Non-Proprietary UHPC for Anchorage of Large Diameter Column Bars in Grouted Ducts
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Accelerated bridge construction (ABC) is a bridge construction method that employs innovative construction techniques and can be applied in seismic or non-seismic regions of the nation to effectively reduce the onsite construction time. A non-coupled plunged, also referred to as precast column with no couplers (PNC), detail for column to footing and column to cap connections using ducts filled with ultra-high performance (UHPC) has been demonstrated as an effective connection for seismic applications. To expand the use of this ABC connection, a feasible and non-proprietary UHPC mix is crucial. The overall objective of this research is to develop a non-proprietary UHPC mix using locally available materials in the West, mainly from California and Nevada, that would reduce the UHPC cost and sole source problem without compromising the essential properties required for the grouted ducts ABC seismic connection. The study first presents an extensive literature review for high performance cement-based materials that most frequently used and locally available in the US market. The non-proprietary UHPC mix design process and material characterization is discussed next. Two sources of aggregates (Nevada and California) with two different characteristics were selected for the study. The aggregate from Nevada is a blended concrete sand that is 100% crushed. The aggregates from California is a concrete river sand that is uncrushed. The optimum gradation for dense aggregate packing and proportions of constituents were selected based on 28-day compressive strengths and flow characteristics of the mix. It was found that the aggregate gradation with fineness modulus less than 3.0 meets the minimum 28-day compressive strength criteria of 12 ksi and flow of 10 in. The 28-day compressive strength of the mix developed using river sand aggregates from California, designated as UNR-UHPC-A, and the mix developed using 100% crushed aggregates from Nevada, designated as UNR-UHPC-B, was found to be 15 ksi and 14 ksi, respectively as measured using 4-in-by 8-in cylinders. The non-proprietary UHPC mixes were further evaluated for flexural and direct tensile strength properties after meeting the minimum compressive strength and flow criteria. A major part of this study used the finalized UHPC mix designs from both sources of aggregates to evaluate grouted ducts anchorage behavior using 22 full-scale tests with #10 rebars. Several parameters were varied to evaluate the effect of embedment depth, single versus bundled rebars, duct sizes, and duct material. Moreover, the tests also compared the anchorage behavior of the developed mixes with the commercially available UHPC and standard grouts; the other alternatives in such connections. All rebars were eccentrically placed into the ducts to emulate more practical field and worst case conditions. Based on the tests results, development length equations of rebars eccentrically placed in galvanized steel corrugated ducts filled with UHPC have been revised and presented.
Report No. CCEER-19-03