• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.113-116
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• 2009

This study analyzed fire-resistant characteristics according to changes in repair methods of PFH mixed high-strength concrete roof structures having undergone fire damage. The results of the study are as follows. First, as a repulsive characteristics of structures, the remaining repulsion was shown to increase following fire-resistance tests according to increases in depth of coverings. The results of the relationship between depth of coverings and remaining repulsion rates following fire-proofing tests showed a high correlation. At a covering depth of 67.3mm, remaining repulsion rate was estimated to be 100%. For fire-resistant characteristics following repairs of structure, as for spalling, severe separation was shown in the case of general plaster while general plaster + Metal Lath showed overall superior spalling prevention. For internal structure temperatures, general plaster showed max temperatures of 705℃, average temperatures of 636℃ while general plaster + metal lath showed max temperature of 660℃ and average temperature of 520℃, demonstrating lower temperature distributions than use of only general plaster. In conclusion, after removing the covering of structures damaged due to high temperatures of fires within high-strength concrete installations, the use of fire-resistant mortars and applying metal laths on surfaces of general plaster will provide superior fire-resistance performance in the occurrence of a 2nd fire.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.299-306
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• 2015

In construction materials area, many research on polymer for cement-based materials have been conducted. In spite of these research, general research scope is limited to the normal strength range, and thus in this research, for both normal and high strength range mixtures, the strength and mechanical properties of high strength cement mortar incorporating Vinyle Acetate-Ethylene(VAE) type powder polymer are evaluated. As a result of experiment, in the case of high strength mixture, as the amount of VAE polymer addition was increased the compressive and flexural strengths were decreased while the tensile and bonding strengths were increased because of the formation of the polymer membrane inside of the mortar matrix.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.26-33
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• 2016

The alkali-slag-red mud(ASRC) cement belongs to clinker free cementitious material, which is made from alkali activator, blast-furnace slag(BFS) and red mud in designed proportion. This study is to investigate strength and pore characteristics of alkali-activated slag cement(NC), clinker free cementitious material, and ordinary portland cement(C) mortars using polymer according to red mud content. The results showed that the hardened alkali-activated slag-red mud cement paste was mostly consisted of C-S-H gel, being very fine in size and extremely irregular in its shape. So the hardened ASRC cement paste has lower total porosity, less portion of larger pore and more portion of smaller pore, as compared with those of hardened portland cement paste, and has higher strength within containing 10 wt.(%) of alkali-activated slag cement(NC) substituted by red mud.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.20-27
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• 2021

The present study presents a nonlinear finite element analysis (FEA) approach using the general program of Abaqus to evaluate the seismic response of unreinforced masonry walls strengthened with the steel bar truss system developed in the previous investigation. For finite element models of masonry walls, the concrete damaged plasticity (CDP) and meso-scale methods were considered on the basis of the stress-strain relationships under compression and tension and shear friction-slip relationship of masonry prisms proposed by Yang et al. in order to formulate the interface characteristics between brick elements and mortars. The predictions obtained from the FEA approach were compared with test results under different design parameters; as a result, a good agreement could be observed with respect to the crack propagation, failure mode, rocking strength, peak strength, and lateral load-displacement relationship of masonry walls. Thus, it can be stated that the proposed FEA approach shows a good potential for designing the seismic strengthening of masonry walls.

• Earthquakes and Structures
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• v.16 no.5
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• pp.625-639
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• 2019

The concept of the combined seismic and energy retrofitting of existing reinforced concrete (RC) buildings was examined in this paper through a number of case studies conducted on model buildings (simulating buildings of the '60s-'80s in southern Europe) constructed according to outdated design standards. Specifically, seismic and thermal analyses have been conducted prior to and after the application of selected retrofitting schemes, in order to quantify the positive effect that retrofitting could provide to RC buildings both in terms of their structural and energy performance. Advanced materials, namely the textile reinforced mortars (TRM), were used for providing seismic retrofitting by means of jacketing of masonry infills in RC frames. Moreover, following the application of the TRM jackets, thermal insulation materials were simultaneously provided to the RC building envelope, exploiting the fresh mortar used to bind the TRM jackets. In addition to the externally applied insulation material, all the fenestration elements (windows and doors) were replaced with new high energy efficiency ones. Afterwards, an economic measure, namely the expected annual loss (EAL) was used to evaluate the efficiency of each retrofitting method, but also to assess whether the combined seismic and energy retrofitting is economically feasible. From the results of this preliminary study, it was concluded that the selected seismic retrofitting technique can indeed enhance significantly the structural behaviour of an existing RC building and lower its EAL related to earthquake risks. Finally, it was found that the combined seismic and energy upgrading is economically more efficient than a sole energy or seismic retrofitting scenario for seismic areas of south Europe.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.443-449
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• 2022

When fiber reinforced concrete is manufactured, it is useful to utilize lathe scrap as an aiternative material of steel fiber, because it is not only economical as an by-product of steel manufactures, but also has a very similar composition to that of steel fiber. The purpose of this experimental research is to evaluate the compressive strength and tensile behavior and then propose a material model of lathe scrap reinforced mortar. For this purpose, the lathe scrap reinforced mortars were ma de a ccording to their tota l volume fra ction of 1.5 % for wa ter-binder ra tio of 30 % a nd 40 %, respectively, a nd then the mechanical properties such as compressive strength, direct tensile strength, and stress-strain curve of those were evaluated. Also, based on the experimental results of lathe scrap reinforced mortar the material model for tensile behavior was suggested. It was revealed that the experimental results and the proposed material model corresponded relatively well.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.514-522
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• 2022

In this study, as part of a study to improve the self-healing performance of concrete structures by applying self-healing capsules made of cementitious materials to cement composite materials, the engineering characteristics of mortars according to PCC(Powder Compacted Capsule) size and mixing ratio were compared and analyzed. For this, fluidity, compressive strength, reload test, carbonation, ultrasonic velocity, and water permeability characteristics were measured according to PCC size and mixing ratio of mortar. As a result of the measurement, the fluidity and compressive strength increased as the mixing ratio of PCC increased, and in the case of the load reload test, the healing ratio increased as the mixing ratio of PCC increased in the 03PC formulation. In the case of water permeability test, it was found that when PCC was used, the reduction ratio of water flow was up to 35 % higher than that of Plain, and when PCC with a size of 0.3 to 0.6 mm was mixed with 15 %, it was found to be effective in improving the crack healing ratio of the mortar.

• Computers and Concrete
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• v.30 no.2
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• pp.99-111
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• 2022

In this study, deep learning and k-Nearest Neighbor (kNN) models were used to estimate the sorptivity and freeze-thaw resistance of self-compacting mortars (SCMs) having binary and ternary blends of mineral admixtures. Twenty-five environment-friendly SCMs were designed as binary and ternary blends of fly ash (FA) and silica fume (SF) except for control mixture with only Portland cement (PC). The capillary water absorption and freeze-thaw resistance tests were conducted for 91 days. It was found that the use of SF with FA as ternary blends reduced sorptivity coefficient values compared to the use of FA as binary blends while the presence of FA with SF improved freeze-thaw resistance of SCMs with ternary blends. The input variables used the models for the estimation of sorptivity were defined as PC content, SF content, FA content, sand content, HRWRA, water/cementitious materials (W/C) and freeze-thaw cycles. The input variables used the models for the estimation of sorptivity were selected as PC content, SF content, FA content, sand content, HRWRA, W/C and predefined intervals of the sample in water. The deep learning and k-NN models estimated the durability factor of SCM with 94.43% and 92.55% accuracy and the sorptivity of SCM was estimated with 97.87% and 86.14% accuracy, respectively. This study found that deep learning model estimated the sorptivity and durability factor of SCMs having binary and ternary blends of mineral admixtures higher accuracy than k-NN model.

• Advances in concrete construction
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• v.13 no.4
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• pp.315-325
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• 2022

Reinforced concrete structures are exposed throughout their lifetime to the phenomenon of carbonation, which considerably influences their durability by causing corrosion of the reinforcements. The fight against this phenomenon is usually ensured by anti-carbonation coatings which have the possibility of limiting the permeability to carbon dioxide or with coatings which absorb the CO₂ present in the air. A coating with good crack-bridging (sealing) capacity will prevent water from entering through existing cracks in concrete. Despite the beneficial effect of these coatings, their durability decreases considerably over time with temperature and humidity. In order to use coatings made from local materials, not presenting any danger, available in abundance in our country, very economical and easy to operate is the main objective of this work. This paper aim is to contribute to the formulation of a corrected dune sand-based mortar as an anti-carbonation coating for concrete. The results obtained show that the cement mortar based on dune sand formulated has a very satisfactory compressive strength, a very low water porosity compared to ordinary cement mortar and that this mortar allows an improvement in the protection of the concrete against the carbonation of 60% compared to ordinary cement mortar based on alluvial sand. Moreover, the formulated cement mortars based on dune sand have good adhesion to the concrete support, their adhesion strengths are greater than 1.5MPa recommended by the standards.

• Journal of the Korean Geosynthetics Society
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• v.22 no.4
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• pp.51-61
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• 2023

In this study, in order to improve the fire resistance performance of structures in case of fire in buildings and structures, PVA fibers and the ZnO particles combined with mesoporous nano silica (MSNs) were mixed with cement mortar, and the specimen was exposed to a temperature range of 20~1100℃. Then the residual compressive strength and weight change rate were measured to determine whether the fire resistance performance changed. As a result of the study, it was found that mixing mesoporous nano silica and PVA fiber together did not contribute to improving the fire resistance performance of cement mortar. On the other hand, mixing 0.5% of mesoporous nano silica and 0.1 vol% of PVA fiber showed the best improvement test results, showing that it was advantageous for fire resistance performance.