International Concrete Abstracts Portal

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.

This study explores technological advancements enabling the utilization of GFRP bars in concrete structures, particularly in coastal areas. However, GFRP bars often encounter reduced bend strength at specific bend locations, which may pose a challenge in their practical application. Various properties such as the strength of bent GFRP bars are crucial for quality assurance, yet existing testing methods stated in ASTM D7914M-21 and ACI 440.3R-15 have limitations when applied to different GFRP bent shapes. Furthermore, those methods require special precautions to ensure symmetry and avoid eccentricities in specimens. To address these challenges, CSA S807:19 introduced a simpler standardized testing procedure that involves embedding a single L-shaped GFRP stirrup in a concrete block. However, the specified large block size in CSA S807:19 Annex E may pose difficulties for both laboratory and on-site quality control tests. Therefore, CSA S807:19 Annex E (Clause 7.1.2b) permits the use of a customized block size, as long as it meets the bend strength of the FRP bars without causing concrete splitting. To date, very few prior research has explored the use of custom block sizes. Therefore, this study aims to thoroughly investigate the strength of bent FRP bars with custom block sizes and without block confinement. Such an investigation serves to highlight the user-friendliness and efficiency of the CSA S807:19 Annex E method. The study recommends two block sizes: 200x400x300 mm (7.87x15.75x11.81 in) for bars <16 mm (0.63 in) diameter and 200x200x300 mm (7.87x7.87x11.81 in) for bars <12 mm (0.39 in). Additionally, the study cautions against using confinement reinforcement, especially with smaller blocks, as it could interfere with the embedded bent FRP bar. Furthermore, the study suggests incorporating additional tail length to mitigate the debonding effects resulting from fixing the strain gauges to the bent portion of the embedded FRP bar. By exploring these modifications, the study seeks to enhance the effectiveness of the testing procedure and expand its practical application for both laboratory and on-site quality assurance. The findings hold implications for the reliable testing of GFRP bars' strength, advancing their use as reinforcement in concrete structures.

A successful concrete repair project requires a close coordination of efforts between the three major parties involved: the owner, the licensed design professional (LDP), and the contractor. Lack of coordination and clear understanding of the professional and contractual responsibilities, as well as the expectations, of each party involved in a concrete repair project, could result in long legal disputes to attempt to sort out the responsibilities of each party. The greatest victim of the dispute is usually the structure itself. The American Concrete Institute (ACI) has led the effort to develop responsibility guidelines in concrete construction. ACI 132 identifies and suggests the allocation of responsibilities to various parties involved in concrete construction. ACI 132 document is applicable to general concrete construction, and it does not consider the particularities of evaluating and repairing existing concrete structures. ACI 562 provides minimum requirements for assessment, repair and rehabilitation of existing distressed concrete structures, including a discussion on the responsibilities of the licensed design professional for the evaluation and repair of concrete structures. This paper discusses the responsibilities of the licensed design professional, the contractor, and the owner through a repair case study. The paper demonstrates the need to expand ACI 132 and/or ACI 562 to include responsibility guidelines for concrete repair projects.

The focus of this paper is a new liquid microspheres-based admixture that has been developed to provide freezing and thawing protection of cementitious-based materials under cyclic, saturated conditions, while addressing and eliminating issues typically associated with the use of surfactant-based admixtures for air entrainment. Consequently, this microspheres-based admixture provides unique opportunities and flexibility in reproportioning or optimizing current air-entrained concrete mixtures with respect to using increased levels of supplementary cementitious materials. It is also shown in the paper that the microspheres-based admixture will facilitate the use of materials that typically hinder air entrainment. A microspheres recovery test method that has been developed to measure the microspheres content of fresh content for quality assurance purposes is also presented and discussed.

This synopsis is based on a three-part report to be published by ACI in the near future The origin of ACI’s Innovation Task Group (ITG) 4, High-Strength Concrete for Seismic Applications, can be traced back to an International Conference of Building Officials or ICBO (now International Code Council or ICC) Evaluation Report entitled “Seismic Design Utilizing High-Strength Concrete” (ER-5536). Evaluation Reports are issued by Evaluation Service subsidiaries of model code groups. An ER essentially states that although a particular method, process or product is not specifically addressed by a particular edition of a certain model code, it is in compliance with the requirements of that particular edition of that model code. ER-5536, first issued in April 2001, was generated by Englekirk Systems Development Inc. for the seismic design of moment resisting frame elements using high-strength concrete. High-strength concrete was defined as “normal-weight concrete with a design compressive strength greater than 6000 psi and up to a maximum of 12,000 psi.” It was based on research carried out at the University of Southern California and the University of California in San Diego to support building construction in Southern California using concrete with compressive strengths greater than 6000 psi. The evaluation report (ER-5536) is available on the ICC website for review. A thorough review of the above document brought up several concerns focusing on two primary areas: material and structural aspects. Irrespective of those concerns, it was evident that the evaluation report had been created because quality assurance and design provisions are needed in cities like Los Angeles to allow the use of high-strength concrete in a safe manner. Through the formation of ITG 4, ACI has assumed a proactive role in the development of such provisions with the goal of creating a document that can be adopted nationwide. The mission of ITG 4 is to develop an ACI document that addresses the application of high-strength concrete in structures located in areas of moderate and high seismicity. A structure located in an area of moderate seismicity, in modern terminology, is a structure assigned to Seismic Design Category or SDC C of the International Building Code (IBC) or the NFPA 5000 Building Construction and Safety Code. A structure located in an area of high seismicity is a structure assigned to SDC D, E, or F of the IBC or NFPA 5000. The document is to cover structural design, material properties, construction procedures, and quality control measures. It is to be written or contain example language in a format that will allow building officials to approve the use of high-strength concrete on projects that are being constructed under the provisions of ACI 301 Specifications for Structural Concrete and ACI 318 Building Code Requirements for Structural Concrete. The ITG 4 document, now in draft form, addresses the material and structural design considerations when using concretes having specified compressive strengths of 5000 psi (34 MPa) or greater that must be designed considering moderate to high seismic risk. The term “high-strength concrete,” as defined by ACI Committee 363, refers to concrete having a specified compressive strength for design of 8000 psi (55 MPa), or greater. As such, this document is meant primarily for concretes in that high strength range. However, the strength level at which concrete is considered “high-strength” depends on regional factors, such as the characteristics and availability of raw materials, production capabilities, testing capabilities, and lastly, experience. Therefore, depending on the region, the specifier may wish to selectively adopt considerations referenced in this document also when using concretes with specified compressive strengths between 5000 and 8000 psi (34 and 55 MPa). Irrespective of the location or purpose for which it is used, concrete having specified compressive strength below 5000 psi (34 M