Development of mechanistic-empirical damage assessment procedures for CRC pavements with emphasis on traffic loading characteristics.

Edge punchout has been long recognized as the prevailing mode of structural failure in Continuously Reinforced Concrete Pavements (CRCP) and yet, has remained relatively unexplored and unexplained. The existing design and evaluation procedures for CRCP employ American Association of State Highway Transportation Officials (AASHTO) equations for the jointed concrete pavements and the Equivalent Single Axle Load (ESAL) approach that will neither predict nor address edge punchouts. A comprehensive procedure for prediction of CRCP structural deterioration based on fundamental mechanical principles was developed in this study. This procedure directly considers the key design factors and site conditions affecting formation of edge punchouts found from the results of field data analysis and literature review. The mechanism of CRCP structural deterioration modeled in this study is based on consideration of several critical conditions that take place in the field. These conditions include formation of closely spaced transverse cracks, loss of aggregate interlock across transverse cracks, loss of edge support due to erosion, development of high tensile stresses, accumulation of fatigue damage in concrete under repetitive traffic loading, longitudinal cracking of narrow CRCP segments, and punchout development. None of these factors were addressed in the AASHTO approach to CRCP design and evaluation. Several theoretical models were developed in the course of the study including a CRCP structural response prediction model, a mechanistic-empirical model for prediction of longitudinal cracking leading to punchout, a probabilistic model to estimate the number of narrow CRCP segments susceptible to punchout, and a punchout prediction model. A detailed algorithm for CRCP damage assessment and punchout prediction was developed and validated using data from the national Long-Term Pavement Performance (LTPP) experiment. Theoretical results showed reasonable correlation with the observed distresses. Based on the results of this study, a conclusion was made that traffic loading characterization using ESAL approximation developed for jointed concrete pavements is inadequate for mechanistic-based damage assessment of CRC pavements. An alternative approach for traffic loading characterization using axle load spectrum was developed and incorporated in the algorithm for CRCP damage assessment and punchout prediction

Chemo-Enzymatic Synthesis and Biological Evaluation of 5,6-Disubstituted Benzimidazole Ribo- and 2 '-Deoxyribonucleosides

A number of new 5,6-disubstituted benzimidazoles have been prepared and their substrate properties for recombinant E. coli purine nucleoside phosphorylase (PNP; the product of the deoD gene) in the transglycosylation reaction were investigated. The heterocyclic bases showed good substrate activity for PNP and the ribo- and 2-deoxyribonucleosides were synthesized. The predominant (OMe and OEt) or exclusive (Oi-Pr, morpholino, and N-methylpiperazino) formation of the 5-substituted 6-fluoro-1-(β-d- ribofuranosyl)benzimidazoles was observed. The formation of the regioisomeric 6- methoxy-, 6-ethoxy-, or 6-isopropoxy-substituted 1-(2-deoxy-β-d- ribofuranosyl)-5-fluorobenzimidazoles was observed in the trans-2- deoxyribosylation reaction of the corresponding bases. The predominant or exclusive formation of the regioisomeric N1-nucleosides with bulky 5-substituents of 6-fluorobenzimidazole points to a large hydrophobic pocket in the E. coli PNP active site that can accommodate these groups. The biological activity of the synthesized nucleosides was studied and revealed no inhibitory activity against a broad variety of DNA and RNA viruses. The compounds also lacked significant cytotoxicity. © Georg Thieme Verlag Stuttgart New York.status: publishe