Smart Materials & Structures

Biography

Biography: Nirmalya Karar

Abstract

Building materials and their usage depend on the climatic conditions of an area. In the Indian context, concrete based roofing and reinforced concrete structures have gradually replaced all other brick and mortar based structures, whenever people can afford these. A major reason is the touted long life of reinforced concrete based structures. Most Indians spend a substantial part of their savings in building a house with a permanent durable roof, which is expected to last at least a few generation. The earlier roofing method was lime mortar covering over stone slates/slabs, supported by wood, stone or steel beams. These have been gradually replaced with reinforced concrete, due to their supposed long life, touted to be a few hundred years. However, in many parts of India, these do not last beyond 50 years or so. In contrast, famous reinforced concrete structures of Europe based on Portland cement have lasted for 120 to 150 years. The Roman era concrete structures have lasted two thousand years or so. So it needs to be understood why this construction principle often fails in tropical India with a much heavier rainfall and peculiar climatic and ground water conditions. The issue to be looked at is: a ) is it about not adapting the methodology properly or b ) is it an issue about other parameters which are absent in the European and American scenario. As a preliminary study, some locations in Delhi national capital region were studied which are quite badly affected where severe cracks appeared in all buildings requiring urgent extensive repairs in all concrete components, including roofing and columns. The steel rebars had totally degraded and separated out from the cementing material. These cross-sections were tested across the radius for understanding the corroding material and to pin point their source. The experimental technique used was TOF-SIMS. The components for concrete preparation are cement, sand, steel rebars, stone and water used extensively. All these areas also had non - potable ground water, which had also been used extensively for construction. The same salt impurities that were present in water in large quantities were also found in the outer regions of the degraded steel rebars. So as correlation, it was surmised that these salts presence of water slowly degrades the concreting material and also the steel rebars inside. The methodology is slow chemical etching. However, the chemical parameters for cement can in reality also fluctuate a lot while the components for sand used are not always known in the Indian context. The content of salt in ground water also varies a lot all over India and changes with time. More extensive analysis is under progress.