Master of Science

Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science

yes / A mechanism analysis based on the upper-bound theorem of concrete plasticity for monolithic concrete joints without transverse reinforcement is presented. Concrete is modelled as a rigid–perfectly plastic material obeying modified Coulomb failure criteria. Existing stress–strain relationships of concrete in compression and tension are comprehensively modified using the crack band theory to allow for concrete type and maximum aggregate size. Simple equations for the effectiveness factor for compression, ratio of effective tensile strength to compressive strength and angle of concrete friction are then mathematically developed using the modified stress–strain relationships of concrete. In addition, 12 push-off specimens made of all-lightweight, sand–lightweight and normal-weight concrete having maximum aggregate size between 4 and 19 mm were physically tested. Test results and mechanism analysis clearly showed that the shear capacity of monolithic concrete joints increased with the increase of the maximum aggregate size and dry density of concrete. The mean and standard deviation of the ratio between experimentally measured and predicted (by the mechanism analysis shear capacities) are 1·01 and 0·16 respectively, showing a closer prediction and less variation than Vecchio and Collins' equation, regardless of concrete type and maximum aggregate size.

Yes / Demolition and reconstruction of degrading structures alongside with the repetitive repair, maintenance, and renovation applications create significant amounts of construction and demolition waste (CDW), which needs proper tackling. The main emphasis of this study has therefore been placed on the development of concrete mixtures with components (i.e., aggregates and binder) coming entirely from CDW. As the binding phase, powdered CDW-based masonry units, concrete and glass were used collectively as precursors to obtain geopolymer binders, which were then incorporated with CDW-based fine and coarse concrete aggregates. Together with the entirely CDW-based concretes, designs were also proposed for companion mixtures with mainstream precursors (e.g., fly ash and slag) occupying some part of the CDW-based precursor combination. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2) were used at various concentrations and combinations as the alkaline activators. Several factors that have impact on the compressive strength results of concrete mixtures, such as mainstream precursor replacement rate, al-kaline molar concentrations, aggregate-to-binder ratios and curing conditions, were considered and these were also backed by the micro-structural analyses. Our results showed that through proper optimiza-tion of the design factors, it is possible to manufacture concrete mix-tures entirely out of CDW with compressive strength results able to reach up to 40 MPa under ambient curing. Current research is believed to be very likely to promote more innovative and up-to-date techniques to upcycle CDW, which are mostly downcycled through basic practices of road base/sub-base filling, encouraging further research and increas-ing the awareness in CDW issue.

Yes / This paper presents an experimental investigation of a new dry connection for reinforced concrete slab elements. Seven full-scale slabs were tested; one slab was monolithic as control specimens, while the other six were assembled using top and bottom steel plates joined by high tensile steel bolts. Two scenarios were proposed for the connection, a simple bolted connection, and a connection with a shear key. The parameters studied were the use of stirrups at the connection section, the step size of the shear key as well as the bolt diameter and number. The test results showed that using a shear key at the assembled section in demountable slabs is more efficient than the simple bolted connection, providing higher flexural stiffness, load capacity, and less deflection. However, increasing the shear key step size improved the flexural performance of the demountable slabs. In addition, adding stirrups to the assembled section enhanced the flexural stiffness and the total load capacity of the demountable slabs. Furthermore, the predictions for the moment capacity and deflection demountable slabs have reasonably good agreement with the experimental results but require additional calibrated data from experiments to be generalized. / Department for Business, Energy and Industrial Strategy (BEIS)

Call number: LD2668 .T4 1935 W32

Call number: LD2668 .T4 1960 C45

Call number: LD2668 .T4 1984 R66 / Master of Science

The extensively used AASHTO structural design procedures for flexible pavement indicate the required pavement design in terms of a structural number. For a particular pavement thickness design, this structural number can be computed from the sum of each pavement layer's thickness multiplied by its strength parameter, called the structural layer coefficient. The research work reported herein presents methods for determining the structural layer coefficients for asphalt emulsion-aggregate mixtures. A hot plant-mixed asphaltic concrete was evaluated for structural layer coefficient, and the radial stress vs. fatigue failure relationship was developed using circular specimens and the Jimenez deflectometer. Relationships between structural number and load repetitions to failure for different loading conditions were developed. These relationships were used to evaluate the structural numbers of other specimens when tested to failure in flexural fatigue. Three asphalt emulsion-aggregate mixtures were designed using CSS-lh asphalt emulsion. The aggregates used for the three mixtures were: (1) Type I aggregate using dense-graded, crushed, river gravel; (2) Type II aggregate using pit-run, coarse sand; and (3) Type III aggregate using a silty sand. These mixtures were evaluated for Marshall stability, Hveem stability and cohesiometer value, unconfined compressive strength, double punch tensile strength and dynamic modulus of elasticity at various ages from 3 to 28 days. Flexural fatigue life, when tested in the deflectometer, was determined for all mixtures at 7 and 28 days. Structural numbers for the specimens and structural layer coefficients for the mixtures were determined. Relationships were developed between the evaluation tests performed and the structural layer coefficients at various mixture ages by using test results from the three mixtures and a regression analysis procedure. A fourth asphalt emulsion-aggregate mixture using CSS-lh asphalt emulsion and a Type II crusher-run aggregate was designed. Evaluation tests were performed at 3 and 7 days and layer coefficients for the mixture were predicted for 7 and 28 days using the regression equations developed. Layer coefficients at 7 and 28 days were also determined by testing specimens in fatigue in the deflectometer and computing their structural numbers and layer coefficients. Layer coefficients determined in these two manners indicated favorable comparisons. The results of this research provides information about the structural layer coefficients for asphalt emulsion-aggregate mixtures. The relationships between the evaluation tests and structural layer coefficient can be used for determining layer coefficients for other asphalt emulsion-aggregate mixtures. Because the evaluation tests used were tests commonly performed in most asphalt laboratories, these determinations can be made without the necessity of additional equipment or procedures in most cases.

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