• Resources Recycling
• /
• v.28 no.6
• /
• pp.54-63
• /
• 2019

This study investigated on the compressive strength and the length change test with using the waste glass and graphene oxide for recycling the waste glass as the aggregate. Curing on 3-day and 7-day, the compressive strength was enhanced as the usage of waste glass was increased. Especially, the huge difference in the compressive strength was observed when the amount of substituting on the waste glass was used on 10~50%. With 50% of waste glass condition, the compressive strength was portionally enhanced as the usage of graphene oxide was increased and its value was 42.6 N/㎟ with 0.2% of graphene oxide. In terms of the length change test, the use of high content of waste glass led length change value to increase, but it was dropped down as the portion of waste glass was above 50%. Furthermore, in the case of using 50% of waste glass, the use of high amount of graphene oxide tended to decrease the length change value. That is, graphene oxide may contribute on boosting the cement hydration reaction and blocking the ion's movement.

• Steel and Composite Structures
• /
• v.46 no.1
• /
• pp.75-92
• /
• 2023

The novel composite cold-formed steel (CFS)/engineered cementitious composites (ECC) beams have been recently presented. The new composite section exhibited superior structural performance as a flexural member, benefiting from the lightweight thin-walled CFS sections with improved buckling and torsional properties due to the restraints provided by thinlayered ECC. This paper investigated the shear performance of the new composite CFS/ECC section. Twenty-eight simply supported beams, with a shear span-to-depth ratio of 1.0, were assembled back-to-back and tested under a 3-point loading scheme. Bare CFS, composite CFS/ECC utilising ECC with Polyethylene fibres (PE-ECC), composite CFS/MOR, and CFS/HSC utilising high-strength mortar (MOR) and high-strength concrete (HSC) as replacements for PE-ECC were compared. Different failure modes were observed in tests: shear buckling modes in bare CFS sections, contact shear buckling modes in composite CFS/MOR and CFS/HSC sections, and shear yielding or block shear rupture in composite CFS/ECC sections. As a result, composite CFS/ECC sections showed up to 96.0% improvement in shear capacities over bare CFS, 28.0% improvement over composite CFS/MOR and 13.0% over composite CFS/HSC sections, although MOR and HSC were with higher compressive strength than PE-ECC. Finally, shear strength prediction formulae are proposed for the new composite sections after considering the contributions from the CFS and ECC components.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.48 no.1
• /
• pp.51-60
• /
• 2006

This study was conducted to investigate experimentally the drying shrinkage and the strength properties of redispersible SBR and PAE powder-modified mortars. Polymer-cement ratio, content of shrinkage-reducing agent and antifoamer content were manipulated as the experimental variables. The peculiarity of this study is to obtain a high early-age strength by using the portland cement and alumina cement with the ratio of 8 : 2. Until 7 days of age, the drying shrinkage remarkably increased up to $1\~2\times10^{-4}$, while it tended to decrease as the ratio of polymer to cement ratio and the content of shrinkage-reducing agent increased. Polymer-cement ratio was effective in improving the flexural, tensile and adhesive strengths: As the ratio increased, the strengths correspondingly increased. The flexural strength was in the range of $7\~11$ MPa, the tensile strength was $3.5\~5$ MPa and the adhesive strength was $1.2\~3.9$ MPa. On the other hand, the compressive strength tended to decrease as the polymer-cement ratio increased, and it was in the range of $23\~39$ MPa. All strengths, flexural, tensile, adhesive and compressive strengths, decreased as the content of powder shrinkage-reducing agent increased. It turned out that the polymer-cement ratio influenced more on the behavior of drying shrinkage and the properties of strength than the powder shrinkage-reducing agent did.

• Journal of the Korea Concrete Institute
• /
• v.23 no.6
• /
• pp.817-826
• /
• 2011

Concrete using eco-cement has a problem with long-term strength development. However, currently, a long-term strength development mechanism is not confirmed, resulting in a lack of application of eco-cement in construction fields. In this study, the curing humidity influence on development in long-term strength of concrete using eco-cement and the relationship between strength and pore structure were examined. The results showed that wet cured eco-cement with a high water/cement ratio showed serious long-term strength reduction due to non-reduction of pore volume (pore size over 10 nm) in mortar caste with eco-cement. Also, the study results on improvement of long-term strength of eco-cement by partial replacement with ordinary portland cement and finely-ground fly ash showed that both of these alternatives improved long-term strength of concrete caste with eco-cement due to gradual refinement of their micro-structure.

• Explosives and Blasting
• /
• v.33 no.1
• /
• pp.1-12
• /
• 2015

In this study, the domestic bench blasting sites were researched to set the blast coefficient C according to the type of rock and type of industry. With the use of the experimental data on the representative industrial explosives and the data of the manufacturers'data on explosives, powder coefficient e was set up. The blast coefficient C was 0.21~0.30 when the average value for 5 representative kinds of rocks including granite was searched. The blast coefficient C for quarrying, mining and construction sites were 0.22, 0.13 and 0.26 respectively. On the other hand, powder coefficient e was obtained in four elements such as reactive energy, ballistic mortar test, VOD, Langefors'strength per unit weight. e value for emulsion which is one of the representative explosives was found to be 1 while those of high performance emulsion and ANFO were found to be 0.9 and 1, respectively.

• Journal of the Korea Institute of Building Construction
• /
• v.12 no.4
• /
• pp.377-385
• /
• 2012

In this study, the Impact resistance of steel fiber and organic fiber reinforced concrete and mortar was evaluated and the improvement in toughness resulting from an increase in compressive strength and mixing fiber for impact resistance on performance was examined. The types of fiber were steel fiber, PP and PVA, and these were mixed in at 0.1, 0.5 and 1.0 vol.%, respectively. Impact resistance is evaluated with an apparatus for testing impact resistance performance by high-speed projectile crash by gas-pressure. For the experimental conditions, Specimen size was $100{\times}100{\times}20$, 30mm ($width{\times}height{\times}thickness$). Projectile diameter was 7 and 10 mm and impact speed is 350m/s. After impact test, destruction grade, penetration depth, spalling thickness and crater area were evaluated. Through this evaluation, it was found that as compressive strength is increased, penetration is suppressed. In addition, as the mixing ratio of fiber is increased, the spalling thickness and crater area are suppressed. Organic fibers have lower density than the steel fiber, and population number per unit area is bigger. As a result, the improvement of impact resistance is more significant thanks to dispersion and degraded attachment performance.

• Journal of the Korea Institute of Building Construction
• /
• v.20 no.1
• /
• pp.19-26
• /
• 2020

This study aimed to develop non-sintered cement that could replace portland cement which emits large amount of carbon dioxide during firing process. For this purpose, ground granulated blast furnace slag, type c fly ash and slaked lime were used. In addition, through the experimental results, the characteristics of the non-sintered cement binders according to the mixing ratios will be identified, and the utilization plans for the precast concrete products will be presented. In this experiment, non-sintered cement binders using industrial by-products were prepared to compare the flexural strength and compressive strength of each of the 3, 7 and 28 days. As a result, the results satisfy the KS of the target product proposed in this study. Therefore, this study presents the possibility of using precast concrete products by developing non-sintered cement binders using industrial by-products.

• Journal of the Korea Concrete Institute
• /
• v.16 no.5 s.83
• /
• pp.651-657
• /
• 2004

The effects of polymer-cement ratio, antifoamer content and shrinkage-reducing agent content on the air content, setting time, drying shrinkage and strength of high-fluidity polymer-modified mortars using redispersible polymer powder are examined. As a result, the air content of the polymer-modified mortars using redispersible polymer powder tends to decrease nth increasing polymer-cement ratio and antifoamer content. Regardless of the antifoamer content, the setting time of the polymer-modified mortars using redispersible polymer powder tends to delayed with increasing polymer-cement ratio. Irrespective of the antifoamer content, the drying shrinkage of the polymer-modified mortars using redispersible polymer powder tend to decrease with increasing polymer-cement ratio and shrinkage-reducing agent content. Regardless of the antifoamer content, the flexural and tensile strengths of the polymer-modified mortars using redispersible polymer powder tends to increase with increasing polymer-cement ratio, and tend to decrease with increasing shrinkage-reducing agent content. However, the compressive strength of the polymer-modified mortars using redispersible polymer powder decreases with increasing polymer-cement ratio and shrinkage-reducing agent content.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.4
• /
• pp.651-668
• /
• 2017

For initial stability of the tunnel, the primary support, Shotcrete and rockbolt shall be placed in the most appropriate time. This is because the role of such support plays a vital role in long-term and short-term tunnel stability. In this study, the rock bolt is an important supporting system that receives the external pressure generated by the stress relaxation during tunnel excavation as axial force and transmits it to the shotcrete on the tunnel excavation surface. Until now, most of the materials of rock bolts have been used in the field, but there have been many problems such as uncertain quality of Chinese materials entering the market, poor packing due to falling down of rock bolts when filled with mortar, and corrosion due to water. Therefore, in this study, we have developed a high strength steel pipe rock bolt using Autobeam material to solve and improve various problems of existing rock bolts. In order to evaluate the performance of the developed bolt, field tests were carried out and the existing mortar filler in order to improve the performance of the rock bolt, the design and construction criteria were studied and the results were included in this paper.

• Earthquakes and Structures
• /
• v.12 no.6
• /
• pp.699-712
• /
• 2017

This study evaluates the effectiveness of a newly developed retrofitting scheme for masonry-infilled non-ductile RC frames experimentally and by numerical simulation. The technique focuses on modifying the load path and yield mechanism of the infilled frame to enhance the ductility. A vertical gap between the column and the infill panel was strategically introduced so that no shear force is directly transferred to the column. Steel brackets and small vertical steel members were then provided to transfer the interactive forces between the RC frame and the masonry panel. Wire meshes and high-strength mortar were provided in areas with high stress concentration and in the panel to further reduce damage. Cyclic load tests on a large-scale specimen of a single-bay, single-story, masonry-infilled RC frame were carried out. Based on those tests, the retrofitting scheme provided significant improvement, especially in terms of ductility enhancement. All retrofitted specimens clearly exhibited much better performances than those stipulated in building standards for masonry-infilled structures. A macro-scale computer model based on a diagonal-strut concept was also developed for predicting the global behavior of the retrofitted masonry-infilled frames. This proposed model was effectively used to evaluate the global responses of the test specimens with acceptable accuracy, especially in terms of strength, stiffness and damage condition.