A Study To Determine The Content Of Water-Insoluble Admixture In Cement By Potentiometry And Influence Factors

This study utilized conductance measurements, to focus the continuously changed characters, influence factors and mechanisms of cement suspension (W/C=500). In this study the temperature of cement suspension is25℃, and test circle is8min. The conductance is successive acquired by computer.To study the influence between admixture content and conductance of cement suspension, different cement, different types and dosage of admixture are used to prepare into cement samples. The results show that the the relationship between conductance and the clinker content is accorded with quadratic polynomial at most test point. Then determine content of water-insoluble admixture in cement by potentiometry is presented based on the relationship.The specific method to determine content:First, a series of cement samples which contains known admixture content are prepared, and determine their conductivity curve in cement suspension. Second,we search the data in maximum multiple correlation coefficient at Tmax (time of multiple correlation coefficients between clinker) to get the regression equation of determining clinker content in cement by regression analysis. Third, determine the conductivity curve of test sample. Then plug the conductance at Tmax into regression equation to work out the clinker content in test sample. The content of water-insoluble admixture in cement, which symbolized Y, thus Y equals the difference between100and content of clinker (contains gypsum)(%).In this investigation, some experiments are made to explore the influences between conductance of cement suspension and the factors. The factors include pre-hydration degree, specific area and composition of clinker mineral. In addition, main composition, species and characteristics in suspension filtrate are investigated. The experimental results indicate:When the pre-hydration degree is less than15%, conductance decreases slightly as pre-hydration degree rise; whereas conductance sharply decreases with the increase of pre-hydration degree over15%; when the pre-hydration degree is up to40%, the conductance among samples containing different content of admixture have less difference.The relationship of specific area-conductivity with different clinker might be described by a linear function, but some relations of samples are more consistent with quadratic polynomial. The relation of specific area-conductivity can be corrected to conductivity of test sample. Meanwhile it also can be used on rapid determination for specific area of test sample.Theoretical analyses have shown that each clinker single mineral has contributed to the conductance of cement suspension. When the single mineral hydrating alone, the order of capacity in effecting conductance is C3A, C4AF and C2S; the C3S content of clinker has a direct and important effect on the contribution of conductance, and the contribution of other single mineral will gradually increased with increasing specific area.In measurable concentration range, main ions in suspension filtrate are Ca2+, Si4+, and Al3+. Fe3+is difficult to measure because of low concentration. After transforming these ions into oxide, the concentration of CaO has a fine linear correlation with conductance, while the total concentration of CaO, SiO2and Al2O3also has a fine quadratic non-linear relationship with conductance.