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High performance concrete and mortar coating with active sílica from rice husks


The total worth of constructions in Brazil is around three trillion reals. The need for economic growth points to a large increase in the use of structural concrete. The quality of concrete has improved both in Brazil and worldwide owing to the increasing aggressiveness of the environment. However, strong agglomerants are needed not only for concrete itself but also to protect concrete reinforcements and this is achieved using silica fume and additives. Although modern processing techniques enhance the performance of concrete, it is known that the addition of amorphous silica contributes strongly to its improvement, mainly in the formulation of high performance concrete, HPC. The scientific media has reported mechanical resistance to simple compression of up to 1000MPA, although a figure of this magnitude is uncommon. However, this figure is an indication of the efforts that are still required to exceed the maximum value of 110MPA achieved in Brazil and the parameter of 18MPA still used today. In addition to the increased mechanical compression strength, HPC is characterized by less porosity, which reduces corrosive attacks both on concrete and on reinforcements. The latter characteristic is often even more significant. The quality of silica for this purpose is very important, i.e., the grains must be minute so that the silica can fill up small voids and become evenly distributed in the concrete. It must also have a high specific area and be amorphous and pozzolanic, allowing it to react with calcium hydroxide. It has already been demonstrated that the silica contained in rice husks, if properly extracted, can have characteristics that are superior to the requirements of this application. The large volume of rice husks and waste resulting from the annual national production of 10 million tons of grain creates extremely grave environmental and health problems, particularly in regions where rice is cultivated on a large scale. On the other hand, the silica present in those rice husks offers a considerable potential for the production of HPC, since the conversion of all that waste into silica would represent approximately 300 thousand tons/year. Because the maximum amount of Portland cement that could be substituted by silica is around 10% for most applications, this would represent annual quantities in excess of 7,5 millions tons of concrete. Thus, if this project is successful, the environmental problem could be solved while simultaneously creating an additional source of income for the rice farmers, in addition to allowing for the development and use of HPC in Brazil... (AU)

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