• Computers and Concrete
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• v.24 no.2
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• pp.137-150
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• 2019

In this paper, surrogate models such as multivariate adaptive regression splines (MARS) and M5P model tree (M5P MT) methods have been investigated in order to propose a new formulation for the 28-days compressive strength of self-compacting concrete (SCC) incorporating metakaolin as a supplementary cementitious materials. A database comprising experimental data has been assembled from several published papers in the literature and the data have been used for training and testing. In particular, the data are arranged in a format of seven input parameters covering contents of cement, coarse aggregate to fine aggregate ratio, water, metakaolin, super plasticizer, largest maximum size and binder as well as one output parameter, which is the 28-days compressive strength. The efficiency of the proposed techniques has been demonstrated by means of certain statistical criteria. The findings have been compared to experimental results and their comparisons shows that the MARS and M5P MT approaches predict the compressive strength of SCC incorporating metakaolin with great precision. The performed sensitivity analysis to assign effective parameters on 28-days compressive strength indicates that cementitious binder content is the most effective variable in the mixture.

• Advances in concrete construction
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• v.11 no.2
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• pp.127-140
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• 2021

In this study, twenty-five geopolymer (GP) mixes were prepared by varying the alkaline solids to Metakaolin (MK) and sodium silicate to NaOH ratios from 0.1 to 0.5 and 0.2 to 1.0, respectively, thus giving a wide range of molar ratios of silica to alumina, sodium oxide to alumina and water to sodium oxide. The compressive strength of these GP mixes was determined for four curing schemes involving oven curing at 100℃ for 24 h and three ambient curing with the curing ages of 3, 14, and 28 days. The test results revealed that for the manufacture of GP binder for structural applications of strength up to 90 MPa, the molar ratio of silica to alumina should be greater than 2.3, sodium oxide to alumina should be between 0.6 to 1.2, and water to sodium oxide should not exceed 12. The compressive strength of ambient cured GP mortar gets stabilized at 28 days of ambient curing. Experimental findings were also corroborated by GP microstructure analysis. The embodied energy of MK-based GP mortars, especially of high strength, is significantly less than the cement mortar of equivalent strength.

• Advances in concrete construction
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• v.14 no.5
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• pp.341-354
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• 2022

Treatment of solid waste building materials is a crucial method of disposal and an area of ongoing research. New standards for the treatment of solid waste building materials are necessary due to multisource features, huge quantities, and complicated compositions of solid waste. In this research, sustainable nanomaterial mixtures containing nano-paper waste (NPW) and nano-metakaolin (NMK) were used as a substitute for Portland cement. Portland cement was replaced with different ratios of NPW and NMK (0%, 4%, 8%, and 12% by weight of cement) while the cement-to-water ratio remained constant at 0.4 in all mortar mixtures. The fresh properties had a positive effect on them, and with the increase in the percentage of replacement, the fresh properties decreased. The results of compressive strength at 7 and 28 days and flexural strength at 28 days show that the nanomaterials improved the strength, but the results of NMK were better than those of NPW. The best replacement rate was 8%, followed by 4%, and finally 12% for both materials. The combination of NMK and NPW as a replacement (12% NMK + 12% NPW) showed less shrinkage than the others because of the high pozzolanic reactivity of the nanomaterials. The combination of NMK and NPW improved the microstructure by increasing the hydration volume and lowering the water in the cement matrix, as clearly observed in the C-S-H decomposition.

• Conservation Science in Museum
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• v.17
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• pp.101-116
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• 2016

Ceramic cultural artifacts restored with gypsum-based materials are prone to decay over time due to gypsum's natural absorption and release of atmospheric moisture, often leading to distortion and peeling of painted layers. This study proposes a new restoration material which utilizes extra hard stone, significantly superior in strength to regular gypsum. In order to enhance its physical properties and make it suitable for restoration of ceramics, extra hard stone is mixed with metakaolin. This mixture far surpasses regular gypsum in compressive strength(119MPa vs. 26MPa) while also maintaining a much lower wear rate(0.88% vs. 2.53%). Furthermore, the water absorption rate(2.9%) of the mixed material is over five times lower than that of regular gypsum(17.2%). When examined using a SEM(Scanning Electron Microscope), this mixture also proved superior to extra hard stone in terms of hardened density. The addition of metakaolin increases the mixture's strength and water resistance over that of extra hard stone and also improves its surface density, making it ideal for the restoration of ceramics. It has already been used to repair ceramic objects in the Museum's collection: Clay basin(sinan 18892), Buncheong ware bottle with incised peony design(jubsu 2034), Buncheong ware bowl with chrysanthemum(jubsu 1730). Results thus far have shown the mixture to be easy to inject and layer as well as harden into an even surface, which allows for smooth application of paint for color matching.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.499-506
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• 2007

According to the high demand of concrete structures with high performance, various studies have examined on the high performance concrete, especially high strength concrete. Various admixtures are required to produce high strength concrete and silica fume has been the most popular admixture. Recently, however, metakaolin, which is similar to silica fume in properties but cheaper, has been introduced to high strength concrete. In this study, high-strength concrete using metakaolin were studied of capillary pore structure by mercury intrusion porosimetry technique and the accelerated chloride diffusivity by electrical difference. In result, it was found that the pore structure improved and compressive strength increased and chloride diffusivity reduced as more metakaolin content was added. In addition, a regression analysis of $5{\sim}2,000nm$ pore volume and both compression strength and chloride diffusivity revealed that each these had a high correlation of about 0.76 and 0.68.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.339-346
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• 2011

The effects of mineral admixtures on the bonding properties of cement mortar to polyolefin based synthetic fiber were evaluated. The mineral admixtures consisted of 0%, 5%, 10%, and 15% fly ash, blast furnace slag, and metakaolin in cement. Bond interactions between the cement mortar and the polyolefin based synthetic fiber were determined by Dog-bone bond tests. Bond tests of the polyolefin based synthetic fiber showed an increase in pullout load with the strength of the cement mortar. Also, the interface toughness of polyolefin based synthetic fiber in cement mortar increased as the fly ash, blast furnace slag, and metakaolin contents increased. The microstructure of polyolefin based synthetic fiber surface was examined after the pullout test to analyze the frictional resistant force according to the replacement ratio of fly ash, blast furnace slag, and metakaolin during the pullout process of polyolefin based synthetic fiber in cement mortar. The scratched of polyolefin based synthetic fibers increased with the replacement ratio of fly ash, blast furnace slag, and metakaolin. Also, the interface toughness was enhanced by adhesion forces induced by the fly ash, blast furnace slag, and metakaolin.

• Magazine of the Korea Concrete Institute
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• v.15 no.5
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• pp.24-32
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• 2003

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.643-648
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• 2002

A research for recycling the demolished-concrete as concrete aggregate has been concerned in all over the world. There, however, are some problems that qualities of recycled aggregates are not only largely different, but also mechanical properties of recycled aggregate concrete decrease a little in comparison with that of natural aggregate concrete. In this study, the resistance of freezing and thawing of concrete using source-concrete recycled aggregate(SRN) and demolished-concrete recycled aggregate(DRA) was investigated. Futhermore a research for improvement of freeze and thaw durability of recycled aggregate concrete was performed. Relative dynamic modulus of elasticity of SRN and DRA recycled aggregate concrete was dropped 60% before 150 of freezing and thawing cycle, and was much lower than that of control concrete. Relative dynamic modulus of elasticity of recycled aggregate concrete was increased to decrease water-cement ratio, but the freeze and thaw durability of recycled aggregate concrete was not enough improved. Futhermore, when metakaolin and silica fume were repalced, the freeze and thaw durability of recycled aggregate concrete containg metakaolin was more improved than that of silica fume.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.153-156
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• 2002

The purpose of this research was to evaluate on the properties of fresh and hardened high-performance concrete(HPC) incorporating high-reactivity metakaolin(HRM). Setting time, heat of hydration, compressive strength, resistance to chloride-ion penetration, and repeated freezing and thawing test were carried out in order to investigate the properties of fresh and hardened state concrete. The properties of the HRM concrete were also compared with those of the portland cement concrete and silica fume(SF) concrete. The laboratory test results indicate that HRM material can be used as a supplementary cementitious material to produce high-performance concrete.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.2
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• pp.65-75
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• 2013

In this study, the engineering characteristics of volcanic ash-cement soil mixtures and zeolite-cement soil mixtures are investigated by using unconfined compression test, freezing-thawing test, SEM and XRD analysis. The samples were mixed with volcanic ash from Mt. Baekdusan or porous zeolite, and cement as the ratios of 3.5:1, 4.0:1, 4.5:1, 5.0:1 with and without metakaolin. It is confirmed that compressive strength degraded with increasing of the amount of volcanic ash or zeolite, and increased with addition of metakaolin as a binder. Moreover, test results suggested that the mixtures provided sufficient freezing-thawing resistance. In addition, ettringite as a product of cement hydration was detected by SEM and XRD, and that possibly contributes to the strength of the mixtures.