ROADS ENGINEERING PRACTICE.

ROADS ENGINEERING PRACTICE FLEXIBLE PAVEMENT AND BITUMEN SEALING DESIGN ASSIGNMENT Question 1 (4 marks) a. Design pavement thickness is dependent on both CBR and design traffic, but is more sensitive to one of these two determinants. Which one? Demonstrate this effect by using Fig.8.4. b. For an existing road that is to be reconstructed, describe how you would determine the design subgrade strength (CBR) at the appropriate subgrade moisture content. Question 2 (2 marks) A section of local access road in a country town is being considered for reconstruction. A traffic count has provided the following data:- AADT (total for two lanes) 2,400 vpd Growth rate 4.0 % pa Commercial vehicles 6 % Calculate the Design number of Standard Axle Repetitions for asphalt, cemented material and subgrade, for a pavement containing these materials for a design period of 20 years. Use the values contained in Tables 12.2 and 12.3 in your notes. Question 3 (2 marks) For a section of road, which is not an arterial road or highway, the results of a Benkelman Beam deflection survey when measured at 35oC are:- Deflection – mean 0.90mm – standard deviation 0.25mm Curvature – mean 0.28mm The WMAPT for the site is 25oC. The road is currently surfaced with 50 mm of asphalt. There are no seasonal moisture variations. Calculate the temperature corrected characteristic deflection and curvature for this section of road. Question 4 (6 marks) A section of rural 2-lane road has a pavement in poor condition. It is proposed to leave the alignment unchanged. Options for its reconstruction or rehabilitation are being considered. The following information is available:- Subgrade CBR 6 Characteristic deflection 1.4 mm Characteristic curvature 0.25mm Design traffic loading 106 ESA (a) Rehabilitation by in-situ stabilisation is one option being considered. Testing of the existing pavement material indicates that the addition of 2% of a slow setting lime binder gives the material a modulus of 1,000MPa, resulting in an unbound granular material. Assuming the pavement will be surfaced with a sprayed seal, design the depth of in-situ stabilisation. (b) Another rehabilitation option is granular overlay with a sprayed seal. Design the pavement thickness for this option. (c) Reconstruction by provision of a new granular pavement is another option. Design the total pavement thickness and layer thicknesses for this option, assuming that it will be surfaced with a sprayed seal plus 30mm of asphalt. Question 5 (6 marks) A section of road has been reconstructed. It has a granular pavement and the traffic on the road is 3,600 vpd/lane with 6% heavy vehicles. You have the following materials available for sealing of the road:- • Cutback bitumen binder • Class 170 bitumen and cutter oil • Adhesion agent (1% additive) • 7mm nominal size crushed aggregate, ALD 4mm, precoated and free of moisture, absorption value <1%, angular average shape • 14mm nom. size crushed aggregate, ALD 8.5mm, precoated and free of moisture, absorption value <1%, angular average shape (a) As the newly constructed pavement will be subjected to traffic immediately following surfacing, it will be primer-sealed. Assuming that the road surface temperature at primer-sealing is 20oC on an autumn day, and that the prepared surface condition will be coarse textured. Using the information in RMS Form 395A, design a suitable primer-seal, giving the cold binder application rate, and aggregate application rate. Ball Penetration test is 1.0 mm. Assume no traffic effects. (b) At least 12 months after primersealing, the road will be sealed with a double/double seal. At this time the primerseal will have a uniform bleeding surface texture and ball penetration test value of 2. Use the information in RMS 395K. Design this seal, giving the cold residual binder application rate and the aggregate spread rate for both first and second layer of the seal. (c) During the spray sealing operation, you have four 10m3 capacity aggregate spreading trucks available. Each of the trucks is full of 14mm aggregate and you are about to spread the aggregate on the sprayed binder. Assuming that the seal width is 8m and the aggregate spreading rate is 95m2/m3, what length of road would you set out for the bitumen sprayer to spray with bitumen?

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