International Concrete Abstracts Portal

In this paper, uniaxial tensile testing of semi-grouted sleeve connectors was carried out by controlling the amount of expansive agent in the grout material. The effects of different steel bar diameters and anchorage depths on the failure mode, bearing capacity, and surface strain of sleeve connectors were studied. It is found that there are three failure modes in the specimens—namely, steel bar pullout failure, steel bar slip failure, and screw thread failure. The expansion characteristics of the grout material can partially compensate for the lack of compressive strength. Based on the analysis of the ultimate bearing capacity of different specimens, a design method to prevent the slip failure of the semi-grouted sleeve is proposed. The addition of 5 to 11% expansive admixture can reduce the circumferential strain of the casing from the steel bar anchorage location to the grouting end by 28.57 to 125.30%, with no impact on the longitudinal strain variation pattern. As the depth of steel bar anchorage increases, the expansive effect of the steel bar anchorage and casing longitudinal strain gradually surpasses the shrinkage effect, while the shrinkage effect at the grouting end of the casing gradually outweighs the expansive effect. With an increase in steel bar diameter, the longitudinal strain at the grouting end of the casing only decreases by 1.75% and 2.10%, essentially having no significant impact.

This experimental study evaluated the correlation between measured concrete expansion from a modified version of the miniature concrete prism test (MCPT) with the concentration of chemical markers leached from the prisms into an alkaline soak solution. Fifteen concrete mixture designs were tested for expansion and soak solution concentrations over time. The changes in expansion and soak solution concentrations were found to correlate well even with variations in alkali loading and substitution of cement with Class F fly ash. A model was developed to estimate the expansion potential of concrete based on an expansion reactivity index (ERI) that incorporated the concentrations of silicon, sulfate, calcium, and aluminum. The relationship between ERI and expansion was then used to identify potentially expansive concrete mixtures using the ERI of cores taken from a structure exhibiting potential alkalisilica reaction (ASR) expansion and concrete cylinders matching the mixture designs of the MCPT specimens.

Alkali-silica reaction (ASR) is one of the most harmful distress mechanisms affecting concrete infrastructure worldwide. ASR is a chemical reaction that generates a secondary product, which induces expansive pressure within the reacting aggregate material and adjacent cement paste upon moisture uptake, leading to cracking, loss of material integrity, and functionality of the affected structure. In this work, a computational homogenization approach is proposed to model the impact of ASR-induced cracking on concrete stiffness as a function of its development. A representative volume element (RVE) of the material at the mesoscale is developed, which enables the input of the cracking pattern and extent observed from a series of experimental testing. The model is appraised on concrete mixtures presenting different mechanical properties and incorporating reactive coarse aggregates. The results have been compared with experimental results reported in the literature. The case studies considered for the analysis show that stiffness reduction of ASR-affected concrete presenting distinct damage degrees can be captured using the proposed mesoscale model as the predictions of the proposed methodology fall in between the upper and lower bounds of the experimental results.

Fiber-reinforced polymer (FRP) tube-confined expansive concrete columns fully use the compressive properties of concrete and the tensile properties of FRP and it significantly increases the strength and ductility of concrete. To clearly understand the FRP-confined expansive concrete under earthquake load, the mechanical properties of glass fiber-reinforced polymer (GFRP) tube-confined expansive concrete (GCEC) under cyclic axial compression were studied. Different core concrete, loading patterns, and GFRP tube thickness were considered and compared. Test results show that the strength enhancement ratio and hoop rupture strain of GFRP-confined expansive concrete cylinders (GCECs) were improved compared with GFRP-confined unexpansive concrete cylinders (GCUCs). Additionally, the strength enhancement ratio of GCUC and the hoop rupture strain of GCUC and GCEC specimens under cyclic axial compression were higher than that under monotonic axial compression. In addition, it was found that expansion of core concrete has no significant effect on the plastic strain-envelope unloading strain relationship as well as stress degradation ratio. For the unloading/reloading path of GCEC, it indicates that the analytical results based on the existing models are in good agreement with the experimental values.

To improve the early-age cracking resistance of self-consolidating concrete (SCC), this paper investigated the effects of an expansive agent (EA), fibers, and the interaction between EA and fibers on the cracking behavior of restrained SCC caused by plastic shrinkage based on the slab test. Twenty-one types of samples were prepared, including one control group, two EA contents (6 and 8% of the mass fractions of cementitious materials), three steel fiber contents (0.25, 0.50, and 0.75% by volume), three polypropylene fiber contents (0.05, 0.10, and 0.15% by volume), three hybrid fiber contents, and nine combinations of EA (8% of the mass fraction of cementitious materials) and fibers. The initial cracking time and propagation of cracks over time were both observed. Test results indicate that an increase of EA dosage presents no significant improvement on early-age cracking resistance capability. Compared with steel fiber (SF), polypropylene fiber (PP) with equivalent fiber factors was particularly effective in reducing the nominal total crack area. In general, crack reduction factors of fiber-reinforced expansive self-consolidating concrete (FRESCC) are 70% greater than that of SCC containing fiber only. It indicates that the combination of EA and fibers enable SCC to present better early-age cracking resistance.