• Structural Engineering and Mechanics
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• v.66 no.2
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• pp.263-271
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• 2018

Compressive strength and elastic modulus of concrete are constantly changing with age. In order to determine long-term development of compressive strength and elastic modulus of concrete, an investigation of C30 concrete cured in air conditions was carried out. Changes of compressive strength and elastic modulus up to 975 days were given. The results indicated that compressive strength and elastic modulus of concrete rapidly increased with age during the initial 150 days and then increased slowly. The gain in elastic modulus was slower than that of compressive strength. Then relationships of time-compressive strength, time-elastic modulus and compressive strength-elastic modulus were proposed by regression analysis and compared with other investigations. The trends of time-compressive strength and time-elastic modulus with age agreed best with ACI 209R-92. Finally, factors contributed to long-term development of compressive strength and elastic modulus of concrete were proposed and briefly analyzed.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.1
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• pp.101-110
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• 2018

This study experimentally investigated the compressive and flexyral strength development characteristics of polymer concrete using four different type polymeric resins such as unsaturated polyester, vinyl ester, epoxy, and PMMA (polymethyl methacrylate) as binders. The test results show that the average compressive strength of those four different polymer concretes was 88.70 MPa, the average flexural strength was 20.30 MPa. Those test results show that compressive and flexural strengths of polymer concrete were much stronger than compressive and flexural strengths of ordinary Portland cement concrete. In addition, the relative gains of the compressive strength development at the age of 24 hrs compared to the age of 168 hrs were 68.6~88.3 %. Also, the relative gains of the flexural strength development at the age of 24 hrs compared to the age of 168 hrs were 73.8~93.4 %. These test results show that compressive and flexural strengths of each polymer concrete tested in this study were developed at the early age. Moreover, the prediction equations of compressive and flexural strength developments regarding the age were determined. The determined prediction equations could be applied to forecast the compressive and flexural strength developments of polymer concrete investigated in this study because those prediction equations have the high coefficients of correlation. Last, the relations between the compressive strength and the flexural strength of polymer concrete were determined and the flexural/compressive strength ratios were from 1/4 to 1/5. These results show that polymer concretes investigated in this study were appropriate as a flexural member of a concrete structure because the flexural/compressive strength ratios of polymer concrete were much higher than the flexural/compressive strength ratios of Portland cement concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.176-177
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• 2019

Recently, efforts are made to apply 200MPa levels of ultra-high strength concrete to structures exceeding 40MPa.. Ultra-high strength concrete has been steadily researched in Korea as well as abroad, and now it is equipped with 200MPa ultra-high strength concrete mixing technology. Because ultra-high strength concrete has a higher range of compressive strength than ordinary concrete, it is difficult to accurately measure the compressive strength of UHPC concrete with existing compressive strength measuring equipment and can be less reliable. In this study, the compressive strength of the SC80 was measured according to the test method to compare the compressive strength of the SC80 by applying various methods of measurement of compressive strength. The compressive strength test method measured the compressive strength according to the size of the specimen, the grinding method, and the capacity of the UTM equipment.

• Journal of Welding and Joining
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• v.18 no.4
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• pp.87-95
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• 2000

Residual stresses and deformations due to welding have effects on the strength of structures. In this paper, the compressive strength of basic welded structures is studied and the effects of the residual stresses and deformations on the compressive strength of beams, plates and shells are investigated,. Theoretical analysis for the basic structures is carried out and simplified methods to calculate the compressive strength are proposed. The proposed methods yield simple formulas to calculate the compressive strength, of which results are much helpful. The accuracy of the proposed method is revealed by comparison with experimental results.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.381-386
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• 2005

In order to have compressive strength tests and frost heaving tests, two sorts of soil samples at Chonbuk-Do area were used. According to this research, the compressive strength of soil which was mixed by quick lime, was largely increased until 28 days but after 28 days, the increment of strength was seldom found and its maximum compressive strength increasing rate for content of quick lime was $10{\sim}15%$ scope. In the mixed rates of quick lime and briquette ash, the compressive strength of soil which was mixed by quick lime and briquette ash, was increased by increasing mixed rates of quick lime and its compressive strength was increased by additional quantity. The compressive strength of mixed soil within freezing-thawing 1 cycle was diminished around 30% compared to non-freezing soil's 28 days compressive strength but there were no movements after 2 cycle.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.145-146
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• 2023

One of the causes of recent construction site collapses was that the compressive strength of concrete was less than half of the allowable design standard strength range. In the safety diagnosis of structures, the compressive strength of concrete is a factor that determines the durability of a building. Therefore, in this study, we aim to examine the characteristics of compressive strength according to the particle size distribution of coarse aggregate among the compressive strength factors using small-diameter cores. To avoid problems when collecting cores, core specimens with diameters of 100×200, 50×100, and 25×50 (mm) were manufactured directly. As a result of measuring the compressive strength of concrete for each diameter, the larger the core diameter, the higher the compressive strength. has increased.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.377-378
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• 2023

This study examined the effect of curing conditions on the compressive strength of dry mortar for floor. The compressive strength according to the relative humidity during curing was compared, and the influence of expansive additives on compressive strength under water curing was reviewed. As a result, low relative humidity conditions during curing was not effective in improving the compressive strength of dry mortar for floor, and it was judged that the continuous hydration reaction insufficient due to lack of the moisture supply. In order to improve compressive strength, high relative humidity maintenance was found to be an important factor. However, under water curing conditions, the compressive strength has decreased as a result of continuous volume expansion due to the use of the expansive additives.

• Computers and Concrete
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• v.21 no.6
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• pp.697-703
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• 2018

Compressive strength is one of the most important engineering properties of concrete, and testing of the compressive strength of concrete specimens is often costly and time consuming. In order to provide the time for concrete form removal, re-shoring to slab, project scheduling and quality control, it is necessary to predict the concrete strength based upon the early strength data. However, concrete compressive strength is affected by many factors, such as quality of raw materials, water cement ratio, ratio of fine aggregate to coarse aggregate, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete. The concrete compressive strength is a quite nonlinear function that changes depend on the materials used in the concrete and the time. This paper presents an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of concrete compressive strength. The training of fuzzy system was performed by a hybrid method of gradient descent method and least squares algorithm, and the subtractive clustering algorithm (SCA) was utilized for optimizing the number of fuzzy rules. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed ANFIS model. Further, predictions from three models (the back propagation neural network model, the statistics model, and the ANFIS model) were compared with the experimental data. The results show that the proposed ANFIS model is a feasible, efficient, and accurate tool for predicting the concrete compressive strength.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.954-964
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• 1999

The effect of fabrication variables and microstructures on the compressive strength of open cell alumina zirconia and silicon nitride ceramics fabricated by polymeric sponge method was investigated. Bulk density and compressive strength of open cell ceramics were mainly affected by coating characteristics of ceramic slurry on polymeric sponge that controlled a shape thickness and defect of the struts. Sintering temperature was optimized for enhancement of strut strength and compressive strength of open cell ceramics. Relative density and compressive strength behaviors were relatively well matched with the predicted values. Open cell ceramics of lower relative density below 0.1 prepared by first relatively well matched with the predicted values. Open cell ceramics of lower relative density below 0.1 prepared by first coating of ceramic slurry had thin triangular prismatic struts that were often broken or longitudinally cracked. With an application of second coating of slurry shape of struts was transformed into thickner cylindrical one and defects in struts were healed but the relative density increased over 0.2 Open cell zirconia had both the highest bulk density and compressive strength and alumina had the lowest compressive strength while silicon nitrides showed relatively high compressive strength and the lowest density. Based upon the analysis open cell silicon nitride was expected to be one of potential structural ceramics with light weight.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.435-443
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• 2020

The objective of this study was to determine the effective compressive strength of a column-slab connection with different compressive strengths between the column and slab concrete. A total of eight column specimens were fabricated, among which four specimens were restrained by slabs while the others did not have any slab, and the test results were compared with current design codes. According to ACI 318, the compressive strength of a column can be used as the effective compressive strength of the column-slab connection in design when the strength ratio of column concrete to slab concrete is less than 1.4. Even in this case, however, this study showed that the effective compressive strength decreased. The specimen with its slab-column connection zone reinforced by steel fibers showed an increased effective compressive strength compared to that of the specimen without the reinforcement, and the interior column specimens restrained with slabs reached the compressive strength of the column.