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This study intends to determine the effect of fiber type and aggregate content on hardened and durability properties of self-consolidating concrete. Steel, glass, and steel/glass hybrid fibers are tested in the present experimental program. Additionally, the effect of aggregate content is considered by using different packing factors and sand-to-all aggregate ratios. Moreover, normal and high strength concrete grades are prepared. Compressive, splitting tensile, flexural, and impact tests are conducted for measuring hardened properties of concrete mixtures. Absorption, desorption, acid attack, resistivity, potential, and chloride diffusion are also durability tests carried out in the present study. Results show that 1.0% and 0.05% are the optimal dosage of steel and glass fibers respectively. Results show that packing factor plays a major role in mechanical characteristics of fiber-reinforced self-consolidating concretes so that an optimal value of 1.12 and 1.14 is obtained for mechanical properties. Also, experimental results reveal that for 1.12 packing factor, the sand-to-all aggregate ratio needs to be equal to the value of 0.50, while 0.57 is achieved as an optimum value for packing factor of 1.14. Overall, results show that hybrid-reinforced self-consolidating concrete is promising for mechanical and durability performance as compared to other mixtures.

Previous research on steel bar-concrete bond behaviour has been concentrated mostly on the intact concrete without considering initial cracks induced by transverse tensile loading called pre-cracking phenomenon. There is no accurate model for evaluating bond behaviour and development length of steel bar in pre-cracked concrete. This paper aims to characterise the bond-slip behaviour of steel bars in pre-cracked concrete by direct pull-out tests, and proposes a constitutive law as a function of the crack width. Results show that induced cracks, notably cracks wider than 0.15 mm, cause a significant reduction in maximum and residual bond strength. Also, results indicate that larger crack widths result in considerably lower dissipated energy by the bond mechanism. The results obtained from both the experimental tests and referenced database demonstrate that the pre-cracking phenomenon has a higher impact on the residual bond strength compared to the maximum bond strength. Unlike existing equations, the proposed model accurately considers cracking effects on the steel bar-concrete bond properties and shows a satisfactory fit with the experimental database. A predictive equation is also proposed for calculation of the development length in pre-cracked concrete, which is more conservative and prudent compared to existing regulations in design codes.

Although extensive bond models have been developed for use in the numerical simulation of uncracked reinforced concrete, no simplified method exists providing satisfactory accuracy and effi...

The addition of nanomaterials affects the workability of cementitious composites by reducing the free water available within the mixtures. In order to address this issue, the present study intends to study the addition of ground granulated blast furnace slag (GGBS) in cementitious materials containing graphene (G) and graphene oxide (GO). An experimental program is considered to measure fresh properties, compressive strength, and service life of cementitious composites. Dosages of 0.03% and 0.06% (by weight of cement) of G and GO are tested in cement pastes and mortars. GGBS in three different dosages of 15%, 30%, and 45% is investigated. A constant water/cement ratio of 0.35 is used in all mixtures. Results show that GGBS improves the yield stress and plastic viscosity of G- and GO-modified cementitious composites. Moreover, GGBS dosages of 30% and 45% compensate the reduced fluidity of 0.03 wt% of G- and GO-modified cementitious composites, respectively. The thixotropy of the composite paste containing GO decreases with the addition of GGBS. Moreover, comparable and slightly improved compressive strengths are obtained for mixtures containing GGBS. The results from the nomogram show a promising trend for the service life of mixtures containing G, GO, and GGBS.

This work discusses the input parameters of discrete element method (DEM) for defining contact element between concrete and rebar. A comprehensive study is performed from a numerical database built in this study. A targeted method of discrete element model considering key parameters of bond strength between concrete and steel bar is developed for reinforced concrete structures so that DEM is customized for defining bond-slip effect between rebar and surrounding concrete. Accuracy of hypothesis is validated by an experimental program. Results show that the targeted method of discrete element model is more applicable and precise than embedded element method in which the perfect bond with no slip is dominant between the materials.

This paper presents a summary of an experimental investigation and the derivation of a bond-slip model for reinforcing steel embedded in moderately confined concrete under monotonic and cyclic loadings. Moderately confined concrete encompasses the domain between unconfined and well-confined concrete, the limits of which are defined in the paper. The proposed constitutive law adapts and extends the well-known Eligehausen-Filippou model for well-confined concrete to moderately confined concrete. It is described by an envelope curve and degradation rules. The former is obtained through a confinement index, defined in this study as a function of the amount of confining steel and concrete, distance between confining steel and the rebar, and concrete segregation effect. It is proposed to adopt the same degradation rules used for well-confined concrete. These rules are validated through statistical tests for moderately confined concrete. They are found to predict correctly the main features of reduced envelope response under increasing cycling amplitudes but to underestimate response degradation under constant cycling limits for the subsequent cycles to the first cycle. To demonstrate the validity and limitations of the proposed model, its predictions under monotonic loading are compared with experimental results and analytical predictions from other studies.

There are no specific models for evaluating bond strength and development length of steel bar in unconfined self-consolidating concrete (SCC). Existing equations for steel bar embedded in normal concrete are not efficient and applicable for SCC. So, it is essential to introduce more precise and efficient models. In this study, pull out tests of referenced literatures are used to present new predicting equations. Unlike existing equations, proposed models demonstrate acceptable fit with the database. Also, in order to evaluate the accuracy of the proposed models, direct pull out tests are performed in this study. The results of experimental test are in good agreement with those obtained by proposed new models.

This paper intends to study the effect of air-entraining admixture (AE) on self-healing method at rebar-concrete interface using superabsorbent polymer (SAP). AE with a constant dosage of 0.83 kg/m3, and 0.25% and 1.0% SAP dosages are considered. Two types of superabsorbent polymer with different chemical compositions and particle sizes are considered for the experimental tests. Pull-out test results of mixtures containing AE admixture are compared with those in non-AE concrete. Scanning electron microscopy/energy dispersive X‐ray spectrometry (SEM/EDS) along with microscopic analysis is performed to study the healing products at crack surface and SAP macro voids around the rebar. Overall, results indicate that AE admixture has a considerable impact on the performance of the self-healing method at the rebar-concrete interface especially for higher dosage of SAP (1.0%). This can be attributed to the internal voids networks around the rebar generated by AE admixture, which can ease the water transfer between SAP macro voids to participate in healing cracks after wet-dry cycles. SEM analysis shows that stalactites, healing products at the external surface of crack, are composed of a large amount of calcium and oxygen.

Although there are different models for determining bond strength and development length of glass fiber-reinforced polymer bar in normal concrete, they cannot evaluate the interfacial behavior of glass fiber-reinforced polymer bar in self-consolidating concrete accurately. This study presents more precise and efficient models for bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete than existing equations. The performance of a model depends very much on test data. Previous researches do not have enough data of bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. So, more extensive data are needed to investigate the efficiency and accuracy of a model. To solve this problem, direct pull-out tests are performed in this study. Unlike existing models for bond strength and development length, proposed models perform very well for predicting bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. The new models considerably decrease the deviation of existing models.

This study intends to determine the effects of incorporating superabsorbent polymers (SAP) within concrete on the bond properties of steel reinforcing bars (rebar) embedded in uncracked and pre-cracked concrete. An experimental program is conducted to check the performance of SAP, as a healing agent inside the concrete, in mitigating internal damage at the rebar-concrete interface due to the pre-cracking phenomena. Two types of SAP with different particle sizes (0.15 and 0.50 mm) and chemistries are considered in the experimental program. Pull-out test results show improved bond properties of steel rebars embedded in uncracked and healed concrete containing lower dosages of SAP. However, concrete containing a high dosage of SAP shows lower bond strength, compared to normal concrete, due to the presence of macro voids. A considerable healing effect is observed for the initial bond-slip curve portion, the bond strength, and the energy absorbed by the bond mechanism, within the cracks of pre-cracked SAP-modified concrete subjected to wet-dry cycles. This study shows that SAP can significantly increase the autogenous healing performance of concrete at rebar-concrete interfacial damage sites.