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 presents the torsional behavior of hollow reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) U-wraps. Test parameters involve variable wall thickness in the section and the width and spacing of the externally bonded CFRP sheets. An experimental program is conducted with 27 beams (three unstrengthened and 24 strengthened) to examine their capacities, shear flows, and force distributions when incorporating a ratio of 0.27 to 0.46 between the areas of the hollow and gross cross sections. The stiffness and capacity of the test beams are dominated by the wall thickness, and the effectiveness of CFRP strengthening becomes pronounced as the void of the beams decreases. The presence of CFRP redistributes internal shear forces in the cross section, which is facilitated by narrowing the spacing of the U-wraps. The effective zone of CFRP retrofit is positioned near the outer boundary of the strengthened section. Regarding crack control, multiple discrete U-wraps with narrow spacings outperform wide U-wraps with enlarged spacings. While the location of a shear-flow path is dependent upon the wall thickness, the width of the U-wraps controls the effective shear-flow area of the beams. The size of the void is related to the stress levels of internal reinforcing components, including yield characteristics. Transverse stirrups are the principal load-bearing element for the unstrengthened beams; however, the reliance of the stirrups is reduced for the strengthened beams because the U-wraps take over portions of the torsional resistance. Through a machine learning approach combined with stochastic simulations, design recommendations are proposed.

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.