الفهرس 
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Abstract
The work concluded in this study dealt with the quality control test of determining the bitumen content and aggregate gradation of asphalt mixtures. The main objectives of this study were: (1) to evaluate the reliability of the ignition furnace method compared to the centrifuge extraction method on dominant asphalt mixes in Egypt, and (2) to conclude the significant factors affecting the ignition furnace correction factors of bitumen and aggregate gradation. This chapter represents a summary of the study, its main conclusions and recommendations for future studies and applications.
5.1 Summary
Determination of bitumen content and aggregate gradation in the asphalt mixtures are necessary for quality control in highway construction. Two commonly used methods are used for the determination of bitumen content worldwide: the extraction test (AASHTO T 164) and the ignition furnace test (AASHTO T 308).
Although the extraction test is the most commonly used method in Egypt, it has many disadvantages; the test has high running costs due to the solvents used to separate the bitumen from the aggregates and the precautious disposal procedures needed for these solvents. Furthermore, without taking the suitable precautions, the solvents used are hazardous to the health of the technicians performing the test. It also requires a longer test time and has lower accuracy in comparison with the ignition test method. On the other hand, the ignition oven test does not require any solvents to separate the bitumen from the aggregates. However, due to the extreme temperatures, aggregates are subjected to mass losses. The mass losses change between each different asphalt mixture, that is why the standard test procedures in AASHTO T 308 state the necessity of determining correction factors for each mix prior to any testing. Correction factors can be determined by the preparation of correction samples with materials and properties identical to the job mix formula mix design for the samples to be tested. These procedures are time- and labor-intensive and require the availability of reliable data about the mixtures to be tested.
As a result, the main aims of the research were to evaluate the usage of the ignition furnace method for determination of bitumen content and aggregate gradation in Egypt in comparison with the extraction tests. Another aim of this study was to monitor the main factors affecting the values of the correction factor and to study whether a direct correlation could be established between these factors and the correction factor, which could help determine the correction factors without the need of specific mix data, which may not always be available. Required tests were conducted using the ignition furnace and the centrifuge extraction methods using different dolomite aggregate sources, aggregate gradations, and bitumen contents. Test times were monitored and recovered aggregates from the ignition furnace method retained on sieve No. 4 were tested for absorption, disintegration, and specific gravities.
5.2 Conclusions
The following points summarize the conclusions and recommendations for this study.
• The study concluded through ANOVA test that there were no significant differences between ignition oven and centrifuge extraction test results.
• The study concluded through ANOVA test that changing the aggregate source has a significant impact on the bitumen content correction factor.
• The study concluded through ANOVA test that changing the aggregate gradation did not have a distinct effect on the bitumen content correction factor.
• Regression analysis showed that there is a strong relation between the correction factor and the test time with a correlation coefficient 0.87, where specimens whose test times exceed 90 minutes are considered to contain high mass loss aggregates.
• No significant relations were found between the absorption or specific gravities of recovered aggregates and the bitumen content correction factor.
• There is a moderately strong inverse relation between the percentage of disintegration of recovered coarse aggregates from the ignition test and the bitumen content correction factor.
• Standard deviations for correction factors for high mass loss aggregates are higher than standard deviations for non-problematic aggregates.
5.3 Recommendations
Based on the above conclusions, the following points are recommended:
• Future studies should be carried out to determine the sources containing high mass loss aggregates in Egypt.
• Extensive experiments should be carried out to establish a wide database to find a high correlation relationship which allows prediction of the correction factor without the need for correction samples prior to testing.