A massive earthquake on the 25th of April left Nepal and parts of India devastated. It is another sad reminder to our human race that we are puny against Mother Nature. No amount of planning could have prevented current loss of life. The main reason for the loss was lack of building materials and construction practices suited to the region.
Although it is not possible to reverse this happened loss, we can try to minimize such loss-risks in future. One way of doing it is to have a look at building materials and construction practices that offer higher survivability, easy availability, cost-effectiveness and faster construction times for reconstruction. One such solution – in form of alternative AAC products – exists in the neighbourhood and with minor modifications, it can offer the right building material, not only for Nepal and India but also for other developing and developed countries. This solution is called Block Composite Elements (BCE). It relates to an equivalent technology with AAC panels used for three row-house projects in Mexico City in the 1970s, designed by the same engineer. These houses survived the great earthquake that hit Mexico City in 1985. Also, experience from Japan and the Great Hanshin earthquake in 1995 (sometimes named after Kobe) confirms to the fact that AAC is well suited to resist severe earthquake stresses.
Introduction of BCE
Block Composite Elements (BCE) is a hybrid combination of AAC (PFA or sand), and HCM (High-strength Concrete Mortar). BCE is attractive for a block producer, who wants to expand his production to a complete building system. Interestingly, an organization not producing AAC blocks can still produce pre-fabricated elements by sourcing and processing blocks.
It also offers the ability to move beyond the 6 m span of traditional horizontal member. It may go upto 9 m for floor panels and 12 m for roof panels. This reduces the required number of beams and columns, thereby lowering consumption of concrete and steel.
BCE units are composed of AAC blocks, stacked in vertical or horizontal directions in a second production stage. The compatibility is secured by pre-stressing, which is carried by the HCM-component, while AAC is an ”in-fill” component, building up the body of the structure. The pre-stressing is designed to eliminate the dead weight deflection and/or tensile stress under service load, hence eliminating cracking.
Depending on project requirements, production of such units can be adapted to CAD/CAM conditions. This allows design and production of customized elements as per project specifications.
Essentially, concrete mortar is used for compression but also for shear and anchorage of the reinforcement. This leads to savings of up to 75% of steel compared to steel-reinforced genuine AAC products and 75% of the concrete used in genuine concrete elements. Such a product makes financial and environmental sense by not only reducing consumption of concrete and steel but also by reducing effective emissions and the embodied energy required for a particular project.
The BCE-system is a high capacity building technology that characteristically carries a live load double its dead weight, while genuine concrete members carry only half. When combined with lower capital investment, flexibility and superior performance compared to genuine concrete, BCE-system offers a perfect solution for producers and users in India.
BCE from an Indian perspective
AAC material has got off to a delayed but good start in the Indian construction industry. Of course, AAC industry across India is in a very nascent stage with a major concentration in the western part of the country. Northern and Southern India are catching up in terms of production and usage of AAC blocks. Even though the absolute production/consumption figures look impressive, in relative terms they amount to around 1% of the total block market. We definitely have a long road ahead of us. While increasing the market share, we also need to focus on consumer expectations and on innovations to make AAC more lucrative and beneficial to manufacturers, users and occupants.
Keeping these factors in mind, the AAC industry in India needs to graduate from blocks to bigger pre-cast components like panels, slabs, lintels, etc. As many of you are aware, currently there are only two manufacturers that offer AAC panels, slabs, lintels, etc. There are multiple reasons for lower production of AAC panels and slabs. Lower production of such AAC products (other than AAC blocks) is also responsible for lack of awareness among users and limited penetration in India.
1. Lack of upgrade options:
We have witnessed a spurt of growth in the Indian AAC industry over last five years. Eager to get a share of this market, a lot of promoters chose to set up AAC blocks plants. In their haste, they ignored options for integrating equipment required for manufacturing steel-reinforced AAC panels, slabs and lintels. Major constraints behind this conscious choice were capital squeeze and space requirements. Although a number of these plants did well and can afford extra capital now, they may not be able to upgrade due to unavailability of space or massive changes required to existing works for integrating reinforcement module. BCE may offer an economical solution under such circumstances.
2. Unavailability of sand
Sand is a basic raw material for manufacturing steel-reinforced AAC products. Apart from Eastern India, availability of sand is extremely restricted. Moreover, cost and fluctuating availability of sand rule it out as a material of choice. So, most AAC plants in India have to rely on PFA as the basic raw material. As most of you may know, it is not possible to manufacture steel-reinforced AAC products by using a full PFA recipe (100% PFA), necessitating the need for a proportion of sand.
By applying the BCE technology is it possible to use a full PFA recipe blocks and combining them to produce sophisticated building members with very low capital investment. BCE offers a range of alternative AAC products to suit to Indian market.
This article was written by Vishal Kansagra under guidance of Prof. Bo Goran Hellers. Image courtesy – Prof. Bo Goran Hellers.