International Concrete Abstracts Portal

Lined rock cavern (LRC) hydrogen storage requires concrete linings with high tensile ductility and stable crack-control capacity under circumferential tension. Although polyvinyl alcohol (PVA) fibers exhibit high tensile strength and good alkali resistance, their hydrophilicity may induce a loose interfacial transition zone (ITZ), thereby limiting effective fiber bridging. This study proposes a cost-effective fiber-surface modification strategy by combining polydopamine (PDA) with nano-CaCO3. Unlike conventional single surface-treatment methods, the proposed system simultaneously introduces a protective slip-buffering layer and a mineral particle-enhanced ITZ. The PDA layer serves as an adhesive carrier and a protective slip layer, reducing direct abrasion between the fiber and cementitious matrix during interfacial sliding. Meanwhile, nano-CaCO3 particles anchored on the PDA layer increase fiber-surface roughness and provide nucleation/filling sites for hydration products, promoting ITZ densification and stronger mechanical interlocking. SEM and FTIR results confirm the successful formation of the PDA/nano-CaCO3 coating, while tensile tests and DIC analysis show that the modified fibers promote stable strain hardening and more uniform multiple cracking. Numerical simulation further indicates that the improved HDC lining can disperse localized cracking and alleviate damage transfer to the surrounding rock. These results demonstrate that the PDA-assisted nano-CaCO3 modification provides an effective physicochemical route for enhancing PVA fiber-reinforced HDC used in LRC hydrogen storage.

This study investigated the evolution of strength and drying shrinkage together with microstructural properties of ground granulated blast furnace slag (GGBFS)-based ambient-cured alkali-activated reactive powder concrete (AARPC) incorporating reactive MgO. The AARPC is fundamentally characterized by its very high binder content, low water-to-binder ratio, and dense particle packing, which alter hydration reactions and shrinkage behavior compared to typical alkali-activated concretes. Six AARPC mixtures incorporating 0 to 15% reactive MgO were tested for compressive and flexural strength development up to 120 days and drying shrinkage up to 56 days. Microstructural investigations, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), were conducted to identify hydration products and clarify phase evolution. Results showed that the addition of 5% reactive MgO led to a 6.5% improvement in compressive strength and a 32.8% increase in flexural strength at 28 days, while significantly reducing drying shrinkage through pore refinement and matrix densification. However, Higher reactive MgO contents reduced shrinkage but caused strength loss due to excessive hydrotalcite formation and microcracking. Overall, this study clarifies the mechanism by which reactive MgO influences strength and shrinkage in ambient-cured AARPC and highlights its potential for the development of cement-free, high-performance alkali-activated reactive powder concrete under ambient curing conditions.

This study investigates the bond performance of thermo-mechanically treated (TMT) steel rebars embedded in concrete pull-out (PO) specimens, with and without accelerated corrosion, focusing on the effects of specimen geometry, water-cement ratio (w/c), and corrosion level (CL). Tests on cubical direct PO and beam-end (BE) specimens captured differing confinement and stress-transfer mechanisms. Uncorroded direct PO specimens showed ~14% higher peak bond stress (τ_max) compared to BE specimens due to more uniform confinement, a difference that increased to nearly 80% under corrosion. Comparison with the literature confirmed the strong influence of confinement, bonded length, and stress distribution on peak and post-peak response. Increasing CL and bar diameter consistently reduced τmax, as corrosion-driven radial expansion generated microcracking and early splitting of the concrete cover. The effect of w/c was minimal at moderate CLs (≈3 to 5%), where corrosion damage dominated bond degradation. A simplified model is proposed to quantify τmax reduction as a function of corrosion and key geometric and mechanical parameters.

A detailed nonlinear finite element (FE) model of the ribbed profile of reinforcement is used to investigate the effects of bar size, bonded length, confinement, and cover-to-bar ratio on the characteristics of local bond strength-slip laws and the type of anticipated bond failure. The ribbed bar model is verified first against experimental results from direct tension pullout tests, and then it is used to investigate and corroborate the parametric behavior of the model with the evidence provided by the experimental database compiled by ACI Committee 408, Bond and Development of Steel Reinforcement. The objective of the study is to extend the bond-slip laws used in FE simulations of concrete structures by accounting for important design variables that affect bond behavior, with particular emphasis on the effects of large bar diameters and confinement. The detailed ribbed bar model is further used to investigate the upper limit of the confinement index, (K_tr+C)/Db, which is set at 2.5 in ACI CODE-318-25, and marks the transition from bond splitting failure to pullout failure.

This study investigates the seismic performance of precast concrete column-foundation connections incorporating dry mechanical splices, so-called column shoes, designed as strong connections per ACI CODE-318-25 and ACI PCI-319-25. Two precast concrete connection specimens—designated PF (full-dry connections, bolted-column shoe only) and PS (semi-dry connections, bolted column shoe combined with grouted splice sleeves)—were tested alongside a reinforced concrete (RC) control specimen with a monolithic connection detail under quasi-static reversed cyclic loading. The precast specimens were designed to satisfy the strong-connection details of the precast concrete special moment frame system to promote the plastic hinge formation outside the mechanical splices. Their seismic response was compared with that of the RC control specimen to justify the emulative seismic performance. The precast specimens exhibited comparable cyclic responses, including the lateral strength, hysteretic behavior, and deformation capacity to that of the monolithic specimen. Strain responses in longitudinal reinforcements in the precast concrete columns across the joint showed that inelastic deformation was relocated to the intended plastic hinge region rather than the location of the mechanical splices. Although the precast specimens exhibited slightly lower post-peak strength, primarily due to localized grout damage for dry connections, the overall seismic performance fully satisfied the acceptance criteria of ACI 374.1. The results indicate that bolted-type dry mechanical splices, when designed using the strong-connection concept, can provide code-compliant seismic performance under severe cyclic inelastic demands while preventing premature damage concentration in the splice region.