Preparation method of ultra-high performance concrete with carbon dioxide as internal curing agent

The invention provides a preparation method of ultra-high performance concrete with carbon dioxide as an internal curing agent. The method comprises the following steps: carrying out modification treatment on steel fibers by adopting a polyethyleneimine (PEI) solution with a certain concentration to obtain PEI coated steel fibers; the PEI coating steel fiber is placed in a carbonization box to capture CO2, and the CO2-captured PEI coating steel fiber is obtained; the preparation method comprises the following steps: adding dry materials (cement, silica fume, quartz powder and quartz sand) and a dry powder polycarboxylate superplasticizer into a stirrer, uniformly mixing, and then adding mixing water; when the mixture is in a wet state, adding the PEI coating steel fiber for capturing CO2; and stopping stirring when the expansion degree of the freshly mixed concrete meets the requirement. After the fresh mixed concrete is subjected to pouring molding and static curing, the ultra-high performance concrete with