Behavior of corroded bonded fully prestressed and conventional concrete beams

AbstractPrestressed concrete is widely used in the construction buildings. And corrosion of steel is one of the most important and prevalent mechanisms of deterioration for concrete structures. Consequently the capacity of post-tension elements decreased after exposure to corrosion. This study presents results of the experimental investigation of the performance/behavior of bonded fully prestressed and conventional concrete beams, with 40MPa compressive strength exposed to corrosion. The experimental program of this study consisted of three fully prestressed and two conventional concrete beams with overall dimensions equal to 150×400×4500mm. The variables were considered in terms of corrosion exposure effect, prestressed level, and corrosion location effect for fully prestressed beams. Mode of failure, cracking width/distribution, ultimate load and the corresponding deflection of each beam were recorded. The results showed that the fully prestressed beam in comparison with conventional beam was considered to be even more resistance to corrosion because it was perceived to be crack-free as a result of prestressing. Also the mention deterioration incident in fully prestressed beams fully corrosion exposure level unnoticed that deterioration incident in partially corrosion exposure level. The most of deterioration incident in fully prestressed beam acts on compression of non-prestressed steel reinforcement. Because the bonded tendons are less likely to corrode. Cement grout/duct is a barrier to moisture and chloride penetration, especially plastic duct without splices. The theoretical analysis based on strain compatibility and force equilibrium gave a good prediction of the deformational behavior for fully prestressed beams

Thermal protection of reinforced concrete columns strengthened by GFRP laminates (experimental and theoretical study)

Fiber reinforced polymer (FRP) has been used over the last decade in the form of laminates for strengthening reinforced concrete elements. Non-corrosive characteristics, high strength and good fatigue properties of FRP significantly increase the service life of structures. However, FRP have a negligible resistance to fire. This is mainly due to the fact that the epoxy adhesive used in the application of FRP is badly deteriorated by high degree of temperature. The current paper studies fire protection of glass fiber reinforced polymer (GFRP) laminates used in strengthening reinforced concrete columns. The experimental program of this study included testing of seven reinforced concrete circular columns. Two columns were tested as control columns. Five columns were exposed to high degree of temperature, while being loaded, to simulate the actual situation in structures. Two different systems for protecting GFRP laminates against fire were used with varying thickness. Specimens were exposed to high degree of temperature by different durations and then reloaded to measure the residual strength. The behavior and failure modes of the strengthened concrete columns exposed to high degree of temperature are presented. Recommendations for application of protective coating to FRP systems against high degree of temperature are given. Theoretical analysis was also carried out to predict the load capacity of the reinforced concrete columns strengthened by GFRP laminates. Evaluation of the analytical work was introduced and compared to the results of the experimental work

Behavior of corroded bonded partially prestressed concrete beams

Prestressed concrete is widely used in the construction industry in buildings. And corrosion of reinforcing steel is one of the most important and prevalent mechanisms of deterioration for concrete structures. Consequently the capacity of post-tension elements decreased after exposure to corrosion. This study presents results of the experimental investigation of the performance and the behavior of partially prestressed beams, with 40 and 80 MPa compressive strength exposed to corrosion. The experimental program of this study consisted of six partially prestressed beams with overall dimensions equal to 150 × 400 × 4500 mm. The variables were considered in terms of concrete compressive strength, and corrosion location effect. The mode of failure, and strain of steel reinforcement, cracking, yield, ultimate load and the corresponding deflection of each beam, and crack width and distribution were recorded. The results showed that the partially prestressed beam with 80 MPa compressive strength has higher resistance to corrosion exposure than that of partially prestressed concrete beam with 40 MPa compressive strength. Not big difference in deterioration against fully/partially corrosion exposure found between partially prestressed beams at the same compressive strength. The most of deterioration incident in partially prestressed beam acts on non prestressed steel reinforcement. Because the bonded tendons are less likely to corrode, cement grout and duct act as a barrier to moisture and chloride penetration, especially plastic duct without splices and connections. The theoretical analysis based on strain compatibility and force equilibrium gave a good prediction of the deformational behavior for high/normal partially prestressed beams. Keywords: Beam, Corrosion, Deterioration, Partially prestressed, High strength concret

The behavior of ultra-high-strength reinforced concrete columns under axial and cyclic lateral loads

In general Ultra High Strength Concrete (UHSC) is a new class of concrete that has been developed in recent decades. UHSC is characterized by extraordinary mechanical and durability properties. The UHSC-Matrix is very brittle material behavior. In this research an experimental program consists of twelve square UHSC columns is being carried out to study the behavior of UHSC columns subjected to constant axial load combined with cyclic lateral loading in order to simulate the case of seismic action. The main parameters of this program were: longitudinal reinforcement ratio, percentage of steel fiber, stirrups ratio, axial load level and concrete compressive strength. In this experimental program each specimen represents a column extending on both sides from the beam-column connection to the location of the point of inflection. Particular attention is paid to the effect of each variable on the strength enhancement, stiffness degradation, energy dissipation capacity, curvature ductility and displacement ductility of the tested columns. Valuable conclusions were obtained from the research results. By increasing the concrete compressive strength the column capacity increases accompanied by a decreasing in the ductility aspects, increasing the longitudinal steel ratio from 2% to (3.6% and 4.5%) leading to an increase in the column capacity and ductility aspect of the tested columns. Using steel fiber between (1.33–2.67)% is recommended in UHSC columns in seismic zones. The Egyptian concrete code of practice limits for the columns stirrups is suitable in seismic zones for columns subjected to a low axial load level

Recycled construction and demolition concrete waste as aggregate for structural concrete

In major Egyptian cities there is a surge in construction and demolition waste (CDW) quantities causing an adverse effect on the environment. The use of such waste as recycled aggregate in concrete can be useful for both environmental and economical aspects in the construction industry. This study discusses the possibility to replace natural coarse aggregate (NA) with recycled concrete aggregate (RCA) in structural concrete. An investigation into the properties of RCA is made using crushing and grading of concrete rubble collected from different demolition sites and landfill locations around Cairo. Aggregates used in the study were: natural sand, dolomite and crushed concretes obtained from different sources. A total of 50 concrete mixes forming eight groups were cast. Groups were designed to study the effect of recycled coarse aggregates quality/content, cement dosage, use of superplasticizer and silica fume. Tests were carried out for: compressive strength, splitting strength and elastic modulus. The results showed that the concrete rubble could be transformed into useful recycled aggregate and used in concrete production with properties suitable for most structural concrete applications in Egypt. A significant reduction in the properties of recycled aggregate concrete (RAC) made of 100% RCA was seen when compared to natural aggregate concrete (NAC), while the properties of RAC made of a blend of 75% NA and 25% RCA showed no significant change in concrete properties