International Concrete Abstracts Portal

Researchers and educators who specialize in the material science of concrete will find a lot to interest and challenge them in this Symposium Publication. It contains 35 papers presented at a symposium honoring Surendra P. Shah, Director, Center for Advanced Cement-Based Materials, Northwestern University. Shah has made many contributions to the knowledge of concrete material science, fracture mechanics, high-performance concrete, and fiber-reinforced concrete—all subjects that were covered at the symposium. Topics for the presented papers include: • Advances in fatigue and fracture; • Creep, shrinkage, and early-age cracking; and • Laminated and fiber reinforced cement composites. The last group of papers covers the future of research and education in concrete, with topics ranging from fracture mechanics applications for concrete to sustainable development for concrete. Thus, SP-206 examines the past, present, and future of concrete material science. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP206

This report presents an experimental investigation on the effect of polyvinyl alcohol (PVA) polymer modified alkali resistance (AR) glass fiber reinforced cementitious composites (GFRC). The performance of the alkali resistance glass fibers in blended cementitious matrix was evaluated by a series of tensile and flexural tests. Specimens with different amounts of PVA polymer were tested. Specimens under dry air and moist curing environment were compared. The results indicate that the addition of 2% (weight)PVA polymer shows improvement in strength, toughness, ductility, and deflection. SEM studies indicated that PVA forms a thin film covering on the glass fiber surface, which inhibits the nucleation of calcium hydroxide crystals on the glass bibres surface and to enhance the formation of C-S-H during the hydration. The presence of PVA shows the ability to reduce the embrittlement of the GFRC and changes the failure mode from brittle to ductile. EDAX results shows that the Ca/Si ratio in the fiber interface of the PVA modified specimens is greatly reduced.

Impact resistance of concrete remains to date one of its least understood properties. There are no standardized test methods and no meaningful comparisons can be made between results from various labs. This paper describes some of the issues at hand, and examines the response of plain and fiber reinforced concrete to impact loading through a multi-pronged investigation using instrumented drop weight impact tests. The study involved understanding the influence of machine specific parameters such as hammer mass and drop-height, specimen specific parameters such as specimen geometry and size and, several material related parameters including the type of fiber reinforcement. Amont the fibers investigated, particular attempt was made at comparing steel and polymeric fibers under varying rates of load application. It was found that machine parameters such as the hammer mass and drop height greatly influence the apparent resistance of concrete to impact and its apparent sensitivity to stress rate. Both flexural strength and thoughness factors were seen to exhibit a size effect under impact loading. In the case of fiber reinforced concrete, both plain and fiber reinforced concrete exhibited an increase in strength with strss-rate. In the case of poypropylene fiber, however, due to the viscoelastic nature of the fiber material, a much greater improvement in fracture energy absorption under impact loading was noted. This effect was so pronounced, that under very high concrete exceeded that of steel fiber reinforced concrete. The paper discusses the relevance of these data in designing structures under impact and blast loading, and identifies areas of further research.

Ferrocement and more generally laminated cement based composites are in a state of revival worldwide. Looking back and looking ahead, this paper focuses on three aspects of development that are at the basis of the current revival of ferrocement: 1)the application side, where some new limits and new daring ideas were demonstrated; 2) the professional side, particularly the activities of the International Ferrocement Society and the publication of the first Ferrocement Model Code, and 3) the technical side, where high performance fiber reinforced polymeric (FRP) meshes are introduced either alone or in combination with fibers or micro-fibers leading to hybrid composites with improved performance and reduced cost. Prospects for the near future are also discussed.

One of the most efficient ways to obtain a high performance cementitious composite is by reinforcement with continuous fibers. Production of such composites can be accomplished by the use of textile fabrics, which are impregnated with cement paste or mortar. The present paper provides and overview of the major characteristics in predicting the performance of cement (weft insertion warp knit, short weft warp knit and woven fabrics) as well as found that the geometry of a given fabric could enhance the bonding and enable one to obtain strain hardening behavior with low modulus yarn fabrics. On the other hand, variations of the geometry in a fabric could drastically reduce the efficiencey, resulting in a rduced strengtheniong effect of the yarns in the fabric relative to single yarns not in a fabric form. The improved bonding in low modulus yarn was found to be mainly the result of the special shape of the yarn induced by the fabric. Therefore, in cement composites, the fabrics cannot be viewed simply as a means for holding together continuous yarns so that they can be readily placed in the matrix.