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 from 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 designs)
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.
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