This study investigated the friction shear behavior of concrete consisting of recycled aggregates and natural reinforced steel fibers. The concrete’s natural aggregates were 50% substituted for recycled ones. The addition of steel fibers was evaluated in two different percentages in volume: 0.5 and 1.0%. Thus, 27 non-cracked push-off specimens were produced. The recycled aggregates were separated into two groups according to the strength of the original concrete: Group 1 (15 to 20 MPa) and Group 2 (35 to 40 MPa). Data analysis showed that the concrete’s original strength and steel fiber percentage influenced the shear transfer capacity. Experimental data from natural concrete (NC) and high-strength concrete (HSC) with steel fibers tests performed using the push-off model and shear test methods were recompiled from the technical literature. Using models proposed by some researchers, it was concluded that both methods showed high dispersion in results.

Although several JSCE-SF6 tests have established the strength improvements caused by fiber reinforcement, it is unknown whether the measured strength improvements are caused by shear strength improvements (that is, Mode II), or by tensile or flexural strength improvement (Mode I). This paper provides a basic understanding of the state of stress: 1) in a JSCE-SF6 test; and 2) in an ASTM D5607 direct shear test, which has never been used earlier to investigate the shear strength of fiber-reinforced concrete (FRC). It was found that the JSCE-SF6 standard does not test the shear strength of a material, and it cannot be used to obtain shear characteristics of FRC. On the other hand, the ASTM D5607 standard can be used effectively to obtain shear characteristics of FRC because it creates a stress field very close to pure shear. The addition of steel fibers to concrete does not increase the peak shear strength of concrete.

This paper aims to find the effects of viscosity on concrete behavior in pipelines. Concrete was prepared according to ACI 304.2R-96. Experiments were conducted for measuring its workability by means of slump test. Fluidity and rheology measurements of fresh mortar were investigated. The concrete behavior in pipes was directly investigated using computational fluid dynamics (CFD) simulation, which is based on the Eulerian approach and the dense discrete phase model (DDPM). Concrete behavior including flow profiles, aggregate distributions, and migration was analyzed and discussed. It was observed that the flow characteristic varies from shear flow to plug flow with increased viscosity, and the aggregate distribution along the central axis is more homogeneous. Aggregate radial migration is more pronounced with increased shearing time, decreased viscosity, and enlarged size of aggregates. It was also found that concrete between 12 and 22 Pa·s (1.74 × 10–3 and 3.19 × 10–3 psi·s) is more suitable for pumping.

Based on the unified strength theory as the yield criterion, an elastic-plastic constitutive model of autoclaved aerated concrete block (AACB) considering the intermediate principal stress was proposed. Meanwhile, the mechanical properties and failure mechanism of AACB were investigated by the uniaxial compressive, tensile, shear, and static triaxial compressive tests. The yield function based on the unified strength theory of AACB was derived. Moreover, the proposed model was integrated into the general finite element package ABAQUS by UMAT to simulate the deformation process of AACB under triaxial compressive. The numerical simulation results of AACB were in good accordance with but slightly larger than the static triaxial test results, which implied that the proposed constitutive model could be used to characterize the mechanical characteristics of AACB under complex stress states with high computational efficiency.

ASTM C618 and AASHTO M 295 specifications for fly ash represent the primary documents used by U.S. state and federal agencies to determine the suitability of a fly ash source for use in concrete. Other countries have broadly similar specifications for fly ash. The article compares specifications from the United States, Canada, Europe, Australia, and New Zealand, noting similarities and differences. Despite its common use, several criticisms of the ASTM C618 specification exist and are discussed in this document. Specifically, concerns exist regarding its dependence on strength activity index testing for determination of fly ash reactivity and strength generation potential, and loss on ignition for quantification of unburnt carbon content, as these tests relate somewhat poorly to performance of the fly ash in concrete. Recently developed test methods that could improve some of the most problematic components of the ASTM C618 specification are discussed.