Cover Block Size used for Reinforcement & IS code

quiz answer:

       Racked Back - The incomplete end of the brick work is racked back, by stepping the brick work.

Clear Cover to Main Reinforcement: 

1. Footing : 50mm
2. Raft Foundation Top : 50mm
3. Raft Foundation Bottom and Sides : 75mm
4. Strap Beam : 50mm
5. Grade Slab : 20mm
6. Column : 40mm
7. Shear Wall : 25mm
8. Beam : 25mm
9. Slab : 15mm
10. Flat slab : 20mm
11. Stair Case : 15mm
12. Retaining Wall : 20mm or 25mm 
13. Water Retaining Structure : 20mm or 30mm  

IS code: 

   IS  1629 - Rules for grading of cut timber

   IS  2645 - specification for integral cement water proofing compounds

   IS  1791 - specification for batch type concrete mixer

   IS  2438 - specification for roller pan mixer

   IS  2505 - specification for concrete vibrator , immersion type

Today's quiz:

    what is mean by Datum ?