International Concrete Abstracts Portal

The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.

This paper presents an overview of shear analysis and design based on the ACI 318-19 Building Code Requirements for Structural Concrete as it relates to an introductory reinforced concrete course. The important content related to this topic is summarized and several effective active learning strategies and pedagogical resources are presented to augment and enhance student learning for this challenging topic. The description of each active learning activity also includes a discussion of the underlying pedagogical theory, an estimate of preparation and implementation time, and recommendations for implementation. The paper also highlights lessons learned from the authors based on observations from several years of instruction.

This paper presents an overview of the theory behind flexural strength of reinforced concrete beams and design for different failure modes according to ACI 318-19. Focus is given to concepts that are appropriate for an undergraduate reinforced concrete course. The technical content critical to this topic is summarized and pedagogical techniques for presenting this content effectively are described. Examples of applying these pedagogical techniques in the classroom are provided with estimates of required preparation and classroom time. These examples include several models and illustrations that can be used in the classroom and a sample large-scale laboratory exercise illustrating the different possible flexural failure modes. Finally, lessons learned from the authors over many years of instruction at multiple institutions are provided regarding techniques that have worked well when teaching this topic in a typical undergraduate reinforced concrete course.

This paper presents pedagogical techniques used to teach detailing of reinforced concrete structures. Detailing includes the ACI 318 code specifications for reinforcement placement and layout in a structural component. Students sometimes view this topic as a set of rules and standards; however, students must also understand the reasons these specifications exist. Therefore, the authors include a variety of methods to address both how to apply detailing and why detailing matters. These methods allow students to make critical assessments and experience higher-order learning. The authors utilize a variety of active and student-centered learning methods to teach the topics of detailing. The specific approaches discussed within this paper include skeleton-style notes, case studies, field work, experiential learning opportunities, projects, and the inverted classroom. This paper presents the pedagogical significance of each method, provides examples of implementing each method, and includes lessons learned by the authors based on their own implementation of these methods in the classroom.

Post-earthquake evidence shows that shear failure in non-ductile detailed columns is a major source of structural collapse and earthquake deaths. Nonlinear continuum finite element (FE) models were constructed and calibrated to experimental tests for nine columns sustaining shear and axial degradation during cyclic loading. The primary objective of this study was to develop FE guidelines for simulating the lateral cyclic behavior of concrete columns sustaining shear degradation and axial collapse, such that wider parametric studies can be conducted numerically to improve the accuracy of assessment methodologies for such critical columns. Selected columns covered a practical range of axial loads, shear stresses, transverse reinforcement ratios, longitudinal reinforcement ratios, and shear span to depth ratios. The crack width, the damage in concrete and reinforcement, the drift at axial and lateral collapse, and the shear capacity of columns are compared with experimental results and standards equations from ASCE 41-17 and the ACI 318-19. It is observed that material model parameters recommended in this study are delivering relatively high accuracy for columns with span-to-depth ratios above 2 up to the axial collapse, and for columns with span-to-depth ratios below 1 up to the lateral failure.