Ladle slag as new constituent for blended cement: a microstructural study

Steel and cement production are very demanding productive processes in terms of energy costs, gas emissions and waste generation. However, waste such as slag generated by blast furnace for pig iron production can be fruitful used to produce a well known type of cement (CEM III, blast furnace cement) where clinker content can be reduced up to 5 wt%. In these last years, with the aim to lower the environmental pollution caused by blast furnaces, steel production has been addresses to the use of electric arc furnaces, which in their turn generate waste characteristic of the process. Usually, two main types of residues are obtained by electric arc furnace for steel production: black slag directly coming from the furnace and ladle slag coming from the steel refining process. In this work blended cement containing 25 wt% of ladle slag have been prepared. The promotion and use of blended cement is today encouraged as it usually means a lower production of clinker compared to the amount necessary to produce Portland cement. Moreover, a low clinker production can be envisaged as a minor exploitation of natural resources and less CO2 emissions in atmosphere. The possibility that ladle slag can be involved as active constituent in the hardening process of the new binder is here taken into account. Chemical-physical-mechanical parameters of the blended cement are reviewed, but the investigation here proposed is mainly focussed on the microstructure analysis of phases formed during curing time (up to 90 days). Measurements by mercury intrusion porosimeter (MIP) associated to electron microscopy observations with energy dispersive X-ray analysis (SEM-EDX) have been used to investigate the development of the microstructure during the curing time and to identify if traditional (such as C-S-H gel) or new phases are formed.