C ement being the indispensable constituent of concrete, the building industry faces the major challenge of finding ways to low-carbon based construction around the world. Nations across the world produce 4.4 billion tonnes of cement annually. Though steel, wood and glass too are major constituents, their consumption by the industry is much smaller in terms of volume.
Although cement is produced in a powder form, it transforms into a different component while getting into construction. Cement production leaves a large carbon footprint on the environment as kiln furnaces have to be heated up to 1,500 degree Celsius using enormous amount of fossil fuels. Globally, 8 to 10% of total carbon dioxide emissions are believed to be contributed by the cement manufacturing process. A search is therefore on to find alternatives and replacement for cement in the construction industry.
If statistics pertaining to global final energy consumption are any guide, building industry consumes the major amount of energy i.e., 31% against 28% by all other industries, 27% by transport and 15% by other sectors. Conversely, the building industry contributes 29% to global emission (2014 figures) against 22% by transport, 35% by industry and 12% by other sources.
Carbon emission
India produced 425 million tonnes of cement last year. Of the total energy consumed, around 30% goes for buildings (construction, cooling, heating, lighting put together). Figures pertaining to annual growth in building floor area suggest that by 2050, India will overtake North America and Western Europe. In 2015, Indian construction industry built 15.8 billion square metres of floor area which is set to more than double by 2030 and rise up to 57 billion square metres in 2050. Going by these figures, the carbon emission scenario will be extremely dangerous.
Low clinker factor
Sharing worldwide concern on hazards posed by the industry, Anjan K. Chatterjee, Chairman, Conmat Technologies and former wholetime director of ACC, says the task of tackling emission is enormous as well as complex.
Delivering the keynote address at the Innovative World of Concrete-2018 organised by the Indian Concrete Institute in Bengaluru on Thursday, he said strategies should focus on using cement with low clinker factor, cutting down volume of cement in construction and using recycled coarse and fine aggregates. He said composite cement comprising 35 to 65% Portland cement clinker, 15 to 35% fly ash, and 20 to 50% of granulated slag could be one alternative but cautioned that very limited types of supplementary cementitious materials were permitted to be used. Even widely available and proven materials like silica fume, calcined clay (metakaolin) and limestone were left out.
Mr. Chatterjee opined that the studies so far have focussed only on testing and not on making the composite cements of superior performance and application-friendly. “The industry needs to probe if the partial substitution of natural aggregates by recycled aggregates could be made mandatory.”
The discussants were unanimous that transition to low-carbon concrete construction required multidisciplinary approach. Large volumes of construction in widely varying environment makes the tasks complex much beyond simple proprotioning and testing. Adoption of modelling at multiple scales based on actual field data is necessary. Though much innovation has happened, more is needed in finding substitutes for cement.
Affordable housing
India has a huge latent demand for affordable housing. There were 280 million households in India in 2016 but only 190 to 200 million of them were living in pucca structures. With current population growth at 1.3% and nuclear families growing at a pace of 0.9%, the nation faces the challenge of providing 10 million housing units to fulfil the latent gap in housing.
Arun Kashikar, MD and Head, R&D, Tata Housing, who figured out the housing situation at the summit, says continuous demand is currently the driver of growth in the affordable housing sector but there was not much prospect of reduction in pricing.
Mr. Kashikar says precast process helps brings down the cost and speed up construction with the added benefit of cutting down waste. He says latest innovations in prefab technology have addressed the issues of leakage, seepage, joint weakness and misalignments and developers could easily go for ground plus floors in the LIG sector. He said a complex of precast houses coming up in Peenya (under Tata Housing) is totally shorn of noise and dust. He says even if four to five million housing units are built a year, the current gap of pucca structures needed to house all people will take a decade.
Houses off the shelves
S.J. Vijay, Chairman, Salmon Leap Associates and Director, Home Mission India, said the new era in construction was one of ”industrialising the buildings” where homes could be bought off the shelves. He said that precast technology had progressed from precast slabs to building monolithic modules of rooms and washrooms which are built offsite and moved to the site of the housing complex. He said these modules could be incorporated with doors, windows and ventilators and washrooms with sanitary fitting offsite. He said 85% of housing construction has moved offsite in Singapore due to induction of new technology and laws mandating such practices.
Nagesh Puttaswamy of Ultratech introduced ‘Umix’, a ready-to-use and mix-in-the-bag product that may help households to carry out repairs, and enable filling of cracks quickly without creating a mess. The concrete can be prepared by adding two litres of water to a 20 kg bag.
