• Journal of the Korea Concrete Institute
• /
• v.20 no.5
• /
• pp.583-592
• /
• 2008

Recently, the effects of high temperature on compressive strength, elastic modulus and strain at peak stress of high strength concrete were experimentally investigated. The present study is aimed to study the effect of elevated temperatures ranging from 20 to 700 on the material mechanical properties of high strength concrete of 40, 60, 80 MPa grade. In this study, the types of test were the stressed test and stressed residual test that the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating and when target temperature is reached, the specimens are loaded to failure. And another specimens are loaded to failure after 24 hour cooling time. Tests were conducted at various temperatures ($20{\sim}700^{\circ}C$) for concretes made with W/B ratios 46%, 32% and 25%. Test results showed that the relative values of compressive strength and elastic modulus decreased with increasing compressive strength grade of specimen and the axial strain at peak stress were influenced by the load before heating. Thermal strain of concrete at high temperature was affected by the preload level as well as the compressive strength. Finally, model equation for compressive strength and elastic modulus of heated high strength concrete proposed by result of this study.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.16 no.3
• /
• pp.3472-3476
• /
• 1974

This test was attempted to investigate the effects of some mix designs of concreteon the compressive strengths and corrosive rates when exposed to sea water of the West Sea. In this test, concrete mixes consisted of an ordinary concrete, a pozzolan concrete and concretes with different admixtures such as fly ash, pozzolith and vinsol resin. Compressive strengths of the concrete were measured at ages of 1-year and 2-years when exposed to both sea water and fresh water. Corrosive rate was tested at ages of 1-year and 2-years when exposed to sea water only. The results obtained from the test may be summarized as follows: (1) When all of concretes were exposed to fresh water, compressive strength of an ordinary concrete was the lowest at all mixes of concretes, and all of them showed higher strength as the exposing age is longer. It was evidance that the uses of pozsolan cement, fly ash, pozzolith and vinsol resin in mix design of concrete had an effect on increasing compressive strength and that fresh water also had an effect on curing concretes even though at a long-time age. (2) When concretes were exposed sea water, a concrete with fly ash was the highest in compressive strength and its strength was increasing as the exposing age is longer, but the other concretes were decreased at 2-year exposure. It was found that a concrete with fly ash was the most effective on compressive strength of all concrete, but the other concretes were attacked by action of the sea water. (3) The use of vinsol resin admixture was the most resistant to corrosion by sea water, while the use of pozzolith was the most serious at corrosion and the others were corroded to almost same extent. (4) The relationship between corrosions and compressive strengths of concretes was not clearly correlated yet. It was known that the corrosive rate of concretes could not affect to compressive strengths by 2-year exposure of the sea water. (5) Pozzolan concrete was the most effective in compressive strength when exposed to fresh water only, However, the use of a fly ash admixture was available for compressive strength when exposing to both fresh water and sea water. It was also noticed that the use of vinsol resin was not available for strengths of concrete but for resistance to corrosion when exposed to sea water. (6) It was found that the use of pozzolith was so defective in compressive strengths and corrosiive resistance when exposing to sea water that it was only available for fresh water.

• KCI Concrete Journal
• /
• v.14 no.1
• /
• pp.43-50
• /
• 2002

In this study, size effect tests were conducted on axial compressive strength of concrete members. An experiment of Mode I failure, which is one of two representative compressive failure modes, was carried out by using dimensionally proportional cylindrical specimens (CS). An adequate notch length was taken from the experimental results obtained from the compressive strength experiment of various initial notch lengths. Utilizing the notch length, specimen sizes were then varied. In addition, new parameters for the modified size effect law (MSEL) were suggested using Levenberg-Marquardt's least square method (LSM). The test results show that size effect was apparent for axial compressive strength of cracked specimens. Namely, the effect of initial notch length on axial compressive strength size effect was apparent.

• Steel and Composite Structures
• /
• v.9 no.6
• /
• pp.519-534
• /
• 2009

This study intends to examine the characteristics of compressive behavior and conducts comparative analysis between normal compressive strength under existing equations (LRFD, ACI 318, EC 4) and experimental the maximum compressive strength from the compression experiment for the unstiffened steel plate-concrete structures. The six specimens were made to evaluate the constraining factor (${\xi}$) and width ratio (${\beta}$) effects subjected to the compressive monotonic loading. Based on this experiments, the following conclusions could be made: first, compressive behaviors of the specimens from the finite element analysis closely agreed with the ones from the actual experiments; second, the higher the width ratio (${\beta}$) was, the lower the ductility index (DI) was; and third, the test results showed the maximum compressive strength with a margin by 7% compared to the existing codes.

• Journal of the Korea Concrete Institute
• /
• v.12 no.6
• /
• pp.99-108
• /
• 2000

The size effect on axial compressive strength in notched concrete specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimens under compression were discussed. In this study, experiments of axial compressive failure, which is one of the two failure modes, was carried out by using cylindrical specimens. Adequate notch length was taken from the experimental result of strength variation based on the notch length. And, by taking various sizes of specimens the size effect on axial compressive strength of concrete was investigated. Also, model equations were suggested by modified size effect law (MSEL). The test results show that size effect appears conspicuously for all series of specimens. Additionally, the effect of initial notch length on axial compressive strength was also apparent.

• Journal of the Korea Concrete Institute
• /
• v.17 no.3 s.87
• /
• pp.313-322
• /
• 2005

Recently, as the remodeling market gradually substitute for new construction market and safety diagnosis for reconstruction apartment become a matter of principal Interest, it is demanded that scientific diagnosis and evaluation for existing concrete structure state. And it is increasing that the significance for reliability of data which is used for estimating the concrete compressive strength by nondestructive test. As a result, it is found that different proposal to material age and hitting angle is good to improving the reliability of presumption of concrete compressive strength in the linear hitting rebound test hammer. And for the reason that mutual relation between the compressive strength and rebound degree is highest in linear hitting rebound test hammer 25mm in all portion according to early md middle material age and hitting angle except the early material age $-45^{\circ}$, analysis showed that linear hitting rebound test hammer is more reliable than existing schmidt hammer in presumption of concrete compressive strength.

• Geomechanics and Engineering
• /
• v.19 no.4
• /
• pp.353-360
• /
• 2019

The elastic modulus is an important parameter to characterize the property of rock. It is common knowledge that the strengths of rocks are significantly different under tension and compression. However, little attention has been paid to the bi-modularity of rock. To validate whether the rock elastic moduli in tension and compression are the same, Brazilian disc, direct tension and compression tests were conducted. A horizontal laser displacement meter and a pair of vertical and transverse strain gauges were applied. Four types of materials were tested, including three types of rock materials and one type of steel material. A comprehensive comparison of the elastic moduli based on different experimental results was presented, and a tension-compression anisotropy model was proposed to explain the experimental results. The results from this study indicate that the rock elastic modulus is different under tension and compression. The ratio of the rock elastic moduli under compression and tension ranges from 2 to 4. The rock tensile moduli from the strain data and displacement data are approximate. The elastic moduli from the Brazilian disc test are consistent with those from the uniaxial tension and compression tests. The Brazilian disc test is a convenient method for estimating the tensile and compressive moduli of rock materials.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.5 no.6
• /
• pp.9-13
• /
• 2002

This study has been performed to investigate the physical and mechanical characteristics of compaction, volume change and compressive strength for reinforced soil mixed with cement. And confirm the reinforcing effects with admixture such as cement. To this end, a series of compaction test and compression test was conducted for clayey soil(CL) and cement reinforced soil. In order to determine proper moisture content and mixing ratio, pilot test was carried out for soil and cement reinforced soil. And the mixing ratio of cement admixture was fixed 3%, 6%, 9% and 12% by the weight of dry soil. As the experimental results, the maximum dry unit weight(${\gamma}_{dmax}$) was increased with the mixing ratio and then shown the peak at 10% reinforced soil, but the optimum moisture content(OMC) and the volume change was decreased with the ratio increase. And the compressive strength volume change was decreased with mixing ratio increased.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.10a
• /
• pp.3-9
• /
• 2002

Paper sludge ash was assured as material of a sort of pozzolan. For the reason of fluidity decrease caused by the strong absorption of paper stooge ash and the decrease of compressive strength in case of using over30% replacement by the weight of cement, paper sludge ash is not suitable for blending material. Therefore, it is necessary to find proper replacement ratios between paper sludge and blast furnace slag to insure compressive compensation and appropriate slump. Accordingly, as varied the blending ratios of paper sludge and blast furnace slag, testing mortar was made. This study was aimed to investigate the possibility of using blending replacement of paper sludge ash and blast furnace slag throughout compressive test, flow test, SEM(Scanning Eletron Microscope), MIP(Mercury Intrusion Porosity test), and TG-DTA(Thermal analysis).

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.198-203
• /
• 1995

The objective of this study is to provide the information on the techniques of manufacturing and experiment in small scale modeling of precast concrete(P.C.)large panel structures. The adopted scale was 1/5th 4types of experiments were performed : material tests for model concrete and model reinforcement, compressive test of horizontal joint, shear test of vertical joint and cyclic static test of 2-story subassemblage structure. Based on the experimental results, the following conclusions are drawn: (1)Model concrete may have in general larger compressive strength than expected. (2) Model reinforcement can show less ductility if the annealing processes were performed without using vaccuum tube. (3) Failure modes of horizontal and vertical joints were almost same for both prototype and model. But the strength of model appears to be higher than required by similitude law. (4)Hysteretic behavior of 1/5 scale subassemblage model can be made quite similar to prototype's if the ductility of model reinforcement and compressive strength of model concrete could be representative of those of prototype.