Advanced Waterproofing and maintenance techniques of concrete structures
Advanced Waterproofing Techniques of Concrete Structures:
Waterproofing products are developing every day. For waterproofing of concrete structures, there are systems like Brick bat coba in use for more than 60 years. At the same time, new products are developed continuously and added to market. The recent trend is to avoid bulky – heavy treatments like brickbat coba. The aim is to avoid load on structure and save efforts on breaking. This has given rise to adding different waterproofing membranes which are improvised over existing waterproofing membrane techniques.
Waterproofing membrane include:-
E P D M (Rubber) membrane
Loosely laid membranes
Chemically reactive treatments
E. P.D.M. membrane
What is E.P.D.M. membrane? The full name is Ethylene Propylene Dien Monomer. This is a kind of Rubber. The rubber membrane is better than Bitumen / Tar based membrane in following respects:-
Temperature sensitivity – They are not sensitive like Bitumen, which softens during summer months.
Chemical resistance – Bitumen membranes are sensitive to acids present in bird droppings. Rubber has better resistance to acids.
Longevity – The rubber is having better longevity due to improved temperature and chemical resistance.
The E.P.D.M. membranes are used widely over terrace. However, it requires protection from mechanical damage like tearing due to sharp objects. This protection is provided by the concrete screed. The EPDM membrane is bonded to base by rubber solution.
Loosely laid membrane: PVC Membrane
These are normally loosely laid over a base. The membranes are factory made and supplied in roll form. The PVC is sensitive to Ultra Violate rays and hence normally not used on terrace. It is used in underground structure like basements, water tanks etc. The base is prepared by laying P.C.C. Pipes are fixed at regular intervals. The membrane is then laid over the P.C.C. The pipes are allowed to penetrate through the membrane. The raft concrete is then laid over the membrane. The pipes are passed through raft.
The side wall construction is then taken up. The membrane is then taken over side walls and brought above ground level. The underground structure is thus enveloped in a membrane. This membrane envelope prevents the water to come in contact with structure and prevents leakage. The base below P.C.C. is grouted with cement at different stages to prevent subsoil water to enter through a slab.
Chemically reactive waterproofing
a) Using crystallization chemical as a concrete admixture.
These chemicals are added to concrete while mixing. The chemical starts reacting with free lime as soon as hydration process is complete. The crystals are formed as reaction products and block the pores. Another version is using chemically reactive waterstops at the construction joints. The most common leakage spot in the underground structure is construction joints in walls, walls, and raft. The chemically reactive waterstop is placed at the time of construction. The chemical is liberated as soon as it comes in contact with water. This reacts with free lime and forms the crystals. These crystals block the entry of water.
b) Grouting with Gel forming compounds As already discussed in the section of Tanking waterproofing, it is not possible to excavate around underground structure during the service life of a structure, to carry out waterproofing. The only way then remains to act from the inside (i. e. negative side of waterproofing). This is achieved by tanking. It is necessary to grout the structure to stop active leakage, with cement grout. This is sometimes possible but many times leakage does not stop with mere cement grouting. Thus a need of better chemical is essential. This need is fulfilled by chemically reactive grout. These chemicals are polyurethane based. The chemical is injected in liquid form. It forms a gel like substance as soon as it comes in contact with water/moisture forms foam or Gel like substance. This foam prevents the entry of water into concrete and renders the structure waterproof.
We have seen in previous section about how water leakage takes place. We have also seen various waterproofing techniques and how they work. You will find that there are more than 200 companies manufacturing a variety of waterproofing products. It becomes extremely difficult to select a system suitable for your particular project when such a wide spectrum of choice is available to choose something for your requirement. Then the question comes, as how to select the right product? This requires careful consideration.
Factor no. 1: Establishing cause of water leakage:-
This is the first important factor which governs the water leakage. For example, if leakage is caused by entry of water through a crack in the structure, then we have to look options for sealing the crack.
Factor no. 2: Climatic Conditions:- Climatic conditions include several factors like:-
b) Relative Humidity
Let us see the details of each factor:-
Rainfall needs to be considered in different ways like annual rainfall, per hr rainfall or maximum continuous rainfall etc. When you consider annual rainfall, it needs to be considered as what is the duration of rainfall in months vis – a – vis how many millimeters of rainfall.
For example, Mumbai gets annual rainfall of 2000 to 2500 mm, but it is restricted to only 4 months. Whereas Kanyakumari receives about 1200 mm rainfall, but it continues to rain almost throughout the year. The other factor is per day rainfall. In the city like Mumbai you may get 200-300 mm rainfall in 24 hrs, also there are occasions when rainfall continues for 7 to 8 days without stopping.
In each of the cases, the effect of rain to cause leakage will be different. When it rains continuously for 7 to 8 days, it will saturate the building surface and profuse leakage caused will take place. Whereas leakage caused by a single shower lasting for a few minutes will be very less.
b) Relative Humidity:- Relative humidity will have an effect on the expansion contraction of waterproofing coatings/membranes. The expansion-contraction will be different in a dry climate as compared to humid climate.
c) Sunshine:- Sunshine contains Ultra violate rays. The effect of ultra violates rays will be very much more in areas of bright sunshine. Whereas in the cloudy climate effect of Ultra violate rays will be less. The places like Bengaluru or Belgavee in Karnataka will have a cloudy climate on many days as compared to places like Jaisalmer in Rajasthan, where sunshine is present on almost all the days.
d) Temperature: -Temperature plays a very important role when expansion – contraction of waterproofing material is to be considered. This needs to be considered in two ways viz. Di-urnal and seasonal.
Di-urnal – This is the difference of temperature in 24 hrs of the day. For example, during summer, a place like Nagpur will have Max temp of 480C and minimum of 240C. This gives a difference of 240C in just one day. If you consider seasonal fluctuation it will be 480C in summer and 50 in winter, giving a difference of 430C. In contrast to this, in a place like Mumbai, the difference in a day & In season will be quite moderate. More the temperature difference, more the expansion – Contraction of waterproofing material. This excessive expansion – contraction can lead to failure of a waterproofing system.
Factor no. 3:- Previous performance of a system
This is a most important factor in selection. If a system has performed well under similar conditions for a considerable length of time, then the likelihood of its success is much more. This is the most useful factor while deciding for selection of waterproofing using new technologies.
Side wall leakage:
We have seen leakage and techniques for a terrace and underground structure. The other major area of waterproofing is side walls. The water leaks through the side walls of the buildings. This problem is common to new as well as old buildings. The waterproofing measures are required in both the stages, i.e. new construction as well as maintenance waterproofing.
Common causes of side wall leakage
What are the common causes of water leakage through the side wall?
The leakage of water takes place through cracks present in the concrete / plastered surface. These cracks are formed due to following causes:-
These are formed either due to overload or structural failures. The main & most commonly observed cause is corrosion of reinforcement bars. These cracks are formed due to expansive forces created by corrosion products along the bar. These cracks are wide and allow entry of water easily.
ii) Shrinkage Cracks
These are formed due to shrinkage of plaster mortar/concrete. The water enters through these cracks.
iii) Separation cracks
These are normally formed due to improper filling of joints between masonry and R.C.C. Columns/beams.
b) Cascading effect of rainwater over Dead walls This is the most common cause of sidewall leakage. The rainwater after hitting the top of wall cascades down the vertical surface. This cascading water saturates plaster during heavy & prolong spell of rain. This saturated plaster transfers this water to brick masonry. The bricks take this water to the internal surface. This water emerges out from the internal surface and spoils the paint etc.
c) Plumbing / Sanitary pipe
Many a time there are leakages through broken pipe joints, broken pipe fittings. This leakage water seeps into the wall.
d) Construction defects:
The scaffolding holes or concrete tie holes are many time not filled properly. These improperly filled holes then allow entry of water.
e) Leakages through Aluminium sliding windows:-
This is one more common cause. The aluminum sliding channels are fixed to sub-base with screws. If these screws are not fixed properly, the water will leak through them
How the side wall leakage can be stopped?
a) Structural cracks – These shall be treated with Polymer Modified Mortar or Superfluid micro concrete.
b) Shrinkage cracks – These cracks shall be sealed with crack sealers or bandage prepared out of polymer + fabric reinforcement.
c) Separation cracks – These shall be sealed with polymer modified mortar
d) Cascading rainwater – The best way to prevent this leakage is to create horizontal projections which will keep the wall dry by stopping cascading effect. Other methods are applying putty which blocks the pores in plaster/concrete The next method is an application of waterproof paints. These paints block the pore & prevent entry. e) Construction defects – The tie holes or scaffolding holes shall be filled with polymer modified mortar.
f) Plumbing sanitary pipes – The broken pipes & fittings shall be 39 replaced.
g) Aluminum Windows – All the screw holes, gaps shall be sealed properly. The incidence of rainwater shall be reduced by fixing weather sheds.
Advanced Maintenance Techniques of Concrete Structure
The execution of waterproofing at Construction Stage is the reasonably straightforward job. At the time of construction access to various areas etc is readily available. This is not the case with maintenance waterproofing. There are many restrictions during the service life of a structure. The main difference is, structure is occupied by the residents. The work has to be carried out from whatever space available, without causing nuisance to the occupier.
Leakages through roof
Many times leakages are noticed from roof. To decide whether to go in for full blanket treatment or localized treatment, we need to study : - i. The extent of leakage ii. Cause – Effect Analysis. If leakage is noticed only through few localized spots then there is no need for going in for a blanket treatment. These leakages can be stopped by studying Cause – Effect Analysis. The measures may include cracks sealing etc.
Wet Area Leakages
This is the most tough & daunting task. It is essential to establish cause effect relationship before arriving at the solution. The establishing cause – effect relationship can be done by following steps given below.
1. Decide whether it is really a leakage. Many a times user shows you a spot which is just a mark of old leakage.
This shall be tested first by filling the surface. If it is a leakage then the surface will be wet or cold to touch. Once it is established that leakage is present, then following rules shall be applied.
The common proverb “Prevention is better than cure” is very apt for waterproofing work also. In human life we are more than willing & ready to take medicine than to maintain the health with proper lifestyle. Same is very much applicable to waterproofing works also. The prevention can be achieved by different ways given below:-
The principle is “Do not allow water to come in contact with building surface”. Normally we allow water to touch the building. Allow it to leak and then look for the remedy. If we don’t allow water then all this botheration is saved. This is achieved as shown in photographs below:-
Precautions during construction
Following precautions, if taken during construction can help to achieve good waterproofed buildings
a) Lay good concrete by proper mix design, compaction, curing, proper cement content, less water-cement ratio.
b) Sealing of all joints of pipes and pipe fittings, conducting hydrostatic pressure test or smoke test.
c) Filling of gaps around door frames with micro – concrete rather than using white cement
d) Paying attention to all the details of waterproofing at proper stages
e) Stage wise testing
f) Proper detailing of service elements keeping enough space.
Managing waterproofing works:
Waterproofing is a very burring problem as discussed in the Initial introduction. It is imperative that it needs to be managed carefully to achieve the best results.
There are two class of waterproofing viz:
a) Construction Waterproofing
b) Maintenance Waterproofing
The perspective in both the cases is different. Let us see details:-
i) Construction Waterproofing:- The cost of waterproofing is always less than 5% of construction cost. This makes it a very un-important item to builder/contractor. The builder does not pay much attention to detailing or maintenance as it is very low cost item. At the same time, he is aware that the item of waterproofing has a lot of nuisance value. If waterproofing fails it brings a lot of ill publicity.
Organization the works – New Construction
Let us first see the organizing details for New Construction work.
This start from the design stage, which involves:-
a) Considering all aspects of maintenance
b) Avoiding complicated design
c) Avoiding small sized sanitary ducts of 450 x 600 mm
d) Providing enough space for maintenance e) Involve waterproofing consultant at design approval stage.
Some examples of bad design practice:
Avoid horizontal drain pipes
This is followed by precautions to be taken at the pre-construction stage. The details are as follows:-
Write down Tender specifications & BOQ, do not leave it to a contractor
Select contractor after scanning his past record
Contractor selection shall be done on the past performance basis, rather than lowest price.
The maintenance waterproofing needs to be organized in a different way. There are major differences like:-
a) Long shutdown times are not available.
b) Budget constraint:
This gives rise to decide whether to go in for full repair or to go in for part work as a stop gap measure. If the affected area is only a small part of the whole area, then it stops gap arrangement (or part work) is worth considering. This will help to postpone full work. If the damage is small and full work is considered, then there is every likely hood that structure may get damaged while breaking the good work.
Advanced Waterproofing and maintenance techniques of concrete structures | Advanced Waterproofing techniques of concrete | Managing waterproofing works | selection of right waterproofing technique