Wednesday 24 July 2019

Test's for Base Course Material | Base Course




Required Tests and Minimum Repetition for As- Laid Base Course Material



  CONTROL ON SITE AFTER LAYING AND COMPACTION: 

 Required Tests 
 Frequency 
1

2
Gradation of Materials

3
Plasticity Index

4
Test for every 500 m for each layer and lane width and when material source or properties changed.
5
Abrasion

6
Sand equivalent

7
Clay lumps & friable particles

8

9
Thickness
Test for every 1000 m2  and for every layer.









 MEASUREMENT:  

A. Aggregate Base Course shall be measured by the cubic metre of aggregate materials furnished, crushed, screened, mixed with water, placed, spread, compacted and finished, completed, and accepted. Measurements shall be of volumes computed from the cross sections shown on the Drawings and of the field measurements of the area and compacted depth for each Trial Section. 



B. Rates for Aggregate Base Course in Temporary Diversions shall also include for removal and disposal of the sub-base material and reinstatement of the area of the temporary diversion, to the satisfaction of the Engineer, on completion of use.



C.  No measurement shall be made for direct payment of over depth construction, regardless of the Engineer's permission for it to remain in place.



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Tuesday 23 July 2019

AGGREGATES FOR BASE COURSES | Road works

 AGGREGATES FOR BASE COURSES 


A.  Aggregates for use in base course construction shall be either crushed stone or crushed gravel. The fine aggregate shall consist of screenings obtained from crushed stone, gravel or sand. Aggregate shall be washed if necessary to remove excessive quantities of clay, silty clay or salts.

B. Crushed stone shall consist of hard, durable particles or fragments of stone, free from dirt or other objectionable matter and shall contain not more than 8% of flat, elongated, soft or disintegrated pieces.

C. Crushed gravel shall consist of hard durable stones, rocks and boulders crushed to specified sizes and shall be free from excess flat, elongated, soft or disintegrated pieces, dirt or other objectionable matter

D. The method used in the production of crushed gravel shall provide a uniform material quality. The crushing of the gravel shall result in a product having at least 90% by weight of particles with at least one fractured face. All stones, rocks, and boulders of inferior quality occurring in the pit shall be discarded.

E. Any material passing the 4.75 mm (No. 4) sieve and produced in the crushing process may be incorporated in the base material up to the grading limits required for the base course aggregate.

F. Crushed aggregate for base course shall meet the requirements of Class A or Class B gradings as shown in Table 3.1.3 when tested in accordance with AASHTO T 27 after mixing with water, just before spreading and prior to compacting. The class of aggregate to be used shall be as shown on the Drawings or as selected by the Engineer. The actual grading shall be continuous and smooth within the specified limits for each Class. Gap graded aggregate shall not be accepted. If gradings are tested after compaction a tolerance of 3% shall be allowed in the upper limit for the percentage of material passing the 200 sieve.

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Table   Grading of Base Course Aggregate by Class 

                   Sieve Designation                          Percent by Weight Passing
                   (Square Openings)                          Class A                 Class B  
                   50 mm (2 in.)                                    100                           - 
                   25 mm (1 in.)                                 75 - 95                      100 
                   9.5 mm (3/8 in.)                             40 - 75                   50 - 85 
                  4.75 mm (No. 4)                             30 - 60                    35 - 65 
                  2.00 mm (No. 10)                           20 - 45                    25 - 50 
                  0.425 mm (No. 40)                         15 - 30                    15 - 30 
                  0.075 mm (No . 200)                      5 - 20                      5 -15 



G. The amount of the fraction of material passing the No 200 mesh sieve shall not exceed one half of the fraction passing the No. 40 mesh sieve.

H. The loss in weight shall be in the range of 45% after 500 revolutions, when tested in accordance with AASHTO T 96 (Los Angeles Abrasion Test) and the sand equivalent shall be a minimum of 43% when tested in accordance with AASHTO T176.

I. The crushed aggregate base course material shall have a 4-day soaked CBR of not less than 80 when compacted at 100% of modified proctor AASHTO (T180-D) and tested in accordance with AASHTO T 193.

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

K. The portion of aggregate, 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 Plasticity Index (P.I) of not more than 6 when tested in accordance with AASHTO T 89 and T 90. 

L. If additional fine material is required to correct the aggregate grading or for adjusting the L.L. or P.I. of the fraction passing the 0.425 mm (No. 40) sieve, it shall be uniformly blended and mixed with the aggregate material at the crushing plant or by a method approved by the Engineer. Reworking of the material in situ to obtain the specified gradation shall not be permitted. Additional fine material shall only be obtained from the crushing of stone, gravel or natural material. 

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