Effect of Weathering on Rubberized Porous European Mixture

This project investigated the effect of weathering (UV light, oxidative, and water) on the performance of rubberized porous European mix (PEM) by laboratory tests and field pavement investigation. Three rubberized PEM mixes were produced by three processes: the dry process, the wet process, and the terminal blend in the laboratory. For comparison purposes, PEM mixture containing styrenebutadiene- styrene (SBS)-modified binder was also used. Weathering for 1,000 and 3,000 h on compacted PEM mixes were conducted. Dynamic modulus, rutting/moisture resistance, and Cantabro loss were measured for each mixture and aging condition. Additionally, the test sections of rubberized and SBS-modified PEM in Georgia were investigated through a visual inspection on the pavements and laboratory testing on core samples. The results indicated that (1) the weathering had increased the elastic properties and the rutting resistance, but had no significant effect on the moisture resistance and decreased the raveling resistance of PEM mixes; (2) the effect of weathering was more on the performance properties of rubberized PEM mixes in the dry process and the wet process than those of the SBS control PEM; (3) the first 1,000-h weathering had more effect on the dynamic modulus and the Cantabro loss of PEM mixes than the last 2,000-h weathering; and (4) all PEM field test sections of the dry process, the wet process, and the control showed excellent performance after 3 or 5 years of service

Comprehensive Evaluation of the Long-Term Performance of Rubberized Pavement

This project investigated the long-term performance of hot asphalt mixes containing crumb rubber modifiers (CRM) added in dry or wet processes. A total of eight asphalt mixtures—four Porous European Mixtures (PEMs) and four Stone Matrix Asphalts (SMAs)—were designed with PG 76-22 modified with CRM, which was added in either a dry or wet process. These mixtures were compared to control mixtures using an SBS-modified PG 76-22. Mixtures incorporating a “hybrid”-modified PG 76-22 were also evaluated. First, the samples were weathered in the Georgia Weathering Asphalt Device (GWAD) for 1,000 hrs and 3,000 hrs and tested to determine their dynamic modulus, fatigue life, rutting, and Cantabro. Binders extracted from the weathered samples were then evaluated using a dynamic shear rheometer (DSR), gel-permeable chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR). Second, the interactions of dry- and wet-processed CRM with asphalt binder were compared during storage and paving. Results indicated: 1) adding TOR to the CRM binder improved PG grade and separation resistance; 2) the dynamic modulus, |E*|, of both rubberized PEM and SMA in dry process did not differ significantly from that of the control mixtures or mixtures using the “hybrid”- modified binders before and after weathering; 3) the fatigue life (Nf) of unaged rubberized PEM and SMA in the dry process was similar to that in wet process, although lower than that of control SBS; 4) after 3000-hrs aging, the fatigue life of the dry-processed rubberized SMA is similar to that of the wet-processed but lower than that of hybrid and SBS SMA, regardless of strain and stress levels or test temperatures; 5) the rutting and Cantabro loss of the rubberized PEM and SMA in dry process were higher than those of control SBS after weathering; 6) CRM and asphalt binder interact during the production and paving stages based on DSR, GPC, FTIR, and AFM results. The effect of weathering on the properties of the asphalt binders in rubberized, dry-processed PEMs and SMAs was similar to that in the wet-processed mixtures but greater than that in the control SBS

EFFECTS OF KAOLIN ON THE ENGINEERING PROPERTIES OF PORTLAND CEMENT CONCRETE

The focus of this study was to determine the feasibility of using kaolin, a very small particle clay, as partial replacement of fine aggregates in Portland cement concrete (PCC). Kaolin clay is a locally available (Macon, GA, USA) and inexpensive clay mineral. The product, KaMin 90©, used has an average particle size of 1.5 microns and has a low embodied energy. The slump, air void content and compressive strength were examined on samples of PCC with different % of Kaolin. This research indicated the maximum kaolin substitution of fine aggregate for workability. An optimal dosage range for PCC cylinder compressive strength was also defined and found to be 33% greater than the control group. It was also noted that Kaolin engenders a soft and cohesive concrete mix that prevents segregation. A brief cost analyses was performed and determined the economic feasibility of Kaolin PCC

Multi-Scale Evaluation on the Interaction between Asphalt and Crumb Rubber

Crumb rubber modifier (CRM), made from scrap tires, has been introduced into the production of different types of Hot Mix Asphalt (HMA) in either wet or dry process. There has been few research about the interaction between asphalt and the crumb rubbers added in the dry process. In the study, dynamic shear rheometer (DSR) and atomic force microscopy (AFM) were used to explore the interaction between the asphalt binder and CRM in dry and wet process. The results indicated: (1) rubberized binder in dry process have similar modulus, phase angle and complex viscosity with wet process, regardless of unaging or short-term aging, (2) rubberized asphalt in dry process has lower roughness of topographical image than wet process before short-term aging. However, the short-term aging may decrease the difference of the microstructures of the binders in two processes, i.e., wet and dry processes

Evaluations of Nano-sized Hydrated Lime on the Moisture Susceptibility of Hot Mix Asphalt Mixtures

The objective of this study was to evaluate the effect of nano-sized hydrated lime on the moisture susceptibility of the hot mix asphalt (HMA) mixtures in terms of three methodologies to introduce into the mixtures. The experimental design for this study included the utilizations of one binder source (PG 64-22), three aggregate sources and three different methods introducing the lime. A total of 12 types of HMA mixtures and 72 specimens were fabricated and tested in this study. The performed properties include indirect tensile strength (ITS), tensile strength ratio (TSR), flow, and toughness. The results indicated that the nano-sized lime exhibits better moisture resistance. Introducing process of the nano-sized lime will produce difference in moisture susceptibility

Selecting Warm Mix Asphalt Additives by the Properties of Warm Mix Asphalt Mixtures ‒ China Experience

The objective of this research was to select the most effective warm asphalt additives for mix practice based on a series of laboratory testing programs such as density, Marshall stability, freeze-thaw splitting strength, dynamic stability, and bending beam strain. The experimental design of warm mix asphalt included the use of three commonlyused additives, two typical aggregate gradations, one crushed aggregate, and one modified asphalt. Results showed that: (1) the bulk specific gravity and air voids of all the mix specimens were similar to those of controls; (2) the Marshall stability and flow values of the warm stone mastic asphalt were 6.8%–26.6% and 3.5%–10.3%% higher than those of controls, respectively, and those of the warm asphalt concrete were 6.1%–15.6% and 6.5%–9.7% higher than those of controls, respectively; (3) the indirect tensile strength of two types of mixtures was 1.7%–14.4% lower than that of controls, and the average tensile strength ratio of the warm stone mastic asphalt and asphalt concrete was 4.3% and 1.3% higher than that of controls, respectively; (4) the dynamic stability of warm mix specimens was 10.8%–16.6% lower than that of the controls; (5) the average bending failure strain of warm stone mastic asphalt was 7.6% higher than that of the controls, and that of warm asphalt concrete was 12.8% lower than that of the controls; (6) Overall, warm asphalt mixtures with Sasobit and Rediset had relatively best performances required in Southeast China, where rutting and stripping are the main failures of asphalt pavements