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Robust Methods for UHPC Early-Strength Determination and Quality Control for Accelerated Bridge Construction
AuthorIbrahim, Mohammed Shaker
Civil and Environmental Engineering
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Ultra-high performance concrete(UHPC) is an advanced cementitious construction material that has been widely used recently. The significant advantage of UHPC is that it can reach high compression strength of about 10-12 ksi after one day and about 21-23ksi after 28 days of casting. Such advantage is crucial for accelerated construction, especially bridges where the roads are fully closed when traditional construction methods are used. To minimize road closures and enhance construction zone safety, accelerated bridge construction (ABC) techniques are becoming more common. Using advanced materials like UHPC for connecting bridge components is a major aspect of ABC. However, to confidently move from one construction phase to the next or eventually open bridges to traffic, a quality control method is needed to verify the specified strength of connections and other critical materials like UHPC. Therefore, this research focuses on assessing and developing the maturity method for UHPC at early ages as a quality control method to provide accurate strength predictions. For this purpose, more than 900 specimens of 3"×6" cylinders and 4"×4"×4" and 2"×2"×2" cubes from eight different UHPC mixtures were cast and tested. Overall, this research showed that the maturity method is applicable for UHPC at early ages and can lead to a good strength prediction when proper guidelines as presented in this thesis are adopted. However, the results show that the current existing ASTM C1074 maturity method procedures and recommendations are ineffective in predicting UHPC strength for ages of one day and less. Also, the 4"×4"×4" cubes showed better strength predictions than the 3"×6" cylinders at ages less than one-day. Moreover, the Arrhenius method has slightly better results than the Nurse-Saul. Finally, new maturity constants were proposed, the lab breaking points' ages were determined, and new curve fitting equations were developed and proposed to predict the UHPC strength with minimal errors. Furthermore, cubes showed better strength predictions than the cylinders, and since cylinders require surface preparation, this consumes time and makes the quality control results sensitive to the specimens’ preparation procedure, especially for early age. Thus, the second part of this research focuses on using cubes as an alternative to cylinders. For such, the size effect of the cubes and cylinders with different sizes and various strength levels from less than 1 ksi to over 20ksiwas studied. Furthermore, other factors were considered, such as different fiber content and curing regimes. The mentioned factors helped study the size effect effectively and propose robust conversion factors and functions between specimen shapes and sizes.