Effect of pressure after casting on high strength fibre reinforced mortar

This study investigates the effects of applying pressure after casting on the flexural response of high strength fibre reinforced mortar in which up to 5% fibres by volume were premixed. High mortar strength was achieved by reducing mix porosity (low water-cement ratio), adding fly ash and using superplasticisers. Variables included eigth different types of fibre, their volume fraction in the mix, two mortar matrices, two values of pressure after casting, and the casting orientation. It is found that pressure improves the proportional limit and the flexural strength of the composite but may lead to a deterioration in its postcracking response and toughness. Composite moduli of rupture of more than 5000 psi (37 MPa) are observed with steel fibres while highest toughness indices of up to 90 are reported with polypropylene fibres. It is concluded that the application of pressure after casting to improve composite properties is not economically justifiable.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26082/1/0000158.pd

Combined effect of steel fibres and steel rebars on impact resistance of high performance concrete

The investigation on the impact properties of normal concrete (NC)and reinforced concrete (RC) specimens, steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibres dosages were carried out with the drop-weight impact test recommended by ACI Committee 544. The results indicate that the number of blows to final failure greatly increased by addition of steel fibres. Moreover, the combination of steel fibres and steel rebars demonstrates a significant positive composite effect on the impact resistance, which results on the improvement in impact toughness of concrete specimens. In view of the variation of impact test results, the two-parameter Weibull distribution was adopted to analyze the experimental data. It is proved that the probabilistic distribution of the blows to first crack and to final failure of six types of samples are approximately two-parameter Weibull distribution.Funded by the National Natural Science Foundation of China (NSFC) (Grant No.50578026)Financial support provided by the Research Center of Mathematics of the University of Minho through the FCT Pluriannual Funding Progra

Report on design and construction of steel fiber-reinforced concrete elevated slabs

ACI 544.6R-15Construction of slabs in areas with weak soil conditions has commonly used pile-supported slab structural design so that the adverse effects of soil-structure interaction in terms of differential settlement, cracking, or long-term serviceability problems are avoided. In this application, the construction of slabs on closely spaced pile caps (typical span-depth ratios between 8 and 30) is referred to as elevated ground slabs (EGSs). These slabs may be subjected to moderately high loading, such as concentrated point loading of up to 44 kip (150 kN) and uniformly distributed loadings of 1000 lb/ft2 (50 kN/m2 ). The dynamic loadings may be due to moving loads such as forklifts, travel lifts, and other material handling equipment. Fiber-reinforced concrete (FRC) has been successfully used to address the structural design of these slabs. Based on the knowledge gained, the area has been extended to a construction practice for slabs supported by columns as well. Applications are further extended to multi-story building applications. This report addresses the methodology for analysis, design, and construction of steel FRC (SFRC) slabs supported on piles or columns (also called elevated SFRC [E-SFRC]). Sections of the report address the history, practice, applications, material testing, full-scale testing, and certifications. By compiling the practice and knowledge in the analysis design with FRC materials, the steps in the design approach based on ultimate strength approach using two-way slab mechanisms are presented. The behavior of a two-way system may not require the flexural strength of conventional reinforced concrete (RC) because of redistribution, redundancy, and failure mechanisms. Methods of construction, curing, and full-scale testing of slabs are also presented. A high dosage of deformed steel fibers (85 to 170 lb/yd3 [50 to 100 kg/m3 ]) is recommended as the primary method of reinforcement. Procedures for obtaining material properties from round panel tests and flexural tests are addressed, and finite element models for structural analysis of the slabs are discussed. Results of several full-scale testing procedures that are used for validation of the methods proposed are also presented

Report on indirect method to obtain stress-strain response of fiber-reinforced concrete (FRC)

"ACI 544.8R-16"Development of proper design procedures for fiber-reinforced concrete (FRC) materials requires use of material tensile and compressive stress strains that reflect the contribution of fibers to the post-cracking behavior. While uniaxial tension tests provide the most fundamental material properties, conducting closed-loop tension tests are difficult to accomplish; therefore, methods based on indirect measurement of tensile properties using flexural tests are typically used. This report presents the methodologies that are used for data reduction and presentation of the flexural test results in terms of an equivalent tensile stress-strain response for FRC materials. Existing methods for estimating uniaxial tensile stress-strain response of strain-softening and hardening FRCs from flexural beam-test data are introduced. Different approaches applied to beam tests based on elastic equivalent, curve fitting, or back-calculation of flexural data are introduced. These are divided into two general categories: elastic equivalent approach or inverse analysis method. In the elastic equivalent approach, a summary of available test methods by various code agencies are presented. Using back-calculation methods, tools based on the finite element method and analytical closed-form solutions are presented. An approach is presented that uses closed-form moment-curvature relationships and obtains load-deflection responses for a beam of three- or four-point loading. The method is used to obtain equivalent parametric tensile stress and strain relationships for a variety of FRC materials. The methods are compared against the available residual strength and also elastically equivalent residual strengths obtained by different specimen geometries. Results for a range of FRC materials studied show the backcalculated post-peak residual tensile strength is approximately 30 to 37 percent of the elastically equivalent flexural residual strength for specimens with different fiber types and volume fractions