Autogenous Shrinkage of Concrete: A Comprehensive Guide

Autogenous shrinkage is a complex and often overlooked phenomenon that can have a significant impact on the durability and longevity of concrete structures. This comprehensive guide will delve into the causes, consequences, and mitigation strategies of autogenous shrinkage, empowering you to make informed decisions to ensure the integrity of your concrete structures.

Autogenous shrinkage is a form of internal volume reduction that occurs in concrete due to chemical reactions, without the influence of external factors such as evaporation or temperature changes. These chemical reactions, primarily involving the hydration of cement, lead to the formation of hydration products that occupy a smaller volume than the original cement particles. This reduction in volume results in the shrinkage of the concrete.

The primary cause of autogenous shrinkage is the hydration of cement, which involves the reaction of cement particles with water to form hydration products such as calcium-silicate-hydrate (C-S-H) and calcium hydroxide (CH). These hydration products occupy a smaller volume than the original cement particles, leading to a decrease in the volume of the concrete.

Autogenous Shrinkage of Concrete

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Other factors that can contribute to autogenous shrinkage include:

• High cement content: Concrete with a higher cement content will experience greater autogenous shrinkage due to the increased amount of hydration reactions.
• Low water-to-cement ratio: A lower water-to-cement ratio results in a denser concrete with less capillary porosity, which restricts the movement of water and can lead to increased autogenous shrinkage.
• Rapid hydration: Rapid hydration, typically due to high temperatures, can accelerate the formation of hydration products and exacerbate autogenous shrinkage.
• Use of supplementary cementitious materials: Materials like fly ash and slag can influence the hydration process and affect the extent of autogenous shrinkage.

Autogenous shrinkage can have several adverse consequences on concrete structures, including:

• Cracking: If autogenous shrinkage exceeds the concrete's tensile capacity, it can lead to the formation of cracks. These cracks can compromise the structural integrity and durability of the concrete.
• Loss of prestress: In prestressed concrete structures, autogenous shrinkage can cause a loss of prestress, reducing the load-bearing capacity and increasing the risk of failure.
• Reduced durability: Cracked concrete is more susceptible to moisture penetration and corrosion, leading to reduced durability and a shorter service life.
• Aesthetic concerns: Cracks caused by autogenous shrinkage can detract from the aesthetic appearance of concrete structures.

Several strategies can be employed to mitigate the effects of autogenous shrinkage and ensure the longevity of concrete structures:

• Use low-shrinkage cement: Cements specifically designed for low shrinkage are available and can help reduce autogenous shrinkage.
• Control cement content: Optimizing the cement content to meet the required strength requirements can minimize autogenous shrinkage.
• Use water-reducing admixtures: Admixtures that reduce the amount of water required for a given workability can help mitigate autogenous shrinkage.
• Provide adequate curing: Proper curing practices, such as keeping the concrete moist, can slow down the hydration process and reduce autogenous shrinkage.
• Consider shrinkage-compensating concrete: This type of concrete contains expansive admixtures that counteract autogenous shrinkage and minimize the risk of cracking.
• Use internal curing: Internal curing techniques, such as the use of saturated lightweight aggregates, can provide additional moisture to the concrete and reduce autogenous shrinkage.
• Monitor and manage temperature: Controlling the temperature during concrete placement and curing can help prevent rapid hydration and excessive autogenous shrinkage.

Autogenous shrinkage is a complex phenomenon that can significantly impact the performance of concrete structures. By understanding the causes, consequences, and mitigation strategies, you can effectively address autogenous shrinkage and ensure the durability and longevity of your concrete projects. Remember, proper planning, careful material selection, and diligent construction practices are crucial to maximizing the resilience of concrete structures against autogenous shrinkage.

Autogenous Shrinkage of Concrete

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Language	:	English
File size	:	24082 KB
Print length	:	424 pages

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