This research was conducted to investigate the possibility of devising and utilizing an accelerated curing procedure in order to estimate the 7-day and 28-day normal curing (72(DEGREES)F and 100% humidity) compressive strengths of soil-cement mixes. Based on information reported in the literature on accelerated curing in lime stabilization and concrete, the accelerated curing procedure adopted in this research was a modified version of the boiling water method given by ASTM 684-81. By this procedure compacted soil-cement specimens were boiled in distilled water for certain periods of time. After a 30-minute cooling period, the specimens were soaked in water for 24 hours and then tested for strength. Mechanical as well as physico-chemical tests were conducted on accelerated- and normally cured specimens. Mixtures of clay (kaolinite Hydrite 10), sand and portland cement (Type I/II) were utilized in preparing the specimens. The unconfined compression test results indicated that accelerated strength values increased with increasing boiling time and with increasing cement content. The strength values also increased with decreasing clay content down to 30%. Below 30% clay content the strength decreased. As for predicting normal curing strengths from accelerated curing strengths, two procedures were adopted. Procedure A predicted the 7-day and 28-day strengths by boiling specimens for 3 hours and 40 minutes and 4 hours and 20 minutes, respectively. Procedure B predicted the normal-cure strengths using linear regression equations. The predictions by both procedures were found to be satisfactory, within (+OR-) 15% of the normal-cure strengths. X-ray diffraction data suggested less hydration had occurred in the accelerated-cure specimens than in the normal-cure specimens. This probably was due to the shielding of cement grains by clay and hydration gels. pH measurements showed that specimens cured by both procedures exhibited highly alkaline environment. Electron micrographs of selected samples appeared to confirm the existence of more unhydrated and/or partially hydrated cement in the accelerated-cure samples.

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Excessive early-age concrete surface moisture evaporation causes many problems of concrete pavements, such as plastic shrinkage cracking and delamination; the use of liquid membrane-forming curing compounds is one of the most prevalent methods to mitigate the issues. However, the present standard test, ASTM C 156-98, “Standard Test Method of Water Retention by Concrete Curing Materials” has some inherent limitations in assessing the curing effectiveness of concrete. To better apply curing practices and qualify the curing compound, a new evaluation protocol is introduced in this study. The new protocol consists of using measured relative humidity and temperature to calculate an effectiveness index (EI) which serves as an indicator of the effectiveness of curing. Moistures loss and surface abrasion resistance measurements were made on concrete specimen, and were found to have significant correlation with EI, where higher EI were associated with lower moisture loss and higher surface abrasion resistance. EI was also found to be sensitive to ambient wind condition, types of curing compound and the application rate of the curing compound. Dielectric constant (DC) measurements were also made on concrete specimens indicating the free moisture content on the surface concrete. The DC measurements were also found to differentiate the quality of curing under different ambient conditions, with various types of the curing compounds and the w/c of the concrete mixture. The utility of using the new protocol to assess concrete curing compound effectiveness was also evaluated under the field condition. Both EI and DC measurements showed potentials to distinguish the curing quality for concrete pavement construction.

Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4’-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions

In an effort to be able to use photoinitiators to their maximum potential, the sequence of events that occurs in an ink formulation during the UV curing process has have been studied and information presented to allow more effective formulation. Emphasis has been placed on highlighting the variables that have the greatest impact both on photoinitiator efficiency and on the suitability of individual photoinitiators and synergists for use in particular applications. These variables were found to be photoinitiator thermal stability, UV light utilisation, reaction mechanisms and cure reactivity. A wide range of photoinitiators and synergists were investigated using thermogravimetric analysis (TGA) and thermogravimetric analysis-mass spectroscopy (TGA-MS) to define both their thermal stability and whether under heating they thermally decompose or merely evaporate. Differential photocalorimetry (DPC) was used to determine which wavelengths from a typical medium pressure mercury curing lamp are the most important for providing cure, with both theoretical and practical methods being used to define the extent to which these wavelengths penetrate into pigmented and non-pigmented coatings. A procedure was devised and validated for this purpose. The reaction mechanism and photodecomposition products of a range of photoinitiators were investigated using gas chromatography-mass spectroscopy (GC-MS) and radical trapping experiments. The reaction mechanisms are discussed in terms of available literature knowledge. Evidence is also presented suggesting that, with only particular exceptions, cleavage photoinitiators can also react by a hydrogen abstraction mechanism in the presence of an amine synergist. A real time infrared spectrometer (RTIR) was set up and a method validated for following the UV curing reaction through changes in the acrylate double bond concentration. The advantages and disadvantages of this instrument are discussed in terms of other similar instruments reported in the literature, and the technique subsequently used to measure the reaction rates of a wide range of photoinitiators. Other factors such as photoinitiator concentration, amine synergist type I level and formulation viscosity were also investigated to determine their influence on the cure process.

A prime coat is defined as a low-viscosity bituminous material such as cutback, asphalt emulsions, or polymer-based chemicals applied onto the surface of road bases in order to protect the base from the penetration of moisture into the base layer. Other functions of prime coat include (1) providing good adhesion between a granular base and the bituminous surface, (2) strengthening the surface of the base by binding the fine particles, and (3) sealing against any voids along the base surface in order to reduce water absorption. To achieve these functions, a prime coat should successfully penetrate the granular base and should cure fully. In this study, field-curing data on selected prime coats was collected during March 12th-18th, 2014 and April 12th-18th, 2014. Oven-curing data was also collected in a laboratory using an adjustable oven. Identical prime coats including the four most commonly used prime coats by TxDOT ((1) Cutback MC-30, (2) asphalt emulsions and cutback mixture AEP, (3) polymer emulsions EC-30 and (4) asphalt emulsions SS-1H and CSS-1H) and base materials were divided into the two types of testing environments, one field-cured, and one in an accelerated and controlled indoor, oven-curing environment. Once the specimens were fully cured, evaluation of the engineering properties of the specimens were carried out in order to determine if oven-cured specimens can be expected to exhibit the same engineering characteristics as the field-cured specimens. Evaluation of water absorption tests, indirect indicator of relative strength, and penetration tests were performed on all specimens for both field-cured and oven-cured specimens. Importantly, a comparison of these results shows the viability of using accelerated, laboratory curing procedures. Prime coat field-testing procedures will be suggested using oven-curing rather than field-curing, reducing the amount of time required for sample preparation. Prime coat testing could conceivably be completed in a single day due to the accelerated curing rates. This advantage would reduce cost and man-hours of new prime coat material testing. / text

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