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Today, almost world-wide, there is a general shortfall in resources required to provide appropriate road networks. This is mostly the result of cuts in government funding of roads as other facilities gain higher priorities e.g. housing, schools and hospitals. At the same time, the cost of obtaining good road construction materials is increasing and these materials are becoming scarcer as resources are being depleted, necessitating long haul distances. This situation is forcing a re-evaluation of conventional road designs, material standards and construction methods.
Faced with these problems, engineers are having to specify the use of sub-standard materials on many roads. This, however, leads to additional problems, particularly on earth and gravel roads, such as:

  •  Safety, health and environmental problems related to dust or loose surface material;

  •  Maintenance problems related to surface durability under wet and dry conditions;

  •  Level of service problems related to general surface deterioration such as rutting and pot holing, caused by poor materials, high traffic volumes and heavy loads.

Frequent maintenance by experienced and good operators can limit the latter problem to a significant extent but is costly and disruptive to traffic flow and has serious road-safety implications.
In an endeavour to overcome some of the problems, road engineers internationally, have over the past few years embarked on a series of trial evaluations using various chemical additives in gravel wearing courses and pavement layers. These evaluations have fallen into the following groups:

  • The use of synthetic additives to modify existing gravel wearing courses and in situ and local materials to improve the durability and load carrying capacity of the materials.

  •  The use of synthetic additives under conventional thin bituminous surfacings to improve sub-standard pavement layers with a resultant cost benefit.

Roadbond is one such additive which has been used in several countries to facilitate the utilisation of marginal quality construction materials for road pavement layers. ROADBOND allows the use of appropriate in situ or local materials to provide a pavement layer with a number of advantages, e.g.

  •  Reduced material borrow and haul costs

  •  Improved riding quality of unpaved roads

  • Reduced dust generation of unpaved rods under traffic

  • Reduced deterioration rate of unpaved roads

  • Reduced maintenance requirements

  • Improved safety characteristics

  • Stable layer for application of thin bituminous surfacing

Roadbond: Soil Stabiliser And Compaction Aid
Roadbond is a water soluble, environmentally-friendly, liquid chemical, which when added in small quantities to natural soil or rock material can result in substantial improvements in the physical properties of the material, after compaction. These improvements are brought about by increasing the compatibility of the material and by decreasing the water sensitivity of certain components of appropriate materials. This enables low cost, higher strength, durable pavement layers to be constructed with a reduction in compactive effort.

As A Soil Stabiliser
Many natural gravel materials contain clay minerals. In their dry state these materials have high strengths and would provide acceptable structural layers in pavements or wearing course layers in unpaved roads provided they stay dry. However, should these materials become wet there is a significant loss of strength resulting in problems with the road. Roadbond has the ability to modify certain clay minerals in such a way that the water adsorption capacity of the clay minerals is reduced and the material can retain its strength better under adverse moisture conditions.

Suitable materials, typically identified by X-ray diffraction, have a high active clay component which is strongly affected by the ionic reactivity of Roadbond. This reduces the water layer adsorbed to the surface of clay particles and results in a water repelling effect by the clay. This essentially reduces the activity of the clay and makes it less water-sensitive. In this way, the quality of the material is effectively improved.

Other materials which do not have an abundance of clay minerals, but have an excess of hydrated metallic ions can also be effectively improved with Roadbond. The reaction in this case reduces the water of hydration surrounding the free metallic ions and results in a lower hydration potential and an improved compactability.
Roadbond is normally diluted in water for use as a soil stabiliser at a ratio of 1 : 200 to 1 : 2000 depending on the prevailing soil moisture content, the optimum moisture content (OMC) determined for the soil, weather conditions and the prescribed application rate.

Roadbond allows the use of in situ soils containing clays which would not normally be acceptable for use in road construction. It can be used for main, district, municipal, access, mining, military and agricultural roads, where a good bearing capacity is required to take heavy vehicles and traffic volumes. Roadbond can also be used in the subbase and lower layers in highway construction and for aircraft runways and hardstandings.

As A Compaction Aid
Using Roadbond with conventional compaction methods and equipment, compaction is made easier due to its super-plasticising effect and its ability to reduce the surface tension between particles during compaction. This results in higher densities with correspondingly higher strengths and layers which are less permeable to water.
Roadbond as a compaction aid is normally diluted in water for use at a ratio of 1 : 1000 to 1 : 3000 depending on the prevailing soil moisture content, the optimum moisture content (OMC) determined for the soil and weather conditions.
Roadbond is not a substitute to overcome poor engineering practice and whilst allowing a wide range of materials to be used, it does not necessarily make an inferior type soil acceptable.

Construction Procedures
Once the initial material investigation and laboratory work have shown Roadbond to be an appropriate product for improvement of the soil, the following procedures can be followed for its application, in roadworks.
No construction equipment additional to that normally required for the proper construction of unpaved roads or pavement layers is necessary for the construction of Roadbond treated roads.

New Construction / Rehabilitation
a) Remove top soil, vegetation and root systems where necessary.

b) The in situ material or existing road which is to be used must be scarified to the required depth, ensuring that the final road will be raised above natural ground level.

c) Cut side-drains adjacent to the proposed shoulders in the required positions. Use the material from these drains (if suitable) to augment the scarified in situ material in order to make up the required thickness. Shape the road to the line and levels required. It may be necessary to import additional material to ensure that an adequate thickness of material exists or if the in situ or existing material requires improvement in its properties to ensure successful use of Roadbond (e.g not enough suitable fines). All in situ, drain and imported material must be tested to comply with material requirements, before being placed on the roadway.

d) From the laboratory determined Optimum Moisture Content (OMC) and the in situ moisture content, determine the quantity of water required to bring the material up to OMC + 1%.

e) Add the laboratory determined quantity of ROADBOND to the full water bowsers. Avoid excessive frothing or foaming of the solution.

f) Spray the water / Roadbond solution onto the material layer which now consists of the scarified in situ material, the material removed from the side-drains, imported material or a combination of these. Apply the water/chemical solution continuously whilst processing with a grader or other suitable equipment to break down large lumps of material and obtain an even moisture content through the material. All stones and other solid material larger than the specified nominal size (usually 100 but preferably 50 to 75 mm) must be removed from the surface layer.

g) When all the Roadbond / water solution has been applied, the soil should be slightly above OMC. Mix the soil until homogenous.

h) Compaction should commence at OMC or slightly above using conventional compaction equipment. Water can be added from time to time to supplement any losses through evaporation. Compaction should be carried out until the specified density is obtained i.e. a minimum of 95% Mod AASHTO (98% preferred), while retaining a crown and appropriate cambers.

i) After compaction, the surface of the road can be lightly skimmed with the grader. It is recommended for most materials that the material is then heavily sprayed with water and a pneumatic tyred roller is repeatedly applied in order to produce a tightly bound surface (slushing).

j) Curing should be carried out over a 4 day period using a light spray of pure water on the road surface.

k) Once the road has dried back so that there is no slippery material on the surface, it can be opened for traffic access. Any deformation should be corrected by grading before the material dries out fully

The Roadbond chemical formulation was developed as a result of extensive research followed by laboratory and field testing in South Africa and Russia. Where comparative testing has been carried out against other commercially available additives, results have unfailingly shown that ROADBOND gives superior results.

Roadbond is different from other products, in as much as it can be supplied in the form of a super concentrate RBX25 for export, 24 times stronger than commercial strength product. Shipping, handling and storage costs are considerably reduced and the concentrate can be safely diluted to commercial strength, before use, in the country of destination.

Super concentrate RBX25 can be shipped against urgent orders in 25 litre containers suitable for delivery by air cargo.

 Super concentrate RBX25 can be easily adjusted with readily available, inexpensive ingredients should it be necessary to alter the formulation for optimum results in specific problem materials.

Research and development continues with the object of providing users of Roadbond with a product and technical service which is superior in all respects to any alternative product. 

Summary and Conclusions
Roadbond is not a wonder product marketed to solve all the problems experienced by the civil engineering fraternity. It will not always overcome problems associated with inherently poor materials, but proper testing prior to its use will indicate when and in what quantities it will be effective.

Roadbond when used with the correct material types offers the following advantages:

  • Definite increase in bearing capacity which can be quantified in terms of Californian Bearing Ratio (CBR) increases.

  • The use of otherwise marginal materials with cost savings of up to 75%.

  • Due to the above, low class roads can now be surfaced with a thin bituminous or asphalt seal, creating a durable weatherproof road, requiring minimum of no maintenance for a period of five to seven years.

Roadbond has shown to be effective in full scale roadworks as a compaction aid and stabiliser due to its ability to densify the soil forming a ‘stiffer’ and more impermeable layer.
Roadbond can offer enormous potential in the road construction field particularly in the sphere of low cost roads.
Roadbond reduces the dust generated on gravel roads.
Roadbond reduces the maintenance requirement of gravel roads.
Roadbond should also be used as a means of upgrading available materials in more substantial road pavements.

Plasticity Index (PI) Moisture Passing 0.075mm sieve Mod.AASHTO density
Lower Limit Upper Limit Lower Limit Upper Limit Lower Limit Upper Limit
8 35 Moisture before compaction should be optimum moisture content +1% 15% 55% 95% N/A
If lower, adjust by blending in a suitable material to increase P.I. If higher, adjust by blending in a suitable material to decrease P.I. If lower, add fines. If higher, add stone or good gravel. (98% preferred)