concrete is a concrete containing
little or no fine aggregate. The coarse
aggregate should preferably be a single-size material (nominal maximum
10mm and 20 mm being the most common).
blended aggregates (10 and 7mm;
and 20 and 14mm) have been found to perform satisfactorily. Because it
characterized by uniformly distributed voids, it is not suitable for reinforced
or prestressed concrete construction.
in buildings: Primarily in external and internal walls of
park paving: Provides free-draining pavements for light traffic
courts: Using a small nominal aggregate size, e.g. 5mm, a
surface is achieved.
layers: Used as drainage layers on civil engineering projects.
size is preferred but the surface finish is poorer than that achieved
courses: Has been used as a lightweight screed for levelling on
the cement: aggregate ratio by
volume is in the range 1:6 to 1:8.
(1:8 to 1:10) reduce the likelihood of the pores being blocked by
Thus for drainage layers where lower strength can be tolerated, 1:10 is
preferred. The water-cement ratio
needs to be kept low, e.g. 0.4–0.45, to
ensure the cement paste coats the aggregates and does not run off.
Strength: This is lower than conventional concrete and is a
function of the
aggregate: cement ratio, the water-cement ratio, and the degree of
(the density). Typical strengths are in the range 5 to 13 MPa. A mix
aggregate: cement ratio of 8:1; a water-cement ratio of 0.4; and a
of1850kg/m3has strength of approximately 7.5 MPa.
Shrinkage: Much lower than conventional concrete, e.g. in range
High. Water and air flow easily through it but no quantitative data is
available. As noted above, blocking of the pores is more likely to
smaller the aggregate size.
(Source: Concrete Data: Cement and Concrete
Association of Australia)