of concrete cubes, and visual inspection of concrete specimens to cracks. The study showed that MK replacement of cement increased the sulfate resistance of concrete. The sulfate resistance of MK concrete increased with increasing the MK replacement level. The sulfate resistance of MK concrete at w/b ratio of 0.5 was found higher than that at w/b ratio of 0.6. Autoclaved MK concrete specimens showed superior sulfate resistance compared to moist cured ones. The pore volume of autoclaved MK concrete was found less than that of moist cured MK concrete. The air entrained MK concrete showed higher improvement in the sulfate resistance than the non-air entrained MK concrete. However, the air entrained plain concrete showed lower improvement in the sulfate resistance than the non-air entrained concrete.

Effect of solution concentrations and replacement levels of metakaolin on the resistance of mortars exposed to magnesium sulfate solutions

This paper reports an experimental study on the magnesium sulfate resistance of mortar and paste specimens incorporating 0%, 5%, 10% and 15% metakaolin (MK). The resistance of mortar specimens was evaluated using visual examination, reduction in compressive strength and expansion measurements. Results confirmed that mortar specimens with a high replacement level of metakaolin showed lower resistance to a higher sulfate concentration of magnesium solution. However, in a lower concentration, there were no visibly remarkable differences in the deterioration of mortar specimens, even up to 360 days of exposure, regardless of replacement levels of metakaolin. The negative effect of metakaolin on the magnesium sulfate resistance is partially attributed to the formation of gypsum but not ettringite and thaumasite. In addition, the reduction of calcium hydroxide and the increase of secondary C–S–H in the cement matrix due to pozzolanic reaction of metakaolin provided an opportunity to lead to the conversion of primary and secondary C–S–H gel into the M–S–H gel. It is concluded that it is necessary to pay special attention when using metakaolin in concrete exposed to highly concentrated magnesium sulfate solution.

Effect of metakaolin on creep and shrinkage of concrete

The effect of metakaolin (MK) on the creep and shrinkage of concrete mixes containing 0%, 5%, 10%, and 15% MK has been investigated. The results showed that the early age autogenous shrinkage measured from the time of initial set of the concrete was reduced with the inclusion of MK, but the long-term autogenous shrinkage measured from the age of 24 h was increased. At 5% replacement level, the effect of MK was to increase the total autogenous shrinkage considered from the time of initial set. While at replacement levels of 10% and 15%, it reduced the total autogenous shrinkage. The total shrinkage (autogenous plus drying shrinkage) measured from 24 h was reduced by the use of MK, while drying shrinkage was significantly less for the MK concretes than for the control concrete. The total creep, basic creep as well as drying creep were significantly reduced particularly at higher MK replacement levels. Compared with estimated values by the CEB 90 model, total creep of all concretes was overestimated, especially in the mixes containing the higher levels of MK. For basic creep, estimates for low levels of MK were acceptable but, for the higher levels, creep was overestimated.

Workability of concrete incorporating pulverized fuel ash and metakaolin

Workability of concrete incorporating combinations of pulverized fuel ash (PFA) and metakaolin (MK) as partial replacements for Portland cement (PC) has been investigated. The aim of the research work is to explore the potential of using PFA and MK as blends with PC in terms of the flow properties of the resulting concrete. Ninety mixtures containing 0, 10, 20, 30 and 40% total replacement of cement with combinations of metakaolin (0–15%) and PFA (0–40%) for concretes with water to binder ratios of 0·4, 0·5 and 0·6 were prepared. The workability of the concrete was measured by the slump, compacting factor and Vebe time tests. Substantial reductions in the workability were obtained when the mixtures contained MK only, with greater reductions being experienced as the MK replacement level increased. In contrast, the mixtures with PFA showed considerable improvement in workability with increase in replacement level. It was found that, for concretes containing blends of PC, PFA and MK, the loss in workability due to the presence of MK can be compensated for by the incorporation of PFA. However, at low cement replacement levels, improvement in workability by the PFA can be achieved only if a superplasticizer is used. The degree of restoration of workability provided by PFA is influenced by the level of cement replacement, MK/PFA ratio and water to binder (w/b) ratio. In particular at low w/b ratio (= 0·4), where superplasticizer is used, there is a critical MKIPFA ratio (∼0·4) above which workability decreases and below which workability increases with increasing replacement level. In general, the incorporation of PFA not only compensates for the loss of workability resulting from the presence of MK but also provides economic benefits.