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Showing 1-5 of 53 Abstracts search results

Document: 

SP172-22

Date: 

December 1, 1999

Author(s):

Jin Keun Kim and Yun-Yong Kim

Publication:

Symposium Papers

Volume:

172

Abstract:

In this study, the wedge splitting test(WST) was carried out for the fatigue crack growth behavior of concrete. Selected test variables were concrete compressive strength of 28, 60 and 118 MPa, and stress ratio with 2 levels (6, 13 %). In order to make the designed stress ratio, the maximum and the minimum fatigue loading were 75-85 % and 5~10 % of ultimate static load, respectively. Fatigue testing was preceded by crack mouth opening displacement(CMOD) compliance calibration and fracture energy test, and then the fatigue crack growth was computed by crack length vs. CMOD compliance relations acquisited by the CMOD compliance calibration technique. In fatigue test, the frequency of loading cycle was 1 Hz, and the initial notch length(%) was 30 % of specimen height. To evaluate the validity of CMOD compliance calibration technique, the crack length measured by the method suggested in this study was compared with that predicted by linear elastic fracture mechanics(LEFM). On the basis of the experimental results, a LEFM-based empirical model for fatigue crack growth rate(da/dN-AKi relationships) considering the effects of concrete strength was presented. The fatigue crack growth rate increased with the strength of concrete. It appears that the da/dN-AK1 relationships was influenced by stress ratio, however, the effect is diminished with an increase of strength. In addition, the effect of initial notch length on the fracture energy were shown, and the comparisons between CMOD compliance calibration technique and LEFM gave the validity of CMOD compliance calibration technique for the WST.

DOI:

10.14359/6144


Document: 

SP172-12

Date: 

December 1, 1999

Author(s):

Yiching Lin and Tzonghow Liou

Publication:

Symposium Papers

Volume:

172

Abstract:

The objectives of the studies presented in this paper were to investigate the effects caused by steel reinforcing bars on determining the depth of cracks which appear on the surface of a concrete structure. Numerical studies were performed to investigate the interaction of stress waves with reinforcing bars. A full scale reinforced concrete beam was constructed as an experimental specimen. The specimen was loaded until cracks occurred. To measure the depth of a crack penetrating into the specimens, two receivers were used and located on the opposite sides of the crack. The first receiver on the impact side is used to obtain the time of impact initiation. The second receiver located on the other side of the crack is used to trace the arrival of the P-wave diffracted from the bottom edge of the crack. Subsequently, the depth of the crack can be determined. Experimental results show that if tests are performed on the regions without reinforcing bars, the crack depth can be obtained easily because the second receiver initially responds to the arrival of the diffracted P-wave. In the presence of reinforcing bars, the initial disturbance at the second receiver is caused by the arrival of P-wave propagating through reinforcing bars but its amplitude is much smaller than that associated with the following arrival of the P-wave diffracted from the bottom edge of the crack. It is concluded that the presence of reinforcing bars does not make it difficult to measure the crack depth.

DOI:

10.14359/6134


Document: 

SP172-44

Date: 

December 1, 1999

Author(s):

Ryoichi Sato, Ming Xu and Yang Yang

Publication:

Symposium Papers

Volume:

172

Abstract:

The autogenous shrinkage strain and restrained stress due to autogenous shrinkage and heat of hydration effects in high strength concrete were investigated experimentally. It was clear that at early age the autogenous shrinkage strains develop more rapidly in concrete without the admixture, and in concrete containing silica fume, than in concrete containing blast-furnace slag. The final autogenous shrinkage strains in concrete containing blast-furnace slag are largest, and are smallest in concrete without admixtures. The autogenous shrinkage strains under the environment with temperature of 40 “C develop faster at early age and slower in the late than 20 “C . In correspondence with autogenous shrinkage, the stresses due to autogenous shrinkage in concrete containing blast-furnace slag is greatest. The restrained stresses due to autogenous shrinkage in concrete tends to be smaller at early age and to be greater in the late at 20°C than that at 40°C. The numerical analysis results by FEM agreed comparatively well with experimental stresses.

DOI:

10.14359/6166


Document: 

SP172-34

Date: 

December 1, 1999

Author(s):

Jin-Kuen Kim and Sang-Hun Han

Publication:

Symposium Papers

Volume:

172

Abstract:

In this study, the properties of self-flowing concrete, of which flow was more than 60 cm, containing fly ash were experimentally investigated and compared with those of ordinary concrete. Flow test, slump test and setting time test on five types of self-flowing and three types of ordinary concrete mixtures were carried out to obtain the properties for flowability and workability of fresh concrete. The mechanical properties of hardened concrete were also investigated in terms of compressive strength, splitting tensile strength, modulus of elasticity, creep and drying shrinkage. In fresh concrete, it was found that self-flowing concrete had excellent workability and flowability compared with ordinary concrete. Self-flowing concrete also had good mechanical properties at both early and late ages with compressive strength reaching as high as 40 MPa at 28 days. The creep of self-flowing concrete investigated was greater than that of ordinary concrete at early ages, and drying shrinkage was much higher.

DOI:

10.14359/6156


Document: 

SP172-40

Date: 

December 1, 1999

Author(s):

Somnuk Tangtermsirikul and Yukio Aoyagi

Publication:

Symposium Papers

Volume:

172

Abstract:

This paper explains the development of a roller-compacted concrete for constructing or renovating concrete pavement (RCCP), using lignite fly ash in Thailand. A method for proportioning the lignite fly ash RCCP based on the ratio, y, between paste volume and void content of total aggregate is proposed. It was found from the tests conducted by varying fly ash replacement ratio, water to total binder ratio, and paste content that the range of value of y which gives rise to optimum strength and density of the RCCP were in between 1.02 and 1.05 for the tested materials. The design curves for compressive strength were derived based on test results with varied fly ash replacement ratio and water to total binder ratio of the RCCP with y being equal to 1.02. Some selected RCCP mixtures were compared with conventional concrete for constructing pavement in terms of flexural strength, drying shrinkage and abrasion resistance. The tested RCCP specimens were found to have higher flexural strength than the ACI-proposed formula for conventional concrete. Drying shrinkage of RCCP was smaller than that of the conventional concrete and was even smaller when lignite fly ash replacement ratios were larger. Similar to the conventional concrete, the abrasion resistance of the RCCP was found to have a good correlation with compressive strength.

DOI:

10.14359/6162


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