In recent advancements, a novel strengthening approach employing engineered cementitious composites (ECC) and fibre-reinforced polymer (FRP) materials has emerged. This method integrates ECC as the matrix, carbon fibre-reinforced polymer (CFRP) grid as the internal strengthening component, and epoxy resin for bonding the overlay to the concrete substrate. This study conducted tests on four reinforced concrete (RC) beams under a four-point load configuration. One beam served as an un-strengthened control specimen, while three were subjected to different shear strengthening methods: polymer-modified mortar (PMM), ECC, and CFRP grid-reinforced ECC matrix composites layer (FGREM). The investigation covered failure modes, load-deformation relationships, and load-strain relationships. Finite element (FE) analysis was employed to reproduce the test results. Key findings include the ability of ECC as a matrix to substantially reduce concentrated interfacial bond stresses, preventing debonding failure. The FGREM-strengthened specimen exhibited a failure mode characterized by side concrete cover separation, resulting in a notable 124% enhancement in shear resistance. The proposed FE model, incorporating interfacial behaviour, accurately simulated the performance of all specimens.
Over the past years there has been an increasing trend to use supplementary cementitious materials in concrete to improve its sustainability credentials and durability properties. Perhaps amongst the most popular supplementary cementitious materials is ground granulated blast-furnace slag (GGBS). While the hydration and setting characteristics of mixes with GGBS cured under standard conditions (20°C) has been adequately investigated, the effect of temperature on heat of hydration and setting and the interrelation of these properties has not been evaluated for GGBS containing mixes. In this study, the heat of hydration and setting behaviour of mixes with various levels of GGBS (0, 20, 35, 50 and 70%) cured under elevated temperatures (20, 30, 40, 50 and 60°C) is determined. Elevated curing temperature accelerates the hydration reactions and can significantly reduce the setting time of GGBS-containing mixes. The investigation of heat of hydration at very early ages, can provide an indication of the initial and final setting times of cementitious mixes. The “apparent” activation energy used to characterise temperature sensitivity of cementitious systems, is calculated based on heat of hydration and setting time measurements. It was found that the “apparent” activation energy increases with GGBS content for both heat of hydration and setting behaviour. The value of “apparent” activation energy differs significantly depending on the material property that is considered, such as compressive strength, heat of hydration or setting time.
Low-field Nuclear Magnetic Resonance (LF-NMR) technique has been attracting increasing concern in nondestructively characterising cement-based materials (CBMs), whose nanoscale pore structure are sensitive to water removal. In order to achieve the multi-exponential inversion of relaxometry data preferred by the interpretation on local pore structure of CBMs, an algorithm incorporating L1 regularisation with capability of yielding sparse solution is developed with the aids of Interior-Point method and various principles for optimising the regularisation parameter. Numerical analyses on representative cases show that, the proposed algorithm equipped with the Morozov discrepancy principle is capable of resolving all artificially designed exponential components of various intensities with satisfactory accuracy and precision, even at relatively low signal-to-noise ratio. When applying to resolve the relaxometry data obtained on a cement paste, the algorithm is good at characterising its pore structure with clear significance and capturing its detailed evolution during curing under hot water with good precision.
Post-installed rebar (PIR) is extensively utilized for rehabilitating, strengthening, and retrofitting existing concrete structures, and its anchorage design greatly concerns the failure mode and tensile behavior. PIR anchored in joints or columns generally suffers pressures normal to its anchorage section in one direction, and PIR's failure mode and tensile behavior can be greatly affected. However, limited research on the unilateral pressure effect for PIR has been conducted, with remaining uncertainties on applications and designs for PIR. Thus, this paper carried out the pull-out tests of 38 specimens with various anchorage conditions (20 unilateral pressure specimens, 14 no-lateral pressure specimens, and four bilateral pressure specimens) to investigate the bond behavior for PIR subjected to unilateral pressure. Besides, the effects of concrete strength, rebar diameter, and anchorage length on PIR under unilateral pressure were also considered in the tests. The test results showed that the no-lateral pressure specimens split in the concrete and adhesive layer. In contrast, the unilateral and bilateral pressure specimens occurred two typical failures [adhesive-rebar (A-R) interface failure and adhesive fracture failure]. In addition, the interfacial damage and cracking pattern were discussed in detail. Then, the bond strength and bond slip of specimens were investigated. The result showed that the bond strength under unilateral pressure was greater than that under no-lateral pressure but less than that under bilateral pressure, and there was no obvious change in bond strength while the unilateral pressure increased. Regarding bond slip, it was found that the bond slip increased with the bond strength. This paper performed an experimental investigation on failure modes and cracking patterns for PIR under unilateral pressure. It analyzed the unilateral pressure effect on the bond performance for PIR, raising the safety considerations about PIR applications in load-bearing structures.
To secure good quality post-installed anchors with a relatively short anchorage length and sufficient pull-out/shear resistance, an anchoring method with enlarged diameter at the end of drilled holes has been developed. Anchors were provided with head plates and fixed into the enlarged holes using non-shrinkage high-strength cementitious grout. Pull-out and shear preliminary tests were conducted to investigate the behavior and evaluate the strength of such anchors set in concrete. Furthermore, an evaluation method, based on the Japanese recommendations for design of composite constructions, was proposed. The evaluated pullout and shear capacities of all tested anchors designed to fail by steel yielding ensured sufficient safety margin as to test results, whereas those of some anchors designed to fail by concrete cone breakout should be reduced.