This research was undertaken to study the effects of high performance concrete (HPC) mix design modifications on the propensity of early-age cracking. Seven mixtures were tested: one 35 MPa conventional concrete (CC) mixture made with ordinary Portland cement with blended slag; one typical 50 MPa HPC mixture containing slag and silica fume; and five modified HPC mixtures using extra set-retarder, increased slag replacement, shrinkage-reducing admixture (SRA), pre-saturated lightweight aggregate (LWA), and decreased cement paste content to improve thermal and/or shrinkage properties. The mixtures were tested for durability, mechanical, thermal, and shrinkage properties. All modified HPC mixtures showed reduced shrinkage relative to the HPC control mixture, and the most shrinkage mitigation was observed in the mixture containing LWA. While SRA reduced restrained shrinkage in HPC to the magnitude of CC, it provided very low rapid chloride penetrability, and using LWA in HPC resulted in significant restrained shrinkage reduction compared to CC.

No description available.

No description available.

Stress corrosion cracking (SCC) susceptibility of the phosphorus de-oxidized copper has been evaluated in synthetic seawater polluted by sulfides using slow strain rate test (SSRT). The effect of concentration of sulfide, temperature, and applied cathodic and anodic potentials on the final strain values and maximum stress were also studied. No cracks were found under the tested conditions. The final strain and maximum stress values decreased but not significantly, with increase in the temperature, applied anodic potential and sulfide concentration. The observed effect is due to the section reduction by uniform corrosion. Lateral cross section and microscopic examination of the fractured specimen ruled out the existence of the localized corrosion. Electrochemical measurements showed that the Cu2S film is not a protective film and also exhibits a mass transfer limitation to the inward diffusion of the sulfides. Based on these results the reasons for the absence of cracking are also discussed.

Stress corrosion cracking (SCC) susceptibility of the phosphorus de-oxidized copper has been evaluated in synthetic seawater polluted by sulfides using slow strain rate test (SSRT). The effect of concentration of sulfide, temperature, and applied cathodic and anodic potentials on the final strain values and maximum stress were also studied. No cracks were found under the tested conditions. The final strain and maximum stress values decreased but not significantly, with increase in the temperature, applied anodic potential and sulfide concentration. The observed effect is due to the section reduction by uniform corrosion. Lateral cross section and microscopic examination of the fractured specimen ruled out the existence of the localized corrosion. Electrochemical measurements showed that the Cu2S film is not a protective film and also exhibits a mass transfer limitation to the inward diffusion of the sulfides. Based on these results the reasons for the absence of cracking are also discussed.

Thesis (doctoral)--Technische Universiteit Delft, 1998. / Includes bibliographical references.

Thesis (doctoral)--Technische Universiteit Delft, 1998. / Includes bibliographical references.

Master of Science / Civil Engineering / Hayder Rasheed / Reverse diagonal shear cracking at the supports of many reinforced concrete girders is a phenomenon affecting a number of KDOT’s low-volume bridges built in the early-to-mid 1900’s. This phenomenon is not addressed in the AASHTO Bridge Design Manual (2002) or ACI specifications. This study investigates the causes of this cracking and creates BRIDGE (Bridge Rating of Inclined Damage at Girder Ends), an Excel-based software to determine the load rating of a user specified bridge exhibiting reverse diagonal shear cracking at the girder supports. A user-interface is created which allows a user to create a grillage model of an existing bridge and to place various rating trucks on the bridge. Equivalent flexibility analysis is used to distribute the truck live loads from within the deck panels to the surrounding girders and diaphragms. Stiffness matrices are utilized to find the nodal displacements then the reactions at the girder supports caused by the truck live loads and bridge dead load. These reactions are checked against RISA software models to test the accuracy of the stiffness matrix application. ABAQUS FE models and Mohr’s circle stress distribution is used to find the driving and clamping forces on the crack. These forces are caused by resolving the dead and live load reactions and the friction force generated between the concrete girder and the rusty steel bearing pad along the shear crack orientation. These clamping and driving forces are used, along with the simplified modified compression field theory to determine the shear capacity of each girder at the reverse cracks. A modified version of Equation 6B.4.1 from the Manual for Bridge Evaluation (2011) is used to find the operating and inventory rating factors for the bridge.

Stress corrosion cracking of a 14 wt% Cr martensitic stainless steel, with commercial names PH-15Cr5Ni, FV520B or X4CrNiCuMo15-5, used for the manufacture of low pressure turbine blades, has been studied with the intention of gaining a better understanding of the processes involved, how they occur and why. Industrially this is very important as stress corrosion cracking is considered to be a delayed failure process, whereby microscopic cracks can potentially propagate through a metal undetected until catastrophic failure occurs. The aim of this work is to establish links between crack length and external factors, such as exposure time, in order to devise a method of dating stress corrosion cracks and therefore predicting their possible occurrence in-service.

The failure of graphite moderator bricks in an Advanced Gas cooled Reactor (AGR) is potentially a serious problem. This thesis describes the generation of self stress in the moderator brick during irradiation and the derivation of a simple analytical model to predict the magnitude of this stress. The magnitude of the self stress in the brick is affected by the variations in the material properties of the graphite used for the brick and this is also examined, developing a statistical approach to the analysis. Property variations between bricks are considered but no allowance has been made for material property variations within a brick. Finally, the thesis compares the self stress in one of the critical peak rated moderator bricks to the strength of the irradiated oxidised material on a statistical basis and predicts the failure probability of a brick due to self stress to be extremely low at 25.5 full power years (FPY). However, the failure probability rises steeply and for the peak rated bricks at 29 FPY it approaches 100%.