According to the related national standards, codes and specifications, this article discussed the compressive strength evaluation methods of existing concrete, pointed out that the present provisions in related norms can not meet the construction practice, so the existing methods should be improved as soon as possible to make the concrete strength evaluation more standard and scientific.

The background engineering in this paper is the existing concrete structures under the natural chloride environment.

The chloride ions\' concentrations in existing concrete in tidal estuary environment of the Qiantang River are measured,the relation between erosion depths and concentrations of chloride ions in concrete is analyzed.