Key Engineering Materials Vol. 509

Abstract: The property of aggregate has a significant effect on the performance of asphalt mixture because of its high proportion. Asphalt mixture prepared by some kind of aggregate cause the inadequate compaction problem, which results in moisture damage due to its large air void. Limestone manufactured sand is considered as one of the useful solution to overcome the compaction problem. In this paper, fine aggregate is substituted by different proportion of limestone manufactured sand (LMS). The effect of replacement ratio on volume properties and pavement performance is studied. The results show that the limestone manufactured sand can improve the pavement performance and is benefit to the compaction of andesite asphalt mixture. Furthermore, this research also provided some valuable parameters for guiding the pavement construction in the future.

Abstract: The effect of substitution of recycled aggregate by natural aggregate on related properties of blended aggregate (without asphalt and mineral filler) and asphalt mixture was investigated in this paper. Demolition waste obtained from Wenchuan earthquake-damaged buildings was used as recycled aggregate in AC-25 asphalt mixture. The absorption, specific gravity and strength of both blended aggregate and asphalt mixture were tested. Results indicate that fine recycled aggregate is not suitable to be used in asphalt mixture because of its high absorption. The substitution of recycled aggregate by natural limestone aggregate can decrease the asphalt absorption and increase the effective specific gravity and indirect tensile strength of asphalt mixture. The quantitative relationship between related properties of blended aggregate and asphalt mixture was obtained. It was concluded that the substitution of recycled aggregate by natural aggregate is a feasible way to use recycled aggregate in asphalt mixture.

Abstract: Research in the laboratory was carried out to determine if addition of warm mix asphalt additive (Sasobit) has potential to reduce the temperature comparison with control mix. To fulfill this purpose five types of asphalt binders have been produced with a Sasobit additive in concentration range from 0 to 10% by weight of the asphalt. Viscosity test and dynamic shear rheometer test are conducted for the investigation of effects of Sasobit on rheological properties characteristics of binders. Viscosity tests on binders indicated that the Sasobit binders had significantly lower viscosities compared to control binders at the temperature above 100°C, indicating that Sasobit can reduce the mixing and compaction temperatures above the melting point of Sasobit. Sasobit modified binders are more sensitive cracking and had more excellent rutting resistance properties at service temperatures compared with original bitumen. Based on the test results, the suggest content of Sasobit addition is 3% by weight.

Abstract: With regards of discussing cellulose and polyester fibers reinforced asphalt mixtures, the contribution of cellulose (CEL) and polyester (PET) fibers had therefore been experimented. And on the basis of different reinforcement mechanisms, this research focused on the cellulose (CEL) - polyester (PET) hybrid fibers reinforced system, consequently determined the feasibility of utilizing CEL-PET hybrid fibers in asphalt mixture. Asphalt mixtures had been prepared, according to the specifications, following both the SHRP procedure and the traditional one. Mechanical characteristics of the mixtures were evaluated with Marshall stability (MS), indirect tensile strength (ITS), moisture sensitivity, high temperature rutting test and fatigue test. This study compared the performance of mixtures containing hybrid fibers with mixes made with and without commonly used cellulose and polyester fibers produced specifically for use in hot mix asphalt (HMA). The research results showed that no significant differences in MS, ITS or moisture susceptibility were found in mixtures containing hybrid fibers compared to cellulose or polyester. Also, the hybrid fibers significantly improved the permanent deformation resistance of the mixtures compared to cellulose fibers, say nothing of the control one without fibers.

Abstract: Bitumen pavement suffers from moisture damage mainly due to loss of durability and stability in a short span of service life. Filler is known to be capable of increasing the stiffness of bitumen binder, contributing to improvement of moisture sensitivity of bitumen mixture. In this paper a new type of filler named 'Compound Fly Ash Modifier' (CFAM) was introduced in order to enhance the bond strength between acidic aggregate with bitumen. The primary object is to determine the effect of CFAM on the moisture sensitivity of bitumen mixtures prepared by gneiss and granite respectively, which are termed acidic aggregate. Modified Lottman test and fatigue test were conducted. The results show that CFAM improves the resistance of mixes to moisture damage in the increase in indirect tensile strength and the extension of fatigue life. Finally the mechanism of modified effects for CFAM is discussed.

Abstract: This paper investigated the influence of nanoclay on the properties of polymer modified bitumen(PMB). The nanoclay-polymer modified bitumen has been produced by mixing a standard 70/100 pen bitumen with polymer at a fixed proportion and then mixed with different amount of nanoclay. The rheological behaviour of the samples have been determined using dynamic shear rheometer. The morphology of the samples as well as the distribution of polymer and nanoclay throughout the bitumen have been characterized with a fluorescence microscopy. The result indicate that the rheological properties of nanoclay-polymer modified bitumens dependent on the percentage nanoclay. The morphology result shows that dispersed polymer particles existed in continuous bitumen phase and the addition of nanoclay does not seem to change the particle size of the polymer.

Abstract: Aggregate distribution of asphalt mixture had an obvious characteristic of fractal. Based on fractal theory, the distribution function of aggregate of conductive asphalt mixture based on the granular fractal model was deduced. This paper used linear regression analysis to different gradings to get the grading fractal dimension of conductive asphalt mixture and the conductivity of the mixture was tested. Test results indicated that the grading fractal dimension of conductive asphalt mixture was controled by the fine aggregate. On the other hand, the fractal dimension had a congruent relationship with conductivity. The conductive asphalt mixture had good pavement performance and conductive when the fractal dimension of AC-20 grading ranged from 2.43 to 2.53. The fractal dimension can be used as a quantification index of grading evaluation.

Abstract: The key point of preparing conductive asphalt concrete for deicing and snow melting is pavement performance must satisfy the requirements before it can melt snow successfully. This study prefers to prepare electrically conductive asphalt concrete choosing steel slag as the whole aggregates and conductive minerals, while mixed with graphite and carbon fiber. Moisture susceptibility has been evaluated through water-saturated Marshall Stability test and indirect tensile splitting strength test. High temperature performance and fatigue performance were analyzed through dynamic creep test and indirect tensile fatigue test. Results indicate: High temperature performance of steel slag conductive asphalt concrete is better than ordinary basalt asphalt concrete, while its moisture susceptibility and fatigue performance is not good enough and need to be improved.

Abstract: This study investigated the fatigue properties of organo-montmorillonite modified bitumen mortar. Organo-modified montmorillonite（OMMT）with a content of 5 wt% was used to modified one base bitumen mortar which consist of filler and bitumen at a weight ratio of 0.8:1. The fatigue properties of these bitumen mortars have been determined using a dynamic shear rheometer（DSR）through time sweep test. Result indicated that, due to the addition of the OMMT, the fatigue properties of modified bitumen mortar was superior to those of pristine mortar. Therefore, the OMMT would be an alternative to modifiers used in the bitumen to improve the lifetime of asphalt pavement. Meanwhile, some fatigue equations were estabilished.

Abstract: The comprehensive performance, such as water demand, hydration heat, expansion, and self-hardening of circulation fluidized bed combustion (CFBC) fly ash ground by the laboratory mill were studied in this paper. Results show that the percentage of fine particles and fluidity of CFBC fly ash increased with grinding time. However, the water demand at normal consistency of the CFBC ash decreased with grinding time. The hydration exothermic rate of the paste has been accelerated and the time of reaching the volume stability has been shortened. Meanwhile, the compressive strength of the paste and the content of ettringite in the matrix increased with the curing time in the early age, but reversed later.