• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.651-654
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• 2005

Fast-setting cement is usually used for emergency repair construction of roads, bridges, buildings and so on. In this study, we tried to develop fast-setting ultra early strength mortar for prepacked concrete and evaluated the properties of fresh and hardened concrete with it. The flowability of the mortar was high enough to be easily poured into coarse aggregates. It showed high early strength development which can make it possible to use newly constructed structures within $3\~4$ hours regardless of curing conditions such as curing temperature and curing environment. And it also showed good resistance to drying shrinkage and chemical attack.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.210-217
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• 2023

Various performances of ultra-high performance concrete (UHPC) applied with microplastics and expanded polystyrene (EPS) beads were evaluated. CompressIve and flexural strength, performance after ignition, flow-down in fresh state, and effective bond strength were evaluated. Designed weight of the cement panel with these mixtures was calculated based on the flexural strength. As a result of the experiments, it was confirmed that the EPS could reduce the density of UHPC with largest range. By maximum addition of EPS beeds, the density of UHPC decreased to 1300 kg/m³, and the compressive and flexural strengths for this mixtures were in ranges of 20-30 MPa and 15-20 MPa, respectively. On the other hand, lightest cement panel could be designed with UHPC having a density ranges about 2.0 g/cm³.

• Journal of the Korea Institute of Building Construction
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• v.24 no.1
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• pp.23-34
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• 2024

This research aims to assess the flexural bonding efficacy of polymer-cement composites(PCCs) in mending cracks within reinforced concrete(RC) structures. The study involved infilling PCCs into cement mortar cracks of varying dimensions, followed by evaluations of enhancements in flexural adhesion and strength. The findings indicate that the flexural bond performance of PCCs in crack repair is influenced by the cement type, polymer dispersion, and the polymer-to-binder ratio. Specifically, the use of ultra-high early strength cement combined with silica fume resulted in an up to 19.0% improvement in flexural bond strength compared to the application of ordinary Portland cement with silica fume. It was observed that the augmentation in flexural strength of cement mortar filled with PCCs was significantly more dependent on the depth of the crack rather than the width. Furthermore, PCCs not only acted as repair agents but also as reinforcement materials, enhancing the flexural strength to a certain extent. Consequently, this study concludes that PCCs formulated with ultra-high early strength cement, various polymer dispersions, silica fume, and a high polymer-to-binder ratio ranging from 60% to 80% are highly effective as maintenance materials for crack filling in practical settings.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.61-62
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• 2015

This study has analyzed the engineering characteristics of resource-cycling mortar according to the variation of fine aggregate type using illite with high development potentials by setting the goal as developing eco-friendly construction materials. As a result, while flow has increased if recycled fine aggregate and waste refractory are used separately or mixing them adequately in case of flow and compressive strength, the flow had somewhat declined followed by illite replacement. However, the possibility of such usage is determined to be adequate if used by mixing illite, recycled fine aggregate and waste refractory properly due to the dry shrinkage effect.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.229-237
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• 2019

This study examines the estimation of strength through a ultra-high strength concrete mock-up specimen using the rock compressive strength test hammer. According to the test result, the commonly used strength estimation formulae showed differences among them when the data of this test were applied. In additional, it show that these formulae underestimated the actual measurements further when the compressive strength was 30MPa or greater and deviated the distribution range of actual measurements in all strength ranges. The rock test hammer showed a higher correlation than type N Schmidt hammer regardless of the direction of hit for each type of W/B and the inclusion of coarse aggregate, and mortar showed a little higher correlation than concrete. As a result, it can be suggested that the coefficient of variation and the standard deviation of the mortar(2.26%/1.36) are lower than those of the concrete(4.06%/2.5), and the smaller the size of the coarse aggregate, the smaller the coefficient of variation and the more accurate the value.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.27-34
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• 2017

Recently, the importance of the industrial warehouse floor has been increasing due to the development of the distribution and logistics industry. In this present study, an early-hardening polymer floor mortar which can compensate for the limitation of conventional cement based floor mortar regarding fluidity and long curing time was developed. In order to achieve the early-hardening of mortar characteristic ultra rapid hardening cement was used as binder. Four types of mixture proportions in accordance with the vinyl acetate ethylene(VAE) polymer contents with range from 10% to 20% and the other proto proportion without VAE polymer were designed. Mechanical experiments including the fluidity test, compressive strength test, bending test, bond test, and abrasion test were conducted for all mixture proportions. From the flow test result, it was possible to achieve the high flow with 250 mm by controlling the amount of superplasticizer. The incorporation of VAE polymer was found to affect the compressive strength reduction, however, the flexural strength was higher than that of the proto mixture, and it was evaluated to increase the compressive strength / flexural strength ratio. Moreover, at least 2.6 times higher bond strength and more than 4 times higher abrasion resistance were secured. From the mechanical experiments results, the optimum mixing ratio of the VAE polymer was determined to be 10%. As a result of application and monitoring, it shows that it has excellent resistance to cracking, discoloration, impact, and scratch as well as bond performance compared to the cement based floor mortar.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.489-495
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• 2007

Effects of ultrafinely ground ash on the rheological properties of cement paste were investigated. Also compressive strength development and setting time of ultrafine ash blended cement mortar were investigated in the study. A sample with silica fume was included for comparison. According to the results of ultra fine ash blended cement paste in the lower W/B ratio, the fluidity were high, and the setting time was a little retarded. And the compressive strength of ultrafine ash blended mortar was increased in the long term. In the case of hardened cement paste at 28 days, $Ca(OH)_2$ contents was decreased in order of control, ultrafine ash, silica fume blended cement due to difference of the pozzolanic reaction.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.151-156
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• 1994

This study is to investigate the quality of superplasticizers in domestic market. Therefore, the physico-chemical characteristics, the fluidity characteristics of fresh cement paste and mortar were tested. Also fresh and hardened properties of mortars and concretes using these superplasticizers were tested. From these results, differences of quality among superplasticizers are checked clearly in low water/cement ratio. And it is concluded that several superplasticizers have better dispersion ability than others in every tests. It has known that all samples are naphtalene sulfornate formaldehede types by the UV(ultra-violet) test.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.43-44
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• 2023

This study evaluated the mechanical and electrical properties of low-cement mortar using a large amount of industrial by-products to reduce carbon emissions from the cement industry. As types of industrial by-products, blast furnace slag and fly ash, which are representative materials, were used, and ultra-high fly ash was mixed and evaluated to solve the problem of initial strength loss. In addition, in order to evaluate the electrical properties, 1% of MWCNT was incorporated relative to the powder mass. As experimental items, the compressive strength was measured on the 1st, 3rd, 7th and 28th days of age, and the rate of change in electrical resistance was measured on the 28th day of age. As a result of the experiment, the initial strength of the test specimen mixed with blast furnace slag and fly ash was significantly lower than that of 100% cement, and the specimen mixed with blast furnace slag showed strength equal to that of cement at 28 days of age. As an electrical characteristic, the electrical resistance was reduced when the load was loaded, and this reason is judged to be the effect of improving the conductivity as the connection between CNTs is narrowed by the compressive load.

• Journal of the Korea Institute of Building Construction
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• v.10 no.6
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• pp.145-154
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• 2010

As buildings have become higher and larger, the use of high performance concrete has increased. With this increase, interest in and use of ultra fine powder admixture is also on the rise. The silica fume and BSF are the admixtures currently being used in Korea. However, silica fume is exclusively import dependent because it is not produced in Korea. In the case of BFS, it greatly improves concrete fluidity and long-term strength. But a problem exists in securing early strength. Furthermore, air-cooled slag is being discarded, buried in landfills, or used as road bed materials because of its low activation energy. Therefore, we investigated in this study the usability of nano-slag (both rapidly-chilled and air-cooled) as an alternative material to the silica fume. We conducted a physic-chemical analysis for the nano-slag powder and performed a mortar test to propose quality standards. The analysis and testing were done to find out the industrial usefulness of the BFS that has been grinded to the nano-level.