No description available.

No description available.

No description available.

This paper describes how the author studied the "workability" of freshly mixed concrete. Workability is a very important and necessary property which forms part of the specifications for concrete but its meaning is rather vague. Concrete is usually required to have a certain slump or flow, as determined in a standard manner, with standard apparatus, but the readings obtained are comparative only and have no absolute value. The question which the author asks and tries to answer is, can we treat freshly mixed concrete as a fluid and measure its absolute viscosity and if so how are slump and flow etc. related to it? What does slump and flow really mean in terms of absolute units? An apparatus was developed which does measure a quantity similar to viscosity and values were obtained for nine different mixes. Readings were however obtained at only one velocity so that the non-Newtonian behaviour of the concrete was not investigated. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Environmental factors such as temperature, air, and water can have a profound effect on the durability of asphalt concrete mixtures. In mild climates where good quality aggregates and asphalt cement are available, the major contribution to deterioration may be due to traffic loading and the resultant distress is manifested in the form of fatigue cracking, rutting, and raveling. But, when more severe climates are coupled with poor materials and traffic, premature failure may result. The objectives of this research are twofold and includes: (1) development of a test system to evaluate the most important factors influencing the water sensitivity of asphalt concrete mixtures; and (2) development of laboratory testing procedures that will predict field performance. This research also addresses the hypothesis that much of the water damage in pavements is due to water in the asphalt concrete void system. It is proposed that most of the water problems occur when voids are in the range of about 5% to 12%. Thus, the term "pessimum" voids is used to indicate that range (opposite of optimum). In order to evaluate the hypothesis and the numerous variables, the Environmental Conditioning System (ECS) was designed and fabricated. The ECS consists of three subsystems: (1) fluid conditioning, where the specimen is subjected to predetermined levels of water, air, or vapor and permeability is measured; (2) an environmental cabinet that controls the temperature and humidity and encloses the entire load frame; and (3) the loading system that determines resilient modulus (M[subscript n]) at various times during environmental cycling and also provides continuous repeated loading as needed. The ECS has been used to evaluate four core materials and also to investigate the relative importance of mixture variables thought to be significant. Many details regarding specimen preparation and testing procedures were evaluated during a "shakedown" of the ECS. As minor variables were resolved, a procedure emerged which appears to be reasonable and suitable. An experiment design for the four core mixtures was developed, and the overall experiment design included three ranges of void ( <5% low; 5-12%, pessimum; > 12% high). Six-hour cycles of wet-hot (60° C) and wet-freeze ( -18° C) are the principle conditioning variables, while monitoring MR at 25° C before and between cycling. A conventional testing procedure (AASHTO T-283) was also used on the core mixtures to provide a baseline for comparison. Results to date show that the ECS is capable of discerning the relative differences in "performance" such as MR. Three hot cycles and one freeze cycle appear to be sufficient to determine the projected relative performance when comparing different aggregates, asphalts, void levels, loading, etc. Based on these results, a water conditioning procedure has been recommended and also a procedure for water conditioning specimens prior to testing in fatigue, rutting, and thermal cracking. / Graduation date: 1992

Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1984 R43 / Master of Science

The report presents an evaluation of a modification to an asphalt-debonding test procedure when used with a water debonding apparatus developed at the University of Arizona, the Pore-Water Pressure Debonding Device. The method being modified is that outlined by Jimenez in his report "Testing for Debonding of Asphalt from Aggregates". A regular test specimen, 4 inches in diameter by 2½ inches high, is water-saturated at 122°F and subjected to repeated pore-water pressure varying from 5 to 30 psi. The above factors are kept constant and the following ones are varied: air void content, stress frequency, stress repetition, stress duration and testing temperature. Test results of the modified testing procedure demonstrated the following trend: the higher the value of any of the aforementioned test variables, i.e., the void content, stress frequency, stress repetition, or stress duration, or any combination of these variables, the greater the loss of the mix resistance to stripping.

In this report the influence of several variables including asphalt content, mixing temperature, compaction temperature and compaction energy on void content, voids-in-the-mineral-aggregate (VMA), density and stability of asphaltic concrete mixtures was established. Straight lines were obtained on double logarithmic paper for each asphalt content when the logarithm of Marshall stability values as ordinate were plotted versus the logarithm of the corresponding number of blows of a Marshall compactor as the abscissa. The straight lines were very nearly parallel and therefore, it was possible to develop a single empirical formula expressing the relationship between stability at any compactive effort, within the range of 20 to 110 blows per face, in terms of the standard stability at 75 blows per face of specimen. Results indicate that void content, VMA, density and stability were significantly affected by compaction temperature, asphalt content, compactive effort and mixing temperature.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy