Browsing by Author "Masebo, Partson Malambang'ombe"

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    Assessment of diametral compression and marshall tests for characterizing bituminous mixes.
    (University of Dar es Salaam, 1996) Masebo, Partson Malambang'ombe
    Bituminous mixes are some of the most important and commonly used building materials. The properties of these mixes are important in determination of pavement performance and in the analysis rega response of materials to traffic loading in given environmental condition. As it is not always possible to obtain all the mix properties in one test, the two test methods, Marshall and diametral were considered in order to complement one another. The study was carried out on two types of musing binder 80/100 penetration grade in both granite and limes aggregates. The aggregates were taken from Lugoba and Kunduchi, source which are used in the construction of bituminous roads in Dar es Salaam City and else where in the country. The purpose of the study was to evaluate the mix properties using Mars design criteria and there after, using the same mixes to evaluate other properties by indirect tensile methods; namely Indirect Tensile Modulus test and Repeated Load Indirect tensile tests. The same mixes v manufactured using a similar procedure. The difference was compaction rolling, moulding and specimen testing procedures. Parameters obtained under Marshall tests Method include Marshall stability and flow density and voids including bitumen content. The test results discussions following therefrom are provided in chapters 4 and 5. Under indirect tensile modulus tests, parameters considered include ela modulus, tensile stress and total recoverable strain. Resilient module resilient strain and permanent strain were obtained under repeated indirect tensile tests. In the latter methods, specimens were tested u controlled stress levels and at various anticipated pavement temperatures. The same were put in a conditioning chamber to bring them to required test temperatures. Results in the indirect tensile methods indicated maximum elastic and resilient modulus values of 1000/2123 (MPa) at 25°C test temperatures and minimum values of 240/1 1 (MPa) at 47°C test temperatures for granite and limestone materials respectively, showing that temperatures influence material properties. Resilient, permanent and total recoverable strains increased with temperature. The results and discussions for the observed behaviour are provided in similar chapters described above. It has been concluded that both methods be used for characterizing bituminous mixes as they complement each other. Mix properties obtained under Marshall method, i.e., densities were used to manufacture mixes whose other properties were established and evaluated under diametral test. This is a dynamic type of test method which takes into consideration the environmental influence the material is likely to encounter in service (4,14). Marshall method which is static in nature should be used in the early design stages of mixes and during construction works for quality control. Indirect tensile methods, however, should be utilized in setting out working limits of mixes. As for this study, minimum stiffness values for granite was 349 MPa and the corresponding maximum strain was 1 101 (ue) both of these values were recorded at a test temperature of 47°C. Like wise for limestone minimum stiffness value was 12 (MPa) and maximum strain of 31957 (ue) at the same test temperature. The fundamental values should be set for each temperature range considered. The same may be used in the analysis of mechanistic design of pavements where minimum allowable limits shall be set pending compromise with other researchers' findings, if any, obtained in similar materials and environmental conditions. The material response to environmental conditions are different for different materials or similar materials in different localities. "Care should be taken in utilizing values at higher temperatures". This caution was given also by other researchers (4). The author has tried to give the trend of bituminous mixes under the influence of pavement conditions. It is recommended that further research be carried out on other gradations and on different materials as used in road construction works. Also that environmental condition 'data' for different localities where roads are passing or likely to pass be collected and made available when need arises. The findings under this study are not exhaustive and may change without notice.