Method of the concrete equivalent mortar (CEM) - A new tool to design concrete containing admixture

This paper deals with a new method to design concrete containing admixture. Its principles is to design a mortar, deduced from the concrete composition and called concrete equivalent mortar (CEM), for which the rheological properties display correlation with those of concrete. The aim is to reduce the amount of concrete batches. This article presents the scientific approach which has led to this method, its field application and limits. The test procedure and the apparatus ate detailed. An example of correlation between the rheological properties measured on CEM and an the corresponding concrete is presented. After monitoring fluidity versus time relationship, thermal measurements on CEM were carried out. These measurements allow to anticipate the effects of different admixtures on the setting time. One shows that the setting delays obtained on CEM are in good agreement with the difference of compressive strengths measured at early age. With rheological and thermal results, the CEM method permits to select between numerous admixtures, which is the most likely to fit in with the specifications of effectiveness (proportion/cost ratio), capacity of keeping the rheological properties over time and delay of formwork removal.