Effect of soil overburden pressure on mechanical properties of carbon FRP strips

Vahid Toufigh,Meysam Pourabbas Bilondi,Farshid Tohidi 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.5

Carbon fiber reinforced polymers (CFRPs) have been recently investigated as an alternative material for Geosynthetics to improve soil properties. One of the factors influencing the fiber orientation and mechanical properties of CFRP is the effect of soil overburden pressure. This study investigates the tensile behavior of cast-in-place CFRP. During the curing time of specimens, a wide range of normal stress is applied on specimens sandwiched between the soils. Two different soil types are used to determine the effect of soil grain size on the mechanical properties of CFRP. Specimens are also prepared with different specifications such as curing time and mixing soil in to the epoxy. In this study, tensile tests are conducted to investigate the effect of such parameters on tensile behavior of CFRP. The experimental results indicate that by increasing the normal stress and soil grain size, the ultimate tensile strength and the corresponding strain of CFRP decrease; however, reduction in elastic modulus is not noticeable. It should be noted that, increasing the curing period of epoxy resin and mixing soil in to the epoxy have no significant effect on the tensile properties of CFRP.

Behavior of FRP bonded to steel under freeze thaw cycles

Vahab Toufigh,Vahid Toufigh,Hamid Saadatmanesh 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.1

Fiber reinforced polymers (FRP) materials are increasingly being used for strengthening and repair of steel structures. An issue that concerns engineers in steel members which are retrofitted with FRP is stress experienced due to temperature changes. The changing temperature affects the interface bond between the FRP and Steel. This research focused on the effects of cyclical thermal loadings on the interface properties of FRP bounded to steel members. Over fifty tests were conducted to investigate the thermal effects on bonding between FRP and steel, which were cycled from temperature of -11°C (12°F) to 60°C (140°F) for 21-36 days. This investigation consisted of two test protocols, 1) the tensile test of epoxy resin, tack coat, FRP and FRP-steel plate, 2) tensile test of each FRP compound and FRP with steel after going through thermal cyclic loading. This investigation reveals an extensive reduction in the composite’s strength.

Finite element analysis of a CFRP reinforced retaining wall

Ouria, Ahad,Toufigh, Vahab,Desai, Chandrakant,Toufigh, Vahid,Saadatmanesh, Hamid Techno-Press 2016 Geomechanics & engineering Vol.10 No.6

Soils are usually weak in tension therefore different materials such as geosynthetics are used to address this inadequacy. Worldwide annual consumption of geosynthetics is close to $1000million\;m^2$, and the value of these materials is probably close to US$1500 million. Since the total cost of the construction is at least four or five times the cost of the geosynthetic itself, the impact of these materials on civil engineering construction is very large indeed. Nevertheless, there are several significant problems associated with geosynthetics, such as creep, low modulus of elasticity, and susceptibility to aggressive environment. Carbon fiber reinforced polymer (CFRP) was introduced over two decades ago in the field of structural engineering that can also be used in geotechnical engineering. CFRP has all the benefits associated with geosynthetics and it boasts higher strength, higher modulus, no significant creep and reliability in aggressive environments. In this paper, the performance of a CFRP reinforced retaining wall is investigated using the finite element method. Since the characterization of behavior of soils and interfaces are vital for reliable prediction from the numerical model, soil and interface properties are obtained from comprehensive laboratory tests. Based on the laboratory results for CFRP, backfill soil, and interface data, the finite element model is used to study the behavior of a CFRP reinforced wall. The finite element model was verified based on the results of filed measurements for a reference wall. Then the reference wall simulated by CFRP reinforcements and the results. The results of this investigations showed that the safety factor of CFRP reinforced wall is more and its deformations is less than those for a retaining wall reinforced with ordinary geosynthetics while their construction costs are in similar range.

Mechanical Performance of Alkali-activated Stabilized Sandy Soil Reinforced with Glass Wool Residue Microfibers

Mohamad Kianynejad,Mohamad Mohsen Toufigh,Vahid Toufigh 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.2

Alkali-activated binders have been introduced as promising alternatives to conventional binders such as lime and ordinary Portland cement (OPC). However, alkali-activated materials exhibit a brittle behavior and crack formation due to tensile stresses is inevitable. To overcome these limitations, incorporation of fibers into the cementitious matrix is among the well-known techniques to improve the flexural behavior and energy absorption of the corresponding composites. The present study aimed to investigate the feasibility of using reinforced alkali-activated metakaolin as an alternative to common stabilizers to improve the engineering characteristics of sandy soil. Calcium carbide residue (CCR) was used as an alkali activator, and glass wool residue (GWR) microfibers were used as reinforcement elements to maximize waste stream utilization. Unconfined compressive strength (UCS), California bearing ratio (CBR), and three-point bending tests were performed to evaluate the mechanical behavior of the alkali-activated products. Moreover, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were employed to determine the microstructure and elemental composition of these products. The results indicate that the compressive strength and ductile behavior of the stabilized soil samples improved significantly. Furthermore, the SEM/EDX analysis of the reinforced alkali-activated samples revealed the interfacial bond between the microfibers and alkali-activated binding gel, enhancing the mechanical performance between the microfibers and cementitious matrix.

Recycling and Utilization Assessment of Municipal Solid Waste Materials to Stabilize Aeolian Sand

Amin Amiri,Mohammad Mohsen Toufigh,Vahid Toufigh 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3

Municipal solid waste management is a global concern due to the growth rate of population and urbanization. This paper aims to determine the possibility of utilization of municipal solid wastes such as fired clay brick powder (FCBP), eggshell powder (ESP), and recycled glass powder (RGP) for the stabilization of aeolian sand. Using such green binders can eliminate the perils associated with inappropriate waste disposal. Different combinations of FCBP, ESP, and RGP were added to the soil, and two activators (KOH and NaOH) were used to study the effects on its engineering and chemical properties. The effects of various parameters were investigated based on unconfined compression strength tests (UCS), pH tests, and scanning electron microscopy (SEM) tests. The results revealed that using all of these three precursors leads to the co-existence of calcium silicate hydrate (C-S-H) gel with the geopolymeric gel (N-A-S-H) and provides the highest UCS value. According to the obtained results, NaOH had a better ability to dissolve the precursors' particles than KOH, resulting in better polymerization. The optimum composites found in the research had a 91-day UCS of 5.32 MPa, which are suitable for the base material in pavement construction.

Durability and Strength of Geopolymer with Recycled Glass Powder Base for Clay Stabilization

Mohammad Ali Mohammadzadeh,Mohammad Mohsen Toufigh,Vahid Toufigh 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.1

Glass powder is one of the solid wastes that is being created at an increasing rate across the globe. Soft clayey soil, on the other hand, generally has to be improved before it can be used in building projects. The durability and strength of clayey soil changed by geopolymer produced with recycled glass powder (RGP) were investigated. The investigation included thawing-freezing (T-F), wet-drying (W-D), and unconfined compressive strength (UCS) tests. The curing duration, weight % of employed RGP, and activator (M) concentration were all investigated in this study. Experiments were also carried out on specimens that had been treated with 10% Portland cement for comparison. When comparing geopolymer-modified to Portland cement-modified specimens, UCS measurements revealed a fourfold improvement in compressive strength. The number of durability cycles for the specimen treated with geopolymer (10 cycles) was greater in the T-F experiment than for the specimen changed with 10% Portland cement (9 cycles), indicating that geopolymer with RGP base outperforms Portland cement in locations with frequent thawing-freezing. The cement specimens with 12 cycles durability were more durable in contrast to geopolymer specimens with 6 cycles durability in the W-D test. Geopolymer specimens were more durable against T-F than cement specimens in general.