• 한국세라믹학회지
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• 제53권1호
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• pp.116-121
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• 2016

The amount of carbon dioxide ($CO_2$) released while producing building materials is substantial and has been targeted as a leading contributor to global climate change. One of the most typical methods of reducing $CO_2$ in building materials is the addition of slag and fly ash, like pozzolan material another method is to reduce $CO_2$ production by developing carbon negative cement. MgO-based cement from the low-temperature calcination of magnesite required less energy and emitted less $CO_2$ than the manufacturing of Portland cements. It is also believed that adding reactive MgO to Portland-pozzolan cements can improve their performance and also increase their capacity to absorb atmospheric $CO_2$. In this study, basic research on magnesia cement using $MgCO_3$ and magnesium silicate ore (serpentine) as the main starting materials, as well as blast furnace slag for the mineral admixture, was carried out for industrial waste material recycling. In order to increase the overall hydration activity, $MgCl_2$ was also added. In the case of the addition of $MgCl_2$as accelerating admixture, there was a promoting effect on the compressive strength. This was found to be due to the production of needle-like dense Mg-Cl hydrates. Mgnesia cement has a high viscosity due to its high specific surface area therefore, when the PC-based dispersing agent was added at a level of more than 1.0%, it had the effect of improving fluidity. In particular, the addition of $MgCl_2$ in magnesia cement using $MgCO_3$and magnesium silicate ore (serpentine) as main starting materials led to a lower expansion ratio and an increase in the freeze-thaw resistance finally, the addition of $MgCl_2$ as accelerating admixture led to good overall durability.

• Carbon letters
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• 제23권
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• pp.22-29
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• 2017

The compressive strength and electrical resistance of pitch-based carbon fiber (CF) in cementitious materials are explored to determine the feasibility of its use as a functional material in construction. The most widely used CFs are manufactured from polyacrylonitrile (PAN-based CF). Alternatively, short CFs are obtained in an economical way using pitch as a precursor in a melt-blown process (pitch-based CF), which is cheaper and more eco-friendly method because this pitch-based CF is basically recycled from petroleum residue. In the construction field, PAN-based CFs in the form of fabric are used for rehabilitation purposes to reinforce concrete slabs and piers because of their high mechanical properties. However, studies have revealed that construction materials with pitch-based CF are not popular. This study explores the compressive strength and electrical resistances of a cement paste prism using pitch-based CF.

• 한국세라믹학회지
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• 제52권1호
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• pp.48-55
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• 2015

Hardened cement-based materials exposed to the high temperatures of a fire are known to experience change in the pore structure as well as microstructural changes that affect their mechanical properties and tend to reduce their durability. In this experimental investigation, hardened Portland cement pastes were exposed to elevated temperatures of 200, 400, 600, 800, and $1000^{\circ}C$ for 60 minutes, and the resulting damage was studied by thermogravimetry (TG), mercury intrusion porosimetry (MIP) and density measurements. These results revealed that the residual compressive strength is increased at temperatures greater than $400^{\circ}C$ due to a small pore size of 3 nm and/or rehydration of the dehydrated cement paste. However, a loss of the residual strength occurs at temperatures exceeding 500 and $600^{\circ}C$. This can be attributed to the decomposition of hydrates such as portlandite and to an increase in the total porosity.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 가을 학술논문 발표대회
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• pp.55-56
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• 2022

As global warming becomes serious, research is continuously being conducted to reduce CO2 emissions. Among building materials, the carbon emission of cement is so high that it accounts for 6.8% of the carbon emission of the entire industry. Studies replacement of cement with blast furnace slag and fly ash are steadily increasing. In addition, efforts are being made to reduce air pollution due to increased damage caused by increased concentrations of harmful substances such as fine dust and heavy metals in the air. There is an increasing number of studies that enable adsorption by mixing adsorbents into building materials. This study reviewed the strength properties to make an adsorbable non-cement finishing material by mixing tourmaline, an adsorbent, based on the non-cement composite, and confirmed that the strength decreases as the replacement ratio increases.

• Computers and Concrete
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• 제16권2호
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• pp.329-342
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• 2015

The present paper aims at developing a method to accommodate multi-surface concrete plasticity from the point of view of a consistency concept applied to general tangent operators. The idea is based on a Taylor series expansion of the actual effective stress at the stress point corresponding to the previous accumulated true stresses plus the current increment values, initially taken to be elastic. The proposed algorithm can be generalized for any multi-surface criteria combination and has been tested here for typical cement-based materials. A few examples of application are presented to demonstrate the effectiveness of the multi-surface technique as used to a combination of Rankine and Drucker-Prager yield criteria.

• Computers and Concrete
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• 제21권6호
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• pp.649-659
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• 2018

Adaptive neuro-fuzzy inference systems (ANFIS) can be efficient in modelling non-linear, complex and ambiguous behavior of cement-based materials undergoing combined damage factors of different forms (physical and chemical). The current work investigates the use of ANFIS to model the behavior (time of failure (TF)) of a wide range of concrete mixtures made with different types of cement (ordinary and portland limestone cement (PLC)) without or with supplementary cementitious materials (SCMs: fly ash and nanosilica) under various exposure regimes with the most widely used chloride-based de-icing salts (individual and combined). The results show that predictions of the ANFIS model were rational and accurate, with marginal errors not exceeding 3%. In addition, sensitivity analyses of physical penetrability (magnitude of intruding chloride) of concrete, amount of aluminate and interground limestone in cement and content of portlandite in the binder showed that the predictive trends of the model had good agreement with experimental results. Thus, this model may be reliably used to project the deterioration of customized concrete mixtures exposed to such aggressive conditions.

• Computers and Concrete
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• 제5권4호
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• pp.295-328
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• 2008

A previously published multiscale model for early-age cement-based materials [Pichler, et al.2007. "A multiscale micromechanics model for the autogenous-shrinkage deformation of early-age cement-based materials." Engineering Fracture Mechanics, 74, 34-58] is extended towards upscaling of viscoelastic properties. The obtained model links macroscopic behavior, i.e., creep compliance of concrete samples, to the composition of concrete at finer scales and the (supposedly) intrinsic material properties of distinct phases at these scales. Whereas finer-scale composition (and its history) is accessible through recently developed hydration models for the main clinker phases in ordinary Portland cement (OPC), viscous properties of the creep active constituent at finer scales, i.e., calcium-silicate-hydrates (CSH) are identified from macroscopic creep tests using the proposed multiscale model. The proposed multiscale model is assessed by different concrete creep tests reported in the open literature. Moreover, the model prediction is compared to a commonly used macroscopic creep model, the so-called B3 model.

• 한국재료학회지
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• 제20권1호
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• pp.1-6
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• 2010

Geopolymer materials are attractive as inorganic binders due to their superior mechanical and eco-friendly properties. In the current study, geopolymer-based cement was prepared using aluminosilicate minerals from fly-ash with KOH as an alkaline-activator and $Na_2SiO_3$ as liquid glass. Then, calcium carbonate powder from a clam shell was mixed with the geopolymer and the mixture was coated on a concrete surface to provide points of attachment for environmental organisms to grow on the geopolymers. We investigated the effect of the shell powder grain size on the microstructure and bonding property of the geopolymers. A homogeneous geopolymer layer coated well on the concrete surface via aluminosilicate bonding, but the adhesiveness of the shell powder on the geopolymer cement was dependent on the grain size of the shell powder. Superior adhesive characteristics were shown in the shell powder of large grain size due to the deep penetration into the geopolymer by their large weight. This kind of coating can be applied to the adhesiveness of eco-materials on the surface of seaside or riverside blocks.

• 공업화학
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• 제20권5호
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• pp.505-510
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• 2009

콘크리트의 내구성에 대한 대표적인 물리적 특성인 압축강도, 투수성능, 수밀성 등은 시멘트 재료의 미세구조에 의해 영향을 받는다. 특히 콘크리트의 내구성 향상을 위해서는 수밀성이 가장 중요하다 할 수 있다. 콘크리트의 수밀성 향상을 위한 재료는 유기 재료 및 무기질 재료가 다양하게 이용이 되고 있다. 본 연구에서는 불소계 에멀젼이 시멘트 수밀성능에 미치는 영향을 검토하였다. 불소계 에멀젼이 혼입된 시멘트 재료는 시멘트 계면 활성에 의한 수밀성능 개선 및 시멘트 pore 내에서 $CaF_2$ 미세 결정의 생성에 의해 시멘트 재료의 수밀성능을 개선시킬 수 있는 것으로 나타났다.

• 한국농공학회논문집
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• 제52권3호
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• pp.9-17
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• 2010

This study aims to evaluate a porous concrete using hwang-toh, blast furnace slag and blast furnace slag (BFS) cement instead of type I cement. The tests that were carried out to analysis the properties of porous hwang-toh BFS cement concrete included compressive strength, continuous void ratio, absorption rate, and pH value, repeated freezing and thawing test were conducted. Test results indicated that the performance in porous hwang-toh concrete are effective on the kaoline based binder materials. The pH value were shown in about 9.5 ~ 8.5. The compressive strength was increased and void ratio was decreased with increasing the kaoline based binder materials, respectively. The void ratio and compressive strength were in the range of about 21 ~ 30 %, 8 ~ 13 MPa, respectively. The increased in void ratio of more than 25 % is showed to reduce the resistance of repeated freezing and thawing. Also, the resistance of repeated freezing of thawing and the compressive strength of porous hwang-toh BFS cement concrete are independent with hwang-toh content and BFS cement amount. But, the void ratio was decreased with increasing the high volume hwang-toh contents (more than 15 %).