Recycling of the product of thermal inertization of cement-asbestos for the production of concrete.

A novel field of research in materials science is the recycling of secondary raw materials for constructionand building materials such as concrete. This paper describes the successful recycling of as much as20 wt% of the product of thermal transformation of cement–asbestos for the formulation of concrete.The main mineralogical phases present in the product of transformation of cement–asbestos are C2S, ferrite,and Al-, Ca-, Mg-rich silicates such as akermanite (ideally Ca2MgSi2O7) and merwinite (ideallyCa3Mg2Si2O8). The behavior of this secondary raw material, termed KRYAS, in commercial concretewas investigated using five different mixtures in which various portions (0, 5, 10, 15 and 20 wt%) ofcement were substituted by KRYAS. The results of preliminary technological tests (slump test, compressivestrength, flexural strength after 28 days, and depth of penetration of water under pressure after28 days) were discussed and interpreted with the aid of chemical, mineralogical and SEM analyses.One of the major results is that after 28 days, although all the concrete samples are invariably classifiedas ‘‘ordinary concrete’’ according to the UNI 6132 tests, those diluted with KRYAS display a lower resistanceto compression with respect to the standard. On the other hand, they recover compressive strengthand display values identical to that of the standard after 90 days. The addition of the secondary raw materialhas the effect to slow down the kinetics of setting/hardening because the main cement phase presentin KRYAS is C2S which has a slower rate of hydration with respect to C3S.