Asbestos cement partition• Partition walls constructed from asbestos

cement sheeting or galvanized sheet fixed to wooden or steel members are mostly adopted in works of temporary character.

• For superior type of asbestos cement sheet partition walls, specially manufactured slabs of the other materials are used.

• Each slab consists of core or corrugated asbestos cement sheet with the plain asbestos cement sheet attached to it on either side

MERITS• Asbestos is non-flammable even

at very high temperatures and is extremely flexible and durable

• It is fibrous and crystalline, elastic and brittle

• Newer garages that are part of the house can have asbestos sheet or fibro to assist in hindering the spread of fire if a fire were to start in the garage.

• It has good heat and sound insulation properties.

• These walls are economical, light and fairly rigid if constructed properly.

PROBLEMS Problems may be classified into two broad categories:

1) Natural or inherent

2) Vandalism and human-induced problems

NATURAL CORROSION a. The zinc coating on galvanized iron and steel develops a natural carbonate on its surface by exposure to the atmosphere and by the action of rainwater.

b. Since the zinc coating on the iron or steel is very thin, it can corrode up to the base metal exposing the base to the atmosphere as well.

c. In industrial atmospheres, the zinc carbonate coating can be broken down by the same acids that attack zinc d. These acids often staining the adjacent building elements.

CHEMICAL CORROSION

a. Galvanized iron and steel have good corrosion resistance to: Concrete, mortar, lead, tin, zinc and aluminum.

b. Galvanized iron and steel have poor corrosion resistance to: Plasters and cements containing chlorides and sulfates. c. Acidic rainwater run- off from roofs with wood shingles moss, or lichen, condensation on the underside of zinc plates.

GALVANIC (ELECTROCHEMICAL) CORROSION

a. This type of corrosion is an electrolytic reaction between the zinc coating and dissimilar metals when in the presence of an electrolyte such as rain, dew, fog or condensation.

b. Galvanized iron and steel are corrosive to all metals except lead, tin, zinc and aluminum.

HUMAN-INDUCED PROBLEMS

It consist of Mechanical or Physical Deterioration

1. Abrasion: Causes removal of the protective metal surface.

2. Fatigue: A type of deterioration caused by cyclical expansion and contraction of sheet metal features. a. Zinc is very vulnerable to fatigue failure because it has a relatively high coefficient of thermal expansion. b. Fatigue failure may also occur when the metal sheets are too thin to resist buckling and sagging.

3. Creep: The permanent distortion of a soft metal which has been stretched due to its own weight. 4. Distortion: Permanent deformation or failure may occur when a metal is overloaded beyond its yield point because of increased live or dead loads, thermal stresses, or structural modifications altering a stress regime.

RISK

Products which contain asbestos can generate fibres when they are damaged, disturbed, weathered or old: in these circumstances, fibres are released into the atmosphere and asbestos exposure through respiration can occur.

It is widely believed that exposure to asbestos contained in buildings presents a relatively small risk.

PREVENTION A. Applying a protective coating such as paint to galvanized iron and steel will alleviate the problems caused by corrosion of the protective zinc coating.

B. To prevent the corrosion of the zinc coating due to galvanic action, contact between galvanized items and copper or pure iron or steel should be avoided. C. Creep may be prevented by the use of properly sized individual sheets and bays,

properly designed joints, and an adequate number of fasteners.

D. Galvanized iron and steel's resistance to corrosion depends largely on the type and thickness of the protective zinc coating and the type of corrosive environment; so it should be kept in mind while doing galvanization.

EXAMPLES• Toilet cisterns can comprise asbestos

molded products either above the toilet or behind walls in cavities whilst

• toilet cubicle partitions can commonly comprise 20 mm thick compressed asbestos cement sheet

• External garages can contain asbestos cement walls, eaves and corrugated asbestos roofs.

• Partition walls constructed from asbestos cement sheeting or galvanized sheet fixed to wooden or steel members are mostly adopted in works of temporary character.