Browsing by Author "David W. Johnston, Committee Member"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Comparison of Fatality Data by Ethnic Group Within North Carolina Construction Industry
    (2006-04-26) Inserny-Mazuera, Michele; David W. Johnston, Committee Member; William J. Rasdorf, Committee Member; Michael L. Leming, Committee Chair
    The purpose of this study was to evaluate Occupational Fatality Investigation Review (OFIR) data to compare fatality data by ethnic groups in different construction trades in the North Carolina construction industry from 2000 to 2004. This research involves the estimation of the number of employees in each construction trade broken down by ethnic group using the data from the annual American Community Survey. It also requires the calculation of fatality rates by ethnic group within each construction trade according to the Bureau of Labor Statistics data and procedures. The results show an overall increasing trend of Hispanic employment in construction, a decreasing trend in White employment and a somewhat constant trend in the Black employment. The overall fatality rates for minority groups in construction were about two times that of White laborers. The overall Hispanic fatality rate was essentially equal to that of Black employees. The occupation with the highest fatality rate in North Carolina, Construction Laborer, also had the largest percentage of minorities. The sparse data for many occupations makes firm conclusions. The lack of comparable occupation classification systems between the different sources of data and changes in the classification system created difficulty in the analysis.
  • No Thumbnail Available
    Effects of Mixture Composition and Time on Dielectric Constant of Fresh Concrete
    (2007-05-30) Leon, Cesar Octavio; George F. List, Committee Member; Michael L. Leming, Committee Chair; David W. Johnston, Committee Member
    The strength and durability properties of concrete are related to its water to cement ratio. Previous studies have shown that electrical properties of concrete appear to be related to both the water and cement contents of a mixture as well. In this study, a new technique and device were developed to measure apparent dielectric constant of a concrete mixture at early stages of hydration. The ability of the device to be used as a tool for fundamental understanding of dielectric properties of fresh concrete and its potential to be used as field testing for quality control during early stage of concrete were analyzed. Differences on the apparent dielectric constant measurements due to external variables such as time and frequency were studied. Analysis was made for variations of the apparent dielectric constant due to changes in the mixtures components such as water, cement and fly ash contents. The effects on the apparent dielectric constant due to inclusion or not of water reducing admixture were also analyzed. The relationship between apparent dielectric constant and the compressive strength of the concrete was of special interest for this study. The method was found to be potentially useful in identifying changes which would cause differences in compressive strength among similar mixtures. The analysis showed a limitation for using the apparent dielectric constant alone in order to identify between any given mixtures, however.