Variability of efficiency factors characterising mineral admixtures

The decision of public authorities to recycle industrial wastes leads to th e quasi-systematic use of mineral admixtures in concrete. Predicting the st rength of these concretes induces the engineer to characterise the mineral admixtures: ordinarily, a single coefficient is used, calculated with an em pirical law like Bolomey's or Abrams' formulas. Many results, reported in b ibliography and completed by the authors, show that the determination of th is single coefficient is not sufficient to characterise the activity of the admixture. Many factors like the nature of cement, the substitution rate, the fineness of the admixture and the age of concrete induce a great variab ility of the efficiency coefficient of the admixtures. Up to now, there is no general law explaining this variability. The authors warn against the ex cessive use of a single equivalence coefficient and recommend to take into account not only the physicochemical parameters but also the nature of the works themselves.