Introduction:
No-fines
concrete is a concrete containing
little or no fine aggregate. The coarse
aggregate should preferably be a single-size material (nominal maximum
sizes
10mm and 20 mm being the most common).
However,
blended aggregates (10 and 7mm;
and 20 and 14mm) have been found to perform satisfactorily. Because it
is
characterized by uniformly distributed voids, it is not suitable for reinforced
or prestressed concrete construction.
Applications:
Walls
in buildings: Primarily in external and internal walls of
low-rise and
multi-storey flats/units.
Car
park paving: Provides free-draining pavements for light traffic
Tennis
courts: Using a small nominal aggregate size, e.g. 5mm, a
free-draining playing
surface is achieved.
Drainage
layers: Used as drainage layers on civil engineering projects.
20-mm aggregate
size is preferred but the surface finish is poorer than that achieved
using
10-mm aggregate.
Levelling
courses: Has been used as a lightweight screed for levelling on
floors and
roofs.
Mix
Proportions:Generally,
the cement: aggregate ratio by
volume is in the range 1:6 to 1:8.
Leaner mixes
(1:8 to 1:10) reduce the likelihood of the pores being blocked by
cement paste.
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.
Properties:
Compressive
Strength: This is lower than conventional concrete and is a
function of the
aggregate: cement ratio, the water-cement ratio, and the degree of
compaction
(the density). Typical strengths are in the range 5 to 13 MPa. A mix
with an
aggregate: cement ratio of 8:1; a water-cement ratio of 0.4; and a
density
of1850kg/m3has strength of approximately 7.5 MPa.
Drying
Shrinkage: Much lower than conventional concrete, e.g. in range
0.0002–0.0003
microstrain.
Permeability:
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
occur the
smaller the aggregate size.
(Source: Concrete Data: Cement and Concrete
Association of Australia)