• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1199-1202
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• 2001

The objective of this study is to examine the effect of frost damage immediately after placement on compressive strength of concrete. Obviously frost damage produced under low curing temperature at early ages causes the loss of compressive strength of concrete. In order to find the degrees of the loss of compressive strength, compressive strength tests was peformed at 7 and 28-day ages on concrete specimen with various curing temperature history. The results from the tests showed that the loss of compressive strength relative to concrete cured under isothermal temperature at $20^{\circ}C$ was generally from 20 to 50% for 7-day ages and below 20% for 28 day ages. Considering the serious loss of compressive strength over 50% for some cases, careful attention may be needed to placing of concrete under low atmospheric temperature.

• Computers and Concrete
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• v.5 no.5
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• pp.461-473
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• 2008

The paper explores the potential of Support Vector Machines (SVM) approach in predicting 28-day compressive strength and slump flow of self-compacting concrete. Total of 80 data collected from the exiting literature were used in present work. To compare the performance of the technique, prediction was also done using a back propagation neural network model. For this data-set, RBF kernel worked well in comparison to polynomial kernel based support vector machines and provide a root mean square error of 4.688 (MPa) (correlation coefficient=0.942) for 28-day compressive strength prediction and a root mean square error of 7.825 cm (correlation coefficient=0.931) for slump flow. Results obtained for RMSE and correlation coefficient suggested a comparable performance by Support Vector Machine approach to neural network approach for both 28-day compressive strength and slump flow prediction.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.1
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• pp.3685-3701
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• 1975

This study was conducted to investigate the strength of soil cements for varied molding water content and cement content(3,6,9,12%) in four cementstabilized soils(KY: sand, MH: sad, SS: sandy loam, JJ: loam). The eoperimental results obtainedfrom unconfined compressive strength tests are asfollows: 1. The optimum moisture content increased in accordance with the increase of the cement while maximum dry density didn't change uniformly. 2. The moisture content for maximum strength was higher than the optimum moisture content in the higher cement content. Moisture-density curves showed a dull peak in the higher cement contents, on the other hand, a sharp peak in the lower cement contents. 3. In molding the specimen with the approximate optimum moisture content, the maximum strength showed at the wet side of the optimum moisture content. 4. SS and JJ maybe used as cement-stabilized base of road to require 300PSI of compressive strength cured seven days, but MH and KY may be not adequate. 5. In soil cement, the better the grain size distribution was, the stronger the compressive strength was itn general. 6. The relation between 28-day strengh and 7-day strength in the cementstabilized four soils may be expressed as follows: q28=1.55q7+1.5 in which q28:28-day strength. q7:7-day strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.137-140
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• 2004

Hydraulic structures have been constructed with low cost concrete so as to increase the investment efficiency. As the construction of agricultural irrigation and drainage project is concentrated on off-farming season and come to construction less than 28-day strength in quality control. As we are aware the major thrust construction of short period is now in hydraulic structures rather then the large- scale. This paper will propose the relationship between the 7-day and 28-day compressive strength of concrete be investigated. Test will be carried out on nine different concrete mixes and 180 core drilled form the hydraulic structures with 7-day and 28-day compressive strengths ranging approximately from 24 to 30Mpa.

• Advances in concrete construction
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• v.13 no.6
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• pp.411-422
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• 2022

Aggregates mineralogical, and petrographic properties directly affect the mechanical properties of the produced high strength. This study is focused on the effects of magmatic, sedimentary, and metamorphic aggregates on the performance of high strength concrete. In this study, the effect of the mineralogical properties of aggregates on the compressive strength and modulus of elasticity of high-strength concrete was estimated by Artifical Neural Network (ANN). To estimate the compressive strength and elasticity modules, 96 test specimens were produced. After 28 days under suitable conditions, tests were carried out to determine the compressive strength and modulus of elasticity of the test specimens. This study also focused on the application of artificial neural networks (ANN) to predict the 28-day compressive strength and the modulus of elasticity of high-strength concrete. An ANN model is developed, trained, and tested by using the available test data obtained from the experimental studies. The ANN model is found to predict the modulus of elasticity, and 28 days compressive strength of high strength concrete well, within the ranges of the input parameters. These comparisons show that ANNs have a strong potential to predict the compressive strength and modulus of elasticity of high-strength concrete over the range of input parameters considered.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.96-97
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• 2020

In this study, the compressive strength and porosity characteristics of cement mortar mixed with liquid and powder composite water repellent were evaluated. When the liquid water repellent was mixed, the compressive strength at 28 days of age was 42% compared to OPC, and the compressive strength was greatly reduced. However, the 28-day compressive strength of the powder water repellent mixture and P5L1, P6L1 liquid and powder composite water repellent was about 97% compared to OPC, and there was little decrease in compressive strength.

• Magazine of the Korean Society of Agricultural Engineers
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• v.24 no.3
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• pp.92-99
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• 1982

The objective of this study was to investigate the compressive and bending strength characteristics of epoxy resin mortar, which is still in an early stage of its use and study in Korea. The results obtained are summarized as follows; 1. The compressive strengths of epoxy resin mortar after 1 day, 2 days and 3 days were gained 87%, 91% and 95%, respectively, in view of that of mortar at the age of 7 days. This result showed that the initial compressive strength within 1 day was very high. 2. The highest compressive strength of epoxy resin mortar was 914 kg/cm2 at the point of having the mixing ratio of one to two. It reached up to 3.7 times that of the normal portland cement mortar at the age of 28 days. 3. The bending strengths of epoxy resin mortar after 1 day, 2 days and 3 days came up to 88%, 93% and 97%, respectively, in comparing that of mortar at the age of 7 days. It was expressed to be simielar to the tendency of compressive strength. 4. The highest bending strength of epoxy resin mortar was 384 kg/cm2 at mixing ratio of one to two. It came up to as much as 6.5 times in comparing with that of the normal portland cement mortar at the age of 28 days. Therefore, the epoxy resin mortar would be effective for promoting the bending strength of structural members. 5. The regression equation between compressive and bending strength was obtained as follows; oo~=0.391 oc+27.54 (r=0.99) And the estimated value of bending strength was corresponded to about 44 per cent in comparing with that of the compressive strength.

• Computers and Concrete
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• v.15 no.3
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• pp.473-484
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• 2015

In this study, the availability of Schmidt hammer has been investigated as a reliable method to determine the quality of concrete in irrigation networks. For this purpose, the 28-day compressive strength of concrete material used in the construction irrigation channel of Bafra lowland, which is one of the most fertile plains in Turkey was examined by means of concrete compression and as well as concrete Schmidt hammer in laboratory conditions. This study was carried out on cylindrical samples to represent the everyday concrete party ($150m^3$) produced by contractor firm as 3 replications. The statistical analysis of experimental data showed that the correlations between the values of 28-day compressive strength of Schmidt hammer and the rebound number was found to be 0.98. Differences of the compressive strength between compression testing and Schmidt hammer were statistically significant at P<0.01. In this context, it was found that the reliability of compressive strength of the concrete compression test are excellent, also the reliability of compressive strength of Schmidt hammer are fair in assessing the quality of concrete irrigation channels.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.82-89
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• 2014

The purpose of this study is to propose a simple model to evaluate the compressive strength development of concrete with various supplementary cementitious materials (SCMs) and cured under different temperatures. For the generalization of the model, the ACI 209 parabola equation was modified based on the maturity function and then experimental constants A and B and 28-day compressive strength were determined from the regression analysis using a total of 265 data-sets compiled from the available literature. To verify the proposed model, concrete specimens classified into 3 Groups were prepared according to the SCM level as a partial replacement of cement and curing temperature. The analysis of existing data clearly revealed that the 28-day compressive strength decreases when the curing temperature is higher and/or lower than the reference curing temperature ($20^{\circ}C$). Furthermore, test results showed that the compressive strength development of concrete cured under $20^{\circ}C$ until an early age of 3 days was marginally affected by the curing temperature afterward. The proposed model accurately predicts the compressive strength development of concrete tested, indicating that the mean and standard deviation of the ratios between predictions and experiments are 1.00 and 0.08, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.223-228
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• 2000

Although construction company try to get good quality control it's enough to study about developing objective evaluation method and checking quality method. It is important to meaning concrete quality at placing point, immediate quality checking method is limited. The purpose of this study is to develop new method to know early 28-day concrete for getting faithful quality control. The results of this study are as follows :1) With sealed molds, reduced moisture volatilization to more than 50% and enlarged 20% accelerated compressive strength than before one. 2) Accelerated compressive strength of concrete specimen shows higher strength when it was in the air for long time 3)Interrelation with 7-day and 28-day strength were 0.781,0.90, It is higher than before one