Buildings are subject to different kinds of defects. One of these is deterioration. Buildings and structures deteriorate as a result of various factors, including the strength and durability of the building materials used for construction. Though almost all building materials start to decay with time, some give buildings more strength and durability than others. Strength reveals the ability of a building to bear present and future loads while durability means the duration the building will spend before requiring service.
Other factors responsible for deterioration of buildings may include concrete corrosion, moisture, the activities of thermal agents, chemical agents, and cracking.
- Concrete corrosion
- Thermal Agents
- Faulty Designs/Construction
- Biological Agents
Corrosion is said to be responsible for up to 90% of damage to reinforced concrete structures. It is a chemical process that occurs when the iron rod used to reinforce concrete structures start rusting. It is identified as destruction of metal by chemical, and electrochemical reactions in its environment. Electrons migrate from the anodic zone to the cathodic zone, releasing ferrous ions at the anode and hydroxide ions at the cathode. This leads to a potential difference between the anodic and cathodic areas at the surface of the steel reinforcement.
This results in the creation of rust. Rust causes the surrounding concrete to crack and become damaged. These cracks then make their way to the surface of the concrete which causes even more CO2 and chloride to penetrate the concrete and speed up the process of corrosion.
Moisture also causes deterioration in buildings. It is the penetration of the external fabric of cladding, or through ground floor constructions giving to dampness which may create a suitable condition for fungi growth and attack. Excessive moisture in the internal atmosphere may lead to excessive condensation and corrosion, and irrigation.
Temperature is relevant to components that are exposed to unobstructed sky such as the roofing, cladding and external structural members. The actual temperatures reached can lead to either temporary or even permanent changes in physical or chemical properties. Changes of the temperature are also relevant when assessing the consequences of thermal expansion and contraction – such as stresses within materials when changes of size are restrained and strains imposed on jointing materials when components are free to change size.
Deterioration can be caused by poor detailing at the design stage of a building. This includes insufficient allowance for expansion or contraction, absence of weathering, poor jointing between different materials or components, poor specification, lack of adequate consideration of future maintenance problems, and inadequate provisions for access to carry out maintenance activities. In relation to construction, the factors may be lack of supervision during construction period, failure to understand or follow exactly the specification and/or drawings, failure to replace defective work, failure to monitor works in progress, lack of skilled labour, and over emphasis on quantity rather than quality.
These include bacteria, fungi, algae, lichen and mosses that cause surface growth; pests that harm building materials such as are rats and mice, which gnaw timber, other organic substances and PVC casings to electric cables. There are also plant agents that cause damage to building from tree roots, disrupting foundations and penetrating underground drains. The damage is mostly evident in buildings with shallow foundations or faulty infilling that have been erected on shrinkable clay subsoil and with trees and large shrubs nearby.
The aforementioned factors cause deterioration and decay in buildings which may lead to damage and collapse. Efforts should be made to guide against such factors right from the planning stage. Only high quality building materials should be used for all the structural members. Also, there should be proper detailing at the design stage. This will guide against frequent repairs and improve the lifespan of the building.