Types of base course
1-Crushed limestone base course.
2-Crushed gravel base course.
3-Vibratory -compacted Macadam stone base course..most common used (crushed limestone and crushed gravel)
Crushed-Limestone and Crushed-Gravel Base Course
The material for the crushed limestone or crushed gravel base course shall be composed of hard sound, durable crushed limestone, particles free from thin elongated, soft and disintegrated material or other objectionable matter for crushed limestone and crushed gravel grading as determined by (AASHTO) passing by weight. (sieve:37.5mm %100 pass)…(sieve:25mm(1in)%80-%100 pass )…(sieve:12.5mm %50-%80 pass)…(sieve:NO.4(4.75mm) %30-%60 pass) …(sieve:NO.40 (0.425mm) %10-%30 pass)…(sieve:NO.200 (0.075 mm) %5-%15 Pass).
The difference between (crushed limestone and gravel) from the (sieve NO.200 (0.075 mm)) crushed limestone:%5-%15 passing. crushed gravel: %5-%12 passing. The abrasion loss of the crushed limestone as determined by AASHTO shall not exceed 45%. maximum liquid limit =%25 maximum plasticity index =%0-%4 The California bearing ratio(CBR) of the base course when tested in accordance with ASTM shall not be less than %80 minimum compaction =%98 MDD Tolerance of base course layer level:- +8mm to -20mm
Notes
1- The moisture content shall be OMC +/- 2-3%
2- Sand Equivalent shall be not less than 45%
3- The stone/aggregate shall have at least 2-3 crushed faces
4- The soundness shall not exceed 2-3% When it tested using chloride calcium or Sodium sulphate
5- Water Absorption shall not exceed 2-3%
