Special admixture for maritime work

The invention belongs to the field of concretes, in particular relating to a special admixture for maritime work. The technical scheme in the invention is as follows: the admixture is prepared from ultrafine high-activity slag powder serving as a raw material and an excitant in a certain proportion, wherein the admixture comprises the following components in parts by weight: 94-98 parts of slag powder with a specific surface area of 800-1200 m /kg and 2-6 parts of excitant. As the admixture is prepared by doping single common slag powder or admixing slag powder, fly ash and silicon ash, the mechanical property of the admixture is worse than that of the concrete obtained by doping the ultrafine high-activity slag powder, and the durability of the concrete is greatly improved. Under the condition of low doping amount (accounting for about 10% of the total gel material amount), the early strength of the concrete is strengthened, the work property of the concrete is improved, the anti-permeability and freezing resistance of the concrete are obviously improved, and simultaneously the production cost is greatly lowered.