Design of Pavements and Surfacings - Pavement Design Life, Flexible Pavement Rehabilitation - Term Paper Example

1.1.1 Pavement Design A) Unbound Flexible Pavement – A pavement that is constructed with a granular base that is unbound with either a surface of thin asphalt or sprayed bituminous. B) Deep Strength Asphalt Pavement – A pavement that comprises of an Asphalt wearing, with the base and intermediate courses that are placed on a cement treated sub base. C) Full Depth Asphalt Pavement – A pavement consisting of asphalt wearing with the intermediate and base courses that are placed directly upon an unbound sub base material layer. (D) Rigid Pavement – A concrete pavement structured with Portland cement. (E) Mechanistic Pavement Design – This pavement design procedure consists on bound layers that are based on the strain determination of the material performance in order to calculate the amount of load repetitions that are allowed. In Australia, pavements require a granular base that is unbound specified carefully for reducing construction costs and a surface that is approximately 30mm of asphalt. Aggregates of high quality are required for the base pavement course layer, because of road surface proximity. The design and pavement analysis currently in place in Australia is regarded as sub-standard. Highways and roads in Australia exhibit a high rate of surface damage due to increasing vehicles that are in use. This resulted in the development of design consisting of a Hydrated Cement Treated Crushed Rock Base (HCTCRB).Pavement design and analysis relies predominantly on empirical design, basic experimentation and experience. The reasons for damage in present conditions are difficult to assess. Europe and USA entered and era of pavement analysis and design where mechanistic design has replaced empirical design. The mechanistic approach explains characteristics of the pavement under pavement conditions in real operational modes. It is based on parameters of design derived from tests that are sophisticated and simulate pavement conditions in the protocol of test (WSDOT2008). Pavement design via the mechanistic approach produces relevant and useful results, together with analysis that is linear elastic, introduced to Australia in 1987. AUSTROADS (Association of Australian Road Authority) resulted in the development of design consisting of a Hydrated Cement Treated Crushed Rock Base (HCTCRB). A National pavement research strategy was then published which has served as a keystone for the nation pavement co-ordination research with government and the industry. CBR Percentages Assigned CBR California Bearing Ratio (CBR) is assigned to insitu material that is either at or below the subgrade level of the pavement material .Assigned CBR is determined from CBR testing determines assigned CBR or other related data in compliance with the VicRoads Codes of Practice RC 500.20A3 and RC 500.23 A3 . Subgrade level Insitu Material is the material either at or below the subgrade after the stripping but prior to the commencing of the earthworks. Design CBR is assigned to the earthwork layer that is imported in the fills or insitu material that is prepared in cuts at the subgrade level or below it .This determines the pavement structural thickness.The mechanistic design of flexible or rigid pavements determines the structural thickness but it excludes the tolerances of contruction thickness.Design Thickness is the required thickness of pavements that includes allowance for tolerances of construction thicknesses.A thick layer of crushed rock (minimum of 150 mm )in class 4 is required above the subgrade level on roads that have Design Traffic G 1.0 x 107 HVAG, The CBR calculation of effective subgrade , according to AUSTROADS B1 is defined as : The 150mm material directly below the subgrade level has to have an assigned CBR 10% according to the section 7.1 of the VicRoads Code of Practice RC 500.23A3. Lime Stabilisation for the improvement of the strength and reducing of the swell of clay either at or below the subgrade level is recommended . G 150 mm is the minimum lime amount that is required to satisfy the material properties and the design requirements are required to be determined in compliance with the VicRoads Code of Practice RC 500.23A3. Design of Pavements and Surfacings (VICROADS_n2220344_RC500_22-Selection and DesignPavements and Surfacings.) 1.2 Pavement Construction In the case of expansive utilization of materials for the construction of pavements, the following propositions constitute requirements: (A) A capping layer needs immediate placement above high swell or sub grade material that is expansive for the width formation in order to instill protection from moisture on varying levels. As per section 204 of Vic Roads the capping layer will be Type A. The swell of the capping material of 1.5% is determined according to Vic Roads Code of Practice RC 500.20. Stabilized lime material that meets Type a fill requirements inclusive of permeability criteria may be used as the capping layer. The capping layer thickness has to be either 2.5 times particle size maximum or 150mm, depending on which is greater. The capping layer needs to extend to the embankment edge or at a distance of 1.5m behind the kern back. Footway or Bicycle paths that are separately constructed needs a capping layer over fill material or expansive in-situ providing 400mm minimum cover of capping material or pavement. (B) Pavement Drains located on subsurface pavement needs to be designed with capping layer functionality. The subsurface part of the drainage trench has to be located 150mm apart from the expansive material. (C) Landscaping Design – Landscaping and plantation should conform to the region requirements. For example, trees are to be planted 9 m away from the closest pavement. Srinath PC CONTROL OF MOISTURE DURING CONSTRUCTION OF ROAD PAVEMENTS - RR - FINAL 2014-09-18 Waterproofing Effectiveness Evaluations Field and laboratory evaluations of waterproofing effectiveness of interlaying systems of paving fabric have concluded the following results: Field and laboratory pavement cores have indicated that proper installed paving fabric interlayer’s presence reduces pavement permeability by 1-3 of magnitude orders. By reducing infiltration with additional orders of magnitude, the system becomes efficient in serving as a barrier to moisture and enhances pavement performance. In the pavement design AASHTO (American Association of State Highway and Transportation Officials)) methodology, improved drainage will be of structural benefit and, should be a consideration when dealing with paving fabric interlayer’s, as reduced infiltration equates to drainage improvement. The new rehabilitation and pavement designs include larger coefficients of drainage incorporated to ensure benefits. Fabric interlayer’s of paving reduces moisture levels below pavements. This maintains sub-base, sub grade and base layers strength, limiting damage as a result of saturated conditions of pore pressures. In order to provide a moisture barrier that is continuous, enough asphalt cement has to be used in order to saturate the paving fabric and bond the system of interlays - approximately 1.04 - 1.13 liters for every square meter. A lowered quantity of asphalt cement diminishes effect of waterproofing. This tack coat of asphalt cement must be uniformly applied. Quality control of the field installation is crucial. If the permeability of a pavement base is greater than between 1 and 10-1mm/sec, improvement of pavement drainage is a viable rehabilitation option. If drainage improvement and not an option that is possible, a barrier of paving fabric for moisture needs to be installed. Further research is a requirement for moisture in pavements and improved tools of development for efficient measuring and monitoring. Technology that is cost effective is available to create moisture barriers in pavements with interlays of paving fabric. Code of Practice RC 50022 Selections and Design of Pavements and Surfacing\ Key factors to adhere to in construction: Longitudinal Slope, Pavement height, Drain depths, Material quality, Quality control tests during construction The stability merits of unbound pavement materials is decreased when there is an increase of moisture content or the DOS(degree of saturation).DOS is the ratio measurement of the water volume to the combined air void and water volume in material. Materials with a 100% saturation level have high pore pressure and instability under loads. When the DOS reduces it corresponds with stability. Unbound pavement materials stability improves when pavements dry to seventy percent or sixty percent in the case of sensitive materials like crushed rock base. 1.3 Pavement Testing Data from several moisture models were gathered to summarize procedures for the determination of moisture conditions in soils and practical pavement design applications. New materials for construction require new development results. The moisture content in pavement design must correspond to possible adverse conditions during the construction phase and during the lifetime of the pavement project. Pavement design methods assumed that material cannot reach a further level of adversity if they were left to soak for four days in water. Field observation has shown that the well know format of the CBR soaked value was conservative for many roads that were well drained. Water content during the construction phase is crucial as many years may pass by before ultimate conditions are reached. Special attention is crucial during earthworks to prevent water infiltration. Due to the fact that the water content during construction may differ from the pavement phase of service justifies a 2 stage pavement design. Mechanistic design needs plastic and resilient sub grade soil properties to be obtained during construction and for the road structure lifetime. 1.3.1 Deep water Table Parameters inclusive of the Thornthwaite moisture index, optimum moisture or plasticity limit influences the water content. These models should be adjusted according to conditions of the site by sampling the soil under surface moisture change and take into consideration boundary and drainage conditions. If the water table is deeper than values presented for different soil types, the moisture conditions will balance by rainfall and evapotranspiration (Russan and Coleman, 1961). There are many cases where rainfall for a period of two months exceeds evapotranspiration. These sites have rainfall that is greater than 250mm. The equilibrium moisture content measured from the Thornthwaite moisture index and soil suction curve. 1.3.2 Shallow Water Table Moisture content is dependent on groundwater as per material suction curve. The water depth table represents a prominent parameter that can influence moisture. A drainage system functioning properly is indispensable during the road lifetime. In practicality the ratio of the plasticity limits remains constant to the moisture content. This ratio is determined by sampling soil beneath the roads that have exceeded five years of existence. In areas of lower rainfall than 250 mm per annum, atmospheric humidity controls soil suction. 1.4 Pavement Damages Observations have indicated damages to the pavement are caused by moving traffic, especially in the case of heavy moving commercial vehicles. In the early 20th century there was minimal attention of damages to axle loads as there was a low volume of vehicles and magnitude loads. During the industrial revolution period the magnitude of heavy vehicles and axle loads increased significantly . Bearing failure results in shape loss and extensive cracking, delaminating of surfaces as a result of pore pressure, fatigue and cracking prematurely due to unstable pavement stiffness. Pavements are subjected continuously to loads that are transferred through moving vehicles. Responses in the form of stresses and strains are then induced within all the pavement layers. The occurrences of these responses occur in the in-situ soil stratum, the sub grade .The low modulus gradually accumulates with the traffic volume increase, even though the magnitudes of the responses are low. .Other pavement layers constructed with road authority specifications are recoverable as they have high moduli. Road pavement performance depends on sub grade behavior linked to moving traffic action. Literature reviews reveals that non linear sub grade behavior under moving traffic action is not incorporated into design charts currently in use. Sophisticated finite element computer codes produce results that are accurate. Moisture represents the root cause pavement damage. Although there is an understanding of how water sources and mechanics of moisture damage pavements, these principles are not incorporated in final pavement design. In some cases, incorporating drainage improvements into the rehabilitation of a pavement are difficult. Techniques of pavement rehabilitation generally address repairs of the pavement rather than treating the root cause of moisture problems. Moisture control has not been a pavement maintenance or design focus. There is an availability of technology that controls moisture sources but it is not recognized or as widely practiced in comparison to traditional repair technologies of pavements. The two ways of controlling pavement structure moisture: 1- Utilization of subsurface drainage 2- Sealing (capping) the pavement, reduce infiltration. Rainwater is the main source of pavement moisture. Moisture can enter pavements from drainage seeps or subsurface flows like a spring. Actual rainwater is the primary water source .The other types of water sources are secondary. Extensive studies have been done to examine surface infiltration of rainwater. The increasing scarcity of quality and natural granular material and rock sources suitable for the manufacture of aggregate base courses, there was extensive research undertaken in Australia to increase the design life of pavements at reduce depths. A key factor is to avoid environmental damage due to the clearing of natural vegetation during the stages of harvesting materials. Studies reveal that 33-50 % of rain water that falls on AC pavements and 50-67 percent on PCC, Portland cement concrete infiltrates from pavements to road bases. Global infiltration rates are 0.001 - 0.002 mm/sec. The results of various tests have indicated that there was a low amount of waterproofing effectiveness with rubber additions to an asphalt mix. Sound pavements are therefore quite permeable. The root source of base pavement moisture is the water infiltration through the pavement. Pavement cracking increases the water infiltration rates to almost 100 % and increases the moisture problems that are prevalent within the pavement structure. If pavement bases become saturated, water pressures from traffic loading negate base stone support function of load spreading. Traffic load is then applied to the smaller area of the sub grade. If the localized loading exceeds the sub grade bearing capacity it causes progressive pavement failure. A pavement base that gets saturated by 10 % makes the useful pavement life to be reduced by 50 %. The test results on gravel or crushed suggest that levels of saturation above 60 -70 % may result in major deformation. Water that jets from joints or cracks can permeate sub grade and base materials to road surfaces. This causes a void beneath the pavement eventually leading to pavement failure. Pavement structures are moisture damaged by weakening the sub grade soil. The pavement load that the sub grade soil bears, may eventually result in a remold of the soil, resulting in shear strength that is lower and moisture content that is higher. The freeze/thaw damage effect occurs in sub grade, base or sub base layers depending on permeability or porosity and frost penetration depth. In cold regions drainable pavement bases are difficult to maintain during cold seasons. Pavements are moisture damage exposed on multiple levels of moisture depending on the speed of the drainage of pavement structures after the infiltration of rainwater. The stone type, the base grade, the base thickness and bas contamination from sub grade intrusion and base layer slope, determines the drainage time of infiltration. Data should be collected in order to verify where moisture could have been the cause of pavement failure or dysfunction. Moisture content needs to be tested after the construction period. Testing must be adhered to in satisfactory as well as failed sections where the similar materials and work processes were undertaken for elimination and comparison. These parameters are useful in resourcing data for testing: Pavement failure in early stages locations. The details of design , the sub grade ,base and sub base thickness Quality of material Drainage depth and water levels expected in relation to the sub grade base Details of construction Size of particle distribution and pavement material properties Excess moisture existing in pavements can cause: Failures by construction loading upper layers, traffic loads or bituminous layer. Extensive cracking, shape loss casing bearing or shearing failure. Premature rutting from unstable material. Blow outs or lifting of the delaminating of road surfaces as a result of pore pressure. Loss of the surface texture as a result of cover aggregate of chip seal embedment. Fatigue cracking prematurely of asphalt surfacing due to inadequate stiffness of pavement. 1.5 Flexible pavement The most common type of pavements in Australia sealed 300000km road network is structures of flexible pavement which comprises of granular materials that are unbound and thin bituminous surfaces. Approximately 6 billion is utilized on a yearly basis for preservation and enhancement. The Hume Highway, a major arterial road including Western Ring Road and railway corridors bisect the Hume municipality. Over the next ten years, major subdivisions developments necessitate a link to these transport corridors. Natural sub grade materials including basaltic clay or high plasticity is covered by the municipality. The treatment of sub grade material that is highly reactive requires special construction and design in order to minimize damage of the pavement from environmental cracking. The past five year period has witnessed major pavement failures that will most possibly impact on road rehabilitation and road maintenance budgets In order to ensure uniformity in design and construction approaches of pavements, and meeting the necessary minimum standard for achieving long term performance and minimizing maintenance requirements .Unbound materials of high quality , ( local gravels local quarry crushed rock) meeting the specifications of State Road Authority are permissible for use in the construction phase. Sub grade Strength The subdivisions proposed require classification into homogenous sections in accordance with traffic loads, the drainage, typography and sub grade type. Hume City council consists of sections with high reactive, high plasticity of clay upgrades. Materials that are highly reactive exhibit volume changes that increase the moisture content. This leads to the pavement losing shape as well as longitudinal cracking of the pavement outer edges. They consist of swells exceeding 2.5%. These pavements need a capping layer to minimize moisture content in the sub grade. The true component factors of a flexible pavement are the “elastically” it yields to the traffic loading. Construction consists of surface that is either bituminous-treated or layered with hot mix asphalt of unbound base courses that are resting on a sub grade. The strength of the layered system ultimately serves as protection of each layer as well as the sub grade. The upper structure consists of progressive materials for resisting high surface stress from traffic loads. These materials are inclusive of a surface that can withstand all weather conditions. It is erosion resistant from traffic and the environment. Should the temperatures of pavements exceed 150ºF, the bituminous surface remains stable and counters fatigue damage. The bituminous surface layer must be fatigue damage resistant and remain stable under traffic loads with excessive pavement temperatures. The FPDTF (Flexible Pavement Design Task Force) designed deep Hot Mix Asphalt structures of pavement types that are typically associated with a surety of a pavement life that is lasting. The intention of the FPDTF studies was mainly to address increasing demands regarding structures for heavy truck load traffic. Sprayed seals form surfacing over thirty percent of the road network in Australia. Performance of these seals is crucial to network sustainaibility . Eighty five percent , 19,000 km of the Victoria road network in Australia contains sprayed surface seals. A survey byt the State road authorities indicated that the Victoria structures, the seal life varied between 7 and 12 years fro 7mmm and 144mm seals. The survey indicated that double coat seals achieved a low percentage of additional life in contrast to single seals. Roads within the arterial network of Victoria roads were resealed two to three years earlier than expected based on performance. The design of durable foundations requires special attention .The investigation of underlying soils to determine stabilization levels and types needed are crucial. Sub grade stabilization requires a granular base of high quality, cement-treated base, or other engineered foundation should be used. A formula designated consists of hot-mix asphalt (HMA) thin surface over unbound base courses that resting on the sub grade. The layered system characteristics determine the strength to protect every underlying layer inclusive of the sub grade from shear failure compression. Upper structures use materials that are progressively better in order to resist the stress of near surface conditions that are caused by wheel loads of traffic. These materials are inclusive of a surface compatible to weather conditions and have resistance to environment erosion and traffic. The bituminous surface layer needs to be fatigue damage resistant and stable under the traffic loads when temperatures of pavements exceed 150ºF. Pavement Design Life A requirement for flexible pavements is a minimum twenty year design life. Rigid pavements are designed for forty years Pavement Thickness design Table 3.1 reflects thickness designs of pavements Flexible Pavement Rehabilitation Developing a design of rehabilitation requires thorough investigation into existing conditions of the pavement structure, laboratory testing of the materials and performance history to establish suitability that exists and possible proposed materials to be used in the rehabilitation design. Key procedures would include a deflection survey, a drainage survey, and additional surveys within the range of ground penetrating radar (GPR), seismic and dynamic cone penetrometer (DCP). Examination of the multi-year Pavement Management Information System (PMIS) ride and distress data will reveal performance issues related to performance. After the conduction of preliminary surveys, material sampling and locations may be established. These samples need lab evaluation to verify conclusions the field survey has established for basic properties assessment to quantify the moisture susceptibility, blending requirements and stabilizer compatibility The rehabilitation strategy should take into consideration: cost-effectiveness, specific problems in need of repair on pavement that exists, prevention of any future problems that may transpire and meeting constraints present in the project. Flexible pavements consist of wearing surfaces created over background surfaces and on certain sections of the compressed sub grades. Persistent change in climate has led to rainfall that was unexpected leading to pavement constructions. Pavement thickness influences functionality. The flexible pavement design needs to be rational in finite elements analysis. The thickness of a pavement has parameters that vary in the range of elasticity and pressure that are under consideration in the design format. Pavement design relies on opinion dissolute though ground depth beneath the succeeding granular materials layer. The surface courses existing in flexible pavements have been applied globally. Flexible Pavement Design Analysis It has been argued that there veritable designs of flexible pavements. The Canadian resistance value method, McLeod method, Group index and CBR (Sinhala, Chandra, and Kumar (2014). Beskou, Tsinopoulos, and Theodorakopoulos, (2016), argument states that flexible pavements thickness and surfacing is connected to traffic level within the Group Index method. Gupta and Kumar (2014) assert curves located between pavements and CBR thickness for different levels of high, medium or light traffic. Abed and Al-Azzawi (2012) outlay problem of dependability associated with bituminous pavement plans, based on empirical approaches. Beskou, et al. (2016) added tests for identifying pavement performances and the loading freeze-thaw cycles machines, repeated numerous times, especially during thawing periods. Gupta and Kumar (2014) applied the method of finite element to analyze and design pavements. Bodin, et al., (2014) note that the methodology of finite element has the capability to analyze stability and issues related to material nonlinearity, as well as problems connected to time dependence. Abed and Al-Azzawi (2012) identified that flexible pavements are analyzed with the use of two methods, multilayer system theory and finite element methods and comparing the results with use of significant parameter and correlation coefficient . The examination outcomes of finite elements are suitably compiled using outcomes of the multilayer theory, which leads to valuable differences lack in the mean value of the techniques. Bodin, et al., (2014) identified that flexible pavements economically based on initial investment and maintenance. Flexible pavements occupier a lower ration of space for traffic, making them less expensive, they last for about 15 years with lower investment costs, and require minimal amount of maintenance expenses. Flexible pavements according to analysis are highly reliable. Reliability is identifiable through simulation and applied techniques. The total thickness of flexible pavements has a total that is determined via group index methodology. The CBR method is conducted on flexible pavement based on the strength parameter of the materials. This becomes more rational in comparison to the group index methodology. The flexible pavement is present when there is design curve that is located between pavement thickness and cone bearing ratio. There are four design charts, inclusive of three parameters each that are in development. The design charts are compiled through four approaches of the finite, which enhance solving complex problems present within various pressures as well as the elastic modulus of the soil. . References Bodhinayake, Beatrice Chandrani. (2008)A study on nonlinear behaviour of sub grades under cyclic loading for the development of a design chart for flexible pavements, Doctor of Philosophy thesis, School of Civil, Mining & Environmental Engineering, University of Wollongong. http://ro.uow.edu.au/theses/868 Eng. Ratnasiri Rupasinghe .(2014) Control of moisture during construction of road pavements www.iesl.lk/resources/SLEN/DS16/DS16_Road-moisture-control.pdf Kay, DJ; Buys, HG; Donald, GS; Howard, MD and Pells, PJN. Management of the Hume Highway pavement for subsidence impacts from longwall mining [online]. In: Mine Subsidence 2011: Proceedings of the Eighth Triennial Conference on Management of Subsidence, The. Pokolbin, N.S.W.: Mine Subsidence Technological Society, 2011: 247-256. Availability: ISBN: 9780958577946. [cited 24 May 16]. Wolthuis, Lart (2014) Decision support system to conduct life cycle cost analysis for service life road pavement design using an object oriented model. Vicroads ,Code of Practice RC 50022 Selection and Design of Pavements and Surfacings, oct 2013 https://www.vicroads.vic.gov.au/.../codes-of-practice/code-of-practice-rc-50... Austroads (1993) ‘Guide to the Structural Design of Road Pavements’. APRG Report No 21 (1998) ‘A Guide to the Design of New Pavements for Light Traffic.’ VicRoads (1993) Technical Bulletin No 37 ‘VicRoads Guide to Pavement Design.’ VicRoads (1982) Technical Bulletin No 32 ‘ Drainage of Subsurface Water from Roads’. Roads and Traffic Authority NSW (1996) ‘Concrete Roundabout Pavements – A Guide to their Design and Construction Read More