Building pathology Flashcards
What is carbonation?
CO2 in the air reacting with the concrete to form calcium carbonate AND reacts with water to form “carbonic acid”
Carbon “front” moves through concrete and reacts with concrete close to steel reinforcement.
Reaction lowers alkalinity which protects steel along with the “passive layer”, which then rusts/expands/corrodes/pops concrete off.
Moisture worsens it. At least 50mm coverage needed
Explain the testing procedure when testing for concrete carbonation
In-situ or lab testing.
Apply a pH indicator (spray phenolphthalein)
high pH = pink (good!), lower pH = clear (bad)
What is a speedy carbide test?
Understanding accurate moisture content in non-timber.
- Take physical sample of masonry, weigh it
- Add to sealed cannister with specific measure of calcium carbide
- Shake, chemical reaction given off. Gas accumulates in cannister.
- Gauge reads off amount of gas that corresponds with moisture content
When investigating structural cracking to brickwork caused by adjacent trees what recognised standards would you refer to
- NHBC guidance on foundations
- BRE digests (240/241, 298, 412)
- BRE book - “Subsidence damage to domestic buildings”
How would you work out the “zone of influence” of tree roots?
Zone of influence = mature tree height x water demand multiplier
Refer to NHBC tables.
How would you advise treating Japanese Knotweed?
I wouldn’t!! I would advise they seek specialist advice from a company specialising in the management of JK.
Typically treatment means:
- Cycles of herbicides to kill it
- Excavation of it and the 2-3m of soil around it
