Engineering Commons^™

Establishment Of A Numerical Model For Sulfate Attacked Concrete Considering Multi-Factors, Shanshan Qin, Dujian Zou, Jun Jiang, Tiejun Liu

International Conference on Durability of Concrete Structures

Sulfate attack is one of the major durability problems of concrete structures, which is manifested by expansive cracks and deterioration of cement paste. In this study, a numerical model is proposed to predict the process of ionic diffusion into concrete under external sulfate attack. The chemical reaction and diffusion processes are considered in this model. Furthermore, the influence of calcium leaching, chemical activity of multi-ions, temperature and changes in porosity are also taken into account. The initial porosity and tortuosity are assumed to be homogeneous in concrete, and the chemical potential gradient is regarded as the driving force for ions …

Meso-Scale Fracture Modelling Of Concrete Cover Induced By Non-Uniform Corrosion Of Reinforcing Bar, Xun Xi, Shangtong Yang, Chun-Qing Li

International Conference on Durability of Concrete Structures

Corrosion-induced concrete cracking is a significant durability problem for reinforced concrete structures. In practice, critical corrosion degree to surface cracking and crack width evolution are of significance in regards to the assessment of serviceability of reinforced concrete structures. Literature review suggests that, although considerable research has been undertaken on corrosion-induced concrete cracking, little has been focused on non-uniform corrosion of reinforcing bar, especially by considering concrete as a three-phase materials. In this paper, a meso-scale fracture model, consisting of aggregates, cement paste/mortar and ITZ, is established. To simulate arbitrary cracking in concrete, cohesive elements are inserted in the fine meshes …

A New Model For Corrosion-Induced Concrete Cracking, Xun Xi, Shangtong Yang, Chun-Qing Li

International Conference on Durability of Concrete Structures

Corrosion of reinforced concrete is one of the major deterioration mechanisms which result in premature failure of the reinforced concrete structures. Due to the actual diffusion of chloride ingress, the corrosion products distribution is seldom uniform along the reinforcing bar. Recently, some non-uniform corrosion models have been proposed to investigate the corrosion-induced cracking mechanism of concrete. In this paper, a new corrosion model based on von Mises distribution is formulated and validated against experimental data. The developed model is then compared with the existing non-uniform models and the advantages are discussed. To demonstrate the application of the developed corrosion model, …

An Image-Based Local Homogenization Method To Model Mass Transport At The Steel-Concrete Interface, Zhidong Zhang Dr, Ueli Angst Prof, Alexander Michel Prof, Mads Jensen Dr

International Conference on Durability of Concrete Structures

Mass transport (moisture and ions) at the steel-concrete interface is closely related to corrosion of rebar in reinforced concrete structures. Thus, in the model simulating mass transport, the structure of the steel-concrete interface must be well represented. In this study, an image-based local homogenization method is proposed based on images taken in the scanning electron microscope (SEM) under the backscattered electron (BSE) detector. According to the gray level of the image, porosity can be calculated and then proposed equations are used to associate the transport properties (sorption isotherms, diffusion coefficients and permeability) with porosity. Experimental data of chloride concentration taken …

Residual Service Life Estimation And Its Importance For Pretensioned Concrete (Ptc) Bridges In Coastal Cities, Dyana Joseline, Deepak K. Kamde, Sripriya Rengaraju, Radhakrishna G. Pillai

International Conference on Durability of Concrete Structures

Many pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis - to plan for corrosionpreventionorcontrolmeasuresandensuresafetyofexistingbridges.Criticalchloridethreshold(Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation …

Estimating Fractal Dimension Of Cement Matrix For Predicting Chloride Ingress Into Cement-Based Materials, Elakneswaran Yogarajah, Satoshi Yoshida, Akira Hatanaka, Toyoharu Nawa

International Conference on Durability of Concrete Structures

The durability performance of cement-based materials in service environments is affected by numerous factors, many of which involve attacks due to ionic transport, leading to reduced service life. The durability must be ensured in both an economically and environmentally responsible manner. Chloride-induced steel corrosion is a serious threat to the durability of reinforced concrete structures in marine environments, and the diffusion is the dominant transport mechanism of chloride ingress into concrete. Therefore, clear understanding of chloride transport mechanism, particular the diffusion path, is important for designing the durability performance of reinforced concrete structures. The purpose of this study is to …

Effect Of Time-Dependent Chloride Profile And Temperature Variation On Chloride Diffusion In Concrete, Feras Alsheet, A. Ghani Razaqpur

International Conference on Durability of Concrete Structures

Reinforcement corrosion due to chlorides diffusion is one of the main problems in reinforced concrete structures exposed to certain environments. The diffusion rate is function of chloride surface concentration, concrete temperature, humidity, composition and microstructure. The intruded chlorides are partially chemically bound by the concrete and it is the unbound or free chloride which upon exceeding a defined threshold initiates corrosion. The time to corrosion initiation depends on the above variables; therefore, it is important to model their spatial and temporal variations in a manner that will yield a realistic estimate of the actual initiation period. In this study, the …

Modelling Of Capillary Pore Structure Evolution In Portland Cement Pastes Based On Irregular-Shaped Cement Particles, Cheng Liu, Mingzhong Zhang, G Fang, Yun Bai, Y Zhang

International Conference on Durability of Concrete Structures

The pore structure plays a crucial role in durability performance of cement-based materials. However, the pore structure in cement pastes is highly dependent on the initial packing of cement particles and cement hydration process, which seems to be related to the shapes of cement particles. This paper proposed a numerical method to investigate the effect of cement particle shapes on capillary pore structures in cement pastes. In this study, irregular-shaped cement particles with various shapes are generated using a novel central growth model, and then incorporated into CEMHYD3D model to simulate Portland cement hydration. Some home-made programs of determining pore …

First Principles-Based Design Of Economical Ultra-High Performance Concrete, Aashay Arora, Matthew Aguayo, Farrokh Kianmofrad, Yiming Yao, Barzin Mobasher, Narayanan Neithalath

International Conference on Durability of Concrete Structures

This paper presents a novel strategy to design the binder phase of ultra-high performance concrete (UHPC) from commonly available cement replacement (fly ash, slag, microsilica, metakaolin) and fine filler (limestone) materials. A packing algorithm is used to extract the number density, mean centroidal distance, and coordination number of the microstructure. Similarly, rheological studies on the pastes provide yield stress, plastic viscosity, and mini-slump spread. The selection criteria involves using the three microstructural and three rheological parameters individually or in combination to define packing and flow coefficients. The selection criteria is flexible enough to allow users modify the constraints depending on …

Durability Design Of Segmental Linings For Intended Service Life Of Tunnels, Mehdi Bakhshi, Verya Nasri

International Conference on Durability of Concrete Structures

In one-pass lining systems, the durability of tunnel structure is directly related to durability of concrete segments acting as both the initial support and the tunnel final lining. In this paper, most-frequent degradation mechanisms of concrete linings are discussed including chloride- and carbonation- induced corrosions, sulfate, acid and freeze-and-thaw attacks, and alkali-aggregate reactions. Mitigation method for each specific degradation mechanism is explained. A durability factor specific to railway and subway tunnel known as stray current corrosion is presented. Mitigation methods for this specific corrosion together with coupling effects with other conventional damage mechanisms are explained. Prescriptive approaches for durability design …

Durability Design Based On Serviceability Stage For Corroded Reinforced Concrete Structures, Zhongxiaoping Zhongxiaoping, J Zhu, Cb Yuan, Wl Jin, J Xia

International Conference on Durability of Concrete Structures

After analyzing such factors as the structural durability failure state, environmental load and resistance, the durability limit state equation considering steel corrosion initiation, concrete cover cracking and maximum corrosion-induced damage value is established to meet its durability service life requirements under chloride environment. For three different durability limit states, the design theory of reliability, the partial factors of variables for load and resistance are introduced to reflect the target reliability requirements of structural durability, and subsequently the partial factors expression form of structural durability design is established. According to the principle of the same reliability level for partial factors design …

Durability Of Cement-Based Materials In Drinking Water Storage, Matthias Schwotzer, Andreas Gerdes

International Conference on Durability of Concrete Structures

In order to provide a hygienic storage drinking water reservoirs have been coated with mineral mortar linings in all epochs of European history. However, modern cement-based materials often show in this special operational environment an inadequate durability. Even though drinking water is commonly not considered particularly harmful to cementitious systems, the chemical degradation of mortar linings in drinking water storage systems can occur very fast compared to other common deterioration reactions. This results in cost intensive repair measures and thus high life-cycle costs as well associated with an ecological burden. Furthermore, an insufficient understanding of degradation mechanisms and their underlying …

Experimental And Numerical Study Of Macro-Cell Corrosion Between Crossed Steel Bars, Zheng Dong, Xianglin Gu, Zhihao Jin

International Conference on Durability of Concrete Structures

Reinforcing steel bars embedded in concrete are always intersected with each other to form rebar mesh or three-dimensional steel cage. The present study aims to investigate the phenomenon of severe corrosion observed at stirrups or some intersections of steel rebar mesh, which has not been well studied before. Macro-cell corrosion between crossed steel bars was considered to be the major cause for this phenomenon. In this regard, crossed steel bars were divided into intersected zone (IZ) and non-intersected zone (NIZ). The macro-cell current at the face-to-face IZ was calculated by Ohm’s law. A one-dimensional model based on transmission line method …

Effect Of Multi- Steel Bolt Anchorages On Composite Beams, Dawei Zhang, H. F. Shi, W. L. Jin, Tamon Ueda

International Conference on Durability of Concrete Structures

Using fiber-reinforced polymer (FRP) to retrofit or strengthen the concrete structures is an attractive option in construction areas nowadays. However, premature debonding failures limit the efficacy of fiber utilization. It is presently accepted that anchorage system is an attractive option to solve this problem. Much efforts has been made through experimental testing and numerical modeling to investigate the anchorage systems, meanwhile various systems were created and developed. However, researches on the mechanism of the anchorage systems are still too rare to build a countable and union design guideline with respect to different premature debonding failure modes. The present paper focused …

Effect Of Corrosion On The Shear Transfer Behavior Of Stud Shear Connectors, Wen Xue, Ju Chen, Ao-Yu Jiang, Wei-Liang Jin

International Conference on Durability of Concrete Structures

The effect of corrosion on the shear transfer behavior of stud shear connectors was investigated in this study. Experimental investigation was performed using an innovative test setup for single stud shear connector. Two series of specimens having different stud diameters were fabricated and tested. The test specimens were firstly corroded to different corrosion rates by electronic accelerating method. Loading test were then performed to obtain the load-slip curves and ultimate strengths of corroded test specimens. Corrosion rates were measured from the studs obtained from the failure test specimens. Test results were compared with standard push out test specimens having the …

Drying Shrinkage Of Hardened Cement Paste And Its Relationship To The Microstructure, Xin Wang, Chaojun Wan, Xiaojing Zhang, Heng Chen

International Conference on Durability of Concrete Structures

The aim of the present study is to relate microstructure to the drying shrinkage of hardened cement paste. Three microstructural features, calcium silicate hydrate(C-S-H), calcium hydroxide(CH) and pore structure were studied. A new method to determine the C-S-H content of hardened cement paste is presented. Drying shrinkage behavior of cement pastes were investigated by drying specimens through successive steps of RH 100% to 7% RH and re-saturating the specimens. The total shrinkage of cement paste after drying to 7% RH and irreversible shrinkage were decreased with the increasing amount of C-S-H and CH. Prolonged curing resulted in a paste with …

Effect Of External Loading On Durability Properties Of Pre-Stressed Concrete Girders With Microcracking, Savitha Sagari Srinivasan, Raissa Douglas Ferron, Michael Rung

International Conference on Durability of Concrete Structures

Over the last fourteen years, very early in the service life of pre-stressed concrete girders, unexplained microcracks have been observed. Their presence led to concerns about the future integrity of the girders, with one of the major concerns being corrosion of pre-stressing strands. As such, a comprehensive study aimed at understanding the effects these microcracks have on the service life of the girders was initiated. Eight in-service girders, under external loads, and five rejected girders, not under external loads, were selected for the study. In this paper, we present work on the temporal evolution of the cracks during a one-year …

Electrochemical Behaviour Of Passive Layers In Weathered Reinforced Mortars, B. Díaz, B. Guitián, X.R. Nóvoa, M.C. Pérez

International Conference on Durability of Concrete Structures

Electrochemical methods are widely employed for assessing the corrosion performance of steel rebars embedded in concrete. Corrosion potential and polarization resistance are the main parameters considered for this purpose; under the assumption that the cathodic process corresponds to oxygen reduction and the anodic process to steel corrosion. Although these assumptions are mostly true, they are not able to explain some transitions from passive to active states, as well as some corrosion potential evolutions. The present contribution is intended to provide an in depth approximation to those questions based on the study of thick passive layers formed over years in atmospheric …

Influence Of Surface Retarders On Texture Profile And Durability Of Upper Layer Of Exposed Aggregate Concrete Pavement, Mariusz Dąbrowski, Miachał Antoni Glinicki, Karolina Gibas, Aneta Antolik, Kinga Dziedzic

International Conference on Durability of Concrete Structures

Exposed aggregate concrete (EAC) pavement technology is used in Poland for construction of major highways and expressways. When properly executed, it is an efficient technique to provide desired friction for skid resistance without compromising the noise limitations. Concrete mix uniformity, proper dosing of retarding agent and optimal time to brush with a mechanical broom are supposed to have a major impact on the properties of the upper pavement layer. An experimental investigation was performed on exposed aggregate concrete specimens manufactured in the laboratory in a way to simulate the industrial production of two-layer concrete slab with exposed aggregate. The texture …

Performance Of Anaerobic Digestion Systems: A Review, Douglas Thompson, Sree Nanukuttan, Daniel Mcpolin

International Conference on Durability of Concrete Structures

Anaerobic digesters contain extreme environments that change drastically during the production cycle. Organic material is broken down first into amino and fatty acids, then into volatile fatty acids, ammonia, CO₂, H₂S and other by-products. These acids and alcohols are converted to acetic acid as well as CO₂ and H₂, which is then used to create methane. All these biological processes mean that the pH, temperature and type of bacteria vary, creating conditions outside the scope of current standards, such as a concentration of ammonium ions 8 times greater than the upper limit of …

Study On Accelerated Microbial Corrosion Of Concrete By Artificially Intensified Sewage, L. J. Kong, M. F. Cao, Xiangming Zhou Prof, H. R. Lu, H. Lu, G. Kastiukas

International Conference on Durability of Concrete Structures

In this study, the artificially intensified sewage with different levels of chemical oxygen demand (COD) were prepared, and the changes in weight and strength, as well as the micro morphology, mineral compositions and pore structure of concrete specimens immersed in the artificially intensified sewage and water were investigated in comparison. In parallel, the COD, pH, H₂S and O₂ values, as well as the microbial species and contents of sewage were monitored in the corrosion process. Furthermore, the microbial structure and activities within biofilm developed on concrete surface were also analyzed. The results indicated that the increase of …

The Tsa Degradation Process Within Cement-Based Materials In The Electrical Field Environment, Chong Wang, Zheng Fang, Yaoling Luo

International Conference on Durability of Concrete Structures

The thaumasite form of sulfate attack (TSA) of cement-based materials is a complex degradation process. The degradation process needs abundant water, carbonate, sulfate and silicate. However, there is no detailed study on the TSA degradation process. X-Ray Diffraction (XRD) and chemical analyses were used to study the TSA degradation process based on the present studies. The results indicated that the degradation process of the electrical field was similar to the full immersion, with the main difference being the degradation rate. The electrical field can obviously accelerate the TSA degradation process. The degradation had progressed to the core of the sample, …

Sulfate Resistance Study Of Carbonated Low-Calcium Silicate Systems, Raikhan Tokpatayeva, Jan Olek, Jitendra Jain, Anuj Seth, Nicholas Decristofaro

International Conference on Durability of Concrete Structures

This paper summarizes the results of sulfate resistance study of carbonated mortar specimens made with Solidia CementÔ (SC) and tested for expansion according to ASTM C1012 specification while exposed to three types of soak solutions: sodium sulfate, magnesium sulfate and deionized water. A control set of ordinary portland cement (OPC) mortars was also evaluated. Besides the length change measurements, visual observations of changes in the appearance of specimens were conducted after various lengths of exposure. In addition, microstructural characterization of the specimens was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) techniques. …

Freeze-Thaw Resistance Of Concrete: Insight From Microstructural Properties, Sam Adu-Amankwah, Leon Black Dr, M Zajac, J Skoceck, M Ben Haha

International Conference on Durability of Concrete Structures

Composite cements offer low carbon alternatives to conventional CEM I. These binders also generally tend to perform better than CEM I in aggressive chemical environments. However, their freeze-thaw resistance, evident through surface scaling and internal damage is usually impaired. Postulated theories on freeze-thaw induced damage do not fully explain the origin of this weakness in composite cement concretes.

This paper systematically presents the phase assemblage changes associated with the freeze-thaw of concrete specimen made from composite cements with and without limestone. The freeze-thaw test was performed on concrete according to CIF method based on CEN/TR 15177 and the corresponding cement …

Investigation On The Influence Of Concrete Pores On Steel Corrosion Process, Xiaowen Zhang, Yuxi Zhao

International Conference on Durability of Concrete Structures

Concrete pores on the steel/concrete interface have a great influence on the corrosion process of steel bars. The effects of these pores on the corrosion of steel bars are observed and explored in this paper. The specimens which are in the same size and concrete proportion but have a different curing and exposure history are compared and investigated. This paper mainly observes the process of corrosion products filling into macro pores (10-4-10-2m in diameter) which including compaction pores (10-3-10-2m in diameter) and air voids (10-4-10-3 m in diameter). These pores have different effect on the steel corrosion process, and these …

Effect Of Corrosion And Corrosion Rate On The Mechanical Performance Of Carbon And Stainless Steel Reinforcing Bars, Hailong Wang, Xiaoyan Sun, Hangting Kong

International Conference on Durability of Concrete Structures

Steel corrosion is a predominant factor leading to age-related structural degradation. To understand the different effects of pitting corrosion on the mechanical performances of deformed carbon and stainless steel reinforcing bars, an artificially accelerated method was conducted to corrode the steel bars. Using a 3D laser scanner, the three-dimensional models of corroded steel bars were reconstructed. The corrosion characterization was identified based on these 3D profiles. The results indicate that the number and the depth of corrosion pits of both types of steel increase with the increase of corrosion rate, however the pitting corrosion of stainless steel is much more …

Sustainable Concrete With Seawater And Corrosion Resistant Reinforcement: Results Of Monitoring Of Corrosion Behaviour, Elena Redaelli, Maddalena Carsana, Federica Lollini, Matteo Gastaldi, Forood Torabian Isfahani

International Conference on Durability of Concrete Structures

The use of seawater for mixing concrete for reinforced concrete structures is prohibited, since it can promote steel corrosion. However, the use of seawater would contribute to decrease the environmental impact of concrete, in particular in those regions of the world where potable water is a precious resource. The project SEACON-INFRAVATION between University of Miami and Politecnico di Milano, with various industrial partners, aims at investigating the use of seawater for the construction of sustainable and durable reinforced concrete structures and infrastructures. Within the project, that included a vast campaign of laboratory tests, also two demo projects – one in …

Experimental And Numerical Investigation On The Irregularity Of Carbonation Depth Of Concrete Under Supercritical Condition, Hao Bao Masc, Min Yu Dr., Jianqiao Ye Dr., Lihua Xu Dr., Yin Chi Dr., J Ye

International Conference on Durability of Concrete Structures

The heterogeneity of a cement-based material results in a random spatial distribution of carbonation depth, which may significantly affect the mechanical properties and durability of the material. Currently, there is a lack of both experimental and numerical investigations aiming at a statistical understanding of this important phenomenon. This paper presents both experimental and numerical supercritical carbonation test results of concrete blocks. The random fields of porosity and two-dimension random aggregate model of concrete were proposed for the simulation. The carbonation depths are measured and distributed along the carbonation boundary by the proposed rapid image processing technique, which are then statistically …

Interactions Between Reinforcement Corrosion And Chloride Ion Diffusion In Mortar, Chun-Tao Chen Prof., Yi-Chieh Chuang, Chieh-Hao Wu, Chin-Wei Hsu

International Conference on Durability of Concrete Structures

This study explored the diffusion of the chloride ions influenced by the reinforcement corrosion in the mortar. It is believed that, during the corroding process, a small current is generated at the surface of the reinforcement. Such current is supposed to influence the diffusion of the chloride ions, but the relationship between both was not well studied in the literature. In this study, the corroded reinforcements were prepared by applied currents. Reinforced mortar specimens with w/c of 0.6 were then prepared and cured by either salt or fresh water. Results showed that the chloride ion distribution was likely associated with …

Influence Of Cracks On The Carbonation Resistance Of Concrete Structures, Abbas Al-Ameeri Mr., Muhammed Imran Rafiq Dr., Orania Tsioulo Dr.

International Conference on Durability of Concrete Structures

Carbonation-induced corrosion of steel rebar embedded in concrete is one of the major issues influencing durability of reinforced concrete structures. It has been acknowledged that structural cracks in concrete influences the carbon dioxide (CO₂) diffusivity and accelerates the carbonation-induced reinforcement corrosion, however most of the previous studies on the carbonation induced corrosion have concentrated on the un-cracked / unloaded concrete. This study investigates the impact of cracks caused by loading on the depth of carbonation into concrete. Concrete prisms (100x100x500 mm) were subjected to four different crack widths (0, 0.05-0.15 mm, 0.15-0.25 mm and 0.25-0.35 mm) and the …