Mechanical treatment of excessive fines in crushed stone base (CRS)

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University of Dar es Salaam
The improvement of road construction materials using Mechanical Treatment is not a common practice in Tanzania. In tropical countries where the weathering is intense, like the coast regions of Tanzania including Tanga, Coast, Dar es Salaam, Lindi and Mtwara where coral and calcrete materials dominate, •lack of fresh rock in reasonable 'hauling distance is very common. The excessive fines are normally resulted •from the low quality of raw material prior to crushing, wide range of allowed raw materials which ranges from gravel to fresh rock make it difficult to control the final product during crushing, pockets contained in coral and accrete allows soil to pack in textures and when crushed increases the fines in a mixture. The presence of excessive fines in base coarse materials results in volumetric changes, low stability, draining inability and other undesirable effects that contribute to low strength and durability of the road. The preliminary results of the rejected CRS materials from Mchinga Quarry revealed to have poor grading and high linear shrinkage and these were the basis of rejection. The two non-conformity parameters caused the material top oases a CBR of 70% and hence categorized as G60 materials instead of CBR of 100% and above. The Standard Specification for Road Works — 2000 which is also the guidance to this research, require the CRS to remain unbound, it is restricted to use any chemicals as a treatment measure whenever the material failed to comply with the specification. This condition automatically enforces the use of Mechanical Treatment as the only method to implement. After Mechanical Treatment the quality of the material was improved, the Particle Size Distribution complied with specification; linear shrinkage reduced from 6% i%, CBR increased from 70% to 102% and TFV increased from 120 KN to specified 4 The Mechanical Treatment proved successful, and it is recommended often be 122 KN. exercised in projects where improvement of materials is required.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF TE239.N56)
Stone, Crushed, Testing
Nkolante, N. E (2008) Mechanical treatment of excessive fines in crushed stone base (CRS), Master dissertation, University of Dar es Salaam. Dar es Salaam.