Guillermo Thenoux

Degree of Influence of Active Fillers on Properties of Recycled Mixes with Foamed Asphalt

Active fillers in foamed asphalt mixes are added to modify the fine fraction of aggregate gradation or to reduce the moisture sensitivity of the mix. Some countries use cement as an active filler, and other countries use lime or fly ash, among other ingredients. However, limited information is available concerning the influence of different types of active fillers on the mechanical properties of foamed asphalt mixes. This paper presents the results of a project carried out to study the relative influence of active fillers on the mechanical properties of recycled mixes with foamed asphalt. Four active fillers were studied: portland cement concrete, cement kiln dust, hydrated lime, and fly ash Class C. Indirect tensile strength, triaxial resilient modulus, and triaxial permanent deformation tests were carried out to quantify the influence of these active fillers on the properties of one particular full-depth reclamation material. Different curing methods and moisture conditioning were used to evaluate the role of active fillers after the mix production process. As a result of this study, it was concluded that, for the full-depth reclamation material tested, whereas some active fillers have an important influence on the mechanical properties and long-term performance of foamed asphalt mixes, others act only as mineral fillers of the aggregate gradation. Also, because foamed asphalt takes a long time to cure, some active fillers play an important role in contributing to the early strength of foam recycled mixes.

Development of a Methodology for Measurement of Vehicle Dust Generation on Unpaved Roads

This paper presents the results of a field study aimed at developing a methodology for measuring vehicle dust generation on an unpaved road. The methodology is based on the use of portable standard equipment known as Dust Mate. This equipment measures the number of particles per cubic centimeter for different particle sizes: particles less than 10, 2.5, and 1 μm in diameter. The methodology was developed to improve the management of unpaved roads and to study the performance of earth road dust suppressants. The Dust Mate equipment may be mounted in various types of vehicles, and measurements may be performed at various speeds. The equipment can record dust generation continuously and may be programmed to save the data for measurements over various time spans. This last feature will allow evaluation of short segments of the road (less than 10 m). The study was performed in three stages: determination of (a) the best design position of the equipment for different types of vehicles in combination with the effect of speed, (b) the repeatability of results for different operation parameters, and (c) the effectiveness of various dust suppressants. The research was done on test sections of unpaved mining and rural roads with different types of soil and surface conditions. The study indicates that the methodology developed for dust measurement with the Dust Mate equipment may be considered an improvement over the methods currently in use. The measurements are reliable, and the repeatability of the results is better than is required by todays standards.

Laboratory and Field Evaluation of Fluid Bed Combustion Fly Ash as Granular Road Stabilizer

This paper presents the result of laboratory and field research on soil stabilization using fluid bed combustion fly ash. This type of ash is the result of the combustion of petroleum coke and limestone in an electric power generation plant (Petropower, located in the south of Chile), which makes it different from other types of ash used regularly in soil stabilization. The ash differs from the traditional ash used in soil stabilization, particularly because of (a) a high concentration of lime that may produce cementing compounds and (b) the presence of sulfates that may produce a secondary reaction such as the formation of gypsum and ettringite, resulting in a different level of expansion in some types of soils. The main objectives of the research were to characterize fluid bed combustion fly ash from the Petropower plant and to evaluate the technical feasibility of using this ash as a soil stabilizer. The laboratory and field research showed that this type of ash improves the mechanical properties and water susceptibility of most types of soils. Although laboratory experimentation proves that the secondary reaction produces soil expansion in clayey soils, field experimentation indicates that the secondary reaction that produces soil expansion may be controlled by an adequate laboratory design and an appropriate dose of fly ash.

EVALUATION OF HEXAHYDRATED MAGNESIUM CHLORIDE PERFORMANCE AS CHEMICAL STABILIZER OF GRANULAR ROAD SURFACES

The performance was evaluated of hexahydrated magnesium chloride (MgCl2·6H2O) as a chemical stabilizer of granular road surfaces. MgCl2·6H2O is a salt with properties that are useful for chemical stabilization of granular road surfaces, such as its capacity to absorb and retain humidity from its surrounding environment, increase water surface tension, and decrease water vapor pressure. Its effect on the physical and mechanical properties of soils was evaluated in laboratory, and its functional performance and durability were evaluated in field trials. Field trials were performed in arid and semiarid regions in the Atacama Desert in northern Chile. Field results showed that roads stabilized with MgCl2·6H2O remain free of dust and corrugations and exhibit a considerable reduction in pot-holes and surface erosion. The period of effectiveness for MgCl2· 6H2O has proven to be more than 2 years, without any type of road maintenance.

Study of Aircraft Accident Related to Asphalt Runway Skid Resistance

On February 20, 1991, a brand-new British Aerospace BAE 146-200 aircraft, operated by a commercial airline, landed at Guardiamarina Airport in Port Williams, Chile. The aircraft landed under good weather conditions on an asphalt surface treatment runway and skidded more than 1,000 m into the Beagle Channel. It was a charter flight with 60 tourists on board; 40 survived. A long investigation provided evidence on why the aircraft skidded off the end of the runway.

Stiffness Evolution of Granular Materials Stabilized with Foamed Bitumen and Cement

From the literature, it is possible to find two trends regarding the stiffness evolution of foamed bitumen stabilized–recycled mixtures. The first trend indicates that once the foamed bitumen mix reaches a constant value because of the curing process, the stiffness decreases with time because of load cycles. The second trend indicates that stiffness remains constant after the curing process. In this research, the stiffness evolution of foamed bitumen mixes stabilized with different bitumen and cement contents was studied. The stiffness was measured by using the indirect tensile fatigue test. Results indicated that once the foamed bitumen mix reached a constant value because of the curing process, stiffness decreased or remained constant depending on the stress level applied to the foamed bitumen layer. If the stress level is lower than a specific value, the stiffness of the mix will remain constant at a value extremely close to the initial stiffness. If the stress level is greater than a specific value, the stiffness of the mix will decrease gradually. In addition, the reduction rate of the stiffness will be greater with higher stress level. The analysis of results from mixes with different bitumen and cement contents allows identification of the effect of both stabilizing agents in the long-term stiffness evolution.

Interpretation of laboratory and full-scale testing of New Zealand foamed bitumen pavements using finite-element modelling

A large research project on foamed bitumen (FB) stabilisation was conducted in New Zealand. The project consisted of an extensive laboratory and full-scale testing of FB pavements. The objective of this paper is to interpret the performance of FB pavements by using finite-element (FE) modelling. The mechanical properties of the materials were calculated using testing data and used as material inputs in the FE modelling. The Mohr–Coulomb and Drucker–Prager material models were adopted to calculate plastic deformation, which is related to pavement rutting. Results of the modelling indicate that increasing the FB content increases the tensile strength and modulus of the pavements, reducing the plastic deformations in the subgrade and the stabilised layer. In addition, adding FB reduces sensitivity to rutting when pavement is overloaded or the asphalt surface layer is cracked.

Chilean structural design guide for low-volume roads

The practical and theoretical principles used for development of the Chilean Structural Design Guide for Low-Volume Roads 2002 and the guide’s conceptual model and hypotheses are presented. The design guide is a simplified methodology for selection of different pavement structure alternatives for a variety of conditions (traffic, soil support capacity, and climate). The design guide provides solutions for four traffic ranges, six ranges of soil support capacity, and three climate conditions (dry, normal, and saturated). The design charts contain more than 150 solutions. Pavement structural design was solved by mechanistic analysis with the BISAR computer program and fatigue models developed in South Africa. The design guide may be considered an engineering application with upto- date research tools and results.

The antioxidant effect of grape pomace in asphalt binder

ABSTRACT Asphalt binder ages on time mainly due to oxidation during mixing, and in service along the years. The aging effect will diminish material viscoelastic properties until it becomes brittle. Once asphalt binder reaches its brittle stage, the material will reduce its capability to withstand repeated traffic loads while in service, (fatigue). There are four methods to enhance fatigue life of an asphalt pavement; among these methods is the use of antioxidants. The work presented in this paper summarises the research work where grape pomace residue has been used as an antioxidant. The research objectives were to evaluate and understand the antioxidant effect of this additive. Consistency and rheological tests where used to prove the relative effect for reducing aging when adding grape pomace residue. It was possible to demonstrate the antioxidant properties of the additive but at the same time, it was found that the small solid undissolved particles of the additive would produce a secondary effect that will it make more difficult to isolate the pure antioxidant effect.

Evaluation of Additional Laboratory Tests for Design of Full-Depth Reclamation Mixtures Using Foamed Bitumen

The mix proportion design methods for full-depth reclamation mixtures using foamed bitumen normally fix a constant active filler content, and an indirect tensile strength (ITS) test is used to determine the optimum bitumen content. However, it has been reported in the literature that for some materials the ITS test is not sufficiently sensitive to bitumen content. This lack of sensitivity is a problem for the practitioner engineer who has to validate the bitumen content adopted in the mixture design. The main objective of this work is to examine the sensitivity to bitumen content of additional laboratory tests that could complement current design methods based on ITS. The mixtures used in the study were prepared by using three recycled blends of reclaimed asphalt pavement and aggregate that were mixed with bitumen foam contents of 1.25%, 2.5%, and 3.75%. Test results confirmed the low sensitivity of the ITS test, and it was found that the indirect tensile fatigue (ITF) test was the most sensitive among all tests. To explain the higher sensitivity of the ITF test compared with the ITS test, a stress–strain diagram and a simple unidirectional mechanical model were developed. In addition, an S-N fatigue diagram was used to illustrate that at a larger number of load cycles, the effect of the foamed bitumen content is clear, as shown in the experimental work. Overall, the laboratory program and material behavior analysis indicate that when the ITS test does not provide conclusive results, the laboratory program should be complemented with ITF tests to determine the optimum foamed bitumen content with more reliability.