Waste high-magnesium rock flour-based composite mineral admixture and application of same in high-strength concrete

The invention discloses a waste high-magnesium rock flour-based composite mineral admixture and application of the same in high-strength concrete. A preparation method for the admixture comprises the following steps: (1) drying waste high-magnesium rock, wet discharged fly ash and manganese slag until water content is lower than 1.0%; and (2) separately grinding 70 to 85 parts by weight of the dried waste high-magnesium rock, 10 to 20 parts by weight of the dried wet discharged fly ash, 0 to 10 parts by weight of the dried manganese slag, 0 to 10 parts by weight of mineral waste residue and 0 to 10 parts by weight of clinker, and then carrying out mixing or carrying out mixing and then grinding until the specific surface area of the obtained mixture is 901 to 1200 m2/kg so as to obtain the waste high-magnesium rock flour-based composite mineral admixture. According to the invention, the morphological effect and filling effect of the waste high-magnesium rock flour are utilized to improve compactness of a concrete mixture and fluidity of concrete; slump loss is small, and adsorption of additives like polycarboxylic acid is low; and early strength of the concrete develops fast, and later strength of the concrete develops steadily. Moreover, both the admixture provided by the invention and coarse and fine waste high-magnesium rock aggregate can be applied in the concrete, so the utilization rate of the waste high-magnesium rock is substantially increased.