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Abstract: Despite significant economic and environmental benefits, performance of warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP) remains a matter of concern. Among the current WMA technologies, the plant foaming technique (called “foamed WMA” in this study) has gained the most attention, since it eliminates the need for chemical additives. In the present study, the laboratory performance, namely rutting and moisture-induced damage potential of foamed WMA containing RAP were evaluated and compared with those of similar hot mix asphalt (HMA) containing identical amount of RAP. Dynamic modulus, Hamburg wheel tracking (HWT) and flow number tests were performed to assess the rutting resistance of the mixes. Also, stripping inflection point from HWT tests and tensile strength ratio after AASHTO T 283 and moisture induced sensitivity test (MIST) conditioning were used to evaluate the moisture-induced damage of asphalt mixes. It was found that MIST conditioning effectively simulates the moisture-induced damage and can capture the propensity of asphalt mixes to moisture damage more distinctly compared to AASHTO T 283 method due to application of cyclic loadings. The foamed WMA was found to exhibit higher rutting and moisture-induced damage potential due to lower mixing and compaction temperatures compared to HMA. However, the increase in RAP content was found to reduce rutting and moisture-induced damage potential for WMA. Therefore, the lower stiffness of foamed WMA may be compensated with the addition of stiffer binder from RAP.

Microbially induced calcite precipitation is an environment-friendly method for improving stiffness, strength, and dilatancy of loose or weak soils. Although many experimental studies have been performed on biocemented sands, few efforts have been devoted to establishing constitutive models for such materials. A critical-state-based bounding-surface model for biocemented sands was proposed in this research. An exponential equation of the plastic deviatoric strain was used to describe the degradation in a biocemented bond. The established model was applied to predict the drained triaxial test results of biocemented calcareous sands at different confining pressures and biocementation levels. We found that the current proposed biocemented model can well predict the softening and dilation of biocemented calcareous sands. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) is a novel cementation technique. The improved responses of biotreated soils are mainly attributed to interparticle MICP bonds and have been extensively studied by element-scale tests. However, the particle-scale mechanism of MICP bonds has not been fully understood, especially when considering the discrepancy in particle morphology. In this paper, we carried out a series of particle-scale tensile tests on biotreated quartz sands and glass beads and found that tensile strength of the MICP bonds increased with an increase in cementation level or a decrease in regularity of particle shape. We also interpreted the statistical distribution of the tensile strength and tensile failure modes. The results of this study could provide a solid base for theoretic modeling of biotreated soils. [ABSTRACT FROM AUTHOR]

Selection of a proper binder–aggregate combination is an important step to ensure optimum resistance to moisture-induced damage in asphalt mixes. In recent years, such selection has become more crucial as asphalt industries are using various additives and modifiers in asphalt mixes that can substantially change bonding strength of a binder–aggregate system. Also, environmental factors such as oxidative aging can affect the chemical compositions of the binder and influence moisture-induced damage resistance of a mix. In order to understand the mechanisms of moisture-induced damage, it is important to determine the chemical and thermodynamic properties of constituent materials of a mix and identify their contributions to the bond strength. The present study was undertaken to explore the effects of aggregate types, additives, and aging on the moisture susceptibility of asphalt mixes using chemical and thermodynamic approaches. For this purpose, a PG 64-22 and a PG 76-28 binder were blended with a warm mix asphalt (WMA) additive, an antistripping agent (ASA), a reclaimed asphalt pavement (RAP) binder and polyphosphoric acid (PPA). The surface free energy (SFE) components of these binder blends under unaged, short-term aged, and long-term aged conditions were determined using the dynamic Wilhelmy plate (DWP) method for measuring dynamic contact angle. Chemical analyses of the binder blends were carried out using x-ray fluorescence (XRF) analysis and Fourier transform infrared (FTIR) spectroscopy. Properties of five commonly available local aggregates were determined using XRF and universal sorption device (USD) testing. The SFE components of the binders and aggregates were used to quantify bonding characteristics of binder–aggregate systems under dry and wet conditions. Aggregate properties significantly influenced the moisture-induced damage potential of a mix. In addition, an increase in carbonyl and sulfoxide functional groups resulted in increased moisture susceptibility with aging. Therefore, the presence of amine functional groups in both WMA and ASA is expected to provide resistance to moisture-induced damage and conversely the presence of PPA may reduce resistance to moisture-induced damage of a binder–aggregate system. [ABSTRACT FROM AUTHOR]

Source amnesia is an explicit memory (declarative) disorder, particularly episodic, where source or contextual information concerning facts is severely distorted and/or unable to be recalled. This paper reviews the literature on source amnesia, including memory distrust syndrome, and its accepted correlation with the medial diencephalic system and the temporal lobes, and the suggested linkage between the frontal lobes, including special interest with the prefrontal cortex. Posthypnotic induction was the first presentation of source amnesia identified in the literature. The Wisconsin Cart Sorting Test (WCST), Positron Emission Topography (PET), Phonemic Verbal Fluency Test, Stroop Color Word Interference Test, and explicit and implicit memory tests are defined and linked to empirical research on amnesiacs.