Asif Ahmed

Vitamin-D status is not a confounder of the relationship between zinc and diarrhoea: a study in 6–24-month-old underweight and normal-weight children of urban Bangladesh

Background/Objective:The role of micronutrients particularly zinc in childhood diarrhoea is well established. Immunomodulatory functions of vitamin-D in diarrhoea and its role in the effect of other micronutrients are not well understood. This study aimed to investigate whether vitamin-D directly associated or confounded the association between other micronutrient status and diarrhoeal incidence and severity in 6–24-month underweight and normal-weight children in urban Bangladesh.Subjects/Methods:Multivariable generalised estimating equations were used to estimate incidence rate ratios for incidence (Poisson) and severity (binomial) of diarrhoea on cohorts of 446 normal-weight and 466 underweight children. Outcomes of interest included incidence and severity of diarrhoea, measured daily during a follow-up period of 5 months. The exposure of interest was vitamin-D status at enrolment.Results:Normal-weight and underweight children contributed 62 117 and 62 967 day observation, with 14.2 and 12.8 days/child/year of diarrhoea, respectively. None of the models showed significant associations of vitamin-D status with diarrhoeal morbidity. In the final model, zinc-insufficient normal-weight children had 1.3 times more days of diarrhoea than sufficient children (P<0.05). Again zinc insufficiency and mothers education (1–5 and >5 years) had 1.8 and 2.3 times more risk of severe diarrhoea. In underweight children, older age and female had 24–63 and 17% fewer days of diarrhoea and 52–54 and 31% fewer chances of severe diarrhoea.Conclusion:Vitamin-D status was not associated with incidence and severity of diarrhoea in study children. Role of zinc in diarrhoea was only evident in normal-weight children. Our findings demonstrate that vitamin-D is not a confounder of the relationship between zinc and diarrhoea.

Prediction of Strength and Stiffness Properties of Recycled Pavement Base Materials Using Non-destructive Impact Echo Test

Reclaimed Asphalt Pavement (RAP) and Recycled Crushed Concrete Aggregates (RCCA) are being used increasingly as an alternative to the conventional base materials in pavement construction. However, product variability and lack of strength-stiffness characteristics are limiting the use of recycled materials in pavement application. A non-destructive evaluation technique could provide a better quality control tool for the highway officials during the construction. Therefore, the objective of the current study is to develop a correlation between the non-destructive impact echo and Unconfined Compressive Strength (UCS) test for RAP and RCCA materials. Both impact echo and UCS tests were performed on specimens prepared with 100% RAP and RCCA. The RAP and RCCA were separately treated using four (0, 2, 4 and 6%) different dosages of Portland cement. Based on the experimental results, the range of P-wave velocity was found between 175 m/s to 475 m/s, the compressive strength varied between 67 kPa to 2860 kPa and tangent modulus range was 19 MPa to 280 MPa. Dynamic modulus of elasticity was also calculated from the P-wave velocity, density, and Poisson’s ratio. At 4% and 6% cement contents, dynamic modulus of elasticity was within 10% of the tangent modulus found from UCS test. At 0% and 2% cement content, higher variation was observed. Inadequate fines to fill the voids might be the reason of lower P-wave velocity at 0% and 2% cement contents. This could eventually have predicted lower values of dynamic modulus.

Parametric Study on Slope Stability Using Recycled Plastic Pin

Expansive clay soil in the North Texas region contributes to frequent shallow slope failures on highway embankments, which require a substantial maintenance budget to repair. Through several field demonstration projects, the recycled plastic pin (RPP) has been proven to be a sustainable and cost effective alternative for the Texas Department of Transportation (TxDOT) in stabilizing shallow slope failure. In the current study, an extensive numerical analysis using the finite element method (FEM) was conducted to evaluate the most influential parameters in designing a slope stabilization scheme with RPP. A parametric study was conducted using five different soil strengths, six slope heights (1.52 m increments from 4.57 m to 12.19 m), three slope ratios (4H:1V, 3H:1V and 2H:1V), three RPP lengths (2.44 m, 3.05 m, and 3.66 m) and five RPP spacing configurations (0.91 m, 1.22 m, 1.52 m, 1.83 m, and 2.13 m). By employing the strength reduction technique in PLAXIS 2D, the factor of safety (FS) was determined for all combinations of the above parameters. The obtained FS values ranged from 1.51 to 3.76. Regression analysis showed that soil strength and RPP spacing had the greatest influence on the FS of the reinforced slope. INTRODUCTION Soil in North Texas is expansive and clayey, making it particularly susceptible to shallow slope failure (Khan et al. 2013). The depths and plan dimensions for such slides vary with soil type and slope geometry and are generally characterized by sliding depths of less than 3.05 m (10 ft.); however, depths of 0.9 m (3 ft.) to 1.8 m (6 ft.) have become more common (Loehr and Bowders 2007). Slope stability issues are typically solved with retaining walls, soldier piles and lagging, and grating cribs (Khan 2013). North Texas roadways are plagued with slope stability problems, and repairs often require a significant maintenance budget. Across the United States, costs associated with the repair of shallow slope failures (resulting in sliding depths between 0.9 (3 ft.) and 3.05 m (10 ft.)) are estimated to be greater than or equal to costs associated with major landslides (Turner and Schuster 1996). In addition, shallow failures often cause significant damages to guard rails, shoulders, and portions of roadways. If not properly maintained, these structures require more extensive and expensive repairs (Loehr et al. 2000). Slope stabilization Geo-Risk 2017 GSP 283 226

Expansive Subgrade Behavior on a State Highway in North Texas

Expansive soil in pavement subgrade experiences volume change due to the seasonal moisture and temperature. For the clear understanding of the subgrade behaviour, it is necessary to study the pavement behaviour in real time which connects the gap between moisture, temperature and suction variation with induced pressure on the pavement and pavement deformation. The current study presents an extensive instrumentation program on a subgrade soil and performance of an asphalt pavement over expansive clay subjected to seasonal variation of moisture temperature and suction. A section over 2- lane State Highway (SH) 342 in Lancaster, Texas, maintained by Texas Department of Transportation (TxDOT) was instrumented with moisture and temperature sensor, water potential probe, pressure sensor and piezometer to monitor the seasonal variation on continuous basis using automated data collection system. In addition, horizontal inclinometer was installed across the pavement and routine topographic survey was conducted to monitor the pavement deformation. Based on the preliminary monitoring results of almost a year, a 5-7% variation of moisture was observed in the subgrade soil whereas; 2 inch of movement was noticed over the pavement. Additionally, a temperature prediction model was developed based on 15 months monitoring data.

Data-Based Real-Time Moisture Modeling in Unsaturated Expansive Subgrade in Texas

Moisture variations significantly influence the strength and stiffness of expansive subgrade soils, shortening the service lives of pavements and increasing the associated maintenance costs. Accurate measurements of soil moisture can be obtained through soil sampling and testing, but the process can be extensive and costly. Empirical models can accurately predict the moisture variations in an expansive subgrade in a shorter period of time, with lower accompanying costs. The objective of the current study was to develop moisture models, using real-time field monitoring data from two hot mix asphalt roads in North Texas. The collected data were analyzed in a statistical environment to solve two first degree Fourier series. The solution produced a moisture variation model that captured variations associated with seasonal effects and temporary variations associated with rainfall. The outputs of this model were within 90% of the values measured on site. Application of the developed models will facilitate noninvasive estimations of the response of soil strength and stiffness properties to variations in moisture.

Monitoring of Moisture Variation in Highway Slope through Resistivity Imaging

Moisture flow dynamics in roadway systems affect the performance and serviceability of pavements. Accurate measurement of moisture requires direct collection of soil samples, followed by testing in the laboratory. Nondestructive measurements from neutron probes, time or frequency domain reflectometry, and radiometry in remote sensing are also used by researchers to record changes in moisture content. However, these methods either yield discrete point information or have depth limitations. Geophysical testing provides a continuous portrayal of the subsurface moisture flow. During this study, a geophysical testing method known as electrical resistivity imaging (ERI) was adopted. Monthly testing was performed on a selected two-lane highway slope. The objective of the study was to determine seasonal moisture fluctuations in a side slope of highway pavement. Over a monitoring period of 12 months, two distinct seasons were observed. April to October was determined to be the dry season, whereas November to March was found to be the wet season. Resistivity values ranged from as high as almost 25 Ohmm in the dry period to as low as 10 Ohm-m in the wet period. In addition, the zone of moisture variation was found to be nearly 3 m. Moreover, the possible zone of moisture intrusion could be detected from resistivity imaging after rainfall. The ERI data was further statistically analyzed and correlated with temperature and precipitation data. The findings will further advance understanding of the dynamics of moisture flow in roads.

Mitigation of Subgrade Moisture in North Texas by Using Modified Moisture Barrier

In addition to causing shrinkage and swelling in expansive subgrade, seasonal moisture variations may alter material properties, hence pavement serviceability. In order to prevent moisture variation in the subgrade, moisture barriers may be used. The current study observes the effects of a modified moisture barrier on subgrade moisture control. The modified moisture barrier that is used in this study is a combination of a 40-mi LLDPE (linear low density polyethylene) geomembrane and an 8-oz. HDPE (high density polyehtylene) geocomposite. Insitu moisture sensors were employed to observe subgrade moisture variation. Edge moisture intrusion was observed along farm-to-market (FM) 987 near Kaufman, Texas. Based on the observation of edge moisture intrusion, the moisture barrier consisting of a geomembrane and a geocomposite (geonet sandwiched between two nonoven geotextiles) was placed in a 50-ft section of FM 987. A 50-ft control section was also established along the roadway. Moisture sensors in both the barrier and control sections continuously monitor the moisture content of the subgrade soil. In the barrier section, preliminary results indicate a steady moisture content which is not influenced by rainfall. In the control section, the moisture content levels are influeced by rainfall. This ongoing study shows promise for using the modified moisture barrier to prevent subgrade moisture intrusion and provide for better pavement serviceability.

Moisture Variation in Expansive Subgrade Through Field Instrumentation and Geophysical Testing

Seasonal climatic variations in subgrade soil affect pavement responses and can reduce pavement serviceability. In addition to causing shrinkage and swelling in expansive subgrade, variations in moisture suction may alter the material properties of soil, which ultimately affect pavement performance. The current study monitored the seasonal variation of subgrade moisture content, rainfall, and pavement deformation of a section over State Highway 342, in Dallas, Texas. Moisture sensors were installed at different depths up to 4.5 m. The soil was found to be highly plastic clay (CH) in the selected site. In addition to acquiring real-time moisture data from sensors, geophysical testing was also conducted on the slope of the pavement. Electrical Resistivity Imaging (ERI) was carried out at the slope of the instrumented pavement section to observe the moisture flow at the edge of the pavement. Based on the field monitoring data, moisture variation ranged from 5% to 14%, with higher moisture contents correlating with rainfall events. While moisture sensors provided point information, resistivity imaging yielded a continuous portrayal of subsurface moisture flow. Furthermore, rainfall-associated deformation of the pavement was monitored. Based on the monitored data, it was observed that pavement deformation varied with rainfall. A total deformation of 38 mm was recorded over the monitoring period.

Potential Applicability of Slab Impulse Response (SIR) in Geophysical Investigation of Pavement Structures

Proper functionality of pavement structures can be ensured with adequate quality assurance and quality control during construction. By monitoring pavement health throughout its design life, authorities can reduce structural damages, and achieve subsequent reduction in maintenance cost and time. Geophysical investigation is growing significantly as a tool of QA/QC of pavement structures. The increased use can be attributed to (i) decreased time consumption, (ii) reduced expense, (iii) lower variability of test results compared to laboratory tests, and (iv) the nonreduction of structural integrity and serviceability of pavement compared to destructive testing. The current research work evaluated the applicability of the Slab Impulse Response (SIR) method in pavement health monitoring by conducting in-situ test results at four different locations of a construction project in Dallas, Texas. The dynamic cone penetrometer (DCP) and Geogauge were utilized alongside SIR to determine the resilient and elastic modulus of the pavement layers. Field investigation results indicated that SIR can be useful in identifying damages associated with low stiffness, such as delamination, honeycombing, cracking, and voids below the slabs-on-grade. Comparisons presented in this paper demonstrated the effectiveness of SIR as an alternative tool to conventional methods of pavement health monitoring. Introduction The United States of America is comprised of 4,064,000 miles of public road network. The total length of paved roads is 2,646,000 miles, and the remaining 1,418,000 miles are unpaved (Greene and Wegener, 1997). The satisfactory performance of the road network highly depends on the quality assurance and quality control (QA/QC) during the construction process (Mahedi et al. 2017b). Proper QA/QC measures are needed to be adopted during construction to ensure the design requirements. Moreover, proper design life can be ensured only if proper quality control is maintained throughout the construction process. Traditionally practiced test methods for QA/QC have been proven unreasonable in terms of time, cost, reliability, and applicability (Graveen 2001). Laboratory tests are often time consuming, and sometimes are not practical during construction work. The use of in-situ techniques that can efficiently evaluate the material properties through simple and less time-consuming procedures would be ideal (Mahedi et al. 2017a). Airfield and Highway Pavements 2017 222