ALGERIAN AND Malaysian researchers have designed cheap eco-friendly bricks that can be made from waste materials. Population growth in many urban areas of the developing world is outstripping available housing, prompting interest in making bricks from cheap and durable local materials. Fifty six per cent of the African population is expected to live in urban areas by 2030 (up from 18 per cent in 1950). Malaysian scientists at the Tenaga National University have produced prototype bricks using waste from the mining, coal and steel industries. They mixed the materials — including quarry dust, the iron oxide that forms on steel during production, and ash from furnaces — with cement and water. Traditional brick manufacturing uses high pressure or firing in a kiln to shape the bricks. But the scientist formed the bricks within moulds without applying pressure, reducing costs and simplifying the brick-making process, they say. The researchers add that using waste materials rather than clay or shale conserves resources and maintains the soil quality needed for sustainable agriculture development. According to the scientists, whose findings are published in the April edition of Construction and Building Materials, the new bricks have a variety of promising properties, including resistance to corrosion and compression. Mohamed Heikal, a professor of inorganic chemistry and building materialsat Egypt’s Benha University, says that the new bricks can be used as an alternative to conventional bricks, as they are more durable than traditional bricks in resisting weather-related freezing and thawing. They also have lower water absorption properties. Elisa Adorni, a researcher at the Italy-based University of Parma’s Department of Civil–Environmental Engineering and Architecture, says: “The use of waste materials for the production of bricks and concrete blocks is an optimal method to solve the problem of storing waste materials and to optimise the cost for the production of building materials.” But it is important to take into account the chemical reactions that may occur when the bricks swell upon coming into contact with moisture, Adorni says. Elsewhere, Algerian scientists at the University of Kasdi Merbah and the Polytechnic School of Algiers have also developed and produced prototype bricks. Theirs are made from concrete made from desert sand, and are strong, and provide good heat and sound insulation. The bricks could be produced cheaply in the southern region of Algeria, where Saharan sand is especially plentiful and available at minimal cost, according to the study, which was published in December 2012 issue of the Arabian Journal for Science and Engineering. The researchers carried out 750 laboratory tests to hone the brick. “If the compression and the thermal resistance of [the brick] are validated by Algerian building material codes, it could solve the building material crises which Algerian builders are suffering from,” Ali Zaidi, a researcher in the Department of Civil Engineering of Algeria’s University of Laghouat, says. Zaidi explains that bricks in Algeria are often stressed by the hot summers and cold winters, and assailed by sandstorms. Mohammed Hebasha, who manages an Egyptian building construction company, says firms should be established to exploit the commercial potential of both brick types. (SciDev)
GM cotton linked to rise in aphid numbers
IN AN unexpected trade-off, the cultivation of cotton that has been genetically engineered to reduce caterpillar damage by producing its own insecticide has been linked to higher numbers of another pest — aphids. Previous studies had linked the increase in aphids to reduced insecticide use by farmers cultivating Bt (Bacillus thuringiensis) cotton. Now researchers have for the first time tied the suppressed production of natural defence compounds in Bt cotton — caused by the lack of caterpillar attacks — to a surge in non-target pests such as the cotton aphid. The researchers studied the correlation between Bt and non-Bt cotton plants, defence compound levels and aphid populations in both glasshouse and field conditions. In the glasshouse, they artificially infested Bt and non-Bt cotton plants with caterpillars and monitored the levels of various defence compounds known as terpenoids that are released in response to caterpillar damage. The plants were then artificially infested with aphids. In the field, one set of Bt and non-Bt cotton plants were artificially infested with caterpillars and another was left to natural infestation by caterpillars. Terpenoid levels were measured and both sets were then exposed to natural aphid infestations. In the glasshouse, caterpillars on the Bt cotton plants died. As a result, the plants were less damaged and therefore contained less defence compounds than their non-Bt counterparts. The researchers thus attribute the resulting increase in aphid populations on these plants, compared with non-Bt plants, to lowered terpenoid production. Although a relative rise in aphid numbers was noted on a few occasions on Bt cotton plants in the field, the scientists found no correlation between aphid populations and terpenoid levels in this part of the experiment. Jörg Romeis, one of the paper’s authors and head of the biosafety research group at the Agroscope Reckenholz-Tänikon Research Station ART, Switzerland, says, “Our study shows that a technology like Bt cotton should not be used in isolation. To control other herbivores we have to use the technology as part of integrated pest management approach.” TM Manjunath, a consultant in agrobiotechnology and integrated pest management from India, where Bt cotton is cultivated, says: “What this study shows with Bt cotton can happen with any other insect-control measure. Infestation by aphids and other non-target pests has been seen before the introduction of Bt cotton”. (SciDev)
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