LIST OF EQUATIONS
2. Chapter 2 Impact of Climate Change on Pavement Resilience Resilience
2.4. Pavement Deterioration
2.4.2. Pavement Deterioration Distress Risks
2.4.2.1. Cracking
One of the fundamental phenomena that occur on the surface of the flexible pavement, as a failure sign, is cracking. Moffatt and Hassan (2006) stated that cracking should be taken into consideration as a vital element regarding new pavement design
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thickness or rehabilitation activities, especially on overlaying an existing pavement.
According to Alaswadko et al. (2016), cracking is a very active segment which gives a high weight when assessing pavement condition. Cracks are a sign of pavement defect.
Qiao (2015) introduced cracking as a phenomenon that may appear either as small openings or partial fractures. Such cracking can be seen on pavement surfaces or bottoms of asphaltic layers. Fwa (2006) described cracks as “fractures [that] exist on the pavement surface in various forms ranging from single cracks to interconnected patterns”. He also added that the main reasons for cracking are fatigue failure of the asphalt concrete, shrinkage, deformation, crack reflection from underlying pavement layers and poor construction joints of the asphalt concrete, and daily temperature cycling. AASHTO (1993) defines cracks as having a minimum length of 25 mm and a minimum width of 1 mm (NCHRP 2004). Cracks can result from traffic loading, environmental impact or both. Commonly, cracks spread on the pavement structure by two methods: top-down propagation and bottom-up propagation. In practice, if the cracks appear on the surface, the continuous load will make them wider, and with time this creates a path; thus, infiltration of water penetrates the pavement sub-layers and finally accelerates pavement deterioration to failure (Rohde 1995a; NCHRP 2004).
There are several types of cracks (see figure 2-6). For example, the NCHRP (2004) defined fatigue cracking, longitudinal cracking, and transverse cracking and block cracking. Park et al. (2008) defined longitudinal cracking as it “consists of cracks or breaks that run approximately parallel to the pavement centreline and is measured as the total length in linear feet per road segment". Moreover, alligator cracking or fatigue can be classified as significant structural distress. Such cracks can be considered as a series of longitudinal and interconnected cracks caused by repeated traffic loading, leading to a severely damaged road (Huang 2004). This phenomenon occurs because of repeated bending stresses on the top layer. Consequently, over time, cracks occur at the bottom of the asphalt layer, leading to surface deficiency.
The traffic loading and environmental impact are the main factors for cracking (Moffatt and Hassan 2006). Cracking can be generated from traffic loads and overstressing from heavy vehicles (more details were provided earlier, in 2.4.1.3 Risk due to traffic loading). Moreover, the impact of environmental conditions leads to
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pavement structure moisture fluctuation as well as to the expansion of subgrade soils.
Oxidation or chemical shrinkage is also a sign of environmental impact (see section 2.4.1.4 Risk due to environmental loading for more details).
On the other hand, the rate of pavement deterioration will increase dramatically in cases where widespread cracking occurs in pavement surface layers. The reason why pavement deterioration speeds up is because water is allowed to penetrate the pavement layers, which eventually will weaken both asphaltic subgrade layers (Paterson 1987). In other words, Paterson (1987) defied cracking in two stages. Stage one is the initiation stage. In this phase, the cracking starts to appear on the pavement surface after construction due to reasons discussed earlier. Then, the second stage, called the progression stage, begins. Cracking starts to develop gradually both vertically (widening) and horizontally (extending over the surface area). The climate change phenomenon worsens the rate of pavement deterioration in the form of cracking. More details of the impact of climate change on the pavement were discussed earlier in this chapter, in section 3.4.1.
Figure 2-6: Example of cracking types by Fwa (2006)
44 2.4.2.2. Rutting
Papagiannakis and Masad (2012) described rutting as a phenomenon that appears in wheel paths of the pavement segment. It usually deforms as longitudinal depressions in the pavement. Such events result from structural failure of the sub-layers under wheel loadings. Paterson (1987) presented another description of surface rutting.
He stated that rutting appears in the shape of plastic flow of the asphaltic material generated from stress. Fwa (2006) defined rutting as permanent deformation in the wheel path. Rutting can result for many reasons such as unstable hot mix asphalt (too much asphalt or too soft asphalt binder), densification of hot mix asphalt (poor compaction during construction) or deep settlement in the subgrade (drainage or weak subgrade). Technically, stress that occurs as a result of the traffic load that exceeds the shear strength of the asphaltic material is another reason for surface rutting. TRL (1993) stated that the increase in axle loads, channelised traffic, high maximum temperatures, and slowing and stopping of travelling vehicles could shape the rutting phenomenon.
However, Morosiuk, Riley and Odoki (2004) argued that those factors are not the leading cause of rutting as these elements are always taken into consideration by pavement designers. Therefore, they suggested taking asphalt properties into account as a crucial element. Table 2-6 summarises the influence of asphalt material on rutting failure (Sousa, Craus and Carl 1991).
Table 2-6: Implication of material properties and other factors on rutting (Sousa, Craus and Carl 1991)
Material Properties/Factor Change in Material Properties Resistance of Asphalt Mixture to Rutting
Binder Stiffness increase increase
Air Void Contents increase decrease
Voids in Mineral Aggregate increase decrease
Temperature increase decrease
State of Stress/Strain increase in tyre pressure decrease
Load Repetition increase decrease
Rutting could occur at two levels, either on lower layers of the pavement or upper pavement layers. It is believed that, if the rutting is wide and evenly-shaped, then it can be classified as a failure in the pavement lower layers, whereas narrow and sharp
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ruts indicate pavement upper layer failure (CASRA 1992). Byrne and Aguiar (2010) stated that rutting can result from many factors such as climate change. For example, the consequences resulting from climate change impact can either reduce or magnify the cost of road construction and maintenance costs, depending on the location and area (Chinowsky, Price and Neumann 2013). Therefore, in this research, rutting and cracking distress are studied in conjunction with the change in roughness. More details are provided in Chapter 5 section 5.4 and Chapter 6 sections 6.2 and 6.3. More details on the impact of climate change on the pavement are also provided in Chapter 3 section 3.2. A considerable amount of literature on pavement failure has been discussed. A summary of the main and sub-risks is provided in Table 2-7. It is proposed to use this and the earlier tables in designing the questionnaire. More details are provided in Chapter 5.
Table 2-7: Generic pavement failure developed by the author
Code Sub-Risk Factors Main Risk Factor Evidence
S.1 High volume of heavy trucks R.1 Traffic Loading Lin et al. (2005)
S.2 Axle group type R.1 Traffic Loading Cebon (1999)
S.3 Tyre configuration R.1 Traffic Loading Cebon (1999)
S.4 Gross vehicle mass R.1 Traffic Loading Cebon (1999)
S.5 Dynamic wheel loading R.1 Traffic Loading Cebon (1999)
S.6 High traffic loading (all vehicles type)
R.1 Traffic Loading Sen (2012)
S.7 Vehicle speed R.1 Traffic Loading Mikhail and Mamlouk
(1998)
S.8 Precipitation R.2 Climate Change Schlotjes (2013) and
Alaswadko (2016)
S.9 Weathering R.2 Climate Change Schlotjes (2013) and
Alaswadko (2016) S.10 High temperature R.2 Climate Change Schlotjes (2013) and
Alaswadko (2016) S.11 Low temperature R.2 Climate Change Schlotjes (2013) and
Alaswadko (2016)
S.12 Drainage R.2 Climate Change Schlotjes (2013) and
Alaswadko (2016)
R.5 Pavement ageing R.2 Climate Change Roberts and Martin (1998)
S.14 Increased oxidation R.2 Climate Change Roberts and Martin (1998) S.15 Increased viscosity and softness R.2 Climate Change Roberts and Martin (1998) S.16 Increased brittle of asphaltic layer R.2 Climate Change Roberts and Martin (1998) S.17 Increased moisture/excess water R.2 Climate Change Harvey et al. (2004) S.18 Material quality and properties
(Aggregate/soil)
R.3 Pavement Composition
Zuo, Drumm and Meier (2006)
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S.19 Pavement thickness R.3 Pavement
Composition
Harvey et al. (2004) S.20 Availability of material R.3 Pavement
Composition
Pearson (2011) S.21 Bitumen supply and quality R.3 Pavement
Composition
White and Embleton (2015) R.1 Traffic loading R.4 Pavement Strength Pearson (2011) S.22 Insufficient value of structural
number (SN)
R.4 Pavement Strength Pearson (2011)
R.2 Climate change R.5 Pavement Ageing Harvey et al. (2004)
R.1 Traffic loading R.5 Pavement Ageing Harvey et al. (2004) R.6 Subgrade soil R.5 Pavement Ageing Harvey et al. (2004) R.8 Maintenance R.5 Pavement Ageing Harvey et al. (2004) S.17 Increased moisture/excess water R.6 Subgrade Soil Jones and Jefferson (2012) S.13 Selection of construction soil R.6 Subgrade Soil Austroadds (2018) S.17 Increased moisture/excess water R.7 Drainage Haas, Hudson and Zaniewski
(1994)
S.23 Insufficient drainage system R.7 Drainage Haas, Hudson and Zaniewski (1994)
S.24 Delay maintenance R.8 Maintenance Harvey et al. (2004) S.25 Maintenance priorities/plan R.8 Maintenance Harvey et al. (2004) S.26 Limited budget R.8 Maintenance Adlinge and Gupta (2013) S.27 Design and specification R.9 Construction Quality Bubshait (2002) and Abu El-
Maaty, Akal and El- Hamrawy (2016) S.28 Construction process R.9 Construction Quality Bubshait (2002) S.29 Construction management R.9 Construction Quality Abu El-Maaty, Akal and El-
Hamrawy (2016)