• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.397-400
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• 2002

The mechanical properties of concrete such as modulus of elasticity, bond strength and shear strength are proportional to square root of compressive strength. And compressive strength of concrete is developed rapidly at early ages. Thus the relationship between compressive strength and its mechanical properties should be verified because the mechanical properties of early age concrete and hardened concrete are different. In this study, to predict the concrete slab deflection at early ages, modulus of elasticity and effective moment of inertia(Ie) are observed and compared with experimental results.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.837-851
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• 2013

In construction industry, strength is a primary criterion in selecting a concrete for a particular application. The concrete used for construction gains strength over a long period of time after pouring the concrete. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting for 28 days for such a test would serve the rapidity of construction, nor would neglecting it serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction of the strength of concrete would be of great significance. On this backdrop, the method is proposed to establish a predictive relationship between properties and proportions of ingredients of concrete, compaction factor, weight of concrete cubes and strength of concrete whereby the strength of concrete can be predicted at early age. Multiple regression analysis was carried out for predicting the compressive strength of concrete containing Portland Pozolana cement using statistical analysis for the concrete data obtained from the experimental work done in this study. The multiple linear regression models yielded fairly good correlation coefficient for the prediction of compressive strength for 7, 28 and 40 days curing. The results indicate that the proposed regression models are effectively capable of evaluating the compressive strength of the concrete containing Portaland Pozolana Cement. The derived formulas are very simple, straightforward and provide an effective analysis tool accessible to practicing engineers.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.528-531
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• 2004

Nowadays, many of PSC bridges has constructed because high performance and long span bridge is required. Therefore, it is required that the evaluation of PSC bridges which retain various structure performance. In this study, nonlinear FEM analysis was performed with two parameter, concrete compressive strength and effective prestress force which is dominant factor for evaluating structural behavior of PSC bridge. Concrete compressive strength was adapted between 30Mpa and 100Mpa and effective prestress force was used the value which is considered effective rate for time-dependant effect. In the result of this study, it was showed that concrete compressive strength and effective prestress force is important factor for evaluating structural behavior of PSC bridge.

• Journal of the Korea Institute of Building Construction
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• v.2 no.4
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• pp.163-168
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• 2002

The object of this study is to define the characteristics of high performance concrete with varing compressive strength of concrete and curing temperature. The major test variables are 1) high strength concrete(500kg/$cm^2$) and ordinary strength concrete(240kg/$cm^2$) compressive strength, 2) curing temperature and condition, 3) concrete curing age, 4) three types of cement. From the test results were shown that curing temperature and curing conditions were also very effective for high strength concrete and ordinary strength concrete, and concrete were largely effected by cement type and temperature during the hydration reaction process. This paper describes the effect of curing temperature for strength and characteristics of high performance concrete.

• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.71-78
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• 2000

This paper presents a study on the flexural rigidity of reinforced high strength concrete beams. Thirty six beams with different compressive strength of concrete, tensile reinforcement ratio, compressive reinforcement ratio, and pattern of loadings(1 point loading and 2 points loading) were tested to evaluate the effective moment of inertia. According to the experimental results, the eqation(1) proposed by ACI code for the effective moment of inertia overestimated that of simply supported reinforced high strength concrete beams. Thus, in this paper, an empirical equation(3) is proposed as a lower bound of 90% confidence limit to estimate the effective moment of inertia of simply supported reinforced high strength concrete beams.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.183-186
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• 1998

This paper deals with 28, 56, 91 days age compressive strength and ratio of weight when OPC and Low-Heat cement mortar immersed in chemical solution. As a result of experiment, the resistance of Low-Heat Cement motar in chemical attack is more effective than that of OPC, because of lower $C_3$A content and Pozzolanic reactions. Especially in long term age compressive strength, Low-Heat cement mortar shows higher strength in all kind of chemical solution compared with compressive strength of OPC motar.

• Food Science and Preservation
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• v.6 no.3
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• pp.303-307
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• 1999

Compressive strength reduction characteristics of 4 different linerboards(SC, KA, SK and IK) as influenced by temperature and humidity were investigated by ring crush test. No significant effect of temperature on the reduction of compressive strength was found for samples prepared at 5$^{\circ}C$ and 30$^{\circ}C$. At the relative humidity of 66 percents, IK linerboard showed the lowest reduction of the compressive strength. At the relative humidity of 93 percents, KA linerboard lost 40 percents of its initial compressive strength while SK linerboard lost its strength up to 56 percents. The result indicated that KA linerboard was the most cost effective and material with the highest compressive strength among tested linerboards.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.242-252
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• 2024

To date, methods used to assess the interfacial transition zone (ITZ), which represents the boundary between the aggregate and paste inside concretes, have primarily relied on destructive tests, and non-destructive tests has received little attention until recently. This study assessed the interfaces of concretes with lightweight aggregates based on electrochemical impedance spectroscopy (EIS) for high-strength concretes and examined the possibility of estimating the compressive strength of concretes through non-destructive testing using EIS. The experimental results revealed that the impedance of the hardened cement increased with increasing compressive strength and aggregate density. In particular, when the results of impedance measurement were displayed as a Nyquist plot, the intercept of the x-axis depicting the effective conductivity was proportional to the compressive strength. Furthermore, an equivalent circuit was selected to interpret the correlation between cement aggregates and impedance. Consequently, the compressive strength was found to increase with the value of the resistances of the electrolyte filled in continuous pores in the cement aggregate. And, the pores formed in the ITZ affect this value. The resistance at the ITZ for different aggregates was also obtained, and it was found that the resistance was consistent with the results predicted by SEM images of the ITZ and correlated with the strength of the concretes. The proposed method can be used as a way to easily determine the strength of cement according to differences in aggregate.

• Advances in concrete construction
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• v.14 no.2
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• pp.115-130
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• 2022

This paper presents an application of the maturation effect on the strength of high-strength concrete which is produced with different origin aggregates. While investigating the maturation effect on HSC 384 specimens were prepared with 22 different origin aggregates. These prepared specimens were subjected to the standard compressive tests which were applied after curing for 2, 7, 28, and 56 days under appropriate conditions. The test results revealed that bright surface-low adherence behavior is valid in normal strength concretes, but is not as effective as expected in high-strength concretes. The application of artificial neural networks (ANNs) to predict 2, 7, 28, and 56 day compressive strength of HSC is also investigated in this paper. An ANN model is built, trained, and tested using the available test data gathered from experimental studies. The ANN model is found to predict 2, 7, 28, and 56 days of compressive strength of high-strength concrete well within the ranges of the input parameters considered. These comparisons show that ANNs have strong potential as a feasible tool for predicting the compressive strength of high-strength concrete within the range of the input parameters considered.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.5
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• pp.120-126
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• 1998

Second step shot peening was applied on both smooth specimen and U-notch specimen in order to investigate the stress distribution and the improvement in fatigue strength. Various experiments and measurements such as rotary bending fatigue test and the measurement of compressive residual stress were performed. The results showed that the fatigue strength of second step shot peened specimens increased by 34 percent compared to that of unpeened ones. Compressive residual stress also considerably increased, which resulted in the increase of fatigue strength. finite element analysis showed that shot peening is effective in decreasing the bending stress by external force. The effectiveness of shot peening in reducing the compressive residual stress was anticipated by the superposition of the concentrated stress and the compressive residual stress.