International Concrete Abstracts Portal

This paper describes an integrated experimental and numerical investigation of the behavior of lapped, grouted connections for modularized construction of safety-related nuclear reinforced concrete (RC) shear wall structures. The novel lapped geometry of the proposed connection provides “face-to-face” (rather than “end-to-end” or “butt”) joint interfaces with large, grouted construction tolerances and large surfaces to develop the required continuity of the strength and stiffness of the wall. A total of five modular beam specimens and one state-of-practice (monolithic) beam specimen were tested under three-point simply supported monotonic loading conditions. These beam specimens represented horizontal slices taken out of the length of a nuclear shear wall structure. Continuum finite element analyses were conducted to compare with the experimental test results and to develop information regarding the effects of material differences between the specimens. The experimental and numerical results showed that adequate clamping of the connection, as well as additional reinforcement on both sides of the grout joint, are necessary to achieve the desired “strong” connection behavior with full strength and stiffness continuity between adjacent RC modules.

Although grouted splice-sleeve connectors (GSSCs) are notably used in precast concrete structures, steel sleeves are heavy and have corrosion issues. The bond characteristics of GSSCs using cylindrical and tapered fiber-reinforced polymer (FRP) sleeves—lighter alternatives—were investigated in this study. A series of pullout tests for 144 specimens were conducted to evaluate the effects of FRP type, number of layers, shape, and length on the bond characteristics of GSSCs. The test results showed that for FRP GSSCs, tapered FRP sleeves effectively developed confinement compared with cylindrical FRP sleeves, leading to better bond strength and shorter development length. A design equation was proposed for estimating the tensile strength of FRP-based GSSCs, which predicted well the test results. The tapered FRP sleeves reduced the development length compared with cylindrical FRP sleeves, implying greater FRP GSSC efficiency in precast concrete structures, which provides engineers with valuable insights for efficient FRP splice-sleeve design in precast concrete structures.

Conventional anchor bolt-confined flexible formwork concrete walls for gob-side entry retaining have clear inherent technical limitations, including incompatible deformation between steel anchors and concrete, low construction efficiency, and grout leakage. However, existing studies have not fundamentally solved the core mechanical problem of confinement efficiency loss caused by deformation mismatch, nor established a complete theoretical design framework for new high-compatibility confined systems, which severely limit their application in complex underground conditions. This study develops an innovative prefabricated stirrup-confined flexible formwork concrete system, identifies two primary surrounding rock fracture modes via theoretical analysis, establishes corresponding mechanical models for support design, and verifies the system through laboratory tests and full-scale field trials. The high-strength fiber stirrups achieve tensile strength equivalent to deformed steel bars with an elongation of ≤6%, significantly improving deformation compatibility with concrete. Field results show that the optimized system delivers excellent surrounding rock control, with a maximum roof subsidence of 65 mm, wall displacement of 30 mm, and floor heave of 35 mm. This study provides a validated design framework for high-efficiency confined concrete underground support structures.

In this work, novel polycarboxylate admixtures were synthesized by two different free radical polymerization systems: methacrylic acid (MAA) and methoxy polyethylene glycol methacrylate (MPEG-MA) for PC-1, and acrylic acid (AA) and isoamyl alcohol polyethylene glycol (IAA-PEG) for PC-2. Thioglycolic acid as a chain transfer agent and ammonium persulfate as an initiator were used. The synthesized carboxylic polymers were characterized using Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TG). The influence of the chemical structure of polycarboxylates on the rheology of the concrete, as well as the prognosis of the superplasticizer’s development, is also presented through measuring of water consistency, setting times, flow table, slump test, zeta potential, and compressive strength. The cementitious products were investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The developed superplasticizers showed good dispersion effects and slump performance in workability and fluidity retention tests, adsorption performance, and SEM performance. Intriguingly, the PC-1 and PC-2 mixtures achieved flow table values of 230 and 200 mm, respectively. The compressive strength values at various curing ages up to 28 days exhibited double and triple values compared with the control sample. Additionally, compared to the control ordinary portland cement paste, a reduction of the water-cement ratio (w/c) of approximately 0.25 and the development of excessive hydration products give PC-1 and PC-2 extensive pastes a more dense and compact structure in XRD and SEM investigation.

This study uses six large-scale experimental tests to investigate the seismic behavior of external socket connections for reinforced concrete columns. The tests evaluated the effects of key design parameters, including socket height and grout strength, on the performance of these connections under reverse cyclic lateral loads. The results indicate that socket height significantly affects whether the plastic hinge forms in the column above the connection or inside the socket and influences the required strength of the structural components. Shorter socket heights required higher grout strengths and increased shear capacity to avoid undesirable failure modes. Three primary failure modes were observed: grout crushing, shear failure, and flexural failure above the socket. Regardless of socket height, all tests showed that external socket connections effectively protect adjoining structural members by limiting plastic strain demands. These findings provide valuable insights into optimizing the design and performance of external socket connections in seismic regions.