• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.11-30
• /
• 2000

Structural properties of reinforced concrete, such as bond and shear strength, that depend on the tensile properties of concrete are much lower for high-strength concrete than would be expected based on relationships developed for normal-strength concretes. To determine the reason for this behavior, studies at the University of Kansas have addressed the effects of aggregate type, water-cementitious material ratio, and age on the mechanical and fracture properties of normal and high-strength concretes. The relationships between compressive strength, flexural strength, and fracture properties were studied. At the time of test, concrete ranged in age from 5 to 180 days. Water-cementitious material ratios ranged from 0.24 to 0.50, producing compressive strengths between 20 MPa(2, 920 psi) and 99 MPa(14, 320psi). Mixes contained either basalt or crushed limestone aggregate, with maximum sizes of 12mm(1/2in). or 19mm(3/4in). The tests demonstrate that the higher quality basalt coarse aggregate provides higher strengths in compression than limestone only for the high-strength concrete, but measurably higher strengths in flexure, and significantly higher fracture energies than the limestone coarse aggregate at all water-cementitious material ratios and ages. Compressive strength, water-cementitious material ratio, and age have no apparent relationship with fracture energy, which is principally governed by coarse aggregate properties. The peak bending stress in the fracture test is linearly related to flexural strength. Overall, as concrete strength increases, the amount of energy stored in the material at the peak tensile load increases, but the ability of the material to dissipate energy remains nearly constant. This suggests that, as higher strength cementitious materials are placed in service, the probability of nonductile failures will measurably increase. Both research and educational effort will be needed to develop strategies to limit the probability of brittle failures and inform the design community of the nature of the problems associated with high-strength concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.580-583
• /
• 2004

Due to the tendency of increase in demolished-concrete produced by alteration and deterioration of concrete structures, recycling of those demolished-concrete is necessary to solve the exhaustion of natural aggregate, in order to save resources and protect environment. In this an experimental study herein, the Chlorine-ion and Carbonation resistance of the recycled aggregate concrete was investigated. Coarse aggregate was replaced with $100\%$ of the recycled aggregate and cement and fine recycled aggregate was replaced with various amount. It was shown that the concrete can obtain resistance of chlorine-ion, when fly ash replaced with up to $30\%$ of cement.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2010.05a
• /
• pp.57-61
• /
• 2010

In this study, many concrete specimens were tested to investigate the variations of strength characteristics of high-strength concrete due to amount of recycled coarse aggregates, and to investigate the effect of steel-fiber reinforcement on concrete using recycled coarse aggregates. Test results showed that all of the variations of compressive, tensile and flexural strength appeared in linear reduction according to icrease the amount of recycled coarse aggregates, and steel-fiber reinforcement of 0.75% volumn of concrete recovered completely spliting tensile strength and flexual strength and recovered greatly compressive strength of concrete using recycled coarse aggregates of 100% displacement. And test results showed that the shear strength falled rapidly at 30% of replacement ratio so far as 34% of strength reduction ratio, but after that it falled a little within 3% up to the replacement ratio 100%, and steel-fiber reinforcement of 0.75% of concrete volumn recovered completely the deteriorated shear strength, moreover improved the shear strength above 50% rather than that of concrete using natural coarse aggregates.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1996.04a
• /
• pp.112-116
• /
• 1996

This experimental study was performed to produce high flowing nomal strength concrete using viscosity agent. Test variables were selected to the viscosity agent contents with 4 levels, the cement contents with 5 levels and the coarse aggregate contents with 3 levels, etc. As a result, the high flowing and filling properties of concrete were obtatined by proper amount of viscosity agent and superplasticizer in the normal strength concrete. For the concrete mix proportions, it was found that unit weight of cement was more than 364kg/㎥ and volume of coarse aggregate was less than $280\ell/\textrm{m}^3$ in this study.

• Structural Engineering and Mechanics
• /
• v.87 no.3
• /
• pp.221-229
• /
• 2023

Urbanization and industrialization have significantly increased the amount of solid waste produced in recent decades, posing considerable disposal problems and environmental burdens. The practice of waste utilization in concrete has gained popularity among construction practitioners and researchers for the efficient use of resources and the transition to the circular economy in construction. This study employed Lytag aggregate, an environmentally friendly pulverized fuel ash-based lightweight aggregate, as a substitute for natural coarse aggregate. At the same time, fly ash, an industrial by-product, was used as a partial substitute for cement. Concrete mix M20 was experimented with using fly ash and Lytag lightweight aggregate. The percentages of fly ash that make up the replacements were 5%, 10%, 15%, 20%, and 25%. The Compressive Strength (CS), Split Tensile Strength (STS), and deflection were discovered at these percentages after 56 days of testing. The concrete cube, cylinder, and beam specimens were examined in the explorations, as mentioned earlier. The results indicate that a 10% substitution of cement with fly ash and a replacement of coarse aggregate with Lytag lightweight aggregate produced concrete that performed well in terms of mechanical properties and deflection. The cementitious composites have varying characteristics as the environment changes. Therefore, understanding their mechanical properties are crucial for safety reasons. CS, STS, and deflection are the essential property of concrete. Machine learning (ML) approaches have been necessary to predict the CS of concrete. The Artificial Fish Swarm Optimization (AFSO), Particle Swarm Optimization (PSO), and Harmony Search (HS) algorithms were investigated for the prediction of outcomes. This work deftly explains the tremendous AFSO technique, which achieves the precise ideal values of the weights in the model to crown the mathematical modeling technique. This has been proved by the minimum, maximum, and sample median, and the first and third quartiles were used as the basis for a boxplot through the standardized method of showing the dataset. It graphically displays the quantitative value distribution of a field. The correlation matrix and confidence interval were represented graphically using the corrupt method.

• Computers and Concrete
• /
• v.5 no.5
• /
• pp.435-448
• /
• 2008

Self-compacting concrete (SCC), characterized by the high flowability and resistance to segregation, is due to the high amount of paste (including cement and mineral admixtures) in contrast with normal concrete (NC). However, the high amount of paste will limit the volume fractions of coarse aggregate,and reduce the tendency of coarse aggregate to suppress drying shrinkage deformations. For this reason, SCC tends to produce higher values of drying shrinkage than NC for the most part. In order to assess the drying shrinkage of SCC quantitatively for application to offshore caisson foundations, the formulas presented in the literatures (ACI 209 and CEB-FIP) are used to predict the values of drying shrinkage in SCC according to the corresponding mix proportions. Additionally, a finite element (FE) model, which assumes concrete to be a homogeneous and isotropic material and follows the actual size and environmental conditions of the caisson, is utilized to simulate stress distribution situations and deformations in the SCC caisson resulting from the drying shrinkage. The probability of cracking and the behavior of drying shrinkage of the SCC caisson are drawn from the analytic results calculated by the FE model proposed in this paper.

• Korean Journal of Agricultural Science
• /
• v.38 no.1
• /
• pp.145-151
• /
• 2011

This study was performed to evaluate the void ratio, compressive and flexural strength, and permeability coefficient used powdered waste glass, $CaCO_3$, recycled coarse aggregate and unsaturated polyester resin to find optimum mix design of permeable polymer concrete for pavement. The void ratio and permeability coefficient of permeable concrete for pavement was decreased with increasing the powdered waste glass, respectively. The compressive strength and flexural strength was increased with increasing the powdered waste glass, respectively. In addition, this study found out that required amount of binder was decreased with increasing the powdered waste glass. This fact is expected to have economical effects during the use of powdered waste glass in the manufacture of permeable polymer concrete for pavement. Therefore, powdered waste glass and recycled coarse aggregate can be used for permeable polymer pavement.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.04a
• /
• pp.271-275
• /
• 1998

Recently, in the trend of using aggregate, it is common that coarse aggregate is replaced with crushed stone and fine aggregate is replaced with sea sand as a replacing aggregate. In this study, to judge the adaptability of using antiwashout underwater concrete, we used mixed sand (river sand : sea sand= 5 : 5) and changed W/C. After carrying out the research on the strength development of the compressive strength of specimen, tensile strength, fluxural strength which is produced and cured in the air and salt water, we founded that when W/C was low and the amount of AWA and SP were increased, the state of strength development was excellent.

• Journal of the Korea Concrete Institute
• /
• v.17 no.5 s.89
• /
• pp.793-801
• /
• 2005

This study investigates fundamental properties of recycled aggregate concrete which incorporated 100% recycled coarse aggregate and various amount of recycled fine aggregate. In addition, for the purpose of the improvement of long term strength and durability, a part of cement was replaced with fly ash. Compressive strength and resistance to chloride ion penetration and carbonation were investigated. When the coarse aggregate was completely replaced with the recycled the replacement ratio of the fine aggregate with the recycled was recommended to be limited below 60% in the consideration of strength. The strength of the steam-cured specimen was very comparable to the wet-cured at 28 days. As fly ash content increased the resistance to chloride ion penetration was increased. The chloride ion penetrability based on the charge passed was found to be low at 21 days and very low at 56 days, respectively. Carbonation depth and carbonation velocity coefficient increased as the fly ash content increased and the relationship between the carbonation depth and recycled fine aggregate replacement ratio was not clear. Up to 28days, however, the measured carbonation depth was mostly less than 10mm which could be considered as low.

• Journal of the Korea Concrete Institute
• /
• v.28 no.4
• /
• pp.445-454
• /
• 2016

With the increase of decrepit facilities, construction waste increased to a certain level and now the increase is more or less stabilized. Yet construction waste still constitutes the largest portion of the overall wastes. Also, it is inevitable to spend a huge amount of the national budget due to the aggravating shortage of aggregate caused by prohibition on collection of natural aggregates as well as due to the damage to the land and environment caused by development of the sources of aggregates. As a countermeasure to the situation, the Ministry of Land, Infrastructure and Transport promulgated the quality standard for recycled aggregate to manage the usage of recycled aggregate according to its quality. But use of recycled aggregate for the purpose of high added value still remains nominal. Therefore, this research aims to study the applicability of recycled aggregate concrete as structural concrete by evaluating the quality improvement effects and the performance of the recycled aggregate concrete including recycled fine aggregate and recycled coarse aggregate that have undergone carbonation for 4 days and 14 days respectively in the condition of 60% RH, 20% $CO_2$ and $20^{\circ}C$ temperature, suggested for carbonation modifying from the advance research. The result shows carbonation modify contributed to quality improvement with 0.91% decrease in absorption rate for recycled fine aggregate and 0.7% decrease in absorption rate for recycled coarse aggregate. The physical properties and durability of the recycled aggregate made of aggregate modified by carbonation showed results similar to general concrete, which confirmed the possibility of applying the recycled aggregate made of recycled aggregate modified by carbonation to structural concrete.