Moneeb Genedy

Controlling off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer using alumina nanoparticles

This investigation experimentally examines the effect of incorporating alumina nanoparticles on the off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer composites. Four epoxy–alumina nanoparticle nanocomposites incorporating 0.0, 1.0, 2.0, and 3.0 wt% alumina nanoparticles of the total weight of epoxy are examined. Off-axis tension stiffness and stress-relaxation tests were performed on carbon fiber-reinforced polymer coupons fabricated with alumina nanoparticles–epoxy nanocomposites. Dynamic mechanical analysis testing of neat epoxy and epoxy nanocomposites incorporating alumina nanoparticles was used to identify the stiffness and relaxation behavior of the alumina nanoparticles–epoxy nanocomposite matrix. Fourier transform infrared spectroscopy was used to observe chemical changes when alumina nanoparticles are mixed with epoxy. It is shown that using alumina nanoparticles at a concentration close to 2.0 wt%, can reduce the off-axis stiffness by ∼30% and increase the off-axis stress-relaxation of carbon fiber-reinforced polymer by ∼10%.

Development Length of Steel Reinforcement in Polymer Concrete for Bridge Deck Closure

Accelerated bridge construction techniques are getting attention due to their ability to reduce construction time and thus lower cost of bridges. Precast concrete girders and bridge deck panels are typically used today in the construction of bridges. This construction method creates the need for flowable yet high strength and good bond for filling the joints between the precast elements. To achieve the required integrity and enable high bond strength, polymethyl methacrylate (PMMA) polymer concrete (PC) has been suggested for bridge deck closure. This paper examines the development length of steel reinforcement when embedded in PMMA-PC. The results of the experimental investigation show that PMMA-PC has a development length shorter than that used with ultra-high performance concrete (UHPC).

Improving shear strength of bolted joints in pultruded glass fiber reinforced polymer composites using carbon nanotubes

The structural design of the bolted fiber reinforced polymer elements is typically governed by the capacity of the joint rather than the fiber reinforced polymer member, while the joint capacity is typically governed by the shear strength of the fiber reinforced polymer. Here, the possibility of improving the shear strength of bolted joints is investigated in the unidirectional glass fiber reinforced polymer plates by incorporating the multiwalled carbon nanotubes during glass fiber reinforced polymer fabrication. Glass fiber reinforced polymer double-shear bolted lap joints were fabricated using up to 1.0 wt% multiwalled carbon nanotubes–-epoxy nanocomposites. Finite element modeling using multicontinuum theory and element deletion techniques was performed to explain the joint behavior. The experimental investigations show that incorporating multiwalled carbon nanotubes improved the shear strength, ductility, and energy absorption significantly. Microstructural analysis proves that a chemical reaction between multiwalled carbon nanotubes and epoxy improves the shear strength of the matrix.

Improving Fracture Toughness of Polymer Concrete Using MWCNTs

Polymer concrete (PC) are used in bridge deck overlays due to its superior durability specifically freeze-thaw and corrosion resistance. The excellent durability of PC is related to its impermeable microstructure and good bond to concrete or steel substrates. However, there is an increasing need to improve PC resistance to crack propagation (fracture toughness) to enhance its fatigue resistance and extend its service life. Researchers showed that objective becomes possible using dispersed chopped synthetic fibers (6-12 mm long). However, this approach was criticized for its dramatic impact on PC flowability. Here we suggest improving fracture toughness of PC using Multi-Walled Carbon Nanotubes (MWCNTs). PC mixes were produced using epoxy and standard aggregate with varying contents of MWCNTs being: 0 (Neat), 0.5, 1.0, 1.5 and 2.0 wt.% by weight of epoxy. Flowability of PC incorporating MWCNTs was tested. The tensile strength of PC incorporating MWCNTs was evaluated using direct tension test. A closed loop notched beam three-point bending test fracture test was used to evaluate fracture toughness of PC. The crack mouth opening displacement (CMOD) clip gage was used to provide feedback. The inverse analysis approach was used to extract the bilinear stress-crack opening displacement relation and calculate the fracture toughness (GF) of PC with and without MWCNTs. It is shown that MWCNTs significantly improves the fracture toughness and toughness of PC without significantly impacting its flowability. Microstructural analysis using Fourier Transform Infrared Analysis (FTIR) of polymer used to produce PC explains the effect of incorporating MWCNTs. DOI 10.21012/FC9.184