Low-heat micro-expansion composite cement and preparation method thereof

The invention relates to a low-heat micro-expansion composite cement and a preparation method thereof. The composite cement comprises the following components: 1-8 parts of a magnesium oxide expanding agent, 25-70 parts of industrial waste residue, 25-70 parts of portland cement clinker, and 1-4 parts of gypsum. The preparation method includes: mixing and grinding the magnesium oxide expanding agent, the portland cement clinker and the gypsum to prepare magnesium oxide expansive cement with a specific surface area of not lower than 300m /kg, then mixing the magnesium oxide expansive cement with the industrial waste residue evenly according to the ratio to prepare composite cement; or burdening and mixing the magnesium oxide expanding agent, the cement clinker, the gypsum and the industrial waste residue in proportion, and carrying out grinding together to obtain composite cement. The composite cement prepared by the method has fineness of 80-micrometer square hole screen residue of less than 10%, and a specific surface area of not less than 300m /kg. The composite cement provided by the invention can generate expansion in the early stage, also can generate expansion in the middle and late stage, simultaneously satisfies compensation of concrete shrinkage in the early stage and the middle and late stage, and prevents shrinkage crack of concrete.