Waterproofing Mechanism of Concrete Structures and Types of Waterproofing Methods
Water leakage is the most burring problem for all type of structures. It is common for R.C.C. Buildings, steel structures with Steel Roof, water tanks, Basements etc. includes We have advanced in the construction activities very much. Waterproofing mechanism of concrete structures is the process of making objects or structure waterproof or water-resistant so that it can't be affected by an external environment. We can construct 100+ storied buildings with totally Indian technology. Similarly, we have advanced in Infrastructure construction like tall bridges (Konkan Railway), Fully underground metro, highways in difficult Himalayeen terrain without any imported expertise. This technological advance is somewhat missing when it comes to waterproofing field. Waterproofing performance of concrete structure method protects against water ingress and corrosion. We have many products available. Many of them are manufactured with Technical Collaboration with MNCs from advanced countries from Europe, America etc. The achievement to have properly waterproof structure is not seen regularly. It is still elusive to have 100% waterproof structure.
This result in various measures taken like shown photographs below:-
Why does this happen? What is that so difficult part, which does not allow fool proof achievement?
We are going to deal with various facets of this problem in this 2 days workshop. The first question comes to mind is why water leaks through a seemingly strong, stone like material concrete.
Waterproofing Mechanism of Concrete Structures:
Concrete is a mixture of cement, sand, and aggregates. This achieves strength because of a chemical reaction is known as hydration of cement. The main ingredients essential for this reaction are cement and water. The quantity of required water cement ratio is 0.23 to 0.25. However, if we prepare concrete with this water cement ratio, it will be very stiff. Such stiff mix cannot be placed in formwork. To overcome this problem water cement ratio needs to be increased to 0.4 to 0.5.
Porosity in concrete
This extra water, which is used for workability does not take part in the hydration process. This remains as free water. This free water eventually evaporates. The space occupied by this water is now empty and becomes porosity of concrete.
This porosity is in two forms viz:-
- Gel Porosity
- Capillary porosity.
The same is shown graphically
The gel porosity is of very less dimension (nanometers) and not continuous. Gel porosity does not allow water to leak. The capillary porosity, on the other hand, is having more dimensions and is continuous. The capillary porosity allows water to flow.
How does water flow through concrete?
The water flow takes through porosity in the following ways:-
- Under hydrostatic pressure
- Through capillary action
The water flows under hydrostatic pressure in case of walls of water tanks, underground structure, slabs etc.
The capillary flow takes place due to sucking action caused by capillaries. The water is sucked from one end and transported to other. This happens in case of wall plaster and through walls of underground structure
We have noted that for water to leak following factors are essential:
- High water cement ratio
- Capillary porosity
- Hydrostatic pressure
This information is very useful when we have to select or design a waterproofing system. This is particularly so because it gives us cause-effect analysis. Once this relationship is known, then we can remove the cause and in turn, the effect will be stopped.
Class of Waterproofing:
When we carry out waterproofing? We have to carry out waterproofing during construction for new structures. We also have to carry out waterproofing during the service life of structure. This is called as maintenance waterproofing. These are the two main branches of waterproofing. The factors governing these branches are entirely different and will be dealt with in greater detail in subsequent chapters.
Types of Waterproofing Methods:
The market is full of different waterproofing systems. There are many companies manufacturing different type of systems. However, if you study all the systems, you will notice that they can be broadly categorized in 5 different categories. All the available systems can be easily fit into these categories.
These categories are:-
- Chemically reactive treatments
This categorization helps to understand various features, pros & cons of each system. This helps for proper selection of treatment.
Let us see the details of each system:-
Details of various systems:
There are two types of coating systems viz:-
- Film forming
- Changing surface properties (Water repellents)
Film forming coatings:-
These are supplied in liquid form or combination of liquid + power form. This is applied by brush or spray on the surface to be waterproofed. The liquid on drying forms a film over the surface. This film prevents the water to enter the porosity of concrete. The coatings are either elastic or nonelastic depending on the properties of liquids used.
Common materials used for coating:
Following are the common materials used for coatings:
- Bitumen / Tar based
- Cement based
- Epoxy based
- Acrylic polymer based
- Polyurethane based
- Polyester based
Bitumen / Tar Based:-
These are one of the oldest system, which is still in use. They are economical.
They are supplied in 2 forms viz:-
- Cold applied
- Hot applied
Cold applied systems are in the liquid state when supplied. These are applied by brush/broom. It forms a film on drying. Hot applied systems are supplied in a solid mass. There are heated to melt. They form liquid on melting. This liquid is then applied to the surface. Following are some application photographs.
Changing surface Properties (Water repellents):
These are chemicals supplied in liquid form. These liquids are applied to surface either by brush or spray. The surface tension properties of concrete (or surface to be waterproofed) changes on application.
The surface does not get wet when water drop (Rain) falls on the surface. When the surface does not get wet it remains dry & prevents water leakage. To understand this let us imagine our body surface. If you put water drops on a normal body surface, then the surface gets wet. But if you take an oil massage and then put drops of water, then drops of water slides down the body surface without wetting it.
This type of action is achieved when you apply these chemicals.
Common water repellent:
These chemicals are based on:-
i. Silanes / Silicones
ii. Aluminium Stearates
Siles / Silicones are solvent based and longer lasting. Aluminium Stearate based compounds are water based having short life. These repellents are suitable only for vertical surfaces. The common use to apply over stone facades, which prevents algae growth on stone and maintains the beauty of stone surface.
Membranes are thicker then coating. Their thickness varies from 3 to 10 mm.
There are 2 main type of membranes viz:-
- Factory made
- Site made
The factory made membranes are supplied in Roll form (like cloth) with standard width (about 0.9 to 1.2 m). Whereas site made membranes are supplied in two components, liquid + fabric. In membrane, fabric serves the purpose of reinforcement, whereas liquid acts as a binder and keep the fabric in place.
Factory made membranes or suitable for large areas without such offsets. The site made membranes are suitable where the geometry of the surface is complex, having many offsets, up-downs etc.
There are further subcategories of membrane like:-
- Loosely laid
- Bonded to surface
Common materials used for membrane are:-
- Bitumen / Tar Binder + polypropylene / glass fiber as fabric
- Cement + polymer Binder + Glass fiber / Nylon as fabric
- Rubber based membrane (EPDM)
- PVC v. Metal Foils
Loosely laid membranes are not bonded to surface to be waterproofed (Base). Hence any movement base is not transferred to the membrane, i.e. if the base cracks or existing cracks are widened it will not affect the membrane. In case of bonded membranes, the movement of a base is always reflected in a membrane. If base cracks, then there is every chance that membrane also will crack.
Following are some photographs:-
Advantages of membrane treatment:-
Faster laying – Job can be completed in short time
Lightweight – Does not impose too much load on structure.
No breaking – Breaking of old treatment is not essential.
Chances of Puncture – The membranes can get punctured under the movement of sharp objects.
Formation of blister – Water can enter through punctures. This water while evaporating in dry weather can create blisters due to vapor pressure. These blisters can create holes on rupturing, 19 rendering the treatment useless.
Temperature sensitivity – Some of the membranes are temperature sensitive like the bitumen based membrane.
Ultra violate ray sensitive – Many polymer/epoxy based materials are sensitive to Ultra violate rays of the sun. the properties of such materials changes when they are exposed to ultra violate rays. ? Bond failure – The bond between the membrane and base can fail. This may lead to failure.
What is barrier treatment?
A barrier treatment is a treatment which obstructs the flow of water. This obstruction dissipates the hydrostatic pressure. When the hydrostatic pressure is dissipated the flow reduces or stops. Also, it prevents water to enter into the porosity.
Which are the different treatments, come under the category of Barrier treatment?
a) Brick bat coba on terrace with different finishes like I.P.S. or china Mosaic
b) Box type waterproofing carried out on underground structures like a basement, water tanks etc.
How the barrier treatments dissipate the hydrostatic pressure?
The barrier treatment is having a considerable thickness of the order of 100+ mm. When water tries to enter porosity of concrete, this thickness obstructs the flow. This obstruction dissipates hydrostatic pressure.
How the brickbat coba is laid?
The slab is cleaned of all the loose material. The surface of the slab is then grouted with very thin cement slurry. The surface is then tested for water tightness. In case leakage is noticed, the surface grouting is repeated till leakage stops. Then the brickbats are laid over mortar bed to the required slope (1: 100). It shall then be ponded with water and tested for water tightness for 7 days. If any leakage is noticed, same shall be rectified. The surface shall then be covered with mortar layer (like I. P. S.) It shall then be finished with China mosaic. The box type waterproofing is similar in nature but natural stone like Shahabad /Tandur is used. Some photographs of Brick bat coba.
Box type waterproofing System– wall
Details of Box Type Waterproofing System:
What are the advantages of brickbat coba?
It is in vogue since last 65 -70 years
Reasonably proven system.
- Uses principal of recycling the material
- Considerable weight on the structure 24
- Cumbersome to break during maintenance waterproofing
These are recent additions to waterproofing treatments. The main type is crystallization treatment. In this treatment, the concrete surface is pre-wetted for 24 hours. It is then applied with 2 coats of a chemical. This chemical then dissolves in the water (of pre-wetted concrete) and travels into the porosity of concrete. The chemical then reacts with the Ca(OH)2 [lime] which is liberated during hydration of cement. This chemical reaction forms crystals. The crystals thus formed blocks the porosity of concrete and in turn prevents the water entry. There is excess chemical present on the surface. If a new crack is developed in the future, then same is again blocked by crystal formation. Thus this treatment has very good longevity.
Many a times leakage of water is noticed in the underground structure during the service life of structure. It is very difficult to access the outer face of the basement by carrying out the excavation. Under such circumstances, it becomes imperative to treat the structure from inside. This is achieved by tanking treatment.
The tanking treatment comprises of following steps:-
Inspect the surface and note active leakages
Stop these active leakages by repeated grouting till all the leakages are stopped.
Apply 2 coats of SBR polymer + cement slurry at right angle to previous coat.
Apply bond coat of polymer + cement and cover the area with polymer modified mortar.
The polymer modified mortar is well bonded to the surface. It has very high tensile and flexural strength and can with stand hydrostatic pressure upto 2 kg / cm2 (20 m water head).
Waterproofing Performance on Concrete| Types of Waterproofing Methods | Types of Waterproofing Membrane System | Evaluation of Waterproofing Membranes