Defects - Concrete and Masonry Flashcards
Explain the process of carbonation of concrete.
Concrete is naturally alkaline, providing a level of chemical protection to the reinforcement. Acidic gases can enter the concrete in solution and reduce the alkilinity, risking corrosion ot the reinforcement.
What happens when the reinforcement corrodes in concrete structures?
When steel corrodes it expands by circa 7% which creates pressure and can cause the surrounding concrete to crack or fail completely.
What is the remedy for carbonated concrete?
Carbonation can be prevented or halted with the application of a anti-carbonation coating system, including epoxy coatings, acrylic sealers and silane sealers.
If the reinforcement is exposed or damage is extensive, the appropriate remedy is to descale/clean the reinforcement, apply an anti-corrosion coating and replace the missing concrete and apply an anti-carbonation coating.
What are the indicators of wall tie corrosion?
Corroded wall ties will cause the opening up of horizontal mortar joints, brickwork displacement and horizontal cracking. In extreme cases, the masonry wall may bow.
What is the remedy for wall tie corrosion?
Undertaking a wall tie survey to confirm the extent of the defect, followed by the removal of the existing wall ties and replacement with stainless steel ties. The wall will then need repointing to make water tight.
You notice stepped cracks appearing in a masonry wall. What are the potential causes?
Stepped cracking is indicative of some form of building movement.
These can be:
- Settlement
- Differential Settlement
- Heave
- Subsidence
You see stepped cracking and suspect this is due to ground movement. How could you identify what type of ground movement has occured?
Where the cracks are larger at the bottom and thinner to the top, this is most likely due to heave, which is the movement of the ground upwards.
Where the cracks are larger at the top and thinner at the bottom, this is most likely due to subsidence, which is the movement of the ground downwards.
How would you identify lintel failure?
Typically a triangular shaped crack is presnt above the window to one side.
What size of cracks are of concern?
Up to 2mm - Very slight
2-5mm - Slight
2-15mm - Moderate
15-25 - Severe
Over 25mm - Severe with concerns of stability
What types of soil are susceptible to heave?
Clay soils
A newly cast reinforced concrete slab is exhibiting crazing on the surface. What could be the cause?
Poor or inadequate curing as a result of high evaporation or lack of protection.
Excess moisture in the concrete mix and excessive floating.
