In maintenance engineering, deterioration of structure is defined as the gradual and continuous process of degeneration of a structure or its components that render it unusable.
Deterioration or decay is the development of defects in a structure that may be due to natural causes of ageing. If deterioration is not checked or is allowed to occur, decomposition of materials results and replacement becomes the only solution. The rate of deterioration depends on the resisting capability of materials.Topic Repair and maintenance of buildings notes
FACTOR RESPONSIBLE FOR DETERIORATION
The process by which a structure deteriorates or disintegrates is a very complex phenomenon. Structural deterioration may be due to one or a combination of multiple factors.
- Human factors
- Chemical factors
- Environmental factors
- Miscellaneous factors
1. HUMAN FACTORS
Most of the deterioration of structures is caused by human factors. This can be either due to a lapse in the construction phase or due to misuse of the building by its occupants or due to improper and inadequate maintenance of the building.
- Use of bad quality building materials.
- Improper execution during construction.
- Failure to supervise during construction.
- Lack of awareness of factors that cause deterioration.
- Failure to perform ongoing maintenance.
- Lack of awareness of service requirements among users.
- Failure to establish a maintenance standard that is acceptable.
- Inadequate planning, budgeting and allocation of funds for maintenance activities.
- Have an occasional approach to repairs with a negative attitude of waiting until emergency measures are required.
- Flagrant misuse of buildings, facilities, finishes, etc.
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2. CHEMICAL FACTORS
Chemical reactions are caused by the interaction of certain materials with the surrounding environment. This leads to dissolution, softening or discolouration of the material or components. Corrosion is the result of chemical reactions of materials with air and water in the environment.
3. ENVIRONMENTAL FACTORS
Environmental factors refer to the exposure of building components such as sun, wind, rain, ground salts etc.The various environmental factors causing the deterioration of Buildings are :
(i) Atmospheric moisture: Atmospheric moisture is regarded as the principal-agent causing the deterioration of the structures. Moisture is always present in the atmosphere and when the surface temperature falls, condensation can occur. Water frozen in the pores of materials can cause spalling of the surface, cracking or disintegration.
(ii) Temperature effects: The temperature change causes temperature stress in the material of the structure. These stresses cause breakage and failure of the building material.
(iii) Gaseous pollutants of air: Increasing pollution is also a major contributor to structural damage. SO2 is the most aggressive gaseous pollutant which causes corrosion of some metals and causes some stones to blister and spall. CO2 also forms a weak acid, capable of slowly eroding limestone. The extent of carbonation in concrete has a marked influence on the corrosion rate of steel.
(iv) Solid contaminants: Environmental pollution in the form of solid contaminants also has an adverse effect on buildings deterioration. Dirt also contains some soluble salts. it absorbs water from the atmosphere and accelerates the corrosion rate of metals and the deterioration of some stone surfaces. The dirt also contains some soluble salts. It. absorbs water from the atmosphere and accelerates corrosion rate of metals and deterioration of some stone surfaces.
Causes of Deterioration pdf | Causes of Deterioration pdf
(v) Groundwater and salts: The salts present in the groundwater rise in solution through capillary action. Upon evaporation of water, salts accumulate on the surface and cause damage to the building. This usually causes flaking and deterioration of building surfaces and finishes. More seriously if magnesium sulphate is present in groundwater. Rendering and masonry surface discolouration may occur. Acidic groundwater can cause concrete to disintegrate.
(vi) Biological agencies: Some building materials are affected by biological agencies like algae, mosses, termites etc. Termite attacks on the wood are very prominent.
4. MISCELLANEOUS FACTORS:
(i) Poor construction materials: Use of substandard construction materials, inadequate inspection of materials, poor on-site storage facilities for construction materials and inconsistent mixing of materials on site are the factors responsible for the deterioration of buildings at a later stage.
(ii) Poor design: Poor and faulty design lead to more immediate deterioration of structures.
(iii) Poor workmanship: Poor workmanship is a major factor that affects the durability of the structure. Include, Failure to understand/follow exactly the specifications and drawing, Lack of skilled labour, Lack of supervision during construction, Failure to replace the defective work noticed if any and Over-emphasis on quantity rather than the quality of construction.
(iv) Misuse of buildings: This includes the use of buildings for which it is not designed. The condition of the building can deteriorate due to open misuse of the building, its fittings, furnishings etc.
EFFECTS OF DETERIORATION ON MATERIALS
(i) Ability to withstand the effects of climate
(ii) Ability to accomplish designed tasks
(iii) Reaction with the surrounding material
(iv) Ease of maintenance and replacement
(v) Overall economic acceptability.
- Efflorescence (deposition of white powdery materials causing disfigurement of bricks).
- The spalling of the external surfaces.
- Change in appearance.
The following are the effects on the durability of timber:
- Timber decays as a result of the destructive action of 'fungi' (called dry rot) growing on it.
- Dry rot requires a moisture content of about 20% and spreads very rapidly.
- Insect infestation (i.e. beetles, termites) destroys timber used in buildings.
- Exposure to natural weathering agents such as rain, wind and temperature contribute a lot to the fast decay of timber.
- Proper seasoning of timber (reduction of moisture content to optimum levels is done to make it last longer.
- Preservatives are used to preserve the timber from decaying. Such treatment is done to ensure a long, trouble-free life of the timber.
3. CONCRETE: |effects of deterioration on concrete
Concrete is a relatively durable material but its durability is affected due to the following factors :
(i) Freezing and thawing: Water entering the pores (voids) of concrete freezes in cold climates. An increase in the volume of water on freezing results in Agencies Causing Deterioration disintegration of concrete. Concrete located in exposed conditions is more susceptible to such attacks.
(ii) Sub-soil salt attack: The water-soluble sulphates in soil when it comes in contact with concrete causes its expansion, spalling and disintegrations. The extent of damage to concrete will depend upon the amount and types of sulphate present in the groundwater and the quality of concrete.
(iii) Alkali-aggregate reactions: Silica present in aggregates reacts with the alkalis of cement in the presence of water and causes expansion and subsequent damages to concrete.
Effect of deterioration of concrete can be controlled by the following steps :
(i) Using optimum water-cement ratio.
(ii) Using sound and fresh cement.
(iii) Using durable, densely graded and non-reactive aggregates.
(iv) Using proper batching and mixing equipment and methods.
(v) Providing thorough and uniform compaction.
(vi) Providing proper curing.
4. METALS: |effects of deterioration on steel
Mild steel used extensively in building construction, is rarely exposed, but has a protective coating of paint, bitumen, or is surrounded by other materials, usually RCC. Protective coatings reduce the rate of corrosion. RCC In the member, it is the solid cover that breaks down first. Therefore, R.C.C. In steel cover. The structure should be in accordance with the risk of the structure to the environment. Only when the steel is heavily corroded can we see both broken concrete and fabricated steel.
The cast iron pipe buried in the ground also gets rusted, but the rusty part remains in its place and does not deteriorate and acts as a protection against further corrosion. Many cast iron pipes buried under the ground last for a very long time in the field. Steel pipes don't last that long.
5. PAINTS |effects of deterioration on Paint
Paint is a coating of coloured liquids applied to the surface of finished parts of a building, which are drying. Forms an impervious coat and protects surfaces from the effects of atmospheric agencies, corrosion of wood and metal corrosion and also serves as a decorative surface.
The following defects are observed in painting due to various agencies of deterioration :
(i) Blistering: This is due to the trapping of water vapour behind the painted surface. This forces the paint into little bubbles or blisters.
(ii) Fading: When the painted surface is exposed to direct sunlight, gradual fading of colour due to loss of brightness of pigment occurs.
(iii) Blooming: This is the development of dull patches due to the presence of moisture or dialling of the surface glossy coat.
All other defects in paints are due to the following reasons :
(a) Use of poor material: All the paints should be selected of good quality in relation to their exposure condition and backing material.
(b) Application on the damp surface: Dampness breaks down the adhesion of the paint with the surface of the component causing flaking and cracking from the surface.
(c) Poor workmanship: It is one of the main causes of paint wear and blemishes. Poor workmanship can be attributed to incorrect, inadequate or non-existent surface preparation. Over-thinning of paint Improper brush selection, poor brushing technique and failure to apply the specified number of coats can result in tarnishing of the paint.
6. PLASTICS |effects of deterioration on Plastics
A wide range of plastics is used in buildings. Polyvinyl chloride (PVC) has wide applications. Plasticized PVC is widely used as a floor covering, false ceilings under pitched roofs. Rigid aplastic PVC, a covering membrane in flat roofs and plastic membranes for waterproofing, is primarily used for domestic soil and vent systems. Rainwater drainage. Wall cladding. Ducting etc. Expanded PVC is also available for thermal insulation Glass-reinforced plastics (GRP) are also used for structural purposes.
Special plastics are used for large drainage chambers, plumbing, drainage fittings and wall ties. Foamed plastic provides the cellular material used for thermal insulation.
The following defects are observed in plastics :
- Shortwave solar radiation degrades plastics due to changes and changes in surface appearance.
- In general, the effect of moisture is very small, but it can reduce the bond strength between the glass fibre and polyester resin.
- The breakdown of polyethene in cold water tanks is due to the use of oil-based joint compounds.
- PVC and polycarbonate have high thermal expansion. Unless properly allowed, movement of PVC gutters and downpipes can lead to joint failure and leakage.
- Plastics tend to creep under constant load and require special precautions when the stress is high.
Natural stones are classified as belonging to one of the three main groups-igneous, sedimentary or metamorphic.
- The atmospheric pollution causes the deterioration of limestones and sandstones. If wetting and drying are frequent due to rainfall, the surface of the stone gets slowly eroded.
- Frost may also attack some limestones.
- Marble is attacked by sulphuric gases.
- Slates are used for roofing, cladding and D.P.C. Roofing slates are exposed to the most severe conditions and can be affected by sulphuric gases.
- One major cause of damage in all types of stones can be the corrosion of embedded fixtures. Rusting of iron and steel cramps and dowels cause extensive damage to limestones and sandstones.
- Human factors
- Chemical factors
- Environmental factors
- Miscellaneous factors
- Use of poor construction materials.
- Poor workmanship during construction.
- Lack of supervision during construction.
- Lack of knowledge about factors causing deterioration.
- Failure to carry out routine maintenance.
- Atmospheric moisture
- Temperature effects
- Gaseous pollutants of air
- Solid contaminants
- Groundwater and salts and Biological agencies