![]() The DOT has renamed these as cement-bound material categories 1, 2 and 3 (CBM1, CBM2 and CBM3). Soil cement, cement-bound granular material and lean concrete are all categories of the group known as cement bound material (CBM). The grades of concrete covered in the DOT Specification (Clause 1001) range from those suitable for unreinforced and reinforced slabs to Cement Bound Granular Material Category 4.Ĭoncrete for road pavements will be covered under the Rigid Road construction. The composition of rolled asphalt for road base construction is a mixture to BS 594, containing 65% of coarse aggregate and normally made with 50 or 70 pen bitumen.Ĭlause 1036 Cement-bound granular material, category 1 (CBM 1)Ĭlause 1037 Cement-bound granular material, category 2 (CBM 2)Ĭlause 1038 Cement-bound granular material, category 3 (CBM 3)Ĭlause 1039 Cement-bound granular material, category 4 (CBM 4) Rolled asphalt is the oldest established bituminous material used for road base construction and has load-spreading properties superior to those of other flexible road bases. Rolled Asphalt to BS 594 (DOT Clause 904) It is obtained from the standard penetration test which is described in Section 10.20. ‘Pen’ is the abbreviation for ‘penetration grade’ and is a measure of the hardness of a bitumen binder. ‘Evt’ is the abbreviation for ‘equi-viscous temperature’ which is the temperature in degrees Celsius at which a tar a has a viscosity of 50 seconds as determined by the British Standard Test (see Section 10.21). 50,54 or 58☌ evt tar, or 50 pen, 100 pen or 200 pen bitumen. The main requirements in the composition of the dense macadam for use in road bases are that the materials have a fines content (aggregate passing 3.35 mm sieve) of 38% and are made with high-viscosity binders, i.e. The need for strong but truly flexible bases that will not crack has led to the use of these dense bituminous materials. ![]() Care should be taken to keep the moisture content within the optimum limits drying out, or excess moisture will have a serious detrimental effect.ĭense Roadbase Macadam to BS 4987 (DOT Clauses 902/903) ![]() The material is usually laid in compacted layers not exceeding 200 mm, the aggregate grading being within the stated limits. The purpose of the water is not so much to make a ‘wet’ mix as a ‘damp’ mix, with the result that segregation during transport and laying is minimized, while at the same time the material is more easily compacted. This is a ‘plant manufactured’ material using crushed rock or slag accurately graded and batched, and mixed with 2-6% water according to the nature of the aggregate. Μ = micrometer = one millionth of a metre The Table below shows the grading requirements and variations between type 1 and type 2 stone. This is a much smaller sized material than type I, therefore natural sand and gravels may be used as this material. This has to be crushed rock, slag or other hard materials graded as follows
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