The process by which a road is actually built according to established design standards and construction plans. 2. Rehabilitation
Activities which improve the existing road and restore its geometric characteristics to the original recommended design standards.
3. Upgrading
The process by which the standard of an existing road is altered to allow the achievement of an increased capacity for the safe use by a greater volume of traffic.
4. Maintenance
The work which is required to retain the original standard of the road. Horizontal Alignment
The direction of the centreline of a road in plan. Horizontal Curve
Transition Curve
A curve, whose radius changes continuously along its length, used for the purpose of connecting a straight with a circular arc or two circular arcs of different radii.
Transition Length
The length of the transition curve. Shift
The lateral displacement of a circular curve, measured along the radius, consequent upon the introduction of a transition curve.
Compound Curve
A curve consisting of two or more arcs of different radii curving in the same direction and having a common tangent or transition curve where they meet.
Reverse Curve
A composite curve consisting of two arcs or transitions curving in opposite directions. Intersection Angle
The internal angle formed by two successive straights. Deviation Angle
The external angle formed by two successive straights measuring the angular change of direction. Deflection Angle
Successive angles from a tangent subtending a chord and used in setting out curves. Vertical Alignment
The direction of the centreline of a road in profile. Vertical Curve
A curve on the longitudinal profile of a road. There are two types of vertical curves:
• Crest Curve - A convex vertical curve with the intersection point of the tangents above the road level. • Sag Curve - A concave vertical curve with the intersection point of the tangents below the road level. Gradient
A rate of rise or fall on any length of road with respect to the horizontal. It is usually expressed as a percentage. Longitudinal Profile
Superelevation
The inward tilt or transverse inclination given to the cross-section of a carriageway throughout the length of a horizontal curve to reduce the effects of centrifugal force on a moving vehicle. It is expressed as a percentage. Design Speed
A speed selected for purposes of design and correlation of those features of a road, such as curvature, superelevation and sight distance, upon which the safe operation of vehicles depends.
Surfaced road
A surfaced road is a road which has been provided with an all-weather riding surface. For the purposes of this presentation two surfacing options will be considered, viz.:
• A Bituminous seal utilizing a bituminous emulsion binder, and
• An asphalt surfacing manufactured with a bituminous emulsion binder. Bituminous Seal
A bituminous seal consists of aggregate of a specified size (or grading) held in place with a bituminous emulsion binder, penetration grade or cut back bitumen binder. For the purposes of these guideline three types of seal will be discussed. These are:
• Sand Seal • Cape seal
• Modified “Otta” seal or Penetration Seal Sand Seal
A Sand seal comprises a single or double seal of aggregate (river sand, crusher dust or grit) held together with a bituminous binder. For a permanent wearing course at least a Double sand seal would normally be required. A single sand seal can be used as a temporary seal until the permanent seal can be applied.
Penetration seal (Modified Otta Seal)
The penetration seal was developed to provide a more labour friendly alternative to the “Otta” seal. A Penetration seal comprises a graded aggregate held in position with a bituminous binder. The binder is applied in two applications in the form of a tack coat followed by a penetration application.
Asphalt surfacing
Asphalt consists of a mixture to predetermined proportions of aggregate, filler and bituminous binder prepared off the road under controlled conditions. The asphalt described in the guidelines makes use of a bituminous emulsion as binder.
Aggregate
Aggregates (coarse aggregate) for bituminous seals as a rule consist of approved inert hard rock type material which has been crushed and/or screened to comply with certain specifications and requirements. Crusher sand or washed natural sand, used in the manufacture of slurry, is also classified as an aggregate (fine aggregate). The grading of the sand used in the manufacture of slurry will determine the texture of the slurry
Average Least Dimension (ALD)
This expression is used as one of the characteristics for aggregate used in bituminous seals for surfacing e.g. Cape seal, penetration seal etc., and is of importance when determining the rate at which the aggregate must be spread to prevent over or under application of the aggregate as well as determining the application rate of the bituminous binder.
The ALD can be described as follows:
Any particle of aggregate is not perfect in shape – a 19mm aggregate is not 19mm in all directions, it has long and short sides.
Average Least Dimension of aggregate (ALD)
If dropped on a surface it will always fall on the surface with its smallest dimension vertical to the plane of the surface. It does not matter what the shape of the particle of aggregate is, it will always fall on the road with d1 and d2 (Figure A-7) i.e. the least or smallest dimension vertical to the road surface; e.g. a sample if dropped in the road will never come to rest on the road in this position where d the maximum dimension is vertical to the road surface.
Aggregate Crushing Value (ACV)
The aggregate crushing value (ACV) of an aggregate is the mass of material, expressed as a percentage of the test sample which is crushed finer than a 2.36 mm sieve when a sample of aggregate passing the 13.2 mm and retained on the 9.50 mm sieve is subjected to crushing under a gradually applied compressive load of 400 kN. Bitumen
Bitumen which is a by-product of the petroleum industry is the cementing (binding) agent used in bituminous seals or asphalts. The viscosity47 (stiffness) of bitumen is given in terms of a penetration. The penetration value of
bitumen is the distance a standard needle will penetrate a sample of the bitumen at a certain standard temperature. Bituminous emulsion
A bituminous emulsion is a liquid mixture of small droplets of bitumen suspended in water with the assistance of an “emulsifier” An emulsifier is an agent included in the bitumen water mixture to distribute the bitumen droplets in the water and regulate its stability and “breaking” time. There are a variety of bituminous emulsions either anionic or cationic, spray grade, mix grade or stable grade. The correct emulsion must be used for the correct application. For instance, Anionic emulsions rely on the evaporation of the water component for breaking the emulsion and are generally most suitable for use with basic aggregates e.g. dolerites, whereas the Cationic emulsions rely on a chemical reaction for breaking the emulsion and are most suitable for use with acidic aggregate e.g. granites. The types and grades of emulsion referred to in this guideline are listed below.
Anionic spray grade emulsion (60/40)
This is an emulsion of 60% bitumen and 40% water and is used to bind the aggregate in the construction of bituminous surfaces such as the Cape seal.
Plane of surface d1
B
l1 l2
d2
Figure A 7: Average Least Dimension of aggregate (ALD)