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International Concrete Abstracts Portal

Showing 1-10 of 16 Abstracts search results

Document: 

SP151-15

Date: 

July 1, 1994

Author(s):

R. Navarro, R. J. Bucheral, R. J. Gulyas, and C. Glasscock

Publication:

Special Publication

Volume:

151

Abstract:

In the early 1960s, the city of El Paso constructed the Texas, Piedras, Raynor Street Bridge, a mile-long, four-lane artery leading to the center of downtown, and a main road important to many businesses and merchants. Time and the effects of chloride penetration from road salts, plus carbonation, took its toll on this bridge. Corrosion of the reinforcing steel led to spalls on pier caps and corrosion of columns, in addition to massive spalling and delaminations of the bridge deck and parapets. Early in 1990, a complete structural repair of the bridge was conducted. Attempts to repair the bridge were unsuccessful. Cracks and delaminations in the substrate and in the areas that had been repaired were evident. Due to safety concerns, the bridge was closed for structural repairs. Repairs began again in November 1991. The first stage of repair consisted of removing the previous failed materials and all unsound concrete. Once all areas were prepared, the low-pressure spraying of a structural, one-component, high-strength fiber reinforced, shrinkage-compensated product began. Three men were employed in the batching and spraying of the material--two at the hopper/mixing unit, and one operating the spray nozzle. Using a pump for placement, the contractor was able to realize a maximum of 3 yd 3 per hr. Workers with trowels followed closely behind the nozzle man, and, using a finishing aid, were able to finish the placement quickly and efficiently. Circular bridge piers were finished with a template to maintain the design cross section. A water-based curing compound was applied to insure maximum moisture retention and full hydration of the mortar. All patches were covered with thermal protection for 7 days, to allow for cure. Because the sprayed material adheres well, it performed exceptionally on all of the vertical and overhead repairs required on this bridge. Its excellent bond strength, outstanding structural properties, and low permeability provided the needed characteristics for this job. The sprayability of the product meant less labor required on the job and faster turnaround. Since this was the second repair of this bridge, these characteristics were very important. The product performed exceptionally well and resulted in a hard and dense repair.

10.14359/4374


Document: 

SP151-14

Date: 

July 1, 1994

Author(s):

R. S. Lanyi

Publication:

Special Publication

Volume:

151

Abstract:

Explains the technology developed by Alberta Transportation and Utilities for field prestressing repairs to precast, prestressed concrete bridge girders. This repair technique restores structural integrity quickly and cost effectively. Applications regarding high load impact damage and corrosion of prestressing strand are discussed, based on Reid Crowther's experience and application of this repair technique.

10.14359/4373


Document: 

SP151-13

Date: 

July 1, 1994

Author(s):

S. K. Ojha

Publication:

Special Publication

Volume:

151

Abstract:

Describes investigation and design of repairs to the approach decks of the Verrazano Narrows Bridge in New York City. In addition, all the joints will be replaced, electric manholes and pull boxes will be rehabilitated, and new power and communications cables will be pulled. These bare concrete decks exhibit extensive deterioration in the form of spalls, cracks, leakage, and efflorescence. A total of approximately 787,000 square feet of deck area will be repaired; this includes approximately 150,000 square feet of deck replacement. Total estimated cost is $45 million, and the construction duration is 5 to 6 years.

10.14359/4366


Document: 

SP151-12

Date: 

July 1, 1994

Author(s):

D. G. Manning and A. K. C. Ip

Publication:

Special Publication

Volume:

151

Abstract:

The concept of applying electrical current to concrete to move chloride ions away from the reinforcement has been known for many years, but only recently have practical techniques been developed. Paper describes, in chronological order, the treatment and performance of three structures in Ontario and a summary of theoretical and model studies undertaken in support of the field activities. In 1989, a section of a large bridge pier was treated with a commercial electrochemical migration process developed in Europe. The same process was used to treat the spirally reinforced columns on a freeway overpass in 1990. An alternative electrochemical migration process, developed under a SHRP contract, was applied to portions of the concrete abutments of a bridge in Northern Ontario in 1992. A novel aspect of the treatment was the use of lithium borate in the electrolyte to suppress any negative effects of the treatment on alkali-silica reactivity in the concrete. Recommended criteria for the selection of candidate structures and for treatment parameters are presented.

10.14359/4350


Document: 

SP151-11

Date: 

July 1, 1994

Author(s):

P. C. Hoffman and R. E. Weyers

Publication:

Special Publication

Volume:

151

Abstract:

A computer simulation study of the penetration of chloride through concrete bridge decks with overlays was undertaken. The chloride transport was modeled as apparent diffusion. The apparent diffusion approach was based on the analyses of chloride concentrations obtained from field measurements. Part of the field data included untreated concrete decks and decks overlaid with latex-modified concrete, low-slump dense concrete, or microsilica concrete. The overlay field data was limited in number and repair details. In particular, the overlay data base did not include three significant details: the amount of original deck material removed, the thickness of the overlay placed, and the resistance to chloride penetration of the overlay material versus the original deck material. Consequently, a computer simulation was used to investigate the impact these three repair details have on enhancing the service life of a deck repaired with an overlay. Quality of material was defined by the apparent diffusion constant, a measure of the resistance to chloride penetration. The ranges for apparent diffusion constants were estimated from the overlay data base. Service life was defined as the time required to reach a critical chloride threshold level.

10.14359/4349


Document: 

SP151-10

Date: 

July 1, 1994

Author(s):

S. Feliu, J. A. Gonzalez, and C. Andrade

Publication:

Special Publication

Volume:

151

Abstract:

On-site monitoring of the rate of corrosion of reinforcements is a priority task. There are various available devices for measuring I corr. Most of them entail a prior measurement of the {DELTA}E/{DELTA}I, which defines the polarization resistance (R p). However, direct estimations of R p from the {DELTA}E/{DELTA}I ratio are usually unfeasible with large structures because they provide an apparent polarization resistance (R p app) that differs to a greater or lesser extent from the true R p value depending on the experimental conditions. This paper analyzes the influence of some experimental factors (that is, the use of unconfined or guard ring-confined electric signals, the CE size, and the presence of active and passive areas in reinforcements) on the R p app accuracy of the I corr values derived from it. The more correct I corr values can be obtained by sensorized confinement of the electric signal applied with the aid of a guard ring and supplementary reference electrodes for monitoring the electric field confinement.

10.14359/4383


Document: 

SP151-09

Date: 

July 1, 1994

Author(s):

J. P. Broomfield

Publication:

Special Publication

Volume:

151

Abstract:

The linear polarization technique has been used in the laboratory for corrosion rate measurements of reinforcing bars in concrete, but some modifications are needed for its application to structures in the field. A new device has been developed, using this technique with a sensor-controlled guard ring to measure corrosion rates in concrete structures. Describes the performance of this device and its application. It also summarizes some results from reinforced concrete structures, including bridges, in Europe and the U.S.

10.14359/4348


Document: 

SP151-08

Date: 

July 1, 1994

Author(s):

M. L. Sennour, H. G. Wheat, and R. L. Carrasqillo

Publication:

Special Publication

Volume:

151

Abstract:

The role of concrete in the corrosion of steel in reinforced concrete has received a considerable amount of attention in recent years. This is due to the recognition of the strong relationship between the nature of the concrete and its ability to protect embedded steel. Therefore, in addition to some of the commonly used corrosion protection methods that focus on either coating the concrete, increasing the cover of the concrete, coating the reinforcing steel, or the use of inhibitors that change the nature of the surface of the reinforcing steel, other methods should be included that emphasize the role of the concrete mix design. Paper deals with the contribution of concrete to the corrosion of reinforcing steels in reinforced concrete. Twenty-six mix designs that represent concretes that could be used today were selected for study. Variables included cement content, water content, amount and type of fly ash, the addition of superplasticizers, and air entrainment. Strength and macrocell current were measured as a function of chloride exposure. The results of 1 year of cyclical exposure to 3.5 percent NaCl solution revealed that the concrete influences the corrosion process greatly. Furthermore, modification of concrete can become another method of corrosion protection through a better understanding of the relationship between the corrosion process and concrete mix design.

10.14359/4014


Document: 

SP151-07

Date: 

July 1, 1994

Author(s):

K. Recker

Publication:

Special Publication

Volume:

151

Abstract:

The importance of solvent- and plasticizer-free sprayable PU elastomers in the field of waterproofing of concrete structures has increased considerably over the last 10 years. Due to their excellent mechanical properties, their resistance to hydrolytic and microbial attack and chemical resistance, waterproofing membranes produced from spray-applied PU elastomers have proved to be very successful in many application areas in the building industry. Report deals with the chemical development of the PU system, the optimization of the processing technique, including the methods of preparing the concrete's surface to get good adhesion values and a seamless, watertight elastomeric membrane, the spray process itself, and the recommended machinery. Special attention is given to the influence of environmental conditions, such as temperature and relative humidity, on the mechanical properties and the performance of the waterproofing membrane in service. As the most important field application for spray-applied PU elastomers in Europe, bridge deck waterproofing membranes are discussed with special reference to the requirements set out in the regulations of the German "Bundesministerium fur Verkehr" and the "Bundesanstalt fur Materialprufung." The performance of spray-applied PU elastomers as waterproofing membranes for roofs, terraces, terracing in sports arenas, and car parks is discussed.

10.14359/4347


Document: 

SP151-06

Date: 

July 1, 1994

Author(s):

P. Schie, L. W. Breot. And M. Raupach

Publication:

Special Publication

Volume:

151

Abstract:

In recent years, corrosion of the reinforcement caused by chlorides, carbonation of the concrete, or low quality of the concrete cover has caused serious damage to concrete bridges. Apart from other measures, one possible means of repairing damage at the concrete surface due to reinforcement corrosion is to apply a coating to the concrete surface to reduce the water content of the concrete. If the coating has a sufficient high-penetration resistance against water and if no water enters the concrete from other sources, the water content of the concrete will remain low after the application of the coating, or the concrete will dry out slowly, provided that water can evaporate through the coating or through the opposite concrete surface. A multi-ring electrode method for determining the water distribution within the concrete near the reinforcement and the steel surface has been developed at the Institute of Building Materials Research in Aachen, Germany. The electrode is used to determine AC resistance between nine noble metal rings, allowing the water content to be estimated at eight different distances from the concrete surface. To estimate the effect of different types of coatings, time-dependent changes in resistance following wetting of coated and uncoated concrete surfaces were monitored. Fundamental laboratory investigations of the influence of concrete compositions, carbonation, and chloride application were also carried out.

10.14359/4346


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