Details Of Defects And Damages In Concrete | Types | Causes | Investigation Method |

 

Brief details of defects and damages occurred in concrete are  indicated below along with their possible causes and suggested  investigations for ready reference:

 

CONCRETE

 

VISIBLE DEFECT	POSSIBLE CAUSES	INVESTIGATION  SUGGESTED
Rust on the surface.	Iron compounds in aggregates, nails/wires left in formwork.	Chemical analysis of samples.
Rust stains on the surface.	Corrosion of binding wires, corrosion of reinforcement steel.	Check cover and carbonation of concrete.
Cracking of concrete cover, exposure of  reinforcement and  spelling of concrete	Corrosion of reinforcement and other steel due to moisture and chloride ingress, frost attack and poor quality of concrete low density, high porosity and high water to cement ratio).	Check cover, test for chlorides and carbonation, check reinforcement adequacy.
Surface crazing.	Concrete Mix too wet and poor curing.	Check concrete mix and construction method used.
Random diagonal cracking, lateral cracking at equal spacing	Inadequate protection against shrinkage, over-rich or over wet and non-cohesive concrete.	Check reinforcement, spacing of joint, analyze samples of concrete.
Repetitive vertical or horizontal cracks.	Joint spacing too large.	Examine joint details/spacing check concrete sample and aggregates used.
Wet and damp spots, Deteriorated applied finishes without cracking.	Honeycombs due to poor placement of concrete mix, poor compaction or water stopper missing.	Check concrete after recovering applied finishes, checks detailing of joints, check for water stopper, test and analyze concrete.
Cracks at intervals.	Restrained shrinkage, reinforcement too near the surface, corrosion of reinforcement, moisture movements.	Check to space of joints design), check the distribution of reinforcement, concrete sample.
	Faulty movement joints, faulty or missing water stopper, inadequate or improperly constructed join, inadequate reinforcement.	Check concrete at joints, check water bars and reinforcement details.
Rust stains below mortar covering of external pre-stressing.	Tendon corrosion, poor grouting of tendons.	Check location/ extent of corrosion.
Map cracking.	Alkali-silica reaction (ASR), early drying out conditions, over-rich mixes, over compaction and poor curing.	Check concrete constituents, petrographic analysis.
Surface abrasion.	Excessive wear.	Check abrasive loading, check the quality of the concrete surface, check the history of usage.
Cracking or spelling with or without staining  (generally parallel to the direction of reinforcement steel).	Corrosion of reinforcement steel or pre-stress tendons corrosion of encases steel,  alkali-silica reaction (ASR),  restrained by reinforcement.	Check the condition of embedded steel, check cover, carbonation,  chloride content, check the presence of ASR.
Deflection.	Shrinkable aggregate, premature removal of formwork, overloading.	Analysis of concrete samples design check.
Local settlements along with diagonal cracks on  footings (foundation)	Poor subgrade compaction, inadequate reinforcement, ground movement due to water/erosion/ mining/ shrinkage clays, peat or other causes.	Investigate foundation design and substrate.
Vertical or slightly inclined cracks on sides and soffit on the central part of RCC beams.	If less than 0.3 mm: Normal if wider than 0.5  mm: Overload, excessive shrinkage of the slab,  premature removal of props.	Check design, compare actual load with design  load, check span/ depth ratio with code  requirements, check  temperature gradient
Diagonally inclined cracks in beams, generally at or close to the supports.	Overloading, inadequate beams depth, inadequately provided reinforcement to prevent shear.	Check actual shear resistance against coal allowance.
Vertical cracks in RCC beams at regular intervals.	Shrinkage around stirrups.
Helical cracks in RCC beams face and extending around the section perimeters.	Tensional shear stresses.	Check actual tensional resistance against coal requirement
Excessive deflection of RCC beams.	Inadequate depth, overloading, formwork defect, inadequate or displace reinforcement, shrinkable aggregate, materials defective or deteriorated, bond failure between reinforcement and concrete.	Check span/depth ratio with code requirements, compare actual and theoretical deflections,  check to load history,  cover meter check, test concrete, check for defects in construction.
Pre-stressed concrete beams with excessive deflection, excessive handing, loose or defective anchorage segment separation,  grout disturbance and distribution not proper,  segmental shear cracks.	Overloading,  Overstressing Or poor concrete,  inadequate pre-stresses,  displaced tendons,  material defective or deteriorated.	Check deflection, and stresses against actual load, check conditions of all tendons, check design,  check cover by the cover meter.
Bowing of pre-stressed columns.	Distortion during erection, concrete creep or shrinkage, tendon fractures, defective material or material deterioration.	Check loading conditions, check design and construction defects, check cover by cover meter, check tendon condition at any fracture.
Excessive deflection in slabs and/or the heaving of tiles or cracking of tiles on the top surface.	Inadequate depth, overloading, for long period, defective formwork, inadequate or displaced steel reinforcement, material defective or deteriorated,  lack of continuity.	Check span/depth ratio with code requirements, compare actual and theoretical deflections, check loading history, check cover by cover meter, check for shrinkable aggregates.

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