07-07-2012, 01:18 PM
Cracks and Repairs R.C.C. Structures
Session4.10_RCCcracks_repair(Rev).ppt (Size: 918 KB / Downloads: 248)
Non Structural cracks:Moisture Changes
Building materials expand on absorbing moisture and shrink on drying. These are generally reversible. Shrinkage in concrete or mortar depends on a number of factors
Cement concrete: Richer the mix greater is the drying shrinkage.
Water content: More water in mix induces greater shrinkage
Aggregates : Large aggregates with good grading has less shrinkage for same workability as less water is used
Some Measures for controlling shrinkage
Shrinkage in plastering can be reduced by ensuring proper adhesion. The plastered should not be stronger than the back ground.
Shrinkage cracks in masonry can be minimized by avoiding use of rich cement mortar and by delaying plastering till masonry has dried after proper curing and has undergone most of its initial shrinkage.
Prevention of Thermal Cracks
To prevent thermal cracks expansion joints, control joints and joints in case of change of shape and direction of wing in a structure are to be provided
Movement due to chemical reaction
Certain chemical reaction in building materials result is appreciable change in volume of resulting products and internal stresses are set up which may result in outward thrust and formation of cracks.
Soluble sulphate reacts with tricalcuium aluminate in cement and hydraulic lime and form products which occupy larger volume and ends in developing cracks. An example of cracking of a floor due to coming in contact of the sub base made of brick khoa with heavy sulphate content and water can be seen in fig