Title : CURRENT CONCEPTS ON DURABILITY OF CONCRETE STRUCTURES
Authors : Satander Kumar
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Price : 250
Abstract : Durability and long term performance of concrete structures are two important criteria with respect to prevailing environmental and foundation/soil conditions. Durability can not be sacrificed to attain high strength alone, there is need to see high variation in environmental conditions and properties of soil lying below the foundation of concrete structures during its design life. Although, high ultimate strength is accompanied by a low W/C ratio, proper compaction, extra grinding of cement, proper removal of excess air by using needle/shutter vibrator, vacuum dewatering, autoclaving yet this is not, in itself, adequate to satisfy all durability-related requirements. All types of concrete must provide acceptable frost resistance, repeated heat resistance, sufficient fatigue life, adequate serviceability and long term sustainability for concrete structures which are normally designed for 100 years under present foundation and environmental conditions. To achieve these properties, concrete containing approved quality of mineral and chemical admixtures at low water/cement ratio having adequate workability i.e. high performance concrete (HPC) or ultra-high performance concrete using fibres is need of the day to protect embedded steel from corrosion and for long term durability of concrete. HPC is being used in shotcrete with or without fibres where erection of form work is very difficult. HPC is being used in self-compacted concrete for heavily reinforced concrete structures and where pouring of concrete from single point is not possible and also at places where concreting with slip-form is the requirement. Periodically monitoring, protecting, timely repairing of the concrete structures further extend the service life of the structures. This general conclusion is supported by the good performance observed for offshore high performance concrete structures/ dams in the regions near sea in India, where concrete of compressive strengths of 45 to 80 MPa has been used. For these structures, problems due to corrosion of embedded steel has not been reported so far, even after 20 years of the combined exposure to design loading and heavy mechanical loading under severe marine environment. Good quality very fine particles of mineral admixtures along with super-plasticizer make the cement concrete extra durable with improved long term performance because of least permeability (of air, water and chloride) due to very slow chemical reaction of HPC with harmful compounds present in the concrete. Proper design, curing, finishing, concrete cover, lap length, epoxy coated steel in marine environmental conditions, requirement of coupling/ welding and other workmanship requirement as per approved/ marked with “Good for Construction” drawings/IRC:112/IS:456/ MORTH specification/standard drawings is the back bone for making durable reinforced or pre-stressed or post tensioned concrete structures. The paper describes in brief current concepts, experience and IS IRC and MORTH specifications to be followed in making durable concrete structures, for protection of plain, reinforced and pre-stressed concrete structures.