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International Concrete Abstracts Portal

Showing 1-10 of 15 Abstracts search results

Document: 

SP224-14

Date: 

December 1, 2004

Author(s):

Momahed Boulfiza and Nemkumar Banthia

Publication:

Special Publication

Volume:

224

Abstract:

Cement-based composites, reinforced with randomly distributed short fibers exhibit a nonlinear behavior, called damage, which could be described in terms of microcrack initiation, growth and coalescence leading to the creation of macrocracks. A micromechanics-based continuum damage mechanics, MBCDM, model is proposed for the prediction of the effect of initial microcrack configuration and propagation on the macroscopic Young’s modulus and thermodynamic force associated with the chosen damage variable. Parametric studies for a number of periodic crack distributions in a two-dimensional case have been carried out. Both unreinforced (brittle) and pitch-based carbon fiber reinforced thin sheet cementitious materials have been considered. It is shown that despite the relative simplicity of the damage measure used, the model was able to capture the main effects of cracking patterns on the overall behavior of the composite. Simulation results also reveal that, whereas the evolution of the normalized stiffness is practically the same for all configurations over the entire range of damage variation, the damage thermodynamic force is different for each case. The results predicted by the proposed approach, appear to be consistent with experimental observations regarding the tensile behavior of CFRC composites.

10.14359/13417


Document: 

SP224-13

Date: 

December 1, 2004

Author(s):

B. Mobasher

Publication:

Special Publication

Volume:

224

Abstract:

Techniques for modeling the mechanical response of thin section cement-based composites intended for structural based applications are presented using a micromechanical approach. A layer model is used and the property of each layer is specified based on the fiber and matrix constituents in addition to the orientation and the stacking sequence in each lamina. The overall axial and bending stiffness matrix is obtained using an incremental approach which updates the material parameters. The simulation is conducted by imposing an incremental strain distribution, and calculating the stresses. A stress based failure criterion is used for the three failure modes of initiation of cracking, ultimate strength of matrix, and ultimate strength of lamina. As the cracking saturates the specimen, it results in a gradual degradation of stiffness. A continuum damage model based on a scalar damage function is applied to account for the distributed cracking. The model predicts the response of unidirectional, cross ply and angle ply laminae under tensile loading in longitudinal and transverse directions. The load-deformation responses under tension and flexure are studied. It is shown that by proper selection of modeling approach, parameter measurement, and theoretical modeling, a wide range of analysis tools and design guidelines for structural applications of FRC materials are attainable.

10.14359/13416


Document: 

SP224-12

Date: 

December 1, 2004

Author(s):

Luca Sorelli, Nemkumar Banthia and Giovanni A. Plizzari

Publication:

Special Publication

Volume:

224

Abstract:

Hybrid fiber reinforcement of cement composites is rapidly emerging as an innovative and promising way of improving mechanical performance and durability of cement-based materials. In the present paper, fracture behavior of medium, high and very high strength mortars reinforced with hybrid fibers was experimentally studied by using contoured double cantilever beam specimens. Different combinations of small steel fibers and fibrillated polypropylene micro-fibers are investigated. These composites are very suitable for thin sheet products such as roofing sheets, tiles, curtain walls, cladding panels, permanent forms, etc. Aim of the paper was to study the influence of matrix strength, fiber type and fiber combinations on the fracture toughness of the resulting fiber reinforced mortars. Results indicate that some combinations of fibers and matrix strengths exhibit a higher resistance to crack growth and evidence the contribution of polypropylene fibers to mortar toughness.

10.14359/13415


Document: 

SP224-11

Date: 

December 1, 2004

Author(s):

Katherine G. Kuder and Professor Surendra P. Shah

Publication:

Special Publication

Volume:

224

Abstract:

Fiber-reinforced cement board (FRCB) is increasing in consumer popularity because it is more durable than conventional wood products. However, concerns exist about the freeze-thaw durability of the material due to its laminated structure and high porosity. To overcome these weaknesses, some manufacturers have begun to press the material after it is formed. The objective of this work is to evaluate the effects of this new processing on the durability of the FRCB. Three commercially-available FRCB products – two that had been pressed and one that had not – were subjected to accelerated freeze-thaw cycling according to a modified version of ASTM Standard C1185. The flexural strength, interlaminar bond (ILB) strength and porosity were measured. The results indicate that pressure might improve the ILB and flexural strength of the FRCB after freeze-thaw testing. However, porosity is not affected by pressure after freeze-thaw.

10.14359/13414


Document: 

SP224-10

Date: 

December 1, 2004

Author(s):

K C G Ong, C P Teo, C H Shum, L H J Wong, S T Tan and C T Tam

Publication:

Special Publication

Volume:

224

Abstract:

The use of microwave technology to speed up the production of precast ferrocement secondary roofing slabs is explored in this paper. In particular, the use of discrete on-off microwave curing regimes and the effects of such regimes on the strength and durability of the ferrocement slabs are investigated. By a regime of on-off microwave application to maintain the temperature of the slab within a specified range during microwave curing, overheating of the slabs can be avoided. High early age strengths were attained in slabs cured using such regimes, with no strength loss at 28 days. In addition, the durability of such slabs need not be compromised. The use of an appropriate reduced power level during the later stage of the curing process was found to result in a marginal improvement in the near surface quality without any reduction in early age strength.

10.14359/13413


Document: 

SP224-09

Date: 

December 1, 2004

Author(s):

Daniela Hesselbarth and Josef Kaufmann

Publication:

Special Publication

Volume:

224

Abstract:

Concrete tubes are usually produced by a centrifugation method using steel bar reinforcements. The reinforcement of concrete with steel bars is expensive, susceptible to corrosion and leads to rather thick and heavy structural elements. The application of short fiber reinforced cement (FRC) or mortar is a suitable alternative. The paper presents the development and evaluation of a suitable FRC for this particular application. First, the cement matrix was optimized for use in a conventional casting forming process. A mixture of ultra-fine cement and ordinary Portland cement improves the rheological properties of the fresh mixture and results in a very dense cement matrix with excellent mechanical properties. This optimized cement matrix was then reinforced with different kinds of carbon and polymeric fibers such as PVA and PP. Hereby, the carbon fibers primarily increase the flexural and tensile strength of the material, whereas the polymer fibers tend to improve the ductility of the cement matrix. Furthermore, the influence of water-reducing agents, of different constituents (microsilica, filler, sand), and the mixing process on the mechanical properties were studied. The mechanical properties were found to depend also on the curing conditions of the hydrated samples. The microstructure and the fiber-matrix interface were investigated by ESEM (Environmental Scanning electron microscope). In a further test series, the mixtures were optimized with regard to the flow properties needed for the centrifugation process. The mechanical properties and the microstructure were investigated. As a result, this work shows the possibility to apply the FRC for industrial production of centrifuged tubes.

10.14359/13412


Document: 

SP224-08

Date: 

December 1, 2004

Author(s):

Yixin Shao, Emmanuel Blain-Cosgrove and Brad Robinson

Publication:

Special Publication

Volume:

224

Abstract:

The balance between sustainability and affordability is hard to achieve when considering choices of building envelopes. A simple and easy-to-construct stressed skin structural sandwich system that is both affordable and sustainable is evaluated in this paper. The system is composed of an expanded polystyrene (EPS) panel core, wrapped in polymer mesh and covered with a thin cement skin on both sides. This system design leads to a highly energy efficient building envelope system. A full-scale sandwich wall was constructed and tested to examine the possibility of its use as a load bearing wall in one story residential house without traditional timber frames. Based on the requirements imposed by the National Building Code (NBC), the test results from this experimental program were found to be promising. The wall carried a gravity load, a wind load and seismic in-plane shear load at least 4 times as high as the NBC design load with negligible lateral displacement and no visible cracking. At buckling failure, the load-carrying capacity of the wall exceeded 10 times the design load. The EPS-core stressed-cement skin sandwich building system thus provides a good example of the use of thin cementitious products in load bearing exterior wall structural applications.

10.14359/13411


Document: 

SP224-07

Date: 

December 1, 2004

Author(s):

Edouard Parant and Pierre Rossi

Publication:

Special Publication

Volume:

224

Abstract:

This paper first proposes a reviewing and a critical analysis of the different UHPFRC which exist, and secondly presents a new cement composite, the CEMTECmultiscale®, patented by the Laboratoire Central des Ponts et Chaussées (Paris, France). This cement composite has been tested under static bending and asymmetric fatigue bending From this experimental study, the following comments can be made : - The characteristic strength and ultimate strain in compression are respectively equal to 205 MPa, and 4 10-3. - the Young modulus is equal to 55 GPa and the Poisson coefficient is equal to 0.21. - The average modulus of rupture (MOR) is equal to 61.5 MPa; - The average strain related to the average MOR is equal to 9.2 10-3. - A critical initial static strain threshold exists. Before this threshold a specimen in CEMTECmultiscale® does not fail during a bending fatigue loading and beyond this threshold the failure fatigue cycles number linearly depends of the initial static strain. The strain threshold determined in this study is between 1.24 x 10-3 and 1.44 x 10-3. - Below a loading ratio R = 0.65, failure during bending fatigue test never appears with a specimen of CEMTECmultiscale ®.

10.14359/13410


Document: 

SP224-06

Date: 

December 1, 2004

Author(s):

Don Zakariasen and Vic Perry

Publication:

Special Publication

Volume:

224

Abstract:

Ductal® is a new material technology offering a unique combination of superior characteristics including ductility, strength, and durability, while providing highly moldable products with a quality surface. The technology provides compressive strengths up to 200 MPa (30,000 psi), and flexural strengths up to 50 MPa (7,200 psi). The material’s unique combination of superior properties enables the designer to create thinner sections, longer spans, and higher structures that are lighter, more graceful and innovative in geometry and form while providing superior durability and impermeability against corrosion, abrasion, and impact. This material provides the precast industry with opportunities to improve many existing products and manufacture new products that will compete with other materials such as stainless steel, cast iron, ceramics, and others. This paper presents properties of the material, design assumptions for project solutions and the manufacture, installation and assembly procedures for specific projects including roof panels, 5 sided-boxes and anchor plates. Many economies gained from this new technology are a result of engineering new solutions for old problems. By utilizing the unique combination of superior properties, designs can eliminate passive reinforcing steel and experience reduced global construction costs, form works, labour and maintenance. Additionally, this relates to benefits such as improved construction safety, speed of construction, extended usage life and others.

10.14359/13409


Document: 

SP224-05

Date: 

December 1, 2004

Author(s):

J. Hegger, H. Schneider, A. Sherif, M. Molter and S. Voss

Publication:

Special Publication

Volume:

224

Abstract:

The composite material textile reinforced concrete (TRC) offers a number of advantages, in particular for the manufacturing of façades. The textile reinforcement and the possible thin concrete cover, enable the construction of thin-walled structural components. Filigree cladding panels made of textile reinforced concrete open up new ways for an entirely new application of the construction material concrete and give architects and engineers more freedom in the design. In this paper some basic information about the load bearing behavior of textile reinforced concrete is given and the use of textile reinforced concrete in a pilot project for the exterior claddings of the extension of the laboratory hall at the RWTH Aachen University, Germany, is described.

10.14359/13408


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