Distribution of mortar film thickness and its relationship to mixture cracking resistance

ABSTRACT

The film thickness of asphalt mortar, which is a mix of binder and fine mineral aggregates, has been considered as an important indicator for assessing the durability of asphalt mixture. This study proposes a novel method to characterise distribution of mortar film thickness in asphalt mixture through image processing techniques. Four asphalt mixtures with unmodified and modified binders were produced at various compaction temperatures in the laboratory. Their internal images were scanned and analysed. The values of mortar film thickness along the boundary of each aggregate in the scanned image were measured. And their mean value (Tm) and standard deviation (SDt) were calculated for characterising the distribution of mortar film thickness. The results indicate that both binder modification and compaction temperature have significant effects on the mortar film distribution. Furthermore, the proposed parameters were employed for understanding the correlation between the mortar film thickness and mixture cracking resistance. The flexibility index of short-term and long-term aged mixtures were measured and correlated with the mortar film parameters. The findings show that asphalt mixture with a lower mortar film thickness and a wider distribution is more sensitive to oxidative aging, which may result in a dramatic decrease of mixture’s resistance to cracking.

KEYWORDS:

• Asphalt mortar
• film thickness
• image processing
• binder modifier
• compaction temperature
• flexibility index

Disclosure statement

No potential conflict of interest was reported by the author(s).