• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.49-55
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• 2011

The distresses of alkali-silica reaction (ASR) was recently reported at highway cement concrete pavement in Korea, which showed typical cracking and spalling patterns of ARS. Korea is was no longer safe zone against ASR, needding to find a control methodology against ASR. The purpose of this research was to provide a control methodology against ASR using mineral admixtures through a series of laboratory test program. Laboratory works included the accelerated mortar bar test (AMBT) by ASTM C 1260 regulation with five types of aggregate and three types of mineral admixtures (fly ash, ground granulated blast-furnace slag and silica fume). The result of ASTM C 1260 test for five types of aggregates without mineral admixtures showed that Siltstone and Mudstone were found to be "reactive." Tuff and Andesite-1 were found to be "possiblely reactive." In case of concrete mixed with 10, 20, and 30% fly ash, all specimens except Mudstone mixed with 10% FA were found to be "non-reactive". In cases of concrete mixed with 30, 40, and 50% ground granulated blast-furnace slag and 5, 7.5, and 10% silica fume, all specimens were found to be "non-reactive." These results could be selectively applied in constructions in Korea.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.74-80
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• 2011

In this study, it is evaluated on the properties of mechanical performance, autogenous shrinkage and chloride resistance for application of high performance concrete for bridge deck overlay used slag powder and fly ash as a representative by-product of industrialization. According to test results, it is evaluated that the durability of concrete is improved the properties of chloride resistance, autogenous shrinkage and alkali aggregate reaction by using hydraulic mineral admixtures. It is considered to have a green construction and an economic feasibility on recycling of by-product as a improved concrete for durability and efficiency in materials and constructions.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.06a
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• pp.211-220
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• 2005

The concrete structure is being considered for the main engineered barrier of low and intermediate level radwaste disposal facility. Concrete of low permeability can minimize infiltration of water and effectively prevent release of nuclide to ecosystem. But if concrete degrades, structural stability of disposal structure will decrease while permeability increase, resulting in increased possibility of nuclide release due to water infiltration. Therefore disposal concrete structure degradation shall be minimized to maintain capacity of nuclide isolation. The typical causes of concrete structure degradation are sulfide attack, reinforcement corrosion due to chloride attack, leaching of calcium hydroxide, alkali-aggregate reaction and repeated freezing-thawing. The common cause of these degradation processes is infiltration of water or adverse chemicals into concrete. Based on the study of these degradation characteristics and mechanisms of concrete structure, the methodology of design and service life evaluation of concrete structure as an engineered barrier are reviewed to ensure its long-term durability.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.701-704
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• 2008

The case of failure of Alkali-silica reaction (ASR) on the cement concrete pavement was reported in Korea. In the United States America, the fly ash has less than 10 percent Cao reported that prevent expansion by ASR. Most of all fly ash in Korea have less than 10 percent CaO, therefore it is similar ASTM F fly ash in the USA. Crushed aggregates of the test section had expansion behavior by potential ASR that the ASTM C 1260 test method tested expansion 0.17 percent during 14 days. The test section of concrete pavement used crushed aggregate was constructed that fly ash have 20 percent weight of cementitious materials to prevent expansion by ASR. This study was performed flexural strength test for elapsed days and durability by freeze-thaw test. It was shown that flexural strength was increased elapsed days and good performed freeze-thaw test. This study shown that fly ash concrete pavement was good performance in the test section.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.247-257
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• 2021

This study was started to investigate why autoclave curing (AC) specimen showed an improvement in compressive strength after immersion in water for a long time, although AC specimen did not showed a high initial compressive strength unlike our expectations. Distilled water and alkaline solutions were used for immersion and three different curing methods were engaged. It was expected that the compressive strength would be improved after immersion in alkaline solutions; however, there was little difference in compressive strength after 21 day immersion because both new crystallites produced by additional geopolymerization and expansion caused by the alkaline aggregate reaction may prevent the additional improvement in compressive strength. It was concluded that in order to secure the long-term commonality and underwater stability of the geopolymers, it is desirable aging geopolymers while immersing it underwater for more than 21 days after curing using an autoclave.

• Korean Journal of Agricultural Science
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• v.18 no.2
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• pp.140-147
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• 1991

This paper was performed to obtain the data applied to use of synthetic lightweight aggregate concrete affected by alkali silica reaction. The results obtained were summarized as follows : 1. The expansion of each type concrete was increased with increase of curing age, respectively. Also, at the curing age 90 days, the rate of expansion of type A, B, C and D concrete was increased 0.173%, 0.575%, 0.230% and 0.680%, respectively. Specially, the rate of expansion of type D concrete was shown 3.93 times higher than the type A concrete. The cracks width were increased with increase of expansion and at the 0.680% expansion, the maximum width was shown 0.5 mm. 2. The dynamic modulus of elasticity of each type concrete was increased with increase of curing age, respectively. At the curing age 30 days, the highest dynamic modulus of elasticity was showed at each type concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete, respectively. Also, at the curing age A, B, C and D concrete was increased 24.3%, 33.7%, 28.1% and 37.0%, respectively. The rate of loss in type D concrete was shown 1.52 times higher than the type A concrete. 3. The ultrasonic pulse velocity of each type concrete was increased with increase of curing age, respectively. At the curing age 30 days, the highest ultrasonic pulse velocity was showed at each type concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete, respectively. Also, at the curing age 90 days, the percentage loss of ultrasonic pulse velocity of type A, B, C and D concrete was increased 6.4%, 8.7%, 8.5% and 14.2%, respectively. The rate of loss in type D concrete was shown 2.21 times higher than the type A concrete. 4. The relation between dynamic modulus of elasticity and ultrasonic pulse velocity was highly significant. The dynamic modulus of elasticity was increased with increase and decreased with decrease of ultrasonic pulse velocity. Also, the decreasing rate of the dynamic modulus of elasticity was shown 2-7 times higher than the ultrasonic pulse velocity at each age, respectively. 5. The dynamic modulus of elasticity and ultrasonic pulse velocity were decreased with increase of expansion, and the decreasing rates were increased with increase of curing age. The increasing rate of expansion was shown higher than the decreasing rate of dynamic modulus and ultrasonic pulse velocity.

• 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).

• The Journal of Engineering Geology
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• v.5 no.2
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• pp.193-200
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• 1995

It has been well known that the alkali-aggregate reaction between the aggregates and cement paste is one of the reasons of a concrete siructre expansion. Because of a serious demage on the concrete stnicture from the expansion, in many countries, the safety of the materials is checked in laboratory by mortar-bar test and the upper limit of expansion in length is 0.1%. The prescriptions are presented in the ASTM C227 and 490 of U.S. which has been international currency and in the KS Handbook F2503, F2546 and L5107 of Korea published by Korean Standards Association. Both of the prescriptions are almost same in their contents. Actually, in the process of preparing and measuring the mortar-bar according to the prescription mentioned above, it seems that there are no problems for its own purpose but a few points are found to be improved upon the methods to increase the accuracy for laboratory work as follows. 1. The prescription of blending ratio(aggregate, cement and water) should be noted by volume not by weight. 2. It is unreasonable to measure the initial length of mortar bars after 24$\pm$2 hours at once regardless the kind of aggregates. 3. It may bring about errors in calculating the expansion ratio under the condition of the denominator value fixed as 254mm. 4. The measuring methods of specific gravity are selected according to the purposes but the pure specific gravity displays the highest accuracy among them.

• Clean Technology
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• v.28 no.1
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• pp.46-53
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• 2022

The agglomeration characteristics of coal and silica sand were investigated under various conditions using mixed samples consisting of coal, silica sand, and potassium hydroxide, which is an agglomeration accelerator. The samples were prepared by either physically mixing or using aqueous solutions. The experiments using the physically mixed powder samples were performed with a two hour reaction time. The results showed that the number of aggregates generated increased as the reaction temperature and the total potassium content increased. The experiments using aqueous solutions were performed at 880 ℃, which is the operating temperature of a fluidized bed boiler, and at 980 ℃, which assumes a local hot spot. The amount of agglomeration generated as the reaction time increased and the total potassium content increased was identified. In the experiment performed at 880 ℃, the amount of aggregate generated clearly increased with the reaction time, and in the experiment performed at 980 ℃, assuming a local hot spot, a large amount of aggregate was generated in a relatively short time. The aggregates became harder as the potassium content increased. When the total potassium content was less than 1.37 wt.%, the aggregates were weak at both temperatures and collapsed even with a slight impact. Additionally, the surface characteristics of the silica sand and ash aggregates were observed by SEM-EDS analysis. The analysis revealed a large amount of potassium at the bonding sites. This result indicates that there is a high possibility of aggregation in the form of a eutectic compound when the alkali component is increased.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.95-102
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• 2015

In this paper, the effects of sodium hydroxide (NaOH) and aluminum potassium sulfate ($AlK(SO_4)_2{\cdot}12H_2O$) dosage on strength properties were investigated. For evaluating the property related to the dosage of alkali activator, sodium hydroxide (NaOH) of 4% (N1 series) and 8% (N2 series) was added to 1~5% (K1~K5) dosage of aluminum potassium sulfate ($AlK(SO_4)_2{\cdot}12H_2O$) and 1% (C1) and 2% (C2) dosage of calcium oxide (CaO). W/B ratio was 0.5 and binder/ fine aggregate ratio was 0.5, respectively. Test result clearly showed that the compressive strength development of alkali-activated slag cement (AASC) mortars were significantly dependent on the dosage of NaOH and $AlK(SO_4)_2{\cdot}12H_2O$. The result of XRD analysis indicated that the main hydration product of $NaOH+AlK (SO_4)_2{\cdot}12H_2O$ activated slag was ettringite and CSH. But at early ages, ettringite and sulfate coated the surface of unhydrated slag grains and inhibited the hydration reaction of slag in high dosage of $NaOH+AlK(SO_4)_2{\cdot}12H_2O$. The $SO_4{^{-2}}$ ions from $AlK(SO_4)_2{\cdot}12H_2O$ reacts with CaO in blast furnace slag or added CaO to form gypsum ($CaSO_4{\cdot}2H_2O$), which reacts with CaO and $Al_2O_3$ to from ettringite in $NaOH+AlK(SO_4)_2{\cdot}12H_2O$ activated slag cement system. Therefore, blast furnace slag can be activated by $NaOH+AlK(SO_4)_2{\cdot}12H_2O$.