Construction of Base/ Sub-base
A base/ sub-base to the concrete pavement provides uniform and reasonably firm support, prevents mud-pumping , and acts as capillary cut-off. Sub-base for concrete pavement could be constituted with brick flat soling, WBM, granular aggregates, crushed concrete, slag, stabilized soil etc. As per IRC:15 (2002), sub-base could be of three types with (i) Granular material (for example, brick soling with one layer of sand under it, WBM, well graded granular materials etc.) (ii) Stabilized soil (iii) Semi-rigid material, (for example, lime burnt clay puzzolana concrete, lime fly-ash concrete, lean cement concrete roller compacted concrete etc.). Following contains a brief discussion on dry lean cement (DLC) concrete as sub-base, which is popularly being adopted for the current concrete pavement construction in India.
Dry lean cement concrete as sub-base
The thickness of DLC, generally recommended is 100mm or 150mm (IRC:SP-49 1998). The maximum aggregate to cement ratio is 15:1. The average compressive strength of DLC cubes at 7 days, as recommended by Indian guidelines (IRC:SP-49 1998) should not be less than 10 MPa, tested on 5 samples and individual compressive strength should not be less than 7.5 MPa, at 7 days (MORT&H 2001, IRC:SP-49 1998).
(A) is the outer edge, and (B) is the inner edge of the pavement
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Figure-32
Compaction sequence for DLC ( courtesy:
Mr. Ashutosh Gautam, Project Director, NHAI,
Kanpur ) |
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Figure-33 Laying
of DLC ( photo courtesy: Mr. Ashutosh
Gautam, Project Director, NHAI, Kanpur ) |
Before construction of DLC sub-base, the prepared subgrade is sprinkled with water to moisten the surface. The material is to be laid uniformly by a paver without any segregation . The paving machine should have high amplitude paving bars. The curing of DLC can be done by spraying liquid curing compound, or by covering the surface by gunny bags. As per Indian guidelines, the construction of cement concrete pavement can only start after 7 days of DLC construction (MORT&H 2001, IRC:SP-49 1998).
Figure-32 presents a schematic diagram
of the sequence of rolling for DLC construction,
and Figure-33 presents a photograph of DLC construction.
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