Hubbe M.A.,North Carolina State University |
Hasan S.H.,Banaras Hindu University |
Ducoste J.J.,Construction and Environmental Engineering
BioResources | Year: 2011
Recent years have seen explosive growth in research concerning the use of cellulosic materials, either in their as-recieved state or as modified products, for the removal of heavy metal ions from dilute aqueous solutions. Despite highly promising reports of progress in this area, important questions remain. For instance, it has not been clearly established whether knowledge about the composition and structure of the bioadsorbent raw material is equally important to its availability at its point of use. Various physical and chemical modifications of biomass have been shown to boost the ability of the cellulose-based material to bind various metal ions. Systems of data analysis and mechanistic models are described. There is a continuing need to explain the mechanisms of these approaches and to determine the most effective treatments. Finally, the article probes areas where more research is urgently needed. For example, life cycle analysis studies are needed, comparing the use of renewable biosorbents vs. conventional means of removing toxic metal ions from water.
Mertol H.C.,Ankara University |
Rizkalla S.,Construction and Environmental Engineering |
Rizkalla S.,North Carolina State University |
Zia P.,North Carolina State University |
Mirmiran A.,Florida International University
PCI Journal | Year: 2010
This paper summarizes the findings of an extensive research program that examined the shrinkage and creep behavior of high-strength concrete (HSC) up to a strength of 18 ksi (124 MPa). Creep and shrinkage strains of 60 specimens were monitored for up to two years. The variables considered in this investigation were the concrete compressive strength, specimen size, curing type, age of concrete at loading, and loading stress level. Research findings indicate that the current American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications could be used to estimate the creep coefficient and shrinkage strain of HSC up to 15 ksi (103 MPa). However, the current AASHTO LRFD specifications do not provide appropriate predictions for concrete compressive strength greater than 15 ksi (103 MPa). A revised time-development correction factor is proposed to obtain better predictions for HSC up to 18 ksi (124 MPa). For HSC compression members, the current AASHTO LRFD specifications require an excessive amount of minimum longitudinal reinforcement to account for the long-term effects due to shrinkage and creep. Based on an analysis, a new relationship is proposed for the required minimum reinforcement ratio.
Hassan T.K.,Ain Shams University |
Rizkalla S.H.,Construction and Environmental Engineering |
Rizkalla S.H.,Constructed Facilities Laboratory |
Rizkalla S.H.,North Carolina State University
PCI Journal | Year: 2010
The thickness of the panel at different load levels compared well with recent test results conducted at North Carolina State University in Raleigh. The shear-flow capacity of the insulating materials and the CFRP shear grid are determined using the proposed approach. The influence of the degree of the composite interaction on the induced curvature and slip-strain behavior is presented. A simple design chart for estimating the flexural capacity of the wall panels with different shear-reinforcement ratios is proposed. The approach is also verified by using finite-element analysis up to die service-load level. The predicted displacement and strains compared well with the measured values reported by the experimental program.
Gransberg D.,Construction and Environmental Engineering |
Scheepbouwer E.,Private Bag
Construction Research Congress 2016: Old and New Construction Technologies Converge in Historic San Juan - Proceedings of the 2016 Construction Research Congress, CRC 2016 | Year: 2016
The U.S. construction industry is characterized as adversarial; however the same can be said for the construction industry in countries that have adopted alliance contracting as the project delivery method of choice for megaprojects. This paper builds on the results of a rigorous case study analysis of nine alliance megaprojects from Australia, the Netherlands, New Zealand, and the United Kingdom. The research found that alliance contracts were best suited for extremely complex, high-risk projects where a large number of external stakeholders demand a highly integrated and highly collaborative project delivery team. This paper extrapolates the alliance project characteristics to the U.S. infrastructure market by comparing the international projects to a U.S. case study project that the Washington State Department of Transportation prevented from delivering as an alliance contract by uncertainties in the legislative authority about key concepts in alliancing such as the "no sue" clause. The paper goes on to develop a framework for making a business case for implementing alliance project delivery for complex infrastructure renewal projects by a typical U.S. state public transportation agency. © ASCE.
Kastrouni E.,University of Maryland University College |
Gkritza K.,Purdue University |
Hallmark S.L.,Construction and Environmental Engineering |
Robert Stephenson W.,Iowa State University
Transportation Research Record | Year: 2015
The vehicle-miles-traveled (VMT) fee has been widely suggested as an alternative funding mechanism to the current state of practice, the fuel tax per gallon. The VMT fee has drawn researchers' and policy makers' attention, particularly regarding its equity performance in various social groups. With the introduction of the concept of vulnerable households, and with the use of socioeconomic-, geographic-, and vehicle-specific attributes from the 2009 National Household Travel Survey, the social groups in the United States that were most likely to be affected under each funding mechanism were identified through the estimation of three-stage least squares models at the national level. The results showed that households located in states with lower fuel taxation operated vehicles of lower fuel efficiency and thus contributed a larger portion of revenues generated by the fuel tax. In contrast, households with higher fuel-efficiency vehicles or with a higher average income generated more trips annually and thus would pay higher VMT fees at the household level. The study also examined whether the identified vulnerable households at the national level were different at the state level. With the use of the state of Iowa as a case study, the results suggested that, despite some similarities in the characteristics of the vulnerable households at the two levels of analysis, the development of state-specific models was statistically supported.