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Effect of corroded reinforcement in RC structures: from cracking to bond performance
No full textReinforced concrete (rc) is the most used building material. The natural ageing of the rc structures moves the attention to the durability aspect. The latter depends on the environmental conditions, which are getting always more severe, but also it depends on the poor detailing and material characteristics during casting. Hence, the deterioration of rc structures becomes a matter of primary importance. The most common cause of deterioration of rc structures is the reinforcement corrosion: it affects the steel reinforcement reducing the sectional area and modifying the mechanical properties. Moreover, corrosion provokes the concrete section loss because of the cracking induced by the expansive phenomenon; hence the resisting section is reduced and the deteriorated reinforcement is further exposed to the aggressive environment. Finally, corrosion deeply changes the characteristics of the interface layer between steel and concrete because of the oxides formation; therefore, bond between the materiala changes. In the present dissertation, steel reinforcement corrosion and its mechanical implications were studied; in particular, the investigation was developed both experimentally and numerically. As far as the former is concerned, pull-out test of corroded RILEM type specimens was performed. The experimental variables were three: the corrosion level; the main reinforcement dimension and the presence of the transversal reinforcement. The maximum corrosion level reached was 20% in terms of mass loss, this values is far greater than those available in the literature which rarely overtake the 10% of mass loss; further corrosion nominal levels were 2, 5 and 10%. The main reinforcement, whose diameter was of 12 and 16 mm, were artificially corroded by means of the application of a low density current in order to reach the nominal corrosion level with a reliable accelerated mechanism. Confined specimens were provided with closed stirrups which were corroded up to the level of the main reinforcement. During the corrosion phase, the specimens were daily soaked in a tank containing water and then stored in a humidity controlled room, those operations allowed to accomplish the wet and dry condition. The cracks were measured every 48 hours and the collected data were merged to other outcomes obtained from the literature. An interpolation curve was proposed: it is able to forecast the corrosion level starting from the crack width measure and taking into account geometrical and mechanical characteristics of the rc elements. The core of the experimental program was the pull-out test stage which allowed to obtain the bondslip curves of the specimens firstly corroded and then tested. At the end of the pull-out test, the reinforcing bars and the stirrups were extracted and the actual corrosion rates were determined. Results of the test integrate the present literature and highlighted the role of the inspected parameters. Furthermore, the outcomes were used for calibrating the numerical model. The numerical study lead to the definition of a simple and modular analytical model which allows to take into account the presence of the confinement and the corrosion products. The modelling was realized in the longitudinal and in the transversal direction: hence the model can be considered three dimensional with axial symmetry assumption. In the longitudinal modelling, the boundary value problem is solved using a local bond-stress similar to that one proposed by the MC2010. The transversal modelling was based on the thick-walled cylinder theory which allowed to determine the pressure acting at the steel to concrete interface. In this context, a softening behaviour of the cracked concrete was assumed. Transversal and longitudinal modelling were linked by means of a friction criteria whose parameter depend on the corrosion level and on the concrete tensile strength. Finally, the model was used to simulate some experimental results in the literature. Taking into account the great scatter of the outcomes from the bond test and also due to corrosion phenomenon, a good agreement between the experimental outcomes and the numerical results is observed
Measuring crack width in RC and R/FRC ties throught laser scanner
No full textDurability of reinforced concrete (RC) structure is strictly connected to the capacity of
concrete mass to protect the embedded reinforcement from corrosion. As cracks are
almost inevitable, crack width is a fundamental parameter that needs to be controlled
during the serviceability stage of RC members. In fact, not only the direct ingress of
aggressive agents, such as oxygen and water, is a function of crack width, but also
concrete carbonation and the chloride ion penetration are accelerated by the presence of
wide cracks. Accordingly, the aim of present research project is to assess the width by
using a new system, based on the optical conoscopic holography. It provides the noncontact
measure of crack profile, taken at the end of each loading cycle, in ties subjected
to sets of repeated loads. Both in plain and fiber-reinforced concrete (FRC), more than
one crack width can be mesured for the same crack
Bond and Corrosion: Experimental Studies
No full textBond between steel and concrete plays an important role in the structural behaviour of reinforced concrete structures. In the present paper, bond tests on r.c. specimens in presence of corrosion are performed in order to evaluate the effect of corrosion on bond mechanism. The results of the tests on concrete specimens with RILEM type shape, reinforced with ribbed steel bars of 12 and 16 mm of diameter, with and without confinement, in presence of an increasing level of corrosion up to 20%, are presented. An electrochemical procedure using a current density of 200 µA/cm2 is employed to produce corrosion. The test results show the effect of oxidation of the reinforcement at the interface with concrete and consequent surface cracking, the change of performance in terms of bond and the change of failure mechanism
Bond-slip model for corroded steel in concrete
No full textBond in concrete is of outmost importance for the definition of resisting mechanisms in
reinforced concrete structures. Bond performance is directly related to both serviceability and ultimate
behaviour of reinforced concrete members, because it influences the stiffness of the elements but also the
ductility of the mechanical response and the anchorage capacities. In presence of corrosion bond between
steel and concrete is modified according to different factors as amount of corrosion, cover/rebar diameter,
strength of concrete, reinforcement characteristics influencing the mechanical response of the contact
surface between the two materials. In the paper, starting from a reference bond-slip law as suggested by
MC2010, a modified relationship in presence of corrosion is studied by using a numerical model specifically
developed and calibrated on experimental results, coming from pull-out test of corroded specimens.
These specimens are characterized by an increasing level of corrosion up to 20%, presence of confinement
and use of a current density equal to 200 μA/cm2. Different relationships are proposed for specimens with
and without confinement
Pull-out tests on r.c. corroded specimens
No full textThe structural behaviour of reinforced concrete structures is strictly related to bond performance between steel and concrete. In the present paper, bond tests on r.c. specimens in presence of corrosion are performed in order to evaluate the damage on bond mechanism due to corrosion. The results of the tests on concrete specimens with RILEM type shape, having side of 120 mm and 160 mm, reinforced with ribbed steel bars with diameter of 12 and 16 mm, respectively with and without confinement, in presence of an increasing level of corrosion up to 20% of estimated mass loss are presented. Corrosion is applied by means of an electrochemical procedure using a current density of 200 μA/cm2. The test results show the effect of oxidation of the steel at the interface with concrete and the change of performance in terms of bond strengt
Discussion of "An efficient tension-stiffening model for nonlinear analysis of reinforced concrete members", by Renata S.B. Stramandinoli, Henriette L. La Rovere
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