Civil Engineering Commons^™

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 …

Emerging Rapid Aggregate And Concrete Test Methods For Formulating Asr-Resistant Concrete, Anol Mukhopadhyay, Kai-Wei Liu

International Conference on Durability of Concrete Structures

The main objective of this study was to develop rapid aggregate and concrete test methods and a combined innovative approach for formulating performance based ASR resistant concrete mixes. An innovative step by step approach has been developed to formulate ASR resistant concrete mixes based on four recommended steps. In step 1, determination of aggregate ASR composite activation energy (CAE) and threshold alkalinity (THA) by using a rapid aggregate chemical test called volumetric change measuring device (VCMD) is performed. The lower the CAE the higher the reactivity is. Based on the measured CAE and THA, mix design formulation is conducted in …

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 …

Influence Of Exposure Environments On The Durability Of Slag-Blended Cements, Joseph Onah Ukpata, P. A. M. Basheer, Leon Black

International Conference on Durability of Concrete Structures

Both chlorides and sulphates combine in seawater to affect the durability of reinforced concrete structures located in marine environments. This paper presents the results of an experimental study on slag blended cement systems, cured for 7 days, before exposure to a combined solution of sodium chloride (30 g/L) and sodium sulphate (3 g/L). Two slags of different chemical compositions, designated as slags 1 and 2 were respectively blended with Portland cement CEM I 52.5R at 30 and 70 wt.% replacement levels. Mechanical tests on mortar samples were complemented by microstructural examination and chemical characterisation on paste samples, all using a …

Mescopic Model Of Drying Shrinkage And Its Application Into Control Of Shrinkage Cracking, Toyoharu Nawa

International Conference on Durability of Concrete Structures

Concrete shrinks when it is subjected to drying, whenever its surfaces are exposed to air of a low relative humidity. In such a situation, cracking is to be expected, since there are various kinds of restraint that prevent concrete from contracting freely. Unless the ambient relative humidity is kept at close to 100%, such shrinkage cracking presents a critical problem in concrete construction, in particular for thin, flat structures such as walls and slabs in buildings, highway pavements, and bridge decks. This paper review the state of art of theory drying shrinkage from focus on the fact that microstructure in …

Fib Model Code 2020 – Durability Design And Through Life Management Of New And Existing Structures, Frank Papworth, S Matthews

International Conference on Durability of Concrete Structures

Work has recently started in fib (Fédération Internationale du Béton) on the preparation of a new fib Model Code for Concrete Structures, under the working title of Model Code 2020 (MC2020). This will be a single code dealing with both new and existing concrete structures, that is both the design of new structures and all the activities associated with the assessment, interventions and the through-life management and care of existing concrete structures. Numerous goals relating to durability and service life design have been identified, including that ideally MC2020 should incorporate:

• Better models for deterioration processes addressing issues such as …

Guiding Principles In Developing The South African Approach To Durability Index Testing Of Concrete, Yunus Ballim, Mark Alexander

International Conference on Durability of Concrete Structures

Focused thinking on the possibility of early-age testing of concrete for long-term durability started in earnest during the late 1980’s in South Africa. Through sustained research, development and trial implementation on construction projects, three durability index (DI) tests have emerged, two of which have been adopted as national standard test methods for concrete construction, the remaining one being prepared a national standard. In this paper we review the guiding or foundational principles that directed the development of these DI tests, with a view to assessing the appropriateness and relevance of these guiding principles to modern concretes. The last 30 years …

Service Life And Life-Cycle Assessment Of Reinforced Concrete With Fly Ash And Limestone Calcined Clay Cement, Ravindra Gettu, Radhakrishna G. Pillai, Manu Santhanam, Sundar Rathnarajan, Anusha Basavaraj, Sripriya Raju, Yuvaraj Dhandapani

International Conference on Durability of Concrete Structures

Environmental impact due to the emission of carbon dioxide during concrete production can be taken care by reducing the clinker content in the cement. The clinker content can be reduced by replacing it with fly ash and limestone calcined clay. Such systems can have a potential to exhibit enhanced durability/service life when exposed to chloride and carbon dioxide. However, estimating probabilistic service life of concretes with such alternative binder systems is difficult due to the lack of quantitative estimates of the input parameters such as chloride diffusion coefficient (D_Cl), ageing coefficient (m), carbonation coefficient (K_CO2), and …

Effect Of Mix Parameters On Strength Of Geopolymer Mortars - Experimental Study, Abdolhossein Naghizadeh, Stephen O. Ekolu

International Conference on Durability of Concrete Structures

In this article, an investigation is reported on development of strength in South African fly ash (FA) – based geopolymer mixtures. Locally available Class F, FA from one of the coal power stations was used in the investigation. The alkali-activator used consisted of sodium silicate (SS) and sodium hydroxide (SH) mixed in varied ratios of 1.0, 1.5, 2.0, 2.5 and 3.0 SS to SH. The SS of silicate modulus = 2.5 was used but the SH concentration in the activator was varied to 10, 12, 14M NaOH. Mortars of 2.25 aggregate/binder ratio were used to prepare 50 mm cubes. In …