Acid Activation of Natural Rocks - A Case Study with Norwegian Anorthosite and Phosphoric Acid

Abstract

Norway is rich in natural resources, especially different types of rocks that could potentially serve as raw material for alternative binder concepts like alkali activated binders or magnesium phosphate and magnesium hydroxy carbonate cements. Another less studied concept, as discussed in this paper, is acid activation of rocks to produce alternative binders. Although these systems cannot compete yet with ordinary Portland cement, they might be applicable for certain specialised areas and thus help to reduce cumulated CO2 emissions by decreasing the total amount of cement used. Alternative binder systems based on Norwegian rocks as raw material show potential for further research and potential implementation of new specialised products for the domestic market. To demonstrate the potential of acid activation, first results of a case study on anorthosite activated by phosphoric acid are presented. Results show that it was possible to produce a binder with 28-day compressive strength of about 20 MPa, by mixing warm phosphoric acid with finely ground Norwegian anorthosite. The paper presents preliminary results and further optimization, and research is necessary to produce higher strength and understand the hardening mechanisms of the acid activated anorthosite binder.