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.

A large volume of freshly produced and harvested coal ash (from landfills and ponds) contains SO₃ content above 5.0%. This exceeds the allowable limit in major SCM specifications (e.g., in ASTM C618), and disallows the use of such coal ashes in concrete. This presentation explores the properties and performance of these coal ashes as SCM. It is shown that SO₃ may be present in ash in the form of CaSO₃, CaSO₄, or Na₂SO₄ (including solid solutions of alkali sulfates and carbonates), and that the form of SO₃ has a large impact on the performance of coal ash in concrete. For example, while ashes containing CaSO₃ may cause extensive set retardation, those containing CaSO₄ may increase the risk of internal sulfate attack and deleterious expansion. In this work, the mechanisms responsible for each behavior are explored, the allowable SO₃ limits are better defined, and strategies for beneficiation of coal ashes that exceed such limits are introduced. The outcome is facilitating the safe and efficient use of large volumes of currently off-spec coal ash to produce durable and low-CO₂ concrete.

Most of the research related to interface shear transfer in concrete elements has utilized steel bars as reinforcement, while GFRP reinforcement has received little attention experimentally and analytically. For this reason, only a few design specifications include provisions for the calculation of the interface shear transfer when using GFRP. In this project, an experimental campaign is being conducted to determine the contribution of GFRP bars to the mechanism of shear transfer by using push-off specimens. The literature review and the test methodology are reported in this paper. The obtained results indicate that the use of GFRP reinforcement significantly enhances the interface shear strength, resulting in a capacity that exceeds those of the specimens without reinforcement. When the GFRP-reinforced specimen reaches the first crack at a load similar to that of the unreinforced specimens, it continues carrying load until it reaches a peak, thus indicating that the reinforcement is providing both dowel action and clamping force prior the shear failure. Additionally, once the peak strength is reached, the use of GFRP reinforcement allows the specimen to deform in a pseudo-ductile fashion thus preventing sudden failure.

Fiber-reinforced polymer-reinforced concrete (FRP-RC) structures have won researchers’ attention for decades as a considerable substitute due to their superb mechanical and non-mechanical properties. Despite the promising potential of concrete structures with glass FRP and basalt FRP that were shown by previous research, there are few specifications for the seismic design of FRP-RC structures to date due to limited research data on their seismic behavior. This paper focuses on the seismic performance of concrete columns with carbon fiber-reinforced polymer (CFRP) reinforcement by finite element modeling. The effect of longitudinal reinforcement type and ratio, stirrup spacing, concrete strength and axial load ratio are included in the parametric analysis in VecTor2. Properly designed CFRP-RC columns with good confinement generally reach high load-carrying capacity and deformation level, while high axial load could induce relatively severe damage. To verify these conclusions, seven full-scale columns are under construction and will be tested under combined lateral reversed cyclic loading and constant axial loading.

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.