Post-Consumer Carpet Fibers in Concrete: Fiber Behavior in Alkaline Environments and Concrete Durability.

The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications.

Low-Velocity Impact Experiments and Modeling of TRC Skin-Aerated Concrete Core Sandwich Composites.

Mechanical response of textile-reinforced aerated concrete sandwich panels was investigated using instrumented three-point bending tests under quasi-static and low-velocity impact loads. Two types of core material were compared in the sandwich composite consisting of plain autoclaved aerated concrete (AAC) and fiber-reinforced aerated concrete (FRAC), and the stress skins were alkali-resistant glass (ARG) and textile reinforced concrete (TRC). The textile-reinforced layer promoted distributed cracking mechanisms and resulted in significant improvement in the flexural strength and ductility. Digital Image Correlation (DIC) was used to study the distributed cracking mechanism and obtain impact force-crack width response at different drop heights. A constitutive material model was also developed based on a multi-linear tension/compression strain hardening model for the stress-skin and an elastic, perfectly plastic compression model for the core. A detailed parametric study was used to address the effect of model parameters on the flexural response. The model was further applied to simulate the experimental flexural data from the static and impact tests on the plain aerated concrete and sandwich composite beams.

Mechanical Characterization of the Tensile Properties of Glass Fiber and Its Reinforced Polymer (GFRP) Composite under Varying Strain Rates and Temperatures.

Unidirectional glass fiber reinforced polymer (GFRP) is tested at four initial strain rates (25, 50, 100 and 200 s-1) and six temperatures (-25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate any possible effects on their mechanical properties and failure patterns. Meanwhile, for the sake of illuminating strain rate and temperature effect mechanisms, glass yarn samples were complementally tested at four different strain rates (40, 80, 120 and 160 s-1) and varying temperatures (25, 50, 75 and 100 °C) utilizing an Instron drop-weight impact system. In addition, quasi-static properties of GFRP and glass yarn are supplemented as references. The stress⁻strain responses at varying strain rates and elevated temperatures are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications.

Refractive change induced by the LASIK flap in a biomechanical finite element model.

PURPOSE: To study the effect of varying four parameters on the refractive change induced by the LASIK flap. METHODS: Using a variety of patient-specific data such as topography, pachymetry, and axial length, a finite element model is built. The model is used in a non-linear finite element analysis to determine the response and change in optical power of the cornea as a function of a material property of the cornea (corneal elasticity), flap diameter and thickness, and intraocular pressure. RESULTS: The central flattening or hyperopic shift occurred atop the flap in all four of the simulated eyes tested with the creation of the LASIK flap. Of the four parameters tested, modulus of elasticity (Young's modulus) had the most profound effect on the results of hyperopic shift, varying from <0.5 diopters (D) in the least elastic (stiffest) cornea to >2.0 D of hyperopic shift in the most elastic cornea. The depth of the lenticular cut was the second-most significant parameter tested varying from 0.24 D at 100 microns to 1.25 D at 275 microns of depth. Varying intraocular pressure demonstrated less difference, and varying corneal flap diameter demonstrated the least difference in induced refractive change on the model. The hyperopic shift was noted to be greater in hyperopic than in myopic eyes (simulated) tested. CONCLUSIONS: Three-dimensional finite element analysis modeling of actual patient data could lead to a better understanding of the biomechanical response of corneal tissue to the lenticular flap creation and potentially for ablation patterns produced by the excimer laser. Understanding these biomechanical responses may lead to greater predictability and improvement of visual outcomes.