(365b) Synthesis of CaSiO3 for Use As a Cementitious Material for Carbonate Concrete

V. Atakan¹, C. Vakifahmetoglu², L. McCandlish¹, J. Krishnan¹, L. Tang², Q. Li², R. E. Riman² and N. DeCristofaro¹

1. Solidia Technologies Inc., Piscataway, NJ 08854

2. Rutgers, Department of Materials Science and Engineering, The State University of New Jersey, Piscataway, NJ 08854

Solidia Technologies is using mineral-based Wollastonite (CaSiO₃) as a cementitious material for a novel carbonate concrete slated for commercial production.  CaSiO₃ is reacted with CO₂ to form SiO₂ and CaCO₃ via a patented process called hydrothermal liquid phase sintering.  The SiO₂ and CaCO₃ products occupy ~65% more volume than the CaSiO₃ reactant and act as cementing phases to bond sand and aggregate in the carbonate concrete.  Unfortunately, the availability of mineral-based Wollastonite does not ensure its wide-scale deployment as a cementitious material.  Approximately 10⁵ T/yr of Wollastonite are mined in North America.  The vast majority of the mineral is used in the ceramics and metallurgical industries, either for its white color, its acicular particle shape or its fluxing capability.  While current production quantities adequately supply these applications, the known reserves of Wollastonite are insufficient to consider this mineral as a substitute for Portland cement in the production of concrete.  By comparison, over 10⁸ T/yr of Portland cement are manufactured in North America.  Additionally, Portland cement can be synthesized virtually anywhere from locally available raw materials such as limestone and clay.  Thus, a more logical approach is to develop an infrastructure of CaSiO₃ manufacturing using the same precursor raw materials as those used for Portland cement. This presentation will describe efforts to use raw materials, reactors and unit operations common to Portland cement to synthesize CaSiO₃ and similar silicate compounds.  The production of CaSiO₃ will be compared to Portland cement production in terms of CaO-SiO₂-Al₂O₃ phase equilibria, the energy requirements to drive the solid-state reaction, and the emissions of toxic Hg vapor and CO₂ greenhouse gases.