Field of Invention:
The invention relates to a method of formation of concrete units inside the formwork of
cells of high density plastic sheets by filling the cells with zero slump concrete and
compaction by heavy roller so as to achieve cell concrete layer units of high elastic
modulus due to interlocking. The invention further relates to the said concrete units inside
the formwork of cells formed by the process of invention so that they have high elastic
modulus.
Background Art
A bituminous road develops potholes within a year of construction during the monsoon.
Low density polyethylenes (LDPE) have been used for construction of model road earlier
by using normal concrete. However, using LDPE does not give good interlocking among
blocks because of higher thickness (0.5mm) of LDPE sheets in making cells.Normal
concrete used earlier gives less interlocking using standard concrete vibrator. Elastic
modulus of 2500 MPa is reported in the prior art
US Patent 6599611 discloses a method of making a composite structure from a support
structure or a plurality of support structures laid side-by-side on a base. The
compartments are arranged in rows and columns so that the tube divided by dividing
walls has a honeycomb structure. The compartments are filled with a filler material.
There is no mention that the framework is made of HDPE sheets and the filler material is
concrete.
The prior art developed in South Africa consists of filling single size aggregates into
plastic cells and grouting cement-sand mortar into the compacted aggregates. Properties
of the material are different at different location due to variable depth of penetration of
the grout. The method fails when aggregates are flaky. Another prior art consists of
pouring normal concrete into a formwork of indented plastic cells and light vibration is
required for the compaction of concrete. But a long wait is necessary to allow the traffic
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on the finished surface because of wet concrete. It gives much lower strength of the road
material and this would lead to faster damage to the road surface.
Thus there is need of low cost, time effective, rainfall resistant and long lasting durable
concrete road especially for rural areas.
The present invention overcomes the aforesaid drawbacks by formation of concrete units
inside the formwork of cells of high density plastic sheets filled with zero slump concrete
and compaction by heavy roller to achieve cell- concrete layer units of high elastic
modulus.
Object of the Invention:
The object of the invention is to provide a method for preparing concrete units using
formwork of plastic cells adapted for low cost long lasting road pavement.
Summary of the Invention:
Thus according to one aspect of the present invention, there is provided a method of
preparing concrete units inside the formwork of plastic cells comprising the steps of:
(a) forming cluster of hollow cubes with high density polyethylene (HDPE) sheets,
open at lower and upper surface;
(b) filling the cells with zero slump concrete comprising larger size aggregates and
mortar of fine particles,
(c) rolling the concrete filled cells with a heavy roller such that the larger size
aggregates develop contacts with each other and the mortar finer aggregate
particles and cement fill up the voids and
(d) curing the concrete for 14 days so as to obtain concrete units having layer elastic
modulus of 3500-5000 Mpa
According to another aspect there is provided concrete units formed by the above
process comprising formwork of plastic cells comprising high density polyethylene
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(HDPE) sheets, filled with zero slump concrete mix and having layer elastic modulus of
3500-5000Mpa
Brief Description of accompanying Drawings
Figurel Formwork of plastic cells placed over a compacted foundation
Figure 2 Zero slump Concrete being placed inside the stretched cells
Figure 3 shows schematic sketch of compaction of the concrete filled into the cells by a
road roller.
Figure 4 a sketch of block taken out from a broken pavement formed by the process of
present invention
Figure 1 shows a formwork of high density polyethylene cells of size 150mmxl50mm
with a depth of 100mm. Cell wall thickness is about 0.2mm.
Iron spikes at the outside corners of the cell keep the cell taught during placing of
concrete. Galvanised iron wires or nylon ropes pass through the holes (1) in the cells and
keep taught so that cells do not collapse during placing of concrete.
Figure 2 shows placement of concrete inside the cells kept taught by iron spikes at the
outside corners and iron wires or ropes. The zero slump concrete is then placed into the
stretched cells
Figure 3 shows schematic sketch of compaction of the concrete filled into the cells by a
road roller with Rolling of Zero slump concrete filled into cells by a road. The deformed
cell walls are seen as heavy roller is used
Figure 4 shows a sketch of block taken out from a broken pavement. The sides get
deformed during rolling ensuring interlocking among blocks. The top surface (3) looks
flat.
Detailed Description of the Invention:
The present invention describes a method of preparing concrete units of formwork of
cells of plastic sheets over a compacted foundation.
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The present inventors have used low water concrete to fill into these cells, which does not
flow easily. Use of zero slump concrete consisting of less amount of water (water-cement
ratio close to 0.28 to 0.30) is filled into cells and heavy roller is used for compaction.
Heavy compaction results in better interlocking. Elastic modulus of cell-concrete layer is
of 3500-5000 Mpa. These concrete filled cells are further used in constructing road
pavement or road, which can be used in 24 hours of the construction.
Prior art of filling LDPE cells with normal concrete with water-cement ratio of about
0.45 with standard concrete vibrator gave a layer modulus of about 2000 to 2500 MPa.
Normal concrete or self compacting concrete filled into HDPE cells in South Africa was
reported to have values of elastic modulus which are less than 2000 MPa even over very
stiff foundation. Only when water content is low and rolling is done by a heavy roller in
the present invention, higher elastic modulus is obtained because of good interlocking.
The road built with this technology has the advantage of a concrete road from durability
consideration. It is less affected by adverse moisture condition and the road life is about
20 years or more even in high rainfall area at a cost lower than a black top road and much
lower than a conventional concrete road.
The method of present invention provides concrete units of formwork which results in
stronger roads with higher durability.
The cells are made of plastic sheets whose thickness varies from 0.15 mm to 0.5 mm.
Reclaimed plastic also can be used for moulding plastic sheets. The size of each cell is
about 150mmxl50mm and the depth is 100mm. Depth may vary depending upon the
traffic and loading.
Plastic sheets are cut in widths depending upon the depth of concreting which can vary
from 75mm to 150mm. The sheets are heat welded/stitched in a staggered manner at a
spacing of 150mm centre to centre and stretched to form squares (in plan) of size
150mmx 150mm. Spikes are driven at corners to keep the cells taut. The spikes are
removed after the concrete is filled up into the cells.
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Concrete with a minimum 28 day strength of 25 MPa and having zero slump is used for
filling into the cells.
The invention requires that optimum water content be used for mixing aggregates, sand
and cement.
Marshall samples using 100mm diameter sample is cast at different moisture content
using 35 blows on each face and the moisture content, which gives the maximum dry
density, is used for obtaining the quantity of water to be added to the mix. Optimum
moist content can also be determined by modified proctor compaction
Moisture content is increased to account for evaporation due to low humidity, high air
temperature and high wind velocity. Indirect tensile strength test is done to determine the
strength of concrete cores after 28 days of curing.
Plastic cells are laid over the prepared subgrade/subbase and filled with concrete. The
mix is then compacted with a vibratory plate compactor/vibratory road roller. The
concrete gets compacted and the cell walls deform under the weight of the roller to
produce interlocking concrete segments. The concrete is cured for 14 days.
Larger size aggregates develop contacts among each other on compaction by heavy roller
and the mortar of finer aggregate particles and cement fills up the voids. Cement paste
coated rough surfaces of aggregates brought about in a state of close packing due to
heavy roller provide interlocking due to friction at the surface. On setting of cement, the
low water concrete formed by rolling develops high strength. During the process of
compaction by a heavy roller, the cell walls get deformed and the blocks of concrete
filled in each blocks dovetail into each other during compaction causing enhanced
interlocking among the blocks. Accordingly the concrete unit formed has much higher
strength leading to higher durability. The units of known art have a strength (layer elastic
modulus) of about 2000MPa whereas a strength as high as 5000MPa was obtained for
concrete units for the units of present invention. The units have higher layer modulus and
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hence the road crust constructed with the same has lower thickness. This is thus cost
effective.
The road formed of such concrete units may be opened to light traffic after 24 hours of
construction. Light traffic such as rickshaw, bicycle, motor cycle etc. start using it after
24 hours. Pedestrian may use it after 3 hours when the surface is covered with wet straw
or wet jute mat.
The concrete road formed fro the concrete units as formed by the process of present
invention has thickness of about 40% to 50% of the thickness of normal concrete road for
a rural area.
The invention is aimed at provide concrete units for constructing roads in rural area
where sophisticated machinery cannot be used because of lower investment for building
short stretch of link roads for connecting the villages to main roads.
Unlike a normal concrete road, the roads formed from the concrete units of present
invention has the necessary flexibility of gravel or bituminous roads to enable the
proposed concrete road surface to conform to the shape of foundation in case of any
possible deformation in the foundation. A standard concrete road will crack badly in case
of foundation settlement.
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We claim:
1. A method of preparing concrete units inside the formwork of plastic cells
comprising the steps of:
i. forming cluster of hollow cubes with high density polyethylene
(HDPE) sheets, open at lower and upper surface;
ii. filling the cells with zero slump concrete comprising larger size
aggregates and mortar of fine particles,
iii. rolling the cells with a heavy roller such that the larger size
aggregates develop contacts with each other and the mortar finer
aggregate particles and cement fill up the voids and
iv. curing the concrete for 14 days so as to obtain concrete units
having layer elastic modulus of 3500-5000 Mpa.
2. Method as claimed in claim 1 wherein the cell walls get deformed and the blocks
of concrete filled in each blocks dovetail into each other during compaction
causing enhanced interlocking among the blocks.
3. Method as claimed in claims lto 2 wherein the zero slump concrete has water-
cement ratio close to 0.28 to 0.30.
4. Method as claimed in any of claims 1-3 wherein the plastic sheets are cut in
widths depending upon the depth of concreting which varies from 75mm to
150mm.
5. Method as claimed in claim 4 wherein the sheets are heat welded/stitched in a
staggered manner at defined a spacing and stretched to form squares (in plan) of
defined size.
6. Concrete units formed by the method as claimed in any of claim lto 5 comprising
formwork of plastic cells of high density polyethylene (HDPE) sheets, filled with
zero slump mix and having layer modulus of 3500-5000Mpa.
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7. Concrete units as claimed in Claim 6 adapted to form pavements having reduced
thickness.
Dated this 27th day of December 2007

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A method of preparing concrete units inside the formwork of cells of high density
polyethylene (HDPE) sheets comprising of the steps of forming cluster of hollow cubes
with high density polyethylene (HDPE) sheets, open at lower and upper surface; filling
the cells with zero slump concrete comprising larger size aggregates and mortar of fine
particles, rolling the cells with a heavy roller such that the larger size aggregates develop
contacts with each other and the mortar finer aggregate particles and cement fill up the
voids and curing the concrete for 14 days so as to obtain concrete units having layer
elastic modulus of 3500-5000 MPa. Concrete units formed by the above method
comprises of comprising formwork of plastic cells of high density polyethylene (HDPE)
sheets, filled with zero slump mix and having layer modulus of 3500-5000MPa