13a. Road Construction Methods.pptx

Road Construction Methods.

1. Road construction methods (1) Roman Road Construction During the roman empire, roads were constructed in large scale and earliest techniques known are those of Roman Roads. 1 Dr. Rizwan Memon

2. The main features of the Roman Roads are: They were built straight regardless of gradient. They were built after the soft soil was removed and a hard strata was reached. The total thickness of the construction was as high as 0.75 to 1.2 m. 2 Dr. Rizwan Memon

3. Roman Pavement Structure Near Radstock, England (after Collins and Hart, 1936) The above construction should have been much stronger than what was required for the animal drawn vehicles in those days. 3 Dr. Rizwan Memon

4. A typical Roman road structure, as seen in the United Kingdom, consisted of four basic layers (Collins and Hart, 1936): Summa Crusta (surfacing).  Smooth, polygonal blocks embedded in the underlying layer. Nucleus.  A kind of base layer composed of gravel and sand with lime cement. Rudus.  The third layer was composed of rubble masonry and smaller stones also set in lime mortar. Statumen.  Two or three courses of flat stones set in lime mortar. 4 Dr. Rizwan Memon

5. (2) Tresaguet Construction Pierre Tresaget (1716-1796), developed an improved method of construction in France. The main features of his proposal was that the thickness of construction need be only in the order of 30 cm. Due consideration was given by him to sub-grade moisture condition and drainage of surface water. The top wearing course was made of smaller stones and compacted to a thickness of 5 cm at the edge and gradually increased towards the center with a cross slope of 1 in 45. 5 Dr. Rizwan Memon

6. TRESAGUET ROAD (1775) 6 Dr. Rizwan Memon

7. (3) Telford Construction Thomas Telford began his work in early 19 th century. He insisted on providing a definite cross slope for top surface of the pavement by varying the thickness of foundation stones. Telford's pavement section was about 350 to 450 mm in depth and generally specified three layers. The bottom layer was comprised of large stones 100 mm wide and 75 to 180 mm in depth. It is this specific layer which makes the Telford design unique.  7 Dr. Rizwan Memon

8. On top of this were placed two layers of stones of 65 mm maximum size (about 150 to 250 mm total thickness) followed by a wearing course of gravel about 40 mm thick.  8 Dr. Rizwan Memon

9. John McAdam put forward an entirely new method of road construction in 1815. McAdam construction introduced the use of angular aggregates. Stresses due to wheel load of traffic gets decreased at the lower layers of the pavement. Importance of Sub-grade drainage and compaction. Sub-grade being the lowest portion be prepared and kept drained to carry the transmitted load of the pavement. (3) McAdam Construction 9 Dr. Rizwan Memon

10. MACADAM ROAD (1815) 10 Dr. Rizwan Memon

11. Angular aggregate (hand-broken with a maximum size of 75 mm) were placed in two layers for a total depth of about 200 mm On top of this, the wearing course was placed (about 50 mm thick with a maximum aggregate size of 25 mm) 11 Dr. Rizwan Memon

12. The total depth of a typical MacAdam pavement was about 250 mm. The term "macadam" is also used to indicate "broken stone" pavement. MacAdam realized that the layers of broken stone would eventually become "bound" together by fines generated by traffic 12 Dr. Rizwan Memon

13. MODERN TRENDS IN PAVEMENT DESIGN 13 Dr. Rizwan Memon

14. Further development of McAdam Construction. In Water Bound McAdam construction (WBM), known after McAdam technique, the broken stones of the base and surface course are bound by the stone dust in presence of moisture. A tar macadam road consists of a basic macadam road with a tar-bound surface. Bituminous McAdam Roads Road mixes, refer to the mechanical mixing of asphalt and aggregate directly on the road bed to form a thin 25 - 100 mm wearing course. 14 Dr. Rizwan Memon

15. Sheet Asphalt Roads The first pavements made from true hot mix asphalt (HMA) were called sheet asphalt pavements.  The HMA layers in this pavement were premixed and laid hot.  A wearing course 40 to 50 mm thick composed of asphalt cement and sand. A binder course about 40 mm thick composed of broken stone and asphalt cement. 15 Dr. Rizwan Memon

16. Cement Concrete Roads were designed to take up the heaviest loads in adverse soil and climatic conditions and to last for long service life. They are known to give a good and even riding surface. Cement Concrete Roads 16 Dr. Rizwan Memon

17. Pavement design : 1) Mix design of material 2) Thickness design of structural layers Pavement design philosophy: 1) Empirical 2) Mechanistic ( Theoretical , Analytical, Structural) 3) Mechanistic-Empirical 17 Dr. Rizwan Memon

18. Design Approaches Road Note 29 (TRRL, UK 1960, 1970, Empirical) Road Note 31 The Asphalt Institute Manual Series AASHTO Guide for Design of Pavement Structures 18 Dr. Rizwan Memon