20 years of experience

BOMAG Mix-in-Place with foamed

bitumen

20 years of experience

BOMAG Mix-in-Place with foamed

bitumen

Mix-in-place

For many years throughout the worldBOMAGs mix-in-place method has beenused to produce bearing and base coursesfor the construction and reconstruction offailed highway pavements. The BOMAG pro-cess is highly flexible in use on both smalland large construction sites with its low ove-rall costs and high productivity. In the lastfew years the use of foamed bitumen as abinding agent or the combination of foamedbitumen and cement has met a growinginterest on an international level.

The key item of equipment has been deve-loped for this process. The BOMAG MPH 122 stabiliser / recycler constantlyproduces good mixing quality, constant wor-king depth and high water and bitumendose rate accuracy.Low running costs are a major feature of themix-in-place method.

BOMAG mix-in-place.

Simultaneous mixing of cement and foamed bitumen.

Tight work schedules and margins on con-struction projects favour the use of recycledmaterials. However the recycling equipmentneeds to be competitively priced with lowmaintenance and servicing costs, high mil-ling performance, low fuel consumption andalso be highly flexible in use. Extensive expe-rience with foamed bitumen technology andthe compact design make the MPH 122 themost economical solution for sub bases and

bearing courses using mix-in-place con-struction in highway, forestry and agricultu-ral applications.

Creating a stabilised base for road construction.

Renewing a damaged pavement.

gravel/sand

water forfoaming process

hot bitumen

water formineral/soil mix

gravel/sand

Mix-in-place methodbefore after

stabilized bearing course

gravel/sandgravel/sand

asphalt asphalt newMix-in-place recycled layer

Mix-in-place methodbefore after

water forfoaming process

hot bitumen

water formineral/soil mix

Road construction in AfghanistanDuring the construction of the 120 km longroad between the Iranian border and theAfghan provincial town of Herat, a stabilisedbearing layer was produced using the mix-in-place method using 3% Portland cement and3% foamed bitumen.Initially the gravel-sand material was collec-ted along the road and, allowing for compac-tion to a final layer thickness of 25 cm, it waslaid and compacted. After pre-wetting thelayer surface with water, the cement wasspread over it using a cement spreader andthen it was milled with the MPH into the gra-vel-sand material for the specified layer thik-kness of 25 cm. At the same time the foambitumen and the water required to attain theoptimum water content were dosed andmixed in. The length of the milling sectionswas limited to 150 m. After pre-compactionof the stabilised layer by two passes of a BW 219 D-3 and levelling the height with agrader, the main compaction was carried outwith a BW 219 D-3 and the surface wasfinally finished with a rubber-tired roller. Theproject was completed by laying a 6 cmasphalt surface layer.

Constructing a national road in SouthAfrica

After uncovering the formation, a 30 cm bea-ring course was laid from 0/60 lateriteaggregate from a nearby pit and pre-com-pacted with a BW 219 DH-3 in 2 passes.Subsequently the material was homogenisedby adding water and compacted in 8 passes.In a second operation, foamed bitumen wasmixed in to a depth of 15 cm together with 1 % of water, to prevent drying out.

Because of the higher proportion of fine grainin the laterite soil used, and to support thedevelopment of stability, 1.5 % of hydratedlime was applied before the second pass.

Additives:1.5% foamed bitumen1.5% lime3% water

Site stories

For many years, BOMAG Recyclers of allgenerations have been used with foamedbitumen systems. The new Recycler MPH 122 was also designed for this appli-cation. High manoeuvrability with the combi-ned articulated and rear axle steering plusall-wheel drive and a powerful rotor ensuresconsistent mixing results and low costs. Thefoam bitumen system is mounted on therear frame and is easily accessible. All bitu-men pipes are heated for trouble-free ope-ration. All spray nozzles and expansionchambers are integrated in the heat insula-ted spray bar which is easily folded up forcleaning.

The nozzles can be controlled in pairs toadjust the spray width so that workingwidths can be changed if needed. Sprayrates for bitumen and water are controlledby the mixing electronics.

Operator console.

Operator console BOMAG dose computer BDS.

BOMAG MPH 122 with foamed bitumen system

MPH 122 with foamed bitumen system.

Documentation of MPH performance with BDS.

The foamed bitumen installation has amanual bitumen dose control as standard.Thus the desired bitumen flow rate for agiven working speed can be selected manu-ally. The installation can be equipped withthe BOMAG dosing computer BDS option.The BDS system controls the addition ofbitumen and water in relation to the workingspeed. The actual flow rates are displayedand registered.

BOMAG has thought of everything: Foamsamples can be taken at any time from thetest nozzle, and uncoupling the bitumenhose is safe and easy with a shut-off valvefrom the bitumen tanker.

MixtureA well graded distribution curve is essentialfor successful mix-in-place with foam bitu-men together with a fine grain proportion ofat least 4 5%. If necessary, the fine grainproportion must be adjusted by adding limeor cement or the grading improved byadding coarse particle fractions.

Adding binderThe illustration opposite gives the requiredquantity of binding agent. Depending onworking speed, the working depth and thequantity of binding agent, the flow rate isshown (assumed density of bitumen: 0.96kg/dm3; assumed density of soil: 2.00 t/m3).

Information relates to the MPH 122 with aworking width of 2.33 m.

OutputProductivity can vary depending on theapplication. The illustration opposite showspotential area output for stabilised layersand the recycling of damaged road pave-ments.

Guidelines for foamed bitumen

Assessment chart for foam bitumen applications.

Calculation of bitumen flow rate for MPH 122 with 2.33 m working width.

Area output of MPH 122 on foamed bitumen applications.

Workingdepth

Production ofstabilized layers

Crushing and reconstructionof damaged pavements

typical performance range

Old asphaltpavement

well suited materialZone 2: suitable material, lime additive

could be helpful for reducing the percentage of fines

Zone 3: unsuitable material, fines and/or fillers have to be added

Per

cent

age

[%]

US sieve sizes

Zone 2

Zone 1

Zone 3

metric sieve sizes [mm]

Example:working speed: v = 15 m/minworking depth: t = 0,25 mbinder content: k = 1,5 %binder quantityper spray section: QB = 34 l/min

v = working speed: [m/min]t = working depth: [m]k = binder content: [%]QB = binder quantityper spray section: [l/min]QM = mix quantityper spray section: [kg/min]

Accepted thickness of the mineral substance/soil mixture: 2.00 t/m3 The illustration applies for 2.33 m working width (MPH 122)

Site Stories

Road reconstruction Yantai, ChinaInitially the existing carriageway, consistingof 10 14 cm of asphalt construction andthe sand-silt mixture underneath, were pul-verized to a working depth of 20 cm. At thesame time, 2 % of lime was also mixed in.Two days later, after compaction of the pul-verized recycling material 50 kg/m2 ofmineral mixture 16/32 was applied and 3%of Portland cement spread over the top.

Subsequently the mineral mixture andcement were milled by the MPH into therecycling material for the specified layerthickness of 20 cm while simultaneouslyincorporating 3% of foam bitumen and thewater required for the compaction.

After good compaction and fine profiling ofthe stabilised layer with a grader the maincompaction is carried out with a BW 219 DH-3. The reconstruction measurewas completed by applying a new 6 cmthick asphalt surface layer.

Widening a motorway in ItalyAfter excavating the road to a depth of 20 cm, newly excavated material 0/26 mmwith a fine particle proportion of 12 % andoptimum water content was applied. Thematerial was distributed with a grader andpre-compacted with a BW 219 DH-3.Subsequently 3.5 % of foam bitumen and 1 % of hydrated lime, which was laid pre-viously, were mixed into the bearing course.

The final compaction was carried out by theBW 219 DH-3 in four passes. The roadreconstruction was concluded by applying anew asphalt bearing course and an asphaltsurface layer.

Additives:1% lime3.5% foamed bitumen

Forming foamed bitumen in the MPHspray bar

The addition of small quantities of water (1.5 3.5%) causes hot bitumen to foam.There will be a 10- to 20-fold increase involume.

The foaming process takes place in theexpansion chamber which is connected inseries with the bitumen outlet openings onthe spray bar. Bitumen and water are com-pressed simultaneously into the expansionchamber. The bitumen foam enters throughthe nozzles into the mixing space of the mil-ling rotor hood. The short-term increase inbitumen volume and the mixing process,which takes place at the same time, lead tothe mineral mixture being coated.

After compaction, foamed bitumen materialsshow increased bearing capacity and elasti-city properties plus a reduced tendency toform cracks. To accelerate the increase instability or to increase the filler content 1 - 2% of hydraulic binding agent (lime orcement) may be added.

Advantages of foam bitumen Wide range of applications including recy-

cled materials from existin