Performance Of PRF Under Acid Attack - Research Paper Example

Author’s Name Instructor’s Name Course Date Introduction History of FRP Historically, many techniques have been developed to enhance the durability of materials in civil engineering (International Conference On Fatigue Of Composites et al. 2012). One of such materials that promote durability is the Fiber Reinforcement Polymer (FRP). The corrosion of reinforcements can adequately be prevented by using the alternative material such as Fiber Reinforcement Polymer instead of the steel replaced process. The composites of Fiber Reinforcement Polymer are primarily developed for the defense and aeroscope industries. These types of composites involve a group of materials that have great potential of being used in civil infrastructures (Lee 2013). Over the years, Fiber Reinforcement Polymer composites have gained popularity among civil engineers. Several factors have contributed to the rapid acceptance in the industry, especially their durability properties. Since early 1980s, Fiber Reinforcement Polymers have proved to be useful in several applications. However, in most instances the materials have been used in form of strips or sheets in order to strengthen existing structures such as bridges. To some extent, the material has been used to provide reinforcement bars, thus substituting steel as the concrete reinforcement (International Symposium On FRP Reinforcement For Concrete Structures, & Shield 2011). Further, many constructions have been built, where FRP composites replace traditional materials in structural elements such as bridge decks, girdles and stay cables. However, it must be noted that among such constructions, there are a number of hybrid structures where only one part of the superstructure uses the FRP composites. In some structures, all materials exclusively use FRP composites. Additionally, it must be appreciated that the use of FRP in civil engineering has tremendously changed the concrete durability thus enhancing the sustainability and the lifespan of structures. Performance under acid attack The result will show that there will be a reduction in the interlaminar shear strength to about 18% after the specimen has been treated with HCL of 5% concentration. The reduction will increase as the concentration increase since at 40% the strength will have reduced with about 30%. It should be remembered that the speed of the crosshead remain the same at 2 mm/min and 500 mm/min. The decrease in the ILSS is due to the degradation that is caused by the stress corrosion cracking (SCC) within the laminates as well the micro cracks in the matrix. Further, the result will show that the amount of water absorbed at 0% concentration of HCL solution is at maximum. However, the water absorbed will decrease as the concentration of the acid solution increases. The reaction is because of the bulky nature of the HCL molecules that slows the ingress rate of water thus reducing the diffusion rate. Evidently, the amount of water or liquid that can be absorbed in the polymer is dependent upon the size of the diffusion molecules in relation to the free volume that is available in the polymer. The experiment shows that the ILSS values are sensitive to the loading rate. The lower figures observed at high speeds could be due to the insufficient time for the proper transfer of load as well as the presence of stress-induced cracks that are growing without blunting. At lower speeds, there are less stress-induced cracks since there is enough time for the redistribution of load. In addition, stress cession cracking mostly depends on the amount of glass fibers that is exposed, which also dependent on the matrix of the polymer. The presence of hydrogen ions, externally applied stress, and the residual thermal stresses contribute to the occurrence of the stress corrosion cracking. In this concentration, the residual thermal stresses are developed due to the fabrication process that is highly controlled by the rate of cooling. Consequently, a temperature gradient is developed within the fiber radius, with highest and lowest temperatures recovered at the center and at the surface respectively. The morphology of the fiber is affected by the availability of the stresses. Three stages are involved in the SCC process after the stress is externally applied. The first stage is when the singe fiber transverses crack initiation while the second stage is where the crack speared to the neighboring fibers through the matrix. The final stage causes failure and poor performance of the material after stable propagation of the crack is achieved though out the specimen. Model development Atomistic Modeling at the Interface of FRP Atomistic modeling is one of the phenomenological predictive models based on the experimental analysis and observation (Jain & Lee 2012). The main objective of the atomistic modeling in the project is to understand the mechanism of deboning and more so studying the interaction of various atoms as well as molecules around the interface. Additionally, it is critical to understand that after moisture is diffused in any adhesive material it is in one of the two forms including the free water or the bound water. The free volume of the epoxy resin is occupies by the free water while without causing any swelling , while the bound water reacts chemically with the polymer chain using hydrogen bonding ( Mertz 2008) . The chemical reaction disrupts the chain and enhances its mobility, thus leading to the occurrence of swelling. This means that the effectiveness of the cross-link density is highly reduced due to the adsorption process. Consequently, the process can interfere with the properties of the material through plasticization or irreversibly through hydrolysis and cracking (Lee 2013). Further, it can lead to the swelling stress as well as strength deterioration in adhesives at the adhered interfaces. The following figure shows the destruction process of the secondary bonds between substrate and adhesive in an environment with moisture. FRP Attack by Water Molecules at the Interface of Adhesive and Substrate Courtesy: International Institute for FRP in Construction (IIFC) Approaches of research Research studies to understand the failures and durability of basic mechanisms of bonded systems such as concrete or FRP have been using various types of approaches. Importantly, it is critical to note that some of the main advantages of fiber-reinforced polymers include their height strength, lightweight, and non-corrosive characteristics, which have made FRP to be the preferred materials in engineering (Hollaway & Teng 2008). The research presented in the paper is an effort to comprehend the interlaminar fracture behavior of epoxy/glass composite laminates after they are treated with acid of varying concentrations. The study uses 3-point flexural test approach in qualitatively assessing the interlaminar fracture behavior for 50-weight percentage of E-glass fibers, which have been reinforced with epoxy composites after being treated with acid. The specimens will be tested at 2 mm/min and 500 mm/min with crosshead speed in order to assess the sensitivity of mechanical response when loading at these conditions. Further, the mechanical functionality of the specimens that are laminated and treated in varying concentrations of acidic solution will be compared through SEM photographs. Therefore, the Phenomenological behavior of these materials will be attributed to the degradation of fiber and matrix due to the water diffusion, acid attack, as well as the generation of residual stresses in the materials of the composite laminates. Fabrication of Composites The glass epoxy or fiber composite laminates will be fabricated using wet lay-up procedure. Therefore, the glass fiber consisting of a woven cloth of appropriate dimension will be laid over a mold. Additionally, the catalyzed epoxy resin will be poured to be absorbed over the reinforcement material. The next step will involve rolling the wet composite in order to distribute the resin and remove the pockets of air available. However, In order to ensure that the desired thickness is achieved, the sequence will be repeated. After curing the layered structure, it will be allowed to harden. The layered structure will be cured at room temperature for two days (48hours). After the process of curing, the laminate will then be cut using the diamond cutter into appropriate sizes based on the 3-point bend (Short-Beam Shear) test. It is after this stage that the stability test will be carried out for the laminates. The process will involve weighing the laminates and heating them at 50oc in an oven. , in order to ensure that the team gets the stable weight, the weight will have to be intermittently checked. It should be noted that with continued heating, there should be no change of the weight of the composite. Acid Treatment After conducting the stability test, the samples will be allowed to turn back to the ambient temperatures. They will then be left in the desiccators so that there will be no any absorption of moisture. Further, the specimens will be exposed to three types of hydrochloric acid solutions at 0%, 5%, and 40% concentrations for one week (seven days). After being exposed to the acidic concentrations, all the specimens will be taken out to be tested in 3-point bend test machine. 3-Point Bend Test As indicated above, the 3-point bend test is meant to determine the interlaminar shear strength (Hanna & Arockiasamy 2012). At this stage, all mechanical flexural tests will be performed at crosshead speeds of 2 and 500 mm/min. The following formula will be used in measuring the interlaminar shear strength (ILSS). ILSS = 0.75p/bt Where, ‘p’ is the breaking load, ‘b’ is the width, and ‘t’ stands for the thickness of specimen being used. In order to perform the SBS tests, an Instron1195 tensile testing machine will be used based on the ASTM D 2344-84 standards. In this process, different samples will be tested at every point of the experiment. The average value will then be determined as the final figure. The conclusion on the mechanical performance of the specimens that are laminated will be compared with SEM photographs. Durability of concrete Concrete durability is the ability of concrete to resist chemical attack, weathering action, and abrasion while at the same time maintaining the desired engineering properties (International Symposium on FRP Reinforcement for Concrete Structures, & Shield 2011). Different types of concrete needs varying degrees of durability based on the exposure to the external environment as well as the desired properties. The ingredients in the concrete, their interaction, curing and placing, as well as the service environment determine the durability of the concrete and its life span. Concrete is resistant to many chemicals and most of the natural environments. However, it can be deteriorated once it is exposed to substances that can attack it. Acidic attack causes the concrete to dissolve the calcareous aggregates and cement taste. Durability of FRP Durability of FRP depends on several factors (Portland Cement Association & Daniel 2006). However, the reaction to external environment including especially water plays a critical role in determining how long FRP will serve the intended purpose in a structure. Additionally the strength of the interface between the FRP and the concrete also plays a pivotal role in determining how the longevity of FRP. Further, it is important to note that concrete carries elements of reinforcement (aggregate) that have low aspect ratio thus it is always termed as a particulate reinforcement composite (Bai 2013). It is for this reason that the reinforcement aspect is given fiber like characterization to ensure durability. Fiber reinforcement polymers have two binding faces that influence its durability. The two phases include fiber phase that constitute stiff fibers and the binding phase that contains the polymers or resin materials. In civil engineering, two types of polymers are used with varying durability based on the environment as well as their characteristics. The two polymers include thermoplastic and thermosetting polymers. Examples of thermoplastic polymers include polypropylene, polybutylene, thermoplastic polyester, polymethypentene, ethylene-vinyl acetate, and polyethylene among others. Thermoplastic polymers have high impact strength and are highly ductile materials. Therefore, the durability of thermoplastic polymers is influenced by their ductility material strength. However, when thermoplastic polymers are exposed to relatively low temperatures, they tend to soften, develop high creep characteristics as well as stress relaxation, which may affect their durability. Therefore, thermoplastic polymers are not recommended to be used in primary engineering applications where long term carrying cap-ability is highly required. On the other hand, thermosetting polymers are low molecular weight liquids with viscosities that are very high. The durability of thermosetting polymers is also affected by the environment in which they are exposed. The solidification of thermosetting polymers takes place through free radicals that leads to cross-linking as well as curing that offers the materials with good resistance capability. Additionally, free radical also paly an instrumental role in ensuring that dimensional and thermal stabilities are enhanced as well as providing thermosetting polymers with stress realization and low creep characteristics (Bai 2013). Based on aforementioned characteristics, it is important note that for durability purposes, thermosetting are suitable polymers in civil engineering. Some of the common thermosetting polymers include vinyl ester, unsaturated polyester, and epoxy. In addition, epoxies are advanced polymeric resins that are highly preferred in engineering compared to vinyl ester and polyester. Further, compared to the rest, epoxies are expensive and mostly used in defense and aerospace applications. The durability level of epoxies is high due to their superior resistance to solvents and chemicals. This is contributed epoxies’ cross-linked internal structures characteristics (Mertz 2008). At the same time, the durability of epoxies is affected by their low cure shrinkage, while they also do not emit any volatile monomer during processing. Further, it is also crucial to point out that there are three commonly used fibers in the production of FRPs in concrete applications (Lee 2013). The three fibers include carbon/graphite, glass, and aramid, which have strong ceramic characteristics depicted by their brittle and stiff behavior that determine their durability levels. Durability of interface The strength of the interface between the concrete and the PRF is instrumental in determining the strength and durability of a structure (Lee 2013). However, it should be noted that the durability of the interface is dependent upon the materials used in both the concrete and the type of PRF used. At the same time, external environment also determines the life cycle of the structure in question. The interface between the concrete and the PRF composites plays a critical role the process of external bonding using fiber reinforced polymer (FRP) composites. However, the use of various approaches such as the synergistic effects, the durability of the interfaces can be determined. The deteriorating effects of environmental factors such as heat educe the durability of the interface thus affecting the strength of a structure (Lee 2013). On the other hand, chemical attack such as acid on the, matrix and the concrete also interferes with the interface’s durability. Correlation between different factors and bonds The properties of mechanical elements in the fiber-polymer bonds are instrumental in ensuring the strength and durability of a structure (Mertz 2008). The properties are mostly determined by the mechanical compatibility and the adhesion between the matrix and fibers. It is also dependent on the angle that exists between the fibbers and the direction of loading. However, in order to ensure that a good mechanical interaction between the matrix and fibers is maintained, the parameters of the two materials should be adapted to the other. Primarily, the approximately linear-elastic behavior of deformation observed in the composite is determined by the reinforcing fibers (Bai 2013). It is critical to note that in order to ensure that the development of microcracks do not appear in the matrix, specially prior to reaching the elongation limit of the fibber, the failure strain of the matrix need to be more than that of the fibers. Further, if the material is compressed, however, the minimum stiffness in the matrix is needed to avoid bucking of the fibers (Bai 2013). In addition, strength and stiffness of the fiber-matrix bond also depends mostly on the angle between the direction of loading and the fibers. In this connection, the highest value is determined based on the constant loading direction as well as the corresponding arrangement of the fibers in the same direction. In this case, if the loading direction might change, the multilayered structures, both non-woven and woven multiaxual fabrics, that exhibit quasiisotropic behavior is utilized (Hollaway & Leeming 2009). Therefore, compared to the unidirectional laminates, the strength and stiffness of the multi-layered structures are reduced considerably. Conclusion Based on the research, it is concluded that the Fiber-Reinforcement Polymers are prone to the acid damage. The result has shown that the ILSS values continue to decrease as the acid concentration increases, which is because of the degradation of the fibers through leaching as well as the development of microcracks within the matrix. The laminates are observed to be sensitive to the loading rate while the moisture ingress decreases with the increase in acid concentration due to the bulky of HCL that affects water diffusion. References Bai, J. (2013). Advanced Fibre-Reinforced Polymer (FRP) Composites for Structural Applications. Burlington, Elsevier Science. Hanna, A. M., & Arockiasamy, M. (2012). Fiber reinforced polymer composites for concrete bridge deck reinforcement. [Washington, D.C.], National Cooperative Highway Research Program. Hollaway, L., & Teng, J. G. (2008). Strengthening and rehabilitation of civil infrastructures using fibre-reinforced polymer (FRP) composites. Cambridge, England, Woodhead Pub. Hollaway, L., & Leeming, M. (2009). Strengthening of reinforced concrete structures Using externally-bonded FRP composites in structural and civil engineering. Cambridge, Woodhead Pub. International Conference On Fatigue Of Composites, Yao, W., Renard, J., & Himmel, N. A. (2012). Fatigue behaviour of fiber reinforced polymers: experiments and simulations : Fifth International Conference on Fatigue of Composites (ICFC5). Lancaster, Pa, DEStech Pub. International Symposium On Frp Reinforcement For Concrete Structures, & Shield, C. K. (2011). 7th international symposium, fiber reinforced polymer (FRP) reinforcement for concrete structures. Farmington Hills, Mich, American Concrete Institute. Jain, R., & Lee, L. S. (2012). Fiber reinforced polymer (FRP) composites for infrastructure applications focusing on innovation, technology implementation and sustainability. , Springer. Lee, S. M. (2013). Handbook of Composite Reinforcements. Hoboken, John Wiley & Sons. Mertz, D. R. (2008). Application of fiber reinforced polymer composites to the highway infrastructure. Washington, D.C., Transportation Research Board. Portland Cement Association, & Daniel, J. I. (2006). Fiber reinforced concrete. Skokie, Ill, Portland Cement Association. Read More