Abstract
A number of researches have been done worldwide to evaluate the damage caused by water in bituminous pavements. The use of the retained strength ratios obtained from laboratory moisture damage tests is a useful tool in making quantitative predictions of the related damage caused by water. This study involved laboratory work on the effect of water on the performance of bituminous mixtures. Comparisons are made between the performances of Hot-rolled Asphalt (HRA) bituminous mixtures containing base bitumen of 50 pen grade to that of a polymer-fibre reinforced HRA mixture. Two types of polymer fibre were studied, namely polypropylene and polyester and these fibre were added in different concentrations in the bituminous mixtures. Changes in both the cohesive properties of the bitumen and the adhesion of the bitumen to the aggregate surface were observed as a result of exposing the bituminous mixtures to moisture. The effect of polymer fibre reinforcement in bituminous mixtures helps reduce the level of moisture damage. This was evident in the lower moisture susceptibility achieved in the polymer fibre reinforced bituminous mixtures as compared to the control mixture. The additional bitumen in the fibre reinforced mixtures also afforded an increased film thickness on the aggregate particles, thus affording additional protection of the mixtures from moisture. The reinforcement of polymer fibres in bituminous mixtures also acts to decrease the moisture sensitivity of the bitumen to aggregate bonding. This may be due to the strengthening of the wetted binder matrix that helps promote both adhesion and cohesion retention.
Highlights
The damaging effects of moisture on the physical properties and mechanical behaviour of bituminous mixtures have been the focus of study for many years
This paper is based on some laboratory work and addresses the damaging effect of moisture in polymer fibre-reinforced bituminous mixtures [1]
The following conclusions can be drawn: i. Changes in both the cohesive properties of the bitumen and the adhesion of the bitumen to the aggregate surfaces may occur as a result of exposing the bituminous mixtures to moisture
Summary
The damaging effects of moisture on the physical properties and mechanical behaviour of bituminous mixtures have been the focus of study for many years. The unfilled void spaces in compacted bituminous mixtures are able to hold sufficient quantities of water that can cause distress and damage and reduce mix performance. The damaging effect of water will give rise to stripping or de-bonding of the bitumen from the aggregate surface This is brought about by the loss of cohesion and softening of the binder due to the action of the moisture within the bitumen or bituminous mix. The creation of a degree of saturation in the laboratory high enough without damaging the specimens and that the retained strength can be determined involves a moisture conditioning process. Saturation by partial vacuuming for a short period of time has been used in moisture damage studies on bituminous mixes. Vacuuming with an absolute pressure of 2.5 cm mercury allowed the water to occupy the through passage accessible voids and most of the dead end accessible voids [13]
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