One of the most serious and costly problems presently facing highway agencies is premature bridge deck deterioration. In many cases decks designed to last forty years have required major surface repairs after only ten years of service due to spalling. This spalling has been determined to be related to deicing chemical "chloride" induced corrosion of the rebars.
In response to this problem, Mn/DOT initiated a comprehensive program to restore damaged decks and protect new decks. At present, the two basic approaches to solving the problem are:
1. Prevent the penetration of chloride ions and moisture into the deck through the use of protective membranes, special concrete overlays and deck sealers.
2. Coat the rebars with epoxy to prevent chloride Ions from reaching the steel once the surrounding concrete has become contaminated.
Bridge decks were constructed or reconstructed using protective membranes, special concrete overlays and coated rebars. Testing and evaluation consist of visual observations, delamination detection, determining depth of concrete cover over rebars, electrical potential measurements and electrical resistance measurements.
This report represents data obtained through a comprehensive field study encompassing some 70 bridge decks with a variety of protection systems in place and subject to varying traffic volumes and conditions of exposure. Decks repaired also exhibited varying initial condition and extents of concrete removal prior to rehabilitation.
The basic categories of protection systems under study are as follows:
1. Membrane and bituminous overlay.
2. Special concrete overlays.
3. Coated rebar systems.
Primary testing of these systems consisted of:
1. Delamination/debonding surveys.
2. Clear cover measurement.
3. Half cell potential testing.
4. Chloride penetration testing.
5. Visual surveys.
The criteria followed for evaluation of system performance were separated into two elements:
1. System effectiveness (how well i.t does its job).
2. System durability (how., long it performs under service conditions
The Minnesota Department of Transportation (Mn/DOT), contracted with Donohue and Associates, Inc. of Sheboygan, Wisconsin to survey five bridge decks and approximately 79 lane miles of continuously reinforced concrete pavement (CRCP) and asphalt-overlaid jointed reinforced concrete pavement in Minnesota. All of the work was in the St. Paul-Minneapolis metropolitan area except for two bridge decks, located in Moose Lake and Cloquet. Several test sections were also surveyed with Mn/DOT's Delamtect for purposes of comparing the results produced by the two techniques.
The objective of this study is to evaluate the effectiveness of various sealers for use on concrete bridge decks. The bridge deck selected for this project carries I-35E over Jefferson Avenue in St. Paul. The bridge was built in 1974 and overlaid with low slump dense concrete in 1983. It was first opened to traffic in November 1984. Traffic volume is 6600 ADT with no heavy commercial traffic.
A delaminated concrete bridge deck was repaired in 1983 using epoxy injection and conventional concrete patching techniques. Approximately half of the deck was repaired by each method.
The deck was monitored for two years to determine the durability of the repairs made by epoxy injection. It appears that these repairs are holding up well. Cost information indicates that the epoxy injection may be a viable alternative to concrete patching where delaminations are present, but the surface deck is sound.
A typical concrete pavement has expansion and contraction joints across and along the pavement surface. The joints allow the pavement to change in dimension with changes in temperature. A continuously reinforced concrete pavement (CRCP) does not have expansion or contraction joints. Random, closely spaced cracks are expected to develop naturally and allow for expansion and contraction due to temperature changes. The many random cracks eliminate expensive joint maintenance. This maintenance-free service life feature has not occurred in Minnesota.
During past years, an increasing number of CRCP s have exhibited deterioration where pieces of concrete separate from the surface of the pavement and potholes result. This is termed spalling. The frequency and extent of this deterioration has progressed from isolated and random to widespread and frequent. A comprehensive program was initiated by Mn/DOT to study this problem and develop possible solutions.
This CRCP inventory is a physical evaluation of the extent of corrosion on random, sections of pavement. It is related to concurrent efforts which will evaluate CRCP rehabilitation, techniques.
Premature deterioration of continuously reinforced concrete pavement (CRCP) has become a serious problem in Minnesota. Spalling and delaminations, similar to those found on deteriorating bridge decks, have appeared on sections of CRCP, many after less than 10 years of service. Tension failures, or rupturing of the longitudinal reinforcing steel caused by loss of section due to corrosion, have also been a problem. Other sections of CRCP remain in good condition, but the potential for early deterioration exists for them, as well. Two methods were tried to halt the ongoing corrosion: a cathodic protection system and a low slump dense concrete (LSDC) overlay. Robert G. Tracy, Research Project Engineer, (now in private business), designed and supervised the cathodic protection system project. Installation was done through the cooperation of District 9 Maintenance and Physical Research personnel. Construction of the LSDC overlay was done by Progressive Contractors, Inc., under the control of Paul Juckel, Project Supervisor, Oakdale. The projects were done in conjunction with the FHWA's Highway Planning and Research Program.
The Minnesota Department of Transportation (Mn/DOT) conducted a comprehensive research program in response to the problem of bridge deck deterioration. This program placed emphasis on protecting newer decks as well as repairing damaged ones. Two basic approaches were applied to protecting bridge decks:
1. Prevent the penetration of chloride ions to the rebars by using special concrete overlays, deck sealers and waterproof membranes.
2. Use galvanized or epoxy coated rebars to protect the steel after chloride ions have contaminated the surrounding concrete.
Bridge decks were constructed or repaired using the systems mentioned above. The decks covered by this study were built or repaired from 1974 to 1978 and were tested annually through 1981. Testing consisted of visual observations, electrical potential corrosion measurements, measuring depth of concrete cover over rebars, delamination detection and determining chloride ion content.
From 1976-1981 the Minnesota Department: of Transportation (Mn/DOT) conducted a research study to evaluate several new types of bridge deck protective systems in an effort to reduce the extent of reinforcing steel corrosion. These systems included membranes with bituminous overlays, modified concrete overlays, and coated rebars.
When the study concluded, it: was felt that a long term study was needed to provide a better indication of service life. Two decks from each system type which appeared promising were selected for extended testing. This extended study continued the evaluation program through 1990.
Pavement drainage systems have become a common addition to construction and reconstruction plans. Several types of transverse and longitudinal drains that vary in shape, size and cost are often included in designs although little is known about their performance.
This study describes and evaluates the drainage characteristics and pavement performance of four drainage systems under jointed portland cement concrete pavement. Included are the Minnesota Department of Transportation (Mn/DOT) standard dense graded base. two dense graded base sections incorporating transverse drains placed under the transverse joints, and permeable asphalt stabilized base, a design which reflects current Mn/DOT drainable base thinking. All sections include longitudinal edge drains.
Construction of the test sections was done during 1989. Monitoring of rainfall and drainage began in 1990 and continued through 1994. Experiment variables include drainage flows, percent of rainfall drained, time to drain, base and subgrade moisture content, and pavement and joint durability. Pavement performance evaluations will continue over the next several years.
This paper presents an overview of the study, examines the data, and summarizes the findings. The study is expected to lead to improvements in the design of positive pavement drainage systems.
