No description available.

No description available.

No description available.

The problem of the investigation of the mechanism of failure in compression of neat cement and mortar specimens is considered in this thesis. The study was made on two hundred specimens of cement paste and mortar, of which approximately one half were tension briquets and the other half compression cylinders. The underlying theory which led to this study was that failure in compression in specimens with aggregate (mortar and concrete) is due to the wedging action of the particles of aggregate within the matrix of cement paste. Steam-curing was used to avoid delay in the hardening of cement. It was found that the cement used was of the type which continues hardening after being steam-cured. The importance of having the specimens at a constant temperature throughout their mass and at room temperature when the tests were performed was realized. An investigation of the effect of end conditions on test cylinders in compression was conducted. It is considered that the confined rubber end conditions used were an improvement on testing with lubricated ends only. Observations were made on the effect of the bursting action of water in compression tests of moist specimens. A study of the effect of stress concentration around voids was made on tension specimens. Compression specimens made of neat cement, mortar and cement with inclusions in the form of balls were studied. Inclusions were placed in cement cylinders to imitate the action of the aggregate in mortar and concrete specimens. Tests on compression specimens with inclusions were useful in the interpretation of results of tests on neat cement and mortar cylinders and in the study of the stress-strain curves. Transverse bending tests of cylinders were made with the purpose of investigating the presence of transverse cracks formed in the cylinders as a consequence of the application of compressive loads. They did not provide a good method of investigation but were very useful in that they were an aid to realizing the effect of the horizontal cracks in the stress-strain curves. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

Project Completion Report OWRT Project No. A-075-ARIZ / Agreement No. 14-34-0001-7006 / Project Dates: July 1976 - June 1977 / "The work upon which this report is based was supported by funds provided by the United States Department of the Interior, Office of Water Research and Technology as authorized under the Water Resources Research Act of 1964, the State of Arizona, and the Arizona Department of Transportation and Federal Highway Administration

No description available.

In view of the fact that prestressed concrete is extensively used in bridge construction and that it holds potentialities for eventual use in pavement construction, and that methods must be investigated to utilize an otherwise rejected aggregate which cannot be used for its poor performance under natural weathering, it has become of paramount importance that further efforts be made to evaluate the effect of prestressing on the durability of concrete. The purpose of this thesis was twofold: 1) To study the durability of prestressed concrete made of poor-performing aggregate; 2) To compare the freezing and thawing effects on prestressed concrete with those on ordinary concrete. Two mix designs having different proportions of poor performing aggregate were used in this study. Half the number of specimens were post-tensioned after they had been cured for a period of 13 to 18 days in water, and were then replaced in the curing room for 24 hours, Level of prestress was 600 psi. Before transferring the specimens - both prestressed and non-prestressed - into freezing and thawing apparatus, they were tested for fundamental transverse frequency and initial weight and length measurements were recorded. Thereafter, transverse frequency, weight, length change and temperature change measurements were made periodically. The relative dynamic modules of elasticity and durability factor were then calculated for each specimen. On the basis of the results furnished by these tests, it may be concluded that prestressing improves the durability of concrete made of poor performing aggregate and that the magnitude of improvement in the durability ef concrete tends to diminish with increasing proportion of good performing aggregate. / Master of Science

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Small amounts of cementation in a sand increase its ability to sustain static and dynamic loads, even in a liquefaction type environment. This has been shown in previous research examining the behavior of both naturally cemented and artificially prepared samples. Cemented sands are present in many parts of the world and can be caused by either a variety of cementing agents or by cold welding at points of grain contact. They are generally quite difficult to sample, but artificially cemented sands have been shown to aptly model the behavior of natural materials, and allow for better test controls. Consequently, artificial samples were used exclusively for the present investigation which has three major objectives: to investigate the effects of a weakly cemented lens within a stronger mass; to determine how cementation affects the volume change characteristics of statically loaded samples; and, to describe the pore pressure generation of sands subjected to cyclic loading. Prior to commencing the test program, a number of index tests were performed on the uncemented and cemented sand used during the laboratory investigation. It was revealed that cementation leads to increased void ratios which distort relative density calculations used to compare cemented and uncemented samples of similar dry unit weight. The practice of identifying samples by dry unit weight was adopted for this report. Static triaxial compression tests were performed on 17 samples. Test results indicate that although the magnitude of volumetric strain at failure does not seem to be dictated by the level of cementation, there is a relationship with cementation and the rate of volume change at failure. A weak lens was seen to lower the static strength of the stronger mass. 26 stress controlled cyclic triaxial tests revealed that a weak lens lowers the liquefaction resistance of the stronger mass. The cyclic strength of the nonhomogeneous material, however, is higher than the independent strength of the weak lens. A weak lens has greater influence at relatively higher levels of cyclic stress. Pore pressure generation in cemented sands are seen to be controlled by strain. At shear strain levels below about 1%, cemented sands behave similarly to uncemented sands with pore pressures increasing more rapidly beyond that amount of strain. Consequently, pore pressure development during cyclic loading is described by a broken-back curve which is defined in the early stages by existing empirical relationships for uncemented sand. Pore pressure prediction may then be achieved using an equation for cemented sand, such as that developed in the present work. / Master of Science