Performance evaluation of pavements with cement stabilized layer using MEPDG program and LTPP data

Khan, Shahbaz (2021) Performance evaluation of pavements with cement stabilized layer using MEPDG program and LTPP data. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The spring season causes melting of wintry ice in pavement structures. Therefore, transportation agencies use axle load limits to protect the pavement from deterioration during springtime. The use of cement treated base (CTB) in the pavement structure can provide a prospect to overcome this problem. Studies conducted in U.S., South Africa, and India suggests that the use of CTB improves overall performance of pavement structure. In the present work, long term pavement performance (LTPP) data from U.S. and Canada for pavement sections with cement treated base were studied. To better understand the design performance of cement-treated pavement, a mechanistic empirical pavement design guide was used and road sections with different climatic conditions were investigated. A parametric study consisting of seven variables, each at two levels (high and low) were considered. These included asphalt thickness, cement treated base thickness, elastic modulus of cement treated base layer, modulus of rupture, crack spacing, traffic, and speed along with the following three categorical variables: subgrade (coarse and fine), moisture (wet and dry), and temperature (freeze and no freeze). Factorial analysis consisting of a 2ᵏ design of resolution V was considered in the design of the experiment, and a total of 128 factors were considered for the analysis. All the combinations were run in the Mechanistic-Empirical Pavement Design Guide (MEPDG) by AASHTOWare and response variables such as international roughness index, total permanent deformation, asphalt layer rutting, asphalt total fatigue cracking (bottom-up cracking+ reflective cracking), asphalt total transverse cracking (thermal cracking + reflective), asphalt thermal cracking, and top-down asphalt cracking were considered. The response was analyzed using DoE and the factors that affect the performance of CTB pavement were determined. The results are presented for each response and all the assumptions of the response are met. Furthermore, apart from the best suited factors for pavement design, the MEPDG results suggest that the CTB layers' reflective cracking is a major distress in the design of these pavements. In general, surface cracks follow the same pattern as cracks in the base, and are therefore called "reflection" cracks. As stated before, the use of CTB design can provide a chance to improve the loading condition during the spring season. However, the stress concentrations and cracking in the base layer can develop on top of the asphalt surface as well. The failure of semi-rigid pavements due to reflective cracking is somewhat discouraging. The literature suggests using geotextile, aggregate interlayer and chip seal between the CTB layer and asphalt layer as a potential solution to the problem. In the present research, the use of aggregate interlayer was attempted to solve this problem. This type of pavement system is named Inverted Pavement and is used in only a few states in the United States such as Louisiana. However, the AASHTOWare software, which is the most popular pavement design software in the U.S., has some issues in terms of versatility of the pavement structure. To be specific, the MEPDG program can not analyze the performance of an inverted pavement system. Therefore, to better understand the use of this pavement structure, a different software was used. A pavement software named CROSSPAVE which can run the aforesaid structure was employed. The results of MEPDG are superior to CROSSPAVE as it gives performance in terms of distress that occur in the pavement system while the CROSSPAVE output only gives stress and strain. These strains/stresses were correlated to the distresses in terms of the number of repetitions using empirical equations. Therefore, another parametric study was carried out to understand the factors affecting the inverted pavement stress/strains at critical locations. Similar to the previous analysis, the DoE analysis was carried and critical factors affecting the design of inverted pavement are listed.

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