[PDF] Performance And Constructability Of Silica Fume Bridge Deck Overlays eBook
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The effects of construction practices and material properties on the performance of concrete bridge decks are evaluated. Emphasis is placed on comparing bridge decks with silica fume and conventional concrete overlays and determining if the silica fume overlays commonly used on bridges in Kansas are performing at a level that justifies the extra cost and construction precautions. Forty continuous steel girder bridges, 20 with silica fume overlays, 16 with conventional overlays and four with monolithic bridge decks are included in the study.
TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 423: Long-Term Performance of Polymer Concrete for Bridge Decks addresses a number of topics related to thin polymer overlays (TPOs). Those topics include previous research, specifications, and procedures on TPOs; performance of TPOs based on field applications; the primary factors that influence TPO performance; current construction guidelines for TPOs related to surface preparation, mixing and placement, consolidation, finishing, and curing; repair procedures; factors that influence the performance of overlays, including life-cycle cost, benefits and costs, bridge deck condition, service life extension, and performance; and successes and failures of TPOs, including reasons for both.
The purpose of this research was to examine the applicability of ternary binder systems containing ordinary portland cement (OPC), class C fly ash (FA) and silica fume (SF) for bridge deck concrete. This was accomplished in two parts, the laboratory part and a field application part. During the laboratory studies, four ternary mixtures, each containing either 20% or 30% FA and either 5% or 7% SF were subjected to four different curing regimes (air drying, 7 days curing compound application and 3 or 7 days wet burlap curing). In general, all four ternary mixtures exhibited very good water and chloride solution transport-controlling properties (resistance to chloride-ion penetration, chloride diffusivity and rate of water absorption). However, it was concluded that in order to ensure adequate strength, good freezing and thawing resistance, satisfactory resistance to salt scaling, and adequate shrinkage cracking resistance the FA content should not exceed 20%, SF content should not exceed 5% (by total mass of binder) and paste content should be kept below 24% by volume of concrete. Further, wet burlap curing for a minimum of 3 days was required to achieve satisfactory performance and to obtain a reliable assessment of in-situ compressive strength (up to 28 days) using maturity method. The second part of this research examined the performance of ternary concrete containing 20% FA and 5% SF in the pilot HPC bridge deck constructed in northern Indiana. Using maturity method developed for the purpose of this study, it was determined that the unexpectedly high RCP values of concrete placed late in the construction season were mostly attributed to low ambient temperature. Additional applications of the developed maturity method were also demonstrated. These include assessment of risk of scaling and reduction in time to corrosion initiation as a function of construction date, as well as estimation of long-term RCP values of concrete subjected to accelerated curing.
Overlaying bridge decks has remained one of the best rehabilitation methods to extend their service life, and the Virginia Department of Transportation (VDOT) has been a leader in the use of bridge deck overlays. Although VDOT has extensive experience in overlays, the long-term performance of overlays has not been entirely understood. One of the biggest challenges for studying the performance of overlays is that only minimal information is available in bridge inventory and inspection records. This limits any scientific assessment of this system. Therefore, the purpose of this study was to provide a strong framework for the understanding of the long-term performance of overlays and the factors affecting them. This Phase II report reports on an extensive data collection process that led to the development of a robust database of 133 overlaid bridge decks after verification of historical inspection reports, verification of as-built plans and communication with VDOT district bridge engineers. This helped in developing a model for understanding the amount of time it takes for bridge decks to require the first major rehabilitation and the major factors influencing the durability. A database of information about overlays that were replaced at the end of their functional service life was compiled. This helped develop a multiple regression model for understanding the factors that affected the durability of overlays. Survival analyses were conducted to estimate the service life of overlays and corresponding risk. As a preventive method, epoxy concrete (EC) overlays were predicted to serve an average of 20.9 years, with 18 to 22 years at a 95 percent confidence level. As a rehabilitative method, rigid concrete overlays were predicted to serve an average of 25.9 years, with 21 to 32 years at a 95 percent confidence level. The recent trend of preferred overlay types has been identified as EC and very-early- strength latex-modified concrete (VELMC) overlays. EC overlays have proven to be one of the better performing overlays through extensive VDOT experience. VELMC overlays are an improvement upon latex-modified concrete overlays by vastly reducing the time of construction and thus become more suitable for decreased construction time, reduced traffic disruption, and lessened worker exposure to the field environment. An important discovery was the identification of the influence of the degree of deck damage prior to overlaying on the service life of overlays. Preventive EC overlays should be used in a preventive sense, as the name suggests. If preventive EC overlays are installed on bridge decks with spalls, patches, or delaminations, irrespective of the amount of damage, an increased rate of deterioration in the overlays is likely to follow. The future performance of rehabilitative overlays such as latex-modified concrete, silica fume, and VELMC overlays will not be influenced by the presence of bridge deck damage prior to overlaying. This might be because of the removal of deteriorated concrete before these rigid overlays are constructed. This emphasizes the importance of proper removal of poor quality concrete from bridge decks before overlaying during rehabilitation.
Bridges in Kansas are exposed to winter conditions, including deicing chemicals used to keep the roads and bridges clear of ice and snow. These chemicals and water are harmful to the concrete and the steel reinforcing bars used in bridge structures. The objective of this study was to develop a durable thin bonded overlay with chloride resistance to protect the reinforcing steel of the bridge deck. Overlays were developed and monitored after their initial placement on four bridges. The overlay materials selected by the Kansas Department of Transportation (KDOT) had promising results from laboratory testing. Four different overlay materials were selected based upon KDOT's laboratory results and were tested on four separate bridge decks. Three of the bridges are located in Greenwood County and one in Sedgwick County. All four bridges were new construction; the three in Greenwood County are pre-stressed concrete girder design and the Sedgwick County Bridge is a steel girder design. The data from the testing and monitoring were used to determine if there are benefits to using thin bonded overlays for bridge deck wearing surfaces and which types of thin bonded overlays have the largest benefits. The materials chosen for the overlays were: Type IP cement concrete, Type IP cement with 3% silica fume concrete, Type I / II cement with 5% silica fume and polypropylene fibers concrete, and Type II cement with 5% silica fume and steel fibers concrete. Construction samples and bridge deck cores were tested for compressive strength, permeability, chloride concentration, overlay adhesion, and cracking resistance. The permeability tests showed the overlays containing the Type IP cement were the least permeable while the steel and polypropylene fiber overlays were the most permeable. The Type IP cement overlays meet the design specification of passing less than 1,000 coulombs (1.5 inch thickness); however, the overlays with the fibers do not. The ability of each overlay to resist chloride ion migration will only truly be known as 'in service' time accrues. Based upon the chloride ion contamination after five years, all overlays would appear to be functioning equally unless there is cracking in the overlay.
The Iowa Method for bridge deck overlays has been very successful in Iowa since its adoption in the 1970s. This method involves removal of deteriorated portions of a bridge deck followed by placement of a layer of dense (Type O) Portland Cement Concrete (PCC). The challenge encountered with this type of bridge deck overlay is that the PCC must be mixed on-site, brought to the placement area and placed with specialized equipment. This adds considerably to the cost and limits contractor selection. A previous study (TR-427) showed that a dense PCC with high-range water reducers could successfully be used for bridge deck overlays using conventional equipment and methods. This current study evaluated the use of high performance PCC in place of a dense PCC for work on county bridges. High performance PCC uses fly ash and slag to replace some of the cement in the mix. This results in a workable PCC mix that cures to form a very low permeability overlay.