CHAPTER 1 PRELIMINARY1.0 INTRODUCTION A flexible pavement structure typically consists of layers of different materials that increase with strength as you move towards the surface (weakest layer on the bottom , strongest layer at the surface). A flexible pavement relies on a layered system to distribute traffic loads over the sub-grade. The load carrying capacity of a flexible pavement is brought about by the load-distributing characteristics of each layer in the layered system. The layers of a flexible pavement structure typically consists of hot mix asphalt (HMA) at the surface, with the stabilized base, base course gravel, and/or sub-base course gravel. Each of these layers contributes to
structural support and drainage. The surface course (typically an HMA layer ) is thestiffest (as measured by resilient modulus) and contributes the most to pavementstrength .The underlying layers are less stiff but are still important to pavementstrength as well as drainage and frost protection . A typically structural design resultsin a series of a layers that gradually decreases in material quality with depth. Figure 1.1 : Basic Flexible Pavement Structure The surface course is the layer in contract with the traffic loads and normally contains the highest quality materials. It provides characteristics such as friction, smoothness, noise control, rut and shoving resistance and drainage , In addition , it serves to prevent the entrance of excessive quantities of surface water into the underlying base , sub-base and sub-grades (NAPA , 2001) . This top structural layer of material is sometimes subdivided into two layers (NAPA , 2001) : i. Wearing Course . This is the layer in direct contact with the traffic loads . It is meant to take the brunt of traffic wear and can be removed and replaced as it becomes worn. A properly designed (and funded)
preservation program should be able to identify pavement surface distress while it is still confined to the wearing course. This way, the wearing course can be rehabilitated before distress propagates into the underlying intermediate / binder course.ii. Intermediate/ Binder Course. This layer provides the bulk of the HMA structure. It’s chief purpose is to distribute load.The base courses are usually constructed out of:i. Aggregate. Base course are most typically constructed from durable aggregates (see Figure 1.1) that will not be damaged by moisture or frost action. Aggregates can be either stabilized or unstabilized.ii. HMA. In certain situations where high base stiffness is desired, base courses can be constructed using a variety of HMA mixes. In relation to surface course HMA mixes, base course mixes usually contain larger maximum aggregate sizes, are more open graded and are subjected to more lenient spec
Figure 1.2 : Limerock Base Course Undergoing Final Grading The sub-base course is between the base course and the sub-grade. Itfunctions primarily as structural support but it can also: i. Minimize the intrusion of fines from the sub-grade into the pavement structure. ii. Improve drainage. iii. Minimize frost action damage iv. Provide a working platform for construction. The sub-base generally consists of lower quality materials than the base course but better than sub-grade soils. A sub-base course is not always needed or used. For example, a pavement constructed over a high quality, stiff sub-grade may not need the additional features offered by a sub-base course so it may be omitted from design. However, a pavement constructed over a low quality soil such as a swelling clay may require the additional load distribution characteristic that a sub-base course can
offer. In this scenario the sub-base course may consist of high quality fill use to replace poor quality sub-grade (over excavation). The sub-grade is considered a part of embankment or natural soil and isthe layer which is 1 meter below the formation level (finished sub-grade surface).It is a layer that provides a platform for materials above it to be constructed. Sub-grade material that is considered suitable road construction. Bitumen as binder material is widely used in flexible pavementconstruction. Bitumen is a residual material which is produced by petroleumdistillation. Bitumen material has a useful characteristic as binder material. Innormal temperature bitumen has semi-solid characteristic and when increase thetemperature, bitumen will be soften and change to liquid. If the temperaturelower down to normal temperature, bitumen will be harden and back to original.Penetration and flash testing are to be used for bituminous grading. Both of theseparameter is a measure of bitumen consistency at certain temperature. When thebitumen to be used in the construction road pavement, bitumen must have theappropriate grade, therefore its consistency will allow the paving work to becarried out smoothly and produce the high quality pavement. Certain test should be performed on each binder that will be used todetermine its properties. Tests are also conducted on the binder material topredict the performance of a bituminous pavement that was constructed usingbitumen, Some test and analysis on bitumen are:
i. Penetration Test ii. Softening Point Testi. Penetration Test This test is to determine the bitumen’s stiffness. In this experiment, the standard depth of the needle into the bitumen can be measured subject to certain conditions specified in the test. Normally the temperature of the bitumen is 25 degree Celsius, the total load is attached to the needle 100 grams and the time for needle penetrates into bitumen is 5 seconds. For the type of soft bitumen, penetration depth is higher than the type of hard bitumen. Therefore, the penetration test is very important and it is widely used in classifying bitumen materials to certain grades. Although the penetration test was defined as empirical testing, the test is useful because it can be handled quickly and easily.ii. Softening Point Test This test is to determine the softening temperature for bituminous material. When the temperature rises, solid bitumen will gradually and imperceptibly change from brittle or exceedingly slow-flowing materials to softer and less viscous liquid. Before bitumen mixed with aggregate to
be used as road pavement material, the condition of bitumen must be soft so that it easily handled for paving works. The easiest way to soften the bitumen is by heating. The softness of bitumen temperature level is when it was tested under certain influence. The commonly performed test for bitumen is ring and ball test. Known that hard grade of bitumen type has a higher temperature level than the soft grade of bitumen. Flexible Pavement Design’s Formula: 1) Vo= ADT x 0.5 x 365 x Pc / 100 2) Vc = Vo [ (1+r)x – 1 / r] 3) Vx = Vi ( 1+ r)x 4) ESA = Vc x e 5) C = I x R x T 6) C = 10 x c 7) n = 8) TA = a1D1 + a2D2 + a3D3Where: ADT = Average Daily Traffic Pc = Percentage of commercial vehicles Vc = Total number of commercial vehicles in one direction Vo = Initial years commercial traffic
r = Rate of annual traffic growth x = design period (year) Vi = Initial daily traffic in one direction I = Ideal hourly capacity R = Roadway factor T = Traffic reduction factor1.1 STATEMENT OF PROBLEM Through some reading and observation, we find out that too much time is taken to determine the minimum thickness and the maximum thickness of the flexible pavement, as it was done through manual calculation. In addition, it is likely possible that calculation error creeps in during the calculation process. If there is any change in the design of flexible pavement, all of the recalculation process should be done at an early stage so that the thickness of flexible pavement and suitability of flexible pavement design is identified early. The thinking of a layman using an automated simple calculation procedure may significantly help out in this process.
1.2 AIM OF THE PROJECT This project is to produce a schematic layout of the calculation to check the suitable measurement in flexible pavement design. The two objectives are: i. To prove that the calculation of Flexible Pavement Design can be calculate by using Microsoft Excel (2007). ii. To develop a software that allows students to compare the result between two method (manually and computerization) as their guidance in learning session.1.3 THE IMPORTANCE OF THE PROJECT The importances of the project are as follow: 1.3.1 Manual design may take longer time compared with computerization design. Thus, at the end of the project, the software (MS Excel) for flexible pavement design thickness is developed that may minimize the time taken in design process. 1.3.2 Generally, the software (MS Excel) also avoid human error made by the students during the calculation because it was developed according to the standard method and all calculation is
computerized. Consequently, the result can be trusted and unarguable.1.4 THE SCOPE OF THE PROJECT The scope for the study is focusing on the thickness design of flexible pavement based on ATJ 1985 Manual. ATJ 1985 Manual is suitable applies to the design of major road where the traffic is medium or heavy. Apart from that, the computer software is verify with the manual calculation to ensure the performance of computer software was satisfactory without any error and provide an accurate result. The project’s scope is getting a manual related to the usage of the Flexible Pavement Design made out for a project, provide a programming procedure with variable options for the flexible pavement design made out for a project. Next, produce a program that meets the needs of the user to compute the thickness and the suitability of the flexible pavement being designed. In this project, no lab work and no site investigation shall be conducted. Printing is to be minimized because going green towards paperless. The project’s scope also includes semester 4, DKA 4C and semester 5, DKA5A students in PUO as respondent.