Optimal Timing: After the aggregate is added, before the water is added, or at the beginning of the water addition. This is the most critical point.Adding at the dry mix stage allows the fibers to be more evenly dispersed during the subsequent addition of water.
Specific operation:Spread the weighed PP fibers evenly over the aggregate being mixed (avoiding a pile-up caused by dumping all at once).
In a forced mixer, dry mix the aggregate and fibers for about 30-60 seconds to ensure initial fiber dispersion.
Then add other powders such as cement and admixtures and dry mix for about 30 seconds more.
Finally, water and liquid admixtures (water reducers, etc.) are added and mixing is continued until uniform (usually 15-60 seconds longer than conventional mixing without fibers, depending on mixer efficiency and fiber volume).
Prohibition: Do not add fibers directly into water or wet concrete that has already been mixed, it is very easy to agglomerate.