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Structural concrete components undergo degradation when e.\posed to sulphate-bearing environments. Diffusion of sulphate ions through concrete pores causes the formation of expansive products such as gypsum and ettringite in the internal microstructure of concrete. This chemical change leads to a significant reduction of strength in structural components. In the literature it has been reported that in blended cements, because of the reduction of calcium hydroxide, magnesium sulphate ions directly react with the cementitious calcium-silicate-hydrate (C-S-H) gel and convert this into non-cementititous magnesium-silicate-hydrate (M-S-H) gel. However, in the present investigation it was observed that, in low-strength concrete (20 MPa), blended cements show more resistance than ordinarv Portland cement (OPC) because of the pozzolanic and dilution effect of added fly ash and slag. In this concrete, the expansive product. namely gypsum, densifies the porous pore structure and does not cause any cracking. In the case of medium-strength concretes (30 and 40 MPa), the po::.::.olanic and dilution effects of blended cements are not very significant and hence they did not show any increase in sulphate resistance compared with OPC cement. In these medium-strength concretes b.ecause of their pore structure, the expansive products cause micro-cracks. The inferior performance of concretes with blended cements due to magnesium ion attack is mainly attributed to the formation of ettringite and gypsum. as in the case of sodium sulphate, and these cause more micro-cracks in comparison with OPC cement. Thermal analysis also confirms this. structural components as well as decreasing the extended to the calcium-silicate-hydrate (C-S

The availability of personal computer based systems has enabled the development of a versatile setup for the testing and characterization of solar cells.Such a system acquires the data for the I-V curve which characterizes the cell and outputs the same on a monitor and in graphics plotter~T he system described here consists of an IEEE-488 standard interface protocol, programmable powersupply and a programmable digital multimeter, graphics plotter and associated software~The cell parameters were calculated using 5-parameter model written in BASIC language and the power versus voltage curve of the solar cell is computed. Automated data acquisition and analysis is the salient feature of this system.