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What is “No Fines” Concrete?

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.

 

Reference: Concrete Data: Cement and Concrete Association of Australia

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