projet civ e 719

Project Presentation-CIVE 719:

Project Presentation-CIVE 719 1 Use of insulation layer in pavement structure to reduce the effect of frost action Name- Saifi Rahman ID-1269184

Quick overview:

Quick overview What is frost action and heave? Frost action is a phenomenon that occurs in winter and early spring in northern climates. Practically all surface soils in cold climates undergo some frost action, the magnitude of which is dependent upon the locally prevailing climate and precipitation and soil type. Frost action divides into two phases: freezing of the soil water (sub-grade) and thawing of the soil water (sub-grade). Heaving of the road from frost action is termed “frost heave.” Result of accumulations of ice lenses moving perpendicular towards pavement surface particularly when in isolated areas, induces uneven support of a pavement. When heavy loads pass over the area of uneven support, crack may form in the pavement surface layer. 2

Quick overview:

Quick overview 3 Gradual formation of ice lenses due to frost action. Impact of frost action on pavement surface : Movement of ice lenses due to capillary pressure which causes heaving or cracking on Pavement surface. 2 nd phase of frost action occurs if, the sub-grade is completely frozen due to frost action and have detrimental effect (potholes) caused by ongoing traffic due to reduction in bearing capacity of the sub-grade soil

Quick overview:

Quick overview 4 Pavements are not generally designed based on frost action. Reason: Complexity Uncertainty Economical feasibility Techniques for reducing frost action : Replacing frost susceptible sub-grade soil with less frost susceptible soil. Designing of pavement structure with reduce sub-grade support. Improve drainage quality. Providing Insulation in pavement system. Limit the depth of frost by increasing the thickness of granular base or sub-base.

Outline :

Outline 5 Introduction Design issues and facts Difference between insulated and uninsulated section in pavement structure. Recommendation Conclusion. HMAC 150 mm Granular base 450 mm Insulation layer(variable thickness) Granular base 300 mm Sub-grade

Introduction:

Introduction 6 An insulated pavement system comprises conventional surfacing and base above an insulating layer (Considering specific material)of suitable thickness to restrict heat flow towards surface or prevent the advance of subfreezing temperatures into a frost-susceptible sub grade . Mechanism of insulation layer: The basic mechanism of insulation layer is to impede the heat flow, which reduces considerable heat loss from pavement system when it is in contact with the cold air & thus soil temperature will hopefully remain above the freezing temperature throughout the winter Facts: Insulated layer is used where sub-grade soil are extremely sensitive to frost action and can also prove cost effective in such condition. Being an integral part of pavement service life , effectiveness and reliability should be adequately considered at strategic, tactical and operation level of design as well as construction.

Design Issues and facts::

Design Issues and facts: 7 There are 6 major aspects or governing factors for designing insulation layer in pavement structure: Placement/depth of insulation layer. Material selection. Structural behavior for inserting a weak layer(insulation layer) into the system. Thickness design and thermal property. Consideration of differential icing ,due to insulation layer. Differential behavior in uninsulated section.

Design issues and facts:

Design issues and facts 1.Placement of insulation layer: It will be placed closer to the surface which will reduce annual thaw depth. The exact location for placing insulating layer should be controlled by the strength of the material and structural adequacy, of the resulting pavement system. Generally insulation layer are placed between base and sub-grade, but in case where the thickness of insulation layer is not sufficient enough to prevent sub-grade freezing an additional granular sub-base is place between insulation layer and sub-grade. For insulating materials like Light weight concrete and aggregate, there is also an additional layer of geo-textile between insulation layer and sub-grade. 8

Design issues and facts:

Design issues and facts 9 Pavement structure with insulation layer (extruded polystyrene) Pavement structure with insulation layer (light weight concrete) Geo-textile

Design issues and facts:

Design issues and facts 2.Material Selection: Material selection for insulation layer is based on thermal conductivity, water content, durability, longjivity, economical feasibility There are several materials (polystyrene, light weight concrete & aggregate, foam glass etc) used for insulation layer in pavement system Polystyrene (Styrofoam): Extruded polystyrene (Styrofoam) is widely used, due to its moderate compressive strength, less sensitive to water content, low thermal conductivity. Expanded polystyrene can be cost effective in comparison to extruded polystyrene but more sensitive to water content , can be minimized by increasing thickness. Only problem associated with polystyrene is the placement of insulation boards, which requires huge manpower, technical skills, special caring e.tc. 10

Design issues and facts::

Design issues and facts: LWCA : are also quite common insulation material. It produce a stiff layer with low thermal conductivity , installation is easy and can be done using the standard construction equipment. Problem: high water intake requires additional layer of geo-textile. Geo-textile : Geo-textiles play a significant part in modern pavement design and maintenance techniques. Typically made from polypropylene or polyester. It can be defined by six discrete functions separation, filtration, drainage, reinforcement, sealing and protection. Depending on the application geo-textile performs one or more of these functions simultaneously. In case of light weight concrete and aggregate acting as insulation material in pavement system there is a strong possibility that sub-grade soil will mix with the insulation layer (light weight aggregate) as well as with the base course thus reducing aggregate strength, by providing a thin layer of geo-textile can prevent such occurrence Recyclable materials: Recyclable materials such as foam glass, saw dust, bark and wood chips which has good thermal properties but poor mechanical property, can be used as insulation material when they are available in large quantities and low cost. 11

Design issues and facts:

Design issues and facts Insulation Material Thermal conductivity Heat capacity kj /m 3 , 0 C Typical water content % Compressive Strength,kPa Comment Extruded polystyrene 0.03-0.04 ~40 0.3-5.0 200-700 Widely used & documented Expanded polystyrene 0.03-0.05 ~40 1.0-10.0 150-400 Low cost alternative to extruded polystyrene .Risk of higher intake in insulation materials must be compensated by an increased layer thickness Light weight concrete 0.5-0.7 1500-1700 1.5-5.0 2000-4000 High stiffness material easy to lay down Expanded clay 0.15-0.25 350-500 5.0-20.0 Variable Separation geo-textile needs to be used to protect the insulation layer against contamination Foam glass aggregate 0.15-0.25 300-360 5.0-20.0 Variable Sawdust & wood bark 0.15-0.5 110-130 E modulus between 5 & 10 Mpa Structural design of pavement layer above the insulation layer is critical. 12 Comparison between different insulation materials.

Design issues and facts:

Design issues and facts 3.Structural adequacy : Insulation layer are mechanically weak material. Design doesn’t involve resisting of load however will be subjected to load caused by traffic volume (wheel load or ESAL). Requires minimum compressive strength to sustain 13

Design issues and facts:

Design issues and facts 14 Comparison between compressive strength of different insulation material.

Design issues and facts:

Design issues and facts On what basis we are designing insulation layer? Answer: Water content, Thermal conductivity, Compressive strength. Insulation materials used for roads and airfields should not absorb water in quantities that change its thermal and mechanical properties significantly over the required service life.( us army and air force, 1985) It is true that soft insulation layer (LWCA) has better compressive strength then Styrofoam but it is seen that Styrofoam shows better mechanical behavior during spring thaw period. In case of long term assessment it is seen that hard insulation material can overcome detrimental effects such as fatigue cracking and thermal cracking associated with soft insulation layer. For LWCA designing layer above the insulation is more critical, time consuming and less cost effective. 15

Design issues and facts :

Design issues and facts So if we are designing base on soft insulation layer it is necessary to make sure that the level of stress transmitted to the insulation layer doesn’t induce excessive deformation of the insulation material and thus result in mechanical and thermal degradation of the layer. What's the solution in this case? Answer: Providing a granular layer above insulation with appropriate thickness which will eventually reduce the stress to certain allowable limit before it transmits to the insulation layer. 16

Design issues and facts:

Design issues and facts There are ways to determine the required thickness for granular layer, such as one equation proposed by (Nixon 1979) which is 17 1/2 Where, Z=Thickness of the material (equivalent granular material), required above the insulation layer (m). ρ= Tire inflation pressure ( kpa ). W = Design wheel load ( kn ). Ϭ a = allowable stress on the insulation layer

Design issues and facts::

Design issues and facts: 18 We can also use this proposed graph to find the thickness of granular layer. Two parameters required 1.Ϭ a = allowable pressure for a specified insulation type and number of vehicle passes. Typical design wheel load is 40 Kn and tire pressure is 700kpa Ϭ a varies with design wheel load it could be equivalent to 0.50Rc, 0.12Rc, 0.10Rc under 103,106,108 traffic volume (ESAL) or 0kn,100kn,250kn . Rc is the compressive strength suggested by manufacturer. 2. Tire pressure. Example : Design wheel load 100kn, Ϭ a =200Kpa, Tire pressure P=400 Kpa . The thickness of the granular material will be 0.38m 0.38 Figure-3: Granular cover requirements for protection of insulation under different wheel loads ( Source: Reproduced with permission from Nixon 1979. Copyright 1979 Canadian Geotechnical Journal).

Design issues and facts :

Design issues and facts 4.Appropriate thickness and thermal design of insulating layer: Thickness of the insulation layer depends on thermal property and surrounding cliamte condition. 0 0 C or critical isotherm designated as critical condition for designing insulating layer against frost action.(ice lenses begin to form at this temperature). When insulation layer is buried the heat flow towards surface is a two step process 1 st step is a balance heat flow movement towards the insulation layer 2 nd step, reduced heat flow (due to insulation layer) movement towards the surface. 19 Reduced heat flow towards surface Insulation layer Surface Heat flow for sub-grade 0 0 C Mechanism of heat flow in context of thermal property .

Design issues and facts :

Design issues and facts Design for frost action in context of critical isotherm involves satisfying 1 out of 3 methods which include: Approved schematic design for each climatic zone. (Climatic zone are based on maximum air freezing index for a defined time period. Trial and error procedure by doing calculation related to certain parameters and the design freezing index.( it is commonly applied and easy approach) Transient heat conduction equation is solved by a finite element technique with appropriate boundary condition. (It is required for high level of detailing 20

Design issues and facts :

Design issues and facts If the parameters such as thermal resistance and thermal conductivity of insulation material which can be obtained from various table and by using the graph below we can easily obtain desired insulation thickness based on thermal property, which was our first method for design of insulation layer against frost action 21 Insulation thickness as a function of required thermal resistance and insulation’s thermal conductivity. The lines are based on t ins = R · γ . Source: Reproduced with permission from Algaard 1976a. Copyright 1976 Norwegian Public Roads Administration/NTNF

Design issues and facts :

Design issues and facts For trial and error procedure we assume an insulation layer thickness, compute the air freezing index by using several parameters including thermal resistance, thermal conductivity, density, water content along with the, base, sub-base, and sub-grade soil and compare against standard air freezing index at that location collected from historical data or weather station, if the computed value is higher than given it is satisfactory to use chosen insulation thickness. Another technique to compute desirable thickness of the insulation layer with different insulation material replacing polystyrene (Styrofoam), can be done by using a simple equation which is Where, x p k p is the thickness and thermal conductivity of polystyrene material R is the thermal resistance and x a k a is the thickness of the alternative insulation material. The result thickness obtained will be equivalent to the thickness of polystyrene. The reason for selecting polystyrene material as a standard is its better performance as an insulation layer against frost action with less thermal conductivity and water content. 22

Design issues and facts:

Design issues and facts Another technique used for polystyrene insulation layer is to design the insulation layer based on combined thickness of base and pavement .The parameters required include surface temperature amplitude A s which can be obtained from the chart below and V o = critical isotherm or mean annual soil temperature (normally 0 0 C or 32 0 F).The ratio V 0 /A s thus used in to find the thickness required for insulation layer to resist against frost action. 23 Graph developed by US army and air force to determine Insulation layer thickness

Design issues and facts::

Design issues and facts: 5.Consideration for the risk of differential icing at the pavement surface: Differential icing happen during late fall. As the freezing front enters into the polystyrene layer (dry material), the granular materials placed above it are completely frozen, and no further latent heat is released. The surface heat balance is then drastically changed, which leads to an increase in the rate of surface cooling of the insulated section compared to that of the uninsulated one where the granular materials still release latent heat while freezing progresses. If air moisture is available, in combination with high humidity and low wind velocities hoarfrost or black ice is formed on insulated pavements. 24

Design issues and facts:

Design issues and facts 25 0 0 C 0 0 C Un-insulated section Insulated section Changes in pavement system by presence of an insulation layer during cold fall periods. Heat flow

Design issues and facts:

Design issues and facts 26 UnInsulated section Insulated section Formation of hoarfrost or black ice in insulated section

Design issues and facts: :

Design issues and facts: Solution: In order to minimize this problem there is a standard minimum thickness of granular material on top of the insulation layer which needs to be maintained throughout the pavement section. The heat contained in aggregate and in interstitial moisture of the granular layer will partly compensate heat loss at the pavement surface, thus reducing the risk of surface icing. Most transportation agency use a thickness around 300-600mm for granular layer or cover ,based on experience and empirical rules based on experimental work done. Poorly graded course material placed above the insulating layer resulted in lower surface temperature causing higher differential icing risks than a well graded granular material ,and also it is better to avoid sharp curves and steep grades in this condition. 27

Design issues and facts:

Design issues and facts 28 Design charts for thickness of granular material for reducing the effect of differential icing for climate context of Quebec province.

Design issues and facts:

Design issues and facts Three parameters required include mean annual air temp T maa which can be obtained from Meteorological Service of Canada (Ottawa, Ontario), from which The effect of the variation in thermal conductivity of solid particles of the granular protection ks can be determined using a chart, and the thickness of the insulation layer h ins . One notable fact about this chart is that water content remains the same, because it is very difficult to estimate the water content in granular material (variation) and uncertainty related to the parameter . However, An equation was obtained by co-relating correction result between minimum thickness required for granular protection h gp , and h gp values obtained for various water contents for every 3.5% in combination with Tmaa and h ins (thickness of insulated material) which is The proposed design approach relies on consistent average data for climate parameters such as air temperature and air moisture, solar radiation, cloud cover, and wind speed, which are readily available from environmental services 29

Design issues and facts:

Design issues and facts 6.Consideration of differential behavior at the end of insulated areas The severity of frost action is not uniform throughout the roadway and total frost protection is used in areas where excessive frost heave or differential frost heave likely to occurs, therefore all through the pavement section insulation is not required. Also it is not a practical approach as well as costly to provide insulation layer all through the roadway for several reasons such as: Adjacent pavement section sub-grade is well compacted , has less frost susceptible soil and moderately sensitive to frost action. Adjacent Pavement system is based on reduced sub-grade support We can define this term for uninsulated section as moderate frost heave behavior where a certain section of the pavement requires insulation whereas the adjacent section doesn’t requires insulation. 30

Design issues and facts:

Design issues and facts Problems: Differential behavior observed , one section remains smooth (insulated) and another section become rough (uninsulated). Crack appears at meeting points. Reduction in ride ability (safety). Solutions: Transition between two section by reducing the effectiveness of insulation layer. Transverse transition reduces edge cracking in the bound surface layer and the risk of heave shoulder obstructing surface drainage. Ride quality reduces due to differential behavior in the longitudinal direction that's why longitudinal transition is necessary .It depends on (traffic speed, thickness of insulation layer, insulation material) 31

Difference between insulated and uninsulated section in pavement structure:

Difference between insulated and uninsulated section in pavement structure 7.Pavement performance regarding existence and non existence of insulation layer in pavement system : Frost penetration depth is much higher in uninsulated section. Heave depth is also higher in uninsulated section 32 The effect of an insulating layer of pavement on pavement frost depth and frost heave (from konard et al.1996) Uninsulatedted scetion Insulated section

Recommendation:

Recommendation Right placement of insulation layer is, necessary in order to obtain optimum performance. In case insulation layer is not sufficient enough to resist frost action, a granular layer between insulation layer and sub-grade soil is placed. In case of thermal efficiency 1 inch of granular layer placed below insulation is much more effective then, granular layer placed above. Performance objective of the insulation layer has to be well defined prior to insulation. Late fall is a critical condition for insulation layer; therefore early prediction is necessary for selecting thickness of granular layer above insulation layer. To reduce differential behavior between insulated and uninsulated pavement it is necessary to main a balance condition by reducing the effectiveness of insulation layer to certain extent. Depth of the cover above the insulation layer should be sufficient enough to prevent crushing cause by cyclic load. Minimum cover depth is between 0.4 to 1.0m. Insulation layer should be adequately design to reduce thaw settlement, which is necessary to maintain permafrost condition. It is seen that after certain depth (900 mm) insulation layer doesn’t have any effect on surface temperature. In case of reconstruction of old roads an insulated flexible or rigid overlay could be more economical due to lesser thickness required, also it can be directly placed over the damage pavement hence preventing frost action and limiting excavation depth. 33

Conclusion:

Conclusion The main objective of insulation layer is to increase pavement service life. Insulation layer doesn’t completely eliminate frost action rather it reduces it. Both insulated and uninsulated pavement has their potential advantage and disadvantages, and an insulated layer should be installed in pavement structure if the other criteria regarding reducing frost action prove inapplicable and costly in comparison. Thickness of insulation layer plays a vital role in every perspective of design discussed above. Before inserting an insulation layer sufficient field studies should be done considering sub-grade soil, and severity of frost action in that particular area. 34

Slide 35:

Question 35