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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-10 of 17 Abstracts search results
April 1, 1997
Allen G. Davis and Bernard H. Hertlein
Large concrete structures such as dams and bridge abutments and piers built over 50 years ago were usually constructed of mass concrete with no or little reinforcing steel. Most of these structures are in service today, and make up a considerable part of the infrastructure. Concern about their reliability and residual life now prompts owners to initiate structural inspections. The traditional approach of coring and visual inspection alone does not necessarily provide a full over for this evaluation. The more familiar nondestructive tests (NDT) such as rebound hammer, ultrasonic pulse velocity and similar surface tests are usually unsuccessfbl in providing information about bulk concrete quality at depth. This paper reviews two novel NDT methods that can address this problem: sonic ogging and parallel seismic, and presents three case histories that illustrate their application.
Allen G. Davis
Two 16-story reinforced concrete apartment blocks founded on drilled shafts (CIP piles) were damaged in the 1994 Northridge earthquake. In order to assess the viability of the buildings for retrofit, it was considered necessary to evaluate the integrity of the existing concrete drilled shaft foundations, which were only partially reinforced. This paper describes the use of various nondestructive testing methods for the foundation evaluation, including ground penetrating radar, parallel seismic and impulse response tests. The selected test methods proved to be successfir!, and provided an economical approach while obtaiuing maximum informatron about the integrity and future performance of the hidden foundation.
Xuli Fu and Il. Il. L. Chung
The contact electrical resistivity was found to correlate with the shear bond strength between steel rebar and concrete, between stainless steel fiber and cement paste, and between carbon fiber and cement paste. For the bond between steel rebar and concrete and that between stainless steel fiber (untreated or acetone washed) and cement paste, the contact resistivity increased linearly with increasing bond strength, due to an interfacial phase of high volume resistivity that helped the bonding. For the bond between stainless steel fiber (acid washed) and cement paste and that between carbon fiber (untreated) and cement paste, the contact resistivity decreased with increasing bond strength, due to the bond degradation by interfacial voids, which were high in volume resistivity. The acid washing of the stainless steel fiber decreased the contact resistivity, but had little effect on the bond strength. The high volume resistivity interfacial phase that enhanced the bonding between the untreated or acetone washed stainless steel fiber and cement paste apparently required for its formation the oxide layer on the stainless steel surface. The removal of the oxide layer by acid washing eliminated this phase, thus decreasing the contact resistivity and causing the contact resistivity to decrease with increasing bond strength. For a given interface at a given curing age, the correlation between bond strength and contact resistivity allows the bond strength to be nondestructively measured via contact resistivity measurement.
Shigen (Eric) Li, Gregory C. Frantz,
and Jack E. Stephens
A test method, which uses pull-off test and partial coring techniques, was developed in this study. This test method is particularly suitable for assessing the durability of bonding new to old concrete subjected to freeze-thaw cycling and exposed to deicing salt. This test method also combines bond evaluation and ASTM C-672 test ( Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals ) into one test method. Laboratory experimental research investigated important factors which influence the test results and their scatter. Test results show that this test method is very promising.
P. A. Muhammed Basheer, Peter R. V. Gilleece,
Robin Andrews, and Adrian E. Long
The resistance of concretes to the transport of chloride ions is defined generally by the coefficient of diffusion. This, combined with a knowledge of the exposure of concrete to chlorides, can be used to estimate the depth of penetration of chlorides over a period of time. Therefore, an indication as to the likelihood of chlorides reaching reinforcement can be determined, and, if there is a risk of corrosion, preventive measures can be taken. The procedure to find the coefficient of diffusion from a standard diffusion test is well established. However, such a test may need several months to finish, depending on the quality of the concrete and the thickness of sample tested. As a consequence this is not a practicalmethod, and different organisations have conducted research to determine the coefficient of diffusion (D) more rapidly. The approach adopted has been to force chlorides through the test sample by applying a voltage, and such tests are known as accelerated chloride migration tests. By using this principle, and following from early studies by Whiting, a new test method for determining the chloride migration coefficient of the near surface concrete in-situ is being developed at Queen’s. This test makes use of a set up similar to the well established Autoclam permeability system. The results of an investigation carried out with this new apparatus is presented in this paper along with a description of the new test method. Early results indicated that this new test method could form the basis to determine the chloride diffusivity of the near surface concrete on site.
M . Cl. A . T h o m a s , D . W i e s e ,
a n d H . Caratin
This paper describes the application of geophysical tomography and scientific visualization techniques for evaluating the internal condition of massive concrete structures. The resulting output is a three dimensional representation of the structure showing the spatial distribution of ultrasound data. As various aspects of ultrasound data (e.g. velocity and attenuation) are related to concrete quality, the location and orientation of areas of inferior material or discontinties can be identified. In addition, specific features within the image can be highlighted and quantified. Results are presented from a preliminary study carried out to assess the potential application of this technique for evtiating the internal condition of large concrete elements. A large concrete block was constructed with a number of internal defects such as cracks, areas of poorly compacted concrete and uncemented aggregate, and large voids. A large number of measurements (ultrasonic pulse velocity) were taken to provide a network of velocities across a section. Algebraic tomographic techniques were then applied to reconstruct a two dimensional image. By taking a series of contiguous sections and stacking them together, a three dimensional model of the sample or structure was then created. Finally the three dimensional data set was visualized using advanced graphics techniques such as vohune rendering. Overall, the initial results are promising, and indicate that the presence and location of internal defects can be determined
Jamal Rhazi, Yahya Kharrat,
Gerard Ballivy, and Michel Rivest
In the past few years, a great progress was done in the field of acoustical imaging. One aspect of this progress has been the application of this evolving technique to the non-destructive evaluation of civil engineering structures. This paper gives a brief review of the basic theory of acoustical imaging. It also describes a case study to highlight the practical aspects and the possibility of using this technique to assess the internal conditions of concrete structures.
Randall Poston and Mary Sansalone
This paper presents both a brief explanation of the impact response of bar-like structures and an application involving the use of the impact-echo method for detecting cracks in the beams and columns of a post-tensioned parking garage structure. The information gained from the impact-echo tests was used to aid in specifying repair measures for the structure. In the process of implementing repair measures, selected impact-echo results were verified. This field study was performed in 1991. This paper was presented at the AC1 Fall Convention in 1992.
N. A. Cumming and 0. S. Ooi
A major structural repair and strengthening program was undertaken at a large grain shipping terminal on Canada’s northwest coast. The work was required to correct problems of excessive cracking and internal delamination in the silo walls. During the repair work, it was necessary to survey 42 silos to locate zones of delaminated or deteriorated concrete. This was done successfully using the impact-echo procedure. This paper describes the impact-echo survey and its findings. It further discusses correlation of test results to actual conditions encountered in the field.
Mary Sansalone, Jiunn-Ming Lin,
and William B. Streett
This paper describes the use of a P-wave-speed measurement technique in conjunction with the impact-echo method to nondestructively and accurately determine the thickness of new concrete pavements and other plate-like structures. Portable instrumentation (computer, data-acquisition hardware, transducers, and impactors) that can be used to perform both wave speed and impact-echo measurements accurately and reliably is described. Results of preliminary field studies carried out on a Strategic Highway Research Program (SHRP) Test Section in Arizona are reported, including results obtained from pavements having different thicknesses, different strengths, and placed on different types of subgrades. The goal of this work 8 to lay the basis for an ASTM Standard Test Method for determining the thickness of concrete pavements and other plate-like structures.
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