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Pozzolanas: the map of the mine

A survey locates precious rocks for the cement industry

After having traveled over 24,000 kilometers, in an effort which began in 1996, a group of researchers from the Institute of Geosciences (IG) of the University of São Paulo (USP) have just finished mapping the principal occurrences of Pozzolanas which exist in the State of São Paulo. This material, formed by rocks or clays, when incorporated into the process of the cement industry, provides a reduction in the production costs, caused less damage to the environment and brings technological advantages such as turning the product more resistant to the action of water. To make use of these benefits, it only required that the industry of São Paulo and of the South East region have a more detailed understanding of the locations of the Pozzolanas.

To know where they are contributes towards incorporating them into the traditional mixture which results in the manufacture of cement, a process invented and patented by the British stonemason Joseph Aspdin during the 19th century. The name comes from its resemblance to the final product of a calciferous rock found in abundance on the isle of Portland in Great Britain. The method consists of a mixture of 80% of the calciferous rock with 20% of clay, which, when submitted to high temperatures, transforms itself into clinker (blocks of cement). This product, after being ground into a powder, results in the so called Portland cement. Pozzolanic Portland cement is that which in its composition allows for up to a 50% addition of Pozzonala.

For its part, the name Pozzolanas comes from the volcanic rocks found in the region of Pozzuoli, close to Mount Vesuvius, in the south of Italy. When mixed with quicklime and ground up, these rocks transform themselves into cement. They were used considerably by the ancient Romans. The cement used in the Coliseum in Rome has Pozzolanas in its composition. Recently the term began to be applied as well to products which have a similar use. For example, Pozzolanas are the acid slag of the steel mills, ashes from electric furnaces, rejects from the cracking of petroleum, the ashes of vegetable residues and sub products from the extraction of coal.

The research work namedThe Evaluation of the Geological Potential of Pozzolanic Material in the State of São Paulo , coordinated by professor Jorge Kazuo Yamamoto, of the Department of Sedimentary and Environmental Geology of the IG of USP, resulted in various maps and in the collection of 350 samples. The researchers chose 60 of them to have their Pozzolanic activity analyzed and finally 32 to be tested within the laboratory. “As well as the importance which it had as a scientific work, the research ended up revealing possibilities for exploration in various regions of the State which don’t actually have any economic activity of importance.” commented the geologist Dr. Tarcisio Jose Montanheiro, of the Geological Institute of the Secretary of the Environment of the State of São Paulo, who wrote the thesis for his doctorate within his assistance towards the research project.

“The results of the survey show a large potential for this product, practically unexplored in São Paulo.” affirmed Dr. Yamamoto. “With the use of Pozzolanas in the manufacture of cement, the industry will reduce production costs. We don’t have a percentage, because this will depend on the proximity or not of the deposits for each factory.” he continued. As well as this, the work has appreciable scientific merit. “Never before was there a mapping so extensive and rigorous on the occurrences of Pozzolanic material in the State of São Paulo.” declared the professor.

Resistance to time
In Brazil Pozzolanas are used principally in the South where the resulting ashes of the burning of coal in the thermoelectric power stations finish up in the mixture which produces cement, and in the North East where the mixture of cement includes calciferous clays. In the South East, the very region of the country which produces the most cement, with 54.25% of the total, the use of Pozzolanas is small, in spite of them having economic, technological, geological and environmental advantages in relation to pure clinker.

It is not only this, but the quality improves as well. “Cement which has had the addition of Pozzolanas shows a noticeable reduction in the reaction alkali-aggregate , common in large civil engineering projects.” declared professor Yamamoto. Or that is to say, with the passage of time, the concrete with Pozzolanas becomes less permeable and more compact than that produced by the use of common cement. “The use of Pozzolanas in the construction of concrete dams is already renowned for its technological benefits of security and durability which it confers to the concrete.”

Another advantage of using pozzolanas is that of preserving the calciferous deposits, the principal component of common cement. Calciferous rock is a product with many other applications such as the correction of the soil’s pH, the primary material for the production of quicklime and in the production of iron slag in the steel manufacturing industry. For the environment, the use of pozzolanas reduces the emission of carbon dioxide. “The production of pozzolanic cement, for example, for the calcination of aggregates, requires temperatures a lot less than those used in conventional cement.” remembered Dr. Yamamoto. The high temperature furnaces used in the roasting of limestone and clay for the production of Portland type cement are responsible for the liberation of enormous quantities of carbon dioxide into the atmosphere. “The adoption of pozzolanic cement is an excellent way to improve the quality and reduce the levels of pollution of the companies.” he added.

High technology
The technological base for the use of pozzolanas is not a problem. “Brazil occupies an outstanding position in the search for viable alternatives in the production of cement.” said another participant in the project, Dr. Yushiro Kihara, professor of the Department of Mineralogy and Geotechnology of the Institute of Geosciences of USP and a researcher of the Brazilian Association of Portland Cement (ABCP). “The use of pozzolanic cement is associates with high technology solutions for the various problems confronted by the civil construction industry.” he completed.

For the researchers, one of the motives for the low use of pozzolanas in the South East is the lack of knowledge of where they are located. This problem has just been solved, in part, by the work of the team from IG. The researchers concluded, in the first place, that the geological area with the highest possibility for the occurrence of the product in the State of São Paulo is in the Basin of the river Parana. There were also selected nine Paulista regions to receive special attention: Leme, Casa Branca, Aracatuba, Franca-Pedregulho, Piraju-Fartura, Assis, Pederneiras, Araraquara and Limeira-Rio Claro-Ipeuna-São Pedro.

When covering the diverse area of the State in search of pozzolanas, the researchers didn’t always have a smooth and tranquil experience. At one time or another, they came up against a special type of Pozzolana, esponjilite. Known popularly as monkey powder, esponjilite cause enormous attacks of itching, no matter how prudent one is when approaching the locations where they are accumulated. However, to the relief of all, the uncomfortable esponjilite represent only a relatively small portion of these deposits. “The monkey powder is an excellent Pozzolana, but the itching which it provokes leaves anyone uncomfortable.” related Dr. Montanheiro, one of their most frequent victims.

Laboratory tests
The tests with the samples were carried out in the laboratories of ABCP. The entity is an organization which represents 11 industrial groups, with 59 cement factories spread throughout Brazil. “The results of the tests showed that the principal occurrences are of basaltic rocks and clays.” revealed Dr. Montanheiro. “These two types were found in the largest quantities, and consequently present the highest possibility of being economically viable.” he added. The largest occurrence of basalt found by the researchers is in Alto Paranapanema, and that of clay in the Center – West of the State.

The details of the occurrences of pozzolanas will certainly contribute to the development of the cement industry in the State of São Paulo. The growth in the production of cement has been large over the last few years. It grew from 25.8 million tons in 1990 to a forecast of40 million in 2000. Brazil is the sixth largest producer in the world, behind China, India, The United States, Japan and South Korea. The sector employs 18,000 workers directly and invoiced US$ 4 billion in 1999.

After the South East which manufactures 54.25% of the national total, the region which produces the most cement is the North East with 17.45%, followed by the South with 14.50%, the Central-West with 10.82% and the North with 9.01%. The largest Brazilian producer is the Votorantim Group with 41.7% of the total. The next places are taken by the João Santos Group with 11.8%, and Cimpor with 9.0%.

The accompaniment of the production of cement is important, since it reveals the oscillations of the Brazilian economy. The civil construction industry, the principal consumer of the product, is one of the first sectors to react when the country is doing well or doing poorly. Over the last five years, the scenario was of a recession. In 1999, for example, the BIP of the sector fell 3.68%. With the return of growth, however, the situation changed and for 2000 it is hoped that there will be an increase in the BIP of 4% and an increase of 6% in the civil construction industry and in the production of cement. For 2001, the prospects are even better, since various construction projects of large scale of popular houses were announced over the last few months.

The heating up of civil construction is good news. Not only because the sector absorbs semi-skilled workers who would be difficult to place in other areas of the economy, but because it drives forward the demand in other strategic sectors such as steel and glass. In this field, the role of the pozzolanas could be very important, since they represent a viable alternative for the sustainable development of the cement industry.

The project
An Evaluation of the Geological Potential of Pozzolanic Materialsin the State of São Paulo (nº 95/08815-3); Modality Assistance to a research project; Coordinator Dr. Jorge Kazuo Yamamoto – Department of Sedimentary and Environmental Geology of the Institute of Geology of USP; Investment R$ 39,571.00 and US$ 2,500.00