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Resistant gypsum

New blocks made from by-products left over from fertilizer production are a low-cost option for home building

Eduardo CesarPhosphogypsum blocks are load-bearing and do not require concrete beams and pillars. They are laid onto small fittings.Eduardo Cesar

A new option is now available for consumers, companies and governments with plans to build houses: the gypsum blocks designed in the laboratories of the São Carlos Institute of Physics at the University of São Paulo (IFSC-USP). The new construction blocks are expected to cut the building costs of low-cost housing by about one third and are made with a by-product from the manufacture of phosphoric acid, a raw material used in the production of agricultural fertilizers. This by-product, known as phosphogypsum or calcium sulfate, is also found naturally in mines.

Designed for use in load-bearing walls as a substitute for conventional concrete and ceramic blocks, the material also features high mechanical strength. The USP Innovation Agency recently licensed the new blocks to three companies – Inovamat and KAJ, from São Carlos in São Paulo State, and Mega Block, from the city of Uberaba in Minas Gerais State –, which are making the final tweaks and necessary adaptations to put them on the market.

The high mechanical strength of the blocks is due to their specific microstructural characteristics. When phosphogypsum is hydrated – an essential stage when the blocks are manufactured –, the crystals that form the material grow and become intertwined and compacted, making them more resistant to compression and bending. “Conventional blocks cannot withstand bending. With our blocks, we are able to use less steel when building, which helps lower the cost of construction,” says João Ailton Brondino, a civil engineer and manager at KAJ.

The low price of the raw materials required for laying the blocks also explains why they make for a lower cost option in building. “Each block is laid in place with the help of a few small fittings, then affixed with the type of white glue that schoolchildren use. We don’t have to use cement,” explains Milton Ferreira de Souza, professor emeritus at the São Carlos Institute of Physics and inventor of the calcium sulfate blocks. “Because the sides of the blocks are perfectly smooth, the construction process does not require mortar for laying and plastering. This saves money on masonry materials and labor.” Phosphogypsum blocks are load-bearing, unlike the blocks used today, which depend on concrete beams and pillars for the walls to stay upright. Cement is only used in the sub-floor and slab. Once a wall has been built, the next step is painting, which can be done with conventional paints that are available on the market. Construction also requires less wood because there is no need to build molds for the beams and pillars, thus lowering the cost even further. Also, the modular nature of the blocks cuts the amount of waste to practically zero.

Environmental solution
One important distinction of the new material is its environmental appeal. Large amounts of phosphogypsum are left over during fertilizer production. Five metric tons of this type of gypsum, also known as agricultural gypsum, are produced for each metric ton of phosphoric acid (a component of fertilizer). Because it is a calcium-rich salt, phosphogypsum is used as a calcium source for agricultural soil. But this application is unable to absorb the large volume that is produced. “An estimated 160 million metric tons of phosphogypsum are currently lying in open-air landfills in Brazil. The large-scale manufacture of calcium sulfate blocks will provide an environmentally sound and economically interesting endpoint use for this material,” says Brondino from KAJ, adding that the product is 100% recyclable. “We believe that companies that use this new technology will be able to earn carbon credits by using less cement and steel in their buildings,” Brondino affirms.

“We have seen a high level of interest in the product, both on the part of construction companies and of end consumers,” says Eduardo Brito, administrative analyst at the USP Innovation Agency in São Carlos, in São Paulo State. “During the August 2012 Innovation and Entrepreneurship Convention [USP-iTec] organized by the university in São Paulo, which brought together more than 10,000 people, the blocks caught the public’s eye.” Four patents related to the phosphogypsum blocks and their manufacturing process have been filed with the Brazilian Industrial Property Institute (INPI). Licensed companies agree to pay 3% of their net revenues from using these patents. “Of the total amount earned through any commercial use, USP will receive 70% and FAPESP will get 30%,” says Brito.

Three prototype buildings – one amphitheater and two houses, measuring 60 m2 and 56 m2, respectively – have already been built by licensed companies in São Carlos using the new blocks. The outcome was good, but this type of construction project can only become eligible for funding from banks and the Federal Savings Bank after the new phosphogypsum blocks receive technical approval and the ensuing certification from the Institute for Technological Research (IPT) or from the Falcão Bauer Technological Center. Brondino estimates that he will be able to start selling the blocks to end consumers by the end of the first half of 2013.

“Because it is an innovative product, there were no machines on the market that could produce parts from calcium sulfate with high mechanical strength. Our first challenge was to design this equipment. We adapted a commercially available device and now the company has mastered the process for designing the necessary equipment to produce calcium sulfate blocks and boards on a commercial scale, reproducing the parts with the strengths observed in the laboratory,” Brondino says. “Our goal is to use the blocks to build multi-story structures, as well as one-story houses, especially ones that could be used to reduce the housing deficit in the country. We estimate that the average savings per built-up square meter will be upwards of 30%.”

Novogesso (nº 2004/02900-0).  Grant mechanism Innovative Research in Small Businesses Program (Pipe) Coordinator Milton Ferreira de Souza. Investment R$ 450,370.00 (FAPESP).