In this blog will reply to all question of Gilsonite user that how they can melt and blend with solvent,bitumen and even water!

Mix of Gilsonite need heat up,wait for a while and mix well with proper impeller.

In this blog will reply to all question of Gilsonite user that how they can melt and blend with solvent,bitumen and even water!

Mix of Gilsonite need heat up,wait for a while and mix well with proper impeller.

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MIXING PROCESS OF GILSONITE

The  use  of  modifiers  to  improve  the  performance  of  bituminous  road  paving  materials  is increasing  worldwide.  These  additives  range  from  polymers  and  fibers  to  lime.  One  product  is

now  being  considered  very  seriously  by  road  paving  engineers  and  paving  contractors  who  are

concerned  both  with  high  performance  and  cost  effectiveness.  This  product,  gilsonite,  has  long

been known as a bitumen reinforcer and hardening agent. New evidence, both from the laboratory

and  from  a  fast  growing  body  of  field  work,  demonstrates  that  gilsonite  offers  a  unique

combination of high performance and economy for high stress paving applications.

The main benefit of gilsonite is in producing road pavement mixes of much higher stability than

conventional ones. A unique, natural hydrocarbon, high in asphaltenes and nitrogen compounds,

gilsonite  is  a  granular  solid  that  is  fully  compatible  with  bitumen.  It  can  be  melted  into  hot

bitumen, or it can be added during hot mix manufacture. In either case, gilsonite dissolves easily in

bitumen and requires only a slight increase in mixing time to achieve a uniform, easily workable

hot mix.

The increased stability of gilsonite fortified pavements makes them more resistant to deformation

problems,  such  as  rutting  and  shoving,  and  increases  the  pavement’s  load  carrying  ability  .  In

addition,  laboratory  tests  and  field  results  show  that  improved  deformation  resistance  can  be

obtained  while  the  pavement  retains  much  of  its  original  ductility  and  ability  to  resist  low

temperature cracking. Other positive benefits include increased resistance to water  stripping and

aging.

What is Gilsonite?

Gilsonite is a natural hydrocarbon, high in asphaltenes and also has nitrogen compounds, and fully

compatible with bituminous pavement materials. It forms true, stable solutions in bitumen and can

be easily incorporated by presolution in the bitumen with agitation or by direct addition during hot

mix manufacture. Gilsonite that is provided by us, has specifications that represented below:

For  using  gilsonite  in  the  case  of  road  paving  binders,  presence  of  this  amount  of  ash,  isn’t

counted an undesirable factor, and even it reinforces asphalt mix features beside other materials

that  used  for  asphalt  production.  In  the  meanwhile  the  results  of  the  some  low-temperature

durability  tests  indicate  that  sulfur-modified asphaltic concretes may be  more  durable than their

unmodified  asphalt counterparts and so existence of  sulfur is  a  desirable  factor for  road paving

mixes. As a result this form of gilsonite is very suitable for incorporation to asphalt mixes.

Gilsonite’s Benefits in Asphalt Paving Mixes

When gilsonite is added to bitumen it modifies the bitumen to lower its penetration, increase its

viscosity and increase its softening point. For the manufacture of road paving mixes, gilsonite

·   Increases the mix stability, thus reducing shoving, rutting and other types of deformation

problems that occur from heavy traffic and hot weather conditions.

·   Reduces  the  temperature  susceptibility  of  most  bitumens,  thus  getting  the  high

temperature performance with little sacrifice in low temperature characteristics.

·   Is extremely easy to add, either to the paving mix directly or to  the hot bitumen. It also

causes minimal disruption of the contractor’s operation.

·   Is a fraction of the cost of most other modifiers, roughly one-third the cost of Ethylene

Vinyl Acetate (EVA) co-polymer or Styrene-Butadiene-Styrene (SBS) rubber.

Several other benefits are also obtained from the use of gilsonite modifier. These benefits can be

important during manufacture and placement of hot mix pavements and often represent problem

areas for polymeric modifiers. gilsonite:

·   Easily combines with other hot mix components;

·   Forms stable solutions that do not separate during hot storage;

·   Does not require changes in pavement design, nor in the contractor’s standard pavement

laying practices

·   Methods of Addition

·   Gilsonite can be easily added to hot mix in a variety of ways. It can be predissolved in hot

bitumen prior to the addition of the bitumen to the mix. The most popular method is to

add  gilsonite  directly  to  the  asphalt  mix  in  the  batch  plant  or  drum  mixer.  All  three

methods  discussed  below.  As  a  free  flowing,  dry,  granular  solid,  gilsonite  can  be  added

directly in small, preweighed, meltable plastic bags, or added in bulk using vein or screw

feeders.

·   In  one  typical  experience,  gilsonite  was  added  directly  to  the  bitumen  tank.  The

temperature  of  the  bitumen  was  approximately  170°C  and  continuous  recirculation

through  the  top  of  the  tank  was  used  to  create  splashing  action.  The product  dissolved

easily  with  moderate  mechanical  agitation.  Even  faster  dissolution  can  be  obtained  by

using a mixer capable of generating a vortex.

·   The  gilsonite  is  readily  combined  and  completely  compatible  with  the  other  hot  mix

components and paving operations are virtually unaffected, i.e., no specialized equipment

is required.

1- Mixing Gilsonite Into Bitumen

This  is  a  fairly  simple  procedure.  A  bitumen  tank with  a  propeller  stirrer  with  enough agitation

action to create a vortex is recommended. The best choice is a “lightning” mixer or some other

type  of  electrical y  powered  mixer.  An  explosion  proof  motor  is  preferred  if  large  dust

concentrations  are  likely  to  occur.  gilsonite  should  be  added  slowly  at  the  vortex.  Provisions

should be made to recirculate the hot bitumen through recirculation piping.

The  most  important  item  is  that  the  minimum  temperature  should  be  about  170  to  175°  C.

Anything  significantly  less  than  this  will  extend  mixing  time.  For  typical  (5-10%)  substitution

concentrations, 2-4 hours of mixing after addition is completed should be sufficient. For master

batch concentrations (over 10% gilsonite) recirculation overnight is preferred. It is so obvious that

percentage of gilsonite added to bitumen depends on initial bitumen specifications and features of

desired product, but always between 5-18%.

The dry gilsonite should be poured into the hot bitumen slowly. If it is added too fast then it may

agglomerate, or “bal  up” at the surface. If this happens then some manual stirring to disperse the

agglomerations may be required.

If  a  horizontal,  cylindrical  tank is  used,  then gilsonite should be added  at an opening at  the  top

(about  0.5-1.0  meters  in  diameter).  Again,  it  should  be  poured  in  slowly  and  stirred  with  a

propel er mixer or a manual paddle so it does not “ball up” or agglomerate. Recirculation piping

will be necessary to insure some agitation effect and proper dissolving.

Recirculation  is  very  important  to  achieve proper  dissolution.  If  mixing  is  done  in  a  horizontal

tank then it is essential that the gilsonite-modified bitumen be recirculated from the front of the

tank to the back, or vice versa. This should be accomplished, even if some re-plumbing of the tank

is necessary, besides if an in-line mixer set in the recirculation line, then reaching for best degree of

mixture must be more successful.

Gilsonite  does  not  dissolve  instantly.  Mixing  a  tank  containing  10-15  MT  bitumen  and  5%

gilsonite  addition  will  take  about  2-4  hours  to  add  in,  and an  additional  2-4  hours  mixing  time

afterwards. Naturally, higher gilsonite dosage levels will require longer mixing times.

Unfortunately,  during  mixing  there  is  no  test  or  checklist  to  determine  whether  the  gilsonite  is

blending wel  in the bitumen. However, if it is not, then large balls or chunks will be visible in the

bitumen.

Afterwards,  the best  method to  check whether  gilsonite  was fully  mixed  into the bitumen  is by

comparing the original and final penetrations of the bitumen.

We have a diagram that showed below, described the process by the picture. As it’s seen, process

is  in  the  batch  system.  Cut  off  line  of  feed  and  product  indicates  the  batch  system.  The  more

recycle  flow,  more  better  mixing.  3  hoppers  design  is  better  than  1  hopper,  because  it  causes

perfect distribution of gilsonite into the mixer

2- Batch Asphalt Plant (Pug Mill) Mixing

First,  gilsonite  should  be  added  during  the  dry  cycle  of  the  mixing  procedure,  onto  the  hot

aggregate  rocks, before the bitumen is added. We recommend extending  the  total cycle time by

about  15  seconds  to  insure  proper  dissolution.  5  additional  seconds  of  dry  mixing  and  10

additional seconds of wet mixing maximized the Marshal  Stability of the paving mix.

The  gilsonite  can  be  stored  in  an  additional  silo  at  the  pug  mill  and  sprayed  into  the  mixer.

gilsonite would be handled in this same manner. A screw feeder or vane feeder that measures out

the  amount of  gilsonite per  batch can be  calibrated to  measure  the  dosage  level  of gilsonite  per

batch.

When  gilsonite  introduced  at  the  plant  site  a  gilsonite  storage  tank  is  required  with  a  totalizing

flowmeter,  which  is  not  capable  of  being  reset,  mounted  in  the  gilsonite  feed  line  just  prior  to

introduction into the mixer.

Meltable Bags

It  may  be  much  easier  to  pre-package  gilsonite  into  small,  polyethylene  bags  with  a  measured

amount of gilsonite and toss them onto the hot aggregate in a batch plant. The sidewal  thickness

of the bag should be about 0.005 cm. The aggregate temperature should be around 180°C. It is the

aggregate temperature that is melting the bags and the gilsonite, not the heat from the bitumen.

Therefore a temperature of 150-165°C entering the pug mill is acceptable, as long as the aggregate

is sufficiently heated.

In  either  case,  spraying  gilsonite  onto  aggregate  or  tossing  bags  into  the  pug  mill,  we

conservatively  recommend  increasing  the  mixing  time  an  extra 15  seconds.  This  will  insure  the

gilsonite is melted properly and dissolving into the bitumen.

Final y, it is possible to just scoop or shovel a precise number of kilos of gilsonite per batch onto

the hot aggregate, no re-packaging is needed.

We produced two process diagrams for batch mixing that display the method described above.

First diagram shows the system that gilsonite storage is not at the pug mill, and gilsonite feedline

with an  inline flowmeter  leads to  mixer,  it’s hard to  see  in the digram that  gilsonite  isn’t mixed

with bitumen before addition to the mixer, but it’s necessary gilsonite must be added to the mixer

before bitumen.

Second diagram is a cross section view of the pug mill and shows the system that gilsonite storage

 is at the pug mill, and a weigh bin controls the amount of gilsonite added to the mixer.

3- Continuous Asphalt Plant (Drum) Mixing

Gilsonite may be introduced into a continuous mixing plant via a screw auger. It should be added

at a point inside the line where the bitumen is added. The screw auger should be controlled by a

drive motor that is calibrated to the plant’s production rate. The auger should enter the drum at

the opposite end from the flame.

Care should be taken to insure that gilsonite is not caught up in the air stream and delivered to the

bag  house.  It  should  be  added right under  the  bitumen  output so that  a  part of  the  gilsonite  is

taken down by the bitumen to mix with the aggregate.

For  more description,  we have a process  flow  diagram for drum mixing  that  easily specify how

gilsonite must be added into asphalt. some design parameters that must be considered represented

below the PFD.

As it’s seen in the digram, gilsonite incorporated into drum by a feedline that must be equipped with an in-line blending system capable of metering the gilsonite within plus or minus 10 percent of the amount specified. Considering the fol owing instructions is necessary:

·   Interlock the metering device with the asphalt binder control equipment in such a manner as  to  automatically  vary  the  gilsonite  feed rate  to  maintain the required  proportions  and which  will  automatically  indicate  in  the  plant  control  room  when  flow  is  obstructed  or stops.

·   Inject  the  gilsonite  into  the  asphalt  binder  feed  line  prior  to  introduction  into  the aggregate.

·   Equip the feed line with a blending device to thoroughly mix the gilsonite with the asphalt binder prior to mixing with the aggregate.

·   Provide  a  system  capable  of  being  calibrated,  checked  and  monitored  for  accuracy  and quantity of the amount used. The in-line blending system will be equipped with an in-line

Totalizing flow meter.

Paving Procedures

We don’t recommend any special paving procedures just because gilsonite has been added to the paving mix. After modification with gilsonite, the final bitumen wil  have a significantly lowered penetration, a significantly increased viscosity and a moderately increased softening point.Gilsonitemodification  creates  a  highly stable,  easily workable paving mix.  We recommend  normal paving procedures  and  normal  lay-down  temperatures.  If  the  increase  in  viscosity  resulting  from gilsonite’s modification presents any flowability problems, we recommend the contractor operates at the higher end of his normal operating lay-down temperature range.

During cold weather, 5 to 10°C, gilsonite-modified mixes may tend to set-up slightly faster than standard mixes. In this case, the initial rol er may follow the paver a little close and the finish roller may not have to stay back as far.