How Crucial Waterproofing of Concrete Structure Is?

Dr. Surendra P. Bhatnagar, Chairman & Managing Director, Tech-Dry (India) Pvt. Ltd., Bangalore.

Water is Elixir but Hydrophilic, Concrete is an Enemy

Waterproofing of Concrete Structure
Cost of repair and rehabilitation is exorbitant.

The amount spent on repair and rehabilitation of concrete structure in US is around $ 8.3 billion per year.

Even 15 years back, the annual cost of corrosion of concrete bridges and support structures was estimated to be in the range of $165 to $ 500 million.

The annual cost of repair of parking garage due to corrosion was estimated at $300 to $400 million.

Out of 500,000 bridges in USA, 200,000 were reported to be under severe distress. Remaining 300,000 also needed repair and rehabilitation. The cost for replacement of 300,000 bridges was worked out to be around $112 billion.

As the third millennium dawns, the United States is in the midst of a "bridge crisis." Maintenance needs for older bridges have far outpaced available resources. This situation indicates the need not only for improved repair and rehabilitation techniques but also for a comprehensive approach to bridge management. In India, Repair and Rehabilitation is more expensive than the original cost of the structure. The Tsunami Housing Reconstruction Programme envisages the construction of about 1,300,00 concrete houses at an approximate cost of Rs. 1,50,000/- each.
Waterproofing of Concrete Structure

Rapid industrialization, urbanization, and population growth in the twentieth century have greatly affected the natural environment, the effect of which is seen as climate change regionally and globally.

Major structural failures during natural calamities is an exception rather than the rule. During these calamities buildings collapse and the devastating result is the end of the hopes, dreams and future of large number of population. Needless to say the recent natural calamities like Tsumani in Tamil Nadu, heavy rains and flood in Mumbai are examples where we have no words to express our grief. Buildings are more likely to suffer a failure of the hydrophilic envelope with consequential interior damage due to the intrusion of wind and water.

The greatest threat to human life and property loss resulting from earthquakes is associated with seismic vulnerability of existing construction that was either not designed for seismic resistance or no care was taken to protect the reinforcement. Reinforcement is like a spinal cord of the building and once the malignancy sets in, these structures are highly vulnerable to the natural calamities.

Reinforced concrete revolutionized the building industry. Water, which is elixir of life, is a serious enemy to hydrophilic concrete structures.

Environmental Impact on Structures

Waterproofing of Concrete Structure
The ingress of damaging materials into structures may occur in the gaseous state or in the liquid state. This makes the design of a durable protection system all the more difficult. Gaseous damaging materials include CO2 , SO2 , SO3 and nitrogen oxides present in the pollution in the atmosphere upon entering the building material as a gas, may dissolve in water present in pores and capillaries forming a dilute acid solution. Water contacting a structure may also contain these dissolved gases and may contain salt from marine conditions or from salts used in de-icing operations (Figure 1 and Figure 2), where water contains acidic gases, evaporation of the water from the surface concentrates the acid to a very high level just before dryness. The frequency of ingress, temperature, and general climatic conditions influence the severity of the attack.

These damages result in high cost of repair and maintenance and sometimes much more than the cost of the building.

Let us address those cases where the awareness of waterproofing and its implication could have not only avoided the tragedies but also the durability of the building and the money that we spend on repair and maintenance could be used in creating infrastructure in India, which is badly needed.

Indian Railways

Indian Railways are more than 150 years old and perhaps an example in the world. The Indian Railways carry 1.40 crore passengers and 140 lakh tones of freight, operating 15,000 trains every day. Its trains cover a distance equivalent to the one between the earth and the moon four times a day! It is interesting to know that the network of 63,000 route kilometres spread across the length and breadth of the country has one lakh and twenty thousand big and small bridges. Forty- four per cent of them are more than 100 years old. There is a general perception that old bridges are unsafe for transport. The network has bridges as old as 135 years but they continue to be safe.

Waterproofing of Concrete Structure
Although these bridges are old a proper repair, rehabilitation and protection of reinforcement by inhibiting the ingress of water can rectify these problems atleast for several years. But unfortunately this programme does not consider the modern scientific methods and the techniques to safe guard the durability of these bridges. The rehabilitation and rebuilding of old and distressed bridges, almost 3000 have been included in the planning and the expenses of about Rs. 1,530 crore have been kept for next few years. This money will go waste and repeated repairs would be required if the consultants and waterproofing experts are not familiar with the modern techniques. The interdisciplinary approach between structural engineer and waterproofing consultants is required.

Fate of Jetties and Briges

Various generations of protective products have been developed to counteract the aggressive actions of the environment against concrete. Good results have been obtained with barrierpenetrants: after penetration in the concrete they form a barrier against water and salts dissolved in it. Different families of these hydrophobic agents or waterproofs are already being used for many years in construction industry: Silicones, siloxanes, silanes. The silanes used for waterproofing are mostly alkyl-trialkoxy-silanes and thus monomer products. The siloxanes are oligomer or polymer alkyl-alkoxysiloxanes.

Waterproofing of Concrete Structure
The starting product for all siliconorganic compounds is alkyl-trichlorosilane, the alkyl-group is represented by the symbol R. By transformation of this silane with alcohol (R’-OH) only, the corresponding alkyl-trialkoxy-silane is produced together with separation of hydrogen chloride. The reaction with alcohol and water gives oligomer or polymer siloxanes, depending on the amount of water used. The last two products differ in their degree of polymerization.

The hydrophobic treatment reduces the absorption and transport of liquid water and salts dissolved in it. Whereas the penetration of water in liquid form should be entirely prevented, the waterrepellents must penetrate as deep as possible into the concrete substrate to obtain a guaranteed long-term durability. At the same time a maximum penetration depth is an essential prerequisite for an effective protection against chloride ingress and chloride induced corrosion of the reinforcements.

The conditions of jetties in our country in general are miserable. Few examples are given below where the structures have deteriorated and got damaged on account of not giving due importance to waterproofing at the time of construction.
  • P & Oliver Port-Chennai
  • Port of Kandla
  • Ontario
  • Zeebrugge Harbour
  • Port of Saint John
We have our own experience —Mumbai Port Trust after complete testing selected the most appropriate waterproofing product, which was not finally included because of so called cost reasons. This is an important point, which I want to make that such kind of consideration will destroy our infrastructure and would continue to have Jetties or for that matter any infrastructure in the same conditions as they are today.

Tech-Dry (India) Pvt. Ltd., has been working on this subject of anti-corrosion and anti carbonation along with Tech- Dry Melbourne who are well-known experts in this field since last 23 years and we take this opportunity to mention our products, which we believe are cost effective and unique.

Role of Waterproofing in other Products

Waterproofing of Concrete Structure
Mineral-based building materials are widely used for their excellent durability. One important characteristic of even the most durable materials is their porous surface structure and hydrophilic nature. Because these structures readily absorb water, exterior walls can quickly become discolored or damaged.

These façade coatings should be able to arrest the ingress of water, pollutants and chemical attack but unfortunately the common problem for many façade is their lack of water vapor permeability. When water enters the interface between the coating and the substrate coating, failures occur in the forms of blistering, cracking and peeling. By allowing water to escape these coatings, failures are avoided. In a well-protected façade, absorbed moisture must be allowed to escape into the atmosphere and the coating itself must last as long as possible.

"Structural integrity is of prime concern in evaluating deterioration of garages. If impaired it must be restored and steps instituted to maintain the structure in a safe condition. Structural distress may be defined as a condition where one or more elements of a building are so impaired that the structure’s ability to carry its designed load safely cannot be assured."

Failure and Damage in Light Construction

Structural failures in light construction, whether bearing masonry or light framing, can be broadly categorized as those events arising from the lack of a continuous path of load resistance from the roof to the foundation, and events arising from the breaching of the envelope, pressurization of the building and consequential blowing out of the leeward walls, sidewalls, windows or roof.

Ultimately, all loads on a structure, wherever placed, will be transmitted to and must be resisted by the foundation. If there is a weak link in the path from point of loading to the foundation, that is where the failure will occur. If the roof is not adequately anchored to the walls, an excessive uplifting load on the roof will not be transferred through the walls to the foundation. At this point we will discuss the common conventional method used in India, which only aggravates the above problem and they should be avoided.

Brick Bat Coba / Surkhi Cracks due to temperature variations

The brick bat coba treatment through successful in the damp heat of coastal regions cracks up completely on contact with the variations of temperature faced in North India and other such climates between day and night temperature.

Imposes Unnecessary Load

This system has the disadvantage of imposing an unnecessary load on the system. Once cracks appear they are almost impossible to repair and water as in the case of the tar felting travels below the coba and exits wherever it finds a path. It is impossible to trace the inlet point let alone repair it.

Almost Impossible to Dismantle for Repairs

Some parts of the coba stick so well to the concrete that even if an attempt is made to dismantle the system the slab gets damaged.

Disadvantages in using Brickbat Coba

  • In due course numerous cracks are developed in the lime terracing. Water penetrates through these cracks to R.C.C. slab below it. Due to shrinkage of cement, lots of cracks are also formed on the plaster of the parapet walls. Rainwater seeps through these cracks into the bricks and slowly comes down to the R.C.C slab.
  • Because of improper compaction, often the concrete of the R.C.C. slab is full of voids and honeycombs. Once the water reaches the R.C.C. slab, it easily seeps inside and corrodes the reinforcement, thus weakening the structure itself.
  • Water, after seeping through the R.C. C. slab, makes the ceiling and walls damp. In severe cases water starts dripping from ceiling. All these leave ugly patches of dampness on the ceiling and walls and paints peel off in addition to the damage to structure and reinforcement.
Leakage in the building is a very common problem and they are on the top of the list of owner’s complaints.

Rainwater intrusion into a recently completed building is one of the most traumatic of all unpleasant events for a new building owner.

The leaks can be variety of them in the whole building envelope and can be repaired and rehabilitated. But the best solution would have been if the waterproofing had been undertaken prior to the building construction these problems could have been avoided.

The cause of repair and rehabilitation covers so many factors but the major cause is water and deterioration.

Cause of Deterioration

Water, incompatible materials, and lack of maintenance are the major causes of damage to the buildings. The introduction of water is usually the result of the incorrect use of materials, particularly non-compatible repair materials, and the lack of maintenance; 95% of all deterioration can be linked to water. Once introduced and allowed to remain, water can weaken the chemical structure and encourage insect infestation. Allowed to continue, a building will eventually become unstable and collapse.

The moisture content of building materials varies in response to changes in the local humidity and will not usually damage the material or induce decay. The paradox of concrete structure is that it is a highly porous material. The concrete structure is forced to absorb high levels of water; however, its porous nature in collaboration with the warm climate allows it to adequately evaporate this to same level without harmful side effects. This cyclical feature is assured as long as the pores are not clogged by incompatible, less porous materials and the structure is being maintained.

Corrosion

Once the water enters into the structure and the reaches reinforcement –corrosion or cancer of the building starts. Concrete has a pH of approximately 12.5, and this provides a protective environment for the steel reinforcement because a thin film of passivating iron oxide forms over the surface of the steel (Hausmann, 1965). However, two processes lead to a breakdown of the passivating film and initiation of corrosion:

1. An acidic environment develops when carbon dioxide from the air mixes with water in the concrete pores (carbonation) that removes the passivating layer.

2. The passivating layer can become permeable due to the presence of chloride ions that penetrate into the concrete from marine environments and chloride in sand and aggregates.

The corrosion of reinforcements has resulted to be one of the most frequent causes of their premature failures, which can set in, as early as 3 months depending on the surroundings. Monitoring the corrosion rate, assuming the uniform corrosion and the loss in diameter decreases linear with the corrosion rate, allows calculating the remaining load carrying and the safety of the structure.

Carbonation

Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous concrete and neutralizes the alkalinity of concrete. The carbonation process will reduce the pH to approximately 8 or 9 in which the oxide film is no longer stable. With adequate supply of oxygen and moisture, corrosion will start.

Waterproofing of Concrete Structure
The reaction of Ca(OH)2 with CO2 takes place by first forming Ca(HCO3)2 and finally CaCO3 , the product precipitates on the walls and in crevices of the pores. This reduction in pH also leads to the eventual breakdown of the other hydration products, such as the aluminates, C-S-H gel and sulfoaluminates.

The relative humidity with which the pore solution is in equilibrium greatly affects the rate of carbonation.

Consequently carbonation occurs at a maximum rate between 50 and 70 percent relative humidity. In addition to atmospheric conditions, carbonation rate is also influenced by the permeability of the concrete, and the cement content of the concrete. Cement content of approximately 15 percent produces a concrete relatively resistant to carbonation.

The two most common causes of reinforcement corrosion are (i) localized breakdown of the passive film on the steel by chloride ions and (ii) general breakdown of passivity by neutralization of the concrete, predominantly by reaction with atmospheric carbon dioxide.

The first mid-long term records concerning the effectiveness of a waterrepellent agent under in-site circumstances. A probability method for interpretation of test results and prediction of the service life of the quaywall was updated.

Rail Corrosion

Rail corrosion is the result of interaction between a damp environment and traction current leakage. The leakage is a greater problem than the humidity factor. We would like to deal with railway sleepers, which are replaced from time to time and are not durable because of the corrosion of the reinforcement.

Waterproofing of Concrete Structure
We also need to take into consideration the crushed stone deposit around the flanges of the rails by modern public works vehicles. Graders/levellers, tamping machines, forming machines, etc., have the ability-and opportunity – to contribute to this problem when put under the pressures of increased productivity expectations and /or demands and reduced working times. In haste, crushed stones tend to be deposited around the flanges of the rails, in essence covering it. It is when there is this lack of above metal plate that it becomes a significant element/ contributing factor in the overall problem of isolating the rail in relation to the ballast. Observations made on the replaced rails confirm that the corrosion sets in where moistness from condensation or dampness is present. This condensation and dampness are crucial elements that produce a catalytic effect on the corrosion.

Railway Sleepers Corrosion

The Railway Sleepers that the Railway departments are making today are not very durable even though they use M50 grade mix. The environment and the toxic substances brought by water ingress in the seepage will definitely affect the sleepers, corrode the reinforcement causing cancer to the same and therefore it is necessary to waterproof concrete sleepers. There has been a continuous effort to produce durable sleepers, which complies with the rising requirements relating to loads on the track and traveling speeds of the trains as usual today.

Internal Environment Pollution
Fungal Growth

Waterproofing of Concrete Structure
Fungal infestation of buildings has become a significant factor in how the integrity of structures is assessed.

Large water intrusions of the building envelope, such as roof leaks and pipe ruptures have traditionally been handled by drying out and removing significantly water damaged material in the affected areas, however, little attention has been given to the effects of fungal growth. Additionally, in the past, small leaks that led to localized fungal growth were not considered significant problems. As a result, the assessment of the amount and spread of fungal growth in buildings has become a significant factor in determining the overall condition of a building.

Construction materials are not manufactured in sterile environments nor is the air brought into buildings sterile, thus fungal spores are readily available in most indoor environments. While fungal spores are ubiquitous, active fungal growth will not occur until moisture and a suitable source of nutrients are available.

The type and level of species and the presence of mycelial fragments are used as indicators of moisture damage and fungal growth in surface and dust samples. Species commonly associated with water damaged construction materials include Aspergillus, Chaetomium, Penicillium and Stachybotrys. Mycelial fragments in samples are used as an indication of active growth.

Needless to say the problem of safe shelter can be solved to great extent if waterproofing is given its due importance.

Waterproofing of Concrete Structure
Before concluding we would like to say please give priority to waterproofing and join us in our efforts to create awareness and:
  • To have a durable structure
  • To save energy
  • To save load on your building
It is only possible if we create scientific society which means people at large should look into these problems rationally and logic should prevail. Do not compromise for cheap products, look for cost effective and durable products.

Do not compromise for cheap products, look for cost effective and durable products.

NBMCW February 2006

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