The test surface meet four design requirements: 3.2.1.1. It be a dense asphaltic concrete. 3.2.1.2. The maximum chipping size be 8 mm (tolerances allow from 6.3 mm to 10 mm). 3.2.1.3. The thickness of the wearing course shall be 30 mm. ≥ 3.2.1.4. The binder shall be a straight penetration grade bitumen without modification. 3.2.2. Design guidelines As a guide to the surface constructor, an aggregate grading curve which will give desired characteristics is shown in Figure 2. In addition, Table 1 gives some guidelines in order to obtain the desired texture and durability. The grading curve fits the following formula: P (% passing) = 100 · (d/dmax) 1/2 Where: d = square mesh sieve size, in mm dmax = 8 mm for the mean curve = 10 mm for the lower tolerance curve = 6.3 mm for the upper tolerance curve Figure 2 Grading curve of the aggregate in the asphaltic mix with tolerances In addition to the above, the following recommendations are given: (a) The sand fraction (0.063 mm < square mesh sieve size < 2 mm) shall include no more than 55 per cent natural sand and at least 45 per cent crushed sand; (b) The base and sub-base shall ensure a good stability and evenness, according to best road construction practice; (c) The chippings shall be crushed (100 per cent crushed faces) and of a material with a high resistance to crushing; (d) The chippings used in the mix be washed; (e) No extra chippings shall be added onto the surface; (f) The binder hardness expressed as PEN value shall be 40 - 60, 60 - 80 or even 80 - 100 depending on the climatic conditions of the country. The rule is that as hard a binder as possible shall be used, provided this is consistent with common practice; (g) The temperature of the mix before rolling shall be chosen so as to achieve by subsequent rolling the required voids content. In order to increase the probability of satisfying the specifications of paragraphs 2.1. to 2.4. above, the compactness shall be studied not
The test surface meet four design requirements: 3.2.1.1. It be a dense asphaltic concrete. 3.2.1.2. The maximum chipping size be 8 mm (tolerances allow from 6.3 mm to 10 mm). 3.2.1.3. The thickness of the wearing course shall be ≥ 30 mm. 3.2.1.4. The binder shall be a straight penetration grade bitumen without modification. 3.2.2. Design guidelines As a guide to the surface constructor, an aggregate grading curve which will give desired characteristics is shown in Figure 2. In addition, Table 1 gives some guidelines in order to obtain the desired texture and durability. The grading curve fits the following formula: P (% passing) = 100 · (d/dmax) 1/2 Where: d = square mesh sieve size, in mm dmax = 8 mm for the mean curve = 10 mm for the lower tolerance curve = 6.3 mm for the upper tolerance curve Figure 2 Grading curve of the aggregate in the asphaltic mix with tolerances In addition to the above, the following recommendations are given: (a) The sand fraction (0.063 mm < square mesh sieve size < 2 mm) shall include no more than 55 per cent natural sand and at least 45 per cent crushed sand; (b) The base and sub-base shall ensure a good stability and evenness, according to best road construction practice; (c) The chippings shall be crushed (100 per cent crushed faces) and of a material with a high resistance to crushing; (d) The chippings used in the mix be washed; (e) No extra chippings shall be added onto the surface; (f) The binder hardness expressed as PEN value shall be 40 - 60, 60 - 80 or even 80 - 100 depending on the climatic conditions of the country. The rule is that as hard a binder as possible shall be used, provided this is consistent with common practice; (g) The temperature of the mix before rolling shall be chosen so as to achieve by subsequent rolling the required voids content. In order to increase the probability of satisfying the specifications of paragraphs 2.1. to 2.4. above, the compactness shall be studied not