Understanding Oxidative Aging of Asphalt Binder and it\u27s Effects on Cracking Susceptibility of Asphalt Mix

Every year around 400 million tons of asphalt mix is being laid in the United States and a significant portion of it is required for pavement rehabilitation. Cracking is one of the most common pavement distresses that is still not fully understood by the researchers. Very few states mandate tests for cracking resistance during the mix design phase; in addition, the test methods vary a lot from state to state. In the presence of oxygen, the asphalt binder over time undergoes chemical changes and becomes stiff which is known as oxidative aging that makes asphalt pavement more susceptible to cracking. Therefore, proper characterization of asphalt aging is a prerequisite to study the cracking mechanism of asphalt mix. In this dissertation, efforts are given for characterization of oxidative aging, investigation of the effect of aged binder on cracking susceptibility, and development of an antioxidant to reduce the aging-induced cracking. In this study, rheological characterization of laboratory aged binder and extracted binder from asphalt mix was performed using dynamic shear modulus of the binder to understand oxidative aging. Then the correlation between laboratory binder aging and binder aging in asphalt mix was established and a Rolling Thin Film Oven (RTFO) aging test protocol for warm mix asphalt (WMA) was developed. Another factor for cracking susceptibility of asphalt pavement is the excessive content of reclaimed asphalt pavement (RAP). RAP is added to the hot mix asphalt (HMA) for economic and environmental interest but the highly aged binder in RAP makes the mix stiffer and escalates the cracking. Because it is quick and simple, the viability of using a handheld Fourier Transformed Infrared (FT-IR) spectrometer was investigated to detect and quantify the aging of binder by measuring the absorbance intensity of carbonyl groups. An in-situ test method was developed to determine the reclaimed asphalt pavement (RAP) content in the plant mix using a handheld FT-IRS. The use of rejuvenators is the most suitable strategy to accommodate a higher amount of RAP in HMA and bio-based rejuvenators are of high interest. In this study, four types of cracking tests were performed on asphalt mix made with two different categories of rejuvenators: petroleum-based and bio-based oil. It was concluded that petroleum-based aromatic oil performed better to restore the cracking potential of the mix with high RAP content. Sound understanding of the cracking mechanism is necessary to find the right cracking susceptibility test for asphalt mix and design a cracking resistant mix. A finite element model of semi-circular bend (SCB) test of asphalt mix incorporating the cohesive zone material (CZM) model was performed using ANSYS to simulate and predict the fracture potential of asphalt mix as conducted in the laboratory according to ASTM D 8044 test method. The CZM properties of fine aggregate mastic (FAM) needed for ANSYS model of SCB test was determined by a laboratory double cantilever beam test and corresponding finite element model of double cantilever beam test., It was concluded that critical energy release rate (Jc) of asphalt mixture predicted from ANSYS model of SCB test was precise when compared with the laboratory SCB test of asphalt mix. Finally, locally sourced Lignin was used as an asphalt performance enhancer as well as an antioxidant. It was observed that lignin could improve the high-temperature performance grade of the binder and reduce the aging index. Mix made of lignin modified binder showed better cracking resistance by improving the flexibility index. Through this study, understanding oxidative aging helped with developing a revised short-term aging protocol for warm mix asphalt. One of the immediately implementable outcomes of this research is the in-situ application of handheld FT-IR spectrometer for quality control during the mix production at the plant through determining the reclaimed asphalt pavement content. This research will contribute to choosing suitable rejuvenators by understanding the cracking mechanism of asphalt mix through different tests. The finite element cohesive zone material model developed in this study can precisely predict fracture resistance of the mix in semicircular bending test by performing a double cantilever beam test of fine aggregate mastic. Viability of using bio based rejuvenator for RAP mixes and also the suitability of utilizing locally sourced lignin as an oxidant in asphalt binder were addressed in this research and the findings will help implement these environmentally friendly alternatives in resolving cracking related problems in asphalt pavements

Human-Powered Concrete Mixer

There are currently many non-profit organizations and social enterprises working to alleviate the hardships of living in a developing economy, such as lack of proper homes, schooling, and bathrooms. The solutions to these problems rely on concrete, and are currently limited by the mixing time for these batches of concrete in rural and remote areas. Mixing with shovels is inefficient and imprecise, and the possible solution of a portable gas-powered concrete mixer is too expensive and too immobile for remote areas. The Human-Powered Concrete Mixer (HPCM) provides an alternative to these methods that is more efficient and more precise than hand mixing with shovels, yet cheaper and more mobile than a portable gas-powered concrete mixer. Our team was able to successfully design a mixer that, in comparison to mixing with shovels, reduced mixing time from 15 minutes to 5 minutes, reduced the necessary number of laborers from 6 to 2, and produced structurally sound concrete. The modular design of the mixer allows the HPCM to be easily moved to remote construction areas, and the cost of the mixer makes it more economically viable for non-profit organizations and social enterprises than a gas-powered alternative. In sum, the HPCM provides a low cost, efficient, mobile, and reproducible alternative that enables non-profit organizations and social enterprises to more effectively help more people

On-Site Measurement of the Water-Cementitious Ratio and Heat of Hydration of Delivered Concrete

In this study, AASHTO T318-15 was adopted to estimate the water content of fresh concrete mixes and then revised to have better precision. The additional step required sieving out the coarse aggregate after drying the sample in a microwave oven, and it was then used in the calculation of the absorbed water and cementitious material content. Several laboratory batches, as well as on-site water-cementitious (w/cm) ratio tests, were performed on concrete mixes containing ordinary Portland cement, ground granulated blast furnace slag, and Class F fly ash. The results of the experiments indicated that the accuracy of the revised method was increased to an average percentage error of 2.16% from the actual w/cm ratio, while the method based on AASHTO T318 was 6.2%. For cases with high chemical admixtures dosages, washing vinegar was used to wash out the particles around the dried sieved coarse aggregate to calculate the w/cm ratio with a more precise mass for each sample. A simple on-site measurement for the heat of hydration of fresh concrete was conducted using an insulated 1-meter cube. The cube was designed to be well insulated with 8-cm of insulation material on each side. It acted as a semi-adiabatic calorimetry since the heat loss was small. The temperature-time history at the center was used to calculate the adiabatic temperature rise (ATR) of the concrete. An average heat loss characteristic parameter was obtained for each delivered batch using the measured concrete temperature-time history after five days of curing. A finite element model (FEM) was developed to analyze the cube at different ambient environmental conditions. A table with the required insulation for various ambient conditions with a range between -10 to 30 °C ambient temperatures was also provided so that the setup can accurately estimate the ATR using only the temperature measurement at the center of the cube. The w/cm ratio and the heat of hydration test methods were evaluated in three on-site castings in the state of West Virginia. Two of the on-site castings contained Grade 100 ground granulated blast furnace slag. The third on-site casting used Class F fly ash concrete. Several compressive strength cylinders were made and cured at a temperature of 23 °C. The materials used in each on-site casting were also collected to perform compressive strength, adiabatic, and isothermal heat of hydration tests in laboratory conditions. The compressive strength measured on-site was lower than the laboratory batches which indicates a higher w/cm ratio was received on-site. The adiabatic temperature rises calculated from the cube’s center temperature compared well with the results from both the adiabatic and isothermal calorimetry. Results show that the on-site temperature measurement using the 1-m cube can be considered as a simple and accurate approach to measure the heat of hydration of a delivered concrete batch

Concrete mixing truck as a rheometer

Publisher's version (útgefin grein)An increasing interest has emerged in correlating the output of the concrete mixing truck to values obtained by rotational rheometers. The output of the former has usually been the hydraulic pressure needed to turn the drum. In such research, experimental errors can be higher than usual, which makes it harder to obtain confident relationships. To better understand the physical characteristics of the truck's Theological values, the above analysis is made by a series of computer simulations (i.e. with CFD). From this, it is evident that the slope H of the truck's pressure values depends both on the plastic viscosity mu as well as on the yield stress tau(0). However, for the intercept G of the truck's values, it is mostly dependent on the yield stress tau(0). In addition to this, both values H and G depend on volume of concrete in the truck as well as on density.The Icelandic Research Fund -RANNIS (grant numbers 163382-051,163382-052,163382-053) and Norcem AS (Heidelberg Cement Group)."Peer Reviewed

Analysis of shear rate inside a concrete truck mixer

In addition to the mixing energy applied to the fresh concrete (i.e. shearing during mixing), the shear history after mixing is also important. This applies especially to binder rich concretes like the different types of high performance concrete (HPC). With this in mind, the shear rate is analyzed inside a drum of a concrete truck mixer. The objective is to better understand the effect of transport of fresh concrete, from the ready mix plant to the building site. The analysis reveals the effect of different drum charge volume and drum rotational speed. Also, the effect of yield stress and plastic viscosity is investigated. The work shows that the shear rate decreases in an exponential manner with increasing drum charge volume. It is also shown that for a given drum speed, the shear rate decreases both with increasing plastic viscosity and yield stress.This work has been funded by the Icelandic Centre for Research - RANNIS [grant numbers 163382-051, 1006100202], Norcem AS (Heidelberg Cement Group) and ReadyMix Abu Dhabi."Peer Reviewed

Development of Specifications for Modified Engineered Cementitious Composites (MECC) for use as Bridge Deck Overlays in Nevada

Engineered cementitious composite (ECC) material is a high-strength, fiber-reinforced, ductile mortar mixture that can exhibit tensile strains of up to 5%. The durability and mechanical properties of ECC make it a desirable construction material. This study presents an extensive evaluation of modified engineered cementitious composite (MECC) using locally sourced raw materials for use as a bridge-deck-overlay material. MECC is a mixture of cement, fly ash, water, concrete sand, and poly-vinyl alcohol fibers. The concrete sand used in this study was used in lieu of the typically used silica sand to reduce the high material cost, which makes MECC a modified ECC mix. Currently, the Nevada Department of Transportation (NDOT) uses a polymer concrete for bridge-deck-overlays in Nevada. While NDOT has had good performance with the polymer concrete overlays, the polymer concrete material is an expensive proprietary material. NDOT believes that MECC may be a viable alternative to the polymer concrete as a bridge-deck-overlay material.In this study, three different representative aggregates from throughout Nevada were selected to understand how the local aggregates would perform in MECC mixes. In total, eighteen different MECC mixes were evaluated using a total of thirteen different tests to determine the fresh and hardened properties of the MECC material. These tests included compressive strength, freeze-thaw durability, resistance to chloride ion penetration, and drying shrinkage. Additionally, a uniaxial tensile test was developed to test the tensile strengths and tensile strains of these different MECC mixes. In addition to evaluating MECC, samples of the polymer concrete and of a traditional Portland cement concrete mix were also tested. These results were used to determine how the performance of the MECC material compares with polymer concrete and traditional concrete. The laboratory test results were then analyzed using several different statistical analyses. First, all of the MECC mixes were compared with each other, and the polymer concrete and traditional concrete mixes. This showed how many mixes had statistically significantly higher/lower performance that both the polymer concrete and traditional concrete. Second, linear regressions were used to determine the standardized regression coefficients (or beta coefficients) which were used to determine which variables (mix proportions, aggregate source, fiber type) influenced the MECC’s properties. Third, additional MECC mixes were batched to determine which aggregate properties would influence the MECC’s properties. From this analysis, several predictive models were developed to predict the properties of an MECC mix that used a specific fine aggregate stockpile. After the completion of the laboratory phase, three different field trials were conducted to determine the feasibility of batching large amounts of MECC at commercial concrete batch plants. In these trials, approximately 6 cubic yards of MECC was mixed using different plant configurations to determine if any special measures would be needed to mix MECC on a large-scale. Additionally, a trial slab of MECC was placed at each of these field trials to determine how easy the MECC material would be to place, consolidate, and finish.The findings of this study are that MECC has many desirable qualities of a bridge-deck-overlay material. MECC has higher compressive strengths, higher tensile strengths and strains, high resistance to chloride ion penetration, and higher abrasion resistance than traditional concrete. Additionally, MECC has similar performance to the polymer concrete, meaning there is not a significant drop in performance between the materials. The large-scale trial batches showed that MECC could be mixed on a large-scale without any special measures. While MECC is harder to place than traditional concrete, it is not expected to require any specialty equipment for placement. The findings of this study were used to draft a specification for NDOT for the use of MECC as a bridge-deck-overlay material. This specification will be used in an upcoming field project by NDOT where a bridge-deck-overlay measuring approximately 28 feet by 140 feet by 4 inches thick will be placed in the spring of 2016 in Northern Nevada

Heat generation in aircraft tires under free rolling conditions

A method was developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions of the wheel and runway surface. Comparison with data obtained with buried thermocouples in tires shows good agreement

Pneumatic Tire

For many years, tire engineers relied on the monograph, \u27Mechanics of Pneumatic Tires\u27, for detailed information about the principles of tire design and use. Published originally by the National Bureau of Standards, U.S. Department of Commerce, in 1971, and a later (1981) edition by the National Highway Traffic Safety Administration (NHTSA), U.S. Department of Transportation, it has long been out of print. No textbook or monograph of comparable range and depth has appeared since. While many chapters of the two editions contain authoritative reviews that are still relevant today, they were prepared in an era when bias ply and belted-bias tires were in widespread use in the United States and thus did not deal in a comprehensive way with more recent tire technology, notably the radial constructions now adopted nearly universally. In 2002, it was preposed that NHTSA should sponsor and publish electronically a new book on passenger tires, under editorship of the University of Akron, to meet the needs of a new generation of tire scientists, engineers, designers, and users. This text is the outcome. The chapter authors are recognized authorities in tire science and technology. They have prepared scholarly and up-to-date reviews of the various aspects of passenger car tire design, construction and use, and included test questions in many instances, so that the book can be used for self-study or as a teaching text by engineers and others entering the tire industry