Dense Concrete Layer as Top Course of Bridge Deck Construction, HR-502, 1990

The use of deicing salts in this part of the country is a necessity to remove ice from our bridges. The use of these salts has always been a problem since the chloride-ions penetrate the concrete and reach the steel and cause corrosion which eventually cause deterioration of both the steel and concrete. One method used to try to prevent this from happening was to apply a waterproof membrane to the concrete after it was placed. This method did help, but was not cost effective as the longevity of the membrane system was of relatively short duration. For this reason, this research project was initiated. After the original deck was placed a second layer of concrete about 1 1/2" thick was placed on top. Biennial evaluation of the decks included testing for delaminations and steel corrosion. Cores were also obtained for a chloride analysis. Testing and observations showed the two-layer bridge deck to be effective in preventing corrosion. Since the time this project was initiated, epoxy steel has been introduced and is a cost effective way to protect the steel from corrosion.

Low Permeability of Concrete for Bridge Deck Overlay, MLR-89-1, 1993

The penetration of chloride ions from deicing salts into the portland cement concrete of bridge decks can cause corrosion and serious damage to the reinforcing steel. Concrete properties which prevent chloride penetration into the bridge deck and provide a good structural and economic wearing surface are desirable. A variety of mix designs have been tried in the past in search of improved performance and lower costs for bridge deck overlay concrete. A group of mixes with various designs have been tested in this project and results are being compared to determine which concrete mix appears to be the most cost effective and resistant to chloride penetration for bridge deck overlay use.

Impact of Deck Cracking on Durability, TR-405, 2000

Concrete bridge decks subjected to corrosive environment because of the application of de-icing chemical could deteriorate at a rapid rate. In an effort to minimize corrosion of the reinforcement and the corresponding delaminations and spalls, the Iowa Department of Transportation started using epoxy-coated rebars (ECR) in the top mat of reinforcing around 1976 and in both mats 10 years later. The overall objective of this research was to determine the impact of deck cracking on durability and estimate the remaining functional service life of a bridge deck. This was accomplished by conducting a literature review, visually inspecting several bridge decks, collecting and sampling test cores from cracked and uncracked areas of bridge decks, determining the extent to which epoxy-coated rebars deteriorate at the site of cracks, and evaluating the impact of cracking on service life.

Protection of Structural Concrete Substructures, HR-220, Progress Report, 1984

The corrosion of reinforcing steel within concrete has always been a problem in construction of bridge decks. With low slump concrete and epoxy rebar, progress has been made in controlling the corrosion. There is concern, however, that the chloride also attacks the substructures, specifically the pier columns. They are subject to chloride attack by chemical deicers in the drainage from the bridge deck. Piers supporting grade separation bridges are also subject to chlorides contained in the direct splash from the lower level traffic. In this project, a field evaluation was conducted to evaluate the effectiveness of commercially available products in preventing chloride intrusion.

Bridge Deck Waterproofing Membrane Study, R-262, 1974

One of the main problems of bridge maintenance in Iowa is the spalling and scaling of the decks. This problem stems from the continued use of deicing salts during the winter months. Since bridges will frost or freeze more often than roadways, the use of deicing salts on bridges is more frequent. The salt which is spread onto the bridge dissolves in water and permeates into the concrete deck. When the salt reaches the depth of the reinforcing steel and the concentration at that depth reaches the threshold concentration for corrosion (1.5 lbs./yd. 3 ), the steel will begin to oxidize. The oxidizing steel must then expand within the concrete. This expansion eventually forces undersurface fractures and spalls in the concrete. The spalling increases maintenance problems on bridges and in some cases has forced resurfacing after only a few years of service. There are two possible solutions to this problem. One solution is discontinuing the use of salts as the deicing agent on bridges and the other is preventing the salt from reaching or attacking the reinforcing steel. This report deals with one method which stops the salt from reaching the reinforcing steel. The method utilizes a waterproof membrane on the surface of a bridge deck. The waterproof membrane stops the water-salt solution from entering the concrete so the salt cannot reach the reinforcing steel.

A Further Evaluation of Concrete Bridge Deck Surfacing in Iowa, MLR-79-1, 1979

The Iowa Department of Transportation has overlaid 446 bridge decks with low slump dense concrete from 1964 through October 1978. The overall performance of these decks has been satisfactory. Nineteen bridges that were resurfaced with either low slump dense concrete (LSDC) or latex-modified concrete were analyzed for chloride content, electrical corrosion potential, delaminations or debonding, and deck surface condition. The resurfacing ages of these bridges range from 5 to 13 years. None of the bridges showed any evidence of surface distress and the chloride penetration into the resurfacing concrete is relatively low. There are delaminations in the original decks below the resurfacing on the majority of bridges examined. The delaminations are concluded to be caused by either (A) reinforcing steel corrosion, (B) not removing all delaminated concrete prior to placing the resurfacing concrete, or (C) creating an incipient fracture in the top surf ace of the original deck through the use of scarification equipment. The active corrosion of the reinforcing steel is predominately in the gutter line on the majority of bridges evaluated. Recommendations for future deck repairs include removal of concrete to the top layer of reinforcing steel in areas where an electrical corrosion potential of -0.35V or more is detected, providing more positive methods of locating delaminated concrete, and treating the curb and gutter line to reduce the potential damage from salt water.

RFID Tags for Detecting Concrete Degradation in Bridge Decks, RB08-011, 2013

Steel reinforcing bar (rebar) corrosion due to chlorine ingress is the primary degradation mechanism for bridge decks. In areas where rock salt is used as a de-icing agent, salt water seeps into the concrete through cracks, causing corrosion of the rebar and potentially leading to catastrophic failure if not repaired. This project explores the use of radio frequency identification (RFID) tags as low-cost corrosion sensors. RFID tags, when embedded in concrete, will fail due to corrosion in the same manner as rebar after prolonged exposure to salt water. In addition, the presence of salt water interferes with the ability to detect the tags, providing a secondary mechanism by which this method can work. During this project, a fieldable RFID equipment setup was constructed and tested. In addition to a number of laboratory experiments to validate the underlying principles, RFID tags were embedded and tested in several actual bridge decks. Two major challenges were addressed in this project: issues associated with tags not functioning due to being in close proximity to rebar and issues associated with portland concrete coming in direct contact with the tags causing a detuning effect and preventing the tags from operating properly. Both issues were investigated thoroughly. The first issue was determined to be a problem only if the tags are placed in close proximity to rebar. The second issue was resolved by encapsulating the tag. Two materials, polyurethane spray foam and extruded polystyrene, were identified as providing good performance after testing, both in the lab and in the field.

Galvanized Bridge Deck Reinforcing, HR-504, 1992

The deterioration of bridge decks due to steel corrosion is a problem encountered several years ago. This project, using galvanized reinforcement, began over twenty years ago. Since that time, epoxy coated reinforcement has become the specified material used in bridge decks. The decks researched in this project are located on 1-35 in Story County. They were constructed in 1967. The results from the testing done on this project show that galvanizing protects steel from corrosion due to deicing salts, resulting in less/no concrete deterioration.

Cathodic Protection for a Continuous Box Girder Bridge Deck, HR-553, 1993

Bridge deck deterioration due to corrosive effect of deicers on reinforcing steel is a major problem facing many agencies. Cathodic protection is one method used to prevent reinforcing steel corrosion. The application of a direct current to the embedded reinforcing steel and a sacrificial anode protects the steel from corrosion. This 1992 project involved placing an Elgard Titanium Anode Mesh Cathodic Protection System on a bridge deck. The anode was fastened to the deck after the Class A repair-work and the overlay was placed using the Iowa Low Slump Dense Concrete System. The system was set up initially at 1 mA/sq ft.

Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials, HR-1069, 2003

Transverse joints are placed in portland cement concrete pavements to control the development of random cracking due to stresses induced by moisture and thermal gradients and restrained slab movement. These joints are strengthened through the use of load transfer devices, typically dowel bars, designed to transfer load across the joint from one pavement slab to the next. Epoxy coated steel bars are the materials of choice at the present time, but have experienced some difficulties with resistance to corrosion from deicing salts. The research project investigated the use of alternative materials, dowel size and spacing to determine the benefits and limitations of each material. In this project two types of fiber composite materials, stainless steel solid dowels and epoxy coated dowels were tested for five years in side by side installation in a portion of U.S. 65 near Des Moines, Iowa, between 1997 and 2002. The work was directed at analyzing the load transfer characteristics of 8-in. vs. 12-in. spacing of the dowels and the alternative dowel materials, fiber composite (1.5- and 1.88-in. diameter) and stainless steel (1.5-in. diameter), compared to typical 1.5-in. diameter epoxy-coated steel dowels placed on 12-in. spacing. Data were collected biannually within each series of joints and variables in terms of load transfer in each lane (outer wheel path), visual distress, joint openings, and faulting in each wheel path. After five years of performance the following observations were made from the data collected. Each of the dowel materials is performing equally in terms of load transfer, joint movement and faulting. Stainless steel dowels are providing load transfer performance equal to or greater than epoxy-coated steel dowels at the end of five years. Fiber reinforced polymer (FRP) dowels of the sizes and materials tested should be spaced no greater than 8 in. apart to achieve comparable performance to epoxy coated dowels. No evidence of deterioration due to road salts was identified on any of the products tested. The relatively high cost of stainless steel solid and FRP dowels was a limitation at the time of this study conclusion. Work is continuing with the subject materials in laboratory studies to determine the proper shape, spacing, chemical composition and testing specification to make the FRP and stainless (clad or solid) dowels a viable alternative joint load transfer material for long lasting portland cement concrete pavements.

Evaluation of Stainless Steel Culvert Pipe in Mahaska County, Iowa, HR-2001

Corrosion of culvert pipe in Iowa in general is not a serious problem. However, it is potentially significant in some local areas. An opportunity to make a limited durability study of stainless steel pipe was presented when a local fabricating company expressed interest in a cooperative field experiment. The potential of stainless steel pipe is to reduce maintenance costs that are incurred through replacement and upkeep. A new stainless steel material, Allegheny Metal MF-1, was used in a partial fabrication demonstration and later these demonstration sections were delivered to the selected field site for placement.

Performance of Poly-Carb, Inc. Flexogrid Bridge Overlay System, MLR-86-04, 2001

Intrusion of deicing materials and surface water into concrete bridge decks is a main contributor in deck reinforcing steel corrosion and concrete delamination. Salt, spread on bridge decks to melt ice, dissolves in water and permeates voids in the concrete deck. When the chloride content of the concrete in contact with reinforcing steel reaches a high enough concentration, the steel oxidizes. In Iowa, the method used to reduce bridge deck chloride penetration is the application of a low slump dense concrete overlay after the completion of all Class A and Class B floor repairs. A possible alternative to the use of dense concrete overlays, developed by Poly-Carb, Inc., is the MARK-163 FLEXOGRID Overlay System. FLEXOGRID is a two component system of epoxy and urethane which is applied on a bridge deck to a minimum thickness of ¼ inch. An aggregate mixture of silica quartz and aluminum oxide is broadcast onto the epoxy at a prescribed rate to provide deck protection and superior friction properties. The material is mixed on site and applied to the deck in a series of lifts (usually two) until the desired overlay thickness has been attained.

Iowa State Highway 92 Over Drainage Ditch #25: Performance Evaluation - Galvanized Reinforcing Bars -- Louisa County, Iowa, 2015

Several strategies are available to the Iowa Department of Transportation (IaDOT) for limiting deterioration due to chloride-induced corrosion of embedded reinforcing bars in concrete bridge decks. While the method most commonly used throughout the Midwestern United States is to construct concrete bridge decks with fusion-bonded epoxy-coated reinforcing bars, galvanized reinforcing bars are an available alternative. Previous studies of the in situ performance of galvanized reinforcing bars in service in bridge decks have been limited. IaDOT requested that Wiss, Janney, Elstner Associates, Inc. (WJE) perform this study to gain further understanding of the long-term performance of an Iowa bridge deck reinforced with galvanized reinforcing bars. This study characterized the condition of a bridge deck with galvanized reinforcing bars after about 36 years of service and compared that performance to the expected performance of epoxy-coated or uncoated reinforcing bars in similar bridge construction. For this study, IaDOT selected the Iowa State Highway 92 bridge across Drainage Ditch #25 in Louisa County, Iowa (Structure No. 5854.5S092), which was constructed using galvanized reinforcing bars as the main deck reinforcing. The scope of work for this study included: field assessment, testing, and sampling; laboratory testing and analysis; analysis of findings; service life modeling; and preparation of this report. In addition, supplemental observations of the condition of the galvanized reinforcing bars were made during a subsequent project to repair the bride deck.

The Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete, TR-480, 2008

This research project investigated the effects of concentrated brines of magnesium chloride, calcium chloride, sodium chloride, and calcium magnesium acetate on portland cement concrete. Although known to be effective at deicing and anti-icing, the deleterious effects these chemicals may have on concrete have not been well documented. As a result of this research, it was determined that there is significant evidence that magnesium chloride and calcium chloride chemically interact with hardened portland cement paste in concrete resulting in expansive cracking, increased permeability, and a significant loss in compressive strength. Although the same effects were not seen with sodium chloride brines, it was shown that sodium chloride brines have the highest rate of ingress into hardened concrete. This latter fact is significant with respect to corrosion of embedded steel. The mechanism for attack of hardened cement paste varies with deicer chemical but in general, a chemical reaction between chlorides and cement hydration products results in the dissolution of the hardened cement paste and formation of oxychloride phases, which are expansive. The chemical attack of the hardened cement paste is significantly reduced if supplementary cementitious materials are included in the concrete mixture. Both coal fly ash and ground granulated blast furnace slag were found to be effective at mitigating the chemical attack caused by the deicers tested. In the tests performed, ground granulated blast furnace slag performed better as a mitigation strategy as compared to coal fly ash. Additionally, siloxane and silane sealants were effective at slowing the ingress of deicing chemicals into the concrete and thereby reducing the observed distress. In general, the siloxane sealant appeared to be more effective than the silane, but both were effective and should be considered as a maintenance strategy.

The Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete, TR-480, Implementation Guide, 2008

This research project investigated the effects of concentrated brines of magnesium chloride, calcium chloride, sodium chloride, and calcium magnesium acetate on portland cement concrete. Although known to be effective at deicing and anti-icing, the deleterious effects these chemicals may have on concrete have not been well documented. As a result of this research, it was determined that there is significant evidence that magnesium chloride and calcium chloride chemically interact with hardened portland cement paste in concrete resulting in expansive cracking, increased permeability, and a significant loss in compressive strength. Although the same effects were not seen with sodium chloride brines, it was shown that sodium chloride brines have the highest rate of ingress into hardened concrete. This latter fact is significant with respect to corrosion of embedded steel. The mechanism for attack of hardened cement paste varies with deicer chemical but in general, a chemical reaction between chlorides and cement hydration products results in the dissolution of the hardened cement paste and formation of oxychloride phases, which are expansive. The chemical attack of the hardened cement paste is significantly reduced if supplementary cementitious materials are included in the concrete mixture. Both coal fly ash and ground granulated blast furnace slag were found to be effective at mitigating the chemical attack caused by the deicers tested. In the tests performed, ground granulated blast furnace slag performed better as a mitigation strategy as compared to coal fly ash. Additionally, siloxane and silane sealants were effective at slowing the ingress of deicing chemicals into the concrete and thereby reducing the observed distress. In general, the siloxane sealant appeared to be more effective than the silane, but both were effective and should be considered as a maintenance strategy.