International Concrete Abstracts Portal

This article provides an overview of a hydration-controlling (stabilizing) admixture and its use for recycling returned concrete. It includes details on a robustness evaluation of stabilization performance in a unique cross-country experiment, as well as information on the potential for lowering the environmental impacts of concrete production.

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.

Nonrectangular cross sections are a common occurrence in reinforced concrete design typically taking the form of flanged beam sections, circular columns, and square or rectangular columns subject to biaxial bending. Instructors typically introduce the theory behind nonrectangular beams using two-dimensional sketches of flanged sections. Students can struggle to visualize the examples when presented in two dimensions; deciphering the multiple resultant compressive forces and their corresponding moment arms are particularly difficult. This paper presents an overview of nonrectangular beam theory and select active learning methods along with three specific examples used by the authors to teach nonrectangular beams in an undergraduate reinforced concrete design course. The first method is a simple problem-based learning example to dissuade students from “plug and chug” calculations using improper equations; the second method illustrates three cases for a traditional flanged T-beam section using physical three-dimensional models; and the third method uses virtual three-dimensional models to derive the depth of the equivalent stress block and corresponding nominal flexural strength for various cross sections. Each description provides the reader with the best practices to implement the respective technique. Lastly, the authors provide some lessons learned from their past implementations. The overall goal is to provide educators with examples to simplify the presentation of nonrectangular beams theory.

The equivalent rectangular stress block is the basis for determining the flexural strength of reinforced concrete members. Instructors commonly present the concept in two dimensions, contrary to its three-dimensional nature. Unfortunately, this can be particularly difficult for students to understand and visualize, especially for students with visual learning style preferences. This paper presents an overview of the equivalent rectangular stress block, select active learning methods, and four specific examples used by the authors to introduce the equivalent rectangular stress block in an undergraduate reinforced concrete design course. The first method focuses on understanding the terms associated with the equivalent rectangular stress block using a visual, hands-on learning activity; the second focuses on visualizing the internal forces and couple moment within a beam; the third uses a virtual three-dimensional model to derive the depth of the equivalent rectangular stress block; and the fourth illustrates the various stress blocks used in reinforced concrete flexure theory via physical three-dimensional models. Each description includes detailed instructions to create the resources and how to facilitate the related activities within a course. The overall goal is to provide educators with several examples that will help students better visualize the three-dimensional concept.

It is well-known that the synthesis of comb-like polycarboxylate superplasticizer (PCE) strongly relies on polyethylene glycol (PEG) macromonomer as side chains to provide good dispersibility. However, ethylene oxide (EO), the main source of PEG, has many disadvantages such as flammability and explosiveness, harsh synthesis conditions, high equipment requirements, and high risk of impact on PCE even concrete industry, etc. Therefore, it is urgently necessary to develop a novel PCE by other substitutes, achieving innovative chemistry of PCE. In this study, polyvinyl alcohol (PVA), which synthesis does not depend on EO, was originally designed as side chains instead of PEG. A comb-like superplasticizer, i.e. PAA-g-PVA, was successfully synthesized by “graft from” copolymerization using butyl acrylate (BA) as main chain monomer and vinyl acetate (VAc) as side chain monomer. Compared with conventional PCE, PAA-g-PVA exhibited better fluidity retention of cement paste, as it can maintain a higher adsorption amount on cement particles. The hydration kinetics and Krstulovic-Dabic (K-D) model showed PAA-g- PVA less retarded the hydration process and rapidly promoted the hydration into the diffusion-controlled period. The aim of this study is to introduce a novel polymer with potential engineering applications and good performance, which can be used as an alternative to PCE.