Effect of Aramid Fibers on Balanced Mix Design of Asphalt Concrete

Fiber-reinforced asphalt concrete (FRAC) was tested using limestone, PG 64-22 binder, and 20% reclaimed asphalt pavement (RAP). After mixing fibers with different lengths and dosages, they were extracted and recovered to evaluate their dispersion in the FRAC. The uniaxial fatigue test, IDEAL CT test, and flow number test were performed on FRAC with different fiber lengths and asphalt contents. The balanced mix design (BMD) approach was then used to analyze the uniaxial and flow number test results in order to evaluate the effect of aramid fibers on fatigue and rutting resistance of the pavement. The dispersion test showed that the 19 mm and 10 mm aramid fibers at a dosage rate of 0.5 g/kg provided the best dispersion. The 19 mm fibers showed better performance test results than the 10 mm and 38 mm fibers. The BMD approach provided ranges of asphalt contents to produce mixes with certain resistances to fatigue and rutting. The BMD approach also demonstrated the effect of fibers with different lengths on increasing the resistance to fatigue and rutting. The study concluded that the 19 mm fibers with a dosage of 0.5 g/kg produce best results. The BMD approach is a good tool that can be used to refine the mix ingredients, including additives such as fibers, in order to optimize pavement resistance to various distresses such as fatigue cracking and rutting.

Empirical correlation of the Modified Wheel Tracker (MWT) and the dynamic creep test for evaluating the permanent deformation of HMA

The Wheel Tracking Test (WTT) has been extensively used for laboratory characterization of permanent deformation of Hot Mix Asphalt (HMA). However, the fully-confined setup of the device is unable to capture the tertiary zone where shear deformation takes place. This makes the permanent deformation resistance characteristics of HMA difficult to analyze. Hence, a modified wheel tracker (MWT), with unconfined lateral sides along the wheel tracking direction was utilized in this study, which can capture the tertiary flow [referred to as the Flow Number (FN)]. The dynamic creep test, which yields FN, is a common laboratory test which has the ability to characterize permanent deformation considering the shear behavior. The study investigated the relationship of the MWT and the dynamic creep test utilizing the permanent deformation and permanent micro-strain data from the respective tests. A novel parameter, FN-Index was explored. The permanent deformation parameters derived from the MWT were well correlated with the dynamic creep test. The MWT showed promising repeatability for the FNs.

Evaluation and Comparison of Mechanical Properties of Polymer-Modified Asphalt Mixtures

Polymer modification is extensively used in the Kingdom of Saudi Arabia (KSA) because the available asphalt cement does not satisfy the high-temperature requirements. It was widely used in KSA for more than two decades, and there is little information regarding the differences in the performance of different polymers approved for binder modification. Pavement engineers require performance comparisons among various polymers to select the best polymer for modification rather than make their selection based on satisfying binder specifications. Furthermore, the mechanical properties can help select polymer type, producing mixes of better resistance to specific pavement distresses. The study objective was to compare the mechanical properties of the various polymer-modified asphalt (PMA) mixtures that are widely used in the Riyadh region. Control mix and five other mixes with different polymers (Lucolast 7010, Anglomak 2144, Pavflex140, SBS KTR 401, and EE-2) were prepared. PMA mixtures were evaluated through different mechanical tests, including dynamic modulus, flow number, Hamburg wheel tracking, and indirect tensile strength. The results show an improvement in mechanical properties for all PMA mixtures relative to the control mixture. Based on the overall comparison, the asphalt mixture with polymer Anglomk2144 was ranked the best performing mixture, followed by Paveflex140 and EE-2.

Rutting and moisture-induced damage potential of foamed warm mix asphalt (WMA) containing RAP

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.

Determining the Circular Flow Number of a Cubic Graph

A circular nowhere-zero $r$-flow on a bridgeless graph $G$ is an orientation of the edges and an assignment of real values from $[1, r-1]$ to the edges in such a way that the sum of incoming values equals the sum of outgoing values for every vertex. The circular flow number, $\phi_c(G)$, of $G$ is the infimum over all values $r$ such that $G$ admits a nowhere-zero $r$-flow. A flow has its underlying orientation. If we subtract the number of incoming and the number of outgoing edges for each vertex, we get a mapping $V(G) \to \mathbb{Z}$, which is its underlying balanced valuation. In this paper we describe efficient and practical polynomial algorithms to turn balanced valuations and orientations into circular nowhere zero $r$-flows they underlie with minimal $r$. Using this algorithm one can determine the circular flow number of a graph by enumerating balanced valuations. For cubic graphs we present an algorithm that determines $\phi_c(G)$ in case that $\phi_c(G) \leqslant 5$ in time $O(2^{0.6\cdot|V(G)|})$. If $\phi_c(G) > 5$, then the algorithm determines that $\phi_c(G) > 5$ and thus the graph is a counterexample to Tutte's $5$-flow conjecture. The key part is a procedure that generates all (not necessarily proper) $2$-vertex-colourings without a monochromatic path on three vertices in $O(2^{0.6\cdot|V(G)|})$ time. We also prove that there is at most $2^{0.6\cdot|V(G)|}$ of them.

Nurse-led telephone outreach for a COVID-adapted suspected colorectal cancer pathway

Background: COVID-19 has brought about unprecedented challenges to healthcare services in the UK. The pandemic led to the cessation of colonoscopy and outpatient clinics. A bespoke COVID-adapted cancer pathway, using computed tomography (CT) scanning and the quantitative faecal immunochemical test (qFIT), was introduced to mitigate the risks of patients referred with potential colorectal cancer. Aims: This study aims to evaluate the workload of patient telephone calls undertaken by nurses and their impact on the operation of the pathway. Methods: Data were collected prospectively and analysed to assess the volume of patient flow, number of calls made and content of conversations. Findings: During a 2-month period, 975 patients (56.6% female, median age 63 years) were registered on the COVID-adapted cancer pathway. The 45.9% (n=448) of patients who did not return qFIT tests in a timely manner were contacted. Of these, 9.4% (n=42) requested to postpone or declined an appointment. Most were appreciative of the opportunity to clarify the rationale of the pathway and address any concerns. Conclusions: Phone calls made and received by nursing staff were helpful to discuss patient concerns and increase patients' understanding of the alternative treatment options available during the pandemic.