Modelling of chloride ingress in concrete based on benchmarking field results

Modelling the ingress of chloride ions into the cover of a concrete structure is a phenomenon that is gaining an increasing attention of the research community, but even more, from the engineering practice. As the mechanism that drives the ingress of chlorides is implicitly responsible for the service-life of concrete structures, its input parameters are a major issue whenever predicting the service-life of new concrete structures. In this paper most relevant parameters involved in the evaluation of chloride ingress models are discussed and related to the benchmark activities that currently run in RILEM TC 270-CIM on benchmarking Chloride Ingress Models. The results provide an overview of the models used in the structural design stage, mostly analytical models, and in the rehabilitation stage, mostly numerical models

Simulation of Volume Changes in Hardening Cement-Based Materials

Civil Engineering and Geoscience

Measuring deflections of a corroded concrete beam loaded dynamically by a four-point-bending test

One of the key-elements in Structural Health Monitoring of reinforced concrete structures is the level of rebar corrosion and the way in which it affects the structural performance. A dynamic four-point-bending test was developed to help understanding the deflections of concrete structures under corrod-ed conditions. With this test, two equivalent beams are loaded under equal conditions. To generate corrosion, one beam was exposed to a chloride-water solution. The other beam was exposed to tap water only, in order to act as a reference. This paper reports and discusses seven weeks of experi-mental data, including deflections and crack widths. Although there was not yet a significant effect of corrosion, some changes in crack widths and in deflections were observed. Furthermore, the influence of temperature and surface wetting exposure on the structural behaviour will be discussed.Structural EngineeringCivil Engineering and Geoscience

Modeling and analyzing autogenous shrinkage of hardening cement paste

In this paper, a conceptual model for analyzing the plastic part of autogenous deformation of cement paste based on the Arrhenius rate theory will be presented. The autogenous deformation will be calculated from the elastic deformations with inclusion of creep. Different kinds of cement paste with a water cement ratio 0.3 are tested and studied, and experimental result compare the model calculation. The results lead to the conclusion that early age creep plays a very important role in the autogenous deformation of hydrating cement paste and should not be neglected in simulation models.Structural EngineeringCivil Engineering and Geoscience

Simulation of macroscopic behavior of a self-compacting mixture based on DEM

Since the early 20th century, the necessity of modeling and monitoring fresh concrete behavior has been recognized by the industry with the objective to ensure adequate mechanical properties and a proper durability of concrete structures. Due to the rapid development of computer technology, the applications of computational simulation tools in the field of concrete technology has significantly increased and help us to understand the mechanisms of rheological systems. The development of proper rheological models and suitable numerical methods are considered as basic needs for a thorough understanding of the flow properties. The main challenge is finding a quantitative correlation between the model parameters and the properties and proportions of the mix ingredients. This paper presents a numerical approach for macroscopic behavior of a fresh self-compacting mixture using Discrete Element Method (DEM). The employed research is based on a conceptual idea where the grain-paste interaction is explicitly modelled as an interactive two-phase system. Each mixture is considered to be an assembly of “grain-paste” systems, which can be characterized according to the mix composition based on the “excess paste theory”. The macroscopic behavior is evaluated based on the slump flow test results. Simulations and experimental laboratory test results show good agreement.Structural EngineeringCivil Engineering and Geoscience

Understanding the impact of degradation of concrete structures

Structural EngineeringCivil Engineering and Geoscience

Changing model properties with time due to corrosion of a dynamically loaded reinforced concrete beam

Structural Health Monitoring (SHM) systems are frequently used in civil infrastructures. One important durability property in reinforced concrete (RC) structures is the level of steel bar corrosion. In a dynamic four-point-bending test, two beams are loaded simultaneously, in which corrosion is accelerated in one of them. Since geophones are commonly used in SHM systems to monitor vertical deformations and to calculate modal properties, the first natural frequency of both beams are analysed in this paper. It is discovered that many properties, like temperature and moisture, may influence natural frequencies. Besides this, calculated natural frequencies may fluctuate. Experiments showed that the first natural frequency in the corroded beam decreases while it remains almost constant in the uncorroded situation.Structural EngineeringCivil Engineering and Geoscience

A performance -based method for granular based method for granular -paste mix design

In this paper a performance-based method for the design of granular-paste mixtures will be proposed. Focus will be on the selection and proportioning of constituents to produce a mixture with a pre-defined shape holding ability. Shape holding ability of mixtures will be characterized by the shape preservation factor SPF. This SPF shows the ability of a mixture to preserve its shape after being demolded from a slump test. SPF is the ratio of the cross sectional area of a sample after and before demolding. By increasing the flowability of a mixture, the SPF decreases. In this study a mixture is first decomposed into aggregate, void paste and excess paste. Then a combination of the consistency of the paste and excess paste volume is determined for a required SPF. Finally, depending on the aggregate grading, the volumes of paste and aggregates in the system are determined.Structural EngineeringCivil Engineering and Geoscience

Modeling aging of cementitious pore structure

Coupled reactive-transport processes in cementitious materials play a crucial role in the aging process pf building materials. Up to now, the effect of aging on microstructure and evolution of it’s properties, in three dimensions, was studied only by dissolution of certain phases at random locations. In this paper we present a new 3D reactive-transport model and results of leaching-induced aging simulations performed on virtual cementitious microstructures generated by Hymostruc model. The outputs are the morphology of the aged 3D microstructure together with aged properties characterised by fuzzy state of each voxel at different times. This allows to simulate the evolution of properties as a function of time as well as a function of the location within the microstructure.Structural EngineeringCivil Engineering and Geoscience

Dynamically loaded beam failure under corroded conditions

De-icing salts, used on roads in heavy winters, may enter reinforced concrete (RC) structures via its capillary pore system or via cracks, initiating reinforcement corrosion and reducing its remaining service-life. Vehicles passing real bridges exert a dynamic impact action that might activate a fatigue failure mechanism. In order to generate more knowledge on the interaction between corrosion and fatigue, a four-point-bending test setup is developed where two lab-scale RC beams are loaded simultaneously. In this setup, RC beams are loaded dynamically, while for one of the beams, corrosion is accelerated by means of a chloridesolution bath mounted on top of it. The second beam, which is the control, is only exposed to tap water. Many test repetitions are foreseen, but so far, three tests are conducted using two different loading levels. It turned out that the reinforcement bar, which corroded due to chloride exposure, failed first in all cases. This paper reports results of the failure mechanism whereby forensic engineering was used to examine the interaction between corrosion and fatigue, and that this might result in a harmful undesirable failure mechanism. The results, therefore, should also be considered for service-life design predictions of infrastructure.Structural EngineeringCivil Engineering and Geoscience