International Concrete Abstracts Portal

Hollow-core (HC) slabs are precast/prestressed concrete members with continuous voids oriented parallel to the span of the slabs. Openings in HC slabs are one of the most common challenges encountered during construction. This study experimentally evaluated the effectiveness of proposed strengthening methods for HC slabs with unforeseen structural openings.

Modular construction has been attracting attention worldwide as a promising solution to reduce construction time and labor demand. In this study, a new inter-module composite floor system that connects the upper module floor beams and lower module ceiling beams was experimentally and analytically investigated with an emphasis on vibration performance under service loading. First, the upper module floor of 2 m [6.56 ft] wide and 6 m [19.7 ft] long was fabricated as a composite system consisting of precast concrete (PC) panels, steel beams and ultra high-performance concrete (UHPC) connectors. Structural integrity between PC panels, steel beams and UHPC connectors were secured using grouting and topping mortar. Then, the lower module ceiling beams were connected to the upper module floor beams by fully tensioned high-tension bolts (i.e., slip-critical connection) to complete the inter-module composite floor. The vibration frequencies, damping ratio, and acceleration responses of the inter-module composite floors were measured from laboratory tests such as impact hammer, heel drop and walking tests, considering the number and location of the connecting bolts as the test parameter. The vibration characteristics of the inter-module composite floors were investigated further through finite element analysis. The measured and predicted vibration performances were compared with the acceptance criteria in AISC Design Guide 11 and ISO 10137.

The movement of ultra-high-performance concrete (UHPC) toward wide scale acceptance within the concrete industry has generated interest in developing improved test methods to provide quality assurance for this material. Most test methods currently used to measure the tensile behavior of ultra-high-performance concrete require specialized testing equipment that is not typically owned by precast or ready-mix production facilities. These test methods provide reliable data for quality assurance of newly developed concrete mixes, but they are impractical as quality-control tests, which would need to be performed for every UHPC placement. This paper presents the development of a simple and inexpensive test to measure tensile strength and ductility for UHPC and serve as a quality-control test. This method was developed from the double-punch test, commonly referred to as the “Barcelona test,” but has been revised to incorporate substantial changes to the loading and data collection requirements to eliminate the need for expensive, specialized equipment. It was determined that the modified test method could produce reliable results using a load-controlled testing procedure with manually recorded data points taken every 0.635 mm (0.025 inches) of vertical displacement for ductile concrete specimens. It was also determined that specimen surface grinding, loading rate, and punch alignment did not significantly influence the test results. However, the fabrication of the specimens, specifically the rate and method at which the molds were filled, had a significant effect on the results. Accordingly, any recommended standardized test method based off of this procedure should have requirements on specimen fabrication.

Through a Change Proposal by Facca Incorporated, the Ontario Ministry of Transportation (MTO) approved the replacement of the as-tendered steel H-piles by newly designed prestressed/precast Ultra-High-Performance Concrete (UHPC) piles for supporting the west abutment of the Lily River Detour Bridge. The 300 mm (~12”) deep UHPC piles were designed and installed at the west abutment based on the previous successful development and testing of a tapered H-shaped pile at Iowa State University. The east abutment, as tendered, was designed to be supported by six steel H-shaped battered piles driven to bedrock. For the west abutment, six UHPC piles were produced and installed using the same batter. Since the site contained occasional boulders and the design intent to drive the piles to bedrock, the UHPC piles were fitted with steel shoes for the first time. All piles were successfully installed to reach the targeted load bearing capacities. After the replacement bridge was constructed, the detour bridge was removed and the UHPC piles were extracted to examine the conditions of the piles. This presentation will provide details of the innovative design of the piles, fabrication and driving of the piles, and lessons learned from analyzing the driving data and removal of the piles. Fellowship and Scholarship recipients. With the help of generous donors from the concrete community, the ACI Foundation awards high-potential undergraduate and graduate students in engineering, construction management, and other appropriate curricula.

The development of low carbon footprint and high initial compressive strength binders for the precast industry is presented. Binders with a substitution of up to 75% of a normal Portland cement (CEM I) with a mixture of metakaolin and two different limestone additions were developed on mortars. Water/binder ratio reduction (down to 0.25) and thermal treatment (up to 50°C) have been applied to improve initial compressive strength (> 14 MPa at 8 hours). Pozzolanic reaction improved 28 days compressive strength (> 50 MPa). The most technically and environmentally performant binders have been applied to concrete. Concretes with low clinker contents have been produced to achieve the C25/C30 and C40/50 strength classes. Durability performances corresponding to XC4 were assessed via a performance approach (FD P 18-480). A wall with integrated formwork has been industrially manufactured which allowed a carbon footprint reduction of around 30% over its whole life cycle.