Cold premixes can conveniently be prepared with bitumen emulsion because the binder is already in a highly dispersed state. This property also renders emulsions very suitable for the preparation of premixes with simple equipment such as concrete mixers and even a shovel and a staging board.
The following range of emulsions is available:
- Anionic Stable Mix emulsion for dense graded cold mixes
- Cationic Premix Grade Emulsion for open graded cold mixes
- MS Grade emulsion for hot or cold dense graded mixes
(a) Anionic premixes with Stable Grade emulsion
Cold dense graded mixes are easily prepared with Anionic Stable Grade 60% emulsion. A typical anionic cold mix composition is as follows:
13,2 mm stone – 1 x 25 litres
9,5 mm stone – 1 x 25 litres
Crusher dust – 2 x 25 litres
Cement – 1,5 kg
Anionic Stable Mix 60% – 17 litres
Water (if required) – 5 litres (max)
Note: The above mix is suitable for patches deeper than 25 mm. For patches less than 25 mm deep, the mix below is recommended:
9,5 mm stone – 2 x 25 litres
Crusher dust – 2 x 25 litres
Cement – 1,5 kg
Anionic Stable Mix 60% – 17 litres
Water (if required) – 5 litres (max)
Mixing procedure with a concrete mixer
- Place the stone, crusher dust and cement in the mixer
- Mix through thoroughly
- Add the stable mix emulsion and mix until evenly coated
- If the coating is not complete, some water may be required to pre-wet the aggregate before addition of the emulsion
- The mix must be placed within one hour of mixing to prevent premature setting of the emulsion
Hand mixing
Cold premixes may also be prepared by hand if a concrete mixer is not available. The measured volume of emulsion can be poured on to the correct volume of stone and mixed on a staging board with a shovel. After placing and curing, the premix may be compacted with a hand tamper if only a small area is involved.
Laying of the cold mix
The emulsion premix, whilst still brown, is spread to the required thickness by means of a suitable paver, or by hand using rakes for leveling the premix. Wooden battens or pegs inserted beforehand into the ground will ensure that the premix is laid to an even thickness, when spreading by hand. It is recommended that the premix carpet be confined within a firm boundary such as a kerb to prevent creeping of the mix
under compaction and the action of traffic. The levelled, emulsion coated premix is then left to break. During this period the premix will be susceptible to washout by rain. Once broken and compacted, no damage will result from rain falling on the premix layer.
Premixes can be compacted with a small self-propelled type of roller.
(b) Cationic premixes with Cationic Premix Grade emulsion
Dense graded cold mixes can unfortunately not be prepared with Cationic Premix Grade emulsions. The bitumen binder in Cationic Premix Grade emulsion is fluxed to a limited extent with hydrocarbon solvent to enhance the coating and stockpiling characteristics of the mix. The addition of the fluxant allows the mix be stockpiled for up to 14 days. Usually no mixing water is required.
The cationic surface active agent in these emulsions will provide good coating and adhesion to “acidic” types of aggregate such as quartzites and granites. Coating and breaking of the emulsion takes place during the mixing process with the aggregate, which lessens the risk of washout of unbroken emulsion by rain. Compaction of the mix can, therefore, commence soon after placing of the material.
Cationic emulsions are ideally suited for premix work during rainy weather conditions when wet aggregates can be used to prepare urgently needed premix for potholes or trench repairs.
. A typical cationic cold mix composition is as follows:
13,2 mm stone – 1 x 25 litres
9,5 mm stone – 1 x 25 litres
6,7 mm stone – 2 x 25 litres
Cationic Premix 65% – 12 – 13 litres
Note: The above mix is suitable for patches deeper than 25 mm. For patches less than 25 mm deep, the mix below is recommended:
9,5 mm stone – 1 x 25 litres
6,7 mm stone – 3 x 25 litres
Cationic Premix Grade 65% – 12 litres
Mixing procedure with a concrete mixer
- Place the stone in the mixer
- If necessary, dampen the aggregate slightly
- Add the premix emulsion and mix until evenly coated
- Over-mixing can result in the binder stripping off the aggregate
- The mix can be placed immediately or stockpiled for a few days.
- The mix can be compacted almost immediately and traffic can be allowed onto to the surface immediately after compaction.
(c) MS Grade emulsion premixes
General information
Continuously graded premixes prepared with MS grade emulsions, must be mixed with aggregate that is heated in either a drum, continuous type mixer or a concrete mixer fitted with a heating device such as a gas burner. The water component of the emulsion evaporates during the mixing process.
Principle features of these premixes are:
- Good stockpile performance for periods up to three months or more
- The mix can be laid hot immediately after mixing, or it can be allowed to cool on a stockpile.
- The hot mix as well as the cold, stockpiled mix can be placed with a paver, grader or be hand applied
- The residual binder has greater resistance to flow at higher temperatures
- Thorough mixing is achieved sooner in the mixer, because the binder is highly dispersed in the emulsified state.
- The mixing process takes place at lower temperatures than hot-mix asphalt and less hardening of the binder thus occurs.
- The water vapour generated during the mixing process effectively excludes air, resulting in less hardening of the residual binder.
- Lower mixing temperatures means reduced costs and no risk of over-heating the binder.
The binder component of MS grade emulsions contain selected fluxes to obtain controlled stockpiling characteristics of the premix. This prevents undue softness after compaction, but allows sufficient workability after stockpiling. Covering the stockpile with a plastic sheet or tarpaulin extends the period during which the mix remains workable.
Colas produce three grades of MS emulsion, viz. MS 150, MS 200 and MS 250. The flux content of MS 250 is the highest and is the most recommended of the MS emulsions. Mixes prepared with MS 250, therefore, have a longer stockpile life. Another aspect of MS grade emulsions is that the residual binder exhibits a marked change in the viscosity vs temperature relationship. The emulsion residue shows a resistance to flow at relatively high road surface temperatures (50 – 55 °C). This means that the binder will not flow from the aggregate during stockpiling, especially if open graded mixes, which have thicker binder films, are prepared with the MS grade emulsions.
Mixing procedure
- The mix can be produced in any approved type of batch or continuous type mixer. A small stationary concrete mixer, fitted with a gas burner, can also be used to produce small quantities of mix.
- The aggregate is heated in the mixer to a temperature high enough that will ensure that the resultant mix exits the mixer at a temperature of 100 to 110 °C
- The mix should ideally be stockpiled for about 10 days before use, to ensure that any residual water evaporates.
Spreading and compaction
- Spread the mix with a premix paver or a grader. Small areas can be covered by hand application
- If the mix is applied hot, allow it to cool sufficiently until it can bear the weight of the roller without signs of waving or creeping under the roller wheels.
- In the case of a cold stockpiled mix, compaction can commence immediately after spreading.
- Rolling should begin with a flat or tandem roller and finished off with a pneumatic tyred roller.
Grading requirements
The following are typical medium and fine aggregate gradings which can be adjusted to suit local conditions:
| Sieve size (mm) | Medium grading | Fine grading |
| 13,2 | 100 | – |
| 9,5 | 82 – 100 | 100 |
| 4,75 | 54 – 75 | 64 – 88 |
| 1,18 | 25 – 42 | 35 – 54 |
| 0,300 | 11 – 23 | 16 – 28 |
| 0,150 | 7 – 16 | 8 – 18 |
| 0,075 | 4 – 10 | 4 – 12 |
Binder Content
5,0 to 5,5% by mass of mix
Compacted thickness
Typical compacted thicknesses are:
Medium grading – 25 to 50 mm
Fine grading – 20 to 40 mm
Emulsion cold-mix being used to repair an edge break problem