156 research outputs found
Time-dependent fibre pull-out behaviour in self-compacting concrete
In the present study, the effectiveness of a fibre as an element for transferring stresses across cracks under a sustained
load was assessed. Single fibre pull-out creep tests were performed, in which fibre slip was monitored as a function
of the time. The influence of the fibre orientation angle (0, 30 and 60 degrees), as well as pre-imposed fibre slip levels,
spr, 0.3 and 0.5 mm on the creep response was investigated. Additionally, instantaneous fibre pull-out tests were carried
out on undamaged-bond specimens in order to quantify the effects of the pull-out creep behaviour. The damage
introduced by the pre-slip levels in the bond of the fibre/matrix interface influenced the long-term fibre pull-out
behaviour and, consequently, accelerated the creep rate. However, the assembled pull-out creep behaviour did not
differ considerably from the instantaneous pull-out behaviour for the adopted pre-imposed fibre slip levels.This work is supported by the FEDER funds through the Operational Program for Competitiveness Factors -
COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project 18 SlabSys-HFRC-PTDC/ECM/120394/2010. The authors would like to acknowledge the materials supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash).info:eu-repo/semantics/publishedVersio
Relation between fibre distribution and post-cracking behaviour in steel fibre reinforced self-compacting concrete panels
In this research, the influence of the fibre distribution and orientation on the post-cracking behaviour of steel fibre
14 reinforced self-compacting concrete (SFRSCC) panels was studied. To perform this evaluation, SFRSCC panels
15 were cast from their centre point. For each SFRSCC panel, cylindrical specimens were extracted and notched either
16 parallel or perpendicular to the concrete flow direction, in order to evaluate the influence of fibre dispersion and
17 orientation on the tensile performance. The post-cracking behaviour was assessed by both splitting tensile tests and
18 uniaxial tensile tests. To assess the fibre density and orientation through the panels, an image analysis technique was
19 employed across cut planes on each tested specimen. It is found that the splitting tensile test overestimates the post20
cracking parameters. Specimens with notched plane parallel to the concrete flow direction show considerable higher
21 post-cracking strength than specimens with notched plane perpendicular to the flow direction.The studies reported in this paper are part of the research project LEGOUSE (QREN, project no 5387). This project is co-supported by FEDER through COMPETE programme ("Programa Operacional Factores de Competitividade"). The materials were supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash)
Steel fibre reinforced concrete for elements failing in bending and in shear
Discrete steel fibres can increase significantly the bending and the shear resistance of concrete
structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre
reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural
elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial
compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a
cross-section layered model and the material constitutive laws, the deformational behaviour of structural
elements failing in bending was predicted from the moment-curvature relationship of the representative cross
sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three
point bending tests with shallow beams were performed. The applicability of the formulation proposed by
RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse
analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed
SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the
response of the SFRC beams failing in shear was predicted.Fundação para a Ciência e a Tecnologia (FCT
Temporal flowability evolution of slag-based self-compacting concrete with recycled concrete aggregate
The addition of by-products, such as recycled concrete aggregate and ground granulated blast furnace slag, modify the in-fresh flowability of ordinary self-compacting concrete both initially and over time. A detailed study is presented in this paper of 18 mixtures (SF3 slump-flow class) containing 100% coarse recycled concrete aggregate, two types of cement (CEM I or CEM III/A, the latter with 45% ground granulated blast furnace slag), different contents of fine recycled concrete aggregate (0, 50, or 100%), and three different aggregate powders (ultra-fine limestone powder <0.063 mm, limestone fines 0/0.5 mm, and recycled concrete aggregate 0/0.5 mm). The temporal evolution of slump flow, viscosity, and passing ability, and the values of segregation resistance, air content, fresh and hardened density, and compressive strength were evaluated in all the mixtures. The addition of fine recycled concrete aggregate and CEM III/A improved initial slump flow and passing ability by 6%, due to their higher proportion of fines. Nevertheless, the temporal loss of flowability within 60 min was 5.8% lower when adding natural aggregate and CEM I. Viscosity and air content increased 26% on average following additions of fine recycled concrete aggregate, unlike with additions of ground granulated blast furnace slag. Flowability and strength increased with the addition of limestone fines 0/0.5 mm. According to multi-criteria analyses, the mixtures with CEM III/A, 50% fine recycled concrete aggregate, and limestone fines 0/0.5 mm showed an optimal balance between their flowability (SF2 slump-flow class 60 min after the mixing process), compressive strengths (around 60 MPa), and carbon footprints.Spanish Ministry MCIU, AEI and ERDF [grant numbers FPU17/03374 and RTI 2018-097079-B-C31]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231, BU119P17]; the Youth Employment Initiative (JCyL) and ESF [grant number UBU05B_1274]; the University of Burgos [grant number SUCONS, Y135. GI], UPV/EHU (PPGA20/26) and, finally, our thanks also to the Basque Government research group IT1314-19
Fiber-reinforcement and its effects on the mechanical properties of high-workability concretes manufactured with slag as aggregate and binder
The feasibility of manufacturing fiber-reinforced concretes of high workability through additions of high volumes of electric arc furnace steel slag is evaluated in this paper, using sustainable binders with ground granulated blast furnace slag and ladle furnace slag as a supplementary cementitious material. An extensive experimental plan is developed to test four (self-compacting and pumpable) concrete mixtures, some reinforced with 0.5% vol. of (metallic or synthetic) fibers, in both the fresh and the hardened state. Very specific mechanical aspects are examined, such as the evaluation of both longitudinal and transversal stress-strain compressive behavior, and the assessment of direct tensile strength through the “dog-bone” test. The results of testing this sustainable concrete design yielded suitable mechanical strengths, and good toughness, ductility and impact strength, among other properties. Good adhesion between the fibers and the cementitious matrix was also evident from the fiber pull-out test results. Finally, the overall results confirmed that the use of electric arc furnace steel slag can make a real contribution to construction-sector sustainability and that the mechanical behavior of these novel concretes meets the basic design requirements for use in real structures.Spanish Ministries MCI, AEI, EU and ERDF [RTI2018-097079-B-C31; 10.13039/501100011033; FPU17/03374]; the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17]; the Basque Government research group [IT1314-19]; Youth Employment Initiative (JCyL) and ESF [UBU05B_1274]; the University of Burgos [Y135.GI] and the University of the Basque Country [PPGA20/26]. Likewise, our thanks to CHRYSO and HORMOR for supplying the materials used in this research
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