This article summarized the reason that caused the overtime retarding of concrete and analyzed the adverse effect which be brought to the concrete per- formance and the project quality,and timber discussed how to avoid this phenomena and reduce the corre- sponding loss.

This paper investigated the effects of WH-Ⅱsuper set-retarding agent on the hydration, the heat of hydration, the setting time and strength of Portland cement.

The author does careful research on effects of WH II super set-retarding agent on the hydration, the heat of hydration, the setting time and strength of portland cement, with the methods of XRD, DTA and SEM.

By the experiments of adding WHⅡsuper retarder to cement and concrete, it is found that WHⅡsuper retarder slackens early releasing of hydration heat of the cement, reduces drying shrinkage of concrete, and has no negative effect on corrosion of steel in concrete and freeze-thaw resistance of concrete, and finally improves durability of concrete.

The effects of WHⅡ super retarder on the hydration, the heat of hydration, the setting time and strength of Portland cement were researched by the methods of XRD, DTA and SEM.

Effect of cement and set retarder on setting time of concrete——extra retarded set and its prevention of premixed concrete;

A kind of super-retard-setting mortar is studied and tested in the paper.

To overcome the ARP spoofing attacks,proposed an algorithm for preventing spoofing based on ARP cache overtime,when the host receives ARP packets and updates its cache items,before the cache items timeout,it will no longer request packet,can not receive ARP response package,yet it won\'t update its ARP cache.