Building Durable Structures
Durability of concrete structures is the prime issue of concern for builders and consumers all over the world. Sustainable construction and sustainable development are the goals which the civil engineering fraternity is aiming at today. The time has come to design and construct structures, targeting a specified service life.
This would not only save precious raw material resources and cut down on wasteful activities, but also help reduce the carbon footprint of cement and construction activities, and preserve the environment. To create sensitivity about these issues and bring designers, engineers, builders and consumers - mainly government agencies like PWD, CPWD and development authorities - on the discussion table and exchange ideas and information, the National Council for Cement and Building Materials organised a seminar on 'Durability and Service Life Design of Concrete Structures' at its Ballabgarh (Haryana) premises on 7th April, 2017.
The seminar evoked an overwhelming response and attracted participation of about 250 delegates from India and overseas. Technical sessions were organised on (among other topics) 'Durability and Service Life Design', and 'Newer Materials and Sustainability', with six papers scheduled for presentation in each session. Eminent experts from IITs, government institutions and agencies, along with the cement and construction industry, presented their views through invited lectures, keynote speeches and panel discussions.
Welcoming the delegates to the seminar, Ashwani Pahuja, (DG-NCB), said, "For environmentally sustainable economic growth, it is necessary to build concrete structures using sustainable materials and ensure that the built facilities retain their required performance over the long term. Therefore, sustainability, durability and service life design are interrelated and an optimum balance amongst all these three parameters is a must to ensure maximum technological mileage in a given situation." He added that in the absence of proper design of life of concrete structures, the annual expenditure for repair and rehabilitation of these structures would increase.
"Using durable and sustainable materials with maximum service lives would be a fundamental challenge for engineers and scientists. Developing effective and durable concrete and repair materials and prolonging the service life of structures is a challenge for researchers and engineers today," Pahuja noted.
In the first technical session, two keynote speakers, Professor B Bhattacharjee from IIT-Delhi and Professor Manu Santhanam from IIT-Madras presented their views. Professor Bhattacharjee dealt with the issue of 'Durability and Service Life Design of Concrete Structures in the Indian Context' and Professor Santhanam spoke about 'Use of Combined Durability Parameters for Different Exposure Conditions'. The session was chaired by Hasan Abdullah, Director, Ministry of Water Resources, River Development and Ganga Rejuvenation, and co-chaired by Dr Subrato Chowdhury, formerly Chief (R&D), UltraTech Cement Ltd. The session had three presentations from NCB and one from JSW Cement.
Professor Bhattacharjee presented different zones required for service life prediction of concrete structures in India which presently needs revision in existing standards for plain and reinforced concrete (i.e., IS 456:2000). A few relevant models were discussed and the results were presented by him. A relatively new approach to durability design of concrete was presented. Professor Santhanam presented a fresh way to specify performance parameters for different service environments, by linking the criteria to the prevalent transport mechanisms in that environment.
By using this approach, several concrete mixtures in the study were analysed for their suitability in different service environments - (i) exposed to airborne salt but not in direct contact with seawater (ii) permanently submerged in seawater and (iii) tidal, splash and spray zones. The results presented by him also confirmed the superior performance of concretes with mineral admixtures in chloride-laden environments.
The second technical session had two keynote presentations on service life design and an invited talk. The first keynote speaker, Dr AK Mullick, Former DG-NCB, highlighted important parameters for 'Prediction of Service Life of Concrete Bridges Designed to New Bridge Code IRC:112'. Thereafter Dr Chowdhury presented his views on 'Service Life Design and Prediction of Concrete Structures'; the paper was co-authored by Ashok Tiwari. Thereafter, Dr Shashank Bishnoi, Professor, IIT-Delhi, spoke about 'Modelling of Carbonation in Portland and Blended Cements'.
This session included one presentation each from Ambuja Cement, DCRUST, Murthal, Haryana and NCB. The session was chaired by Professor Bhattacharjee and co-chaired by Sanjay Pant, Head-Civil Engineering, Bureau of Indian Standards, New Delhi.
Dr Mullick presented the new durability provisions introduced in IRC: 112 to guard concrete structures against chloride corrosion and carbonation corrosion. Chances of carbonation front reaching the reinforcement bars under adverse atmospheric conditions (RH between 50 to 70 percent) were minimised by the choice of w/c ratio and cover depth prescribed, provided the concrete is well-compacted and well-cured. The provisions presented by him indicate that additional protection measures may be required, when the concentration of acid-soluble chloride ions on the surface exceeds 1.0 per cent by weight of cement. Dr Chowdhury spoke about the gaps existing in international and national codes and guidelines dealing with service life design of concrete structures.
In his presentation, he laid emphasis on how no approach for service life design of concrete structure adequately incorporates the concrete preparations and executions policy and practice. Dr Bishnoi (Associate Professor, IIT Delhi), Invited Speaker, spoke on the topic of 'Modelling of Carbonation in Portland and Blended cements'.
The third technical session on 'Newer Materials and Sustainability' also included two keynote presentations, one by Professor Radhakrishna G Pillai, IIT Madras, on 'Effect of Corrosion Inhibiting Admixtures on the Chloride Threshold of Steel and Transport Properties of Cementitious Systems', co-authored by Anand Godara and Sripriya Rengaraju, and the second by Sanjay Pant on 'Approach to Sustainability in Construction of Buildings and Built Environment, with Special Reference to Cement and Concrete'.
This session had a presentation by students - one from Shree Cement and one from NCB. The session was chaired by Ramesh Chandra, Special Director General (HQ), CPWD, New Delhi, and co-chaired by Vivek Naik, President Elect-ICI, Apple Chemie India Pvt Ltd.
Professor Pillai dealt with the performance evaluation of different types of corrosion inhibitors. Highlights of the study show that addition of bipolar inhibitors with nitrites could lead to a significant reduction in compressive strength. Nitrites could accelerate the hydration reaction leading to the formation of microstructure with voids, which in turn leads to a lower strength. This should be considered while designing the concrete mix.
Pant spoke about the approach required for sustainability in construction. According to him, building maintenance is a wide subject covering not only maintenance of building services, but also the maintenance of all other aspects, including the structure itself. Effective operations and maintenance is one of the most cost-effective methods for ensuring reliability, safety and efficiency of a building.
Inadequate maintenance of energy-using systems is one of the major causes of energy wastage. Also, inadequate maintenance of systems that consume water, including plumbing and HVAC systems (as applicable), can result in excessive usage of water. Good maintenance practices result in substantial savings in consumption of energy and water, and should be considered as a resource.
The seminar concluded with a panel discussion, featuring experts like Dr AK Mullick, Professor B Bhattacharjee, Sanjay Pant, Ramesh Chandra and Professor Manu Santhanam. The discussion was moderated by VV Arora, Joint Director and Head-Centre for Construction Development and Research, NCB.