Amorphous calcium carbonate is included in a fire-resistant inorganic mortar system for a fire-resistant chemical fastening of anchors and post-installed reinforcing bars in mineral substrates. The system includes a curable aluminous cement component A and an initiator component B for initiating the curing process. The component A includes at least one blocking agent selected from the group of phosphoric acid, metaphosphoric acid, phosphorous acid and phosphoric acids, at least one plasticizer and water. The component B includes an initiator, at least one retarder, at least one mineral filler and water. Moreover, amorphous calcium carbonate in a fire-resistant inorganic mortar increases load values. Also, a method is used for a fire-resistant chemical fastening of anchors and post-installed reinforcing bars in mineral substrates, such as structures made of brickwork, concrete, pervious concrete or natural stone.