Single, Double & Cape Seals

11.5.2.1 Binder application

The main problem experienced in seal work with the application of binders concerns their application for the tack coat and penetration sprays at specified spray rates. To overcome these problems cognizance should be taken of the following:

• _{When a particular type of seal is specified and the rates of application of the binder are designed, it}

should be borne in mind that there is a limit to the quantity of emulsion which can be applied for the tack coat before run-off of the emulsion occurs because of the cross fall or longitudinal gradients.

• Any shortage in the amount of binder required in the tack coat can be accommodated by increasing the application rate of the penetration spray.

• _{Selection of a binder with higher viscosity can overcome some of the above problems.}

• _{The use of a motorised hand sprayer will overcome many of the problems of uniformity of application if}

it is used by trained operators.

• _{When emulsions are used, the problem of over-spraying/excessive application will only occur if}

untrained staff are used, as over-application is visually discernable.

• _{It is advisable to check the rate of delivery (}ℓ/min) of the sprayer and to determine the rate of application over a measured area before proceeding.

11.5.2.2 Application of aggregate

Hand labour may be used to apply aggregate efficiently and neatly if training of the field staff is done and if the following aspects are borne in mind:

• _{The aggregate to be applied should be neatly and accurately spotted along the shoulder of the road to}

be surfaced before spraying commences.

• _{The aggregate should not be shovelled onto the sprayed surface but should be "pitched" into the air so}

that the chips fall vertically onto the surface without rolling.

• _{The aggregate should lie shoulder to shoulder. Careful back-chipping and brooming of the aggregate,}

to ensure that it does not lie in double layers, can effectively be done with hand labour.

• _{Care should be taken, when the surface is rolled with a pedestrian roller, that only limited vibration is}

used.

• Screens should be used on both sides of the road to avoid contamination of kerbs, gutters or concrete drains. Where there are no kerbs, gutters or drains, the edges of the road should be set out so that neat straight edge lines of the surface are obtained. This may be done by using ±7 mm diameter rope as guide lines on the edges of the surface.

T a b l e 1 1 - 1 - A p p l i c a t i o n r a t e s f o r b i n d e r a n d a g g r e g a t e

ALD (mm) Rate of application of 60

% emulsion (ℓ/m2) Rate of application of aggregate (m3/m2) 4 1,5 0,004 5 1,8 0,005 6 2,1 0,006 7 2,4 0,007 8 2,7 0,008 9 3,0 0,009 10 3,3 0,010 T a b l e 1 1 - 2 - A d j u s t m e n t s t o f i n a l b i n d e r s p r a y r a t e s Traffic count (vpd)

(Est for the road)

Adjustment to calculate total spray 500 250 < 100 No adjustment add 0,25 ℓ/m2 add 0,33 ℓ /m2 Notes:

The aggregate should be applied before the emulsion breaks and turns black.

The surface of the aggregate should be lightly sprayed with water but not flooded before the emulsion is applied.

The above simplified method is included for the use of field staff whom do not have access to the expertise required for the sophisticated design methods described in Chapter 7.

11.5.3 Slurry bound Macadam seals

The principle of this surfacing is to obtain stone-to-stone contact with only the voids filled with a slurry. Using smaller aggregate requires a finer slurry grading to be able to penetrate.

Testing the consistency of the slurry mix on a regular basis is important as workers often tend to add too much water to the mix.

Checking for full-depth penetration is essential, especially at the road edges. During the initial stages of projects, it is often necessary to chip out the surfacing at the edges and to replace both aggregate and slurry.

For uniform mixing and increasing the speed of the work, a small concrete mixer is recommended. For minor work (maintenance repairs), the slurry can be mixed in wheelbarrows.

Figure 11-1 Concrete Mixer (250/175ℓ)

An easily removable ball-valve/tap is used for discharging emulsion into measuring containers in order to ensure a clean and neat operation with minimum wastage. The operation is facilitated by rolling the drum up the ramp onto a steel frame which is high enough to accommodate the measuring cans/containers.

Figure 11-2 Stand for 210 litre drums of emulsion

Measuring Cans

25 litre 10 litre

with handles

For accurate work, measuring containers are essential for both aggregate and emulsion. 25 litre cans with handles are user-friendly. 10 litre measuring cans are used for cement.

3000

150

10

Flat Steel Rail

Flat steel rails ensure a uniform thickness of slurry seal on new work.

The slurry should be placed 10 mm thick when wet. This dries out to ± 6 mm.

Figure 11-4 Flat Steel Rails

100₀

100₀

Steel Squeegee

Rubber Squeegee

Squeegees, both steel and rubber, are required for spreading slurry.

Figure 11-5 Squeegees

The use of a motorised hand sprayer results in more uniform application of binder than a hand- operated sprayer. If cationic bitumen emulsion is used, the material should be heated to between 50°C and 60°C.

Figure 11-6 Motorised Hand Sprayer

Lifting Equipment for 210 litre drum

The lifting equipment can be made up in any workshop. It is most useful and practical for picking up full drums of binder.

½ 210 litre drum open top and bottom

with pipe handles

A half drum container is light and economical to manufacture. For spotting heaps of aggregate along the constructed base, the half drum works well.

Figure 11-8 Measuring Containers

Thinnest galvanised plate bolted to 25x25 angle frame

with two handles (9mm Ø rod)

2000

7

5

0

In addition to the kerbs or side drains being covered with sand, protective screens can be used to ensure a clean neat line when the base is hand-sprayed.

Figure 11-9 Protective Screens

The use of pedestrian rollers (Bomag rollers or their equivalent) is recommended.