• Journal of the Korea Institute of Building Construction
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• v.22 no.5
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• pp.425-430
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• 2022

Concrete used for the foundation of high-rise buildings is often placed through in an integrated pouring to ensure construction efficiency and quality. However, if concrete is placed integrally, there is a high risk of temperature cracking during the hydration reaction, and it is necessary to determine the optimal mixing design of high-performance, high-durable concrete through the replacement of the admixture. In this study, experiments on salt damage, carbonation, and sulfate were conducted on the specimen manufactured from the optimal high-performance low-heating concrete combination determined in the author's previous study. The resistance of the cement matrix to chlorine ion diffusion coefficient, carbonation coefficient, and sulfate was quantitatively evaluated. In the terms of compression strength, it was measured as 141% compared to the structural design standard of KCI at 91 days. Excellent durability was expressed in carbonation and chlorine ion diffusivity performance evaluation. In particular, the chlorine ion diffusion coefficient, which should be considered the most strictly in the marine environment, was measured at a value of 4.09×E-12m²/y(1.2898×E-10m²/s), and is expected to be used as a material property value in salt damage durability analysis. These results confirmed that the latent hydroponics were due to mixing of the admixture and high resistance was due to the pozzolane reaction.

• Journal of the Korea Institute of Building Construction
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• v.17 no.2
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• pp.157-166
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• 2017

In general, carbonation and chlorine ions are the most harmful causes of deterioration of concrete structures. Recently, a method has been developed to control the corrosion of rebar in concrete containing chloride by impregnating a Surface coating material with a inhibitor. In this study, accelerated carbonation and differential thermogravimetric analysis (TG-DTA) and CASS tests were carried out to evaluate the characteristics of Surface coatings containing Organic Corrosion inhibitors which are excellent in corrosion inhibition and fix degradation causes $CO_2$ and $Cl^-$. As a result of the experiment, TG-DTA analysis and accelerated carbonation showed that $CO_2$ was directly reacted with amine derivative in concrete by the incorporation of Organic Corrosion inhibitor. In other words, $CO_2$ was immobilized and carbonation inhibition effect was confirmed. In addition, in the CASS test, the specimen coated with the Surface coating material containing the Organic Corrosion inhibitor with $Cl^-$ fixing property showed no corrosion until the 28th day and had excellent performance in preventing corrosion of a rebar by the chloride ion.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.3-27
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• 1996

분체의 입자 배열이 불규칙한 경우뿐만 아니라 입자 크기가 극미세하여 X선회절분석이 불가능한 경우에도 비정질물질이라 한다. 수용액 속에서 이런 비정질 물질을 합성하기 위해서는 합성용액의 과포화도를 높여 계속 유지시킴에 따라 극미세 1차핵 생성의 지속적인 유도에 따른 입자 성장을 최대한 억제시켜야만 한다. 본 연구에서는 흡습제, 칼슘제 및 식품 첨가제 등으로 이용되는 비정질 탄산칼슘을 계에서 합성하고, 이때 생성된 비정질 상태의 겔을 수용액 환경을 변화시켜가면서 따라 결정화를 유도하고 탄산칼슘의 동질이상을 관찰하였다. CO2의 유속을 11/min, 교반속도를 600rpm으로 고정시키고, Ca(OH)2의 양을 10g에서 50g까지 변화시켜가면서 겔 상태의 비정질 탄산칼슘을 합성하였다. 이때 전기전도도는 CO2의 용해와 더불어 Ca(OH)2의 용해도가 증가함에 따라 변화하였으며, 반응종반부에는 겔화가 시작될 때까지 거의 일정하였다. 따라서, 이러한 사실들로부터 현탁액 내에서의 전기전도도의 변화는 Ca이온의 영향을 받는 것으로 사료된다. 비정질 탄산칼슘은 수용액에서 불안정하여 CO2 가스를 방출하면서 급격히 결정화되는데, 본 연구에서는 Ca(OH)2의 양을 20g으로 하여 위의 방법에 의해 얻어진 겔을 수용액의 종류와 농도 및 결정화 온도, 교반속도를 달리하면서 결정화시켰다. 교반속도를 100rpm으로 하여 물의 온도변화에 다라 결정화시킨 경우 전 온도범위에서 칼사이트상이었으며, 물의 온도가 5$^{\circ}C$일 경우에는 미세한 입자들이 응집된 형태였으나, 그 외의 온도변화조건에서는 모두 평균입경 0.4$\mu\textrm{m}$정도의 비교적 균일하 능면체 형태였다. 또한 교반속도를 500rpm으로 증가시켰을 경우에는 8$0^{\circ}C$에서 침상의 아라코나이트가 소량생성되었음을 SEM사진으로 관찰할 수 있었으며, 소량의 바테라이트도 혼재되어 결정화되었음을 XRD결과로 알 수 있었다. 교반속도를 100rpm으로 한 NH4Cl 0.5mol/l 수용액에서는 입자의 형태와 크기가 불규칙한 칼사이트로 결정화되었으며, MgCl2 0.05mol/l 수용액의 경우에는 순수한 H2O의 경우에서와는 달리 2$0^{\circ}C$에서는 모서리가 무딘 매우 균일한 크기의 칼사이트 입자가 관찰되었으며, 6$0^{\circ}C$부터는 아라고나이트가 생성됨을 관찰할 수 있었다. 따라서, 고온(8$0^{\circ}C$)의 농도 MgCl2 수용액(0.1, 0.2 mol/l)에서 교반속도를 높여(800rpm) 겔을 결정화시킨 결과 아라고나이트의 생성수율이 증가되는 것을 확인할 수 있었다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.204-210
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• 2022

Cement is pointed out as the main cause of carbon dioxide emission in the construction industry. Many researchs are underway to use blast furnace slag, an industrial by-product, as a substitute for cement to reduce carbon dioxide emitted during the manufacturing the cement. When blast furnace slag is used as a substitute for cement, it has advantages such as long-term strength and chemical resistance improvement. However, blast furnace slag has a problem that makes initial strength low. This is due to the impermeable film on the surface created during the production of blast furnace slag. The created film is known to be destroyed in an alkaline environment, and based on this, previous studies have suggested a solution using various alkali activators. But, alkali activator is dangerous product since it is a strong alkaline material. And it has the disadvantage in price competitiveness. In this study, an experiment was conducted to improve the initial hydration reactivity of the blast furnace slag to secure the initial strength of the mortar substituted with the blast furnace slag and to check whether the carbonation resistance was increased. As a result of the experiment, it was confirmed that the mortar using alkaline water showed higher strength than the mortar using tap water, and there were more hydration products generated inside. In addition, it was confirmed that the mortar using alkaline water as a compounding water had high carbonation resistance.

• Journal of Energy Engineering
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• v.27 no.2
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• pp.55-60
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• 2018

In this study investigated the Controlled Low Strength Materials using coal ash and steel slag(KR slag) as the main material in the thermal power plant classified as waste resource. Bottom ash and KR slag are mixed at a ratio of 7: 3 to expand the use of industrial by-products through carbonate($CO_2$-fixation) reactions and inhibit the exudation of heavy metals. The results showed that the water content increased as the content of bottom ash increased. It was confirmed that as the powder content increased, the bleeding ratio decreased. Also, as the content of one kind of ordinary portland cement (OPC) decreased, activation of hydration reaction decreased and compressive strength decreased. However, when the mixed composition is appropriately adjusted, the compressive strength of 2.0 MPa required for the controlled low-strength material can be satisfied.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.53-61
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• 2012

The purpose of this study is to understand the mechanism of cementation of soil induced by bacteria. In order to understand the mechanism of cementation of soft soils treated with bacteria, six types of specimens(Not treated, Normal concentration bacteria treatment, High concentration bacteria treatment, Supernatant high concentration bacteria treatment, Double high concentration bacteria treatment, and 25% Specimen high concentration bacteria treatment) were made. Scanning Electron Microscope (SEM), EDX and X-ray diffraction (XRD) analyses were performed on the soft silt and loose sand specimens. Compared with the normal bacteria concentration treated specimen, a clearer cementation between particles was observed in the 25% specimen high bacteria concentration treated specimen. On the basis of the preliminary results, it appears that microbial cementation can occur in the soft soil.

• Journal of the Mineralogical Society of Korea
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• v.13 no.1
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• pp.22-36
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• 2000

중원지역 지열수의 CO2 가스의 용축과 수반된 탄산염 침전물의 광물학적 특성을 밝히기 위하여 탄산염 침전물에 대해 광물학적 및 지구화학적 분석방법을 적용하여 보았다. 이들은 매년 수 mm의 두께로 저수조내에 침전되며 미세한 층상으로 결정화되어 있고, 검은 갈색의 얇은 층들이 반복적으로 존재하고 있다. 침전물은 비교적 순수한 방해석으로 되어 있으며 1M HCl로 처리하여 잔류물을 XRD 분석한 결과는 카올린 광물 및 일라이트질 광물이 확인되었다. 전자현미분석에 의하면 검은 갈색층은 주로 방해석과 Fe나 Mn 산화광물의 집합체이며 소량의 점토광물도 함께 섞여 있는 것으로 추정된다. Fe의 경우에는 주로 방해석내 Ca자리를 치환하여 존재하며 일부 산화광물로 함께 침전된 것으로 보인다. 반면에 Mn의 경우는 일부는 Fe처럼 방해석결정구조 내에서 Ca를 치환하면서 존재하기도 하지만 주로 산화물의 형태로 존재하는 것으로 보인다. 후방산란전자상(BSEI) 관찰에 의하면 Fe와 Mn 모두 매우 미세한 입자의 산화광물들로 밀집해 있는 부분이 관찰되기도 한다. 중원지역 탄산수로부터 방해석이 침전되는 과정은 CO2 가스가 방출되면서 pH가 증가하면서 방해석 및 Fe, Mn 산화물이 과포화상태가 되어 침전되는 것으로서 해석할 수 있다. 또한 지하 심부를 순환하면서 활발한 물-암석반응의 결과로 Si나 Al 및 기타 이온들의 함량이 상대적으로 높았던 탄산수가 pH가 높아지면서 카올린 광물이나 일라이트질 광물, 석영등의 규산염 광물들이 함께 침전하였을 것이다. 그러나 방해석의 침전과정이 이루어지는 과정 동안에, 온천공으로부터 채수되는 탄산수의 양이 수요에 따라 매우 불규칙해서 탄산수의 수요가 많은 경우 탄산수가 지속적으로 과잉 채수되면 주변 천층지하수가 탄산수에 혼합되어 Fe, Mn 등의 농도를 상대적으로 낮추게 되어 산화물형태로 침전되기가 어려워져서 거의 순수한 방해석만이 침전하게 된다. 결과적으로 거의 순수한 방해석 층에 검붉은 층이 불규칙하게 반복되고 있는 중원지역 탄산염침전물은 침전작용이 일어나는 대부분의 기간 동안 지속적으로 주변 전층지하수의 유입이 일어났음을 지시하고 있다. 또한 Fe, Mn 등의 함량이 높은 탄산수로부터의 침전은 매우 짧은 기간동안 단속적으로 일어났음을 지시한다.

• Economic and Environmental Geology
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• v.49 no.1
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• pp.13-22
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• 2016

The objectives of this study were to recover silica and iron oxides and $CO_2$ sequestration using serpentine via various acid dissolution and pH swing processes. Serpentine collected from Guhang-myeon in S. Korea were mainly composed of antigorite and magnetite consisting of $SiO_2$ (45.3 wt.%), MgO (41.3 wt.%), $Fe_2O_3$ (12.2 wt.%). Serpentine pulverized ($${\leq_-}75{\mu}m$$) and then dissolved in 3 different acids, HCl, $H_2SO_4$, $HNO_3$. Residues treated with acidic solution were recovered from the solution (step 1). And then the residual solution containing dissolved serpentine was titrated using $NH_4OH$. And pH of the solution increased up to pH=8.6 to obtain reddish precipitates (step 2). After recovery of the precipitates, the residual solution reacted with $CO_2$ and then pH increased up to pH=9.5 to precipitate white materials (step 3). The mineralogical characteristics of the original sample and harvested precipitates were examined by XRD, and TEM-EDS analyses. ICP-AES analysis was also used to investigate solution chemistry. The dissolved ions were Mg, Si, and Fe. The antigorite became noncrystralline silica after acid treatment (step 1). The precipitate at pH=8.6 was mainly amorphous iron oxide, of which size ranged from 2 to 10 nm and mainly consisting of Fe, O, and Si (step 2). At pH=9.5, nesquehonite [$Mg(HCO_3)(OH){\cdot}2(H_2O)$] and lasfordite [$MgCO_3{\cdot}H_2O$] were formed after reaction with $CO_2$ (step 3). The size of carbonated minerals was ranged from 1 to $6{\mu}m$. These results indicated that the acid treatment of serpentine and pH swing processes for the serpentine can be used for synthesis of other materials such as silica, iron oxides and magnesium carbonate. Also, This process may be useful for the precursor synthesis and $CO_2$ sequestration via mineral carbonation.

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.29-37
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• 2024

In this study, recycled concrete aggregates (RCA) were treated in a 5-kg-scale prototype reactor with carbon dioxide (CO₂) to enhance their material quality and geotechnical performance. The aggregate crushing value (ACV) and California bearing ratio (CBR) were measured on untreated RCAs and CO₂-treated RCAs. After CO₂ treatment, the ACV decreased from 35.6% to 33.2%, and the CBR increased from 97.5% to 102.4%. The CO₂ treatment caused a reduction of fine particle generation and an increase in bearing capacity through carbonation. When CO₂ treatment was performed with mechanical agitation, which provided additional enhancement in mechanical quality, the ACV was reduced further to 30.3%, and the CBR increased to 137.7%. If upscaled effectively, the proposed CO₂ treatment technique would be an effective method to reduce carbon emissions in construction industries.

• Economic and Environmental Geology
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• v.36 no.5
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• pp.365-374
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• 2003

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, $MgCl_2$ and $Na_2SO_4$ solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({$Ca_6/[Si(OH)_6]_2{\cdot}24H_2O$}${\cdot}[(SO_4)_2]{\cdot}[(CO_3))2]$) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).