Aggregates for concrete - Concrete Mix Design, Quality Control and Specification - page 34

2. Manufactured sand particles will typically have a rougher surface
texture as they have recently been crushed.
3. The potential for contaminants or deleterious materials being present
in the fine fraction may be higher than in natural sands due to the dif-
ferent processing attitude between hard rock and natural sand, and
gravel producers.
4. The particle shape can be significantly more angular.
Taking these differences into account, the volume of manufactured sand
percentage will start is around 5% higher than that of a good natural sand
using the same coarse aggregate. So, as a starting point, rather than around
45% of the total aggregate, the manufactured sand for conventional con-
crete will require around 50%, and reduce through to about 40% as the
powder volume in the concrete increases.
Geology does not determine how good a sand or aggregate will be.
Figure 3.1 shows the compressive strength of mortars made using man-
ufactured sands from varying rock types. A limestone yields the highest
compressive strength but also the lowest compressive strength.
There is a misconception that manufactured sands have higher water
demands than that of their natural sand counterparts. This may be the case
in some instances, and just because it may have ultrafine particles present
that does not necessarily translate into an increase in water demand.
12000
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Aggregate Type
Figure 3.1 Twenty eight day compressive manufactured fine strength of mortar for
different types of aggregate (fixed w/c). (From ICAR 107, 2002.)