Cement

principles of production and use

Friedrich W. Locher

• Publisher: Bau + Technik
• Year: 2013
• ISBN:
  9783764005368
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

The successful launch of the German standard work on cement by Prof. Locher in 2000 is now being followed by the publication of the widely requested English language version "Cement" which takes special country-specific features and standards into account.The book is aimed at chemists, physicists, engineers and technologists in the cement industry, in machine construction, the construction industry, materials testing and environmental protection. This clear and practical book will provide them with the understanding of the chemistry of cement needed for their daily work. It will also make an ideal textbook for the study of building materials science at colleges and universities.

1 Classification of cements

1.1 Definition

Cement is a hydraulic binder, i.e. an inorganic, non-metallic, finely ground substance which, after mixing with water, sets and hardens independently as a result of chemical reactions with the mixing water and, after hardening, it retains its strength and stability even under water. The most important area of application is therefore the production of mortar and concrete, i.e. the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects. The difference between mortar and concrete is governed by the particle size of the aggregate, which in mortar has a maximum value of about 4 mm and in concrete can be as large as 32 mm but in special cases may be smaller or larger.

Hydraulic hardening is caused primarily by the formation of calcium silicate hydrates. Cements therefore consist of those substances, or mixtures of substances which, through reaction with the mixing water, form calcium silicate hydrates sufficiently rapidly in a quantity sufficient to provide strength and durability. However, other compounds, e.g. calcium aluminates, may also participate in the hardening process.

In contrast to these silicate cements the high-alumina cements consist predominantly of calcium aluminates. Their hardening is based on the formation of calcium aluminate hydrates.

1.2 European and German standard cements

1.2.1 General

In practically all countries there are standards for cement as a basic material for the production of mortar and concrete. Differences in economic and industrial development, in raw material deposits and in climatic conditions have led to the development of different construction materials and methods of construction in the different countries, and hence also to different types of cement. There are therefore also substantial differences in the national cement standards which, among other things, also affect the specifications for the durability of concretes produced from the cements.

In Europe the work on compiling the technical basis for a European cement standard has been in progress since 1975. The emphasis was initially on consistent test methods, which are listed in EN 196 [D 42]. A Europe-wide consistent designation of the types of cement, their compositions and cement strength classes was defined in the standard EN 197-1:2000 [E 26]. This was based on all the cements with calcium silicate hardening which are produced in the countries of central and western Europe for general use [A 19]. Cements with additional special properties (special cements) and cements with different hardening mechanisms are to be dealt with in further parts of this standard [E 26, S 193]. Of the 27 cements in EN 197-1 only 12 cements were included initially in the German cement standard DIN 1164 (October 1994) [D 51]. These 12 cements were included because they had already proved successful with regard to the durability of concretes produced from them. Since 1^st April 2001 the European cement standard designated DIN EN 197-1:2000 (Feb. 2001) has had the status of a German standard. It therefore replaces DIN 1164-1 (Oct. 1994). The use of the cements specified in the new standard DIN EN 197-1 is regulated by DIN EN 206-1 and DIN 1045-2 [D 44, D 49, w 2] (Section 1.2.4).

1.2.2 Constituents of the European and German standard cements

Cement constituents defined in DIN EN 197-1:2000 (Feb. 2001) [D 43] are:

1. Portland cement clinker (K)

2. Granulated blastfurnace slag (S)

3. Pozzolanic material (P and Q)

4. Fly ash (V and W)

5. Burnt shale (T)

6. Limestone (L, LL)

7. Silica fume (D)

8. Minor additional constituents

9. Calcium sulfate

10. Additives

The constituents of cement are sub-divided into main and minor additional constituents [E 26, D 51]. Main constituents are the substances listed under 1 to 7, provided their content in the cement exceeds 5 % by mass. Minor additional constituents can be all the substances listed under 1 to 8, provided they have a maximum content of 5 % by mass in the cement, as well as inorganic mineral substances from clinker production. The data concerning the cement composition, and also concerning the proportions of calcium sulfate and additives, always relate to the total of all main and minor additional constituents in the cement without taking the calcium sulfate and additives into account.

1. Portland cement clinker (K)

Portland cement clinker is also known as cement clinker or just clinker. At least twothirds of it consists of the two calcium silicates, namely tri- and di-calcium silicate, which are richest in CaO and can react with the mixing water and harden reasonably rapidly. It is therefore a hydraulic substance.

2. Granulated blastfurnace slag (S)

Granulated blastfurnace slag is a granulated, rapidly cooled, and therefore predominantly glassy, basic blastfurnace slag. It is a latent hydraulic substance because it reacts only slowly with water, but when mixed with activators, such as cement clinker, it reacts and hardens relatively rapidly with the formation of calcium silicate hydrates. It must consist of at least two-thirds by mass of glassy slag and at least two-thirds of CaO, MgO and SiO₂.

3. Pozzolanic material (P and Q)

Pozzolanic materials are natural or industrial substances which, because of their content of reactive silicon dioxide, SiO₂, react when finely ground in the presence of water at normal ambient temperature with dissolved calcium hydroxide, form calcium silicate hydrates, and as a result can harden hydraulically. Reactive silicon dioxide, which is present either as free SiO₂ or combined in aluminosilicates, is therefore essential for the pozzolanic hardening. Calcium aluminate hydrates, which can also contribute to the strength formation, are therefore also formed. The proportion of reactive CaO is unimportant. The content of reactive SiO₂ content must be at least 25 % by mass.

Although fly ash and silica fume have pozzolanic properties they are dealt with separately in Sections 4 and 7.

Natural pozzolanas (P) are usually materials of volcanic origin or sedimentary rock of suitable chemical and mineralogical composition. This also includes trass as defined in DIN 51043 [D 64].

Industrial pozzolanas (Q) can be thermally treated and activated clays and shales, and aircooled slags from the extraction of lead, copper or zinc, provided they contain sufficient concentrations of reactive SiO₂.

4. Fly ash (V and W)

Fly ash is obtained by electrostatic or mechanical precipitation of dust particles from the exhaust gases from furnaces. It may only be used for cement production if it comes from a furnace fired with pulverized coal. The fly ash is either an aluminosilicate or a calcium silicate depending on how the silicon dioxide is chemically combined. Because of the content of reactive silicon dioxide both types have pozzol...

Table of contents

• Deckblatt
• Titelseite
• Impressum
• Foreword
• Table of Contents
• 1 Classification of cements
• 2 History of cement
• 3 Cement clinker
• 4 Other main constituents
• 5 Grinding the cement
• 6 Environmental protection during the manufacture of cement
• 7 Cement hardening
• 8 Constitution and properties of hardened cement paste
• 9 Standard cements with special properties, special cements
• 10 Environmental compatibility of cement and concrete
• 11 Literature
• 12 Index
• 13 Chemical Formulae