In the context of crack formation in reinforced concrete structures, what does IS 3370-2:2009 suggest regarding crack control for water tanks?
1
Crack widths should be kept below 0.1 mm
2
Cracks are permissible if they do not affect structural stability
3
Cracks must be filled with polyurethane sealant
4
Cracks should be avoided at all costs, especially in water-retaining structures