Application of ultra high performance concrete (UHPC) as a thin-bonded overlay for concrete bridge decks

As transportation infrastructure across the globe approaches the end of its service life, new innovative materials and applications are needed to sustainably repair and prevent damage to these structures. Bridge structures in the United States in particular are at risk as a large percentage will be reaching their design service lives in the coming decades. Superstructure deterioration occurs due to a variety of factors, but a major contributor comes in the form of deteriorating concrete bridge decks. Within a concrete bridge deck system, deterioration mechanisms can include spalling, delaminations, scaling from unsuitable material selection, freeze-thaw damage, and corrosion of reinforcing steel due to infiltration of chloride ions and moisture. This thesis presents findings pertaining to the feasibility of using UHPC as a thin-bonded overlay on concrete bridge decks, specifically in precast bridge deck applications where construction duration and traffic interruption can be minimized, as well as in cast-in-place field applications. UHPC has several properties that make it a desirable material for this application. These properties include post-cracking tensile capacity, high compressive strength, high resistance to environmental and chemical attack, negligible permeability, negligible dry shrinkage when thermally cured, and the ability to self consolidate. The compatibility of this bridge deck overlay system was determined to minimize overlay thickness and dead load without sacrificing bond integrity or lose of protective capabilities. A parametric analysis was conducted using a 3D finite element model of a simply supported bridge under HS-20 truck and overload. Experimental tests were conducted to determine the net effect of UHPC volume change due to restrained shrinkage and tensile creep relaxation. The combined effects from numerical models and test results were then considered in determining the optimum overlay thickness for cast-in-place and precast applications.

Erupted magma volume estimates at Santiaguito and Pacaya Volcanoes, Guatemala using digital elevation models

High resolution digital elevation models (DEMs) of Santiaguito and Pacaya volcanoes, Guatemala, were used to estimate volume changes and eruption rates between 1954 and 2001. The DEMs were generated from contour maps and aerial photography, which were analyzed in ArcGIS 9.0®. Because both volcanoes were growing substantially over the five decade period, they provide a good data set for exploring effective methodology for estimating volume changes. The analysis shows that the Santiaguito dome complex grew by 0.78 ± 0.07 km3 (0.52 ± 0.05 m3 s-1) over the 1954-2001 period with nearly all the growth occurring on the El Brujo (1958-75) and Caliente domes (1971-2001). Adding information from field data prior to 1954, the total volume extruded from Santiaguito since 1922 is estimated at 1.48 ± 0.19 km3. Santiaguito’s growth rate is lower than most other volcanic domes, but it has been sustained over a much longer period and has undergone a change toward more exogenous and progressively slower extrusion with time. At Santiaguito some of the material being added at the dome is subsequently transported downstream by block and ash flows, mudflows and floods, creating channel shifting and areas of aggradation and erosion. At Pacaya volcano a total volume of 0.21 ± 0.05 km3 was erupted between 1961 and 2001 for an average extrusion rate of 0.17 ± 0.04 m3 s-1. Both the Santiaguito and Pacaya eruption rate estimates reported here are minima, because they do not include estimates of materials which are transported downslope after eruption and data on ashfall which may result in significant volumes of material spread over broad areas. Regular analysis of high resolution DEMs using the methods outlined here, would help quantify the effects of fluvial changes to downstream populated areas, as well as assist in tracking hazards related to dome collapse and eruption.

VOLUME YIELDS OF SMALLHOLDER Eucalyptus grandis W. HILL EX MAIDEN STANDS IN EASTERN PARAGUAY

Smallholders in eastern Paraguay plant small stands of Eucalyptus grandis W. Hill ex Maiden intended for sale on the local market. Smallholders have been encouraged to plant E. grandis by local forestry extension agents who offer both forestry education and incentive programs. Smallholders who practice recommended forestry techniques geared towards growing large diameter trees of good form are financially rewarded by the local markets which desire saw log quality trees. The question was posed, are smallholders engaging in recommended silvicultural practices and producing reasonable volume yields? It was hypothesized that smallholders, having received forestry education and having financial incentives from the local market, would engage in silvicultural practices resulting in trees of good form and volume yields that were reasonable for the local climate and soil characteristics. Yield volume results from this study support this hypothesis. Mean volume yield was estimated at 70 cubic meters per hectare at age four and 225 cubic meters per hectare at age eight. These volume yields compare favorably to volume yields from other studies of E. grandis grown in similar climates, with similar stocking levels and site qualities.