Uniaxial tensile behavior of aligned steel fibre reinforced cementitious composites

By applying an external uniform magnetic field to a fresh cement mixture during casting, an aligned steel fibre reinforced cementitious composites (ASFRC) was prepared. This investigation compares the performance of ASFRC with its counterpart—ordinary steel fibre reinforced cementitious composite (SFRC) containing randomly distributed steel fibres. First, the orientation of the steel fibres in ASFRC and SFRC specimens was examined using X-ray computed tomography analysis; this confirmed that the steel fibres were effectively aligned in the ASFRC. Then, uniaxial tensile tests were performed to allow a comparison of the uniaxial tensile stress–strain curves of the ASFRC and SFRC; and to determine the advantages, if any of ASFRC over SFRC in terms of uniaxial tensile strength (fUtu), ultimate strain (εUtu) and energy dissipation (Gf-A). The uniaxial tensile test results were also used to show that, if the tensile strength of ASFRC is equal to that of SFRC (actually slightly exceeding) using the aligned steel fibre technology, the dosage of steel fibres can be reduced at least 40%. It was also found that the alignment of the steel fibres affects the strain-hardening and multiple cracking behavior of the composites during uniaxial tension testing. Finally, the multiple cracking behavior of the composites was analyzed using a digital image correlation method. These results show that ASFRC exhibits a multiple cracking pattern at a much lower fibre content compared to SFRC

Verification of shrinkage curvature code prediction models

An attempt is made to theoretically and experimentally verify the shrinkage curvature models presented in Eurocode 2 and BS 8110. These codes claim that the models originally derived and proven for uncracked sections are suitable, with modification, for predicting the behaviour of cracked sections, although this claim has never been proven experimentally. To achieve verification, an alternative theoretical approach is initially proposed in this paper. In this theoretical model, the effect of shrinkage, creep and the variation in the neutral axis position of the section are taken into account. The stresses developed in the steel and concrete at a cracked section according to this theoretical model are then applied to a finite-element (FE) model representing a portion of the beam from the crack to mid-way between the crack and an adjacent crack. Ultimately, the mean curvature is determined. Experimentally, pairs of beams were cast and subjected to a level of flexural loading to produce a stabilised crack pattern in the constant-moment zone. The behaviour of the beams was monitored for up to 180 days. For any pair of beams, one beam was cast using a high-shrinkage concrete and the other with a low-shrinkage concrete. Each concrete type, however, exhibits similar creep. Therefore, shrinkage curvature can be obtained by subtracting the long-term movements of one beam from the other. These experimentally defined curvatures were compared with the mean curvatures obtained from the FE analysis. The comparison showed reasonable agreement. The curvatures were also compared with uncracked and cracked curvatures predicted by the codes. The curvatures derived in this investigation fell within the boundaries of the uncracked and cracked curvatures predicted by the codes and, for the fully cracked case, the curvatures were closer to the uncracked boundary

Push-Out Tests for a Novel Prefabricated Steel-Concrete Composite Shallow Flooring System

This paper introduces a novel prefabricated and shallow steel-concrete composite flooring system which is consisted of two main structural components: two C-channel steel beams and a partially encased concrete floor. The concrete floor, which is in the form of T ribbed slab sections, was constructed using two types of concrete (reinforced normal concrete and reinforced lightweight aggregate concrete). The steel edge beams partially encase the floor slab and provide clear and straight finish edges. The floor slab spans to a maximum of 2.0m inclusive of the width of the steel edges with a finished depth of only 230mm. The unique features of the proposed system are reducing the weight and the number of erection lifts (during installation) by using lighter elements (lightweight concrete and shallow steel beams) while the wider possible units have been proposed to fit on transportation tracks; further reducing the extent of site works by pre-off site fabrication, examining the material cost against the fabrication and site erection costs. For the composite slab in bending, the longitudinal shear force is transferred by a unique shear mechanism which results from the special shear connectors. This paper includes the work of a total 2 full-scale push-out tests aimed at investigating the longitudinal shear behaviour of these novel flooring systems and the effects of additional shear connectors. An analytical work is also carried out to investigate the failure mechanism of the system

Behind the confession: Relating false confession, interrogative compliance, personality traits, and psychopathy

The present study further supports the established notion that personality traits contribute to the phenomenon of false confessions and compliance in an interrogative setting. Furthermore, the study provides an investigation into the more recent interest in the potential effect of psychopathic traits in this context. A sample of university students (N = 607) completed questionnaires measuring psychopathic traits, interrogative compliance, and the big five personality factors. Of these, only 4.9% (n=30) claimed to have falsely confessed to an academic or criminal offense, with no participant taking the blame for both types of offense. Across measures the big five personality traits were the strongest predictors of compliance. The five personality traits accounted for 17.9 % of the total variance in compliance, with neuroticism being the strongest predictor, followed by openness and agreeableness. Psychopathy accounted for 3.3% of variance, with the lifestyle facet being the only significant predictor. After controlling for the big five personality factors, psychopathy only accounted for a small percentage of interrogative compliance, indicating that interrogators should take into account a person’s personality traits during the interrogation.N/

An Experimental Study on Precast Concrete Beam-to-Column Connection Using Interlocking Bars

A new type of precast concrete exterior beam-to-column connection is introduced in this paper. The connection consists of a precast U-beam, precast column with corbel, and interlocking bars to connect the precast column and precast beam; these bars, act as the flexural reinforcement to withstand the hogging and sagging moment subjected during testing. The beam-column joint was designed according to the strong column-weak beam principle. The static-monotonic loading was applied to the first specimen (P1), while a quasi-static loading based on displacement control was applied on the second specimen (P2). Tip deflection and specimen cracking were monitored during the tests. Plastic hinges were formed in the beam of both specimens. P1 has no significant cracks in the joint, while P2 has ‘X’ cracks in the joint but it was still deemed acceptable. The precast columns of both P1 and P2 were free from cracks. The connection met the acceptance criteria presented in ACI 374.1-05. The development length of the interlocking bars, i.e. 800 mm from the column face, was sufficient to transfer the load from the beam to the joints and columns

Mechanisms of strength development in masonry units using blended organic binders

In this paper, there will be a discussion of the mechanical mechanism of strength development in a novel masonry unit. The aggregates used to produce the samples were chosen from the following: Pulverised Fuel Ash (PFA), Incinerator Bottom Ash (IBA) and Natural gravel and sand. The binder was a blend of clean cooking oil and pure glycerol combined using the ratio of 1:3 by weight. The units were manufactured using a compaction pressure of 8 MPa and a curing regime which involved heating the samples for 96 h at a temperature of 160 °C in a convection oven. X-ray diffraction (XRD) was used to analyse the chemical composition of the inorganic compounds and to identify any changes in these compounds due to curing. Energy-dispersive X-ray spectroscopy (EDS) was used to investigate the chemical element distribution in the samples helping to identify the binding mechanism in this novel unit. In addition, the micro structure of the sample was analysed using a scanning electron microscope (SEM). Results from the study show that the material distribution; the creation of a filler-binder paste; and the bonding provided by curing the mixture of cooking oil and glycerol play an important role in the strength development of samples. Also, it was found that after being thermally cured, these two immiscible liquids appeared to work together producing an effective binding effect that creates samples with high compressive strengths

Study of Composite Behavior of Reinforcement and Concrete in Tension

This paper aims to further the understanding of the interaction between reinforcement in tension and the surrounding cracked concrete. This is achieved using the elastic analysis of axisymmetric prisms reinforced with a single central bar. As a preliminary to the analyses, the behavior of axially reinforced prisms is described based on previous experiments. This preliminary analysis confirms that the elastic analysis adopted in this investigation is reasonable. Two analytical exercises are described: the first assumes no slip, plasticity, or internal cracking at the interface between the steel and the concrete; the second introduces internal cracking and debonding between ribs. The first analysis indicates that shear deformation of the surrounding concrete accounts for a substantial proportion of the surface crack width, and therefore that this form of deformation cannot be ignored in crack prediction formulae. The second analytical exercise shows that the internal cracking model described by Goto is appropriate

An Experimental Study on Precast Concrete Beam-to-Column Connection Using Interlocking Bars

A new type of precast concrete exterior beam-to-column connection is introduced in this paper. The connection consists of a precast U-beam, precast column with corbel, and interlocking bars to connect the precast column and precast beam; these bars, act as the flexural reinforcement to withstand the hogging and sagging moment subjected during testing. The beam-column joint was designed according to the strong column-weak beam principle. The static-monotonic loading was applied to the first specimen (P1), while a quasi-static loading based on displacement control was applied on the second specimen (P2). Tip deflection and specimen cracking were monitored during the tests. Plastic hinges were formed in the beam of both specimens. P1 has no significant cracks in the joint, while P2 has ‘X’ cracks in the joint but it was still deemed acceptable. The precast columns of both P1 and P2 were free from cracks. The connection met the acceptance criteria presented in ACI 374.1-05. The development length of the interlocking bars, i.e. 800 mm from the column face, was sufficient to transfer the load from the beam to the joints and columns

Waste rapeseed oil used as a binder for masonry units: NMR spectroscopic analysis

The chemistry of unsaturated oils used as binders for masonry units is under investigation, as it is likely to be relevant to their long term properties and may be used to improve the manufacturing requirements. The mixing process is followed by heat curing for 24 h, during which time the unit gains strength. The chemistry of this process has been assumed to be a complex series of oxidative and thermal reactions due to the double bonds present in the triacylglycerol (TAG) hydrocarbon chains, producing a heterogeneous, cross-linked solid matrix which encapsulates solid aggregates. A number of model samples and binder obtained from cured blocks were analysed via several NMR techniques. The reactions are characterised by consumption of polyunsatu-rated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) and formation of oxygenated compounds, chain-shortened TAG, free fatty acids (FFA), di- and monoacylglycerols (DAG and MAG) and cross-linked material. The analysis facilitates identification of specific products and mechanisms of formation as the curing progresses, and evidence for instability of particular species in the matrix from samples retrieved after 6 months of storage