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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)
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