Concrete with Hydraulic Binders

4.1.1 Introduction

Concrete is a composite material of a cement-based matrix, which is produced by mixing water and a binder, and particles of aggregate.

The binder normally consists of hydraulic cement or cement and additions. The aggregates are granular material, specifically sand and crushed or rounded rock particles. Usually, other components, in smaller amount, known as admixtures, also make part of the concrete, with the aim of improving some characteristics of the concrete. This material, with those constituents, is very versatile both in terms of the characteristics it can have and the applications it can be used for.

This versatility contributes to make concrete the most used construction material in Portugal and most of the world. Among the reasons the use of concrete is so widespread compared with alternative materials such as steel, one can cite the following: its components are economically competitive and available in many different areas of the globe; its application requires little energy, and it has good resistance against both structural and environmental actions; the different structural elements can be moulded easily into different shapes and sizes.

In light of the large number and diverse nature of its components, concrete can have very varied characteristics, which allows it to meet a wide range of requirements. These may be related to the consistency of the concrete, which ranges from dry to very fluid, or its compressive strength, which can range from 0.5 MPa to more than 800 MPa. This wide range of values is difficult to achieve with any other material.

The production of concrete, especially at construction sites, is not carried out under so controlled conditions as other construction materials, such as steel. Producing good concrete requires a set of precautions to be taken. “Bad” con­crete—with inadequate consistency, excess voids and a very heterogeneous struc­ture—is produced using exactly the same constituents as good concrete. The difference is in knowing and understanding the phenomena that govern its behaviour.

When asking what makes a good concrete, there are two criteria to consider: concrete should satisfactorily meet, on the one hand, the requirements of mixing, transport and casting while it is fresh and, on the other, the requirements for when it is in its hardened state. When fresh, concrete should have a consistency that allows it to be compacted by the means planned without excessive force, and it should have a composition that is resistant to segregation during transport and laying so that the concrete element is homogeneous throughout. The main requirements of good concrete when hardened are appropriate mechanical strength, deformability and durability [1].

Updated: 24 августа, 2015 — 3:39 пп