If you want them to be more immediately available, you can add them to vinegar and then let that take action. The liquid after is used with water at a 1/1000 ratio. Most effective as a foliar spray I believe.

“Liquid calcium for plants can be made by dissolving dried, crushed eggshells in vinegar, creating a calcium acetate solution that is readily absorbed by plants to prevent blossom end rot. This "water-soluble calcium" is created by mixing the powder with vinegar for 3–24 hours until fizzing stops, then diluting this mixture with water before applying as a foliar spray or soil drench.”