Properties of Fine Aggregate for High Performance Concrete
We know high performance concrete is not only means high strength concrete but also high durability may be controlling factor for high performance concrete. We have discussed few aspects of high performance concrete in our previous posts. Our concern here is requirements of fine aggregate for this type of concrete.
The fine aggregate should be of uniformly graded and the expected shape is round; but relatively coarser fine aggregate perform better. We know a rich mix design is conducted for such concrete and rich mix means high proportion of cementitious materials. These finer particles should be with relatively coarse fine particles and with coarse aggregate produces a denser pack which additional to cementation action produced a strong and durable concrete.
Sometimes a F.M (fineness modulus) of 2.8 to 3.2 is recommended. It is difficult to provide a generalize recommendation about aggregate (both fine aggregate and coarse aggregate ), geographical regions use different type of aggregate to meet requirement of high performance concrete.
When very small (finer) aggregate is used in mix, it raises the water demand to produce a workable mix. We know when water/cement ratio increases strength and durability are decreased. But this problem may be mitigated by using or increasing dosages of suitable superplasticizer.
The bond stress can be lowered with choosing larger surface area of total aggregate in the matrix having smaller maximum size of them. Lower bond stress obviously offers less susceptibility to bond failure.