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Mechanisms of Concrete Deterioration
Published in Satish Chandra, Yoshihiko Ohama, in Concrete, 2020
Three types of alkali-aggregate reaction can occur: Alkali-silica reactionAlkali-carbonate reaction3. Alkali-silicate reaction
Aggregates
Published in M. Rashad Islam, Civil Engineering Materials, 2020
Alkali-aggregate reaction is the expansive reaction that occurs in PCC between alkali (available in cement) and silica (available in aggregates). In the presence of moisture, the alkalis found in cement break down the silica in the aggregate, producing an expansive gel. This expansion causes tensile forces in PCC, leading to loss of strength and resulting in map or pattern cracking, shown in Figure 2.13. This reaction can be controlled by: Avoiding susceptible aggregates, such as siliceous limestone, chert, shale, volcanic glass, synthetic glass, sandstone, opaline rocks, and quartzite. River rocks are sometimes susceptible.By using the pozzolanic admixture, as the silica contained in a pozzolan may react with the alkali in the cement, leaving less alkali available for the silica within the aggregate.Using low-alkali cementLowering the water–cement ratio, which limits the supply of water to the alkali–silica gel formation.
Actions during service
Published in Geert De Schutter, Damage to Concrete Structures, 2017
Depending on the unstable aggregate phases, two main types of alkali aggregate reaction can be defined: alkali silica reaction (ASR) and alkali carbonate reaction (ACR). While ACR is less common in practice, and thus causes considerably fewer damage cases, ASR is very relevant in many parts of the world and results in a high number of severely attacked structures and important economical losses (Swamy 1992).
Identification of Corroded Cracks in Reinforced Concrete Based on Deep Learning SCNet Model
Published in Research in Nondestructive Evaluation, 2022
Ying Xu, Xuelei Jiang, Tianrui Zhang, Gan Jin
In deep learning, several networks with high recognition rate benefit from their huge and real sample sets. Meanwhile, the accuracy and quality of image features directly affect the training and testing of the subsequent models. The data set of the collected images is divided into three categories: reinforced concrete corrosion cracks, other causes of concrete cracks, and complete concrete. Other causes of concrete cracks are mainly divided into plastic shrinkage cracks, structural cracks, temperature cracks, and cracks caused by alkali aggregate reaction. Plastic shrinkage cracks refer to the irregular crack or parallel crack of concrete perpendicular to the longitudinal reinforcement. The structural cracks or temperature cracks normally occur when the external load or the uneven force caused by temperature difference exceeds the bearing capacity of concrete, with irregular shape and no color change on the structure surface. Alkaline aggregate reaction crack is caused by expansion and compression around the aggregate, which is characterized by surface concrete mesh cracking, besides transparent or yellowish gel precipitation.
Innovative and sustainable operation and maintenance of bridges
Published in Structure and Infrastructure Engineering, 2020
For concrete structures, the CPP shall detail deterioration mechanisms and the strategies that will be used to mitigate deterioration and ensure that service life requirements are met. For reinforced concrete structures, the following deterioration mechanisms are often considered:Alkali Aggregate Reaction (AAR);Sulphate attack;Delayed Ettringite Formation (DEF);Freeze-thaw;Carbonation induced corrosion;Chloride induced corrosion.
Diagnosis of durability-related problems in concrete structures through comprehensive analysis and non-destructive testing: a case study
Published in Journal of Structural Integrity and Maintenance, 2023
Mati Ullah Shah, Muhammad Usman, Rao Arsalan Khushnood, Asad Hanif
The durability of concrete has always received special consideration among researchers from the very beginning and is still a research hotspot. To resolve issues in concrete infrastructure-related durability, significant contributions have been made by researchers around the globe. The durability-related issues in concrete include alkali-aggregate reaction (Helmuth et al., 1993), sulfate attack (Collepardi, 2003), freeze–thaw effect (Tang et al., 2015), corrosion of embedded steel (Bamforth et al., 1997; Kim et al., 2021), carbonation (Lollini & Redaelli, 2021), salt weathering (Thaulow & Sahu, 2004), leaching of calcium hydroxide (CH) (Metha & Monteiro, n.d.), excessive drying shrinkage and abrasion (Kumar et al., 2016; Saidmurodov et al., 2022). These problems manifest in concrete due to environmental factors, ingredients containing deleterious components and mechanical loadings (Tang et al., 2015). In the developed world, durability-based design guidelines have been developed to minimize the durability-related detrimental effects on infrastructures (Li, 2011). Besides these durability-based design philosophies, several mathematical models have been developed to predict the behavior of concrete during service life (Altmann & Mechtcherine, 2013). However, in developing and under-developing countries, the story is total opposite because there is a lack of data and knowledge for the identification of durability-related issues in these regions. Researchers in these regions not only need to focus on the current durability-related hotspot research topics but also need to give attention to the regional durability-related issues.