Assistant Professor,

The impurities in water play a major role in application of concrete. This paper assesses the setting times and compressive strength of natural admixture cements and silica fume is used as an admixture. This study introduces the effect of strong alkalines (carbonates and bicarbonates of sodium) on setting time and compressive strength of natural admixture cements (PPC+SF) is assessed under laboratory conditions. The research programme included tests of soundness, setting times, compressive strength of short and long term and powdered x-ray diffraction analysis. As the experimental results show that Na2CO3 in deionised water accelerates the intial and final setting times where as the other compound NaHCO3 retards the intial and final setting times for all concentrations. Na2CO3 and NaHCO3 in deionised water increase the compressive strength at early age (3-day and 7-day) and decrease significantly from28-day, 60-day, 90-day, 180-day, 1year and 2years.Comparison of the strong alkaline substances with those of control mix levels that both carbonates decrease compressive strength. The rate of decrease is increasing with increase in concentration.The present work analyses the hydration characteristics of admixture cement using X-ray diffraction analysis (XRD) and useful conclusions are obtained regarding the influence of alkaline substances