Types of defects common with Type B waterproofing
The most common defects are:
- Permeable concrete
- Honeycombing through lack of compaction
- Contamination of or cold joints
- Cracks due to thermal contraction and shrinkage
- Poor and inadequate placement of waterbars, hydrophilic strips and joints
The most common defect is “honeycombing / lack of compaction. The main cause is the wrong choice of consistence. Either the consistence was too low making compaction difficult or the concrete had extra water added and segregation took place.
Plastic and long-term drying shrinkage, thermal cracks, induced cracks, cracks caused by restraint are normally associated with Designer and / or Contractor issues and NOT the materials used.
These are caused by temperature differentials, particularly in mass concrete due to the heat of hydration. As the interior concrete increases in temperature and expands, the surface may be cooler and contracting thus causing tensile stresses that may result in thermal cracks at the surface.
As most concrete mixes contain more water than actually required for the hydration process, the remaining water evaporates over time causing the concrete to shrink. Restraint to shrinkage causes tensile stresses to develop in the hardened concrete. Restraint to drying shrinkage cracking is a common cause of cracking in concrete.
These are caused by the evaporation of water from the surface of freshly placed concrete faster than it is replaced by bleed water, thus causing the surface to shrink. Due to restraint from the underlying concrete, tensile stresses develop in the weak plastic surface concrete resulting in shallow cracks of varying widths and depths.