VACUUM DEWATERED FLOORING (VDF)
A. PREPARATION OF SUB-GRADE
Sub-grade should be laid according to specifications, levels as recommended by the consultant
Ensure that proper consolidation of the sub-grade has been achieved before proceeding for the PCC bed
Provide and lay PCC bed above the sub-grade as per thickness mentioned in the drawing
Provide a reinforcement mesh as per specification and the drawings
B. DEWATERING AND FINISHING
Concreting should be carried out with concrete of right grade and slump. (See: Concreting)
Concrete intermediate/ alternate panels shuttered by ISMC runners or continuous bull marks.
Ensure proper expansion joints as per working drawings and protected
Dewatering mat to be used to remove excess water from the concrete surface to ensure concrete of the highest strength is achieved.
The dewatering mat should be properly laid to prevent air leakage. Care should be taken in ensuring that excess water does not enter the dewatered area.
After initial set of concrete (2-3 hours), the top surface of concrete is finished using a power trowel. Care should be taken that no impact load is transferred to the finished surface.
Heavy vibrations should be avoided in vicinity of the VDF area.
C. TESTING OF CONCRETE
SLUMP TEST
Conduct slump cone test, one during the start, one at midday and one towards the close of days work.
Any load under suspicion can be checked for slump on case-to-case basis.
CUBE TEST
The sample is made at point of discharge of mixture.
Take 3 samples after 7 days and 3 samples after 28 days strength.
Every 100 cum or 10 batches of concrete (whichever is smaller) should be represented by a sample of test cubes.
For concrete manufactured at site, there must be representative samples for the day’s work and for different elements like footing, slab, column and wall.
Test results should be discussed with the project in-charge even if the results are satisfactory
In case of cube failure, the element to be identified and non-destructive test to be conducted.
TOOLS TO BE USED BY TRADESMEN
Required tools must be available at site to ensure correct work. Basic tools of the concreting gang are:
1. Vacuum Dewatering machine
2. Power Trowels
3. Trowels
4. Gum boots
5. Dumpy levels
6. Spirit levels 1-3m
7. Measuring tape
8. Screed finishing darby
9. Steel trash tracks
10. Hammer
11. Leveling trowels
12. Wheelbarrow
13. Long handle Aluminium leveler with spirit level
14. Masons brushes and buckets
15. High pressure water cleaners
INSPECTION METHODOLOGY FOR QUALITY ASSURANCE
1. Personnel
Ensure all personnel are wearing gumboots
2. Before Concreting
Ensure shuttering is sealed with sealing tape so as there is no leakage of slurry
All reinforcements are in place especially chairs
All cover blocks damaged during reinforcement layout are replaced
3. During Concreting
Ensure proper grade of concrete as recommended by the consultant is employed
Ensure proper expansion joints as per working drawings and protected
Check the top surface of fresh concrete for eveness of top surface
4. After Concreting
Top surface is checked for straightness using Aluminium straight edge or leveling thread as the case may be.
Curing carried as per guidelines
Water level is maintained during ponding
Ensure the cube test results are available at the end of the term indicated
TOOLS TO BE USED FOR QUALITY INSPECTION
1. Dumpy levels to check finished slab level
2. Aluminium straight edge
3. Leveling thread
4. Spirit levels 1-3m
5. Measuring tape
6. All the relevant related drawings
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