• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10b
• /
• pp.911-914
• /
• 2000

Surface glossing and physical properties of exposed concrete varied with blast furnace slag content are dsicussed in this paper. According to experimental results, as the content of blast furnace slag increases, concrete gains high strength moderately at later stage and surface glossing increase. It shows that glossing decrease with age. Surface glossing shows high as W/B decreases and surface coating is applied. Concrete according to form type shows good results in surface glossing in order for acryl form, fancy form and steel form.

• Computers and Concrete
• /
• v.31 no.2
• /
• pp.111-121
• /
• 2023

The influence of material composition such as aggregate types, addition of supplementary cementitious materials as well as exposed temperature levels have significant impacts on concrete residual mechanical strength properties when exposed to elevated temperature. This study is based on data obtained from literature for fly ash blended concrete produced with natural and recycled concrete aggregates to efficiently develop prediction models for estimating its residual compressive strength after exposure to high temperatures. To achieve this, an extensive database that contains different mix proportions of fly ash blended concrete was gathered from published articles. The specific design variables considered were percentage replacement level of Recycled Concrete Aggregate (RCA) in the mix, fly ash content (FA), Water to Binder Ratio (W/B), and exposed Temperature level. Thereafter, a simplified mathematical equation for the prediction of concrete's residual compressive strength using Gene Expression Programming (GEP) was developed. The relative importance of each variable on the model outputs was also determined through global sensitivity analysis. The GEP model performance was validated using different statistical fitness formulas including R², MSE, RMSE, RAE, and MAE in which high R² values above 0.9 are obtained in both the training and validation phase. The low measured errors (e.g., mean square error and mean absolute error are in the range of 0.0160 - 0.0327 and 0.0912 - 0.1281 MPa, respectively) in the developed model also indicate high efficiency and accuracy of the model in predicting the residual compressive strength of fly ash blended concrete exposed to elevated temperatures.

• International Journal of Highway Engineering
• /
• v.20 no.3
• /
• pp.11-18
• /
• 2018

PURPOSES : Durability of concrete is traditionally based on evaluating the effect of a single deterioration mechanism such as freezing & thawing action, chloride attack, carbonation and chemical attack. In reality, however, concrete structures are subjected to varying environmental exposure conditions which often results in multi-deterioration mechanism occurring. This study presents the experimental results on the durability of concrete incorporating air-cooled slag(AS) and/or water-cooled slag(WS) exposed to multi-deterioration environments of chloride attack and freezing & thawing action. METHODS : In order to evaluate durable performance of concretes exposed to single- and multi-deterioration, relative dynamic modulus of elasticity, mass ratio and compressive strength measurements were performed. RESULTS :It was observed that multi-deterioration severely affected durability of concrete compared with single deterioration irrespective of concrete types. Additionally, the replacement of cement by AS and WS showed a beneficial effect on enhancement of concrete durability. CONCLUSIONS : It is concluded that resistance to single- and/or multi-deterioration of concrete is highly dependent on the types of binder used in the concrete. Showing the a good resistance to multi-deterioration with concrete incorporating AS, it is also concluded that the AS possibly is an option for concrete materials, especially under severe environments.

• Computers and Concrete
• /
• v.24 no.3
• /
• pp.271-282
• /
• 2019

Concrete undergoes a series of thermo-based physio-chemical changes once exposed to elevated temperatures. Such changes adversely alter the composition of concrete and oftentimes lead to fire-induced explosive spalling. Spalling is a multidimensional, complex and most of all sophisticated phenomenon with the potential to cause significant damage to fire-exposed concrete structures. Despite past and recent research efforts, we continue to be short of a systematic methodology that is able of accurately assessing the tendency of concrete to spall under fire conditions. In order to bridge this knowledge gap, this study explores integrating novel artificial intelligence (AI) techniques; namely, artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and genetic algorithm (GA), together with traditional statistical analysis (multilinear regression (MLR)), to arrive at state-of-the-art procedures to predict occurrence of fire-induced spalling. Through a comprehensive datadriven examination of actual fire tests, this study demonstrates that AI techniques provide attractive tools capable of predicting fire-induced spalling phenomenon with high precision.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.183-184
• /
• 2022

In this study, harmonics of 100 kHz ultrasonic pulse transmitted through concrete exposed to high temperature were evaluated. Concrete exposed to high temperatures deteriorates its mechanical properties. In ultrasonic pulse, the fundamental wave was attenuated by the deterioration of the concrete. In addition, it was possible to confirm the occurrence of harmonics. It is thought that the fundamental and harmonics of ultrasonic pulse greatly affected by the internal structure of concrete.

• Computers and Concrete
• /
• v.20 no.2
• /
• pp.185-196
• /
• 2017

Durability problems initiated from steel corrosion are unseen but critical issues, so that many researches are focused on chloride penetration evaluation. Even if RC (Reinforced Concrete) structures are exposed to normal environment, chloride ingress varies with concrete surface conditions and exposed period. This paper presents an analysis technique for chloride behavior evaluation considering time effect on diffusion and surface conditions assumed as double-layered system. For evaluation of deteriorated surface condition, field investigation was performed for concrete pavement exposed to deicing agent for 18 years. In order to consider enhanced surface concrete, chloride profiles in surface-impregnated concretes exposed to chloride attack for 2 years from previous research were investigated. Through reverse analysis, effectively deteriorated/enhanced depth of surface and the related reduced/enlarged diffusion coefficient in the depth are simulated. The proposed analysis technique was evaluated to handle the chloride behavior more accurately considering changes of chloride ingress within surface layer and decreased diffusion coefficient with time. For the concrete surface exposed to deicing agent, the deteriorated depth and enlarged diffusion coefficient are evaluated to be 12.5~15.0 mm and 200% increasing diffusion coefficient, respectively. The results in concrete containing enhanced cover show 10.0~12.5 mm of impregnated depth and 85% reduction of chloride diffusion in tidal and submerged conditions.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2016.05a
• /
• pp.11-12
• /
• 2016

The contemporary buildings are becoming super-taller gradually as the industry evolves. Accordingly, winter concrete also became an important element for the year-round construction since shortening of a construction duration became important. Accordingly, this research team once developed a double bubble sheet as concrete cover curing compound during winter. But since there is no proper countermeasure for the exposed reinforcement bars, it is worried that the concrete can be damaged by exposed frozen reinforcement bars at a low temperature during the initial period. Therefore, in this study, it is intended to review the temperature history of the reinforcement bars depending on changes of the covering methods of the exposed reinforcement bars by using bubble sheets.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1994.04a
• /
• pp.221-226
• /
• 1994

A safety evaluation of cable tunnel, which is a concrete box structure with telecommunication facilities in it, exposed to fire is given. The immediate field observation was performed to find out any sign of sudden structural failure. In some region, where the fire intensity was heavy, the spalling of concrete cover in upper slab occurred. Next, more careful investigation was done with proper non-desturctive testing methods and structural analysis taking into account the changes in material properties due to fire. It seems that there is no severe damage on concrete, reinforcements and over all structural system.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2002.05a
• /
• pp.47-50
• /
• 2002

This paper presents the results of fire resistance properties of high performance concrete varying with fiber kinds and the size of metal lath in order to verify the validities of fiber on the spatting resistance by fire. Metal lath, glass fiber and carbon fiber are used to confine the concrete. According to test results, plain concrete without lateral confinement and confined concrete with glass fiber and carbon fiber show entire failure after exposed to fire, while confined concrete with metal lath take place in the form of slight surface spatting by fire, which has favorable spatting resistance of concrete. As for the effect of the size of metal lath, when the size of metal lath is more than 1.2mm of thickness, the residual strength of concrete exposed to fire maintains more than 80% of its original strength. However, glass fiber and carbon fiber does not perform desirable spatting resistance by fire due to loss of lateral confinement of fiber exposed to fire caused by melting of fiber and reducing bond strength between concrete and fiber.

• Journal of the Korea Concrete Institute
• /
• v.11 no.5
• /
• pp.69-77
• /
• 1999

A spalling is defined as the damages of concrete exposed to high temperature during the fire by causing cracks and localized bursting of small pieces of concrete. It is reported that spalling is caused by the vapor pressure and polypropylene(PP) fiber has an important role in protecting from spalling. This paper is a study on the properties and spalling resistance of high-performance concrete with the kinds of aggregate and the contents of PP fiber. According to the experimental results, concrete contained no PP fiber take place in the form of the surface spalling and the failure of specimenns after fire test regardless of the kinds of aggregate. Concrete contained more than 0.05% of PP fiber with the aggregate of basalt does not take place the spalling, while the concrete using granite and limestone does the surface spalling. It is found that residual compressive strength after exposed at high temperature has 50~60% of its original strength. Although specimens after exposed at high temperature is cured at water for 28days, they do not recover their original strength.