International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-10 of 18 Abstracts search results

Document: 

SP143-17

Date: 

May 1, 1994

Author(s):

A. Scanlon, A. Nanni, and S. Ragan

Publication:

Special Publication

Volume:

143

Abstract:

Describes a large-scale pendulum device for testing reinforced concrete structures under impact loading. Details of the facility, including instrumentation of specimens and pendulum mass, are provided. Sample test results relative to full-scale bridge barriers and beams are presented. These tests show differences between responses under static and dynamic loads.

10.14359/4586


Document: 

SP143-16

Date: 

May 1, 1994

Author(s):

R. Sen and M. Shahawy

Publication:

Special Publication

Volume:

143

Abstract:

The design life of bridge structures is typically 50 years. As highway authorities increasingly consider using fiber reinforced plastics (FRP) to replace steel in reinforced or prestressed concrete structures exposed to aggressive environments, it becomes imperative to develop accelerated test procedures for assessing long-term performance. While acceleration principles for determining long-term material properties, e.g., creep rupture or relaxation, are well known, no similar principles have yet been formulated for determining properties that relate to the interaction between FRP and concrete, such as bond. This is of vital importance since material durability alone cannot guarantee satisfactory performance in concrete. Paper presents a rationale for conducting accelerated tests to evaluate the long-term bond and durability characteristics of pretensioned FRPs used in bridge applications. The principles enunciated are based on recent research findings that have been translated into test setups currently being used to evaluate the long-term performance of pretensioned aramid fiber reinforced plastic (AFRP) and carbon fiber reinforced plastic (CFRP) elements exposed to a marine environment. Preliminary results obtained are quite encouraging and appear to confirm the validity of the approach used. The experimental study is scheduled to end in 1995.

10.14359/4319


Document: 

SP143-15

Date: 

May 1, 1994

Author(s):

S. Pessiki and M. R. Johnson

Publication:

Special Publication

Volume:

143

Abstract:

Describes tests that were performed to evaluate the feasibility of using the impact-echo method to evaluate the in-place strength of concrete in plate-like elements such as slabs and walls. In the impact-echo method, a stress pulse is introduced into an object by mechanical impact on its surface, and this pulse undergoes multiple reflections (echoes) between opposite faces of the object. The surface displacement of the object, caused by the reflected pulse, is monitored at a location adjacent to the point of impact, and the frequency of successive arrivals is determined. Knowing the thickness of the test object, the compression wave (P-wave) velocity is determined. A previously established concrete strength-P-wave velocity relationship can be used to estimate in-place strength. Results indicate that the impact-echo method can be used to determine P-wave velocity through a large volume of early-age concrete such as the slab specimens tested in this study. Use of the impact-echo method to nondestructively estimate the in-place strength of concrete is more appropriately limited to the estimation of early-age strength.

10.14359/4587


Document: 

SP143-14

Date: 

May 1, 1994

Author(s):

S. Drabkin and D. S. Kim

Publication:

Special Publication

Volume:

143

Abstract:

Mortar and concrete samples were subjected to uniaxial compression to determine whether it is possible to distinguish two states of a sample: prior to the subjection to ultimate load, and subsequent to loading but prior to the appearance of visible surface cracks. Stress-strain characteristics, Young's moduli, and frequency characteristics of ultrasonic waves propagating through the samples were studied for each specimen. The qualitative analysis of frequencies and amplitudes of the peaks in resonant P-wave spectra allow the determination of undamaged specimens. The spectral analysis of continuous ultrasonic waves allows the possibility of discovering the specimen damaged by ultimate stress but visually intact.

10.14359/4321


Document: 

SP143-13

Date: 

May 1, 1994

Author(s):

F. F. Tang

Publication:

Special Publication

Volume:

143

Abstract:

Various researchers have attempted to establish correlation between mechanical properties of brittle materials and ultrasonic measurements. Recently, extensive experiments, including ultrasonic scanning tests, strain gage tests, and combined ultrasonic scanning and strain gage tests, have been processed to study the degradation mechanisms and surface effects in concrete-like brittle materials. In this paper, attention is restricted to the variation of energy dissipation with external load level and the relationship between mechanically dissipated energy and ultrasonically dissipated energy for brittle materials under uniaxial compression. Some typical ultrasonic scanning readings are presented. The load-level-dependent relationship between ultrasonically dissipated energy and mechanically dissipated energy is identified and discussed. It is also pointed out that an energy-based degradation instability theory is verified qualitatively by the energy diagram obtained through the experiments. The findings may be applicable to concrete with minor modifications. However, further work would be necessary to draw a firm conclusion.

10.14359/4320


Document: 

SP143-12

Date: 

May 1, 1994

Author(s):

S. Popovics, R. Silva-Rodrigez, J. S. Popovics, and V. Martucci

Publication:

Special Publication

Volume:

143

Abstract:

Describes a laboratory investigation of an ultrasonic method that has the potential to become, through further research, a valuable tool for the nondestructive quality control of concrete during construction. The primary objective of the work is to characterize the development of internal structure of the portland cement paste portion of concrete from very early ages on by making use of the behavior of propagated ultrasonic pulses. To do that, however, a suitable ultrasonic method first had to be developed, since quite a few publications reported difficulties with such measurements in fresh pastes due to high attenuation. Velocity and attenuation of longitudinal ultrasonic pulses were measured at regular intervals in fresh concretes. The first measurements were usually performed 10 min after mixing and continued up to the age of 28 days. Three concretes of different compositions were tested. This paper concentrates on measurements at very early ages. The instrumentation, test setup, and testing procedure are described. The velocity and attenuation results, as well as their interpretation, are then presented. For instance, it is shown that the time of initial set is close to a minimum on the pulse velocity-versus-age relationship, as well as a maximum on the attenuation-versus-age relationship.

10.14359/4318


Document: 

SP143-11

Date: 

May 1, 1994

Author(s):

A. M. Hammad and M. A. Issa

Publication:

Special Publication

Volume:

143

Abstract:

Fracture surfaces of concrete and mortar are irregular, tortuous, and stochastic in nature. To describe irregular and rough surfaces, quantitative fractographic parameters such as profile and surface roughness, fractal dimension, Fourier spectral analysis, etc., are often used. A fractal description of fracture surfaces of concrete and mortar by utilizing a new nondestructive technique, introduced by the authors, will be presented in this paper. Compact tension-fractured concrete specimens with a compressive strength of 46.8 MPa and a maximum aggregate size of 37.5 mm and a projected fracture area (ligament area) of 46,000 mm 2 (367.5 mm long by 125 mm wide), are analyzed. Through this technique, a microphotograph is taken and stored as a binary image using an image analyzer equipped with a stereo-microscope. The result is a topographical map of the fracture surface. Since the elevation of each point on the fracture surface is defined by its intensity value, the need for actual sectioning through the fracture surface, often employed, is eliminated. One-dimensional Fourier spectral analysis (1D FFT) to estimate the fractal dimension is carried out. To check the method of analysis, synthetic profiles with a known fractal dimension are generated. The results of the analysis suggest that concrete fracture surfaces are fractal for the range of scales considered, the digitized fracture surface images are found to mimic the actual fracture surfaces, their spectra follow a power lower behavior, and the technique is very promising and suitable for such materials.

10.14359/4585


Document: 

SP143-10

Date: 

May 1, 1994

Author(s):

M. Wecharatana and A. P. Ranasinghe

Publication:

Special Publication

Volume:

143

Abstract:

The break-off test is a recently developed nondestructive test for concrete. Although many experimental investigations have been carried out on this test, no in-depth theoretical evaluation has been done. In this study, the behavior of the break-off test specimen is investigated, and the theoretical basis of the test is explored. Based on linear elastic fracture mechanics, a model to predict the strength-manometer reading relationship of the test is proposed and compared with experimental results with good correlation. It was found that the ACI recommendation on the modulus of rupture (MOR) may be very conservative for certain members. The MOR of a rectangular beam is different from that observed from a circular cross section, such as the break-off test specimen. New MOR values are suggested for small rectangular beams and members with circular cross sections.

10.14359/4584


Document: 

SP143-09

Date: 

May 1, 1994

Author(s):

R. Y. Miao and W. H. Yang

Publication:

Special Publication

Volume:

143

Abstract:

The interface confining stress between steel tube and core concrete is an important problem in the analysis of the behavior of concrete-filled steel tubes. However, no satisfactory experimental method to measure the interface stress directly has been developed because of the peculiar geometry of concrete-filled steel tubes. In this study, the significance of measuring interface stress is discussed, and the use of hydraulic analogy, or analogous hydraulically loaded control specimens, is introduced. In this paper, the fundamental mechanism, instrumentation, and procedure of hydraulic analogy will be described in detail together with examples.

10.14359/4583


Document: 

SP143-08

Date: 

May 1, 1994

Author(s):

S. M. Kulkarni and S. P. Shah

Publication:

Special Publication

Volume:

143

Abstract:

Discusses important issues relevant to high-rate closed-loop testing of reinforced concrete beams. To obtain a high rate of loading from a closed-loop machine, special considerations are required in the design as well as operation of the machine. These issues are discussed briefly. Useful insight into behavior of a specimen in a high-rate closed-loop test is provided by some analytical expressions supplied here for single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) specimen systems. Advantages of displacement control over load control are apparent from the expressions obtained. Preliminary results of displacement-controlled tests conducted on reinforced concrete beams at low and high rates are reported. The specimen deformation-versus-time curve in these tests indicates that, for this setup, the test machine used in this project can apply an essentially constant velocity. Crack pattern obtained for the beams as well as inspection of load and specimen deformation signals indicate that the manner of loading was quasi-static (that is, free of inertial effects) even for the high-rate case. The load-deflection curve for the high-rate case exhibits a down-sloping portion after a small plateau.

10.14359/4601


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