Up-grading Polished Stone Value (PSV) of Lower Grade Aggregates

As the availability of the road surfacing material, manpower and financial resources become limited, it would be very costly for most of the countries to afford the costs of high quality aggregates [in terms of Polished Stone Value (PSV)] to be used in high frictional demanding locations. It is often believed that the Polished Stone Value of aggregates depends on the process of crushing aggregates. This paper describes a laboratory assessment of the potential for increasing aggregates Polished Stone Value (PSV) of aggregates by adopting simulated methods of crushing aggregates, thereby up-grading Polished Stone Values of lower grade aggregates. The main objective of the work has been to investigate performance in the laboratory condition of aggregates subjected to a mechanical treatment (simulating crushing) to create rougher surface texture to compare with their naturally crushed state, with a view to establishing the suitability of the material to benefit from the type of treatment adopted. Applied methods give a different surface texture from its usual method of crushing, methods adopted are mechanical re-texturing techniques which creates different surface texture in a controlled laboratory condition.Road stone quarrying is the multistage process by which rock is extracted from the ground and crushed to produce aggregate, which is then screened into the sizes required for immediate use as chippings etc.. As far as the Polished Stone Value (PSV) of the aggregate is concerned, the surface of the aggregates roughness which is in contact with the tire is important in the process of aggregate processing, therefore, analyzing different textures of the same aggregate surface is the main objective of this paper. To serve the purpose, an apparatus has been designed and developed to carry out re-texturing of aggregates, using methods which apply needle gun and sand blasting. Aggregate have been arranged according to their Petrographical group classification. Tests have been carried out on more than 300 samples made from 35 quarries under controlled laboratory conditions. Samples were assembled and test specimens were made in accordance to the procedures described in BS 812 Part 114, 1989.Initially, the Unpolished Stone Value (UPSV) of samples have been taken by British pendulum, then, Polished Stone Value (PSV) of each aggregate samples ware measured in a programme of standard tests. The test specimen was subjected to a program of the re-texturing treatments. Pendulum value of the treated samples has been taken (UPSVR). Treated samples have been assembled in a program of testing on accelerated polishing machine in order to assess re-textured polished stone value (PSVr) of aggregates according the BS812 Part 114 1989. As some aggregates have undergone re-texturing treatments it has been established that some end up with significantly higher in performance in terms of their re-textured pendulum value (USVr), and above all, their polished stone value (PSV) than others. It was found that Per graphical group classification have little to no effect regarding the final outcome of the up-grading aggregates PSV procedure. Therefore each aggregate must be considered in the light of its own individual properties and characteristics.