EvaluatingCracking in Concrete
Acrack on a concrete structure is a sign of distress that leads tolack of flexibility in terms of responding appropriately to eitherenvironmental or even volume changes. Cracking often may occur onboth hardened as well as fresh concrete. According to the article,cracking happens as a result of tensile stresses being loaded ontothe concrete at this point the force exceeds the concrete’smaximum tensile strength.
Inorder to properly evaluate cracking on concrete it is inevitable tobe familiarized with the reasons for cracking, types of cracks andtheir effects on structural stability. The article insists on theneed to understand a crack’s status so that the course of actiontaken can be precisely defined. Active cracks demand complexprocedures for repair such as eliminating the actual cause ofcracking for successful long term repair.
Dormantcracks on the other hand, are those that do not threaten astructure’s stability. Environmental conditions surrounding a crackplay a great part in establishing a structure’s integrity. Thismeans that the more exposure there is towards aggressive conditionsthe higher the possibility for structural instability to occur. Thearticle also cites that cracks vary in sizes ranging frommicro-cracks that expose the concrete to efflorescence to largercracks caused by external loading conditions’. Taking note offactors as the sizes of cracks, their shapes and locations is a majorissue to consider when determining the crack’s initial causes.
Cracksin plastic concrete, also called fresh concrete, are categorized intwo plastic shrinkage cracking or plastic settlement cracking. Theyappear approximately six hours after the concrete placement. Plasticshrinkage happens as a result of the bleeding and segregationprocess. Cracks formed as a result of this are usually shallow and inmany instances can self-heal or rather repair themselves. This is soas a result of continual cement hydration or by the precipitation ofcalcium carbonate from the concrete according to the article. Ifself-healing does not occur, repairing with suitable coating becomesinevitable. This action will prevent them from penetrating the fulldepth of the concrete slab which will make them active.
Thearticle observes that plastic settlement cracking happens resultingfrom restraints to the consolidation of fresh concrete such as theuse of steel reinforcing bars or framework. If restraints are usednear the surface and are insufficiently covered with concrete andbleeding occurs,the concrete is bound to bend back around therestraints and cracks appear at the apex.To avoid dealing with suchcracks the article recommends that all superficial restraints arecovered adequately as this noticeably reduces the amount of cracking.
Crackingin hardened concrete my result from a number of factors the main onebeing drying shrinkage. This occurs near restraints because of volumechanges in concrete. This is as a result of factors influencing themagnitude of tensile stresses that cause it as amount and rate ofshrinkage and degree of restraint among others. To minimize shrinkagethe article advises the ‘use of stiff aggregate in high volumesrelative to the cement paste’.
Crackson hardened concrete may also result from thermo stresses that occurwhen tensile stress imposed by change in volume differential exceedsthat of its tensile strength. Corrosion of steel reinforcements isalso possible causes of cracks. Eliminating or limiting oxygensupply, moisture flow and electron flow within the metal reducescorrosion of the steel hence reducing the risk of cracking.