Small idea, major impact
Alternative construction ideas, such as concrete filler slab roof with cement blocks, can be applied where possible.
It feels good to read about radical alternative ideas in the Green Sense column, but how many of us can execute these in our own projects? Even if the owners are interested, the numbers could be very small given the unwilling builders, lack of materials, apprehensive masons or the fear of the risks involved. Each of the ideas written about in this weekly column since May 2010 is proven, in some project of this author, but a guaranteed performance alone cannot mean it will become popular.
Certain construction practices tend to replicate repeatedly, such that they form the mass of what we could call as the conventional. It is not always possible or desirable to replace mainstream ideas with alternatives, yet the spirit of the alternative can be applied where possible. Concrete filler slab roof with cement blocks can be a case in point.
One of the ideas behind the filler slab is reduction in the quantity of concrete, besides passive cooling, cost cutting and light weight construction. However, we need not discard the idea just because a clay ceiling block or Mangalore tile is not available. In most towns across India, cement blocks are available, both in hollow and solid models. Depending upon the slab thickness, an appropriate cement block of fitting size can be placed in between the reinforcement rods, before concreting. Of course, the spacing of rods and design of the roof have to be done by qualified engineers to ensure the roof is cast as per standards. The cement block is much cheaper, lighter and ecologically better than concrete, even though both are made from the same sources.
Nowadays, we get improved versions of cement blocks called autoclaved aerated concrete (AAC), which are light weight thanks to a porous cellular structure. Locally, they could be called as aerocon or siporex blocks. Compared to normal cement blocks, autoclaved blocks have nearly one-third density, but act as better thermal insulators and sound barriers and are water proof. They may not have low embodied energy due to the production technology and centralised factory with long distance marketing, but the fact that they replace an equivalent volume of regular rich concrete itself becomes a eco-friendly and non-conventional approach.
Autoclave blocks come in long sizes, so we need to cut them into three parts to get 8-inch long pieces, to perfectly fit within the spacing of steel rods. Once placed, they tend to shift when workers move around, so a small quantity of mortar can be poured into the gaps to stabilise them. This should not cover up the steel reinforcement. Electrical conduits and openings for fan box and such others can be placed by cutting any block as needed.
Small changes like replacing concrete with autoclaved cement block may appear insignificant, but many such small ideas together would lead to major impacts. We may stick to conventional ideas, yet express our concerns for the environment.