- Definition of generally used terms:
- Bituminous slurry: A processed mixture of bituminous emulsion binder (with or without a polymer modifier), continuously graded aggregate, mineral filler, additives and water, properly proportioned to form a slurry which can be laid evenly on a road surface.
- Break of an emulsion: The process during which the suspended droplets of bitumen in a bituminous emulsion become attached to any available solids, such as the particles of aggregate in a slurry, causing the water to be expelled from the mix. The process may be either physical, chemical or a combination of the two.
- Cure of a bituminous slurry: A transitional state of a bituminous slurry during which expulsion of water from the mix occurs through either chemical or evaporative means, or both, and which is accompanied by an increase in cohesive strength of the slurry mat.
- Microsurfacing: A bituminous slurry surfacing containing a polymer modified binder which is laid more than one stone thick.
- Slurry seal: A thin bituminous slurry surfacing without a polymer modifier.
- Mix Design:
The bituminous slurry mix shall incorporate aggregate, mineral filler and binder complying with the requirements of relevant specifications.
Aggregate shall consist of natural sand particles and / or crushed rock or stone. The aggregate shall be clean, hard, angular, durable, and free from laminated particles, clay and other aggregations of fine material, soil, organic material and any other deleterious material. There may be times when non-conforming materials are available at significant cost savings.
- Mineral filler
Mineral filler shall consist of an approved material, such as portland cement, hydrated lime or fly ash, with a minimum of 85% passing a 0.075 mm sieve. The filler shall be dry and free from lumps, clay, organic material and any other deleterious material and shall comply in all other respects with the requirements of AS 2357. Mineral filler is added to slurry to increase the proportion of fines, give more “bulk” or consistency to the slurry, or as a means of controlling the curing characteristics.
Binder shall be proprietary grade bituminous emulsion. For microsurfacing, the binder shall be polymer modified so that the nominated mix meets the performance requirements.
Water shall be compatible with the other constituent materials such that the performance requirements are met. The water shall be potable and free from any deleterious material.
Additives may be used to control the break and setting times of the bituminous slurry mix, depending on ambient conditions and traffic requirements.
- Mix design criteria:
Grading and mix properties are the two criteria for the mix design. Relevant tables are given in MRTS13 for the combined grading of aggregate and mineral filler and the bituminous slurry mix properties. Bituminous slurry shall be manufactured to a certified mix design.
All plant used in the manufacture and laying of bituminous slurry shall be provided and maintained in good working condition.
- Paving unit
Paving units are usually continuous-flow mixing machines which can accurately proportion and deliver mineral aggregate, mineral filler, bituminous emulsion and water to a pug-mill or similar mixer and discharge the Slurry produced on a continuous basis.
These paving units are usually equipped with a fines feeder that can accurately meter a predetermined amount of mineral filler into the mixer at the same time and location as the mineral aggregate. Calibrated controls for mineral aggregate, water and bituminous emulsion should be provided and be capable of accurately proportioning the component materials.
Paving units should also be fitted with a guidance system, which assists the driver in following the correct line.
Each paving unit shall be calibrated with the component materials of the certified mix design prior to the commencement of construction.
- Ancillary plant
Ancillary plant necessary for the performance of the work, such as rotary brooms, signs, lamps, barricades, hand squeegees, shovels and hand brooms, shall meet all statutory requirements.
- Construction procedure
The Contractor shall submit the identity and address of the registered slurry manufacturer and the procedure for surfacing operations detailing at least the following:
- all equipment to be used in mixing and laying the slurry
- laying program
- details of any required preliminary trial, and
- inspection and test plan
Laying operations shall not commence until expiration of the seven day period
- preparation of existing surface
- Set out
Marks shall be placed on the existing surface at intervals not exceeding 10 m on the line to be followed by the paving unit while laying the slurry.
Care shall be taken to ensure straight lines along kerbs and shoulders and that no runoff of bituminous slurry onto these areas occurs.
Lines at intersections shall be kept straight to provide a neat appearance. If necessary, masking shall be used to provide straight lines.
Laying of bituminous slurry shall not commence until the pavement has been swept to ensure that the surface is free of loose material, stones, dirt, dust and foreign matter.
- Protection of services:
All necessary precautions shall be taken to prevent bituminous slurry or other material used in the work from entering or adhering to gratings, hydrants, valve boxes, manhole covers, bridge or culvert decks or other road fixtures. After the bituminous slurry has been laid, any such material which has entered or adhered to road furniture and structures shall be removed.
- Surface defects:
Surface defects shall be repaired prior to laying of bituminous slurry in accordance with the details stated therein. This may include crack filling, pothole repairs and repairs to failed pavement. It is important that all surface defects, including cracks, potholes and pavement failures, be repaired at least 3 months, but preferably 12 months, prior to the application of slurry to ensure proper curing of repair work.
Temporary coldmix repairs should be removed and replaced with hot mix asphalt at least 3 to 6 months prior to the application of bituminous slurry surfacing to avoid bleeding. Poor pavement and surface repairs will adversely affect the performance of the bituminous slurry surfacing. There should be few, if any, defects for the Contractor to rectify.
- Tack coat:
If required by design, the existing surface shall be covered with a fine sprayed coat of bituminous emulsion at the application rate stated. The bituminous emulsion shall be allowed to break and harden prior to the laying of bituminous slurry surfacing.
Tack coating is generally not required, but may be beneficial on very old oxidised pavements, and on concrete or brick surfaces.
- Water fog coat:
The surface may be pre-wet by fogging ahead of the spreader box. Water used for pre-wetting the surface shall be applied so that the entire surface is damp with no apparent flowing water ahead of the spreader box. The application rate of the fog spray shall be adjusted to suit temperature, surface texture, humidity and dryness of the surface being covered.
- Water fog spray:
The surface may be pre-wet by applying a light spray of water (a fog spray) ahead of the spreader box. Spray water so that the entire surface is damp with no apparent water flowing ahead of the spreader box. Adjust the application rate of the fog spray to suit temperature, surface texture, humidity and dryness of the surface being covered.
- Weather limitations
Bituminous slurry shall not be applied if either the pavement or air temperature is below 10ºC and falling. Bituminous slurry may be applied when both pavement and air temperatures are above 7ºC and rising. Laying shall not proceed during rain or when rain is imminent.
Where wheel ruts are 15 mm or more in depth, a rut-filling course shall be applied, prior to placing the wearing course. Rut-filling shall be carried out using a spreader box capable of laying bituminous slurry across the varying cross-sectional depth such that it fills the rut and is stable.
A correction course may be required to produce a suitable and stable finish over ruts in excess of 10 mm deep, and a purpose-built rut-filling box may be required for ruts in excess of 35 mm deep. Correction courses are usually applied using a stiff strike-off screed on a standard spreader box. Rut-filling courses are usually applied in layers of not more than 1.5 times the nominal aggregate size using a purpose-built rut-filling spreader box.
To obtain an even and uniformly textured surface with acceptable skid resistance, it is most important that rut-filling and correction courses be overlaid by a wearing course. If this is not done, the coarser aggregate fractions can settle into the mix, resulting in a low or uneven surface texture and an unsightly appearance due to ‘fatty’ spots.
The bituminous slurry shall be of the desired consistency when deposited in the spreading box and nothing more shall be added other than minor amounts of water for the purpose of overcoming temporary build-up of slurry in the corners of the spreader box. The mixing time shall be sufficient to produce a complete and uniform coating of the aggregate and the resulting mixture shall be conveyed into the moving spreader box at a sufficient rate to always maintain an ample supply across the full width of the strike-off. The strike-off shall be adjusted to provide an application rate which shall completely fill the surface voids and produce a nominal thickness of bituminous slurry as stated
- Surface finish
Where increased surface texture is required, a fabric skirt of pre-dampened hessian, or similar material, shall be trailed behind the spreader box across the full width of the run. The skirt shall be hosed off thoroughly or immersed in water after each use to maintain its flexibility. The surface texture shall be demonstrated on a short test run prior to full scale manufacture and laying of production slurry. When a satisfactory surface texture is achieved on a test run, then all subsequent work shall be finished to the same texture.
The finished surface of the final wearing course shall not vary by more than two-thirds of the original average maximum deviation from a three metre straightedge.
Longitudinal joints in the wearing course shall be placed at either the edge or the centre of a traffic lane.
If necessary, the edges and joints shall be lightly screeded with a hand squeegee to achieve a smooth uniform appearance and to remove excess build-up of material. The end of each run shall be squared off at the point where there is insufficient material in the spreader box to maintain the full width of the spread.
- Traffic time
Bituminous slurry shall be capable of carrying slow moving traffic (less than 40 km/h) within one hour of application without undue permanent damage occurring, such as rutting or ravelling. When the traffic time exceeds one hour, work shall cease.
- Hand work
Areas which cannot be reached with the spreader box shall be surfaced using hand squeegees to provide complete and uniform coverage. If necessary, the area to be hand worked shall be lightly dampened or tack-coated prior to mix placement. Care shall be exercised to leave no unsightly appearance from hand work.
The same finish as applied by the spreader box shall be provided on hand worked areas. Hand worked areas shall be completed at the same time as the adjacent machine application process.
- Clean up
All surplus slurry shall be removed from the Site. Any aggregate stockpile Site and / or loading area occupied for the construction the work shall be restored to a condition similar to that which existed prior to occupation.
- Construction compliance testing
Compliance testing of the pavement shall be undertaken for each lot. A lot shall be an essentially homogeneous section of the completed bituminous slurry surfacing, not greater than 25 m³, nor greater than half of one day’s production.
- Testing frequencies and number of tests
The Contractor’s testing program shall be such that not less than two samples are selected and tested from each lot
Testing frequencies for the following aggregate source rock property tests used in the slurry mix shall be in accordance with relevant specification:
- Petrographic Analysis
- Wet Ten Percent Fines Value
- Wet / Dry Strength Variation
- Polished Aggregate Friction Value, and
- Sand Equivalent
The geometric tolerances, except for surface evenness, shall be checked by a method of random stratified sampling.
- Bituminous emulsion
Each bulk delivery of bituminous emulsion shall be accompanied by a certification of Standard compliance traceable to the relevant batch at the supplier’s storage tank. Two 2 litre random samples shall be taken from each bulk delivery.
- Bituminous slurry
Two 1.5 kg samples of bituminous slurry shall be taken from each lot at random intervals. The samples shall be taken from the discharge of the paving unit.
The samples shall be tested for residual binder content and particle size distribution in accordance with Test Method Q308C.
Some more information can be found by referring following documents using the download link below:
But some points for quick read is provided below:
Bituminous micro surfacing shall consist of a mixture of emulsified polymer modified bitumen binder, mineral aggregate, mineral filler, additives and water proportioned and mixed to form a slurry which is placed and spread evenly on the road surface. It shall be capable of being spread in variably thick layers for surface correction and for wearing surface applications.
Mean Average Texture Depth: The mean average texture depth is the mean of 10 tests for average texture depth using the Sand Patch Test Method.
High Bitumen Content (HBC) emulsion: A bitumen emulsion with a bitumen content of at least sixty seven percent.
A purpose-built continuous flow mixing unit capable of accurately metering each individual component material into a mixer which thoroughly blends these materials to form a homogeneous bituminous slurry and transfers the slurry into a spreader box for application to the pavement surface.
Generally, bituminous slurry surfacing can be used as an alternative to sprayed sealing or asphalt in the following circumstances:
- Where a non-structural wearing course is required
- Where the increase in surface level must be minimised, for example, at kerbs, etc
- Where a dense graded asphaltic type surface is desirable at minimal cost, for example, within urban areas where traffic noise from a sprayed seal would not be acceptable
- To correct cross-sectional shape and fill ruts
- As a means of improving surface shape and providing a uniform surface texture prior to a reseal (or SAM seal if the existing pavement surface is cracked)
- Where improvement of rideability is required
- Where loose aggregate would be a problem, such as from sprayed sealing operations in shopping and pedestrian areas
- To improve skid resistance, for example, over worn or polished asphalt in urban areas
- To reduce the noise level of sprayed seals.
Microsurfacing is unsuitable over active or environmental cracking or pavements with high curvature functions.
Below is the surface texture requirement in case of Brisbane City Council specification:
After trafficking for one month, wearing course micro-surfacing shall have average texture depths (Volumetric Sand Patch Method) not less than the minimum value specified.
Table 4.4 – Surface texture depth