Binding Process for Pavement Stabilization

Topic: Road materials and pavement design.

Binding process involves mixing physical materials with binder which will act as a glue to attach together the materials, and in the process a higher expectation of improving the mechanical properties, the specified stiffness of material is a factor that considers the pavement modification or pavement stabilization in order to improve the pavement strength especially where heavy running vehicle activities will be required, the binding process includes usage of specified machines that will help proportionally mix the pavement material with the binders.

The best considered method that is cable of showing the pavement materials properties and the properties of the stabilization agent is trilling, the main stabilizing material used are lime, slag and cement, in which the material to be stabilized will rely on the pozzalanic reactions in the process of binding. The slag will always react with a free lime and the end results will be formation of compound cementitious substances that their content will comprise of hydrated calcium silicate.
Binder selection

The nature of the base material for the road that requires to be constructed is a dependent factor that will require stabilizing  agents to be combined, and incase a slow binder setting is required to gain the pavement strength and stiffness in a long period of time then a tripled blend of binders will be required. Specification of combined binder’s material will depend on a process of testing and trialing. A reduction in the permeability of the pavement will be resulted when stabilization will require methods that will improve both the strength and stiffness of the pavement.

Increase in the stiffness has an advantageous results in road construction, where a thin pavement that has resulted from increased stiffness will be formed this will reduce the time of construction since few layers will require few placement and compaction. While designing for pavement consideration should be placed to avoid the formation of excessive strength, since the gain of higher strength will result to loss in flexibility of the pavement and this leads to formation of cracks due to excessive applied stress on it.

Ccps And Binders

Lime and cement can use either fly as got residue on sieve ash based on the properties confined with fly ash in the AS 3582.1 or through properties outside AS 3582.1 [8] as confined with residue on sieve ash to help in either modification or stabilization of road based materials, even though cement can be used alone as a binder but this will require certain restriction with time in order to ensure a proper compaction is achieved and ensure quality is too achieved before the initial setting time, addition of fly ash to the cement will result to development of a slower strength and more working time at appropriate consistency of the cement

The improvement of the quality of the original material in the road construction project, will require lime modification or lime stabilization, lime will improve both the strength and workability of a plastic soil. Therefore, the lime stabilization will mainly be used to;

1. Stabilize the soil to its performance requirements
2. Increase the strength of the pavement
3. Improve volumetric stability on each pavement layers
4. Enhance pavement surface stability

The Role of Base Material and Stabilizing Agents

The process of stabilizing the soil with cement will critical since it will require restriction time, therefore a well structure scheme of time should be understood from the time the cement is delivered, incorporated and compacted on the layers of the pavement before any commencement activity of the project is initiated. In general the average time that cement will effectively require its performance and process of compaction is approximately two hours from the time the cement is incorporated into the moist pavement material, and always it will not require any rework to be done, this is critical and can cause managerial risks due to resultant errors on the site, in addition cement is prone to a higher rate of shrinkage will increase the tendency of cracking. Therefore, in order to solve this in a means that the cement will increase its consistency and be able to stabilize the soil material, than an addition of fly ash to cement binder will be required, to enable it have more time of placement and mitigate other associate risks that may advance.

Fly ash

The size of the particle ranges from one micrometer to two hundred micrometer, and has a spherical irregular shape. Application of fly ash to cement will lead to reaction between calcium hydroxide  in order to form cementitious compounds [4]

Furnace bottom ash

Furnace bottom ash are formed when coal is heated and they attach themselves on the walls of the furnace and on cooling the furnace they fall at base where they are collected and stored, though its characteristic resembles those of fly ash  but they have a higher carbon proportion, its coarse characteristics enables it have a free drainage layer, therefore it helps in granular stabilization to improve the grade of the crusher for a running material, therefore due to its coarse characteristic it less pozzolanic when compared to fly ah

Australian standard (AS) 3582.1 [8] stipulates the fly ash general requirement as a complement cementitious material to be used with blended cement,  the objective has  always been the fly ash should be able to meet all the requirement based on AS 3582.1 [8] in the process of selecting suitable materials used in stabilizations work.  The assumption of using a finely grade fly ash has also been considered in the application of the best modifier and stabilizer of materials, based on the assumption therefore a higher expectation is required when one will use the finest fly ash to achieve a better stabilization in comparison to the application of a coarse concrete grade.

The assumption has not always worked out since the verified test that is required to consider this ability is set at table 3 of AS 3582.1 [8], in addition to the properties listed on the table, the other properties will include;

1. Availability of alkali content
2. The relative density of the material
3. Water requirement specifications
4. The strength
5. The chloride ions

Scientifically the no contrast that arises from a classified ash or unclassified ash, though in relation to the density, strength and specification of the water requirement their different will vary..

Residue on sieve ash are recommended to be used in the processes of stabilization, in accordance with Chapman and Youdale [5] , stabilization of lime with furnace bottom ash will result to a best pavement material. Even though furnace bottom is incompliance to AS 3582.1[8] but part of it chemical properties are similar to fly ash. Therefore more research and testing will be required in confirming the ability of residue on sieve ash to help in improvement of the quarry materials as with furnace bottom ash    

Pavement damages are caused the interaction between the traffic damage effects and the environment. The heavy loads carried with heavy truck, will result to formation of stresses or strains on the structures of the pavement, in which there will be accumulation of the resulted effect for a long period of time, the end effect will result to deterioration of the pavement, example being plastic deformation that occurs in asphalt concrete, similarly cracking may result on Portland cements, therefore the data on traffic loads is a fundamental input when analyzing pavement and designing it. The impacts of traffic loads on pavement are categorized as follows;

1. The number of axles the truck will have
2. The axle configurations
3. The truck loads/ magnitude

The term axle configuration is described as the total number of axles that will share the identical system of suspension and the number of tires attached or fixed in each axle.

The number of axles impacts different amount of stresses or strain on the pavement in regard their multiple, which can either be tandem for two axles or triple for three axles or quad for four axial.

Additional of other related traffic parameters are key important while analyzing a particular pavement, which includes;

• The time an axle will pass
• The speed of the vehicle
• Lateral placement of the vehicle
• The inflation tire pressure

The time an axle will pass on a pavement is important to be determined because of seasonal changing properties of the pavement and the pavement thermal stresses dependability. The vehicle speed is important on pavement since alpha concrete experiences viscoelastic characteristics. The sped of the lateral vehicle influences the lateral distribution of the damage that has accumulated.  Tire inflation has an effect on itself and pavement the contact pressure.

Lime and Cement in Road Stabilization

Tire radius a =

Where,

P is the vertical load that is carried with tire

i is the inflation or contact pressure.

Characteristics of the sub bases and subgrade of the pavement..

The sub base, subgrade and base properties are essential while carrying out a structural integrity analysis and the pavement performance. Considering flexible pavement, the role of the sub base and base of the pavement layers are to provide enough strength, and be able to reduce the resulted stresses to an optimum level of sustainability by the sub grade, whereas, while considering rigid pavement, the layer of the base will be used to level and strengthen subgrades which are weak. In addition if the sub base or base will be constructed to a standard level then they will be in a position of providing proper internal drainage, while preventing infiltration of water to the subgrade. The characteristics of both the sub base and base can be enhanced by both compaction method or stabilizing it with chemicals in the presence of moisture control.

Base or sub bases that are made up of granular will experience elastoplastic characteristics as a result of either loading or unloading responses executed by the traffic load. When unloading takes place the layers will undergo elastic and plastic components of deformation.

As illustrated in the figure below, elastic deformation occurs on the application of small stress, therefore no plastic strain will develop when unloading takes place, therefore the loading and unloading will be equal to each other, and no horizontal shift will be experienced. This is a clear indication that that the deforming energy will be released at the point of unloading.  In case there will be an increase on the force of the applied load the material will start experiencing gradual permanent strain.

Additional of applied loads will result to formation of plastic shakedown,  at this section the aggregate will increase the development of plastic strain which is expected to be higher than elastic shakedown section, then after several cycles the deformation of plastic strain will cease. This condition will be referred to a limit of plastic shakedown, if this condition is surpass then the new condition that will be formed is known as plastic creep, the soil in both plastic creep and plastic shakedown will experience a elastic strain, at an increase rate then a new region of plastic strain will formed and this will continue until there is a complete failure, it is at this stage that the aggregate will undergo crushing, breakdown and abrasion.

If the resilient modulus will be assumed to be constant, then the unbound layers properties of will be taken as isotropic. Therefore the response of elastic will be described by position ratio and elastic modulus alone. The properties of the elastic of unbound layers will be examined by repeatedly carrying a triaxial test.  For example, if we take a specimen of  a cylinder which is subjected to a triaxial stress and confined to a axial compressive load, in such a case the radial stress is a minor principal stress, while major stress ids represented as major principles . the modulus will be equivalent to the ratio of the deviator stress against resilient strain.

where,

σ₁ is the major principal stress

σ₃ is the minor principal stress

ε_1,r is the major principal resilient strain, and

ε_3,r is the minor principal resilient strain.

The modulus of the resilient may be used as a model of elastic analysis to facilitate the calculation of the structural pavement responses; therefore it is important model of calculating the design of structural pavement.

The response resulted on one load cycle for a granular material is shown in the figure and the tables below. It should be noted that this shows what has been recommended by NCHRP study 1-37A.30, and also AASHTO will used to classify the subgrade.

Classification of materials	Ranges of Mr (N/m2)	Typical Mr (N/m2)
A-1-a	265,448,280 – 289,579,920	275,780,400
A-1-b	244,763,980 – 275,790,400	262,000,880
A-2-4	193,053,280 – 258,553,500	220,0632,320
A-2-5	165,474,240 – 227,527,080	193,053,280
A-2-6	148,237,340 – 213,737,560	190,002,500
A-2-7	148,737,560 – 193053,280	165,474,240
A-3	168,912,620 – 244,763980	220,567428
A-4	168,346,540 – 244,764,650	220,567428
A-5	148,237,340 – 213,737,560	220,567428
A-6	148,737,560 – 193053,280	193,053,280
A – 7- 5	148,237,340 – 213,737,560	262,000,880
A – 7 – 6	193,053,280 – 258,553,500	220,567428
CH	148,237,340 – 213,737,560	193,053,280
MH	148,737,560 – 193053,280	262,000,880
CL	148,237,340 – 213,737,560	220,567428
ML	165,474,240 – 227,527,080	220,567428
SW	168,346,540 – 244,764,650	262,000,880
SW-SC	148,737,560 – 193053,280	220,567428
SW – SM	193,053,280 – 258,553,500	220,567428
SP – SM	148,237,340 – 213,737,560	220,567428
SP – SC	244,763,980 – 275,790,400	220,567428
SC	168,346,540 – 244,764,650	262,000,880
SM	244,763,980 – 275,790,400	220,567428
GW	168,346,540 – 244,764,650	220,567428
GP	193,053,280 – 258,553,500	262,000,880
GW – GC	165,474,240 – 227,527,080	220,567428
GW – GM	168,346,540 – 244,764,650	220,567428
GP – GM	193,053,280 – 258,553,500	165,474,240
GC	148,737,560 – 193053,280	220,567428
GM	193,053,280 – 258,553,500	262,000,880

According to Lekarp et al [6], the loads and materials that will affect the responses of resilient on unbound layers are summarized in the level of stresses actin g on the pavements.

According to Hicks and Monismith [7] resilient modulus are influenced highly by pressure configuration and to a small percentage they are influenced by deviators, the figure below shows the relationship between bulk stress and the modulus of resilient values.

The application of the stabilization have the ability to change the characteristics of the pavement materials in dependency of the type and quantity of the binder that will be used, this will include;

• Reduction of plasticity
• Improvement of workability
• Improve the strength that it will gain
• Changing the size of the particle distribution
• Reduction on moisture sensitivity on materials
• Reduction in permeability
• Alteration of the compaction properties
• Reduction on the pavement thickness
• Improving the work platform

The interaction between the traffic loads and environment is key factors that permanently deforms flexible pavements, the core factors that leads to deformation are movements of viscoelastic creeps and peeling out of the asphalt layer as a result of inadequate compaction which happens during construction, the effect of the deformation is categorized as failure criteria in the mechanical – empirical design procedure of the pavement. Based on the design in mechanical – empirical procedure, there are always structural analyses that will estimate the responses of the traffic road and the condition of the surrounding environment, the analysis is aimed at limiting stresses and any damage that may occur from its deformation.

Traffic Loads and Pavement Damage

The methods used are as follows;

1. ELWT (extra-large wheel tracking) programme

The programme is used in studying the development of a fatigue cracking or deformation on the pavement materials which are subjected to different environmental conditions and wheel load. The programme devices are used in evaluation of the performance of rutting on a thin single layer of asphalt. The test is done on a slab that has a dimensional seventy centimeters long and fifty centimeters wide and the thickness of about four to twelve centimeters. The asphalt slab is provided with a support by a wood plate that is placed on a rigid bottom. a load of about 25 kN is applied on the slab test by a single wheel having a maximum pressure of about 1000 kPa, the wheel is allowed to travel with a speed of about 1.0 to 5.0 km/h. The air temperature and pavement are continuously recorded, with a variation of temperature of about 5 degree Celsius and 60 degree Celsius. The pavement deformation is recorded and determined through laser beam devices.

1. HVS (heavy vehicle simulator) test programme.

The programme is a mobile device that is used in studying the characteristics of the structure of pavement subjected on environmental conditions and traffic loading, the study is assumed to be the actual conditions of the field, and the results from this programme serve as a verification of data. The requirement for its effectiveness will require an application of magnitude of about 30 kN and 110 kN of the wheel load which is moving at approximate speed of about 12 km/hour. Traffic wander can also be stimulated if the wheels will be allowed to move in transverse directions, the influences caused by the environment an example being pavement ground water or pavement temperature is controlled and managed through facilities which will be added on.

Field Performance

Example 1

Sydney M4 motorway

The initial two motorway lanes that occupied on each direction were widened [1] three lanes, where the addition lane were constructed at the initial shoulders of the two lanes, this was done using insitu stabilization, the reason why insitu stabilization was considered was because it was the best method that could suite achieving a higher production rates that is adjacent to the busiest Sydney highway. Basically recycling was done on the existing materials of the pavement, this with highest percentage reduce the cost that could have been incurred in transportation of quarry materials. The proportion of the pavement design used were as follows, 50% fly ash binders, lime and slag both of them had 25%, the strength recorded after 28 days was 2 MPa, the binder used allowed for time to and compaction was improved.  

Characteristics of Subgrade, Sub Base and Base in Pavement

Example 2

Eyre Highway In South Australia

Eyre highway was widened for 33 km section starting from Kiamba, the road had a high plasticity soil which is categorized as weak and of poor quality, therefore a stabilization using lime blended fly ash was applied, the proportions of the materials used 2.5% of fly ash and 0.5% of lime, the selected binder improved the stiffness of material and reduction on moisture sensitivity, it also minimized the shrinkage.

The analysis carried out in South Australia transport lab indicated that shrinkage rate reduced shrinkage caused by lime band blended fly ash, as compared to the GP cement, they also confirmed that the appropriate ratio of 1:1 fly ash lime binder helped in provision of a long term cement strength.

Pavement design

The pavement design to carry 80.07 kN equivalent to a single axle load of 2000000. The sub base thickness 8’’, roadbed resilient modulus and elastic modulus sub base are given below.

Load support	1
Concrete elastic modulus	5000000 psi
Concrete modulus of rapture	650 psi
Coefficient of load transfer	3.2
Coefficient of drainage	1.0
Standard deviation	2.9
Reliability	95%
pi	4.5
Pt	2.5

Seasonal variation of both sub base and sub grade pavement layer

Month	Modulus of road bed (MPa)	Modulus of sub base (MPa)
January	124.1057	310.2642
February	124.1057	310.2642
March	27.57904	124.1057
April	34.4738	137.8952
May	27.57904	124.1057
June	55.15808	172.369
July	55.15808	172.369
August	55.15808	172.369
September	55.15808	172.369
October	55.15808	172.369
November	55.15808	172.369
December	124.1057	310.2642

ESAL = 2*10⁵ ESALS/yr

Overall serviceabity loss = p₀ – p_t = 2

Assume annual growth rate = 2%

Design ESALS = multiplier = [(1+g)ⁿ – 1]/g

• 2 * 10⁵[(1+0.02)²⁰– 1]/0.02 = 4900000

For 20- years design life

• 2 * 10⁵[(1+0.02)³⁰– 1]/0.02 = 8200000

 For 30- years design life

• 2 * 10⁵[(1+0.02)⁴⁰– 1]/0.02 = 12100000

 For 40- years design life

Calculate effective modulus of subgrade reaction (k)

This is calculated as per AASHTO guide for design of pavement structures

Determine the composite modulus of subgrade from roadbed resilient modulus and subbase elastic modulus to projected slab thickness

Structural number = a₁*D₁ + a₂ * D₂ * m₂ + a₃ * D₃ * m₃

a₁, a₂, a₃ are structural coefficient of wearing, base, subbase course

for this case a₁ = a

m₂, m₃ is the drainage coefficient for base and subbase

SN = 5 from the graph

Determining relative damage

Month	Modulus of road bed (MPa)	Modulus of sub base (MPa)	Composite , k	Rel damage
January	124.1057	310.2642	1000	92
February	124.1057	310.2642	1000	92
March	27.57904	124.1057	650	65
April	34.4738	137.8952	750	75
May	27.57904	124.1057	650	65
June	55.15808	172.369	850	85
July	55.15808	172.369	850	85
August	55.15808	172.369	850	85
September	55.15808	172.369	850	85
October	55.15808	172.369	850	85
November	55.15808	172.369	850	85
December	124.1057	310.2642	1000	92

Average relative damage

	ESAL	Pavement layer	95% Rel
For 20 years	4900000	PCC	12’’
		HMA base	6’’
		Crushed stones	8’’
30 years	8200000	PCC	14’’
		HMA base	8’’
		Crushed stones	8’’
40 years	12100000	PCC	14’’
		HMA	10’’
		Crushed stones	8’’

Conclusion

Inclusion, we have noticed that unbounded materials that are used in construction will lack enough strength or stiffness, when it is required for as natural material for construction, therefore a process of stabilization or modification of the unbound soil in addition of a small portion of binder will greatly enhance the performance and reduction of cost. The added binder as an effective role of increasing the shear capacity of the materials of pavement and also allows construction of a thinner pavement.

The combination of the binder to the quarry material will alter the blend’s physical and mechanical properties, it is always recommended that the properties of the combined binder are supposed to be well understood before its placement to a pavement structure.

It has also been seen that fly ash is an important component that will help in choosing the right binder for stabilization of a project, where they enhances performance of the binder and will also help in reducing the cost of the project.

It has also been seen that residue on sieve has some properties which are outside AS 3582.1 [8], therefore they are recommended to be used as they are able to achieve the appropriate modification or stabilization of pavement road base.

The application of test involved in long term will help in provision of an indicated pavement right load bearing capacity.

References

[1] Andrews, “Pavement Rehabilitation Report, Department of Transport, South Australia”,, Materials Technology Section, Available from https:// www.roadbondsoil.com/wp-content/uploads/2011/11/Australia%20 -%20Eyre%20Highway%20Report.pdf, 2009.

[2] Ash Development Association of Australia (ADAA), “Guide to the Useof Fly Ash in Concrete in Australia”, Fly Ash Reference Data Sheet No.1, Available from https://www.adaa.asn.au/refdatasheets.htm, August,2009, 4p.

[3] Austroads, “ Guide to Road Design”, Austroads Publication No.AGRD01/10, Third Edition, Austroads Ltd, ISBN 978-1-921551-83-3,August, 2010.

[4] Ash Development Association of Australia (ADAA), “Australian Experience with Fly Ash in Concrete: Applications and Opportunities”, Fly Ash Technical Note No. 8, , Available from https://www.adaa.asn.au/ technicalnotes.htm, November, 2009, 4p.

[5] Chapman, B.R. and Youdale, G.P., “Bottom Ash – From Industrial Waste to Pavement Material”, Proceedings, 11th ARRB Conference, Vol. 11, No. 3, 2009, pp 90-105.

[6] Lekarp, F., Isaacson, U., and Dawson. A, State of the Art, Part I: Resilient Response of Unbound Aggregate, Journal of Transportation Engineering , American Society of Civil Engineers, Vol. 126, No. 1, 2009, pp. 66–75.

[7] Hicks, R. G., and Monismith, C. L. (2009). ‘‘Factors Influencing the Resilient Properties of Granular Materials,’’ in Transportation Research Record 345, Transportation Research Board, National Research Council, Washington DC, pp. 15–31.

[8] Standards Australia, Australian Standard AS3582.1, “Supplementary Cementitious Materials for Use With Portland and Blended Cement – Part 1: Fly Ash”, ISBN 0 7337 1688 1, SAI Global, 2009.

[9] Uzan, Jacob. “Characterization of granular material.” Transportation research record 1022, no. 1, 1985, pp. 52-59