Compatibility of ultra high performance concrete as repair material : bond characterization with concrete under different loading scenarios

The rehabilitation of concrete structures, especially concrete bridge decks, is a major challenge for transportation agencies in the United States. Often, the most appropriate strategy to preserve or rehabilitate these structures is to provide some form of a protective coating or barrier. These surface treatments have typically been some form of polymer, asphalt, or low-permeability concrete, but the application of UHPC has shown promise for this application mainly due to its negligible permeability, but also as a result of its excellent mechanical properties, self-consolidating nature, rapid gain strength, and minimal creep and shrinkage characteristics. However, for widespread acceptance, durability and performance of the composite system must be fully understood, specifically the bond between UHPC and NSC often used in bridge decks. It is essential that the bond offers enough strength to resist the stress due to mechanical loading or thermal effects, while also maintaining an extended service-life performance. This report attempts to assess the bond strength between UHPC and NSC under different loading configurations. Different variables, such as roughness degree of the concrete substrates, age of bond, exposure to freeze-thaw cycles and wetting conditions of the concrete substrate, were included in this study. The combination of splitting tensile test with 0, 300, 600 and 900 freeze-thaw cycles was carried out to assess the bond performance under severe ambient conditions. The slant-shear test was utilized with different interface angles to provide a wide understanding of the bond performance under different combinations of compression and shear stresses. The pull-off test is the most accepted method to evaluate the bond strength in the field. This test which studies the direct tensile strength of the bond, the most severe loading condition, was used to provide data that can be correlated with the other tests that only can be used in the laboratory. The experimental program showed that the bond performance between UHPC and NSC is successful, as the strength regardless the different degree of roughness of the concrete substrate, the age of the composite specimens, the exposure to freeze-thaw cycles and the different loading configurations, is greater than that of concrete substrate and largely satisfies with ACI 546.3R-06.

Comparative study of anchorage strengths of epoxy coated hooked bars

Hooked reinforcing bars (rebar) are used frequently to carry the tension forces developed in beams and transferred to columns. Research into epoxy coated hooked bars has only been minimally performed and no research has been carried out incorporating the coating process found in ASTM A934. This research program compares hooked rebar that are uncoated, coated by ASTM A775, and coated by ASTM A934. In total, forty-two full size beam-column specimens were created, instrumented and tested to failure. The program was carried out in three phases. The first phase was used to refine the test setup and procedures. Phase two explored the spacing of column ties within the joint region. Phase three explored the three coating types found above. Each specimen included two hooked rebar which were loaded and measured independently for relative rebar slip. The load and displacement of the hooked rebar were analyzed, focusing on behavior at the levels of 30 ksi, 42 ksi and 60 ksi of rebar stress. Statistical and general comparisons were made using the coating types, tie spacing, and rebar stress level. Many of the parameters composing the rebar and concrete were also tested to characterize the components and specimens. All rebar tested met ASTM standards for tensile strength, but the newer ASTM A934 method seemed to produce slightly lower yield strengths. The A934 method also produced coating thicknesses that were very inconsistent and were higher than ASTM maximum limits in many locations. Continuity of coating surfaces was found to be less than 100% for both A775 and A934 rebar, but for different reasons. The many comparisons made did not always produce clear conclusions. The data suggests that the ACI Code (318-05) parameter of 1.2 for including epoxy coating on hooked rebar may need to be raised, possibly to 2.5, but more testing needs to be performed before such a large value change is set forth. This is particularly important as variables were identified which may have a larger influence on rebar capacity than the Development Length, of which the current 1.2 factor modifies. Many suggestions for future work are included throughout the thesis to help guide other researchers in carrying out successful and productive programs which will further the highly understudied topic of hooked rebar.

Investigation of using waste engine oil blended with reclaimed asphalt materials to improve pavement recyclability

With the increasing importance of conserving natural resources and moving toward sustainable practices, the aging transportation infrastructure can benefit from these ideas by improving their existing recycling practices. When an asphalt pavement needs to be replaced, the existing pavement is removed and ground up. This ground material, known as reclaimed asphalt pavement (RAP), is then added into new asphalt roads. However, since RAP was exposed to years of ultraviolet degradation and environmental weathering, the material has aged and cannot be used as a direct substitute for aggregate and binder in new asphalt pavements. One material that holds potential for restoring the aged asphalt binder to a usable state is waste engine oil. This research aims to study the feasibility of using waste engine oil as a recycling agent to improve the recyclability of pavements containing RAP. Testing was conducted in three phases, asphalt binder testing, advanced asphalt binder testing, and laboratory mixture testing. Asphalt binder testing consisted of dynamic shear rheometer and rotational viscometer testing on both unaged and aged binders containing waste engine oil and reclaimed asphalt binder (RAB). Fourier Transform Infrared Spectroscopy (FTIR) testing was carried out to on the asphalt binders blended with RAB and waste engine oil compare the structural indices indicative of aging. Lastly, sample asphalt samples containing waste engine oil and RAP were subjected to rutting testing and tensile strength ratio testing. These tests lend evidence to support the claim that waste engine oil can be used as a rejuvenating agent to chemically restore asphalt pavements containing RAP. Waste engine oil can reduce the stiffness and improve the low temperature properties of asphalt binders blended with RAB. Waste engine oil can also soften asphalt pavements without having a detrimental effect on the moisture susceptibility.

Effects of silicon content and cooling rate on mechanical properties of heavy section ductile cast iron

The effects of Si and cooling rate are investigated for their effect on the mechanical properties and microstructure. Three alloys were chosen with varying C and Si contents and an attempt to keep the remainder of the elements present constant. Within each heat, three test blocks were poured. Two blocks had chills – one with a fluid flowing through it to cool it (active chill) and one without the fluid (passive) – and the third block did not have a chill. Cooling curves were gathered and analyzed. The mechanical properties of the castings were correlated to the microstructure, cooling rate and Si content of each block. It was found that an increase in Si content increased the yield stress, tensile strength and hardness but decreased the impact toughness, elongation and Young’s modulus. The fast cooling rates produced by the chills caused a high nodule count in the castings along with a fine ferrite grain size and a high degree of nodularity. The fine microstructures, in turn, increased the strength and ductile to brittle transition temperature (DBTT) of the castings. The fast cooling rate was not adequate to overcome the dramatic increase in DBTT that is caused by the addition of Si.

Processing and mechanical properties of cast aluminum containing scandium, zirconium, and ytterbium

A series of aluminum alloys containing additions of scandium, zirconium, and ytterbium were cast to evaluate the effect of partial ytterbium substitution for scandium on tensile behavior. Due to the high price of scandium, a crucible-melt interaction study was performed to ensure no scandium was lost in graphite, alumina, magnesia, or zirconia crucibles after holding a liquid Al-Sc master alloy for 8 hours at 900 °C in an argon atmosphere. The alloys were subjected to an isochronal aging treatment and tested for conductivity and Vickers microhardness after each increment. For scandium-containing alloys, peak hardnesses of 520-790 MPa, and peak tensile stresses of 138-234 MPa were observed after aging from 150-350 °C for 3 hours in increments of 50 °C, and for alloys without scandium, peak hardnesses of 217-335 MPa and peak tensile stresses of 45-63 MPa were observed after a 3 hour, 150 °C aging treatment. The hardness and tensile strength of the ytterbium containing alloy was found to be lower than in the alloy with no ytterbium substitution.

PERFORMANCE EVALUATION OF LLDPE/CaCO3 MODIFIERS WITH AND WITHOUT TITANATE COUPLING AGENT ON ASPHALT BINDER AND MIXTURE

The complexity and challenge created by asphalt material motivates researchers and engineers to investigate the behavior of this material to develop a better understanding, and improve the performance of asphalt pavement. Over decades, a wide range of modification at macro, meso, micro and nano scales have been conducted to improve the performance of asphalt pavement. This study was initiated to utilize the newly developed asphalt modifier pellets. These pellets consisted of different combinations of calcium carbonate (CaCO3), linear low-density polyethylene (LLDPE) and titanate coupling agent (CA) to improve the asphalt binder as well as pavement performance across a wide range of temperature and loading pace. These materials were used due to their unique characteristics and promising findings from various industries, especially as modifiers in pavement material. The challenge is to make sure the CaCO3 disperses very well in the mixture. The rheological properties of neat asphalt binder PG58-28 and modified asphalt binder (PG58-28/LLDPE, PG58-28/CaCO3, PG58-28/CaCO3/LLDPE, and PG58-28/CaCO3/LLDPE/CA), were determined using rotational viscometer (RV) test, dynamic shear rheometer (DSR) test and bending beam rheometer test. In the DSR test, the specimens were evaluated using frequency sweep and multiple shear creep recovery (MSCR). The asphalt mixtures (aggregate/PG58-28, aggregate/ PG58-28/LLDPE, aggregate/PG58-28/CaCO3, aggregate/PG58-28/LLDPE/CaCO3 and aggregate/PG58-28/LLDPE/CaCO3/CA) were evaluated using the four point beam fatigue test, the dynamic modulus (E*) test, and tensile strength test (to determines tensile strength ratio, TSR). The RV test results show that all modified asphalt binders have a higher viscosity compared to the neat asphalt binder (PG58-28). Based on the Jnr results (using MSCR test), all the modified asphalt binders have a better resistance to rutting compared to the neat asphalt binder. A higher modifier contents have resulted in a better recovery percentage of asphalt binder (higher resistance to rutting), except the specimens prepared using PECC’s modified asphalt binder (PG58-28/CaCO3/LLDPE). The BBR test results show that all the modified asphalt binders have shown comparable performance in term of resistance to low temperature cracking, except the specimen prepared using the LLDPE modifier. Overall, 5 wt% LLDPE modified asphalt binder was found to be the best asphalt binder in terms of resistance to rutting. Meanwhile, 3 wt% PECC-1CA’s modified asphalt binder can be considered as the best (in terms of resistance to thermal cracking) with the lowest mean critical cracking temperature. The appearance of CaCO3 was found useful merely in improving the resistance to fatigue cracking of asphalt mixture. However, application of LLDPE has undermined the fatigue life of asphalt mixtures. Adding LLDPE and coupling agent throughout this study does not sufficiently help in terms of elastic behavior which essential to enhance the resistance to fatigue cracking. In contrast, application of LLDPE has increased the indirect tensile strength values and TSR of asphalt mixtures, indicates a better resistance to moisture damage. The usage of the coupling agent does not change the behavior of the asphalt mixture, which could be due to imbalance effects resulted by combination of LLDPE and CaCO3 in asphalt binder. Further investigations without incorporating CaCO3 should be conducted further. To investigate the feasibility of using LLDPE and coupling agent as modifiers in asphalt pavements, more research should be conducted on different percentages of LLDPE (less than 3 wt%), and at the higher and w wider range of coupling agent content, from 3 wt% to 7 wt% based on the polymer mass.

THE PERFORMANCE AND MODIFICATION OF RECYCLED ELECTRONIC WASTE PLASTICS FOR THE IMPROVEMENT OF ASPHALT PAVEMENT MATERIALS

Bulk electric waste plastics were recycled and reduced in size into plastic chips before pulverization or cryogenic grinding into powders. Two major types of electronic waste plastics were used in this investigation: acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). This research investigation utilized two approaches for incorporating electronic waste plastics into asphalt pavement materials. The first approach was blending and integrating recycled and processed electronic waste powders directly into asphalt mixtures and binders; and the second approach was to chemically treat recycled and processed electronic waste powders with hydro-peroxide before blending into asphalt mixtures and binders. The chemical treatment of electronic waste (e-waste) powders was intended to strengthen molecular bonding between e-waste plastics and asphalt binders for improved low and high temperature performance. Superpave asphalt binder and mixture testing techniques were conducted to determine the rheological and mechanical performance of the e-waste modified asphalt binders and mixtures. This investigation included a limited emissions-performance assessment to compare electronic waste modified asphalt pavement mixture emissions using SimaPro and performance using MEPDG software. Carbon dioxide emissions for e-waste modified pavement mixtures were compared with conventional asphalt pavement mixtures using SimaPro. MEPDG analysis was used to determine rutting potential between the various e-waste modified pavement mixtures and the control asphalt mixture. The results from this investigation showed the following: treating the electronic waste plastics delayed the onset of tertiary flow for electronic waste mixtures, electronic waste mixtures showed some improvement in dynamic modulus results at low temperatures versus the control mixture, and tensile strength ratio values for treated e-waste asphalt mixtures were improved versus the control mixture.