General Construction Problems on Site
Getting fine aggregate free from dust, clay, salts etc.
- Silt clay and silt (sizes below 70M)
- (sizes below 4-5M)
Being small, they absorb lot of water. Water available for cement hydration is less, leaves pores. Clay and silt affect the gel formation. As it does not participate in gel formation, denser cone is not formed. Durability is reduced.
Clay particles tend to flocculate due to cohesion and under stress, may tend to break resulting in voids, therefore weak concrete. These clay particles coat the coarse aggregate, thus presetting the bond between the coating of cement and coarse aggregate. This seriously affects the strength.
Therefore, sand containing silt and clay should be summarily rejected or through washing of sand but expensive.
Quality of water
- Many it is hard water that is available at site. For food concreting job, it requires portable soft water, as the salt contents in hard water may affect the gel formation.
- As a quick test for suitability of water, one can cast three cubes using distilled water (water which is usually used in car battery refilling) and three cubes using normal water available at site for concreting.
On site Tests for Reinforcement Steel
Sources of Steel
- BSI Certification is a must
- Use of steel of good Quality
- Check for the trade mark on every bar
Re-rolled steel (Usually re-rolled form molten scrap)
Re-rolled steel, usually obtained from local re-rolling mills, contains higher impurities and does not confirm to the specified strength requirements.
On Site Bend Test
- If a rod is bent to makes an including angle of 90 degree to 135 degrees and bent back straight.
- The surface of the bend should not show any cracks or bends i.e. it must regain its original straight line shape.
Storage of Steel at Site
- Steel should be stored at Site under shade in dry condition, preventing it from rusting.
- It should not be lefts exposed to outside environment for more than a month.
- If re-bars are already rested, they should be brushed clean before using.
- If Steel bars need to be left outside for more than a month, they can be given a wash with cement slurry.