34 safety factor 34 greater than 3 if at any time the compression due to the expansive forces exceeds the strength of the mortar failure will occur the cement was measured for expansion using astm 806 method both restrained and unrestrained the restrained expansion was 0 08 in 7 days and 0 13 in 28 days an increase of 160 the unrestrained expansion was 0 4 at 5 days after which there was not further expansion a third form of my invention relates to blending of the expansive clinker gypsum and portland cement the blending of these components can be done by three methods intergrinding of the portland clinker expansive clinker and gypsum in a ball mill at the cement plant as described in my u s pat no 4 419 136 incorporated herein by reference particle size control between the portland clinker and the expansive clinker is sacrificed when the grinding and blending is done in the ball mill this results in a less efficient use of the expansive clinker and less control of the expansive characteristics however i have now discovered that in making cement for scc for seven day expansion of less than 0 04 if the grinding of the mixture of portland clinker expansive clinker and gypsum is kept in the range of 4500 u00b1 200 blaine no the uniformity of expansion is good and there is not excessive water.