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.

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.

Thin, fiber reinforced cementitious products offer a useful balance of properties such as strength, toughness, environmental durability, moisture resistance, dimensional stability, fire resistance, aesthetics and ease of handling and installation. For more than 30 years, AR glass fibers have been at the forefront in the development of new applications of such products throughout the World. Glass Fiber Reinforced Concrete [GFRC] is a thin, cement composite based on AR glass fibers with an excellent strength to weight ratio. Extensive early laboratory work produced a test method for determining long term strength. The validity of this work has been proven by the large number of buildings clad with GFRC, as well as a vast range of other GFRC products, used over a this 30 year period. This paper explains the fundamental principles behind GFRC and gives examples of some of its uses. These applications range from high quality, architectural wall panels and decorative elements through to modular buildings down to low cost channel sections and utility components. New developments and techniques will also be discussed.

Thin sheet concrete products are receiving increased attention because of the large number of potential applications. By using crushed glass as aggregate, a multitude of different esthetic effects can be produced, which again open up numerous architectural and decorative uses. Such thin sheets are most effectively reinforced with fiber mesh, whether made of polypropylene, AR-glass, or other types of materials. At Columbia University, a project is currently under way to explore the possibilities of prestressing thin sheet glass concrete products. There are numerous performance criteria that need to be satisfied by the fiber mesh material in order to qualify for the tasks on hand. Most promising to date are high-performance materials such as aramid and carbon fiber mesh. This paper discusses the elimination process by which the most appropriate type of fiber mesh was selected. Various technical problems of prestressing and anchoring the fiber mesh are pointed out, as well as other issues that need to be resolved, before such products can be mass-produced commercially.

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.