Posted at 10.04.2018
The following section looks at what bitumen satbilised materials are and exactly how they are integrated in construction. As much areas of bitumen emulsion and foamed bitumen overlap this section talks about them both collectively, which sub-sections outlining the dissimilarities between your methods.
Bitumen Stabilised materials
Bitumen stabilized materials are materials which have been treated with either bitumen emulsion or foamed bitumen. When adding either kind of bitumen the amount of bitumen shouldn't exceed more than 3% of the full total mass of the dried up aggregate, as this would indicate it is greater than a stabilizing agent. Furthermore in many situations an active filler in the form of cement or hydrated lime can be put into the mix. If it's added however it should not surpass more than 1% of the bitumen stabilizer added. If it does the materials is known as to be concrete treated.
It is also important to notice that stabilisation agent will not the material into sound asphalt like materials. In going through this treatment the material will stay in a granular point out just like how it was before stabilisation. It is only its behavioral characteristics which will change. The material will experience an increase in material durability and a reduction in moisture susceptibility therefore of the way in which where the bitumen is dispersed amidst the finer aggregate allergens.
The idea that the material will remain in a granular express means that procedure is dramatically different from all the pavement materials. The dispersed bitumen changes the shear properties of the materials by significantly increasing the cohesion value whilst triggering little change to the internal friction viewpoint of the material. It will have a void content similar compared to that of a granular layer, nothing like and asphalt.
As the name suggest in this technique bitumen is emulsified in water. This means that bitumen is dispersed in drinking water, with the data that they can not mix; due to the fact an emulsifying agent can be used. The emulsifying agent will also supply the bitumen emulsion a charge, making the bitumen emulsion either cationic or anionic.
This mixture is then put into the aggregate which can make up an integral part of the pavement structure. As the bitumen droplets are incurred, they will be drawn to the aggregate allergens. In attraction they'll be drawn to small particles as they have the greatest surface and charge concentration features. Therefore the type and water of the aggregate in the mix is crucial in efficiently dispersing the bitumen emulsion and stopping premature separation of the bitumen from water during mixing.
Once it has been mixed the parting of water from the bitumen needs to occur. This allows the bitumen to do something as a binder. This parting should only happen after the materials has been fully compacted.
The mixing process associated with Bitumen Emulsion occurs offsite in a manufacturing plant. Here it is can be stored for a number of weeks. The diagram below shows a simplified version of the production process.
To produce foamed bitumen water is injected into hot bitumen, which results in instant foaming of the bitumen. In the foaming process the hot bitumen is converted into vapour, which is trapped in thousands of very small bitumen bubbles. These bubbles dissipate in under one minute.
When the bubbles burst they form tiny bitumen allergens. These spread throughout the aggregate attaching themselves to the finer particles of the aggregate mix. Once the aggregate is compacted, the bitumen covered debris are pressed against the larger allergens in the aggregate. Like a resultant of this localized non-continuous bonds are shaped, like location welds.
As the materials cared for with bitumen will remain in an unbound state, it'll act like the original material. The only difference will be a better cohesive power and reduced moisture awareness, that happen to be both favorable final results. It is because the bitumen only disperses between the finer particles, which sorts a bitumen-rich mortar between your coarse debris. This also means that contrary to the common misconception that the materials will become dark-colored and sticky like a hot-mix asphalt. The material will only just a bit darken in shade.
Through numerous assessments round the world of bitumen stabilized pavements a number of primary observations how the pavement will act have been made. The next behaviours have been assumed.
Materials cared for with either bitumen methods will experience a rise in cohesion.
The friction angle of the cared for material will remain similar to the untreated material.
They obtain flexural power. Which will suggest the pavement is less likely to crack when put through tensile tensions.
Moisture sensitivity and strength are improved. That is because of the fact the finer allergens are encapsulated and immobilized preventing flow channels.
The most frequent mode of failure is everlasting deformation.
All these behaviors will rely upon the following:
The local weather (Temperature, Average rainfall, likeliness of frost or snow)
The properties of the mother or father material
The thickness of the layer
The quantity of binder added
The use of any dynamic fillers
The properties of the helping material
It is important to notice here that BSMs react very different to asphalt and cement cured materials.
There are a number of benefits associated with using BSMs. Included in these are:
The ability to displace top quality materials, meaning a cost saving
Improved dampness sensitivity
Can provide cost and time savings
Typical failure function is permanent deformation, which requires less work to rehabilitate when compared to a material that will fail due to full-depth cracking
They are not temperature sensitive
If the road requires treatment BSMs propose little treat to the environment
They aren't overly sensitive, indicating the quantity of bitumen added may differ slightly
The process will not require heavy engineering traffic. This limits the harm cause to newly constructed levels during construction
When considering whether to work with BSMs or not there are three main limits. These should be carefully considered when making the decision to make use of BSMs. The three constraints are;
Economics - Bitumen treatment can truly add significant costs to a task. Its use of lower caterogory highways should be carefully analyzed as it could not be worthwhile.
Design Expertise - as they are presently been developed and respond differently from all other pavement materials careful design is required.
Construction Expertise - the engineering process requires attention to detail. This implies special training of the work force is required.
Along with this constraints the both bitumen emulsion and foamed bitumen have their own disadvantages
With bitumen emulsion come the next disadvantages
By adding this particular within the emulsion process, the original material may review its optimum normal water content. This will mean the material cannot be compacted properly.
A quick setting up time is required allow the material to get sufficient strength
the building process must be completed with care. If the bitumen breaks prematurely you won't mix properly. In case the material is to steady it can take weeks for the bitumen to break
With foamed bitumen come the following disadvantages
it requires sufficient fines. They required to ensure the bitumen mixes completely.
Foaming equipment must be up stored and become in right working order. The foamed bitumen must be sprayed in standard, regular manner.
The process requires specialist equipment, as both liquid are not compatible.
Materials Suitable for treatment
For bitumen stabilisation to work a suitable materials must be preferred. To begin with the materials must be granular. Because of this materials that are well suited for treatment include;
Previously neglected natural gravels, such as basalt, granite, limestone, quartz, sandstone
It may also be said that calcrete gravels can be used for bitumen emulsion; nonetheless it will not use foamed bitumen.
The first step in an average design for a BSM involves a study of the conditions. This consists of expected traffic amounts, the materials available, the environment and the pavement framework for recycling jobs.
Once this has been done a laboratory analysis of the proposed material occurs. This involves determining the materials category.
The next thing is to create the blend and make the ultimate material classification.
Once all of these steps are completed the structural design is completed. With this design if it's shown that the road is not economically viable the mixture design will be redone and the steps repeated.
Shown below is a circulation graph of the steps included.
In by using a stabilizer it is important that the stabilizer fits its intended goal. The process of design the mix will be mainly dependent of the design traffic, the materials available and the cost concerns. However n creating a mix design it is also important to consider the next;
The primary failing mode - this will define the materials performance requirements.
Appropriate laboratory tests - tests need to be determined that will identify the main element performance conditions and inability mechanisms.
Identifying key mixture properties and intrinsic material properties.
Taking into consideration variability in materials properties
Environmental factors - Climate and moisture conditions.
The capability to effectively compact the material.
In building the mix it's important to notice that maximum bitumen content is not always selected for the combine design. This is because although the most effective bitumen content provides the maximum material strength, this means other characteristics are forfeited. For instance a high durability design will most likely lead to brittle inflexible pavement tiers that are vunerable to cracking. In planning the mix it is important that the look is balance such that it will be suited to it requirements.
Classification of BSMs
Currently South Africa has divided Bitumen Stabilised Materials into three classes. These classes are dependent on the grade of the original material and the design traffic. The three classes include:
BSM1 - The parent material has a high shear durability, and is generally the base layer for large amounts of traffic. Source materials include well graded smashed rock or reclaimed asphalt.
BSM2 - The parent or guardian material has a reasonably high shear power and is generally the base coating for modest traffic tons. Source materials include graded natural gravel of reclaimed asphalt.
BSM3 - The father or mother materials is soil-gravel and/or sand, stabilized with higher bitumen contents. It is a base layer that can only just handle low traffic amounts.
It is thought that Australia will have a classification system similar to this.
BSMs behave in a very complex manner, which gives engineers a great overall flexibility as it pertains to designing a combination that will best meet up with the design conditions. The mix is made up of aggregate, bitumen and sometimes an active filler where required.
In design the blend there are two fundamental failure mechanisms that require to be created for in the mix they are;
Permanent Deformation - This is reliant on the materials shear properties as it is triggered by the build up of shear tensions. Resistance to everlasting deformation as known as rutting is upgraded by:
Improved aggregate angularity form, hardness and roughness
Increased maximum particle size
Reduced wetness content
Addition of limited amounts of bitumen
Addition of a dynamic filler
Moisture Susceptibility - this is actually the damage triggered by the publicity of your BSM to high moisture content items and pore-pressures induced by traffic. This then means a loss of adhesion between your bitumen and the aggregate. Because of water been involved in the mixing stage and the partially coated character of the aggregate makes dampness susceptibility an important thought in the evaluation of materials performance. Moisture amount of resistance is upgraded by
Increased bitumen content
Addition of a dynamic filler
Smooth continuous grading
It is interesting to notice here the difference in suggested bitumen content. To greatly help prevent deformation limited amounts of bitumen are suggested. However to boost moister resistance increased bitumen contents are recommend. This means that a compromise must be produced, utilizing the laboratory testing to determine a bitumen content that may meet the needs of the look.
Mix type selection
As stated in sectionXX the three main factors the impact the type of BSM used are:
The design traffic
The quality of aggregate available
Once the type of BSM has been preferred there are three main factors that have an effect on the bitumen and lively filler selection for the mix design;
Traffic design (volumes and loadings)
Climate (especially moisture considerations)
Supporting layers (durability)
The affect these factors have is exhibited in the next figure. As possible seen heavy traffic loads, a wet climate and weak helping layers all suggest an increased amount of bitumen is required to ensure design requirements are meet.
Mix Design Procedure
To create the best design combination possible several procedural steps have to be done. This ensures that that every criteria is meet, as there are numerous variables that require to be inspected.
The first rung on the ladder of the blend design is to check the material which is treated. That is done to ensure that the materials is suitable for assessment. These assessments include standard lab tests to look for the materials grading curve, moister, thickness and Atterberg limitations.
The next lab tests which are undertaken are the level 1 mixture design tests. These provide an indication of the application rate of bitumen and dynamic filler required to achieve an indicated school of BSM. Level 1 starts off with the preparation of samples that will be used to create the specimens required for all levels of combination design testing's. trials at this level involves preparing 100mm diameter specimens that are compacted and cured for the purpose of considering Indirect Tensile Power testing. These testing results are being used to:
Indentify the most well-liked bitumen stabilizing agent
Determine the maximum bitumen content
Identify when there is a dependence on a dynamic filler and its own type
Tests after level 1 are done with regards to the design traffic. The to begin these are Level 2 mix design tests. The test as of this level consists of making an example which is 150mm in diameter and 127mm long. These are created using vibratory compaction and then treated at the equilibrium wetness content. This sample then goes through Indirect Tensile Power to optimize the required bitumen content.
The level 3 mix design test is only suggested for high capacity highways. This test involves getting ready 150mm diameter by 300mm long specimens, that allows for an increased level of self-assurance. It then goes through the same Indirect Tensile Strength test.
A wide selection of nutrient aggregates are suit for use with both types of bitumen treatment. These include aggregates which range from sands to weathered gravels to smashed stone and can either be virgin or recycled. These must however belong to certain quality standards to guarantee the street will be at it required course.
When analyzing a materials its pursuing properties will be examined:
Durability characteristics of the untreated aggregate
The aggregate used can come from three different resources, Virgin Aggregate, Recycled Granular Tiers and Reclaimed Asphalt
Quality of Aggregate
In using bitumen to stabilize the material it is possible to use a poorer quality of aggregate. For virgin aggregates four lab tests are used to recognize material limits.
Grading - completing a grading will identify any deficiencies in the material
Percentage moving through the 0. 075mm sieve - higher fines articles mean a higher dependence on bitumen
Plasticity Index - for bitumen emulsion the materials PI should be significantly less than 7. For foamed bitumen the materials PI should be significantly less than 10. Materials with a higher PI can be treated with lime.
For recycled granular levels the materials quality depends on:
The structure of the prevailing pavement
Depth of recycling
Age of the pavement
Degree of patching and repair on the existing pavement
Thickness and aspect of old surfacing seals.
Using reclaimed asphalt needs serious concern as some material may not meet up with the quality expectations required. This is particular important on highly used roads, where traffic loads will be large.
When deciding whether the quality of the reclaimed asphalt will meet specifications, the following needs to be looked at.
Climatic region - if the materials is likely to be placed in a warm local climate, shear checks must be completed to symbolize that climate
Axle tons - high strains will bring about accelerated deformation of the street. Which means that if the road is to carry heavy traffic its shear properties will need to be carefully considered
Reclaimed Asphalt Composition - if needed crusher dust particles can be put into the mix. This will provide an angular skeleton that will improve the mixes shear level of resistance.
The grading requirements for both types of bitumen stabilisation is different. This is due to the fact that the bitumen will disperse in another way. The graph and table below give a sign of the grading required for every type of stabilisation.
As the aforementioned table shows the very least filler content of 2% is necessary. This is because the bitumen emulsion will layer the large allergens of the aggregate better than the foamed bitumen.
Foamed bitumen requires more filler; about 5% filler content is necessary. This is because the bitumen droplets disperse through the materials, only partially layer the large debris. It uses the filler to create a "spot welds" hooking up the larger particles using the fines.
The bitumen chosen performs an important part in how well the BSM works. Penetration grade bitumen is employed to create both bitumen emulsion and foamed bitumen. Within the next two sections the precise bitumen requirements for every single form of stabilisation is listed below.
For bitumen emulsion bottom part bitumen's with a penetration value between 80 and 100 are normally selected. In saying this throughout the world softer and harder marks of bitumen have efficiently been used.
In modern times there have been many technological advances that have allowed the bitumen emulsion to get improved balance without prolonging the rest time. However sufficient tests of the bitumen combine needs to happen both in the blend design phase and during structure trials. This will ensure the correct bitumen has been chosen.
Another important consideration is the compatibility of the bitumen emulsion and the aggregate. This is because the type of bitumen chosen is inspired by the sort of aggregate been cured. Certain materials are not well suited for catatonic treatment as well as others are not ideal for anionic treatment. The table below gives a sign of the compatibility of the emulsion with a aggregate.
Furthermore it is normally recommended that the undiluted bitumen emulsion is warmed to between 50 and 60C. This can prevent early breaking of the bitumen emulsion while pumping in the construction equipment. It is also important to note here that when diluting the emulsion the emulsion must be added to the water. This will likely prevent premature breaking.
When it involves foamed bitumen a softer grade of bitumen can be utilized without compromising balance. This is because foamed bitumen only requires low percentages of bitumen in the combination. However like bitumen emulsion typical penetration ideals are between 80 and 100. Harder bitumen is generally avoided because of the low quality of foam it produces.
There are two main properties that determine the suitability of the bitumen for foamed bitumen stabilisation. They are its Expansion Ratio and its Half-Life.
The enlargement raito is a measure of the viscosity of the foam. This is what establishes how well the bitumen will disperse through the mixture. It is determined by locating the ratio between the maximum level of foam in romantic relationship to the initial level of bitumen.
The half-life is a way of measuring the steadiness of the foam and provides a sign of the pace of collapse of the foam during mixing. It can be calculated by deciding the time it requires for the foam to collapse to half its maximum amount. The table below shows the minum restrictions of the enlargement percentage and the half-life of the bitumen.
The ideal factor which will influencing the foam properties is the water injected into the expansion chamber. A greater injection of water will mean an increased expansion proportion, but this is offset by the fact it will imply a short half-life as the foam will subsided faster. Furthermore an increased bitumen heat is usually recommended as it will create a much better quality foam.
There are two types of fillers which may be used to enhance the results of bitumen stabilisation; these are productive and natural fillers. An active filler is a filler that will chemically adjust the blend properties. There are many active fillers which may be used, examples of these are cement hydrated lime and take a flight ash. Natural fillers are fillers such as rock flour.
These fillers can be utilized either by themselves or in a combination with another filler. Their use will depend on their cost, effectiveness during use and the materials availability. Research has shown that it is extremely difficult to predict the effectiveness of a filler. The only way to gain an idea of their effect is to complete tests using different mixes.
Active fillers are added to the bitumen in order to;
Increase the rigidity of the mix
Increase the speed at which the combine will gain strength
Improve the dispersion of bitumen in the mix
Improve adhesion between your bitumen and the aggregate
Improve the curing time of the compaction mix
Along with these standard improvements, there are specific benefits for both treatments. For Bitumen Emulsion a filler will:
Control the breaking time of the emulsion
Improve the workability of the emulsion
For Foamed Bitumen a filler will:
Assist in dispersing the bitumen droplets
Natural fillers on the other palm only become a dietary supplement for too little fines in the materials which is necessary for dispersion.
It is important to note that whenever adding a dynamic filler enough time between the bitumen is combined and it request is dramatically reduced. When an active filler is added the reaction begings immediately when it comes into connection with moist materials. The longer the wait between blending and program the less the filler will work.
To ensure a superior quality product it is important that this used in mixing meets certain expectations. Each approach requires different drinking water qualities.
For bitumen emulsion the pH levels of the water are really important. For cationic bitumen water can't be alkaline. If it's hydrochloric acid can be used to reduce the waters pH.
For anionic bitumen emulsion the opposite applies, this can't be too acidic. To make the normal water more alkaline lime or caustic soda pop can be put into this inflatable water.
The expectations for foamed bitumen aren't as high because they are for bitumen emulsion. It really is acceptable for this used to contain some impurities, however this should be avoided. This is because the water can affect the mixing equipment.
Moisture plays an important part in using bitumen to stabilize material. The role that moisture content plays in the two types of BSM is described in the table below.
Contributes to fluids for compaction
Does not effect
Reduces absorption of bitumen emulsion water into aggregate
Separates and suspends the fines making them open to bitumen during mixing
Prevents premature breaking
Acts as a carrier for bitumen droplets during mixing
Extends curing time and reduces early strength
Reduces early on strength
Provides workability at ambient temperatures
Reduces friction viewpoint and lubricates for compaction
Provides shelf-life for the mix
The term for the best moisture content in the materials is the most effective mixing water content or OMMC. It's important to notice that for bitumen emulsion this wetness value is the moisture in the aggregate plus the moisture from the emulsion.
The release of modern rollers has allowed for high energy compaction. In the case of BSM this implies a lower substance content can be used to produce the same quality of compaction. This has the added advantage of increasing the effectiveness of the BSM.
Below is the essential procedure for the material preparation mixed up in mixing up design.
Determine the grading curve of the aggregate and its own optimum water content of the natural material
Determine the materials Atterberg Limits
Determine the moisture and density relationship of natural material to obtain optimum moisture content
Determine the moisture content and density marriage of the cared for material to obtain optimum moisture content content
Determine the moisture and density romance using vibratory hammer compaction to acquire optimum water content
It is recommended that a pugmill mixer is utilized in both mixes. The use of different mixers can produce up to 25% difference in strength. Experiments have found that the pugmill mixing machine supplies the most comprehensive mix.
Correct compaction of the material is extremely important as it reduces the voids and improves particle contact. The use of bitumen emulsion will help increase the compatibility of the combine, while the use of foamed bitumen will promote the adhesion of the bitumen mastic to the rock.
Curing is the process where the normal water is removed from the compacted covering. Water can be removed from either evaporation, particle charge repulsion and pore-pressure induced stream paths. The reduction in moisture content will lead to an elevated tensile and compressive strength as well as add stiffness to the combine. The curing process differs for both methods
It is chemistry that handles just how bitumen emulsion cured material cures. By detatching this particular from the combination breaking of the emulsion occurs. To get this done this particular is removed by means of evaporation and migration. This healing will need longer than foamed bitumen treating, because of the higher moisture articles.
The healing of the foamed bitumen is a natural process. It really is cured through the migration of drinking water during compaction and carries on as this particular is evaporated.
There are two main tests which are used to check the many mix designs, they will be the Indirect Tensile Power test and a Triaxial Test
Indirect Tensile Strength
This test is completed to measure the overall flexibility of the materials and give an indication of its tensile strength. The stand below provides guide for interpreting the results of the test.
Specimen Diameter (mm)
Indicates optimum bitumen content
Indicates dependence on active filler
Optimise bitumen content
Check value on ITSwet
This test is completed to meause the cohesion of the materials, the friction perspective and the maintained cohesion. The stand below gives a guide for interpreting the results of the test.
Test or Indicator
Friction Perspective ()
Retained cohesion (MIST)
As reviewed in Section XX the structural tiers purpose is to protect the subgrade by dispersing the traffic tons. Which means that the pavement structure and subgrade must interact to guarantee the required design capacity.
For both stabilizing methods once the material has been put together into the material, the various engineering procedures are relavitivily the same as those if the materials wasn't treated. This consists of the operations to put the material, slice levels, compacting the coating and concluding the covering.
Below is a chart showing the principal factors influencing the approach to construction.
As the chart shows there are five main engineering methods that can be used with BSMs. they are cracked into two areas, In Situ Treatments, which include In Situ Recyclers and standard plant which is only suitable to bitumen emulsion. The other section is In-Plant combining which includes classic place, paver laid and labour extensive construction.
In Situ Treatment
There is now an array of new plant which may have made the recycling process easier. Combined with the recycling machine, compactors, graders and water tankers are also needed. Each kind of bitumen stabilisation takes a different create.
In situ treatment is principally done using purpose built machines, which have replaced more mature style construction herb such as graders and ploughs. Although this is actually the circumstance, Bitumen emulsion stabilisation can be done with either. When the purchase of an objective built recycler can't be justified, the aged conventional type herb can be used to construct the street.
Foamed bitumen engineering on the other hand is requires highly professional equipment. It is because the foam needs to mix in to the material in a short time period for the stabilisation that occurs.
Using a recycler the stabilized bitumen is put into the aggregate with the use of pumps which squirt the bitumen on the material. When spaying the pumping system is manipulated by way of a micro-processor, which was created to monitor and adjust the use of the stabilizer. The mixing occurs in a milling chamber.
When compacting the materials usually three types of compactors are employed. First a heavy key roller, which can either be a padfoot or soft roller, is used. This compacts the lower layers. The next compactor used is a smooth-drum roller, which is applied at a low amplitude vibration. This compacts the upper part of the layer. After the level is compacted to a satisfry condition, a pneumatic-tyred roller is employed to complete the level off. This roller allows for a securely knit surface texture.
The graph below provides selection guide to selecting the primary roller.
In Flower Treatment
There are a range of reasons why in-plant treatment can be utilized for a task. These include:
The stabilisation must have constant quality.
The product must be stockpiled for use at a later date.
All aggregates are available at one location
The stabilizer is to be place utilizing a paver.
The plant used to create BSMs must manage to:
Accurately blending predetermined proportions
Consistently producing a homogenous product
In the truth of bitumen emulsion relatively unsophisticated mixes can be utilized, without jeopardising quality. This allows for costs cost savings; on smaller projects a concrete mixing machine can be utilized. This can occur so long as the material is proportioned appropriately and sufficient time is allowed for mixing up.
Due to the fact that the foamed bitumen must be created on site the mixing herb needs to be more specialized. It needs to meet up with the following requirements
Needs to be micro-processor controlled
Needs lots sensor on the material feed conveyor
A consistently weighed auger
Must have the ability to maintain an operating pressure above 5 pubs.
The use of an paver and screed to level the BSM covering requires expertise to obtain a quality product.
When constructing with a paver and screed construction joint parts maybe required. These must be held to the very least however. That is best these joints may lead to weakness in the framework. They should also never be where they are really trafficked wheel paths. Taking this under consideration large pavers is the best option, in either full or half-widths of the street.
A paver part should be placed below 150mm, as it permits better construction. This layer is normally compacted using a vibrating drum roller with a static mass of between 10 and 12 tons. It's important to note a thicker layer will be more difficult to streamlined without rolling the top out of form. It is because coarser materials are definitely more prone to segregation in thicker layers.
In conditions of layers bitumen emulsion can only just have an individual coating when paving. This is because water from the second layer would come across the original part causing it to fail.
Foamed bitumen on the other hands can be successfully paved in two levels although it isn't recommended. Stringent settings are required to ensure a vital bond is made between two layers making construction difficult.
Using Conventional Equipment
This is the most well-liked, rather than paved, method of construction as it pertains to in-plant mixed materials. It is because it permits thick layers of BSM to be laid. That your use of classic equipment there are two main limitations
Thick layers can only just be constructed completely widths.
Moisture can be lost due to the material been spread over large areas.
These two limits mean that this technique is not appropriate for bitumen emulsion as this method requires additional moisture. It also limits the application of the foamed bitumen.
Labour Intensive Methods
BSMs can also be laid using labour intense methods. However levels will be placed to a maximum of 125mm as the material cannot be laid quicker enough to obtain larger layers. Moisture damage is also a problem due to the poor rate of construction.
It's due to its physical limits that the use of labour intensive methods are just advised for smaller careers, where it the negatives can be offset by cost benefits.
Curing and Trafficking
Curing is a comparatively quick process when it comes to BSMs. The strength of using BSMs is within the fact they can withstand traffic loading immediately after the part has been completed. When it comes to rehabilitation work recycling is generally done in half-widths with unidirectional traffic been allowed through with the use of traffic control.
Before the covering is ready for traffic the bitumen emulsion must first break. This escalates the cohesion which is required for amount of resistance. The compaction alone which escalates the density isn't sufficient to ensure level of resistance to traffic harm.
The break usually takes a couple of hours at the top, where evaporation will pressure the break in the action. The bitumen emulsion deeper in the layer will take up to few days.
Once compaction is complete the part will experience an increase in cohesion which can make the bitumen immune to traffic destruction. At this stage nevertheless the bitumen will still remain tender before water content reduces.
A advantage of using BSMs is the early strength the coating can gain. This is from the bitumen improve the cohesion between your particles, which allows the roadway to tolerate traffic without surfacing. This is however not advised for more than 4 weeks. It is because the heavy tyre tons imposed on the road will tend to loosen and remove the coarser allergens at the surface that will cause roughness. By surfacing the road between 2 and 4 weeks are compaction the likelihood of this occurring is reduce, as well as providing protection against excessive traffic abrasion and normal water ingress.
It is recommended an asphalt surfacing, which is just about 30mm thick, be utilized on BSM tiers. This is because Southern African research has proven that the asphalt is incredibly durable on the BSM layers
Improves Shear Strength
Flexibility - means greater resistance to deformation
Ease of Application
Standard test methods are availiable
Moisture Results - where the pavement is close to OMC, saturation will occur
Curing - Takes a long time
Improves Shear Strength
Flexibility - means higher amount of resistance to deformation
Ease of Application
Rate of Strength Gain
Lower moisture material required incomparison to bitumen Emulsion
Ready for traffic almost immediately
Can be completed in situ
Foamed bitumen needs that bitumen is hot - Requires specialized equipment
Purpose built equipment required for construction
Not well suited for all pavement types
Has not been fully researched
Ease of Application
Shrinkage cracking is unavoidable
Increases rigidity in adaptable pavements
Cannot be trafficked immediately