University of Khartoum

Experimental Study Of Unbound Pavement Materials In Khartoum State

Experimental Study Of Unbound Pavement Materials In Khartoum State

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Title: Experimental Study Of Unbound Pavement Materials In Khartoum State
Author: Omer, Omer Gurham
Abstract: The main objective of this study is to characterize and understand the behaviour of natural unbound gravels of Khartoum State, evaluate their different blending and stabilization techniques and assess some construction practices namely dry compaction and relaxation of base course specifications using dynamic testing methods. Accordingly, the research was executed in three major phases. The first (Program1) involved collection of natural unbound gravels from open quarries in Khartoum State normally used in subbase/base course construction, and crushed stone samples from crusher plants, evaluating their use as pavement materials and studied the effect of laboratory compaction methods (impact, vibratory and gyratory) on the engineering properties of representative and selected unbound gravels. The second phase (Program2) studied and evaluated the techniques for upgrading the unbound subbase gravels for use as base course materials i.e. blending and chemical stabilization using resilient modulus (MR) and permanent deformation (PD) tests. Three selected natural unbound gravels representing fine, medium and coarse gravelly materials, as specified by TRL-GB3 were blended with crushed stone and wadi sand to attain base materials specifications and the stiffness (MR) and deformation characteristics were evaluated and compared with those of pure crushed stone base material. Chemical stabilization of the three materials using Portland cement was also evaluated. The third phase (Program3) assessed the effect of compaction dry of optimum on stiffness and permanent deformation (PD) of unbound gravels and the stiffness and permanent deformation of unbound gravels short of satisfying base materials specifications or relaxation of base specification limits. Physical models were used for this evaluation. The tests results of Program1 showed that the materials in the open quarries are of subbase quality. It also showed that impact hammer largely degraded the tested unbound gravels compared to the other two methods (vibratory and gyratory). The measured strength (CBR) using impact method is noticeably high compared to the vibratory and gyratory compaction methods. The field tests showed that the gyratory compaction method simulated better the field compaction conditions compared to the impact and vibratory compaction methods. Therefore, impact hammer over-estimates the strength of natural unbound materials and could lead to unrealistic design. The tests results of Program2 showed improvement in the engineering properties when the unbound materials were blended with wadi sand & rock dust (5-0 mm). Cement was found to be the best option in terms of improvement of the strength of the natural aggregates. The three materials blended with crushed stone showed gradation improvement consequently resulting in high strength and stiffness and in low PD values. The pure crushed samples reported the best results for all laboratory tests on untreated aggregates performed in the program. The blending exercises have shown that proper gradation correction to adequately satisfy base course gradation is required for high stiffness and low deformation of the blended natural gravels. Application of some developed prediction models for estimating MR and PD showed good agreement with the measured results for the tested samples. The tests results of Program3 showed that; for the dry compaction, all specimens watered dry of optimum collapsed upon the dynamic tests. This could indicate that the dry compacted gravely pavements can’t sustain efficiently when subjected to repetitive traffic. For relaxation of base course specifications, the blends satisfying the GB3 base requirements measured the smallest PD values. It was found that as the PI decreased with the increase of sand, the CBR values respectively increased. The individual specimens of the various base blends used in the physical model showed large differences in CBR; however their measured PD and MR values did not show remarkable differences. FAARFIELD airfield pavement design software was used for designing airports pavement and it is observed that the single blended sample that measured the highest MR caused the corresponding physical model to measure the smallest airfield pavement thickness (500 mm).
Description: 273page
URI: http://khartoumspace.uofk.edu/123456789/22948


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