REPAIR AND REHABILITATION OF STRUCTUTRES

REPAIR AND REHABILITATION OF STRUCTUTRES SHASHANK M. DHOLAKIAINTRODUCTION REHABILITATIONReturning of a building or a structure to a useful state by means of repair, modification or alteration. It stops or mitigates the process which is responsible for damage.

RESTORATIONIt is the process or act of depicting the characters & features of a property as it appeared at a particular period.

REPAIRRepairs are used to restore the structural integrity and shape of functional units. Repair methods however do little to address the cause of faults. Therefore, simple repairs typically fail prematurely since nothing is done to mitigate or stop the primary deterioration mechanism. REPAIR MANAGEMENT DURABILITY DISTRESS IN CONCRETESPALLING

CRACKING

WATER CEMENT RATIOThewatercement ratiois the ratio of the weight of water to the weight ofcementused in aconcretemix and has an important influence on the quality of concrete produced. A lower water-cement ratio leads to higher strength and durability, but may make the mix more difficult to place. Placement difficulties can be resolved by usingplasticizersorsuper-plasticizers.Often, the watercement ratio is characterized as the water to cement pluspozzolanratio, w/(c+p). The pozzolan is typically afly ash, orblast furnaceslag. It can include a number of other materials, such as silica fume, rice hull ash or natural pozzolans. The addition of pozzolans will influence the strength gain of the concrete.The concept of watercement ratio was developed byDuff A. Abramsand first published in 1918, seeconcrete slump test.Concrete hardens as a result of the chemical reaction between cement and water (known ashydration, this produces heat and is called the heat of hydration). For every pound (or kilogram or any unit of weight) of cement, about 0.25 pounds (or 0.25kg or corresponding unit) of water is needed to fully complete the hydration reactions. This requires a water-cement ratio of 1:4 often given as a proportion: 0.25. However, a mix with a w/c ratio of 0.25 may not mix thoroughly, and may not flow well enough to be placed, so more water is used than is technically necessary to react with the cement. More typical water-cement ratios of 0.4 to 0.6 are used. For higher-strength concrete, lower water:cement ratios are used, along with a plasticizer to increase flowability.Too much water will result insegregation of the sand and aggregate components from the cement paste. Also, water that is not consumed by the hydration reaction may leave the concrete as it hardens, resulting in microscopic pores(bleeding) that will reduce the final strength of the concrete. A mix with too much water will experience more shrinkage as the excess water leaves, resulting in internal cracks and visible fractures (particularly around inside corners) which again will reduce the final strength.The 1997Uniform Building Codespecifies a maximum 0.50 water-to-cement ratio (1:2) when concrete is exposed to freezing and thawing in a moist condition or to de-icing chemicals, and a maximum 0.45 water to cement ratio for concrete in severe or very severe sulfate conditions.

FACTORS AFFECTING PERMEABILITY OF CONCRETEFACTORS PROMOTING THE PERMEABILITY OF CONCRETE1 Capillary PorosityHigh W/C RatioInadequate Curing

2 Air VoidsImproper Compaction3 Micro CracksLoading EffectsWeatheringInitial/After CareSecondary Effects

3 Macro CracksPlacement Chemical AttackCorrosion Of ReinforcementHeavy LoadingHardening ProcessCAPILLARIESCapillaries nothing but extra volume of water entrapped in the cement paste after completion of hydration, which eventually leads to formation of interconnected pores called capillaries

CAHNGE IN CAPILLARY POROSITY WITH VARYING DEGREE OF HYDRATION

CHANGE IN CAPILLARY POROSITY WITH VARYIN W/C RATIO

MICRO & MACRO CRACKS IN CONCRETEMICRO CRACKSMACRO CRACKS

LOADING DUE TO TEMPERATURE GRADIENT