Abstract: The preparation of calcium carbonate block materials in actual production is extremely difficult, and the manual method of manufacturing calcium carbonate often results in only micrometer-scale powder. Coral powder and vaterite-type calcium carbonate were used as raw materials, and pressing forming was employed to control the transformation of vaterite to needle-like aragonite-type calcium carbonate by utilizing the crystal nucleus effect of coral powder. A three-dimensional spatial structure was formed by interweaving and overlapping the aragonite needle-like structures, resulting in the preparation of well-performing calcium carbonate cement. The effect of coral powder on hardening process and strength of calcium carbonate cement was studied, the phase composition, microstructure and pore structure of hardened calcium carbonate cement were systematically analyzed. The results show that the hardening of calcium carbonate cement is directly related to the transformation process from vaterite to aragonite. When coral powder content is 40% (mass fraction), the mechanical properties of calcium carbonate cement are the best, and the compressive strength of 2 and 6 h reaches 27 and 33 MPa, respectively. The addition of coral powder induces the transformation of vaterite to aragonite, inhibites the transformation of vaterite to thermodynamically most stable calcite, and reduces the most probable pore size and more harmful pores.

Key words: coral powder, vaterite, aragonite, crystal nucleus effect, calcium carbonate cement, hardening, pore structure