The influence of cement composition on the corrosion of steel bar in concrete is studied in this paper． The acceleration test is designed according to the natural mechanism of steel bar corrosion in concrete, and several electrochemical methods are used in the study． The results of research show that the cement composition has a great influence on the corrosion of steel bar in concrete． The concrete produced with blended cement can delay the  corrosion time of steel bar and prolong the beginning time  of steel bar corrosion． The dense effect and absorption effect on Cl^－ can improve the microstructure of interface between the concrete and steel bar and reducing Cl^－ concentration effectively, thus reduce the corrosion rate of steel bar in concrete． 

The degree of deviation of the particle size distribution(PSD)  from the optimum PSD for 12 different samples of cement was calculated by gray relational analysis and fractal dimension evaluation in this paper. The results indicated that estimated results of particle size distribution evaluated both by gray relational analysis and fractal dimension evaluation are almost identical. In order to investigate the application of two methods comparatively in evaluating  PSD, the relationship between the values of fractal dimension difference, the gray relational degrees and some properties of the testing cements was studied further. The result showed that the linear correlation between the values of fractal dimension difference and the properties of testing samples of cement was somewhat better than that between the gray relational degrees and the properties of testing samples of cement. That is, the application of fractal dimension evaluation was better than that of gray relational analysis in evaluating PSD to some extent. At last, the reason for the results was analyzed simply.

Special roller surface, by－pass iron removal and material lock, dam ring structure of grinding table, abrasive buffer between grinding table and roller, high－efficiency separator make the OK mill offering special functions on less mill vibration and wide particle size distribution. Cement quality assurance and succeed refrain from gypsum dehydration thus achieved during grinding.