Experiment And Research On The Calculation Formula Of Sodium Equivalent In Aggregate-alkali Reaction

For a long time, the calculation formula of sodium equivalent, Na₂O_eq=Na₂O +0.658K₂O, has been used when people compute the total alkali content in concrete. The coefficient of K₂O, which is 0.658, in the alculation of formula of sodium equivalent is based on the ratio between the molecular weight of K₂O and the molecular weight of Na₂O, namely exchanging the amount of K₂O for equal amount of Na₂O. However, the influence of K₂O and Na₂O on alkali-aggregate reaction (AAR) vary in degree and maybe not conform to this law of equal quantity in complicated concrete system.The approach of nonlinear regression is applied to research on the problems of fly ash in suppressing expansion due to AAR and to explore the relations of many factors with expansion due to AAR. The suitable coefficient of K₂O in the calculation formula of sodium equivalent is determined by applying approaches of regressive analysis, cluster analysis and graphing analysis, and the mechanism of which K₂O and Na₂O cause different AAR expansion is also explored preliminarily.1. It is one of the disquisitional stress for this document to determine the uitable coefficient of K₂O in the calculation formula of sodium equivalent. Applying the approaches of regressive analysis, cluster analysis and graphing analysis to study the 50 groups of sample data obtained from experiments in which cement is partly replaced by fly ash, it is confirmed that the coefficient of K₂O, which is 0.658, in the calculation formula of sodium equivalent is too large and the conclusion is drawn that coefficient of K₂O is about 0.5 on the primary level. Studying the 21 groups of sample data obtained from experiments in which no fly ash is blended, it is determined that the coefficient of K₂O in the calculation formula of sodium equivalent is also about 0.5 on the condition of which no fly ash is blended.2. It is the other stress for this document to study the problem of fly ash in suppressing expansion due to AAR. For this purpose, a series of experiments are carried from which 50 groups of sample data are obtained. Applying the approach of nonlinear regressive analysis to study these data in an all-round way, the conclusion is drawn that among all of the factors influencing expansion due to AAR two of the most important factors are fly ash content and sodium oxide in cement When flyash content is less than 35%, sodium oxide in cement is the most important factor influencing expansion due to AAR, and especially when sodium oxide in cement is more than 1.4%, the fly ash content must be high enough (more than 30%)to control the expansion due to AAR by 0.1 %. when fly ash content is more than 35%, the influence of fly ash on AAR expansion become obvious and replace odium oxide in cement as the most important factor of influencing expansion, and so long as enough fly ash is used, the expansion due to AAR can be controlled by less than 0.1%.