Specific recommendations for Cape Seals

After application of the first layer of aggregate the following procedures are recommended:

a) Rolling with the heavy pneumatic-tyred rollers should continue from the time the binder and aggregate are applied for a minimum of 8 passes per roller width. As a guide, 2½ hrs rolling with one heavy pneumatic-tyred roller is required for every km of single lane 3,7 m wide surfaced roadway, i.e. approx. 8 - 10 passes over each "width of roller" of surfaced width of the roadway.

b) All loose stone should be broomed off the surface before the fog spray is applied.

c) The fog spray is usually a penetration grade bitumen or a diluted emulsion. If a cationic bitumen emulsion is used as the fog spray, the aggregate should not be precoated with a tar-based precoating fluid. Precoating is important in so far as it assists in the application and preparation of the first application of aggregate.

Note:

Sufficient time should also be allowed between application of the tack coat and the fog spray, especially if emulsion is used in the tack coat.

d) Before the slurry is applied and the surface has been exposed to the elements and construction traffic, there probably will be some disturbance of the aggregate. It is therefore recommended that the surface be given one complete pass with a steel-wheeled roller early in the morning before the surface has warmed up.

e) If the surface has lain for any length of time, it should be inspected for contamination by dust, mud, vegetable matter or water. Loose material can be removed effectively with compressed air.

f) Depending on the texture required for the final surface, either a single or double application of slurry may be required. This may be applied either by hand or spreader box, but the mixing should be done in an approved mixer.

g) Care should be taken to determine the bulking of the fine aggregate used.

h) If the slurry is placed with hand labour, 13 mm diameter sisal rope (50 m lengths) should be placed on either edge of the section to be treated with slurry, i.e. at the edge of the surface and on the centre line. Work should be confined to these limits. The slurry should not be over-applied but levelled off neatly to the tops of the aggregate and finished off by dragging a moist burlap over the slurry before the emulsion breaks. If the slurry is applied with a spreader box, it is advisable to work up to approximately 100 mm from the edge and to use squeegees to spread the slurry to the edge.

Note:

A better result is obtained by hand spreading. However, the slurry must be “moved” too far as segregation could occur.

i) The surface should be well rolled with a heavy pneumatic-tyred roller, preferably 24 hours after application, in order to obtain a dense, well-knit surface. Depending on the texture required, a second application of slurry may be required.

Note:

The final texture will also be dependent on the closeness (shoulder-to-shoulder) of the underlying aggregate. 7.11.5 Construction of modified binder seals

When the modified binder and the spray rates applicable to the traffic, foundation and surface conditions have been selected, the following pertinent points should be observed during the construction process. a) All the preliminary checks applicable to normal bitumen seals, as regards setting out of the work,

traffic control, checking of equipment and aggregate should be carried out meticulously.

b) Sufficient quantities of aggregate, corresponding to the envisaged amount of binder to be sprayed, should be precoated 24 hours before it is required. (Some authorities specify 48 hours.)

c) If bitumen rubber is to be used, the rubber crumbs should be tested well in advance of the work to ensure that they comply with the specifications for grading, cleanliness, percentage of synthetic rubber and percentage of natural rubber.

Note:

Too high a percentage of natural rubber will result in blocked jets and stoppages on site.

d) Distributors spraying modified binders, especially bitumen rubber binders, should be tested on site for evenness of distribution of the spray bar and for delivery of the binder by the distributor pump. (Refer to APPENDIX J.)

e) It is advisable and recommended that when bitumen rubber is to be used, the rubber crumb be

introduced on site, in order that the time for "digestion" can be controlled. The time for digestion i.e., the time between introduction of the rubber and spraying should not exceed 2 hours. The digestion temperature should be between 180 °C and 200 °C.

f) The temperature at which the selected binder is to be sprayed should be obtained from the supplier and adhered to on the work. For bitumen rubber this could vary between 185 °C and 195 °C. If the spraying temperature is too low, "roping" or "tramlines" will result when the binder is applied. Temperature control is equally important for other modified binders.

g) When bitumen rubber is used, it is recommended that the entire contents of the tanker be sprayed out in one operation wherever possible, provided that all the checks for availability of aggregate, equipment, standby equipment and area of road surface available have been carried out meticulously.

h) The treatment of the centre-line joint requires attention:

- The "shoulder" end of the spray bar should be fitted with an end nozzle and fishplate. - The "centre-line" end of the spray bar should be fitted with an end nozzle but no fishplate.

- After the aggregate has been applied, any aggregate which may have fallen beyond the centre- line within the sprayed "flare" of the end nozzle across the centre-line should be removed.

overspray on the aggregate previously applied.

- Any aggregate falling on this overspray should be broomed off immediately so as to prevent the formation of a ridge consisting of a double layer of aggregate along the centre-line of the road. i) The use of rotary brooms and pneumatic-tyred rollers (heavy) working in tandem to remove over-

application of aggregate/double layers of aggregate and to distribute aggregate to the uncovered areas, is essential. This process should continue until all the binder has been completely covered and the aggregate is lying shoulder-to-shoulder.

j) All loose aggregate should be removed from the surface before the road is opened to traffic.

k) Summer grade bitumen rubber should only be used between approximately the middle of September

and the middle of May, when minimum daily temperatures are ± 7-10 °C. Winter grade bitumen rubber may be used between the middle of May and the middle of September, when the minimum daily temperature can fall to -4 °C.

l) Modified emulsions are more accommodating than bitumen rubber and may be sprayed in the dry

winter months, provided that the road temperature is 10 ° C and rising.

m) Hot modified binders should not be sprayed in the cold months, i.e. from May to the end of August unless a special formulation is prepared by the suppliers or construction methods or the seal type can be changed e.g. to keep traffic off the newly constructed seal and/or change to a double seal.

Note:

Information regarding the minimum and maximum temperatures is available from the South African Weather Service on request or from their Website (http://www.weathersa.co.za).