Thursday, 18 July 2019

GRANULAR MATERIAL FOR SUB BASE | Road Works


 GRANULAR MATERIAL FOR SUB BASE  


A. Granular material for use in sub-base courses shall be a naturally occurring gravel, blended as necessary with fine or coarse material and screened to produce the specified gradation. Crushing of natural granular material shall not normally be required, unless for meeting the grading requirements, producing a higher quality sub-base with improved mechanical stability or when shown on the Drawings.

B. Gravel shall consist of hard, durable and sound rock fragments, free from dirt, organic matter, shale and other deleterious substances.

C. Granular materials for sub-base shall meet the requirement of class A or B as shown in table 3.1.2, when tested in accordance with AASHTO T-27 after dry mixing and just before spreading and compacting. The class of granular material to be used shall be as shown on the Drawings or as selected by the Engineer. The actual gradation shall be continuous and smooth within the specified limits for each Class.

 Table 3.1.2: Gradings of Granular Material by Class  

Sieve Designation                             Percent  by Weight Passing 
(Square Openings)                      Class A                          Class B 
50 mm   (2 in.)                            100                                   100 
25 mm (1 in.)                               -                                  75-95
9.5 mm (3/8 in.)                       30 – 65                            40 - 75
4.75 mm (No. 4)                        25 – 55                            30 - 60  
    2.00 mm (No. 10)                       15 – 40                            20 - 45      
0.425 mm (No. 40)                    8 – 20                              15 - 30 
0.075 mm (No . 200)               2 – 8                                 5 - 20 
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D. The material shall contain a maximum 5% clay content at any stage of construction when tested in the Hydrometer Test in accordance with AASHTO T88.

E. The loss in weight of granular material shall not exceed 50% after 500 revolutions, when tested in accordance with AASHTO T 96 (Los Angeles Abrasion Test).

F. The granular material shall have a 4-day soaked CBR of not less than 30 when compacted at 100% of modified proctor AASHTO (T 180-D) and tested in accordance with AASHTO T 193.

G. When tested for soundness in accordance with AASHTO T 104, the material shall not show signs of disintegration and the percentage loss in weight after 5 cycles shall not exceed 12 % in the case of the sodium sulphate test and 18% in the case of the magnesium sulphate test.

H. The portion of granular material, including any blended material, passing the 0.425 mm (No. 40) mesh sieve shall have a liquid limit (L.L.) of not more than 25 and a plasticity index (P.I.) not greater than 6 when tested in accordance with AASHTO T 89 and T 90. 

I. If additional fine material is required to correct the gradation the granular material, or for adjusting the L.L. or P.I. of the fraction passing 0.425 mm (No 40) sieve, it shall be uniformly blended and mixed with the granular material. Additional fine material for these purposes shall be obtained from the crushing of stone, gravel, or slag, if naturally occurring fine material is not available

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