• Advances in concrete construction
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• v.9 no.3
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• pp.227-234
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• 2020

Raw perlite is a volcanic alumino-silicate and is used as aggregate in the construction industry. The high silica and alumina contained in the raw perlite allows the production of geopolymer mortar with the help of alkaline solutions. In this study, different geopolymer mortars are obtained by mixing ground perlite (GP), sodium hydroxide (NaOH), water and CEN standard sand and the strength and microstructure of these mortars are investigated. Mortar specimens are placed in the oven 24 hours after casting and kept at different temperatures and times, then the specimens are cured under laboratory conditions until the day of strength tests. After curing, unit weight, ultrasound pulse velocity, flexural and compressive strengths are determined. Experimental results indicate that the mechanical properties of the mortars enhance with increasing oven-curing period and temperatures as well as increasing NaOH molarity. In addition, SEM/EDS and XRD analyses are performed on the mortar specimens and the results are interpreted.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.238-239
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• 2014

It is well known that the bond characteristics of fiber govern the performance of fiber reinforced composite material. A preliminary study was carried out to investigate the pull-out behavior of amorphous and conventional single fiber in cement mortar in accordance with the JCI(Japan Concrete Institute) SF-8. The test was performed under displacement control, and results showed that the bond strength decreased with increasing fiber length. In addition, the amorphous steel fiber showed much higher pull-out load per unit weight compared to conventional steel fiber.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.931-938
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• 2005

When concrete structures are exposed under marine condition for a long time, the steel in concrete is corroded due to the ingression of chlorides in the seawater. Because the damages of corrosion resulting from the chloride ion are very serious, many researches have been performed. Silver nitrate colormetric method that can measure easily penetration depth of chloride ion has been executed, recent)y. However, characteristics of silver nitrate colormetric method were not fully examined. Therefore, the objective of this paper Is to study the applicability of colormetric method. For the purpose of this, effect factors and reaction mechanism of colormetric method were investigated, and the colormetric method is applied for marine concrete structures. According to the results of silver nitrate colored method, two reactions such as white reaction of AgCl and brown reaction of AgOH were shown when $AgNO_3$ was sprayed in splited section. And velocity constant ratio(K) of two reactions appeared that white reaction, AgCl reacts with the fast speed by 3240. When the colormetric method was applied in concrete, it is reasonable that $AgNO_3$ solution more than 0.05N concentration was sprayed. It is confirmed that the colormetric method is useful tool for estimating the chloride of concrete structures in situ. The average chloride amount of colored parts indicates $0.9kg/m^3$ per concrete unit weight.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.555-562
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• 2016

The objective of the present study is to evaluate the shear transfer capacity of transverse reinforcement at the concrete interfaces with smooth construction joint. The transverse reinforcing bars were classified into two groups: V-type for the arrangement perpendicular to the interface and X-type for inclined-crossing arrangement. The transverse reinforcement ratio at the interface varied from 0.0045 to 0.0135 for V-type and 0.0064 to 0.0045 for X-type. The mechanism analysis proposed for monolithic concrete interface, derived based on the upper-bound theorem of concrete plasticity, was modified to evaluate the shear friction capacity of concrete interfaces with smooth construction joint. Test results showed that the specimens with X-type reinforcement had lower amount of relative slippage at the interface and higher shear friction capacity than the companion specimens with V-type reinforcement. This observation was independent of the unit weight of concrete. The mean and standard deviation of the ratios between the experimental shear friction strength of smooth construction joints and predictions obtained from the proposed model are 1.07 and 0.14, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.389-398
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• 2017

The re-analysis on the stable weight of the concrete armor unit (CAU) at the roundhead and the suggestion of the covering range at the roundhead with the increased weight of CAU were conducted. Tetrapods were applied to the tests and the three dimensional hydraulic tests were performed. The test results for the stable weight at the roundhead area were similar to the guides from Korean Design Standard for Harbour and Fishery Port (MOF, 2014) and Coastal Engineering Manual (USACE, 2005). The investigation of covering range at the roundhead of rubble mound structures armoured with Tetrapods was suggested that the length of five times of the design wave height from the tip of the superstructure was needed and appropriate. Both sides of the superstructure should be covered with increasing weighted CAU to satisfy the stability at roundhead area.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.420-429
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• 2002

The amount of $CO_2$-silicate bonded waste foundry sand(WFS) occurred in Korea is over 800,000 ton per year. WFS, as a by-product, is generated through manufacturing process of foundry may affect our environmental contamination, The reason is that WFS has been buried itself not less than 90％ out of total WFS. So, it can give damage on the ground of contamination in soil and underwater. Therefore, it is necessary to establish the method recycling WFS because of being intensified waste management law. In this study, we performed the research with respect to harmful component analysis, the qualities of WFS mortar and concrete mixed with WFS. As the results the specific gravity of WFS is the same as that of natural aggregate while unit weight and percentage of solids of WFS are smaller than those of it. But it is found that WFS can be used by substituting WFS for natural aggregate after control of poor grade of WFS. The flowability of mortar and concrete with WFS is inferior to those of natural aggregate, and the setting time of concrete with WFS is faster than that with only natural aggregate, On the contrary, the bleeding of concrete with WFS is shown good result, and compressive and tensile strength of concrete substituted WFS for 30％ are higher than those with only natural aggregate regardless of elapsed time.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.94-104
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• 2013

Experiments were divided into two parts; one part is to understand the basic properties of high flowable VA/VeoVa-modified cement mortar with different polymer cement ratio (P/C) and the weight ratio of fine aggregate to cement (C:F) and the other part is to investigate the effect of surface water spread on the concrete substrate on adhesion in tension. To understand the basic performance, the specimens were prepared with proportionally mixing VA/VeoVa redispersible powder, ordinary portland cement, silica sand, superplasticizer and viscosity enhancing agent. Here, P/C were 10, 20, 30, 50 and 75% and C:F were 1:1 and 1:3. As the change of P/C and C:F unit weight, flow test, crack resistance and adhesion in tension were measured. Three specimens with good adhesion properties were selected among specimens with different P/C and C:F. The effect of surface water evenly sprayed on concrete substrate on adhesive strength is investigated. The results show that surface water on concrete substrate increases the adhesion in tension of high flowable VA/VeoVa-modified cement mortar and additionally improves the flowability compared to the non-sprayed case.

• Journal of the Korea Institute of Building Construction
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• v.17 no.6
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• pp.483-492
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• 2017

Recently, the coastal area has become the popular place for infrastructure development. To provide a beautiful scenary of costal area to nearby facilities without any hinderance, and also to protect those facilities from the sea water overflow, it is necessary to develop a new type of wave dissipating block, which is a turning wave block. It is noticeable that the top of the turning wave block is flat and thus can provide spaces for various purposes. However, the unit weight of the block decreases due to the presence of pipeline that is installed for turning the direction of the waves. In order to mitigate such problem, a heavyweight concrete needs to be used to increase the resistance against tidal waves. The copper slag and magnetite were used as a source of fine and coarse aggregate, respectively. The 28 day compressive strength of concrete incorporating ordinary and heavyweight aggregate did not show significant differences. It should be noted that the chloride ion penetration resistance was evaluated using NT-BUILD 492 rather than ASTM C 1202 method because concrete incorporating magnetite as a coarse aggregate showed excessive current flow by ASTM C 1202 method. According to the results from NT Build 492 method, which uses the penetration depth of chlorine ions to obtain chloride ion diffusivity, the heavyweight concrete incorporating the copper slag and the magnetite showed the best resistance against the chloride ion penetration. Therefore, it is reasonable to say that heavyweight concrete made with copper slag and magnetite can be used for production of turning wave block.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.285-293
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• 2001

To improve the vulnerable point and the mechanical property of the existing lightweight foamed concrete, this study was intend to manufacture the lightweight foamed concrete with wasted expanded poly-styrene, examinate and analyze the mechanical property of its. The experiment was being processed with mixing the wasted expanded poly-styrene maximum 40 % by stages and which was mainly basis on the practical mixture. The results of the experiment are following. The flow value is most affected by the mixtured rate of the wasted expanded poly-styrene. The more the mixtured ratio, the less the flow value and the more the more the unit quantity of cement and the W/C, the more the flow value. The apparent specific gravity indicated 0.31∼0.54 and which is seemed to be mainly included in the 0.4 degree and 0.5 degree that are regulated in the KS F 4039. The more the mixtured wasted poly-styrene ratio, the less the apparent specific gravity. The absorbing ratio which was depend on the mixture condition indicated 11 ∼46% and the more the mixtured ratio of the wasted expanded poly-styrene, the less the absorbing ratio remarkably. The compressive strength of the lightweight foamed concrete had a tendency to increase as the mixtured ratio of the wasted poly-styrene, the ratio quantity of cement and the apparent specific gravity increasing but as the ratio of bubble decreasing. The W/C affected little.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.419-426
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• 2015

The purpose of this study is to investigate experimentally the optimum mix design and site application case of soil mixing wall (SMW) method which is cost-effective technique for construction of walls for cutoff wall and excavation support as well as for ground improvement before constructing LNG storage tank typed under-ground. Considering native soil condition in site, main materials are selected ordinary portland cement, bentonite as a binder slurry and also it is applied $1,833kg/m^3$ as an unit volume weight of native soil, Variations for soil mixing wall are as followings ; (1) water-cement ratio 4cases (2) mixing velocity (rpm) 3levels (3) bleeding capacity and ratio, compressive strength in laboratory and site application test. As test results, bleeding capacity and ratio are decreased in case of decreasing water-cement ratio and increasing mixing velocity. Required compressive strength (1.5 MPa) considering safety factors in site is satisfied with the range of water-cement ratio 150% below, and test results of core strength are higher than those of specimen strength in the range of 8~23% by actual application of element members including outside and inside in site construction work. Therefore, optimum mix design of soil mixing wall is proposed in the range of unit cement $280kg/m^3$, unit bentonite $10kg/m^3$, water-cement ratio 150% and mixing velocity 90rpm and test results of site application case are satisfied with the required properties.