Sergio Henrique Pialarissi Cavalaro

Application of constitutive models in European codes to RC-FRC

Abstract The recent publication of codes for the design of FRC is a major step towards extending the use of the material. An in depth analysis indicates several differences between the constitutive models proposed in the existing codes. In this study, these models are compared and a numerical simulation is performed to evaluate their differences in terms of the structural behavior predicted and measured in an experimental program of RC–FRC elements. The predictions provided by the models fit satisfactorily the experimental results for elements with steel fibers and with plastic fibers.

New analytical model to generalize the barcelona test using axial displacement

The Barcelona Test has proved to be very suitable for the systematic control of the tensile properties of Fibre Reinforced Concrete (FRC). Nevertheless, the need to measure the total circumferential opening displacement (TCOD) of the specimen entails the use of an expensive circumferential extensometer. In order to simplify the test, studies from the literature propose the use of the axial displacement of the press (δ) instead of the TCOD, obtaining empirical equations to correlate the energy estimated with both measurements. However, these equations are only valid for δ ranging from 1 to 4 mm and were adjusted based on the test results of just a few types of FRC. The verification of this formulation for other types of FRC shows an average error of 51.1%, thus limiting the simplification proposed for the test. In this paper, a new analytical model to convert the δ into the TCOD is developed and validated for a wide range of FRC. Besides being applicable to the whole range of δ, the new model provides a clear physical understanding of the main mechanism observed during the test and shows an average error of only 6.7%, making it possible to simplify the Barcelona test.

New Unreacted-Core Model to Predict Pyrrhotite Oxidation in Concrete Dams

AbstractPyrites and pyrrhotites are the most abundant minerals of the iron sulfide group in nature and may be found in the aggregates used to produce concrete. In the presence of water and oxygen, such compounds generate expansive reactions that may have severe structural damages. This is especially critical in concrete dams, given the large volume of material used and the restrictions in movement imposed by the surroundings. In these cases, the definition of adequate rehabilitation programs depends on the prediction of the expansive reaction evolution and the future behavior of the structure. Although models that describe solid particle–gas reactions may be used with this purpose, none were specifically developed to simulate this phenomenon in dams. This paper introduces a new kinetic model based on the unreacted-core model for pyrrhotite oxidation. The comparison of the results obtained with this new model and with the direct application of the unreacted-core model show significant differences. Followin...

Influence of the Type of Fiber on the Structural Response and Design of FRC Slabs

Most codes for the design of fiber reinforced concrete (FRC) structures are based on the experience achieved throughout the years with steel fibers. Recent codes include the possibility of applying the same considerations for FRC structures with plastic fiber. However, the consequences of assuming identical design considerations regardless of the type of fiber is scarcely known in terms of the structural behavior of full-scale elements. The main goal of this paper is to assess the influence of the type of fiber on the performance of full-scale concrete slabs, emphasizing on the consequences of using a common design approach. For that, a comparative experimental study was conducted in order to expose differences regarding the crack pattern and load-deflection behavior. Then, finite element simulations were performed using the constitutive equations from the Model Code 2010. The results indicate distinct levels of overestimation of the structural behavior measured experimentally, confirming that specific design considerations are required depending on the type of fiber used. Based on the findings, correction factors are proposed for the design of FRC slabs with each fiber.

Sand-Cement Concrete in the Century-Old Camarasa Dam

Sand-cement emerged in the early twentieth century as an alternative binder in infrastructures that required a significant amount of concrete volume in order to reduce the costs associated with portland cement. This binder was first used in the United States in several dams before being applied in Camarasa Dam in Spain. Nearly a century after its construction, the dam exhibits degradation phenomena in the downstream face, manifested by losses of mass. The present study aims at assessing the state of the sand-cement concrete in Camarasa Dam and evaluate whether the degradation observed could affect the safety and functionality of the 95-year-old dam. For that, the state of the art on sand-cement is reviewed and an experimental program of physical, mechanical, and chemical tests is performed on samples from the dam. The results reveal that the degradation phenomena may be attributed to physical causes and a general degradation of the concrete properties is discarded as well as any effect on the safety and functionality of the dam.

New Design Method for the Production Tolerances of Concrete Tunnel Segments

Some damages observed in tunnels constructed with tunnel-boring machines are caused by contact deficiencies between segments, which are the result of the sum and accumulation of several types of tolerances. Because the relation among the tolerances, the contact deficiencies, and the structural damage is not quite clear, the segmented lining is usually designed to meet very tight tolerances. The existing tolerance recommendations consist mostly of extrapolation of tolerances applied to other types of concrete structures with different characteristics. This explains the wide variation of production tolerances found in the literature, with different repercussions on the cost of molds and on the performance of the structure. The first part of this study shows the relation between structural damage and contact deficiencies. The second part of the study explains how the contact deficiencies found in practice are generated by the tolerances. Finally, a general design method is proposed for the estimation of the production tolerances. Based on this, general recommendations are derived for the maximum admissible production tolerance used to limit the incidence of structural damage.

Performance-Based Procedure for the Definition of Controlled Low-Strength Mixtures

Controlled low-strength material (CLSM) is a self-consolidating cementitious material used as backfill in narrow trenches. The high content of aggregates and water in CLSM leads to a special behavior that is closer to soil than concrete. Consequently, mixture proportioning methodologies for conventional concrete do not apply to CLSM. The objective of this paper is to propose a new methodology to achieve the optimal composition that fulfills the flowability and compressive strength requirements of the material. Instead of computing the aggregate or the cement separately, all solid particles in the mixture are considered concurrently to estimate the water content in terms of water-to-solid ratio (W/S). In this way, the compressive strength can be modified without compromising the desired flowability. An example application is presented and an experimental program is conducted to validate this philosophy. The results confirm that the methodology proposed provides compositions that satisfy the main requirements of CLSM, thus representing a contribution to the use of more economical and adequate materials.

Flexural Post-cracking Creep Behaviour of Macro-synthetic and Steel Fiber Reinforced Concrete

In this paper the post-cracking creep behaviour of FRC beams under flexural load is evaluated in order to determine whether under certain loading conditions plastic fibres may be safely used in the long-term without compromising the serviceability requirements. For that, an experimental program was conducted that involved the testing of 30 beams with dimensions of 150 × 150 × 600 mm reinforced either with plastic or steel fibres. The creep test setup consisted in a four-point bending test in previously cracked beams up to crack widths of 0.25, 1.50 and 2.50 mm. The sustained load ranged between 50 and 60 % of the cracking load and was applied by means of a lever system. The sustained load was controlled throughout the test with a load cell. The tests were performed under two different environmental conditions during 6 months. Despite the large deformations exhibited by plastic fibres under sustained load over time, their use as reinforcement should not be discarded as long as the effects of creep are considered in the design.

Service-Life Assessment of Existing Precast Concrete Structure Exposed to Severe Marine Conditions

The overall performance of a concrete structure is considered to be a key issue when determining its service life. The widespread use of precast concrete and consideration of durability as a design parameter in most of the international codes have the goal of achieving concrete structures with better durability. Nevertheless, the early deterioration of concrete is still common in a large number of concrete structures, which reduces the service life. This paper presents a case study of an existing precast concrete cooling tower for a thermal power station subjected to severe marine exposure conditions, which showed symptoms of serious deterioration after operating for three years. The main goal of this study was to clarify the origin of the accelerated deterioration of the structure. Wetting-drying cycles were identified as the main cause of the early deterioration of the structure. Furthermore, estimations on its remaining service life were made considering the accelerating effect of the wetting-drying cycles. Finally, the variation in the safety factor of the main structural elements was evaluated.

Influence of Fiber Properties on the Inductive Method for the Steel-Fiber-Reinforced Concrete Characterization

The inductive method has shown to be a good method for the estimation of fiber dosage in steel-fiber-reinforced concrete. The current formulations reported a strong correlation between inductance and fiber content, as well as orientation. The objective of this paper is to study how the inductive measurements are affected by fiber properties, such as its dimensions, magnetic characteristics, and sample temperature. The results obtained from numerical, simulated, and experimental data propose a shape factor to be applied in the measurements to take into account the aspect ratio of fibers. They also show that the magnetic composition of the fibers is of great importance. As for temperature, the error introduced is less than 1%, so a corrective factor is not essential.