ارزیابی تاثیر فیلرهای آهکی در کاهش اثرات تخریبی رطوبت و یخبندان با استفاده از آزمایش‌های کشش غیر مستقیم و مقاومت فشاری

Pavement performance in Iran is not compatible with expectations and demands of contemporary society. The poor performance of pavement results in shortening country roadways lifetime and paying heavy cost. One of the pavement major problems particularly in wet conditions is stripping of aggregates. Stripping is a major distress occurring in hot mix asphalt (HMA) pavements in Iran and in various parts of the world The stripping of aggregates in hot mix asphalt not only is considered as an independent problem but also it may cause damages like cracking, rutting, raveling, fatigue cracking. The moisture first inflicts damage on the HMA mix by destroying the bond between the aggregate and the asphalt binder or by destroying the internal cohesive strength of the binder. This loss of adhesion causes the asphalt concrete to ravel under traffic loads. Stripping occurs in the presence of water, so it is often referred to as moisture damage. In this paper, the effective parameters causing stripping have been identified and the methods of increasing asphalt mixture durability have been investigated, focusing on the recognition of how stripping can be made. In this regard, limestone fillers and hydrated lime have been used in different amounts as antistripping agents (which can be found widely in the country) and the optimum resistant mixture against stripping have been prepared. In this thesis two kinds of aggregate from the east and west of Tehran and two kinds of bitumen (60/70) from Tehran and Isfahan refineries have been collected and the required experiment (on aggregates, bitumen and hot mix asphalt) have been carried out. Then according to marshal method and based on ASTM D6926 and ASTM D6927 standards, marshal specimen have been made and the optimum bitumen has been determined, using the required parameters by marshal method. Using indirect tensile strength and compressive strength tests over saturated and dry specimen, according to AASHTO T283 and ASTM D1075 standards, asphalt mixture stripping potential has been investigated. Since the resistance of asphalt mixture again moisture was not satisfactory, two kinds of limestone filler and hydrated lime were used for improving asphalt mixture resistance and their effect was investigated on asphalt mixture. Hydrated lime and limestone filler, when added to the asphalt prior to preparation of the mixtures, dramatically improved mixture resistance to moisture damage for both aggregates. The results obtained from indirect tensile strength and compressive strength tests over saturated and dry specimen, according to AASHTO T283 and ASTM D1075 standards show that using 1.5% hydrated lime or 4% limestone filler (by weight of aggregates) in asphalt concrete, significantly increased the asphalt mixture resistance against stripping. Also in this study the results obtained from two experiments methods (tensile strength and compressive strength tests) are compared.