Stainless Steel Reinforcement Research Articles

Environmentally Assisted Cracking of Duplex and Lean Duplex Stainless Steel Reinforcements in Alkaline Medium Contaminated with Chlorides

Herein, the corrosion performance of different stainless steel (SS) reinforcing bar grades in alkaline solution is presented, including UNS S32205 duplex stainless steel (DSS), UNS S32304 and UNS S32001 lean DDS (LDSS). The electrochemical dissolution kinetics were studied by potentiodynamic polarization and the Tafel slope method. The environmentally assisted cracking (EAC) mechanisms of the different SS grades in the presence of Cl− were revealed with the slow strain rate test (SSRT). The higher activation of the anodic branch and the loss of toughness were related to the austenite-to-ferrite phase ratio. UNS S32205 DSS presented the slowest anodic dissolution kinetics, mainly due to the higher austenite content compared to the other LDSS; however, it suffered a more severe EAC than the UNS S32304 LDSS. In the case of UNS S32001 LDSS, even while having the lowest Ni content (i.e., large ferrite α-phase ratio), it experienced the least decrease in elongation as well as low anodic dissolution kinetics for Cl− contents up to 8 wt.%, where the Cl− threshold was reached.

Effect of high-strength and stainless steel reinforcement on the flexural behavior of UHPC beams

Ultra-high performance concrete (UHPC) is an advanced cement-based composite which shows remarkable properties including very high compressive strength, increased tensile resistance, impressive toughness and excellent durability. One promising application of UHPC is in heavily-loaded beams and slabs where its use can allow for increased design efficiency and improved durability. Conversely, the high bond capacity of UHPC can lead to early bar fracture failures, especially when using low amounts of ordinary steel reinforcement. This paper examines the influence of reinforcement grade on the flexural ductility of UHPC beams. As part of the study, three beams built with either Grade 400 MPa ordinary steel reinforcement, Grade 690 MPa high-strength reinforcement or Grade 520 MPa stainless steel reinforcement, are tested under flexural loading. The key test parameters include the influence of concrete type (UHPC vs. conventional high-strength concrete) and steel type (high-strength or stainless steel vs. ordinary steel). The results show that the flexural strength and ductility of the UHPC beams is influenced by the steel grade/type. The beam with ordinary steel shows a well-defined yield point but fails by bar rupture. Increased resistance by 47% is observed when using high-strength bars, however bar rupture occurs owing to the low strain-capacity of this steel type. Combining UHPC with higher ductility stainless steel does not increase capacity, but leads to remarkable ductility by 75%. As part of the numerical study the behaviour of the beams is predicted using FE modelling and the effects of tension steel ratio, UHPC tensile strength and high-strength or stainless steel type are investigated.

Low-cycle fatigue behaviour of ribbed 1.4362 duplex stainless steel reinforcement

To investigate the fatigue behaviour of stainless steel (SS) reinforcement, monotonic tensile and cyclic fatigue loading tests on 1.4362 duplex SS bars with diameters of 12 mm, 16 mm, and 20 mm are conducted. To keep the characteristics of reinforcement used in engineering construction, the specimens remain unprocessed. Two loading schemes for cyclic tests are considered in this work: (i) constant strain-amplitude, and (ii) variable strain-amplitude. The Ramberg-Osgood model was used to fit the experimental results. The strain-based and energy-based fatigue life equations are obtained. The strain-based fatigue life equation is compared with the present fatigue life estimation equations. Moreover, the ReinforcingSteel material model in OpenSees is calibrated with the experimental data. The results show that SS bars under cyclic experience hardening followed by softening. The bar diameter does not significantly affect the fatigue life prediction. The modified fatigue life equation suggests that SS bars have better fatigue resistance than conventional steel (CS) bars. The numerical analysis indicates that the calibrated steel material model (i.e. ReinforcingSteel) can produce a good simulation of SS bars under cyclic loading. It can improve the accuracy of numerical models of concrete components reinforced by SS bars.

Effect of high-energy shot peening on the corrosion behavior and chloride threshold concentration of AISI 316L stainless steel rebar in simulated concrete pore solution

The corrosion behavior and chloride threshold concentration of AISI 316L stainless steel reinforcement bar (rebar), subjected to high-energy shot peening (HESPed), are compared with its solution-annealed (SAed) counterpart in simulated concrete pore solution (CPS). X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that HESP significantly reduces the surface grain size to the ultrafine/nanometric range and increases the density of various dislocation structures, including dislocation walls and cells. This augmented presence of grain boundaries and dislocations, acting as high diffusivity paths, contributed to the formation of a thicker surface film with higher Cr content and lower donor/acceptor density in the HESPed sample compared to the SAed. Moreover, corrosion behavior analyses in CPSs with NaCl concentrations ranging from 0.0 to 2.0 M demonstrated that HESPed samples exhibit broader passivation ranges, more positive corrosion potentials, and higher polarization resistance under equivalent chloride concentrations. Additionally, threshold chloride concentrations obtained from the potentiodynamic polarization tests show values between 0.5 and 1.0 M for the SAed and between 1.0 and 1.5 M for the HESPed samples. Based on diffusion equations, a physical model is proposed to elucidate the improved behavior resulting from the HESP treatment.

Friction surfacing of AA6061 on AA5083 aluminum alloy with adding 316 stainless steel powders: Effect of volume fraction of reinforcements

The present work aims to study the effect of the 316 stainless steel reinforcement volume fraction during friction surfacing of AA6061 on the AA5083 alloy by tool's rotation, traverse speed, and feeding rate of 1000 rpm, 150 mm/min, and 100 mm/min to improve the tribological and mechanical behaviors of deposited layers. It was found that a fully bonded interface without any void or defect at the bonding interface was formed between the deposited layer and substrate. It was also found that an increase in the number of holes from one to two in the tool resulted in the betterment of the strength of the coating layer by about 18% from 219 MPa to 259 MPa that can be attributed to the complete bonding between the deposited layer/substrate and better scattering of 316 stainless steel reinforcements.

Description of the constitutive behaviour of stainless steel reinforcement

This paper presents a comprehensive analysis of the constitutive relationship of stainless steel reinforcement and proposes new material models for both austenitic and duplex stainless steel bars. These are an advancement on existing models which have largely been developed for structural stainless steel plate, rather than for reinforcement bars. Current design guidance for material modelling of reinforcing bars does not include representative stress-strain relationships which capture the unique mechanical properties of stainless steel reinforcement. Codes include idealised elastic-plastic material models which are inappropriate and inefficient for the highly nonlinear and ductile material response of stainless steel. The present study aims to address this issue by first conducting a series of tensile tests to ascertain the stress-strain material responses and then employing this data to examine the validity of existing approaches and propose new material models where required. It is shown that new material models are required and those that are developed are able to accurately capture the stress-strain response of stainless steel reinforcement, and provide a better, more accurate, representation than existing methods.

Integrity Assessment of Stress Corrosion Cracking Susceptibility of Duplex UNS S32205 and Austenitic UNS S31653 Stainless Steel Reinforcements

Herein, the stress corrosion cracking (SCC) susceptibility of duplex (UNS S32205) and austenitic (UNS S31653) stainless steel (SS) reinforcements was evaluated using integrity assessment criteria. Mechanical properties were analyzed and compared by different SCC susceptibility factors. The integrity assessment was conducted applying Cosenza, Creazza, and Ortega ductility criteria, following three different standards (ACI 318-19, ASTM A615, and FIB). A conventional carbon steel (UNS G10080) reinforcement was also evaluated for comparative purposes, whose high residual stress value (>280 MPa) promoted a high corrosion growth rate. Duplex UNS S32205 SS grade showed a significant decrease in elongation, leading to failure after ductility assessment at high chloride concentrations. Fractographic analysis of both SS grades, duplex and austenitic, revealed less than 40% brittle areas at 8 wt.% Cl−, while UNS G10080 had over 85% at 4 wt.% Cl−.

Pit-to-crack mechanisms of 316LN stainless steel reinforcement in alkaline solution influenced by strain induced martensite

The pit-to-crack transition of AISI 316LN stainless steel reinforcement exposed to stress corrosion cracking (SCC) in chlorides contaminated alkaline environment, was studied by a combination of slow strain rate testing (SSRT) and electrochemical impedance spectroscopy (EIS). The phase angle shift (Δφ) obtained by EIS at low frequencies was utilized to determine the pit-to-crack transition, differentiating from crack nucleation and propagation as identified by shifts in the frequency range of phase angle (θ) peaks. The pit-to-crack transition was developed once the maximum θ value shifted from the low to high frequencies. EIS analysis was corroborated by assessment of repassivation rates and pit growth, in addition to calculating {Delta G}^{{rm{gamma }}to {rm{alpha }}{rm{mbox{'}}}}. Crack nucleation at lath martensite developed transgranular SCC. Strain-induced martensitic transformation was associated with the brittle failure of AISI 316LN stainless steel, where α’–martensite phase preferentially incubated the pit, and favored crack nucleation, thus promoting pit-to-crack transition.

Axial bearing capacity and ductility of seawater sea sand coral aggregate concrete (SSCC) columns reinforced with hybrid GFRP and corrosion resistant rebars

The shortage of fresh water and river sand resources and steel corrosion are becoming increasingly prominent in engineering construction. Seawater sea sand coral aggregate concrete (SSCC) and corrosion resistant reinforcement are promising materials in replacement of conventional concrete and steel in building structures in island and reef construction. This study investigated the axial compression performance of GFRP (glass fiber reinforced polymer) and corrosion resistant rebars hybrid reinforced seawater sea sand coral aggregate concrete columns. A total of eighteen short columns were tested for axial compression performance, including three reinforcement ratios (1.01%, 1.56%, 2.26%) and 5 reinforcement types (pure GFRP reinforcement or G, pure stainless steel reinforcement or S, pure epoxy coated steel rebar (ECSB) reinforcement or E, GFRP-stainless steel reinforcement or GS and GFRP-ECSB or GE). The failure modes of the column are recorded and analyzed, and the axial bearing capacity and ductility are calculated and analyzed. Results show that the bearing capacity of columns is positively correlated with the reinforcement ratio. Generally, the bearing capacity of S-SSCC column and E-SSCC column are not significant different, but both are larger than that of G-SSCC column. The bearing capacity of hybrid reinforcement GS-SSCC and GE-SSCC column is between S-SSCC column and G-SSCC column. Meanwhile, it indicates that the theoretical calculation results of bearing capacity agree well with the experimental results. The ductility analytical results exhibit that the studied column specimens have the highest ductility when the reinforcement ratio is 1.56%. Among different reinforcement types, the ductility of G-SSCC is the smallest and the GE-SSCC and GS-SSCC column show improved ductility compared with G-SSCC columns.

Stainless steel reinforcement: New material in the latest draft of second‐generation Eurocode 2

AbstractThe durability of reinforced concrete structures exposed to aggressive environments is affected by corrosion of carbon steel reinforcement. For this reason, it is of great practical interest to look for alternative solutions guaranteeing durability through the incorporation of corrosion‐resistant materials, such as stainless steel rebars. This type of steel is specially recommended for structures with a long lifespan, located in aggressive environments, with chlorides or de‐icing salts, and for structures where repair, inspection and rehabilitation is complicated. This solution presents a challenge from the point of view of the materials themselves, the mechanical design and their durability. This article presents the material properties of stainless steel and their influence on concrete structures. Furthermore, it is explained how these properties have been taken into account in the latest draft of the second‐generation Eurocode 2.

Characterization of composite material specimens manufactured in 3D printing for the construction of a shoulder Rehabilitation Prototype

The present work seeks to characterize polymer specimens with aluminum and stainless steel reinforcements, using additive manufacturing for their elaboration and thus increase their tensile strength and implement them for industrial, medical and automotive use. The methodology to follow consists of a documentary investigation of related articles and standards such as ASTM D638, where the tensile properties of plastics are specified, continuing with the manufacture of the test tubes in a 3D printer, this according to the corresponding standard., to later carry out stress tests on the universal machine. The contribution of the work developed lies in the increase in the tensile strength of the composite material experienced, resulting for a first test tube an increase of 52.4% in the maximum tensile strength with an aluminum reinforcement, and an increase of 59.1%, this with a steel reinforcement, in the second specimen submitted to tests with aluminum reinforcement an increase of 20.04% was obtained and with the steel reinforcement it was 84.54%.

Effects of stainless steel reinforcement and fibers on the flexural behaviour of high-strength concrete beams subjected to static and blast loading

This research has investigated the effects of stainless steel (SS) reinforcement on the flexural behaviour of high-strength reinforced concrete beams subjected to static and blast loading. As part of the tests, beams built with high-strength concrete (HSC) and Grade 520 MPa stainless steel bars were tested under blast loads using a shock-tube. Companion beams were also tested under quasi-static conditions. The effects of steel fibers on shear and flexural response were also investigated. In the beams with stirrups, the use of SS bars improved blast behaviour by increasing blast capacity and reducing displacements when compared to identical beams designed with ordinary steel. The use of fibers further improved blast performance by reducing displacements and increasing damage tolerance. In beams without stirrups, the use of fibers was unable to completely substitute for transverse steel and prevent failure, however the shear capacity was increased. As part of the numerical study, the behaviour of the test beams was simulated using 2D finite element (FE) modelling. The FE results show reliable predictions of the beams under static and blast conditions.

Experimental investigation on flexural strength behaviour of reactive powder concrete

The performance of a composite conventional beam and a reactive powder concrete beam with various forms of reinforcement, such as PVC tubes, stainless steel tubes, and normal reinforcement, is compared in this project through an experimental comparison. In this study, experimental research on four specimens of conventional concrete beams and four specimens of reactive powder concrete beams was conducted using the two point loading test method, and mechanical properties such as flexural strength of composite beams were tested for M20 grade of conventional concrete beams and reactive powder concrete beams. The flexural strength of reactive powder concrete beams combined with conventional composite beams. Comparing the composite Reactive powder concrete beam with normal reinforcement to the composite concrete beam with normal reinforcement, the flexural strength is enhanced by 8.78%. Comparing the composite Reactive powder concrete beam with stainless steel reinforcement to the composite concrete beam with stainless steel reinforcement, the flexural strength is increased by 7.58%. When compared to composite concrete with PVC reinforcement, the composite Reactive powder concrete beam has a 5.6% higher flexural strength.

Bond prediction of stainless-steel reinforcement using artificial neural networks

Stainless-steel reinforcement has become increasingly popular in the construction industry in recent years, mainly due to its distinctive characteristics and excellent mechanical properties. There is a real need to develop a fundamental understanding of the bond behaviour of stainless-steel-reinforced concrete (RC). This paper investigates the bond behaviour of stainless-steel-RC using the advancement of artificial neural networks (ANNs) and compares the performance with experimental data available in the literature with reference to existing bond design rules according to international design standards. Accordingly, a new bond design formula is proposed to predict the bond strength capacity of stainless-steel reinforcement. The results show an excellent agreement between the experimental results and the predictions of the ANN model. Both Eurocode 2 and model code 2010 are shown to be extremely conservative compared with ANN predictions. The proposed ANN-based formula provides an excellent basis for engineers to specify bond strength of stainless-steel reinforcement in RC members in an efficient and sustainable manner, with minimal wastage of materials.

Passivity Breakdown and Crack Propagation Mechanisms of Lean Duplex (UNS S32001) Stainless Steel Reinforcement in High Alkaline Solution Under Stress Corrosion Cracking

The passivity breakdown and subsequent stress corrosion cracking (SCC) of Type 2001 lean duplex stainless steel (UNS S32001) reinforcement were investigated in a highly alkaline environment containing chlorides at a low temperature. Electrochemical analysis and mechanical testing were utilized to characterize the passive film development. Fractographic analysis was performed, correlating microstructure and corrosion performance, to reveal preferential crack paths. A chloride threshold below 4 wt% Cl− for a high alkaline environment was elucidated, with pitting susceptibility factor values close to unity, having a threshold critical areal cation vacancy concentration for passivity breakdown close to the 1013 cm−2. Pit initiation leading to passivity breakdown and crack nucleation in 4 wt% Cl− was triggered for stresses above σy, developing a low-frequency peak (0.1 Hz to 0.01 Hz) of the cracking process. Current peak deconvolution demonstrated passivity breakdown was triggered by the intensification in the rate of Type II transient and exposure time, while an increase in transient amplitude was related to the crack propagation. The α phase served as a nucleation site for pits, whose propagation was arrested at the γ phase. Predominant intergranular-SCC morphology through the α/γ interface was developed following anodic dissolution given the more active nature of the α phase (most active path); minor transgranular-SCC propagated through γ phase when high-stress concentration was reached, corresponding to slip-step dissolution.

Big milestones in the study of steel corrosion in concrete

AbstractRebar corrosion in concrete has been neglected for a long time in the scientific and technical literature, as reinforced concrete was considered an “eternal” material. Only during the 60s, and more during the 70s and the 80s, several research groups and many corrosion schools gave important contributions. An important impact was also achieved by Italian researchers thanks to the Universities of Roma, Napoli, Ancona, Ferrara, Bergamo, and Politecnico di Milano, where professor Pietro Pedeferri and his school contributed to the study of stainless steel reinforcement, corrosion inhibitors, service life modeling, cathodic protection and cathodic prevention, the latter proposed by Pedeferri in the early 90s. The paper is dedicated to the memory of Pietro Pedeferri (1938–2008) and Luca Bertolini (1966–2017).

Corrosion of Steel Prestressing Reinforcement - The Influence of the Used Construction Technology of Concrete Suspension Footbridges

Stainless steel reinforcement in the form of prestressing wires and ropes, commonly used to reinforce prestressed concrete structures [1], is also used for suspension strips of footbridge bridges. After the accident of some of them, these structures became the subject of an examination of their current state and analyses of the origin and development of corrosion of the prestressing reinforcement used. The issue of the service life of prestressed structures is related, among other things, to their structural arrangement and the construction procedure used. As with most existing prestressed structures, the anti-corrosion protection of the reinforcement has traditionally been ensured primarily by the alkalinity of the environment, ie by concreting or grouting prestressed elements in the pipeline [2].

REINFORCEMENT BONDING PERFORMANCE IN REFRACTORY CASTABLES UNDER ELEVATED TEMPERATURES

Refractory castables, representing a mixture of a refractory aggregate, calcium aluminate cement, ultra-fine particles, and deflocculants, have been created in the mid of past century ’80s for the metallurgy and petrochemical industries. The designed castable binder shows an excellent ability to preserve the material’s mechanical strength in the 600 °C to 1000 °C temperature range. Besides, the micro-scaled silica/alumina activation process increases the strength and sinterability temperature of the castables regarding traditional alternatives. However, a relatively high price (ten times the ordinary concrete cost) limits the structural application of these advanced materials. Therefore, the studies considered reinforcement aspects of these materials are rare. This investigation focuses on the bond performance of ordinary and stainless steel reinforcement in refractory castables. It is a part of the research project on developing structural concrete fire protection systems, employing refractory castables as a protective shell. This experimental program operates a conventional refractory concrete with a 50 MPa target compressive strength and 25wt% of aluminate cement. In addition, the alternative mixture was modified with a 2.5wt% microsilica, doubling the material strength. The pull-out tests of ribbed and smooth bars demonstrate the importance of the ribs’ mechanical interlock, ensuring reinforcement bonding with the refractory material. Moreover, the ordinary reinforcement demonstrates the bonding ability with refractory castables containing microsilica up to the 1000°C temperature, making the proposed fireprotecting system development possible.

Structural Assessment of AASHTO Type II Prestressed Concrete Girder with GFRP or Stainless-Steel Shear Reinforcement

Structural Assessment of AASHTO Type II Prestressed Concrete Girder with GFRP or Stainless-Steel Shear Reinforcement

Seismic performance of concrete bridge piers reinforced by stainless steel bars: A quasi-static experimental study

This paper presents a set of large-scale quasi-static tests on 6 bridge piers reinforced by stainless steel bars and 4 bridge piers reinforced by conventional carbon steel bars as control specimens to investigate the seismic behaviour of stainless steel reinforced concrete bridge piers. Different reinforcement ratios and axial loads are applied on the columns. The damage progression of the columns during the test is recorded. The experimental result is analysed in terms of force–displacement relation, energy dissipation capacity and ductility to evaluate the seismic performance of bridge piers reinforced by stainless steel bars. It is found that concrete columns with stainless steel reinforcement have similar lateral strength and larger deformation capacities compared to the conventional RC column. However, the application of stainless steel may reduce the energy dissipation capacity of RC columns. Dual-wave buckling of stainless reinforcement and severer concrete cover spalling of columns reinforced by stainless bars are observed in this work.