International Concrete Abstracts Portal

Fiber reinforced polymer (FRP) composite rebar is a non-metallic concrete reinforcement alternative that has been successfully deployed in hundreds of structural applications globally. The increasing demand for FRP rebar as a metal alternative is driven by its unique value proposition, including lightweight, high strength, magnetic transparency, and most significantly, corrosion resistance. FRP rebar is fabricated through pultrusion, a high throughput composite fabrication process in which, resin-impregnated fiber undergoes rapid cure when pulled through a heated furnace. Considering the open nature of the open pultrusion process, expansion of production capacity for FRP rebar manufacturing demands the use of advanced resins that are free from Volatile Organic Compounds (VOCs), enable high throughput production, and deliver an outstanding translation of fiber properties following cure. In this work, we will present an epoxy system that is inherently VOC Free and is tailored to enable high throughput manufacturing of glass fiber reinforced polymer (GFRP) rebar at scale. Furthermore, the rapid formation of highly crosslinked structures achieved with this resin system during pultrusion is found to enable outstanding fiber property translation resulting in high modulus (>70 GPa) and corrosion resistance (>80 % tensile strength retention without load) that exceeds existing standards such as ASTM D7957.

This month’s Q&A focuses on evaluation and comparison of test results provided by owner’s and concrete producer’s testing agencies. It discusses responsibilities of the owner’s testing agency specified in ACI 301-20 as well as acceptable differences in test results based on interlaboratory studies and precision statements provided in relevant ASTM standards.

Alkali silica reactivity (ASR) is a reaction of OH- in pore solution with reactive silica aggregate to form an absorptive, deleterious gel and the expansion of mortar or concrete bar specimens is used as a measure of the magnitude of the reaction. Several test methods have been developed to measure ASR expansion and, currently, the ASTM C1567, ASTM C1260, and ASTM C1293 standards are the most widely used test methods. In both ASTM C1567 and ASTM C1260 test methods, mortar bars are immersed in 1N NaOH solution at 80 oC. During the immersion process, two phenomena can occur (1) leaching out of ionic species and (2) NaOH penetrating the mortar bars. The results of these two events might underestimate the ASR mitigating effect of soluble salts, such as Ca(NO2)2. A new ASR expansion test method has been developed and proposed to address these two issues and the details of the new test method will be presented in this paper. In addition, the role of calcium ions (Ca2+) in ASR has been investigated and debated for many years. Using the new test method, the effects of Ca2+ additions on ASR expansion have been investigated. The studies show that if the Ca2+ addition is relatively lower than the alkali content in the system, ASR expansion is increased. However, if the Ca2+ addition is relatively higher than the alkali content in the system, ASR expansion is reduced. If the Ca2+ addition is high enough, the ASR expansion is inhibited. Potential ASR mitigating options based on these findings are presented.

Q. I recently conducted an extensive review of concrete industry standards for requirements and recommendations for air contents specified for freezing-and-thawing durability. Unfortunately, my review shows that the requirements/recommendations included in ACI documents and ASTM standards do not reflect the use of synthetic air-entraining admixtures (AEAs). Rather, these requirements/recommendations are based on concrete mixtures prepared using neutralized vinsol resin AEA, which creates a different air-void system than synthetic AEAs. How can I adjust air content requirements in my specifications to accommodate the use of synthetic AEAs and still meet the requirements/recommendations included in ACI and ASTM documents?

Recently titanium alloy bars (TiABs) have been gaining popularity in civil engineering applications. They offer good deformation capacity, better fatigue performance, high-strength-to-weight ratio, lighter weight (60% that of steel), and excellent corrosion resistance. Recently, TiABs were used in the strengthening of two bridges in Oregon to increase the shear and flexural capacities of the concrete beams. The research in this paper quantifies some common mechanical properties of TiABs using experimental investigation. This is done to explore suitability of the material for wider applications in civil infrastructure. The four types of testing conducted in accordance with ASTM standards included tension, hardness, Charpy V-Notch, and galling tests. Samples of 150 ksi (1034 MPa) high strength steel were also tested for comparison. Test results showed good performance of TiABs. Analytical models are proposed for stress-strain and toughness-temperature relationships.