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Take pollution for instance. With increasing levels of toxins in the air, the living conditions are deteriorating and harming to human life to a great extent. 

 “With each construction project comes many issues with pollution – not just air, but noise and water too,” says Prakash Shah, Head of Technical Support at Elematic.

India can not afford to bury its head in the sand. Today construction plays a key part in the bigger picture in helping India solve its problems. 

Many projects are being implementing with environment in mind and with the use of advanced technology like precast.

“Huge development is under process in India since past couple of decades and it is projected to continue the path even more aggressive in the coming years,” says Shah. 

Every construction site with conventional practices in India create huge amount of waste and projects suffer from pilferages of materials. 

“These can be as high as up to 15 per cent of total materials, depending upon project,” says Shah.

 

Another major aspect is wastage in water being used for curing of concrete at site by just spraying and run-off of it. 

“With controlled temperature and water evaporation of concrete, plant manufactured precast elements would reduce the water consumption to great extent,” Shah notes.

Precast technology, where all precast elements are  produced in controlled factory environment and minimum amount of work needs to be carried out at actual construction sites, is the way forward.

With the potential to use local, recycled materials, precast concrete has much to offer in terms of sustainable construction. Precast concrete products consist predominantly of natural aggregates available locally in most places, making for low-carbon footprint deliveries to the precast factory. 

In relation to recycling, modern precast factories enable high manufacturing efficiency. New precast factories are built with closed-loop recycling systems where all wet waste is automatically conveyed back to a central recycling plant. Disused concrete buildings can be crushed and used in landfill or the loadbearing layers of roads. Water recycling and conservation is also a common feature of modern precast factories.

The precast industry's biggest source of CO2 emissions is cement with a heavy carbon footprint. Cement holds up to 70 percent of the precast product's total CO2 load.

"Cement manufacturing releases CO2 into the atmosphere when limestone is calcinated. Making cement in a kiln at a temperature of over 1,400 Celsius also requires a great deal of heat energy," explains Professor of Practice in Concrete Technology, Jouni Punkki from Finnish Aalto University, School of Engineering.

The precast industry works hard to reduce the CO2 emissions of cement by developing precast products and optimizing the cement content in concrete.

“The use of other cementitious materials, such as ground-granulated blast furnace slag from the steel industry and pulverized fuel ash from coal-fired power stations, is growing. Both of these additions have much lower embodied CO2 than cement,” Punkki says.

The material and energy efficiency of cement plants has been improved by utilizing waste materials from other industries as fuel for the cement kiln.

Precast production in controlled factory conditions has huge potential to improve the resource efficiency of materials, energy, and processes. Compared to cast-in-situ, precast uses less of everything – less cement, less water, and less steel. It produces less waste on-site and in the factory. This makes the carbon footprint of precast much smaller than in cast-in-situ construction.

“Concrete can be effectively heat-treated at the precast factory, thereby reducing the amount of cement needed for concrete products. It is also possible to use alternative binders in certain applications to decrease CO2 emissions,” Punkki says. 

The highly optimized and economical use of material makes precast pre-stressed hollow-core slabs one of the most sustainable products in construction. They feature tubular voids running the full length of the slab, making the slab much lighter than a massive solid concrete floor slab of equal thickness or strength. In the cross section of hollow-core slabs, concrete is used only where it is actually needed. Areas, where concrete acts only as ballast, are replaced with hollows. 

For instance, in 200-mm hollow-core slabs, 49.9 percent of the cross section consists of voids. In 400-mm hollow-core slabs, this percentage may be as high as 55.6. This brings savings of up to 45 percent in concrete compared with a plain cast-in-situ reinforced slab. At the same time, the amount of pre-stressing steel can be cut by 30 percent because of the lower self-weight. For an average apartment, this means savings of 14.4 tons of concrete and 275kg steel. 

The use of cement in hollow core slabs can be further reduced by optimizing their production process through efficient compaction. It is a win-win situation, with less cement used and less waste produced. 

According to Jani Eilola, Product Director Floor technologies at Elematic, a leading supplier of precast concrete production solutions worldwide:  “We have developed the hollow core slab production technology for well over 40 years now. As a result, the current Elematic extruder machines feature very efficient shear compaction that can save even up to 100 kilos of cement per one cubic metre of concrete compared to other compaction methods”. 

Eilola continues, “In 30 years, we have been able to reduce approximately 10 - 15 kilos of the slab weight per square meter without losing any good features. As a matter of fact, efficient compaction leads not only to a lighter slab but also to a stronger slab.”

Hollow-core slabs are typically used in the construction of floors in multi-storey residential, commercial, office, and industrial buildings. 

How to establish a hollow core slab plant?

Are you interested in starting to produce hollow core slabs? Here are some tips from Elematic's Jani Eilola about the points to pay attention to at the pre-planning phase: 

 

First, you should define the present and future needs for the production: the slab types, volume, and capacity as these are the factors that define the optimal factory layout, machinery, and floor area needed.

The required capacity of the plant plays a key role with regard to the machinery, storage and logistics needed. For companies starting in the precast business, it is wise to consider also the future needs for capacity expansion. If these needs are included in the factory layout from the beginning, it is easy to scale the production once the need for higher volume capacity emerges.  

You should also get to know the recommendations, restrictions, laws and regulations that may concern the end use of the product, the construction processes, or environmental issues in your country.

Another key issue is recruitment. What is the employee situation in the location? If the man-hour cost is reasonable and skilled personnel are available, a high level of factory automation may not be needed.  An efficient basic production line – such as Elematic SEMI – is a very good choice in such a case.  

Elematic SEMI hollow core slab production line has a capacity of 144-576 m2 per day, with one casting. It needs 9 people for operation and a land area of 4 500 sq.m.

For more information, please contact:

Marketing Manager, Elematic Oyj

nina.lehtonen@elematic.com