International Concrete Abstracts Portal

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.

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.

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.

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.

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.