BP Questions Flashcards
What is carbonation?
Carbon dioxide mixed with pollutants and water reduce the PH value of concrete making it more acidic, this breaks down the passive layer to reinforcement and causes corrosion.
What is high alumina cement?
An additive used to resist chemical attack from acids and sulphates and speed up the curing process. Mainly used in pre-cast concrete between 1950s-1974 when it was banned. Concrete increases in porosity which results in loss of strength - ‘Conversion’.
What are the symptoms of high alumina cement?
Visual assessment not to be relied on. May have brown tinge. Deflection to structural members.
How would you test for high alumina cement?
Lab testing required > Concrete becomes friable and can often turn a brown colour.
What are the main treatment options for high alumina cement?
Removal of HAC elements. Secondary support. Carbon plate bonding (bonding carbon fibre to the underside of the member).
What are the causes of chloride attack?
Caclium chloride additive - additive used in 1960s - 70s to speed up curing process, Can also be introduced by sea water and unwashed aggregates in concrete.
What are the symptoms of chloride attack?
Whilst cracking and spalling of concrete accompanied by rust staining is indicative of chloride attack, high strength dense concrete may suffer damage to reinforcement without exhibiting such obvious symptoms until substantial loss of steel has occurred.
How would you test for chloride attack?
Rapid chloride permeability test. This test method is used to provide an indication on the penetrability of concrete. It is used for evaluation the resistance of a concrete sample to the penetration of chloride ions.
What are the causes of alkali-silica reaction?
Aggregates containing certain forms of silica will react with alkali hydroxide in concrete to form a gel that swells as it adsorbs water from the surrounding cement paste or the environment. Commonly known as ‘concrete cancer’.
What are the symptoms of alkali silica reaction?
In unrestrained concrete, the cracks have a characteristic random distribution often referred to as ‘map cracking’. In restrained concrete, the cracks tend to follow the line of main reinforcing bars
How would you test for alkali silica reaction?
Microscopic examination
What are the causes of sulphate attack?
Reaction between suphates and water leading to expansion. Likely to occur in ground bearing floor slabs and chimneys (sulphates from flue gases).
What are the symptoms of suphate attack?
Expansion in brickwork (horizontal and vertical), bowing and map cracking to concrete floors, leaning of chimney stacks.
How would you test for sulphate attack?
Microscopic examination
What are the causes of honeycombing in concrete?
Poor compaction of aggregates, poor formwork. Wood wool slabs (shredded timber in concrete) reduce compaction of aggregate around steel reinforcement when used as a permanent shuttering, causing honeycombing.
What are the symptoms of concrete honeycombing?
The honeycombed surface looks very rough with voids and gaps between concrete and reinforcement.
What is Regent Street Disease? (Also known as Deansgate Disorder)
Name given to the corrosion related damage that occurs in some buildings constructed during the first half of the 20th century using a steel frame embedded within the facing stone
What is a cover test used for?
Measure depth of reinforcement
What is a filler joist floor?
Filler joist is an early form of floor slab construction, which was commonly used , between about the 1880s and 1920s. It was formed from iron or steel joists spaced , between 600 and 900mm apart and in-filled with unreinforced concrete. The concrete often had coke breeze in it acting as an aggregate. The cover on the steel joists was often , insufficient. The coke releases acids which change the passivity of the concrete and the , lack of cover increases the risk of carbonation
What would you recommend for the repair of steel reinforcement?
Cleaning the exposed steelwork involves removing the surface rust by either sand blasting or needle gunning and treating the exposed surface with a protective paint coating.
Which part of the Approved Documents cover drainage?
Approved Document H
What are the minimum sizes of foul drainage pipework and minimum gradients?
Pipework should be at least 75mm in diameter. 150mm pipework should be at least 1:150 in accordance with Approved Document H Diagram 3.
What are the causes of dry and wet rot?
Lack of ventilation, give examples. E.g.
Wet rot in roof where source of moisture - usually 50-60% relative humidity.
Dry rot in basement where moisture and lack of ventilation - usually 20-40% relative humidity
What are the symptoms of dry rot?
Deep cuboidal cracking, reduction in weight, dull brown in colour. Strands are typically 3mm in diameter and off-white/dark grey in colour. Fruiting bodies yellow-ochre when young, rusty red when mature. Distinct mushroom smell.
What is the severity of dry rot?
High - can travel through timber, plaster, masonry and concrete
What are the symptoms of wet rot?
Cuboidal cracking on smaller scale, localised infection where dampness is present.
What is the severity of wet rot?
Medium - Affects timber only but can cause structural issues if left untreated.
What is the life cycle of rot?
1 - Spore, 2 - Hyphae, 3 - Mycelium, 4 - Fruiting Body
When would you engage with a structural engineer when you identify cracking?
Review crack size in accordance with BRE Digest 251. Generally cracks over 5mm may cause serviceability issues and anything in category 5, being more than 25mm, are considered to require structural intervention.
What are the typical symptoms of cavity wall tie failure?
Horizontal cracking at regular intervals, every 3rd or 4th course of brick. Typically due to rusting of metal ties.
What could be the possible causes of cracking between a bay window and the main structure?
Differential settlement caused by differences in the foundation depths between the bay window and the main wall. Can also be due to bay window being insufficiently tied to main structure.
