Job #3304 Delta WWTP Phase 1

STATEMENT OF PROBLEM:

This was the third 2" thick sloped Clarifier topping placement. All topping were set up the same and placed using the same method. Elevation at high point ( perimeter wall) was the starting point and zip ties on re-steel were used to set this elevation. Placement started at high point and worked down to center foundation (low point). Concrete elevation was set at 10' intervals from high point at 1/4" per foot slope, see attached SC101 Final Clarifier Plan. Concrete was screed between each 10' interval until reaching center foundation. The problem seams to lie in who was adjusting the laser from pad to pad elevation and didn't maintain the correct slope. Concrete elevations varied 1/2" to 3/4"  in sporadic areas. 

ROOT CAUSE:

COURSE OF ACTION:

When first noticed CCC used chipping hammers to correct slab elevation, see Topping Pic 1.  After checking multiple areas a scarifier was used to correct all other areas, see Topping Pic 2, 3& 4. This took 2 Men 4 days to correct( apprentice Cement Mason and laborer).

LESSON FOR FUTURE PROJECTS:

Double and triple check elevations and bench markers multiple times during placement, Hold a pre-pour meeting and explain the importance of elevations.