Journal of Materials in Civil Engineering

This study was intended to successfully implement asphalt binders modified with electronic waste (e-waste) from recycled computer plastics to improve asphalt binder performance versus conventional asphalt binders. The e-waste powder percentages blended with asphalt binders were 2.5, 5, and 15%, respectively. Rotational viscosity, dynamic shear rheometer testing, and bending beam rheometer testing was conducted upon modified and virgin asphalt binder samples. The addition of e-waste powders increased binder viscosity and blending and mixing temperatures and decreased rutting susceptibility versus virgin asphalt binders, and lower percentages of e-waste powders modified asphalt binders resulted in similar $m$-values at the specified low temperature grade of the control asphalt binder.

Fly ash (FA), silica fume (SF), and ground blast furnace slag (GBFS) were used as the supplementary cementitious materials (SCMs) in cement paste. The autogenous shrinkage (AS) and the shrinkage cracks of cement paste with SCMs were experimentally investigated in this study, and the relationship of AS, tensile strength, and crack area of cement paste were analyzed. The test results show that FA decreases the AS of cement paste and SF increases the AS. Both the AS and the crack area of cement paste decrease with the increase of the water-binder (W/B) ratio. When W/B ratios of different cement pastes are kept the same, the tensile strength of cement paste is not influenced by the AS if the specimens can shrink freely. Equations are established to describe the relationship among AS, tensile strength, and crack area of the cement paste with SCMs.

Despite growing interest in the use of shape memory alloys (SMAs) in civil structures, much is still to be understood about their behavior in real loading environments. This experimental work focuses on characterizing the thermomechanical behavior of a thermally prestressed NiTiNb SMA under thermal and loading conditions pertinent to civil structural applications. The work aims at exploring the feasibility of using this type of alloy in developing seismic retrofitting spirals that could be used to actively confine vulnerable reinforced concrete columns to improve their flexural ductility and shear strength under earthquake loading. Differential scanning calorimetry tests are conducted to determine the transformation temperatures of the used alloy. A testing program is carried out on 2-mm-diameter NiTiNb wires to examine the recovery stress of prestrained wires and the monotonic and cyclic behaviors of thermally prestressed wires under various testing durations and ambient temperatures. A thermal chamber is used to induce a realistic range of ambient temperature ($-10°\mathrm{C}$ to 55°C) during testing. The results show that the recovery stress is quite stable within the studied range of temperature. The prestressed NiTiNb alloy exhibits nonlinear behavior with a modulus that is highly dependent on ambient temperature.

The shear behavior of reinforced ultrahigh toughness cementitious composite (RUHTCC) beams without transverse reinforcement was investigated in the present paper, in which UHTCC has tensile strain-hardening behavior due to the steady propagation of multiple fine cracks. A total of 15 simply supported beams were subjected to a concentrated load at midspan, of which nine beams were RUHTCC beams and six beams were RC counterpart beams. The varied parameters were shear span-effective depth ratio and longitudinal reinforcement ratio. The experimental results showed that an enhanced ultimate shear strength that was about two times larger than that of an RC beam was obtained for slender beams with use of UHTCC, whereas only a marginal improvement was obtained for short beams. All tested RUHTCC beams presented a diagonal multiple-cracking mode and a stable diagonal crack propagation process. The maximum crack width was controlled within 0.1 mm at the service state and the high postcracking shear reserve strength was obtained, which means that there is no need to limit the minimum web reinforcement ratio in the engineering design for a RUHTCC beam. On the basis of the present test and tests by other investigators, a group of empirical formulae are suggested for predicting the ultimate shear strength of fiber-reinforced beams without stirrups. A good agreement between the predicted strength and tested value was shown, with the mean and coefficient of variation of the ratio between them about 1.02 and 0.10, respectively.

Application of power ultrasound to enhance dispersion of commercial densified silica fume leads to increased compressive strengths and refinement of the pore structure in mortars, compared with those that are untreated. This was attributed to the enhanced pozzolanic reactivity achieved by particle dispersion through sonication, leading to higher consumption of portlandite during curing, and formation of a calcium silicate hydrate gel with a higher degree of cross-linking than is identified in specimens with densified silica fume. This suggests that with the use of sonicated silica fume, it is possible to reduce the required quantity of admixture in blended cements to achieve specified performance, with the additional advantage of the formation of a highly densified structure and refined pore network, contributing to potential improvements in durability.

This study elaborates on methods for assessing the material property called zero shear-rate viscosity (ZSV) in asphalt concrete based on shear frequency sweep testing. The purpose of ZSV assessment is for linear viscoelastic permanent deformation modeling. The basic approach was to fit parameters of the Laplace-transformed Burger’s model to the measured shear dynamic modulus data. This method produced multiple solutions, although an approximate measure of the minimum ZSV could be estimated. Therefore, extrapolation was necessary to assess the frequency-independent ZSV based on the measured frequency sweep data. The method was complemented with the simplified Cross extrapolation model that was successfully fitted to the measured data. The extended method also produced multiple solutions, although the minimum ZSV could be assessed unambiguously. The results were in accordance with expectations based on measured dynamic shear modulus and phase angle.

Because the thermal stress restrained specimen test (TSRST) is recommended by the Strategic Highway Research Program (SHRP) as a test method to evaluate low-temperature cracking resistance of asphalt mixtures, many studies have been carried out to investigate the performance of asphalt mixture with this test using fracture temperature as the indicator. However, few of them focus on discussing its reliability. In this paper, six kinds of asphalts mixtures are evaluated by TSRST, and it is found that the evaluation results obtained by the four indices are contradictory. It is also inferred from the results of each index coefficient of variation that fracture temperature and transition temperature are more stable when they are used to evaluate low-temperature performance of asphalt mixtures. Through the application of principal-component analysis (PCA) and the Boston Consulting Group’s matrix on the TSRST results, it is demonstrated that fracture temperature used as the indicator of low-temperature performance of asphalt mixture is reliable, and this conclusion is verified by gray relation analysis between the four indices from TSRST and bending-strain-energy density.

This paper semiquantitatively evaluates the microrheological properties of asphalt binder using atomic force microscopy. It also presents differences between these properties amongst the various microstructures within an asphalt binder, in addition to the influence of oxidative aging on these properties. Nano-indentation experiments performed within a microgrid of asphalt phases determined micromechanical properties such as stiffness, adhesion, and elastic/plastic behavior. The evaluated materials include asphalts AAB, AAD, and ABD from the Materials Reference Library of the Strategic Highway Research Program, chosen because of variations in crude source, chemical composition, and elemental analysis. Analysis of nano-indentation creep measurements corresponding to phase-separated regions revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging induced substantial microstructural change within these domains, including variations in phase structure, properties, and distribution. The form and extent of these changes, however, were different for each asphalt. Interpretation of data collected from the atomic force microcopy experiments in this study advances understanding of the microstructural composition of asphalt binders and the response of the microstructural phases of the asphalt binder under load, in addition to how the mechanical responses in the phases change with aging.

In this study, an experimental configuration that reveals the dynamic response of porous concretes in a drop weight impact test was introduced. Through the measurement of particle velocity at the interface, between the impactor and the concrete target, the dynamic response was obtained in an easily applicable way. Laser Doppler velocimetry (LDV) was used in monitoring the time history of the particle velocity at the interface, which was subsequently analyzed to determine the dynamic strengths of the concrete specimens tested. The velocity measurements were analyzed using a special reverberation application of the impedance mismatch method. The test results showed that the experimental configuration was sufficient to measure the dynamic strengths of porous concretes and a normal concrete with moderate strength. The method was validated by using impactors having different dynamic impedances in testing the same material and was also verified to be precise enough to distinguish between different types of porous concrete mixtures.

To estimate the generated leachate and design of a leachate recirculation system, a clear understanding of the hydraulic conductivity of municipal solid waste with degradation, and the effects of intermixed cover soils, is necessary. Two sets of laboratory-scale bioreactor landfills were simulated and sampled at various phases of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content. The matrix structure of the degradable solid waste component was broken down because of decomposition. However, daily cover soil, a nondegradable constituent of municipal solid waste, remained constant. Therefore, interaction between daily cover soil and municipal solid waste particles are expected to affect hydraulic characteristics resulting from degradation. The current study shows that the hydraulic conductivity of municipal solid waste with cover soil is lower than that without any intermixed cover soils. Based on experimental results, hydraulic conductivity of municipal solid waste samples in (aerobic) phase I is $5.8\times {10}^{-3}\mathrm{cm}/\mathrm{s}$, and drops to $2.6\times {10}^{-3}$ and $1.7\times {10}^{-3}\mathrm{cm}/\mathrm{s}$, with 20 and 30% cover soils, respectively. Hydraulic conductivity decreases with increasing soil percentage. Therefore, the effects of cover soils on municipal solid waste hydraulic conductivity should be evaluated and taken into consideration during the design and operation of a landfill recirculation system.