ACI 345 1R:2006 download free.Guide for Maintenance of Concrete Bridae Members.
1 .2—Concrete bridge maintenance
Bridge deterioration usually occurs slowly at first and is often overlooked. In later stages of deterioration, however. sudden catastrophic events can occur, demanding immediate action. Progressive deterioration can be retarded and sonic- times avoided if proper systematic preventive maintenance is practiced (Carter and Kaufman 1990). Concrete bridge maintenance involves relatively inexpensive, repeatable activities that either prevent or minimize concrete life of bridge elements or are minor repairs that extend the service of the structural concrete members.
Concrete bridge maintenance is performed when the structural concrete member is still in good to fair condition, and can be subdivided into preventive and responsive maintenance.
1.2.1 Prevenlive nsainienance—Preventi ye maintenance procedures are done before deterioration is visible and the structural concrete member is still in good condition, and are usually planned at the design stage and started accordingly. Procedures include sealing, washing, caulking, and crack repair. A procedure not planned is installing retrofit drains.
1.2.2 Responsñe mainlenalzLe—Responsive maintenance procedures are usually more extensive, and are done in the early stages of the visible deterioration cycle. Procedures include small repairs. establishment of positive deck drainage systems. maintaining the functionality of deck joints, and similar activities to extend the service life of structural concrete members in bridges.
1.3—Purpose of maintenance
Maintenance activities are often more cost effective when the concrete is still in relatively good condition and is focused on those parts of a structure that face the most severe exposure conditions. Preventive maintenance addresses causes of the potential deterioration, as opposed to treatment, of the effects of deterioration. For example, sealing the deck surface reduces the infiltration of chloride. Proper preventive maintenance activities can reduce the rate of deterioration. extend service life, and reduce future repair costs (Carter 1989a). Responsive maintenance activities help to keep bridges operating safely and efficiently.
1.4—Limitations
Maintenance is no substitute for proper design and construction. Even proper maintenance will not produce desirable results when applied to improperly designed and constructed concrete bridge elements. Examples of improper design include insufficient reinforcing steel cover depths. excessive surface cracking, and poor drainage characteristics, such as ponding of chloride-contaminated water on a concrete bridge deck.
1.5—Timing of maintenance
Maintenance activities performed at the proper lime are extremely cost effective. Similarly, maintenance activities conducted at the wrong lime can be a poor investment. The wrong time for maintenance is after significant damage has occurred. Maintenance can prevent damage. hu it cannot restore deteriorated concrete. Damage such as scaling,
concrete cover, a reduced water-cement ratio (wic) and permeability, use of air-entrained concrete, corrosion proteclion systems. and eliminated simple spans and deck joints to increase service life and durability.
2.3.2 construction—Improper construction techniques that contribute to deterioration include insufficient compaction. inadequate cover over the reinforcement, inadequately entrained air, or increases in the concrete’s water-cementitious material ratio (wlcm) during placement. Improper surface finishing techniques. such as direct application of water to the surface, reduce durability and service life. Inadequate or late curing increases shrinkage cracking and permeability to chlorides.
2.3.3 Magerials—Material factors that contribute to deterioration include incompatibi lily between air-entraining and other admixtures. high w/cm concrete, and nondurable aggregates vulnerable to aggregate-alkali reactions and cycles of freezing and thawing.
2.3.4 Climate-related exposure conditions—Environment and climatic conditions contribute to varying rates of deterioration. For example, the deterioration of coastal bridges is entirely difkrent from that of high elevation mountain bridges. The mountain bridges are subjected to snow, moisture, cycles of freezing and thawing. and dcicing chemicals (Fig. 2.10), whereas coastal bridges may involve chloride exposure from salt water. The design. construction, and maintenance of bridges in one environment and climate needs to take into account many conditions not relevant to another environment and climate. Concrete maintenance materials are generally sensiti.e to ambient temperature and moisture conditions during application. Many products require moderate weather conditions. and are not suitable for application in extreme conditions (Carter 1989a; Department of Transport I 9)a: Federal Highway Administration 1994:
Bean 1988).
CHAPTER 3—CONSIDERATIONS
IN BRIDGE DESIGN
3.1 —General
Good bridge design details preveni or delay component deterioration. Some design issues related to reducing future bridge repair and rehabilitation Costs are discussed in the following sections.
3.2—Decks and curbs
3.2.1 Function—Bridge decks support traffic and transmit structural loads to girders. bearings, and substructure components. Curbs, medians, and parapets define the limits of vehicular traffic on a bridge deck. They generally serve a dual purpose as both a safety barrier and a deck drainage tool, because installation usually includes gutters and drains.
3.2.2 Typical problems—Decks and curbs are generally the most exposed portions of a bridge, especially where drainage is inadequate, and protective systems such as overlays or membranes are lacking. Curbs collect debris, snow, and salt from the riding surface, staying wet long after the riding surface has dried (Fig. 3.1). They also stay wet when the deck drainage systems listed in Section 4.2 become clogged. Because decks and curbs generally have high deterioration rates and repair and rehabilitation costs. maintenance activities that slow deterioration and delay expenditures are especially appropriate. Deck-maintenance costs vary significantly due to dift’erent exposure conditions. amount and type of traffic. drainage characteristics, environment and climate, and design standards. An example of the influence of design standards on deterioration is an asphalt-wearing surface. Asphalt concrete overlays are often used on bridge decks because they provide a smooth riding surface and are used as a protective wearing surface covering membranes. Asphalt concrete overlays are more permeable than the underlying concrete. The process of asphalt deterioration includes oxidation, shrinkage cracking. and increased permeability with time. Asphalt overlays trap chloride- laden water, thereby promoting and accelerating concrete deterioration (Skeet and Kriviak 1994). To protect the concrete, a membrane should be applied to the concrete surface before placing the asphalt.
Untreated bridge deck cracks result in decreased service life and increased repair and rehabilitation cost, and therefore. potential structural cracking needs to be addressed in
protected slope walls are considered to he nonstructural elements (Fig. 3.8). Stone. concrete, and concrete block are used to protect soil slopewalls.
3.5.2 Problems—Dirt and debris often accumulate on the substructure members below open bridge deck joints, and can become saturated with moisture and deicing chemicals (Fig. 3.9). If permitted to remain for extended periods of time, deicing chemicals will penetrate the concrete, causing corrosion of the reinforcing steel with subsequent spalling of the cover concrete. Leaking end joints result in erosion of soil slope walls, the exposing of foundation slabs and piles. and erosion of support soils from protected slopewalls.
A large number of bridges are built in. or adjacent to, chloride-rich brackish water or sea water. These structures are particularly vulnerable to chloride contamination and subsequent corrosion of reinforcing steel (Sagues 2(X)l). Substructure protection measures, such as low permeable concrete, increased clear concrete cover depth, cathodic protection. corrosion inhibitors, coatings. and encasements should be considered during design.
For structures built adjacent to stream or river crossings and in flood plains, scour protection measures should be considered in the design process. Scour protection measures are generally either scour reduction techniques or structural measures. Substructure settlement often causes movement related maintenance activities. Due to the inability to completely eliminate settlement, designers often estimate the amount of movement that will be induced by applied loads and design accordingly (Barker and Puckett 1997).
CHAPTER 4—DRAINAGE AND WASHING 4.1—General
Accumulation of dirt saturated with water and chemicals on bridge decks, beams, bearing, and other concrete elements accelerate concrete deterioration. While adequate drainage should reduce the need for cleaning, drainage systems can still become plugged and require maintenance. Short of replacing leaking deck joints or installing drain troughs to collect leakage, salt-exposed substructure areas should be cleaned and, if necessary, the concrete sealed to protect against deicing chemicals (Federal Highway Administration 1994).
4.2—Deck drainage
A bridge drainage system (including deck drains, scuppers. pipe. downspouts. and drain troughs) transports rainwater, ice. and snow meltwa;er away from the structural elements of the bridge. Scuppers that allow runoff water to cascade over superstructure and substructure elements should be avoided.
4.2.1 Funciüm—Drainage devices, such as drains and downspouts. prevent ponding of waler on properly sloped decks. Deck drainage is important for several reasons. Water on decks reduces skid resistance and increases the danger of vehicles hydroplaning or skidding on ice. Water on decks increases the rates of most concrete deterioration mechanisms, thereby reducing service life. Chlorides diffuse more quickly through saturated concrete, and reinforcing steel corrosion is usually accelerated.