Structure Repair with Cast-in-Place Conventional Concrete

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Structure Repair with Cast-In-Place Conventional Concrete

The most frequently used and the most economical method of repair is the replacement of defective concrete with new conventionally placed concrete. A repair made with conventional concrete may deteriorate again due to reasons of initial damage such as acid attack, aggressive water attack, or even abrasion-erosion. The service life may be extended by modifying Portland cement concrete with silica fume, acrylics, styrene-butadiene latex, or epoxy. The new cementitious repair material must be compatible with the existing concrete substrate. The best choice is to use same materials and same proportions as the original construction. Conventional concrete is composed of Portland cement, aggregates, and water, while admixtures are used to entrain air, accelerate or retard hydration, improve workability, reduce mixing water requirements, increase strength, or alter other properties of the concrete. Pozzolanic materials, such as fly ash or silica fume, may be used in combination with Portland cement for economy and to provide specific properties such as reduced early heat of hydration, improved later-age strength development, reduced permeability, or increased resistance to alkali-aggregate reaction and sulfate attack. To minimize shrinkage cracking, the repair concrete must have a w/cm as low as possible and a coarse aggregate content as high as possible.   Conventional concrete is often used in repairs involving relatively thick sections (>/= 50mm) and large volumes of repair material. It is suitable for partial and full depth repairs and is most commonly used for repairs of slabs, walls, columns, piers, hydraulic structures, bridge decks and parking structure decks. It is also suitable for repairs in marine environments because the typically high humidity in such environments reduces the chances of shrinkage. Conventional concrete is readily available, economical, and is relatively easy to produce, place, finish, and cure. It can have same properties as the original concrete. Conventional concrete can be easily placed under water using a number of well-recognized techniques. Conventional concrete is not recommended for repairs in cases where the causes of original distress have not been removed. When the new material is being placed in a bonded overlay on a material that has already gone through almost all of its expected shrinkage, extra shrinkage of new material can cause separation of the overlay. Conventional concrete has also problems under hot and cold climates. Low-slump concrete overlays are PCC overlays that have a modified mix proportion to produce a denser and more durable concrete. It sometimes increases the load-carrying capacity of the underlying concrete. Portland cement- concrete bonded overlays provide a protective barrier to deicing salts. Depending on the function, the thickness of an overlay may range from 40mm to almost any reasonable thickness. A Portland-cement-based overlay is suitable for resurfacing of spalled or cracked concrete surfaces, increasing cover over reinforcing steel, adding slip resistance, leveling floors, repair of concrete surfaces damaged by abrasion, freezing, or fire, and the repair of deteriorated pavements. They have good bond characteristics to a properly prepared substrate and increased durability because of lower w/c. These systems are less expensive than modified concrete systems. Portland-cement-based overlays are not recommended in situations where the original damage was caused by chemical attack. The reason is that the chemical attack will continue in the future. Portland cement overlays are used as a wearing course on parking garages and plaza decks to get proper drainage. They may also be used in conjunction with traffic or pedestrian elastomeric membrane systems. Read More: Advance Cast-in-Place Concrete for Repair of Structure