Specificity of Deformation and Strength Behavior of Massive Elements of Concrete Structures in a Medium with Low Humidity

Koryun Karapetyan

• Publisher: Butterworth-Heinemann
• Year: 2019
• Print ISBN: 9780128180273
• eBook ISBN: 9780128154335
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Specificity of Deformation and Strength Behavior of Massive Elements of Concrete Structures in a Medium with Low Humidity discusses the influence of weather conditions, the density of the structure, and how these elements, along with others, affect the concrete curing process. It explores the effects of climate in all phases of construction, its impact on the rheological properties of concretes, and the carrying capacity of compressed concrete and reinforced concrete elements. In addition, it provides the methods to determine the basic heterogeneity of mechanical properties of concrete structures and novel calculation methods for concrete columns and reinforced concrete beams.- Includes new, more accurate design calculation methods for predicting the reliability of concrete structures in hot and dry environments- Actively investigates the behavior of basic physical and mechanical properties of concrete structures- Includes data collected over 18 years of research on the dynamics of strength and deformation of concrete structures

Chapter 1

Strength and deformability of concrete matured in different temperature and humidity conditions. Desorption processes and resistance to deformation and destruction of concrete elements

Abstract

It is known that the classification of moisture in a material, including concrete, is based on the intensity of energy, which depends on a disturbance or restoring of certain forms of bonds between moisture and the material. Based on this, these bonds can be divided into the following three groups:

• A chemical bond.

• A physical-chemical bond.

• A physical-mechanical bond.

The chemical bond of water in concrete is caused by the chemical reaction of cement hydration. At the same time, a certain amount of water is irrevocably (directly) included in the formation of crystalline hydrates in concrete. The intensity of energy of this form of bond is very high and can be broken only by chemical exposure or by calcination.

The physical-chemical bond of water in concrete arises as a result of dispersion or dissolution of cement grains in water with the formation of ion-dispersed and molecular-dispersed solutions. The main reason for this bond formation is the molecular force field. For concrete, the bond is a bond of medium intensity, which can be destroyed by water evaporation for a fairly long time

Keywords

Chemical bond; Mechanical bond; Crystallization structure; Shrinkage deformation; Creep deformation; Hydrotechnical structures

It is known that the classification of moisture in a material, including concrete, is based on the intensity of energy, which depends on a disturbance or restoring of certain forms of bonds between moisture and the material. Based on this, these bonds can be divided into the following three groups [2, 3]:

• • A chemical bond.
• • A physical-chemical bond.
• • A physical-mechanical bond.

The chemical bond of water in concrete is caused by the chemical reaction of cement hydration. At the same time, a certain amount of water is irrevocably (directly) included in the formation of crystalline hydrates in concrete. The intensity of energy of this form of bond is very high and can be broken only by chemical exposure or by calcination.

The physical-chemical bond of water in concrete arises as a result of dispersion or dissolution of cement grains in water with the formation of ion-dispersed and molecular-dispersed solutions. The main reason for this bond formation is the molecular force field. Concrete bond has medium intensity that can break down as a result of the evaporation of water for a sufficiently long time.

The physical-mechanical bond in concrete is carried out in indefinite quantitative relationships. Chemically unbound (free) water refers to this bonding form; it is contained in the pores of the crystallization structure as well as in the macro- and microcapillaries of concrete. In this case, water is retained in concrete due to both mechanical bonding and adsorption forces. The physical-mechanical bond in concrete is weak enough, and it can be easily disturbed by evaporation or artificial creation of internal, mostly capillary pressure.

Concrete and reinforced concrete structures erected in regions with climatic conditions of low humidity as well as hydrotechnical structures or their separate elements during operation are subjected to a cyclic influence of moisture processes. As a result, adsorption of moisture into the pores and capillaries of concrete and its desorption take place alternately. It is believed that the changes in the strength and elastic characteristics of concrete, caused only by the content of the chemically unbound moisture in them, can be very significant [4].

The phenomena of shrinkage and creep are characteristic for all types of concrete.

The manifestation of concrete shrinkage is due to the physico-chemical processes that occur during the hydration of cement, the change in the moisture content of the cement stone during its moisture loss, and carbonization, so it is accepted to divide shrinkage into terms due to contraction, carbonization, and moisture [2].

Contraction shrinkage, developing mostly at a very early age of concrete, almost continues until the completion of the hydration process of cement. In this case, the course of its intensity is largely influenced by the chemical composition of cement and the degree of its grinding as well as the initial ratio between the masses of cement and water in the mixture [5, 6].

Studies of carbonation shrinkage of concrete show that the intensity of its development depends significantly on the scale factor [7, 8].

The humidity shrinkage of concrete, the development of which is directly related to the disturbance of the hygrometric equilibrium in the pores of cement stone and in the surrounding medium [9, 10], depends on a number of technological and physical factors.

The mineralogical composition and fineness of cement grinding, the kind of aggregate and its granulometric composition [12], the content of cement in concrete [10, 11], the value of the water-cement ratio W/С [12, 13], the age of the material [2], the cross-sectional dimensions of the elements under investigation [2, 14, 15], the humidity surrounding the environment [2], and other factors have a significant effect on the value of moisture shrinkage of solutions and concretes [11, 13].

The physical nature of the moisture shrinkage of concrete has been studied insufficiently, which is proved by the existence of various hypotheses aimed to explain this phenomenon [2, 16].

There is an opinion according to which capillary phenomena serve as the main reason for the development of moisture shrinkage of concrete [9]. Some researchers [8, 17] explain shrinkage by the removal of intercrystalline water, while others [10, 13] explain shrinkage with volumetric changes in the gel structural composition of the cement stone caused by changes in the adsorption water content of the gel.

A number of researchers believe that all the above factors participate in the development of moisture shrinkage of concrete, and each of them plays a certai...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Introduction
• Chapter 1: Strength and deformability of concrete matured in different temperature and humidity conditions. Desorption processes and resistance to deformation and destruction of concrete elements
• Chapter 2: Deformable properties and strength of concrete in various zones of the cross-section of mass structural elements, being in the medium with low humidity
• Chapter 3: Influence of natural aging on the behavior of strength and deformation properties of concrete along the cross-section of structural elements
• Chapter 4: Creep of concrete elements under time-varying stresses. Stress relaxation in concrete elements
• Chapter 5: Some remarks on the features of the deformative dissimilar resistance of concrete elements to tension and compression
• Index