PrologueIt rained and people sought protection against rain water falling on the head, Figure 1. The concept, the art and the science of waterproofing developed from this desire for protection against rain water.
In the beginning, most people thought that the objective of waterproofing was to prevent rain water from falling on their head. As people started using delicate and costly materials, and housing equipment, systems, etc. inside buildings, the ensurement of watertightness of building type structures became important. It will be seen that the prevention of the ingress of water into buildings is necessary for reasons more important than the prevention of an inconvenience or an architectural nuisance or for facilitating the proper utilization of the space inside. In the conventional scheme of making buildings waterproof, doors have door leaves, windows have shutters and roofs are made water-tight through specific waterproofing treatments or arrangements.
With time, it was recognized that it would be a good idea to make water retaining structures also water-tight. But it took a while to recognize that there was more to waterproofing than to prevent rain water from falling on the head or arresting water leakages through water retaining structures. It took time to recognize that the failure to waterproof structural elements, in addition to roofs of buildings, could lead to situations like that shown in Figure 2.
With delays to realize, and failures to act, buildings, bridges and other structures started becoming unusable because these were not waterproofed in time. This happened, generally and more quickly in the case of concrete structures, which were built during recent decades, than in the case of structures, which were built before 1965 or so.
The lack of durability of concrete structures has been a worldwide phenomenon. In a paper in 1991, Papadakis, Vayenas and Fardis1 stated : “The last two decades have seen a disconcerting increase in examples of the unsatisfactory durability of concrete structures, specially reinforced concrete ones.”
The problem of unsatisfactory durability is more acute in India where it has reached an alarming state. The alarming situation in India, caused by the early distress in reinforced concrete structures, is reflected in Technical Circular 1/99 of the Central Public Works Department, Government of India, wherein it has been stated that while works as old as 50 years provide adequate service, the recent constructions are showing signs of distress within a couple of years of their completion.
In most cases of concrete structures, the structural distress in the form of cracking in the concrete elements or collapse of the structure is an external manifestation of corrosion in the ferrous elements inside.
There are reasons behind the early or accelerated rate of distress, Figure 2, in modern day concrete structures. The rate, at which modern day structures started reaching states of early distress, accelerated with the use of High Strength Deformed (HSD) reinforcing bars (rebars) in the construction of reinforced concrete structures and also with the use of deicing salts on highways in cold climes of affluent countries.
Among other factors, contributing to the decaying process, was the lowering of the period of wet curing of concrete from 28 days to 3–7 days or none. As there is a move towards a greater use of Portland Pozzolana Cement (PPC) in lieu of Ordinary Portland Cement (OPC) in concrete, this change in the type of cement will have its effect on the durability of concrete structures, unless special provisions will have been made.
This paper addresses the problem of early distress in concrete structures and solutions thereto. As surface protection of structures by waterproofing is proposed as a viable solution to the problem of early distress in concrete structures, it is explained why waterproof structures are durable structures.
Durable and effective waterproofing systems are described later in this paper.
Early Distress and CausesThe alarming state of affairs with constructed facilities of recent decades has put civilization in peril1-3. When humanity is in peril, God comes to show the way. In such circumstances ten years ago in 1996, Lord Ganesh, Figure 3 showed the way when the stone statues started drinking milk on offering by worshippers. Ganesh started drinking water. It was Lord Ganesh of rock or stone who drank milk and water. Ganesh, cast in metal, would neither drink milk nor water.
Lord Ganesh drank milk and water to teach architects and engineers a lesson. The lesson was : concrete, an artificial stone, would absorb water and other liquids. The rate and quantity of water would depend upon the permeability and porosity of concrete.
This absorption of water by concrete, though undesirable, is inevitable in the case of concrete structures without surface protection. This water, that enters inside the structure, creates a moist environment. When air from the environment, containing oxygen, enters into the structure and reaches rebars or prestressing elements of steel, oxidation, the most common of the different processes of corrosion of steel, takes place, if the Fe2O3 protective layer of passivation on the surface of rebars and prestressing elements will have been destroyed due to carbonation (by carbon dioxide from air) or chloride intrusion or due to pozzolanic reaction from the use of PPC or High-Volume Fly Ash (HVFA) cement3-5 in concrete. Though the process of corrosion requires oxygen and a moist environment, carbon dioxide, chlorides, acids and sulphates can further add to the destabilizing processes. It needs to be noted that, like oxygen, even acids and chlorides, the well-known agents of corrosion, will be ineffective in causing or augmenting rebar corrosion unless there will be a moist environment. Similarly, other harmful reactions in concrete, viz., alkali-silica reaction, sulphate attack, etc. will fail to take place unless there will be moisture. On the other side of the picture, water alone will not cause any problem unless there will be oxygen. A case in point is a ship under water on the sea bed. In the absence of sufficient oxygen, the rate of corrosion is very slow even when there are chlorides in the water. Thus, though it is essential, for corrosion to take place, that the concrete environment, surrounding rebars and prestressing elements, be moist, submersion in water is likely to inhibit the process of corrosion.
The above suggests that all structures above ground and those portions of structures below ground, which are exposed to the atmosphere (e.g. basements, tunnels, underground water reservoirs, machine pits, lift pits, and so on), will be vulnerable, if left unprotected, whereas rebar corrosion may not be a problem in the case of foundations. In simpler terms, all structures, exposed to air, will be vulnerable. Of these, concrete structures (primarily reinforced concrete structures), constructed during recent decades, have been characterized by early decay and distress. There must be reasons for this development, that goes beyond any possible shortfall in the quality of construction. This has been borne out in a survey6-9 in Calcutta, that was carried out by the writer’s firm in July 1999.
This writer 3-22 has written extensively on the basic causes of the problem of early distress in concrete structures, constructed during recent decades, and solutions thereto. Of particular interest to the reader will be the articles in Refs. 3, 4, 8 and 9. The writer has shown in Ref. 9 and elsewhere3,4,6,7,16,19-22 that the use of high strength rebars with surface deformations has been primarily responsible for the early decay in concrete structures of recent constructions. The problem has been more acute in India where the HSD bars were of the cold twisted deformed (CTD) type, commonly known as tor bar.
CTD bars are particularly susceptible to early corrosion (Figures 4 and 5) as high post-yield stresses are locked in such rebars from the time of manufacturing, inducing speedy corrosion in keeping with the phenomenon of stress corrosion at high stress levels, even before concrete is cast (Figures 4 and 5). Early corrosion sets in CTD bars also because the protective surface layer of Fe2O3 or Fe3O4 is destroyed during cold twisting of the rebar as a part of the manufacturing process.
Other factors, which can make concrete structures predisposed to early decay and distress, is the lowering of the duration of moist curing of concrete from 28 days of earlier years to 7 days or less and the shift towards the use of fly ash based PPC from OPC that used to be commonly used in construction in earlier days.
The PPC concrete lacks the capacity of OPC (with about a month’s curing) to produce 15 to 25% (by mass of cement paste) calcium hydroxide Ca(OH)2 and with it to maintain a pore water alkalinity of 12.4 and above for prolonged periods of time, thereby protecting rebars and prestressing elements through the formation and preservation of the Fe2O3 layer of passivation. Furthermore, unlike OPC concrete, PPC concrete lacks the properties of self- healing of pores and cracks. Details can be found in Ref. 5.
In summary, in addition to the absorption of water or moisture, porous concrete permits the diffusion of carbon dioxide and oxygen, all of which are present in the atmosphere. Because of the changes in the properties of materials of construction and because of the shortening in the duration of curing, today’s concrete structures, compared to structures of earlier decades, are affected more adversely by the atmospheric and other external agents of corrosion, viz., water or moisture, carbon dioxide, oxygen, etc.
The SolutionAn obvious solution to the problem of early decay and distress in concrete structures would be to use the appropriate rebar and cement and to cure the concrete over prolonged periods of time. That would mean the use of plain round bars of mild steel and OPC with curing for about a month. But since the construction may not be with plain round bars of mild steel and OPC, coupled with a month’s curing, the next best option would be to protect the structures, both new and existing. This protection of concrete structures will have to be, as a minimum against water, oxygen and carbon dioxide. It can be said, as an analogy, that concrete structures, similar to steel structures, can benefit from surface protection. Just as in the case of steel structures, the failure to provide surface protection to concrete structures will mean loss of durability and high life-cycle cost of the unprotected structure.
Effective and durable waterproofing treatments will make structures durable. Such treatments will also prevent any architectural nuisance of damp ceilings and walls.
This concept of providing surface treatment to concrete structures for the purposes of making such structures waterproof as well as durable has been stressed by the writer10 since 1987 through numerous publications and lectures. The concept was adopted by Central Public Works Department of the Government of India in 1999 and subsequently in the code IS 456:200024. It is mentioned in clause 8.1.1. of the code that “One of the main characteristics influencing the durability of concrete is its permeability to the ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious substances.” It has further stated in clause 8.2.1 that “The life of the structure can be lengthened by providing extra cover to steel, by chamfering the corners or by using circular cross-sections or by using surface coatings which prevent or reduce the ingress of water, carbon dioxide or aggressive chemicals.”
It has been explained in details in Ref. 8 that, of the four alternatives, recommended in IS 456:200024, the provision of surface protection systems is the only logical and practical way of ensuring long life for concrete structures.
Even six years after the publication of the code24, architects and engineers appear to have overlooked the mandatory provisions of the code as they have failed to implement the provisions in clause 8 of the code.
The failure to provide the surface protection will not only condemn the unprotected structures to early decay and distress, the constructed structures will also fail to meet the requirements of the code IS 456:200024. The surface protection system is provided as a waterproofing system on the surface of structures, and not on reinforcing bars25. Though the code has recommended the provision of surface coatings, all concrete surfaces are not necessarily amenable to the application of coating systems. Thus, this writer believes that since the objective is to prevent the ingress of harmful elements, coatings or other waterproofing systems should serve the purpose of lengthening the life of concrete structures.
Effective Waterproofing TreatmentsIt has already been explained that waterproofing systems or treatments, provided on the surface of structures, can do much more than preventing an inconvenience or architectural nuisance. Such treatments, if effective, can make structures durable. That, however, requires that the treatments are not only effective in preventing the ingress of water into the structure, but that the treatments are also durable. Many different materials and systems have been tried for the waterproofing of structures. Field experience shows that most of the treatments fail to achieve the desired results even in the short term.
The reasons are many, and these include:
a) Wrong concept
b) Lack of a will to do the work well
c) Failure to adopt an appropriate technology
d) Failure to improvise
Wrong ConceptFailure of waterproofing treatments due to the application of wrong concepts are all around. A few examples will suffice. Waterproofing treatments are provided on compressible treatments for thermal insulation. The excessive compressibility of the material for thermal insulation leads to large movements in the waterproofing treatments and their consequent failures.
Waterproofing treatments are provided on a course of Plain Cement Concrete (PCC), which fails for the lack of reinforcing elements and a lack of adequate bond at the interface between the substrate and the PCC. A small quantity (0.5% to 2.0%) of a plasticiser or a superplasticiser is admixed with concrete in the name of waterproofing, simply because it meets the requirement of the code IS 2645:2003, which, with its name Integral Waterproofing Compounds for Cement Mortar and Concrete ¾ Specification27, has a misleading title, ignoring the fact that the text of the code reads : ‘The permeability to water of the standard cylindrical specimen prepared with the recommended proportions of waterproofing compound shall be less than half of the permeability of similar specimen prepared without the addition of the compound when tested in accordance with the method given in Annex B’, thereby qualifying chemicals, without waterproofing properties, as chemicals suitable for successful waterproofing treatments.
Lack of Will to Do The Work WellIt is believed that the manufacturer of chemicals will be particularly keen to see that the waterproofing system, based on his chemicals, will perform well. In the Indian environment, many manufacturers are keen to sell the chemicals to anyone for any purposes and the work of waterproofing is executed by contractors as authorized/ approved applicators.
In this system of work by applicators, the quality of work generally suffers as:
a) The manufacturer of chemicals is not aware of the field conditions of individual sites, and the developer of the chemicals and systems, generally chemists, have limited knowledge about construction.
b) The applicator is not aware of the limitations of the chemicals.
c) The applicator does not use the right quantity of chemicals as he does not have the reputation of chemicals/ systems to uphold.
Failure to Adopt Appropriate TechnologyWaterproofing is an activity in the domain of civil engineering, and it involves structures. It can thus be very helpful to have a good knowledge of civil engineering and structures. Thus, when chemists and material scientists develop chemicals and systems of waterproofing , they are likely to overlook fine points in civil-structuralconstruction engineering, and the technology for waterproofing may not be appropriate. This is particularly so as most often technologies are first developed, and avenues are sought to apply the technology. The best results are possible when technologies are developed to solve problems, and not the other way round.
Failure to ImproviseEvery work site has a character of its own, requiring improvisation. Though a particular waterproofing chemical and a particular system will be employed as the basic treatment, local conditions frequently require for a successful waterproofing treatment that certain modifications are made to the implementation procedure or that a different chemical and a different system be employed locally as a stand-alone or as an additional treatment. A failure to make necessary improvisation may lead to a failure of the waterproofing treatment.
PERMAKAR TechnologyPERMAKAR Technology for waterproofing is free from the shortcomings, commonly found in other technologies. The waterproofing systems for waterproofing under Permakar Technology were developed to solve specific problems after others had failed to solve such problems by the application of different known systems of waterproofing.
It all started in 1983 when Metro Railway in Calcutta requested Engineering Services International (ESI) to arrest running water leakages and make dry the treated areas of the tunnel. Until that time, ESI excelled in providing consultancy services in wide areas of engineering related to nuclear power plants. Also, starting as the first Indian consultant to the Defence Research and Development Organisation of the Ministry of Defence, Government of India, ESI provided consultancy services on different projects of the DRDO. The experiences of ESI in the cutting edges of technologies in wide areas of engineering came in handy and the PERMAKAR surface treatment method of waterproofing for tunnels and other underground/water retaining structures was developed. The hitherto unknown and unthinkable surface treatment method succeeded where grouting or injection of different materials had failed. Here are copies of extracts from documents of Metro Railway, Calcutta on observations on ESI’s Permakar surface waterproofing treatments (a) inside the tunnels of Metro Rail, and (b) inside Pedestrian Subway at Tollygunge. “The surface treatments (as opposed to grouting) were found to be fully effective and in excellent conditions even eighteen years (in one case) and six years (in other cases) after the treatment.” — certificate.
(b) “However, temporary bored piles locations (total 8 locations), seepage of the leakage could not be stopped in the main subway with cement pressure grouting or Non-Shrinkable, Pumpable, Groutable (NSPG) due to which ‘Permakar’ Technology (surface layer) treatment was adopted and seepage/ leakage arrested completely to achieve ‘bone dry’ condition.” — project report.
The continued success of treatments under Permakar Technology and frequent failures of waterproofing treatments by others 12 gradually led to the development of systems of waterproofing for virtually all types of structures. The effectiveness and durability of waterproofing treatments under Permakar Technology have given beneficiaries of the work the confidence to include waterproofing treatments under Permakar Technology in the schedules of rates of work (SOR) of various organizations of the central and state governments. The versatility of waterproofing treatments in the line of Permakar Technology can be found in examples of waterproofing of different types of work.
Tunnels, Below or Underground Structures And Water-Retaining StructuresFigure 6 is a view of the pedestrian subway in front of Sealdah Station at Calcutta. The structure is known as the only zeroleakage tunnel around. A 6 mm thick Permakar 3 plaster type waterproofing treatment (Figure 7) was provided on the entire inner surfaces of ceiling, walls and floor. There is no water leakage.
Prior to the Permakar 3 treatment with an octadecanoic acid compound, waterleakages at construction joints, point leakage locations and honeycomb areas were arrested with cement, admixed with quick setting compounds Permakar 1 and Permakar 4. There were special treatments at ends of H-piles and at expansion joints.
The waterproofing treatment of the Pedestrian Subway at Sealdah is described in Refs. 26. There is virtually no difference in waterproofing treatments for tunnels, basements, machine pits, below ground structures, underground and overhead water reservoirs, swimming pools and other water retaining structures. Countless such structures have been successfully waterproofed with the Permakar 3 surface treatment. As the continuous Permakar 3 treatment is provided on the entire inner surfaces of the Pedestrian Subway at Sealdah, exposed to air, it provides the protection against carbon dioxide, oxygen, etc. as required in IS 456:200024. The unprotected outer surface, in contact with soil, generally does not pose any problem as there is very limited supply of oxygen and carbon dioxide, and water alone cannot cause rebar corrosion. The case is comparable to a concrete foundation of a structure. There is no corrosion, whereas above ground areas, exposed to air, have problems of early corrosion in rebars and prestresssing elements.
Building StructuresFigure 8 shows a typical building with the Permakar 3 (Figure 7) surface protection (5 mm thick on roofs and other locations, except bathrooms, where the treatment thickness is 6-7 mm). Over the years, over a hundred thousand square metre of concrete and old lime terraced roof structures were provided with the Permakar 3 waterproofing treatment. In most of these cases, earlier treatments by other parties had failed.
At the time of writing this paper steps have been taken for the waterproofing of over a thousand square metre of additional Permakar 3 surface treatments for roofs and walls of buildings in the year 2006.
The Permakar 3 waterproofing treatment can be provided virtually on all types of concrete, masonry and lime terraced structures. Unlike in the case of coating type treatments, the Permakar 3 waterproofing treatment can be provided on surfaces with honeycombs and large irregularities. The treatment can be provided on dry as well as wet surfaces. When tested for leakages, under a water head of 40 metres, a 5 mm thick Permakar 3-cement treatment was found to have zero leakage.
The typical building in Figure 8 can be provided with coating type waterproofing treatments with Permarpoof of modified phenolic resins instead of the plaster type treatment with Permakar 3, except in areas with honeycombs and large surface irregularities. Such areas can, however, be repaired and prepared for the Permaproof treatment. The details of the Permaproof treatment are shown in Figure 9. Figure 10 represents an example of total structural protection, provided in 1996. The concept was later adopted by CPWD in 1999 and included in IS 456:200024 in 2000. When tested for leakage under a water head of 40 metres, a two-coat Permaproof treatment was found to have zero leakage.
Being oil based, Permaproof can be applied only when the surface is dry. ESI has also PERMANAR-D (without or admixed with cement) for water-based polymer treatment. The polymer treatment with the organic compound Permaproof needs to be protected against ultraviolet rays. In the case of a roof, this protection is generally provided with a cover plaster which permits the normal use of the roof. In the more demanding case of roof gardens, advantage can be taken of the soil cover to give protection against ultra-violet rays. The cost of the waterproofing treatment for this more demanding case of roof gardens can thus be provided at costs less than the cost of waterproofing of a roof for normal use. It should be noted that, because of the possibility of roof drains getting choked, the material and system of waterproofing for horizontal roofs should be such that the same can be effectively used inside water reservoirs. Permakar 3 and Permaproof satisfy such requirements.
Roof Gardens for Green BuildingsBoth the Permakar 3 and Permaproof treatments have been widely used to waterproof roofs for roof gardens. Figure 11 shows the Permaproof waterproofing treatment (2 coats) in progress on the 6000 square metre roof of a water reservoir in Central park, Salt Lake City in the year 1996. Figure 11 shows Permaproof bridging fine cracks. Figure 12 shows the same roof with a green cover ten years later in 2006.
Permaproof, which has been used on roof and all other elements of buildings, superstructure and substructure of bridges and inside water reservoirs, provides resistance against chemicals used in gardening. Figure 13 shows an inclined roof with a green cover. Prior to the preparation of the green top, the roof was provided with the plaster type Permakar 3 waterproofing treatment (Figure 7).
BridgeBridges, like building roofs, can benefit from surface protection7,16,18. This writer propagated the idea and need for surface protection of bridges, which are more adversely exposed to the environment than buildings are. The idea is catching in India. Permakar 3, Permaproof, Permacil-GA and Permacil-B have been used to protect quite a few bridges. All areas of the bridge superstructure are given the surface protection with Permaproof, Permacil-GA and Permacil or combinations thereof, except that wet areas, like piers, abutments, etc., are given the Permkar 3 plaster type treatment (Figure 7).
Most often one coat of Permaproof, followed by a coat of Permacil-GA, is provided. Figure 14 shows such protection on the Bankim Setu (Buckland Bridge), a road over-bridge (ROB) at Howrah Station across the river from Calcutta. Figure 15 shows the same treatment on the girders of the Katakhali Bridge over the Goureswar river between Hasnabad and Hingalganj in West Bengal. Figure 16 shows a span of the multi-span bridge over the Ajoy river near Katwa Town connecting Katwa Ketugram Road,
West Bengal. Two coats of Permaproof were provided. In order to provide protection to the polymeric compound Permaproof against ultraviolet rays, sand was bonded to the top coat of Permaproof on the outer faces of the exterior girders. The interior surfaces were not given the sand cover. The piers were given the Permakar 3 surface protection, Figure 7.
Concluding RemarksConcrete structures, constructed with high strength rebars with surface deformations, are characterized by early distress, brought on by corrosion in the rebars. Prestressed concrete structures also suffer from corrosion in the prestressing elements. The presence of a moist environment inside concrete structures is a prerequisite for corrosion to take place. Since concrete, without any surface protection, absorbs water or moisture from the environment, it will be necessary to provide a surface protection system in the form of a waterproofing treatment to prevent the ingress of moisture/water and other harmful elements, viz., carbon dioxide, oxygen, etc. The provision of waterproofing systems on the surface of concrete structures will make such structures durable by delaying and slowing down the process of corrosion in the ferrous elements inside concrete structures. Any failure to provide surface protection to concrete structures will mean that such structures will not meet the requirements of the code IS 456:2000. Chemicals in the line of Permakar Technology, viz., Permakar 3, Permaproof, Permacil, etc. are very versatile and practically all types of structures, bridges, buildings, tunnels, water reservoirs and other water retaining structures can be protected with waterproofing systems, based on such chemicals. The surface protection systems make the protected structures durable, thereby lowering the life-cycle cost of such structures.
- V G Papadakis, M N Fardis and C G Vayenas. ‘Physical and Chemical Characteristics Affecting the Durability of Concrete.’ ACI Materials Journal, American Concrete Institute, March-April, 1991.
- Chief Engineer (Designs). ‘Technical Circular 1/99, Memo No. CDO/DE(D)/ G-291/57 dated 18/02/1999.’ Central Public Works Department, Government of India, Nirman Bhawan, New Delhi - 110 011.
- A K Kar. ‘Concrete Jungle ¾ Calamity May be Waiting To happen.’ The Statesman; Calcutta, 4 August, 2000.
- A K Kar. ‘Concrete Structures ¾ the pH Potential of Cement and Deformed Reinforcing Bars.’ Journal of The Institution of Engineers (India), Civil Engineering Division, Volume 82, Kolkata, June, 2001.
- A K Kar. ‘Concrete in the Context of Durability.’ RITES Journal, RITES Ltd., Vol. 8, Issue 1, April, 2006.
- A K Kar. ‘Deformed Reinforcing Bars and Early Distress in Concrete Structures.’ Highway Research Bulletin, Number 65; Highway Research Board, Indian Roads Congress, New Delhi; December, 2001.
- A K Kar. ‘Durable Concrete Structures for Infrastructure.’ All India Seminar on Improving Transportation in a Congested Metropolitan City; American Society of Civil Engineers ¾ India Section in association with The Institution of Civil Engineers, UK, Eastern Region, India Chapter, at Calcutta, 13 & 14 December, 2002.
- A K Kar. ‘IS 456:2000 on durable concrete structures.’ New Building Materials & Construction World, Vol.9, Issue-6, New Delhi, December, 2003.
- A K Kar. ‘Reinforcing bars in the context of durability of concrete structures.’ All India Seminar on Utilisation of Skyways and Subways in the Cities in India, organised by American Society of Civil Engineers ¾ India Section and Institution of Engineers, UK, Eastern Region, India, at Calcutta, 9th and 10th December, 2005.
- A K Kar. ‘Arresting Water Leakages in Tunnels and Other Underground Structures.’ All India Seminar on Underground Construction with Particular Reference to Metro Railways, organised by the Institution of Engineers (India), West Bengal State Center, at Calcutta, December, 1987.
- A K Kar. ‘Waterproofing of Structures.’ International Symposium on Housing, Energy & Environment, organised by Shelter Promotion Council (India), at New Delhi, 27–29 January, 1996.
- A K Kar. ‘Protection of Structures as a Means to Durability.’ All India Workshop on Preventive Measures Maintenance and Life Extension of Civil Engineering Structures, Civil Engineering Division, organised by The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 18 September, 1997.
- A K Kar. ‘Waterproofing As a Means to a Long Life for Structures.’ All India Seminar on Construction Chemicals, Present Status and Scope for Improvements, organised by The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 30th & 31st July, 1998.
- A K Kar. ‘A Long Life for Structures.’ MDC News, Management Development Centre, National Buildings Construction Corporation Limited (NBCC), New Delhi, September, 1998.
- A K Kar. ‘Durable Concrete Structures.’ MDC News, Vol. 8, National Buildings Construction Corporation Ltd., New Delhi, September, 1999.
- A K Kar. ‘Making Bridges Durable.’ All India Seminar on Development of Inter-State Highway Corridors, organized by American Society of Civil Engineers ¾ India Section, at Calcutta, September, 1999.
- A K Kar. ‘Durability of Containment Structures for Water and Hazardous Liquid Wastes.’ Environcon 99, 15th National Convention of Environmental Engineers, organized by Environmental Engineering Division, The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 26–27 November, 1999.
- A K Kar. ‘Protection of Structures as a Means to a Long Life for Bridges.’ Indian Highways, Vol. 28, No. 7, Indian Roads Congress, New Delhi, July, 2000.
- A K Kar. ‘Concrete Structures in the Twentyfirst Century.’ All India Seminar on Structures in the 21st Century, organised by American Society of Civil Engineers ¾ India Section, at Calcutta, 8–9 December, 2000.
- A K Kar. ‘Role of Cement and Steel in Causing Early Distress in Concrete Structures.’ 1st National Workshop on Ageing and Restoration of Structures, organised by Indian Institute of Technology, at Kharagpur, West Bengal, 11-12 January, 2001.
- A K Kar. ‘Reinforcing Bars and Early Distress in Concrete Structures.’ MDC News, No. 13; National Buildings Construction Corporation Limited (NBCC), New Delhi, January 2001.
- A K Kar. ‘Reinforcing bars ¾ the good and the bad.’ Steel Scenario Journal, Kolkata, Vol. 14, No. Q1, July- September, 2004.
- A K Kar. ‘Waterproofing for Green Buildings.’ Seminar on Elements of Green Buildings in Indian Context, organized jointly by Institute of Public Health Engineers and Central Pollution Control Board, at Agra, 4–5 March.
- IS 456:2000. ‘Indian Standard Code of Practice for Plain and Reinforced Concrete, Fourth Edition.’ Bureau of Indian Standard, New Delhi.
- A K Kar. ‘FBEC Rebars Must Not Be Used.’ The Indian Concrete Journal, Mumbai, Vol. 78, No. 1, January, 2004.
- A K Kar. ‘Waterproofing of Tunnels.’ All India Seminar on Geo-Technical Aspects of Infrastructure and Environment, organised by American Society of Civil Engineers ¾ India Section, and Institution of Civil Engineers, (UK), Eastern Region (India), at Calcutta, 10–11 December, 2004.
- IS 2645:2003. ‘Indian Standard :Integral Waterproofing Compounds for Cement Mortar and Concrete ¾ Specification (Second Revision).’ Bureau of Indian Standard, New Delhi.