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Showing 1-5 of 13 Abstracts search results

Document: 

SP155-09

Date: 

August 1, 1995

Author(s):

N. Banthia, K. Chokri, and J. F. Trottier

Publication:

Symposium Papers

Volume:

155

Abstract:

Describes the construction of two simple impact machines, one small with a capacity of 100 Joules and the other large with a capacity of 1000 Joules, designed to conduct impact tests on fiber reinforced mortars and concretes in the uniaxial tensile mode. During a test, the applied load, accelerations, and velocities are measured such that with a proper analysis scheme, the raw data can be analyzed to obtain fundamental material properties under impact loading. Carbon, steel, and polypropylene micro-fiber reinforced mortars and steel fiber reinforced concrete were tested; it was demonstrated that the proposed technique is a simple and rational method of obtaining meaningful material properties. In general, fiber reinforced composites were found to be more impact resistant than their unreinforced counterparts, with the improvements found to be proportional to the fiber volume fraction. In addition, both the unreinforced matrix as well as fiber reinforced composites were found to be stress-rate sensitive, but the extent of sensitivity observed was smaller than usually reported in the literature for cement-based materials under uniaxial tensile loading.

DOI:

10.14359/934


Document: 

SP155-07

Date: 

August 1, 1995

Author(s):

N. Banthia,, M. Azzabi, and M. Pigeon

Publication:

Symposium Papers

Volume:

155

Abstract:

The usefulness of fiber reinforcement in improving the cracking resistance of cement-based materials under restrained shrinkage conditions is indisputable. In fact, in many instances, this may be the sole reason of adding fibers to concrete. In spite of this general recognition, there is no universally accepted technique of demonstrating or quantifying the effectiveness of fibers under the conditions of restrained shrinkage. This paper describes a newly developed technique in which prismatic specimens with a linear restraint along the longitudinal axis are subjected to a drying environment such that conditions of uniaxial tension are generated. The specimen cracks under these conditions; if fiber reinforcement is present, the influence of fibers on the cracking pattern can be established. Results with seven types of fibers are presented. Based on the observations of the crack patterns, a "fiber efficiency factor" is proposed which appears to be an appropriate basis for characterizing the fibers.

DOI:

10.14359/932


Document: 

SP155-05

Date: 

August 1, 1995

Author(s):

B. Mobasher, C. Y. LI, and A. Arino

Publication:

Symposium Papers

Volume:

155

Abstract:

Procedures to obtain the experimental R-curves using a compliance calibration technique are revisited in this paper. R-curves provide a convenient means to study the process of fracture and the brittle-ductile transition in materials. Single edge notched beam specimens are tested under closed loop crack mouth opening control. The procedure to obtain the R-curves using loading/unloading compliance and the residual displacements are discussed. An elastically equivalent toughness K R as a function of crack extension is defined to compare the R-curves with the available data in the literature. The developed test method is applied to fiber reinforced concrete (FRC) composites with up to eight percent by volume of short, chopped alumina, carbon, and polypropylene (PP) fibers. Significant strengthening of the matrix due to the addition of short carbon and alumina fibers was observed. R-curves in these composites are characterized by an increase in the steady state fracture toughness. In PP-FRC composites, energy dissipation due to fiber pullout increases the ascending rate of the R-curve well after the main crack has formed. The work of fracture is computed from the cyclic loading/unloading tests and the results compared with the R-curves.

DOI:

10.14359/930


Document: 

SP155-10

Date: 

August 1, 1995

Author(s):

A. Pacios and S. P. Shah

Publication:

Symposium Papers

Volume:

155

Abstract:

With the objective of understanding the reinforcing mechanisms of fibers in steel fiber reinforced concrete, the adherence between the fiber and the matrix was studied by conducting pullout tests of fibers from a cementitious matrix. In this paper, the effect of factors such as loading rate, inclination of fibers, and number of fibers have been investigated. An innovative measurement system was developed for high rates. It was experimentally obtained that by increasing the rate of loading, both pullout resistance and slip at peak were increased. Peak pullout force presents a higher rate sensitivity for a higher number of fibers. The lower the number of fibers, the higher the slip at peak rate sensitivity. Regardless of the number of fibers, a higher rate sensitivity for inclined fibers was observed.

DOI:

10.14359/935


Document: 

SP155-06

Date: 

August 1, 1995

Author(s):

P. Balaguru and K. Slattum

Publication:

Symposium Papers

Volume:

155

Abstract:

Presents two test methods that can be used for evaluating durability of polymeric fibers subjected to alkaline environment present in concrete and UV light exposure. The test methods were used to evaluate three polymeric fibers: nylon, polypropylene, and polyester. Durability of the fibers in an alkaline environment was ascertained by measuring the flexural toughness of fiber reinforced concrete specimens that had been aged in lime saturated water maintained at 50 C. The UV light exposure test was conducted at a temperature of 65 C with intermittent water spray. The wet spray was used to simulate conditions in the field. Durability of the fibers was determined by measuring the retained tensile strength of the fibers after light exposure and by observing the surface characteristics of fibers under a microscope. The test results indicate that nylon and polypropylene fibers are durable in the alkaline environment present in concrete. The nylon fibers, which were light stabilized, were determined to be stable under UV light exposure. Polypropylene fibers deteriorated under UV light; the deterioration of the polypropylene single filament fibers was more rapid than for the fibrillated fibers. Hence, these fibers should not be used in applications in which the fiber contribution is needed at cracked-exposed sections.

DOI:

10.14359/931


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