Deterioration of concrete structures due to corrosion of steel reinforcement is a world-wide problem, especially in case of exposure to aggressive environment (e.g. marine atmosphere, aggressive chemicals, de-icing brine). Alternative reinforcing and pre-stressing material which do not corrode in such environments due to their non-susceptibility to ionic dissolution maybe a valuable alternative. Most important properties of these FRP materials for the application for civil engineering structures are: very high tensile strength in fiber direction, excellent corrosion resistance and very low density. More durable concrete structures and a range of new kinds of structural elements and of new applications are realizable with FRP reinforcement anchor pre-stressing.

"Concrete" is a name applied to any of a number of compositions consisting of sand, gravel, crushed stone, or other coarse material, bound together with various kinds of cementitious materials, such as lime or cements. When water is added, the mix undergoes a chemical reaction and hardens. An extraordinarily versatile building material, concrete is used for the utilitarian, the ornamental, and the monumental. While early proponents of modern concrete considered it to be permanent, it is, like all materials, subject to deterioration. This Brief surveys the principal problems posed by concrete deterioration, their likely causes, and approaches to their remedies. In almost every instance, remedial work should only be undertaken by qualified professionals. Faulty concrete repair can worsen structural problems and lead to further damage or safety hazards. Concrete repairs are not the province of do-it-yourselfers. Consequently, the corrective measures discussed here are included for general information purposes only; they do not provide "how to" advice.

Concrete (mixture of cement, aggregates and water) is a mass of aggregates (75%) glued together by a cement matrix (25%) in between all different sizes of aggregates. The cement portion of the concrete although makes up 25% of the volume, really determines all the physical properties in durability and strength areas. It is also where a large portion of concrete problems originates. One of the most critical components of good concrete is water. As pointed out by Mehta et al (1992) that water is "at the heart of most of the physical and chemical causes underlying the deterioration of concrete structures". Among other effects, moisture levels determine the risk of corrosion attack occurring on steel reinforcement and the rate of deleterious mechanisms such as alkali-aggregate reaction (AAR). At the same time a long-term ageing effect caused by drying-out of the cement matrix in concrete will be evident and the result will be reduced strength. A combination of dry and wet concrete may cause differential shrinkage which in turn may well lead to cracking. A balanced and stable moisture level would seem to be desirable, but cannot be achieved since the structural members are subject to different environments.

?Durability of concrete is defined as its ability to resist weathering action, chemical attack, abrasion or any other process of deterioration. Durable concrete will retain its orinal form, quality and serviceability when exposed to environment.? (ACI 201.2 R92).

Repair and rehabilitation of deteriorated concrete is an art as well as a science. The repair engineer must have the imagination to select and adapt any of several repair techniques to fix the existing defect. Why Repair and Rehabilitation of Concrete?"

Preplaced-aggregate concrete gets its name from the method used for placement. Formwork is constructed and the coarse aggregate fraction (3/4- to 1-1/2-in. minimum) (Ref c) is densely placed inside the formwork. The coarse aggregate is washed and screened just prior to placement to remove all fines. Grout is then injected through the forms to provide the matrix. Grouting is begun at the bottom of the preplaced aggregate. The grout typically consists of sand, cement, pozzolan, fluidifier, and an air-entraining admixture. The characteristics of the grout are affected by water content, sand grading, cement, pozzolan, and the types and amounts of admixtures. For each mixture there are optimum amounts of fillers and admixtures which produce the best pumpability or consistency. Proper proportioning of the structural grout mix components is necessary to produce the required strength and durability requirements of the finished preplaced-aggregate concrete. Mixture design tests are necessary for each job. Guidance on grout materials, coarse aggregate, and construction procedures for preplacedaggregate concrete can be found in EM 1110-2-2000.

A thirty page collection of slides highlighting the Latest Technologies for Concrete Repair and Protection, complete with Photographs, Illustrations, Diagrams and text.

Description:
Here are tips and suggestions on how to patch and repair concrete. Take the time to read these directions thoroughly to save time, money and effort. This will also help you end up with a neater, more satisfactory job-with far less waste. In this document you will find information about:

* Repairing Hairline Cracks
* Repairing Cracks in Sidewalks
* Repairing Concrete Driveways
* Repairing Cracks and Holes in Concrete Walls
* Patching Holes in Walks or Driveways
* Repairing Broken Corners on Concrete.

While concrete driveways look nice when they are new, over time the concrete can chip, crack and crumble. Cracks and potholes form due to the freezing and thawing of water that has seeped under the driveway through smaller cracks, weed or grass growth in small cracks, and general wear and tear. Regular maintenance will prevent the need to replace the existing driveway. This is usually easy to do and requires up to a half day to complete depending on the condition and size of your repairs.