الفهرس 
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Abstract
This investigation aims to study the effect of using Portland limestone cement (PLC) on hardened properties, and durability of concrete. The performance of PLC concrete was evaluated through studying the behavior of PLC concrete in normal and aggressive environment compared to OPC concrete.The main variables in this study are the percentage of cement replaced with limestone 0,10,15,20, and 25% by weight, the water to binder ratio (0.65, 0.55, 0.48 and 0.42), the source of the limestone powder ( four different sources of different constituents are used), and the different surface area of limestone (345, 530 and 720 m2/kg). This research study the effect of the previous variables on hardened properties of concrete, as well as, the behavior of PLC concrete in magnesium sulfate attack, corrosion resistance of reinforced PLC concrete exposed to chloride attack and alkali reactivity of PLC concrete. The research contains mathematical and numerical modeling of service life prediction of reinforced concrete specimens exposed to sodium chloride solution. Compressive strength, splitting tensile strength, modulus of elasticity, absorption, porosity, unit weight, specific gravity and shrinkage strain were measured for different mixes to evaluate the hardened properties of PLC concrete. The compressive strength was measured up to two years. The corrosion rate and polarization resistance of reinforced concrete specimens immersed in 5 % NaCl were measured through conducting potentiodynamic polarization technique. The scanning potential of the test was _250 mV through +250 mV, with a scan rate of 0.1 mV/sec. The corrosion rates of some of specimens were also measured using the conventional weight loss method. Potentiodynamic polarization technique was compared to conventional weight loss method to investigate the reliability of measuring corrosion rate by electrochemical techniques. The concrete weight loss, compressive strength loss, expansion strain, visual inspection were measured for PLC concrete exposed to drying and wetting cycles of 5 % magnesium sulfate solution for 540 days. X- ray diffraction (XRD), Thermo-graphical analysis (TGA) and Scanning Electron Microscope (SEM) were conduct on PLC paste to investigate the microstructure and morphology of paste before and after magnesium sulfate exposure. To evaluate the effect of alkali reactivity on PLC concrete, the expansion strains of concrete prisms stored in standard curing for 12 months were measured. from the test results of hardened properties of PLC concrete it was clear that, compressive strength decreases with the increase of cement replacement content with limestone of fineness 345 m2/kg, the percentage of decrease in compressive strength increases with the decrease of water binder ratio, the compressive strength gaining at two years relative to 28 days for PLC concrete specimens were higher than that of OPCconcrete, the increase of limestone fineness enhances compressive strength of PLC concrete, the source of limestone powder plays extremely important role on hardened II properties of PLC concrete and the increase of limestone replacement ratio stabilizes ettringite and decreases portlandite in cement past. The test results of corrosion resistance of PLC concrete showed that, the increase of cement replacement with limestone powder (fineness of 530 m2/kg or more), having w/b ratio of 0.55, decreases the corrosion rate up to 25% limestone replacement. The results indicate also that the average corrosion rate measured by the potentiodynamic technique is very close to the results of the conventional weight loss method (differences between both methods range from 0.64 to 5.2%). The test results of PLC concrete exposed to magnesium sulfate attack revealed that, concrete weight loss and compressive strength loss increase with the increase of cement replacement with limestone, the compressive strength loss decreases with the decrease of water binder ratio and fineness of limestone The test results of alkali reactivity of PLC concrete showed that, the average bexpansion strain for PLC concrete specimens due to alkali reaction decreases with the increase of limestone replacement ratio after the same time of storage in standard curing.The differences between the detected time of first cracking service life of cylindrical reinforced concrete specimen exposed to chloride and the proposed mathematical model vary from +3.8 to -7.3%. The numerical modeling for the thickness of corrosion induced cover cracking gives close values compared to mathematical model especially when the ratio between concrete cover thickness to steel bar diameter (dc/d)decreases.