South Afircan roads are built using a layered pavement system. A road is built from
the bottom up, layer by layer, each layer increasing in strength and is sealed using
a bituminous or concrete surface.
Ecobond is a system in which bitumen emulsion is combined with a resin thereby improving
its engineering properties.
Ecobond is not a road surfacing. It is used beneath the blacktop/bituminous seal to
improve the bearing capacity of the base course and lower layers.
Presently bitumen is plastic (visco-elastic) like soft putty
or plasticine, it does not
return to its original shape and a road will rut and deform
under repeated loads.
Using Ecobond makes bitumen stabilization much stronger
(e.g. from 0.8MPa bitumen stabilisation to 6.9MPa
UCS equivalent), elastic so that it can bend and return
under loads and improves the water resistance (e.g. absorbtion reduced
8% to 0.4% with 1% resin added). Ecobond also reduces
temperature sensitivity of Bitumen.
It is often water that breaks a road and Ecobond helps to keep the road layers dry.
It also improves bitumen performance when using sand, especially fine sand (5MPa
UCS north KZN fine sand) which would normally be considered a marginal material.
There are three conventional stabilizing materials with
effective results, they
are well researched and well documented: cement, lime and
bitumen. Cement is brittle
and needs several layers to prevent it cracking which takes
time and costs money
to construct. Lime needs clay for best results, not usually
found in base courses.
Bitumen is visco-elastic (permanently deformable) but
becomes much better when used
with Ecobond making it elastic and stronger. Partially Bound
Ecobond stabilized aggregates (higher binder content and resin to
bitumen ratio) are used as cemented base courses (e.g. TRH
Better roads can be constructed at standard costs or costs can be reduced by using less chemicals at
the same or increased durability.
The 100mm thick Ecobond base at Duvha, Witbank, has carried approx. 30 MESAs (million
equivalent standard axles) since 1996 and is in excellent condition. The three year
old adjacent conventional road had approx. 100 potholes from Feb. to May. 2011 and
the 15 year old Ecobond section had none.
- Strength: C4 < 1,5 MPa, C3 < 3 MPa, C2 < 6 MPa, C1 < 12 MPa equivalent
soaked UCS has been attained, ITS strengths: BSM1 , BSM2 & BSM3 can be attained
(as per TG2 2009, 24 hour soak). Does not cause shrinkage cracking.
- Water resistance: up to 6,35 x 10-7 cm/s water impermeability,
2 – 6 times less water absorption than standard bitumen stabilization samples have
- Elasticity & tensile strength: Improves the elastic strength of bitumen emulsion (to counter visco-elastic
behavior or permanent deformation) and can bend and return (can be adjusted through variation of binder
content and resin to bitumen ratio).
- Workability with a wide variety of soils, even fine sand. This
can often reduce material import costs and construction time.
- Adaptable to requirements: Ecobond can be applied as a non-continuously bound,
partially bound or bound pavement layer, depending on the aggregate, binder content
and ratio of resin to bitumen used.