Labour Intensive Construction
Introduction to LBS Asphalt (Labour Intensive Asphalt)
LBS is a formulated mixture of inert fillers, bitumen extenders and binder enhancers designed to be blended with selected aggregates and water based bituminous emulsion in the manufacture of asphalt for general road surfacing and repair. The final LBS asphalt mix is designed to conform to TRH 8 specifications for ‘fine continuously graded asphalt’. Being a process carried out at ambient temperatures utilising bitumen emulsion, LBS asphalt is especially suited to labour-based surfacing operations.
LBS Asphalt Material Requirements
Aggregate: The LBS asphalt mixture utilizes two sizes of stone aggregate, crusher sand and 6.7 mm roadstone.
Aggregate Grading
| Sieve Size (mm) | Nominal size of stone (percentage passing sieve) |
| 6.7 mm | Crusher Sand |
| 13.2 | - | - |
| 9.5 | 100 | - |
| 6.7 | 85 -100 | - |
| 4.75 | 0 - 30 | 90 -100 |
| 2.36 | 0 - 5 | - |
| 0.15 | - | 0 - 20 |
| 0.075 | - | 0 - 10 |
Bitumen
An anionic stable grade bituminous emulsion containing a 60% nett bitumen content is used as the binder. The emulsion should conform to SABS 309 specification.
Physical and chemical properties:
- Appearance - brown
- Viscosity at 50°C, Saybolt Furol seconds, max.
- Binder content, % (m/m)
- Residue on sieving, g/100 ml
- Sedimentation after 60 complete rotations
- Coagulation value, % (m/m)
- Dolerite chippings
- Portland cement
|
Min
-
60
-
-
-
-
|
Max
-
62
0.25
Nil
-
2
|
LBS Asphalt Mix Design Procedure
Typical LBS composition – 20 mm seal (25 mm loose placed uncompacted material)
| Material | Mix (%) | Mass (kg) |
| LBS filler | 20 | 200 |
| Crusher sand | 50 | 500 |
| 6.7 mm roadstone | 21 | 210 |
| Bitumen emulsion | 9 | 90 |
| Total: | 100 | 1,000 |
Note: The water content is not included in the above calculations and will need to be adjusted as required dependent on site conditions.
Suggested plant and equipment requirements for LBS Asphalt
(up to 1500 m2/day output)
4 × wheel barrows
8 × shovels
6 × containers (25 l)
1 × broom
2 × hammer (plus 6” nails and fish line)
2 × thickness guides
(25 mm angle iron × 30 m long)
|
3 × metal rakes
3 × watering cans
1 × 4 m level
1 × pedestrian roller (or hand tampers if required)
1 × 500 -1000 L water tank
1 × drum stand
1 × drum tap
|
(excluding spares in case of breakages and all relevant safety signs and devices)
Suggested labour requirements for LBS Asphalt
(up to 1500 m2 / day output)
| Task | Workers | Activity |
Supervision
Traffic control
Materials stockpile
Materials supply
Bitumen emulsion supply
Materials mix
Thickness guides
Sweeping and watering
Spread and levelling of final mix
Final level
Compaction water
Compaction |
2
2
2
4
2
8
2
1
3
2
2
1 |
Check quality and maintain production rate
Maintain safe traffic flows
Supply correct quantities of LBS filler and aggregates
Move materials to work area
Supply correct quantities of bitumen emulsion
Mix measured aggregate LBS filler and bitumen emulsion
Setting out of the road and thickness guides
Clean road surface, apply water and brush surface
Place and roughly level LBS asphalt
Adjust final level of the LBS asphalt
Water the levelled LBS and the compactor drums
Compact the asphalt road surface |
| TOTAL | 31 | |
Note: The above is an indication only as workers' tasks will vary during the day to best meet the output needs of the team.
LBS Asphalt Application Procedure
Site Preparation
- The road surface should be firm, well compacted and swept free of loose material.
- A prime or tack coat can be applied if specified or required.
LBS product preparation
- Adjust the size of the buckets to hold the correct volumes of crusher sand, roadstone and bitumen emulsion for the LBS mix.
- Place the bags of LBS filler at regular intervals along the length of the surface to be sealed.
- Place the required quantity of crusher sand and roadstone next to each bag of LBS filler.
- Mix the crusher sand, roadstone and LBS filler thoroughly.
- Add the required quantity of bitumen emulsion to each stockpile and mix thoroughly.
- If the prepared mix is not to be placed immediately, cover with the empty bag and/or water lightly.
Note: Should it be necessary to improve workability of the mix, add water until the required consistency is achieved.
LBS Product application
- Place thickness guides (25 mm loose placed material for a nominal 20 mm compacted seal).
- Lightly water the base sweeping off any free standing water (no prime is required).
- Spread the prepared LBS mix and level to the required thickness.
- Lightly apply water to the surface of the levelled LBS mix.
- Compact the area by roller with 2 to 3 passes using vibration (water the drums to assist with sticking of material).
- If required lightly water the compacted area again and roll again with 2 to 4 passes without vibration.
- Once the surface becomes saturated with brown liquid, sufficient water and compaction has been applied.
Note: If a greater labour input is required, the road surface can be compacted by hand, using hand tampers. If this is done, however, greater attention should be paid to the quality of the compaction and the densities achieved.
Traffic control
LBS can be opened to traffic within a few hours. However, speed should be reduced for the first 24 hours. Full strength will only be achieved once all the water used has evaporated.
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