Toward sustainable pavement: Surface Evaluation of Experimental Highway Section Containing Additives

Highway pavements are usually subjected to many types of failures “distresses” since these pavements are exposed to traffic load and weather conditions. Therefore, many agents tried to enhance the asphalt mixes to reduce the possibility and severity of distresses by adding additives to replace small amount of binder (bitumen). SBS in one of the most used additives that been used in many states. In recent years, the SBS has been used in pavement of about 1.2km to be experimental sections within Basra-Baghdad expressway. This paper examines the pavement condition index (PCI) for the experimental section after about six years form been paved and exposed to traffic. So far, only minimal distresses including cracks and potholes were recorded without reducing the initial PCI value of 100. Further work will be followed to examine the mechanical properties of the layers such as the indirect tensile strength and rutting resistance.


Introduction
Highway pavements are usually subjected to many types of failures "distresses" since these pavements are exposed to repeated traffic loading and varying climate changes that introduce stresses.Therefore, many highway agents from many countries tried to enhance the asphalt mixtures properties by adding some additives than increases the ability to withstand the traffic loading and climate conditions [1].According to the literatures [1][2][3][4][5], Styrene-Butane-Styrene (SBS) has been globally used as an additive for asphalt pavements.This resulted in successful application to improves the mechanical properties of mixes such as cracking and rutting resistance.Dziadosz et al. [6] reported that the adding of SBS can slowdown the relaxation process of asphalt as an inverse to the aging process.Zhang et al. [1] used compound additive of SBS and Surfactant additive (SA) during laboratory tests for warm mix asphalt and found that the compound effect produce better rutting and cracks resistance.In Iraq, there were many research work considering enhancing asphalt mixtures using additives.Such research work provide "laboratory" evidence that some modifiers may help in enhancing such mixtures.Al-Shaybani [7] used reclaimed rubber with recycled mixes with different percentages.Khudair and Kadhim [8], through laboratory tests, suggested that the use of Polypropylene granules as an additive to the asphalt binder could enhance Marshal stability and ITS.Similarly, Naser [9] suggested that the use of SBS polymer would improve the ITS of HMA.Ali and Ismaeel [10] used ceramic fiber and hydrated lime as additive to enhance the HMA.Their results suggested an increase in tensile strength and in an index of retained strength. .Aboud et al. [11] claimed that PVC polymer and natural rubber would enhance the mechanical properties of HMA.Alnaieli and Al-Busaltan [12] used Acrylic emulsion (ACR) to enhance semi-flexible mixtures.Their findings suggested that ACR resulted in increasing the compressive strength of such mixes.So far, most researchers suggested significant improvements with their additives under laboratory conditions.No research work in Iraq to consider the effect of such additives in the field (real sites).Someone could argue that the laboratory mixing of asphalt pavement component may be different from real plants that provide production control through mixing and heating.Therefore, there is a need to conduct such experimental highway section containing additives.In addition, there is a need to examine the age effect of polymer since Karakaş [13] suggested that there is a significant change in mechanical properties of HMA with SBS after only one year from being subjected to traffic load.In recent years, the SBS has been used as an additive to replace 6% of asphalt binder to pave experimental highway section with a length of about 1.2 km within Basra-Baghdad expressway that opened for traffic before about six years.This work makes surface evaluation to describe the condition of the highway section and estimates the pavement condition index (PCI).The PCI method is widely applied in description of highways surface.The method provides an evaluation scale based on the quantity and severity of the surface distresses [14][15]

Methodology
This research evaluates the surface condition for an experimental highway section with a length of about 1.2km that paved with additives (SBS polymer).The details of additives percentages used with corresponding to asphaltic layer types are shown in Table 1.Two percentages of 6% and 8% from the weight of asphalt binder that used for asphalt layer with 400m length for each percentage.In addition, there is an extra section with 400m were SBS used with two layers (the surface layer (with 8% SBS) and the binder layer (with 6% SBS) that directly below the surface layer).The section was opened to traffic before about six years as a part of Al-Basra-Baghdad freeway at the location shown in Figure 1 within Al-Diwaniyah province.
The PCI provides an evaluation scale for pavement surface ranging from zero (failed condition) to 100 (perfect condition).Table 2 shows the scale used in the PCI and the corresponding evaluation meaning.

Table 2. PCI rankings
The method translates the distresses types, quantity and severity into deduct values that would be subtracted from 100 (perfect condition) after correction process to estimate the surface condition scale (PCI value in Table 1).The procedure for estimating PCI is described in ASTM D6433 [16].

Result
Pavement condition survey was conducted for the site that containing the surface layers described in Table 1.The survey is to estimate the distresses types, quantity and severity according to the requirement of estimating PCI.The survey conducted for each section length (400m) with different SBS percentage or with different number of layers containing additive.In total, three section with 400m each have been considered.
The survey results are shown in Table 3 for these three sections.So far and as shown in the table.only three types of distresses were recorded namely longitudinal cracks, transvers cracks and potholes.However, the quantity and severity of these failures were minor without affecting the original PCI value of 100.Figures 2 and 3 show typical longitudinal and transverse cracking from the survey.No conclusion could be derived about the effect of additive percentage since all used valued provides perfect PCI.Therefore, further study will be conducted to examine the mechanical properties of pavement mixtures with the given additive percentages and for a case without additive.

Conclusions
This paper addressed the examining the PCI for a freeway segment near Al-Diwaniyah city that paved using SBS additive.the highway der the study was opened to traffic before about six years.Distresses survey was conducted according to the requirements of PCI method.The highway was divided for each 400m length according to the percentage of SBS used as a percent from asphalt binder.So far, only minimal distresses including longitudinal and traverse cracks were recorded without reducing the initial PCI value of 100.Further work will be followed to examine the mechanical properties of pavement such as the indirect tensile strength and rutting resistance.

Table 3 .
The surveying and PCI results for site 1