Papers by Keyword: Concrete Cracking

Abstract: The service life of steel reinforced concrete in aggressive marine environments could be increased substantially by embedding a self-healing mechanism that ensures autonomous healing of cracks upon their occurrence. Previous proof-of-concept experiments have shown that the incorporation of encapsulated polymer-based healing agents (HAs) counts as a very appropriate way to achieve this goal. Over the years, several polymer-precursor-capsule systems have been developed in that perspective at our laboratory. Cementitious materials containing either commercial or in-house developed encapsulated HAs have been subjected to preliminary feasibility tests (water absorption, permeability tests, etc.). However, these experiments did not yet allow for a fast and straightforward assessment of the self-healing efficiency (SHE) in relation to the expected durability and service life performance of the material. This approach would have many advantages when having to select the most suitable polymer-precursor-capsule system for a particular concrete application. In this paper, a modified chloride migration test based on the one prescribed in NT Build 492 has been proposed to support the development of self-healing concrete for marine environments. Four polymer-based HAs have been screened that way, i.e. an in-house developed high-viscosity polyurethane (PU) precursor, a commercial low-viscosity PU precursor, the same commercial PU precursor with addition of accelerator and benzoyl peroxide (BPO), and an in-house developed 2-component acrylate-endcapped precursor + cross-linker. For now, a highly repeatable SHE value of 100% could only be obtained for the second option.

Abstract: To solve the problem of early-age concrete shrinkage under constraint, 0%, 2%, 3%MgO expansion agent are mixed in the concrete. Results indicate that MgO expansion agent can ensure the expansion strain of the concrete and produce the self-stress under constraint which is up to 1.8Mpa~2.2Mpa.

Abstract: This paper presents a study on the influence of material parameters of concrete on the mechanical response of prestressed monoblock railway sleepers used on Czech railway tracks. The influence of selected mechanical/fracture parameters of concrete on the structural behaviour of the studied precast structural members is investigated by means of numerical modelling of standardized static loading tests, which are used as a tool for quality control during the manufacture of sleepers according to the European Standards for railway applications. The tests are numerically simulated using ATENA nonlinear finite element method software. The results of the simulations are compared with experimental data obtained via static loading tests performed on sleepers both before their use according to their designated purpose and after 17 years in operational service.

Abstract: Nowadays, influences of concrete cracking on durability of concrete structure are widely reported. However, the influence of macro cracks on chloride diffusion of concrete is unknown under the condition of marine submergence. Therefore, the present paper adopted a notch method to study natural chloride diffusion in cracked concrete with a width of above 0.3 mm. The results show Apparent diffusion coefficient of acid soluble chloride rises from 2.66 ×10^-12 m²/s to 5.92×10^-12 m²/s with increasing crack width from 0 mm to 0.45 mm. Besides, one exponential function was used to describe the piecewise relationship between diffusion coefficient (water or acid soluble chloride) and crack width.

Abstract: With the constant improvement of the national economic level, the requirements on the building security are also increasing. The external temperature is a major factor leading to unsafe buildings. It is very necessary to research the civil engineering and architecture under the thermodynamic environment. The concrete will crack with the change of the temperature. According to this, the paper studies the reason and defensive measures of expansion caused by heat and contraction caused by cold based on thermodynamic principles. According to climatic characteristics, this article proposes the preservation and heat insulation of buildings, protection the buildings from icy frost damage and the ventilation of the buildings through the selection of building materials. It solves the cracking problem of the concrete very good with the change of the temperature. The research of this paper provides some reference for other research on the civil construction.

Abstract: Current maintenance of concrete civil infrastructure such as buildings, bridges, dams and highways, is based on scheduled inspection consisting in visual and/or local inspection techniques (i.e. acoustic/ultrasonic methods, radiography, eddy-current methods). A major trend in the field is the development of automated on-line monitoring systems. The current study is focused on the use of ultrasonic wave propagation techniques based on embedded piezoelectric transducers for the on-line monitoring of the damage state in concrete. The technique is based on the use of an ultrasonic emitter-receiver pair and the construction of a damage indicator focused on the early wave arrival. The proposed simple monitoring system is implemented during several pull-out tests on concrete blocks. The results demonstrate the excellent performance of the system which is able to detect the initiation and follow the evolution of the cracking until complete failure.

Abstract: The bond between concrete and steel is the critical element of reinforced concrete (RC) structures, which directly affects their load carrying capacity and serviceability. Hence the evaluation of bond strength degradation is an essential parameter to predict the residual strength of RC structures affected by reinforcement corrosion. Existing research studies in this field mainly focus on numerical and experimental investigations. Few attempts have been made using analytical approach but there is still a need of reliable model which considers the critical mechanical factors affecting the bond strength of corroded RC structures. This paper presents a simple and realistic analytical model of bond strength degradation by using fracture mechanics combining the action of adhesion, confining pressure and corrosion pressure at steel concrete interface. Finally, the results obtained from the proposed model are examined with published experimental data. The study demonstrates that the proposed analytical model agrees with the experimental data of existing investigations.

Abstract: As a nonuniform and unisotropic material with a relatively low tensile strength in spite of high compression strength, a concrete material is vulnerable to bending and tension. Due to the mechanical properties of the current reinforced concrete structures, it is hard for concrete materials to avoid the damages caused by cracks. Although cracks are the easiest things to detect and the most effectively repairable things due to their characteristics, it is very hard to measure them efficiently. In this research, the author measured cracks by visualizing them through mechano- luminescence(ML) paint. By applying ML paint on the surface of the specimen and using the 3-point bending test, the author conducted a quantitative evaluation on the mechanical properties of cracks such as the cracking aspect and length of reinforced concrete. Through the results of this research, the author confirmed the crack propagation speed by section and the mechanical correlation such as between loads and cracks and between deflection and cracks, which means this research was quite successful in analyzing the characteristics of cracks.

Abstract: Cracks can reduce the service life of a concrete structure by allowing aggressive agents to penetrate through it in easy ways. Free shrinkage evaluation alone is not enough to determine if cracking can be expected in a structure since concrete creep behaviour, stiffness and toughness also influence the potential for cracking. Consequently, it is rather interesting to perform restrained shrinkage tests, such as the ring test according to ASTM C 1581–04. The testing procedure involves concrete ring specimens restrained by an inner steel ring on which strain gauges are placed to determine the age of cracking, since abrupt changes in the steel strain occur when concrete is cracked. Both the ring test and free shrinkage test should be carried out in the same exposure conditions, 21°C and 50% relative humidity. Moreover, compressive and tensile strengths of concrete were evaluated on cubic specimens at the time of its cracking and up to 28 days of curing. By means of analytical and numerical models of the ring specimen, some useful information on the stress induced in the material and on the tensile creep behaviour of concrete can be extrapolated thus allowing to better interpret the experimental results. This experimental procedure enables to study the influence of concrete mixture composition on the potential for early-age cracking of concrete. In particular, in this work the influence on early-age cracking of recycled-concrete aggregate partially replacing virgin sand was tested.

Abstract: This paper studied the main cracking reasons for small and medium-span continuous girder bridge with secondary concreting based on ANSYS. Some prevention measures to concrete crack caused by the inelastic subsidence were also proposed. In considering the global deformation of scaffold-beam, the inelastic deformation of scaffold, the hydration heat of cement, and the characteristics of early-age concrete, influence of inelastic subsidence of support foundation on concrete cracking were analyzed by time-varying transient analysis. It can be concluded that the value of inelastic deformation is the decisive factor for the concrete cracking. Field measurement results of several bridges validate the conclusion.