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Building Materials - common Concrete Problems
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COMMON CONCRETE PROBLEMS
COMMON CONCRETE PROBLEMS
Problem Cause
Prevention & CorrectionsExcessive BleedingExcess water in the mixReduce water content
Not enough fines in the mixIncrease the cement or sand
Aggregate SegregationToo high slumpAdd superplasticizer
Over vibrationReduce vibration in each location
Not enough vibrationIncrease vibrator at close intervals
Too long of drop for placementUse appropriate drop chutes
Lack of homogeneity in the mixIncrease mix time, add air entrainment
Sticky FinishToo much air entrainmentReduce air and/or fines
Surface drying too fastSpray water on subgrade and forms
Setting too fastHigh temperaturesUse cooler water in mix or cool aggregate with water
High cement contentAdd water reducing retarder
Trucks getting hot from sunSprinkle mixing drums during wait or reschedule deliveries for minimum wait time
Setting up too slowMix too leanIncrease cement content or use accelerator
Cold/wet subgradeInsulate and or protect before placement of concrete
Plastic shrinkage crackingToo rapid loss of water. High winds, heat or low humidityFog spray at curing. Do not use vapor retarder. Set up wind breaks
Low yield Wrong ratio of water, cement and aggregatesHave test run
FLAT SLABS
Shrinkage cracksWrong spacing and depth of contraction jointsCut joints the depth of slab. Space joints at 2 times the thickness
Late joint sawingPlan to saw the same day as pour, within 4 hours
No isolation joints at walls or columnsInstall isolation joints
Excessive shrinkageReduce water in mix
Hairline cracksToo high slump of concreteReduce water
Too early trowelling or too much trowellingReduce the methods of trowelling by contractor
Rapid surface dryingCure concrete immediately after finishing
BlisteringSlab closed too soon, trapping air and waterDelay floating and trowelling
CurlingUneven drying between top of slab and lower parts Use lower slump
WALLS
HoneycombNot enough vibrationReduce height of the pour. Insert vibrator more often. Add superplasticizers
Surface voidsAir or water trapped against formworksReduce air entrainment. Vibrate as close to form as possible