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9. Topics in Hardened Concrete

The chapter delves into the various physical and mechanical properties of hardened concrete, encompassing its strength, elasticity, creep, shrinkage, permeability, durability, fire resistance, and chemical attacks. It discusses testing methods and presents modern concrete types such as high-performance, fiber-reinforced, and self-compacting concrete, emphasizing their applications. Understanding these properties and behaviors is crucial for optimizing concrete's structural integrity and longevity.

Sections

Topics in Hardened Concrete

This section explores various aspects of hardened concrete, focusing on its physical properties, mechanical characteristics, and factors influencing these traits.

9 Section Overview

Start current section content and materials

9.1 Strength of Hardened Concrete

This section delves into the strength characteristics of hardened concrete, focusing on compressive, tensile, and flexural strengths, along with factors influencing these properties.

9.1.1 Compressive Strength

Compressive strength is the ability of hardened concrete to resist axial loads, crucial for structural performance.

9.1.2 Tensile Strength

Tensile strength refers to concrete's ability to resist axial tensile loads, crucial for preventing cracking in structural elements.

9.1.3 Flexural Strength

Flexural strength measures concrete’s resistance to bending, crucial for structures such as road slabs and beams.

9.2 Elastic Properties

This section covers the elastic properties of hardened concrete, focusing on its modulus of elasticity and Poisson's ratio, which are critical for understanding the material's stiffness and strain response.

9.2.1 Modulus of Elasticity (E)

The Modulus of Elasticity (E) describes the stiffness of concrete, determining how it deforms under stress.

9.2.2 Poisson’s Ratio (μ)

Poisson's Ratio measures the ratio of lateral strain to axial strain in concrete, typically ranging from 0.15 to 0.20.

9.3 Creep of Concrete

Creep of concrete refers to the gradual and time-dependent increase in strain under sustained load, influenced by several factors such as water-cement ratio and temperature.

9.4 Shrinkage in Concrete

Shrinkage in concrete is critical as it affects the material's integrity and durability, primarily occurring in different forms such as plastic, drying, autogenous, and carbonation shrinkage.

9.5 Permeability of Concrete

Permeability of concrete refers to the ease with which fluids can penetrate the material, impacting its durability and structural integrity.

9.6 Durability of Concrete

This section explores the durability of concrete, focusing on its ability to withstand various deteriorating processes and the major issues that can affect its longevity.

9.7 Thermal Properties of Concrete

This section discusses the thermal properties of concrete, focusing on thermal conductivity, thermal expansion, and the heat of hydration.

9.8 Fire Resistance

Concrete is naturally fire-resistant due to its non-combustible properties, though it can suffer structural damage from high temperatures.

9.9 Microstructure of Hardened Concrete

The microstructure of hardened concrete is critical for understanding its durability and mechanical properties, including the roles of hydrated cement paste, capillary pores, and the transition zone.

9.10 Testing of Hardened Concrete

This section discusses various methods for testing hardened concrete, highlighting both destructive and non-destructive testing techniques.

9.11 Surface Hardness and Abrasion Resistance

This section discusses the importance of surface hardness and abrasion resistance of hardened concrete, essential for pavements and industrial floors.

9.12 Volume Changes and Cracking

This section discusses the causes of volume changes in hardened concrete and the resulting types of cracks.

9.13 Chemical Attack on Concrete

This section discusses various chemical attacks that can compromise the durability of concrete, including sulfate attacks, acid attacks, and alkali-aggregate reactions.

9.13.1 Sulfate Attack

Sulfate attack on concrete leads to deterioration due to expansive reactions with sulfates present in water or soil, causing structural failures.

9.13.2 Acid Attack

This section discusses how acid attacks can deteriorate concrete's durability and structural integrity.

9.13.3 Alkali-Aggregate Reaction (AAR)

Alkali-Aggregate Reaction (AAR) involves the chemical reaction between alkalis in cement and reactive siliceous aggregates, leading to expansion and cracking in concrete.

9.14 Carbonation of Concrete

Carbonation of concrete involves a chemical reaction between atmospheric CO₂ and calcium hydroxide in concrete, which reduces the protection of reinforcement steel from corrosion.

9.15 Corrosion of Reinforcement in Concrete

This section discusses the causes, mechanisms, and prevention strategies related to the corrosion of reinforcement in concrete structures.

9.16 Fiber Reinforced Concrete (FRC)

Fiber Reinforced Concrete (FRC) incorporates fibrous materials to enhance the structural performance of concrete.

9.17 High-Performance Concrete (HPC) and Ultra-High Performance Concrete (UHPC)

HPC and UHPC are advanced forms of concrete designed for increased durability, strength, and workability.

9.17.1 High-Performance Concrete (HPC)

High-Performance Concrete (HPC) possesses improved strength, durability, and workability compared to traditional concrete, making it suitable for demanding applications.

9.17.2 Ultra-High Performance Concrete (UHPC)

Ultra-High Performance Concrete (UHPC) is a specialized type of concrete characterized by its exceptional strength and durability, primarily used in demanding structural applications.

9.18 Self-Compacting Concrete (SCC)

Self-Compacting Concrete (SCC) is a type of concrete that flows under its own weight, eliminating the need for mechanical vibration.

9.19 Recycled Aggregate Concrete (RAC)

Recycled Aggregate Concrete (RAC) refers to concrete produced using crushed concrete waste as aggregate, promoting environmental sustainability.

9.20 Testing Advanced Properties of Hardened Concrete

This section discusses various advanced testing methods for analyzing the properties of hardened concrete, ensuring its structural integrity and performance.

9.20.1 Petrographic Analysis

Petrographic analysis involves the microscopic examination of concrete's composition to diagnose causes of cracking and deterioration.

9.20.2 Thermogravimetric Analysis (TGA)

Thermogravimetric Analysis (TGA) is a technique used to measure changes in mass as a function of temperature, providing insights into the hydration products of concrete.

9.20.3 Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry (DSC) is a technique used to study thermal properties, specifically the exothermic and endothermic reactions occurring in hydrated cement paste.

9.20.4 X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR)

This section discusses the use of X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) as analytical techniques to characterize the phases present in hardened concrete and understand its hydration and deterioration mechanisms.

Learning Objectives

  • Concrete transitions to a rigid state upon hardening, which is essential for its structural function.

  • Key properties of hardened concrete include compressive strength, tensile strength, and flexural strength, which are influenced by factors like the water-cement ratio and curing conditions.

  • Durability issues such as chemical attacks and corrosion can significantly affect concrete's lifespan and require specific preventive measures.

Key Concepts

Compressive Strength

The ability of concrete to withstand axial compressive loads without failure.

Creep

A gradual, time-dependent increase in strain under sustained load, affecting the long-term deformation of concrete.

Tensile Strength

Resilience of concrete against axial tensile loads, crucial for various structural applications.

Permeability

The ease with which fluids can penetrate concrete, affecting its durability and susceptibility to damage.

Durability

The ability of concrete to withstand weathering, chemical attacks, and other deteriorative processes throughout its service life.

Fiber Reinforced Concrete (FRC)

Concrete that incorporates fibrous materials to enhance structural integrity and performance.

Practice Exercises

Total Questions

2

Estimated Time

4 min

Passing Score

70%

Instructions

  • Read each question carefully
  • You can use hints if you need help
  • Complete all questions before submitting
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