Ultrasonic Monitoring of Setting and Strength Development of Ultra-High-Performance Concrete
In this study, the setting and tensile strength development of ultra-high-performance concrete (UHPC) at a very early age was investigated by performing the penetration resistance test (ASTM C403), as well as the direct tensile test using the newly developed test apparatus, and taking ultrasonic pulse velocity (UPV) measurements. In order to determine the optimum surface treatment method for preventing rapid surface drying of UHPC, four different methods were examined: plastic sheet, curing cover, membrane-forming compound, and paraffin oil. Based on the test results, the use of paraffin oil was found to be the best choice for measuring the penetration resistance and the UPV, and attaching the plastic sheet to the exposed surface was considered to be a simple method for preventing the rapid surface drying of UHPC elements. An S-shaped tensile strength development at a very early age (before 24 h) was experimentally obtained, and it was predicted by a power function of UPV. Lastly, the addition of shrinkage-reducing and expansive admixtures resulted in more rapid development of penetration resistance and UPV of UHPC.
Investigation of Different Superplasticizers Effect on Workability and Strength Parameters in Ultra High Performance Concretes
The use of ultra-high performance concretes (UHPC) in the modern construction industry is increasingly widespread. UHPCs are a type of concrete that provides advantages in solving many engineering problems. UHPCs have superior properties compared to conventional concretes in terms of workability, self-settling, as well as high strength and durability. However, although UHPCs have many advantages, achieving the desired workability is one of the biggest challenges of the production procedure, since they contain high amounts of powder materials. Therefore, the aim of this study is to determine the most suitable superplasticizer (SP) additive in terms of workability and strength by using different SP additives in UHPC mixtures. In this study, workability and strength parameters were tested on UHPC mixtures using 8 different SP additives. First of all, the spreading diameters of the obtained mixtures were measured. For each mixture, compressive strength, density, ultrasound velocity, Schmidt hammer rebound and Leeb hardness measurements were performed on 70x140 mm sized cylindrical samples taken on days 2, 7 and 28. Since SPs have a working principle at the interfaces of particles in the internal structure of concrete, different behaviors were observed on workability, even if a little. All the results obtained have been compared with the literature and it has been proven that they meet the UHPC specifications.
Seeing Like a Racial State: the Census and the Politics of Race in the United States, Great Britain and Canada
ii Acknowledgements iv List of Abbreviations vii List of Tables ix List of Appendices x Chapter 1 Invitation 1 Chapter 2 Orientation 26 Chapter 3 Mark One or More: Census Politics in the United States 61 Chapter 4 The Ethnic Question: Census Politics in Great Britain 115 Chapter 5 (In)Visible Minorities: Census Politics in Canada 168 Chapter 6 Seeing Like a Racial State 234 Chapter 7 Alternatives and Outcomes in the Census Policy Sphere 310 Chapter 8 Conclusions 364 Reference List 382