International Concrete Abstracts Portal

The role of limestone (LS) powder replacement and changes in C-S-H due to pozzolanic reactions on the acid resistance of cementitious pastes are studied using thermodynamic modeling. Simulations are performed under equilibrium conditions while hydration products were exposed to increasing levels of sulfuric acid. LS replacement doesn’t show sacrificial characteristics against sulfuric acid attack, and LS acidification starts only after full consumption of portlandite, and most C-S-H. Increased LS replacement causes the dilution of the formed portlandite and C-S-H volumes, which results in their full consumption at lower acid concentrations than mixtures without LS replacement. Pozzolanic reactions of SCMs result in C-S-H phases with lower Ca/Si than OPC-only counterparts, increasing acid resistance. However, highly reactive and/or high-volume SCM replacements might further decrease the available portlandite, reducing the buffer acid resistance capacity. This issue is particularly critical for portland limestone cement-based systems.

This paper proposes a series of empirical modifications to an existing three-step analytical model used to derive the cyclic shear capacity of circular reinforced concrete (RC) columns considering corrosive conditions. The results of 16 shear-critical RC columns, artificially corroded to various degrees and tested under quasistatic reversed cyclic loading, are used for model verification. The final model is proposed in a piecewise damage-state format relative to the measured damage of the steel reinforcement. New empirical decay coefficients are derived to determine the degraded material properties based on an extensive database of over 1380 corroded tensile tests. An additional database of 44 corroded RC circular piers is collected to assist in the modification of ductility-based parameters. Compared to the shear-critical test specimens, the model results indicate that the peak shear capacity can be predicted well across a range of deterioration severities (0 to 58.5% average transverse mass loss), with a mean predictive ratio of ±8.60%. As damage increases, the distribution of the corrosion relative to the location of the shear plane becomes a critical performance consideration, increasing predictive variance.

This experimental study investigates the influence of flexuralcracks and punching shear failure inclination on double-headedstud anchorage within the critical perimeter. The research alsoexplored the technical feasibility of using synthetic coarse aggregatesfrom bauxite residue as a sustainable alternative in structuralconcrete production. The results showed that the overall structuralintegrity is impaired at 40 to 50% due to flexural cracks at thecritical perimeter of 2d (30 degrees); however, the perimeter of1.2d (45 degrees) enhanced the shear reinforcement activationand shear strength up 15%, providing a balanced failure withinthe strengthening zone. Thus, a concrete anchoring capacity (CAC)method was proposed to calculate the contribution of doubleheadedstuds in serviceability and ultimate limit states. In addition,synthetic aggregates performed similarly to natural aggregates,offering environmental benefits such as reducing the carbon footprint and production stages.

Noncorrosive fiber-reinforced polymer (FRP) reinforcement presents an attractive alternative to conventional steel reinforcement, which is prone to corrosion, especially in harsh environments exposed to deicing salt or seawater. However, FRP reinforcing bars’ lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP bar-reinforced concrete members. The deeper cracks and larger crack widths also reduce the depth of the compression zone. Consequently, both the aggregate interlock and the compression zone for shear resistance are significantly reduced. Additionally, due to their limited tensile ductility, FRP reinforcing bars can rupture before the concrete crushes, potentially resulting in sudden and catastrophic member failure. Therefore, ACI Committee 440 states that through a compression-controlled design, FRP reinforced concrete members can be intentionally designed to fail by allowing the concrete to crush before the FRP reinforcing bars rupture. However, this design approach does not yield an equivalent ductile behavior when compared to steel-reinforced concrete members, resulting in a lower strength reduction, ϕ, value of 0.65. In this regard, using FRP-reinforced ultra-high-performance concrete (UHPC) members offer a novel solution, providing high strength, stiffness, ductility, and corrosion-resistant characteristics. UHPC has a very low water-cementitious materials ratio (0.18 to 0.25), which results in dense particle packing. This very dense microstructure and low water ratio not only improves compressive strength but delays liquid ingress. UHPC can be tailored to achieve exceptional compressive ductility, with a maximum usable compressive strain greater than 0.015. Unlike conventional designs where ductility is provided by steel reinforcing bars, UHPC can be used to achieve the required ductility for a flexural member, allowing FRP reinforcing bars to be designed to stay elastic. The high member ductility also justifies the use of a higher strength reduction factor, ϕ, of 0.9. This research, validated through large-scale experiments, explores this design concept by leveraging UHPC’s high compressive ductility, cracking resistance, and shear strength, along with a high quantity of noncorrosive FRP reinforcing bars. The increased amount of longitudinal reinforcement helps maintain the flexural stiffness (controlling deflection under service loads), bond strength, and shear strength of the members. Furthermore, the damage resistant capability of UHPC and the elasticity of FRP reinforcing bars provide a structural member with a restoring force, leading to reduced residual deflection and enhanced resilience.