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.

Accounting for warping and differential drying shrinkage mechanisms in the design of jointed plain concrete payments

When a concrete slab experiences differential volume change due to temperature, moisture, and shrinkage gradients, it deforms. The stresses induced by these differential volume changes can reduce the pavement’s fatigue life. Differential volume change is quantified by the equivalent temperature difference required to deform a comparable flat slab to the same shape as the actual slab. This thesis presents models to predict the equivalent temperature difference due to moisture warping and differential drying shrinkage. Moisture warping occurs because a portion of drying shrinkage is reversible, while differential drying shrinkage is due to the irreversible portion of drying shrinkage. The amount of reversible shrinkage was investigated for concretes made with different types of aggregate, including lightweight and recycled. Another source of differential volume change is built-in curl, which is caused by temperature gradients at the time of paving. This thesis also presents a comparison of methods used to quantify built-in curl.

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.