Effectiveness of using lightweight natural aggregates in hydraulic construction

Abstract

In Armenia SSR there are extremely rich reserves of natural lightweight porous stones (volcanic tufts, pumice, scoria) which are the starting raw material of aggregates not only for structural-insulating but also for purely structural concretes. Investigations carried out at the Armenia Research Institute of Buildings, Materials, and Structures (AISM) [1,2] showed that the impermeability of lightweight concretes with natural porous aggregates is appreciably higher than that of concretes with rock aggregates. As a consequence of the absorption properties of porous aggregates in conc[ete a consolidated cement crust forms around these aggregates, which plugs the surface pores, and this increases the frost-resistance and lowers the permeability of the material As a result of the investigations, lightweight vibrated concretes with natural aggregates for hydraulic construction were obtained which are characterized by an impermeability of grade V10 and higher and a frost resistance of Mrz300; however, the wearability of these concretes is poorer than that of ordinary concretes. The lightweight concretes can be used if the velocity of the water does not exceed 2-8 m/sec, and the concentration of silt in the water is not more than 2%; these conditions are characteristic for most hydraulic structures of Armenia.Lightweight concrete was used in open channels, tunnel linings, pressure chambers, and penstocks, and underground and aboveground parts of the Gyumush hydroelectric power station and others. Field observations of these structures during 15 year s of operation have shown that the life of such lightweight concrete is no less than that of ordinary concrete. At present GOST 4797-64 permits using lightweight aggregates in concrete for hydraulic construction if it is technically and economically substantiated.Rubble and sand of lithoid pumice of the Lusavan deposit, which was found along the route of the diversion, were used in the construction of the Gyumush hydroelectric power station. The economic expediency of concrete with lithoid pumice was substantiated [3] by cheaper transportation costs and selling prices for aggregates of lithoid pumice in comparison with these indexes for ordinary aggregates. According to the budget data the cost of rubble of lithoid pumice was less by a factor of 2 and the cost of sand by a factor of 5 than the cost of corresponding heavyweight aggregates.The successful use of lithoid-pumice concretes in the construction of the Gyumush hydroelectric power station made it possible to use them also at the construction of the other stations of the Sevan-Razdan sequence-the Arznin, Atarbekyan, and Erevan stations. Between 1949 and 1964 the volume of lithoid pumice concrete placed in structures of the Sevan-Razdan sequence quadrupled the volume of ordinary concrete and amounted to more than 1 million m q.The effectiveness of concretes with natural lightweight aggregates is estimated in terms of the index of the reduced sum of expenditures C c + KE 0 by comparing the base costs of concrete (C c) and...