FLEXIBLE PAVEMENTS - RHODESIA

THE MAJORITY OF PAVEMENT BASES IN RHODESIA ARE OF RESIDUAL GRAVEL. THE DEPOSITS ARE LOCATED BY AIR PHOTO INTERPRETATION. ALL MATERIAL WITH A TRIAXIAL CLASS EXCEEDING THREE IS REJECTED, DOWN-GRADED TO SUB-BASE OR STABILIZED. TRIAXIAL TESTS ARE MADE ON LIME STABILIZED MATERIAL. CEMENT STABILIZATION GIVES A CLASS OF LESS THAN 1-2 PERCENT OF CEMENT OR LIME, USED WITH SUBSTANDARD GRAVELS AND CEMENT STABILIZED GRAVEL. ON MAIN ROADS A MINIMUM COARSENESS INDEX OF 35 IS MANDATORY. A DENSITY REQUIREMENT OF 100 PERCENT HIGHER STANDARD MAXIMUM DENSITY IS SPECIFIED AND ACHIEVED. WHEN MATERIAL IS TRULY LATERITIC, PLASTICITY REQUIREMENTS ARE RELAXED BY 50 PERCENT. ALTHOUGH ONLY 2 PERCENT OF CEMENT HAS BEEN GENERALLY USED, CRACKING IS QUITE EXTENSIVE, THOUGH NOT ALL STABILIZED BASES HAVE CRACKS. THE OCCURRENCE OF CRACKS IN FLEXIBLE PAVEMENTS, MANY OF WHICH DEVELOPED IN THE FIRST FEW DAYS IRRESPECTIVE OF SHEARING, IS INEVITABLE REFLECTING THE HIGH YOUNG'S MODULUS OF A THIN SEMI-RIGID BASE OVER THE RELATIVELY FLEXIBLE SUB-BASE WITH A LOW MODULUS. ON FARM-TO-MARKET ROADS SINGLE OR SPLIT SEAL SAND SURFACE TREATMENTS, USING RIVER SAND WITH MC3, ON THE PRIMED BASE, ARE USED, AND THE GRADING OF SUCH SAND IS NOT CRITICAL. ON ROADS WHERE THE TRAFFIC EXCEEDS 100 VPD A SLURRY SEAL OF EMULSION PREMIX WITH PIT SAND OR CRUSHER DUST IS PREFERRED. ON MORE HEAVILY TRAFFICKED ROADS TWO COAT STONE SURFACE TREATMENTS ARE USUALLY EMPLOYED ABOVE THE PRIMED BASE. THE MAJORITY OF SOILS IN RHODESIA EXIST AT A DENSITY OF ABOUT 85 PERCENT AASHO MAXIMUM DRY DENSITY. BEING RESIDUAL THEY POSSESS A STRUCTURE WHICH IMPARTS CONSIDERABLE STRENGTH IN THE DRY STATE AND THEY RESIST COMPACTION UNDER TRAFFIC LOADINGS. HOWEVER, DURING THE RAINS THEY WET ABOVE OPTIMUM AND UNDER THE VIBRATION OF TRAFFIC ARE LIABLE TO COLLAPSE UNLESS THEY ARE VERY COHESIVE. SCRAPERS WERE RUN OVER ROADBEDS AND FILLS PROVIDING A SUFFICIENT COMPACTION IN MANY AREAS. IT IS A PRACTICE TO ROLL ALL FORMATIONS DURING THE RAINY SEASON AHEAD OF CONSTRUCTION.

• Supplemental Notes:
  • No Iii-19, 9 PP, 2 TAB
• Authors:
  • Mitchell, R L
• Publication Date: 1967

Media Info

• Serial:
  • Perm Intl Assoc Road Congresses Proc
  • Publisher: Xiiith Congress, Tokyo

Subject/Index Terms

• TRT Terms: Aerial photography; Base course (Pavements); Calcium oxide; Cement treated soils; Climate; Compaction; Dry density; Excavating equipment; Flexible pavements; Gravel; Laterites; Modulus of elasticity; Pavement design; Paving; Photointerpretation; Plasticity; Sand; Secondary roads; Slurry seals; Stabilized materials; Subbase (Pavements); Surface treating; Traffic; Triaxial shear tests
• Uncontrolled Terms: Cement treated bases; Scrapers (Construction equipment); Subbase
• Old TRIS Terms: Air photointerpretation
• Subject Areas: Construction; Geotechnology; Highways; Operations and Traffic Management; Pavements;

Filing Info

• Accession Number: 00205539
• Record Type: Publication
• Files: TRIS
• Created Date: May 21 1994 12:00AM