Construction Of Hot Mix Asphalt Pavements Research Articles

Comparison of Bond Strength Evaluation Methods Between Pavement Layers

Tack coats are generally used to facilitate a bonding between pavement layers in construction of hot-mix asphalt pavements and overlays. The goal of applying a tack coat material is to ensure the new or consecutive pavement layers respond monolithically under loading and avoid premature failure caused by debonding, mat slippage, or fatigue cracking. Multiple different in-situ and laboratory tests have been developed to evaluate bond strength of tack coat materials under tension, shear, and mixed-mode loading mechanisms. However, there is no universally accepted bond strength test method or performance criteria for tack coats within the United States. While some specifying agencies have gained familiarity and comfort with a particular bond strength test, a gap exists for many states that have not adopted a testing procedure. The objective of this paper is to compare current and newly developed tack coat bond strength tests to help determine which is most indicative in predicting field performance. Field cores from four different pavement sections with varying traffic loading conditions and early bond strength performance were sampled and tested in the laboratory using four different bond strength evaluation methods. Statistical analysis of bond strength testing results shows a strong linear correlation between pull-off and shear strength testing. Meanwhile, a novel approach to tack coat bond testing under cyclic tensile loading was explored and showed appreciable discrimination between sample locations and agreement with early field performance.

ENVIRONMENTAL IMPACT OF VOLATILE ORGANIC COMPOUNDS EMITTED FROM ASPHALT PAVEMENT

Hot mix asphalt (HMA) is a major construction material used for building roads, airport runways, and parking lots (ASCE 2014). During HMA construction, a massive amount of volatile organic compounds (VOC'Ss) is emitted from the hot asphalt mixtures, creating a potential health risk to on-site workers. Few studies have quantitatively investigated (Chong et al., 2013). The constituents and the potential health effects of the VOC's generated from HMA pavement construction were studied. This paper presents the results of a study in which air samples were collected at multiple locations and time points of several projects during HMA pavement construction and were their chemical compositions and concentrations subsequently characterized by using gas chromatography/mass selective detector (GC/MSD). Although the individual concentrations of the identified chemicals were found to be below various exposure limits, their collective effect on human health remains unknown and may not be ignored (Chong et al., 2013).

Quality verification of polymer-modified asphalt binder used in hot-mix asphalt pavement construction

In many regions and countries, highway agencies are interested in verifying the quality of asphalt binders placed on roads for quality assurance purpose. Particularly, as PG-graded, polymer modified asphalt (PMA) is increasingly used, the agencies are interested in examining if the specified PMA is fully used in the field or if the PMA has not been severely degraded after storage, handling, and plant production. This research investigated and compared various test methods for such purpose. Besides laboratory-prepared asphalt binder samples, actual pavements built with neat asphalt (pen 60/70), 30% of neat asphalt with 70% of PG76-16 PMA, 15% of neat asphalt with 85% of PMA, and 100% of PMA were used for study. The mixture production and construction processes were carefully planned and monitored to ensure that they are consistent with real construction operations. Test methods evaluated in this study include indirect tensile (IDT) strength and indirect tensile stiffness modulus (ITSM) of field cores, rheological parameters (G∗, δ, temperatures at which G∗/sinδ=2.2kPa) from dynamic shear rheological tests of binders, Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). The study found that samples made of different proportions of PMA can be effectively differentiated by IDT strength, phase angle (δ), and FTIR spectrum. Even the FTIR spectra of extracted asphalt binders without being subject to strict binder extraction and evaporation procedure reveal useful information for quality assurance purpose. The study also further proved that RTFO-treated PMA samples cannot be used to establish quality criteria for field-extracted PMA binders because RTFO does not well simulate field aging of PMA.

Volatile Organic Compounds Generated in Asphalt Pavement Construction and Their Health Effects on Workers

Hot mix asphalt (HMA) is a major construction material used for building roads, airport runways, and parking lots. During HMA construction, a massive amount of volatile organic compounds (VOCs) is emitted from the hot asphalt mixtures, creating a potential health risk to on-site workers. Few studies have quantitatively investigated the constituents and potential health effects of the VOCs generated in HMA pavement construction. This paper presents the results of a study in which air samples were collected at multiple locations and time points of several projects during HMA pavement construction and were subsequently characterized for their chemical compositions and concentrations by using gas chromatography/mass selective detector (GC/MSD). The analysis results are compared with occupational exposure limits mandated or recommended by various agencies. Although the individual concentrations of the identified chemicals were found to be below various exposure limits, their collective effect on human health remains unknown and may not be ignored. This paper contributes to the knowledge of the types and concentrations of VOCs generated in asphalt pavement construction, their potential health risks to workers, and possible mitigation measures.