Search

This paper investigated the shear transfer behavior between substrate recycled aggregate concrete and new natural aggregate concrete. A total of 72 push‐off tests with substrate‐to‐new concrete specimens were performed considering the effects of concrete strength grade, replacement ratios of recycled coarse aggregate, and lateral constraints ratios. Existing design codes and empirical models for calculating shear strength were reviewed and verified. Results show that concrete cracks occurred and developed along the shear transfer plane. Increasing the concrete grade and lateral constraints can both improve the crack stress and shear strength, while the incorporation of recycled coarse aggregate has a slight adverse effect on them. The model in fib Model Code 2010 based on shear‐friction theory gave the most accurate but still conservative values compared with experimental results and can be used to predict the shear transfer behavior between substrate recycled aggregate concrete and new natural aggregate concrete. [ABSTRACT FROM AUTHOR]

Highlights • Shear failure mechanisms of SCS sandwich beams are explored. • Structural behaviours of SCS sandwich beams are simulated by finite element models. • Parametric studies on failure mechanisms of SCS sandwich beams are investigated. • Theoretical analysis of SCS sandwich beams is carried out considering bond-slip. Abstract The steel-concrete-steel (SCS) sandwich structure has been proposed for containment buildings in third-generation nuclear power plants. In this paper, 27 static tests on SCS sandwich beams (by the authors and others) are adopted serially to summarize the failure modes and explore the failure mechanisms of SCS sandwich beams with different bond-slip conditions between the steel plate and concrete. Further, a three-dimensional finite element (FE) model is developed to simulate the ultimate strength of SCS sandwich beams under different failure modes. The accuracy of the developed FE model in predicting ultimate strength, cracking behaviours and bond-slip behaviours is verified by static tests. Based on the validated FE model, 65 numerical cases are calculated to investigate the effects of analytical parameters on the failure mechanism and ultimate strength of SCS sandwich beams under different bond-slip conditions. The analytical parameters include the steel plate ratio, shear span to depth ratio, spacing of shear studs and shear reinforcement ratio. In addition, theoretical models are proposed to predict the ultimate strength of SCS sandwich beams under different bond-slip conditions. The accuracy of the theoretical model is verified by comparison with current design codes for SCS sandwich beams. [ABSTRACT FROM AUTHOR]

• Assessment of bleeding rate and capillary pressure development of 3DPC under different upper self-weight. • Analyze the behavior of friction-restrained plastic shrinkage of printed concrete and the effect of the upper self-weight on it. • Mechanism on augmentation of risk of shrinkage cracking of 3DPC under higher Self-weight of upper layers. The material properties of 3D printed concrete determine its fragility in preventing plastic shrinkage cracking due to the presence of restraint. Residual friction at the bottom that is positively related to the self-weight of the upper layers is a potential source of constraint that may cause cracking. The present study investigates the effect of self-weight of upper layers on plastic shrinkage of bottom printed concrete at early age. The corresponding surface moisture, bleeding rate, evaporation rate, capillary pressure development, and plastic shrinkage strain of printed concrete specimens under different upper self-weight are determined. It is found that increased self-weight of upper layers can significantly yield more early-age surface moisture and higher bleeding rate of the concrete at the bottom. The increased self-weight of upper layers can induce water to migrate and accumulate on the sides of the printed elements. However, as the self-weight of upper layers reduces the equivalent pore radius, the self-weight of upper layers would still facilitate the development of capillary pressure and further causes larger free plastic shrinkage strain. And when there is friction at the bottom, the horizontal plastic shrinkage is significantly limited by the constraint of the self-weight of upper layers, and the restraint strain increases with the upper self-weight. The maximum principal tensile stress results are calculated by two-dimensional plane strain field on the observation surface, which indicates that the specimen bears a greater risk of plastic shrinkage cracking with larger self-weight of upper layers. [ABSTRACT FROM AUTHOR]

This paper reports an investigation into the autogenous shrinkage, mechanical, and durability performances of alkali-activated slag concrete (AASC) with emulsified cooking oil (ECO). Properties of AASC including flowability, setting time, compressive strength, autogenous shrinkage, and carbonation depth are tested to clarify the effects of the ECO. Commercially available expansion agent (EA) and shrinkage reducing agent (SRA) are also applied on AASC to compare with ECO. Experimental results show that the utilization of ECO could significantly decrease the autogenous shrinkage of alkali-activated slag concrete owing to the reduction of surface tension and the denser internal structure. It also shows that cooking oil after emulsification could have better performances than that of plain cooking oil when applied on AASC. Setting time and carbonation resistance ability are also improved with the utilization of ECO. The application of ECO is considered a cheap and easy way to overcome the limitation of AASC. [ABSTRACT FROM AUTHOR]

• The bond behavior between RAC and deformed steel bars after FTCs was investigated. • The bond stress distribution for RAC after FTCs was discussed. • A bond stress-slip model for RAC after FTCs was proposed and verified. In cold regions, freeze-thaw damage can deteriorate the structural performance of reinforced concrete structures. This paper investigated the bond behavior between recycled aggregate concrete (RAC) and deformed steel bars after freeze-thaw cycles (FTCs). Sixty-three specimens for pull-out tests were prepared with three different recycled coarse aggregate replacement ratios (0%, 30% and 50%) and seven different FTCs (0, 50, 100, 150, 200, 250 and 300). Additionally, nine made-to-measure pull-out specimens with built-in strain gauges were tested to tentatively study the bond stress distribution along the interface between the steel bars and the RAC after the FTCs. The results show that as the FTCs increased, the bond strength decreased and became increasingly significant as the RCA replacement ratios increased, while the bond slip was relatively stable as the FTCs increased and exhibited a similar increasing trend for all the mixtures at the higher number of FTCs. The bond stress focused on local areas and formed local stress concentrations when the pull-out force was close to the peak value. Finally, a two-segment bond stress-slip model to describe the bond behavior between RAC with RCA replacement ratios less than 50% and deformed steel bars after FTCs was proposed, showing a good correlation with the test results. [ABSTRACT FROM AUTHOR]