Etchable iron content (FETCH) proposed as the missing parameter for the better prediction of asphalt mastic stiffening

The voids in the mineral filler are widely used to estimate the stiffening of asphalt mastic and mixture. Until now, there have not been major enhancements for the filler theory within the field. In this study, the discovery of the effect of etchable iron (FETCH) on the stiffening was made. The use of FETCH allowed us to predict the mastic stiffening with an error less than the allowable testing standard deviation. At first, range of fillers and aggregate fines were tested with bitumen in order to estimate mastic stiffening, as expressed by the increase in the Ring and Ball Softening Point. The results were then interpreted according to the most widespread filler models, but very small predictive power was found for the mastic compositions used typically in Finnish asphalt mixtures. The standard physical characterization techniques for the fillers employed by the asphalt industry were then extended for more advanced physical and chemical analysis techniques. This enabled us to discover the effect of etchable iron on the mastic stiffening, the mastic being composed of limestone, fly ash and variable aggregate fines. By including the concept of FETCH, the stiffening of asphalt can be predicted with greater accuracy.