Straw/Cement Blocks

I was asked to review a manuscript entitled "Development of Straw-Cement Composite Sustainable Building Material for Low-Cost Housing in Egypt," which I did below:

First of all, I applaud anyone who is seeking sustainable solutions for building technologies, as these are essential for our continuing health and success as a species. The aspects of the concept presented for manufacturing building blocks from rice straw and cement that I would consider sustainable are:

• One component (the straw) is a surplus renewable material that when utilized will take it out of the waste stream and avoid possible air pollution from burning it.
• The straw is free, which lowers the cost of the production
• The straw-cement blocks can be produced locally by relatively unskilled labor, again lowering costs
• The resultant blocks provide better insulation values than conventional concrete blocks.

On the other hand these blocks call for a substantial component of Portland cement which is known to be a major contributor of CO2 greenhouse gas into the atmosphere. This cement (along with the straw) must be transported to the building site, which also contributes to effective pollution. And the cost of Portland cement is significant ( I suspect much more than the estimated $1.50 per bag estimated in the paper).

If you compare this proposed technology with the vernacular use of straw-reinforced mud (adobe) bricks that have been used since 4,000 years B.C. (according to this paper), then the newer technology does not appear to be as sustainable. Hassan Fathy has clearly demonstrated the appropriate use of mud bricks in Egypt, especially for low-cost housing. Consider these aspects of mud bricks:

• Every component (clay, sand, water, straw) is potentially free
• Every component has little embodied energy
• These materials are potentially available on site, or locally
• These building blocks can be used in load-bearing walls, or for other compressive purposes (which the straw-cement blocks cannot)
• The mud bricks provide nearly as much thermal resistance as the straw-cement blocks (R-1 per inch)...neither of which is very impressive, especially in a hot climate, but at least the mud blocks provide better thermal mass, so under certain circumstances they will perform better thermally.
• Mud bricks can be "stabilized" with a relatively small amount of Portland cement (or asphalt emulsion) for use in circumstances where a greater degree of durability is required.
• Mud bricks can be produced with relatively unskilled labor.

In conclusion, if sustainability is to be the criteria for choosing one technology of the other, I ask why introduce a new cement-based product when the older vernacular material (mud bricks) is superior in almost every respect?