SECTION I

PRELIMINARY INFORMATION

FOR THE

CEMENT AND CONCRETE USER

CHAPTER I

INTRODUCTORY

The Renaissance of Concrete.-The Concrete Age.-Concrete Architecture.-Concrete Literature.-The Future of Concrete.

The Renaissance of Concrete. The history of concrete is a history of an ancient and highly developed art, long lost and forgotten during the dark centuries of the middle ages, and having a new awakening and renaissance nearly two thousand years later. Some of the costly and magnificent structures of concrete built by the Romans during the period of their supremacy still remain as time-defying evidence of their great skill as constructors, and as monuments to the utilitarian character of their art. As a seed planted in an arid soil springs to life at the first visiting of rain, so has concrete been born anew in the twentieth century when the state of industrial and constructive art became favorable to its development; and with such new life, it has reached a much higher state of development, and attained a wider application and a more permanent place in our civilization than was ever dreamed of by our Roman predecessors.

How broadly concrete has entered into our modern lives has been well put by Kerwin in an address before the National Association of Cement Users in the following words:

The Concrete Age.-"Our ancestors progressed from the Stone Age to the Iron Age; we seem to be passing from the Steel Age to the Cement Stone or Concrete Age. We tread on concrete walks, travel in concrete subways, over concrete bridges, live and work in

concrete buildings, store our grain in concrete elevators, draw our water from concrete reservoirs and cisterns, sanitate our cities with concrete sewers, and are finally buried in concrete cases deposited in concrete tombs, and our numerous virtues are inscribed on concrete monuments."

It is certainly well that this development has come at a time when our rapidly disappearing forests have given serious alarm as to our future supply of timber, and what a boon the concrete industry will be to humanity and civilization throughout the world, cannot be appreciated so well to-day as it will years hence when the supply of timber has fallen far below the normal requirements.

Mr. Andrew Carnegie is probably best known as a philanthropist interested in education and free libraries, but it should not be forgotten that he is also probably the greatest living authority on questions relating to the production of steel, and that any statement made by him relating to the position of steel should carry great weight.

At the recent conference of governors and scientists at the White House, Washington, which was held under the chairmanship of exPresident Roosevelt, there was a discussion on the conservation of the natural resources of the United States, in the course of which Mr. Carnegie, speaking of iron, said:

"The next great use of iron is in construction, especially of buildings and bridges. Fortunately the use of concrete, simple and reinforced, is already reducing the consumption of structural steel. The materials for cement and concrete abound in every part of the country; and while the arts of making and using them are still in their infancy, the products promise to become superior to steel and stone in strength, durability and convenience, and economy and use."

For a great steelmaker to announce his conviction that concrete promises to become superior to steel and stone in strength, durability, convenience, and economy, is indeed a matter that should claim the attention of our economists.

The period of the most rapid development of the concrete industry was inaugurated when the value of the combination of steel and concrete was recognized. This combination, fortunate as Carnegie says, opened up a field of unlimited usefulness and gave

to our civilization a new material, possessing nearly all the virtues of the materials hitherto employed in construction and few of their defects, and so superior in strength, heat-resisting, and other qualities as to make its universal adoption a matter of certainty.

Concrete Architecture. It was at first these utilitarian qualities that were recognized and made use of by engineers, but another great step forward was taken when the artistic and æsthetic possibilities of concrete were recognized by architects and builders.

The recognition thus accorded has given the latter what it had sought almost in vain for centuries-a new style of architecture; a style entirely free from the hereditary tendencies of the ancient . and mediæval styles, and which could be rendered possible only by the introduction of a new material, possessing properties entirely distinct from those whose possibilities had been studied and studied for ages. The essential features of the new style, which will be distinctive of the early years of the present century, are pointed out under the section on Concrete Architecture.

Concrete Literature.-Another potent influence in the modern development of concrete work is the broad-mindedness and liberality of the manufacturers of cement and cement products, in bringing home to the public the many marked advantages and possible uses of cement and concrete. Foremost in this class are the many publications of the Atlas Portland Cement Co., the excellence of which, from a typographical, authoritative, and readable standpoint, cannot be overestimated, and in the preparation of this volume the Authors have availed themselves of the Company's kindness in permitting them to extract a number of excellent tables and illustrations from their various publications.

The excellent series of bulletins issued by the American Association of Portland Cement Manufacturers are another source by means of which a wide dissemination of knowledge of the possibilities of cement has been effected, and from which the Authors have drawn some valuable material.

A great deal has been contributed to the industry by the numerous organizations formed for the promotion of knowledge on cement and concrete work. The cement shows held in various parts of the country during the past few years have also given an acceleration to the development of the industry. The proceedings of the

National Association of Cement Users at their Conventions during these shows have been brimful of new ideas and their annual bulletins have preserved the best of these for future reading and study. The Authors have also used these books in drawing material for this volume.

The cement and concrete press of the country have done a great work in spreading widely the gospel of concrete, defending it against attacks by its older but worried competitors and keeping the building public informed of the latest developments in this rapidly growing field.

The Future of Concrete.-Many other influences have contributed to the growth of the concrete industry and these are discussed in the appropriate sections of the book. No doubt the future will witness many new contributing causes, and there is every reason for believing that the future holds out the most brilliant prospect for this apparently homely but invaluable building material.

We can prophesy that future ages will be grateful to the present one for the renaissance of concrete, for with it, as time goes on, will come more beauty in our structures, more healthful conditions of life resulting from the sanitary nature of the material, more buildings of historic fame, and temples far more creditable to our architecture; for when the present monumental structures of timber, steel, and iron shall have succumbed to the corroding hand of time, our concrete structures, built of more enduring stuff, will still live and endure to tell the story of the rebirth of concrete in the twentieth century.

CHAPTER II

.KINDS OF CEMENT AND HOW THEY ARE MADE

Common Lime.-Lime Mortar.-Hydraulic Lime.—Puzzuolana.-Hydraulic Cements. —Theory of Setting.-How Natural Cement is Made.-How Portland Cement is Made.-White Portland Cement.-Slag Cements.-Plaster Cements.-Choice of Cements. How Portland Cement Comes.

LIMES and cements which are used to unite brick, stone, and concrete are nearly all derived from the roasting of pure and impure limestones and can be grouped into three classes.

1. Common, fat, or quick lime, which hardens in air.

2. Hydraulic lime, which hardens in air when slaked, and sets on the addition of water, either when exposed to the air or submerged.

3. Hydraulic cement, which, when water is added, sets either in air or under water and acquires great strength.

Common Lime.-Common lime is a combination of calcium and oxygen, and is obtained by driving off carbon dioxide gas from limestone. When it contains not more than about 12 per cent of impurities, it has the property of absorbing water with great avidity.

The process of absorption of water is accompanied by a great rise of temperature, by the evolution of hot and slightly caustic vapors, and finally by the reduction of the lime to a powder. The powder thus formed is called slaked lime, and the operation of adding water to quicklime is thus known as slaking.

Good lime comes in hard lumps, and contains but little dust. When slaked, its bulk increases from 2% to 31⁄2 times its original volume, while the amount of water which it will absorb is nearly 1/4 of its weight.

When just enough water is added to lime to cause it to slake, it forms a powder; when more water is added it forms a paste. Lime mortar is made by mixing the paste of slaked lime with sand, and is extensively used in the building trades.

The ordinary method of slaking lime consists in first placing the lumps in a layer, 6 or 8 inches deep, in either a water-tight box,