Waterproofing is one of the most critical, yet neglected subjects because the common man is not exposed to the concrete technology. He just wonders and is shocked when he sees leakage in his building, but most of the time he considers it as inconvenience rather than a serious matter.
Water infiltration causes major problems to a structure. Water damages a building first cosmetically then structurally. It is important to realize that by the time a stain shows up on the interior of your building most likely irreversible damage has been caused to the exterior. Water soaked roof insulation will never dry out.
Trapped moisture in insulation can also decay a roof deck and will cause roofs to fail prematurely. Water entering walls will rust steel relieving angles and carrying beams, which support the structure. Moisture penetrating reinforced concrete structures carry chloride ions, which will rust reinforcing bars causing them to expand in size resulting in spalling of concrete. As one begins to understand the mechanics of water infiltration one begins to understand the importance of keeping a building watertight.
Water enters the building and can have immediate and long term undesired effects. Apart from damage to the building contents, structural damage is unavoidable if the problem persists. Water damage can be compared to fire as a cause of building decay and deterioration. Water is hydrophilic and to convert it into hydrophobic is the definition of waterproofing.
Concrete is Hydrophilic But What Makes it Absorb Water?Concrete, bricks, stones and mortars are composed of crystals of carbonate, silicate, aluminates or oxides, whose surfaces are rich in oxygen atoms, which carry negative electrical charge of hydroxyl groups, which carry both negative and positive charges. Such surfaces are polar and are also called hydrophilic. When water comes into contact with these surfaces, hydrogen bonds are formed between the surface and the water molecules. Once the buildingmaterials come in contact with water, they absorb water through their pores by the capillary action.
Concrete, which is prepared by mixing of cement, sand, aggregate and water, is the most successful building material of the modern world. Portland cement is made from clay and limestone. Once the cement has been mixed with water, a reaction commences. The chemical reactions are complex but the hydration reaction of cement with water produces insoluble silicate compounds and calcium hydroxide (Scheme 1.1 and 1.2).
Carbonation starts simultaneously with hydration (Scheme 1.3). Carbonation hardens the concrete and helps reduce the permeability of the concrete. However, carbonation reduces the alkalinity of the concrete and it is the alkalinity of the concrete which protects the reinforcing steel in a steel-reinforced concrete structure.
Strength of Concrete
Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strengthforming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted. The relationship between the water/cement ratio and porosity is illustrated in the figure give below.
During hydration calcium hydroxide is produced which protects the reinforcement from corrosion since the steel cannot corrode in highly alkaline condition. Normally, concrete exhibits a pH above 12 because of the presence of calcium hydroxide-the term pH is a measure of the alkalinity or acidity, ranging from highly alkaline at 14 to highly acidic at zero, with neutrality at 7.
Although the precise nature of this passive film is unknown, it isolates the steel from the environment and slows further corrosion as long as the film is intact. The effect of the environment on mineral building materials is a natural process, which has not attracted significant scientific interest until recently. The initial work in Germany around 1900 investigated the weathering of natural stones. The problem, which has now attracted is the entry of water containing dissolved toxic substances to the inner parts of the concrete by capillary action.
This statement may be extended to the entry of deteriorating agents as a gas or in solution. Later a problem associated with modern concrete construction emerged-that of steel corrosion in steel-reinforced structures causing spalling. Unless this phenomenon of degeneration of reinforcement is not slowed or stopped, buildings will not be durable and can lead to problems of safety. Infact depending on the chemistry of the environment the malignancy can set-in as early as 3 months of the substrates exposure to the strong environment. Rain with dissolved materials from atmosphere, CO2, SO2, SO3, Nitrogenoxides present in the atmosphere around and water penetration by rising damp influence the building structures and cause deterioration. Macing spray + salt water, Gases, deicing salts and rain with dissolved chemicals from atmosphere influence the bridge structures.
How Water Enters?Normally we would be expecting a building to be watertight but there are always ingress points on the concrete, in other parts of the building because of variety of reasons and water can enter through these points to cause the following damages
- Corrosion of metals such as steel reinforcement in concrete structures causing malignancy.
- Swelling of plasterboards and subsequent debonding of ceramic tiles.
- Possible short circuit of lighting and power points.
- Blistering of Paint.
- Damage to structures and finishes such as floor joints, beams, floors, studs, skirting, and frames.
- Health problems due to dampness, which may lead to respiratory problems, growth of micro-organisms and exposure to gas like radon.
The environment is polluted with chloride, carbon dioxide and other gases like sulphure dioxide, oxides of Nitrogen, sometimes known as acid rains and these pollutants dissolve in water, enter into the building and damage the reinforcement.
In some states, in India, there is a report that because of high uranium in stone the presence of highly dangerous and killer gas radon to be checked. Concrete building contributes significantly to the environmental pollution more so when we use products like bitumen and asbestos.
A dark roof coated by bitumen can attain a very high surface temperature and in addition the reflected radiation from adjacent surface can raise the surface temperature much above than attained by direct radiation. The composition of the Asphalt will vary based on the origin of crude oil.
Saturated felts consist primarily of organic or inorganic fibres (asbestos) which are interlocked to form a continuous sheet, then saturated with asphalt or coal tar pitch (organic felts only) and perforated for use in roofing. The coal tar is known to contain chemicals, which can be classified as polycyclic aromatic hydrocarbons, a class of chemical with harmful properties. Polycyclic aromatic hydrocarbons in high concentrations are harmful not only to wild life, but to humans as well.
Inspite of these problems, we would atleast want to live in a house which is comfortable and secured. Unfortunately, indoor pollution is quite prevalent and equally damaging. Important sources of chemical indoor pollutants include outdoor air, the human body and human activities, emissions from building materials, furnishings and appliances and use of consumer products. Microbial contamination is mostly related to the presence of humidity.
The heating, ventilating and air conditioning system can also act as a pollutant source, especially when it is not properly maintained. Two essential components of a healthier home are moisture control and air infiltration. Excess moisture and/or high humidity can contribute to the growth and dispersion of biological contaminants like mold and dust mites. Excess air infiltration resulting from warm and cold air meeting within wall cavities can cause condensation and contribute to mold growth which can cause upper respiratory irritation and infections and a myriad of other health effects, including allergic reactions, hypersensitivity pneumonitis (like bacterial pneumonia), eye irritation, ear infections, skin rashes and various immunologic symptoms.
The typical components of building a healthy home include foundation waterproofing and slab moisture control; advanced framing techniques; air sealing and advanced insulation techniques; energy efficient, high performance windows; energy efficient and sealed combustion appliances; high efficiency air filtration and ventilation; humidity control; and carefully selected interior finishings.
Biological pollutants, which are living organisms, can cause serious problems like fungus growth in the house causing allergies, infections etc. Two conditions are essential to support biological growth; nutrients and moisture. These conditions can be found in many locations, such as bathrooms, damp or flooded basements, wet appliances, rooms with seepage and leakage.
Some diseases or illness have been linked with biological pollutants in the indoor environment. Moisture control and waterproofing of the house is one of the solutions to avoid biological pollutants inside the house. Therefore, it is essential to fix leaks and seepages and it is equally important to ensure that mold surfaces are clean and after waterproofing, there is no further mold growth throughout the house, including attics, basements and crawlspaces, and around the foundation. See if there are many plants close to house, particularly if they are damp and rotting. They are a potential source of biological pollutants.
In view of the fact that water does not only damage the building but also causes health hazards and it is therefore essential to give top priority to waterproofing.
Approaches to Building ProtectionApproach 1
Change the environment—To reduce the level of damage the level of pollutants at particular situations could be reduced, for instance, by the careful siting of industrial areas and by reduction of motor vehicle emissions and other emissions.
Reduce the water ingress—The ingress of water could be reduced by design and by intervention. For instance flashings can be used to run water off buildings and monuments. Rising damp may be stopped by intervention so arresting decay due to salts. Drainage may be improved.
Protect the building material by impregnation—The building material may be impregnated with a material which will reduce liquid water ingress. At the present state of knowledge it is not possible to impregnate the building material and effectively stop damaging gas diffusion.
Protect the building material by surface coating–The surface of the building may be coated with a specialist surface coating to interrupt the diffusion of damaging gases and liquid water. Alternatively, this coating may be a thicker protective coating such as a render. This coating should allow the transmission of water vapour.