Sensitivity analysis of stormpav composite pavement

This study investigates the design and performance of modified composite pavement called StormPav. In this study, the sensitivity analysis is carried out by using available freeware to prove whether the StormPav composite pavement is able to provide long-life pavement and better levels of performance, both structural and functionally, than the traditional pavements. For this case, the sensitivity analysis is included data for fatigue behavior, rutting in the HMA (Hot Mix Asphalt) layer, and temperature gradient reduction of PCC slab with an HMA overlay. The StormPav composite pavement is actually an innovation IBS green pavement with structural, environmental and economic advantages. Inspired from Legos concept, the StormPav is made out of modular panels or “roadblocks” that are like enormous lego pieces that assemble and interlocking together forming a uniform settlement and at the same time acting as the monolithic character. The idea of StormPav is actually to minimize the usage of material in the composite pavement but provide the same strength and benefits as composite pavement.


Introduction
It is undeniable that pavements play an essential part of our daily life as we use them as roads, runways, parking lots and driveways. Like any other engineered structure, pavements are expected to be adequately strong and durable for their design life. Especially when it is related to highway, they are expected to function properly under heavy load and high speed as well as with smooth traveling experience under the various condition of the environment. Unfortunately, transportation agencies and the road building industry of worldwide have designed and used the same traditional pavement system over the years which are no longer competent to withstand the developing and increasing use of traffic nowadays. The two types of traditional pavements are flexible (asphalt) and rigid (concrete) pavement.
Conventional composite pavements generally consist of two parts: rigid base and asphalt surface. With their excellent pavement performance, composite pavements have shown great potential to become a promising alternative for sustainable pavement under heavy traffic [13]. Although there are two different types of pavement design systems which are conventionally used in the construction of roadways such as flexible and rigid pavement, the performances of both rigid and flexible pavements do not provide outstanding quality as composite pavements. There is another alternative pavement which is conventional composite pavements that have been proved to provide better levels of performance, both structurally and functionally, than the traditional pavement designs [3] [11]. The conventional composite pavement is however considered expensive and is rarely used as new The first component is the cover concrete (1); reinforced precast hexagonal concrete panel. The cover concrete will be covering the hollow cylinder concrete top and bottom. Six intermediate rectangular gaps (a) at the edge of each side will provide the interlocking space. The gaps will be filled with cast in-situ concrete as interlocking concrete for the pavement. The second component is the body (2); The unreinforced precast hollow cylinder concrete to provide structural support to the reinforced top and bottom cover. This structure is actually acting as a rigid base. Then, a thin layer of asphalt is placed over a concrete surface to provide a smoother ride. Figure 3 shows the dimension of the StormPav composite pavement.  The idea of StormPav is actually to minimize the usage of material in the composite pavement but provide the same strength and benefits as composite pavement. IBS StromPav composite pavement is combining the most desirable characteristic of both traditional pavements to act like concrete but to be easily maintained like asphalt concrete just like conventional composite pavement system.
The other benefits that IBS StormPav Composite pavement can provide are:  Good levels of the rideability of the pavement and driver comfort by providing a smooth and quiet driving surface  Strong support to the flexible layer provided by the rigid base layer  Adequate pavement surface friction properties  StrormPav that assembled as a rigid base having high stiffness provides strong to HMA overlay.  Potential to provide both excellent surface properties (low noise, non-polishing aggregates, and durability) and long life structural capacity for any level of traffic.  Prevention of the intrusion surface water to the rigid base due to the protection provided by the asphalt layer.  Surfacing to be with high-quality and relatively thin HMA. The minimum thickness of HMA layer to be based on material with aggregate gradation and structure, binder types, etc.  Reduction of the temperature gradient in the rigid layer because of the insulation provided by the overlying asphalt surface layer.  Rapid and simple installation of StormPav as the structures is a precast product  Development of traffic-load-induced critical tensile-stress at the bottom of rigid base thus providing compression mode in HMA.

Methodology
The sensitivity analyses included the variation of different parameters that were plotted against the results obtained for the various composite pavement systems [10]. In this case, the sensitivity analysis covered on the fatigue behavior, rutting in the HMA layer, reflective cracking, and temperature gradient reduction of a PCC slab with an HMA overlay.
The freeware used to analyse the data is "AASHTO_Rigid spreadsheet" freeware, an excel tool developed by HMA Long-term pavement performance (LTTP) program to supplement the AASHTO pavement rigid design system, was used to model the performance of StromPav [1] Conference In order to compare the performance analysis or output using AASHTO_Rigid spreadsheet, it was very important to design the composite pavement systems so that some constant criteria were used throughout the analysis. Since StormPav (Tables A.1

to A.3 and Figures A.1 to A.5) is a new product
of conventional composite pavement, the design procedures were followed to design composite pavement structures based on the same input parameters such as traffic and design life which is from various agencies as mention previously. The parameters used are as followed as Orlando Nunez (2007) recommended are shown in Table 1 and Table 2 shows the typical values used for the material properties of each layer used in composite pavement structures [4][7] [10], as well as Table 3 shown the materials properties used for StormPav.  However, for analysis of temperature gradient reduction of a rigid slab with an HMA overlay, two equation is used which is obtained in the [8], the study were derived as a function of the thickness of the asphalt layer for both a dense asphalt concrete surface and a porous asphalt concrete surface.
where, λ = Reduction factor h p = thickness of asphalt surface course (cm) Only StormPav and Conventional Composite Pavement are being compared for this part. Since the thickness of asphalt conventional composite pavement is greater than StromPav, thus to calculate the reduction factor for HMA layer for conventional composite pavement is using equations (1) and StormPav is using equation (2). The thickness of the asphalt surface course varies 4 cm to 10 cm is used in both equations. The calculation is as followed.

Fatigue Behaviour
The reduction in stresses at the bottom of the rigid layer is apparent as shown in Figure 4. The use of a thicker layer thickness would significantly increase the fatigue life of the base. A stress-ratio plot,  Figure 5 was created to show how the stress ratio would change as the thickness of the rigid base layer increases. From the graph, it is shown that the StromPav has the longest fatigue life than rigid and conventional composite pavement. Although StormPav has fewer layers and thinnest PCC base, compare to these two pavements, but yet the StormPav produce less stress at the bottom layer. This is the advantage monolithic characteristic of StormPav where it is able to develop of traffic-load-induced critical tensile-stress at the bottom of rigid base thus providing compression made in HMA. Preservation of the structural integrity of rigid base ensuring long-life of the pavement.   Figure 6 shows that how severe the rut depth for each pavement under certain ESALs value. As the number of load repetitions increased, greater rut depths were computed in the HMA layer. It is found that the rut depth of StormPav is still under 0.5 inch although it reaches 70,000,000 ESALs, whereby conventional composite and flexible pavement are already under the critical value of rut depth even before they even reach 50,000,000 ESALs. This was an expected outcome because the high rigidity of the base does not allow any significant vertical deformation to occur. Thus, the HMA layer absorbs all the vertical strains and deforms itself. Since StorrmPav is made of Self-compacting concrete (grade 50), therefore StormPav has better rigidity compared to those two pavements.   Figure 7 shows a sensitivity analysis involving the increment of the thickness of the HMA layer and the reduction factor magnitude for the temperature gradient of a concrete slab. This shows that the reduction factor for StromPav is smaller than conventional composite pavement. The hollow cylinder of StromPav provides ventilation and cooling system within the StromPav make it able to withstand the high temperature.

Summary
From the result, the summary is made as shown in Table 4. The StormPav has the best resistance to rutting/deformation followed by rigid and conventional composite pavement then lastly flexible pavement. For lifespan, StormPav has the greater lifespan followed by conventional composite, rigid and flexible pavements. Therefore, in term of maintenance and cost, StromPav is able to provide the easiest and low maintenance cost followed by both rigid and conventional composite which are provided easy maintenance with low cost, lastly flexible pavement provides the difficult and high maintenance cost. Whereby, the reduction factor of the temperature gradient between conventional composite and StormPav composite pavement, it is shown that StromPav is able to provide a lower temperature gradient reduction than conventional composite pavement.

Conclusions
Based on the result presented previously, the conclusions of the sensitivity analysis of the StormPav Composite pavement are drawn as followed:  From fatigue behaviour analysis, it was found that the StormPav composite pavement has the longest fatigue life compared to traditional pavements which are rigid and conventional composite pavement.  For resistance to rutting or deformation analysis, StormPav has the best resistance behaviour among other pavements; the unique structure and monolithic characteristic of StormPav are the main contributions.  The temperature gradient reduction of StormPav with HMA layer is smaller than conventional composite pavement with HMA layer, which means that StormPav has bigger resilience toward heat or high temperature compared to conventional composite pavement. In other words, StormPav indeed has more advantages than typical composite pavement.
Therefore, from these outstanding performance and result of sensitivity analysis, the StormPav composite pavement system has proven to have the potential to become a cost-effective pavement. Nevertheless, this new technology is still under research and adapting to industry standard. There are limitations to this technology, and it should only be used in appropriate situations. For example, StormPav composite pavement is not suitable for installation on the hilly road. The benefits, however, are clear. This technology allows for strong performance, provides the smoothness and sound control that a full HMA pavement has as well as still contribute to the same benefit as composite pavement and strength but able to minimize the usage of materials in the composite pavement. It is also easier to maintain and allows for the more recycled product to be used in the PCC base. It will likely be a technology that society will see implemented more and more in the future