Concrete stone manufacture

Preface

The development of factory-made concrete units has not kept pace with the development of field-made concrete in mass. Factory conditions are obviously more easily controlled than field conditions and standardization of factory methods and of factory products should therefore be the more readily attained. There is little disposition in any quarter seriously to question the commercial and economic value of properly made concrete building units, and the failure of concrete stone manufacture, as an industry, to develop gigantic proportions can be attributed to nothing else than to the fact that too many individual enterprises have had inadequate managerial and mechanical equipment.

Failures are a necessary part of success. The failures in the field of concrete products manufacture have at least justified the assertion, that, simple as the industry's processes have seemed, they are of a nature demanding skill, judgment and thoroughgoing workmanship. To have discovered even so little as this is to have made a beginning in the way of success.

Many have gone forward much further; some have turned failure into success and there are very few who have not learned through bitter experience. Those who have paid the most dearly for their knowledge are the most generous in giving it away. They have appreciated that ultimate success is built upon public confidence and that public confidence is won for a product when its percentage of failure is low. They have seen that they cannot, in a broad sense, succeed in any way more surely than through the success of others. They are themselves but units in the structure of an industry.

It is this modern spirit of co-operation that makes this book possible. I am indebted to hundreds of manufacturers of concrete products whose letters to Concrete- Cement Age have helped to standardize methods in the field of concrete stone manufacture. They have written frank inquiries and acknowledgments of failure and as frank responses to inquiry and detailed explanations of successful practice. I am especially indebted to those leaders in the industry who have contributed valuable articles and discussions to Concrere-Cement Age which have been drawn upon for much material, as acknowledged in the various chapters ; and to the numerous manufacturers who have made me welcome in their factories. I am particularly grateful for and make special acknowledgment of the valued service of J. H. Libberton, Principal Assistant Engineer of the Information Bureau of the Universal Portland Cement Co., Chicago; P. E. McAllister, Manager of the O. C. Barber Concrete Co., Barberton, Ohio; Henry P. Warner, President and Manager of the Onondaga Litholite Co., Syracuse, N. Y., and members of the staff of Concrete-Cement Age generally. Each of these read a great deal of this book in proof and made valuable suggestions. Of particular value have been the suggestions by Mr. Libberton on Surfaces, by Mr. McAllister on Plant Equipment and by Mr Warner on Sand Cast Stone manufacture.

This book comes from the field. It has been my pleasure to make it, so to speak, a report of progress. It is to be hoped that its influence may in some degree discourage efforts in concrete stone manufacture by those incompetent to add something to the sum of progress in that industry, and that it will be the means of putting many others in the possession of such information, developed in successful work, as will lend impetus and direction to important industrial growth.

Harvey Whipple.

January 5, 1915.

Chapters

Pages

The Development of Concrete Building

Units 7-13

Location, Equipment, Layout 14-48

— Materials, Mixtures, Manipulation 49-68

Curing 69-85

Surfaces 118-154

— Shop Records and Cost Keeping 155-166

— Building Regulations — Tests — Specifications 167-182

Selling the Products 183-196

Examples of Layout and Operation 197-247

Index, Page 2J+8

Chapter 1 — The Development of Concrete Building Units

The manufacture of concrete building units is old enough to be the father of the automobile industry, and there are walls of concrete block which were well on in years when the first reinforced concrete building was erected. Examine the record of the progress of the automobile and of reinforced concrete. Examine a similar record of the pre-cast concrete building unit. The development of the automobile and that of the reinforced concrete building have required the closest application, study and investigation on the part of trained men. At the outset, these men have been trained in the sense only that they appreciated the fundamental things involved. Their application, study and investigation constituted the training. The important element in any such development lies in an initial comprehension of the fact that skill — the product of application, study, investigation — is an essential in the undertaking.

The "Block Business" has been handicapped in its development by the apparent simplicity of the operations and the problems involved. A gravel bank, a block machine and a shovel — with a little cement — scarcely form an array to tempt either capital or skill. Yet there was some block machine to meet the limitations revealed by any purse and to reveal its own limitations only in the course in which time tells everything. There was also the allurement of "easy money" to be made in an industry for which any man's woodshed afforded ample space and facilities.

Of the thousands who "went into the block business" on these easy terms there are many remaining. The aspect of their route to achievement by assured simplicity and directness has materially changed for most of them. Those for whom this cheerful aspect of the industry has not changed remain to be swept aside by popular disapproval. Hundreds of men of the better

Fig. 2 — Concrete Window Tracery, Memorial Church, Fall River, Mass. — Emerson & Norris Co.

fibre, promptly disillusioned as to what they might accomplish^ discarded this and that machine; tried one method, rejected it and tried another; tested, investigated, studied and kept at it. Other men were eventually drawn to the industry because they came to see in it, not any man's backyard occupation, but an enterprise worthy of the investment of their capital, their skill and their mettle, because they saw the possibilities and the rewards of real achievements.

The manufacture of concrete building units, considered as an industry, is coming into a position of dignity and importance through the opportunity which it affords alike to capital and to competency. The incompetent putterer has been a drag on the industry. Between his works and those of his able, discriminating and thorough competitor, the public has not yet completely learned to choose. The pasty looking, porous "cement block"

Fig. 3 — Entrance and Window Trim of Concrete Stone, Broadway Presbyterian Church, New York City — Onondaga Lltholite Co.

has been in the majority. Because of it, the real concrete unit, structurally sound and architecturally beautiful, made but sorry progress. Yet the factory-made concrete block of quality has made its impression — has been seen

and used and appreciated at somewhere near its best. Its progress has been slow. It has had to make its way against the prejudices created by unworthy products. It has had to combat that conservatism which requires of a new material proof of quality far beyond that which is expected in the materials with which builders are already acquainted. The concrete block has suffered in being acclaimed a cheap material. It has suffered through the ignorance of human nature which caused it to be urged as a substitute and an imitation, rather than as a material having its own distinctive and superior qualities, its own individual and characteristic charm to commend it to the serious and appreciative consideration of people of sufficient judgment to recognize and value these things.

But there have been pioneers and stalwarts in the industry, men who have come up with it from the beginning and grown with it, and others whose investments of money and skill and study have been drawn into the industry by its show of most promising development along

DEVELOPMENT OF CONCRETE UNITS U

Fig. 5 — Two-Family Concrete Block Cottage at Dunbarton, Scotland.

lines which made it worthy of their best efforts. To all of these will be due the future of the factory-made concrete unit, the synthetic stone, to which Nature has contributed a wealth of beautiful and durable raw materials for man to combine in a beautiful and durable finished product.

And while we shall consider more in detail the various lines in which this manufactured stone is to be developed, in order that it may serve at a maximum of usefulness, it seems important here in these introductory considerations to dwell upon the fact that there is propriety in products of different qualities suited to the fulfillment of different purposes.

The best of concrete stone cannot be made to sell at the lowest price. What is true of practically every product is true also of concrete. The fact doubtless marks the limitations — at least the present limitations — in the development of equipment for use in concrete stone manufacture. Improvements are sure to come. It will doubtless develop that the best of concrete stone, structurally, can be made at a price as low as that of some relatively poor products of today. It is certain to come, because proof of it is already evident, that even the cheapest commercial products of concrete are to be of much better quality from an architectural standpoint. Yet the concrete building unit is a product so far superior, even at something less than its best, to the materials which

Fig. 6 — Concrete Veneer Block in Garage, New Bedford, Mass. — Sturtevant & Hook.

have gone into the walls of the moderate-priced houses of the past, that it must be developed for this broad field of work. While the best of concrete stone, at from one dollar to four dollars per cu. ft., will be specified in place of granite, marble and limestone, where these materials were once required, there is the other field — the largest field — requiring an attractive wall unit at from 15 cts. to 25 cts. per sq. ft. in the wall thickness ordinarily required. This field is the one in which the greatest development must come — is now coming, in providing something better from every possible viewpoint than can now be had at any price competing with concrete. Architects want this new unit; they know that it can be produced, that it is being produced, for walls which are structurally sound and architecturally beautiful.

A proper development in concrete stone manufacture depends upon a study of the market, upon skillful workmanship, economical operation and competent management; upon a utilization of the best available materials and equipment in preference to makeshifts and clumsy, expensive manual labor; it depends emphatically upon artistic perception, upon an appreciation of the demands of the public for materials which shall give beautiful results at a moderate cost, because economy cannot remain synonomous with ugliness ; and lastly, the development of concrete stone manufacture depends upon the develop-

Fig. 7 — Interior of Residence Concrete Stone, New Haven, Conn. — New England Stone Co.

ment of salesmanship. Successful salesmanship must be backed by all the other factors of success already mentioned. It is the affair of the salesman to project, to focus upon the screen for public recognition, the results of the factory efficiency; and in this, his greatest asset is something to show, an example of work well done, an achievement in building for beauty and for posterity.

Chapter 2 — Location, Equipment, Layout

A prospective manufacturer of concrete products should not accept any location for his enterprise. He should seek a location. It is common to look near at hand. A local opening, however, should not be mistaken for a local opportunity. Every community doubtless requires one hardware store, surely one grocery. Careful investigation will reveal a need or lack of need for a concrete products factory. The same inquiry which is to determine what opportunity there is for the development of a successful manufactory of concrete building units in a small town will serve in selecting a city location. In the latter instance the investigation will merely be more complex and the factors making for success or failure less readily discovered. The locality should, in short, have either a friendly aspect or it should reveal possibilities for being made friendly.

The choice of a general location involves two important considerations:

1. The market for the product.

2. The availability of suitable raw materials.

Many things influence the market. It may be overcrowded, either with products similar to those which it is proposed to manufacture, or with competing products. If it is the concrete products of other factories which are to be met there may be public prejudices to be overcome. If the other concrete products on the market are of high quality the prospects are much better than they would be if the other concrete products were inferior and had been used only in erecting structures which stand as poor advertisements of the material. If the prospective manufacturer sets out to compete with good materials he appropriates some of their established reputation for merit, for his own product.

If it is the competition of local stone or brick of low price which is to be met, there must be a full and careful consideration of the way in which that competition

LOCATION OF PLANT

L5 is to be handled. Is the concrete product to be offered for structural and architectural merit and sold at a price very nearly equal to or even more than that of the other products— as is done successfully in some few cases — or is the concrete product to be offered for structural value only, with no attempt to make it with architectural qualities of pleasing color, texture and finish ? In short, is the concrete product to be offered to the public for exposed walls and trim or for foundations and structural walls which are to be given a covering of stucco or some other veneer, or for the walls of such dwellings and other buildings as are believed to be without any claim upon the right to be attractive, while still economical?

If the prospective manufacturer is to set himself up in a locality where the uses of concrete products have in the past been only in those lines of work last mentioned, he has this situation to combat in his first efforts, unless it is his purpose to serve the same class of building enterprise. If his predecessors have made concrete block of poor quality and have stood sponsor, for instance, for their use in construction where the interior plastering has been applied direct on the block and dampness and dissatisfaction have followed as they frequently do — then the prospective manufacturer should at least discover the truth of the situation and be prepared to face and to answer the community's established prejudices.

To make a good unit — a sound unit — for unpretentious work, or for work where quality and economy must serve together, is a worthy enterprise. It is an enterprise which in most localities can be carried forward with no unit more successfully than with concrete block. But to make a cheap unit — with the emphasis all on that feature — is an unworthy enterprise. It is an enterprise which, in the end, must be unsuccessful, for the reason that where the prime motive is cheapness, quality cannot remain. Eventually, the "cheap unit" will be found to have been dearly bought at a paltry price.

If, then, the aspect is unfriendly, the prospective manufacturer must either look elsewhere or be prepared to lay siege. He must have more capital to invest in a campaign of education, and by slow methods, by the con-

PROCESSES stant insistence of a superior building unit, he must build up his business.

The general aspects of a locality do not, however, include all of the factors which make a locality desirable. The market will be influenced by the local building regulations. If these hold difficulties, they may not be serious difficulties. The regulations may be inadequate, or they may be too severe. Consider well the possibility of securing the enforcement of building regulations which may be counted upon to discourage manufacturers of poor products and which at the same time will be fair in their recognition of good products.

The situation as to raw materials is also to be investigated thoroughly.

/Are there local materials of good quality to be had at a price which will insure a profit on the character of concrete stone to be manufactured?

What are the local haulage problems ? What are the facilities for the receipt of materials by rail or by team haul or by boat? Raw materials can be transported a considerable distance and profits still be insured. But the exact nature of the situation should nevertheless be known in advance. In one instance a location where delivery can be made by boat, makes possible a saving of 50% in the price of sand. An idea of possible conditions to be met in this regard will be gained from the chapter on Examples of Layout and Operation. It is usually the case that the raw materials can be transported with greater economy than the finished products.

Processes — General

In a survey of the field in which he looks to find a market for concrete building units, the prospective manufacturer will be confronted very early in his investigations by the necessity for a choice as to the general process which he is to adopt and as to the character of his product. He will have discovered the local conditions as to available raw materials. He will know something of the preferences of local architects and builders. He will have learned the cost and quality of the native

TYPES OF EQUIPMENT building materials. There are three processes among which to choose. He may be prompted in his choice by some previous experience of his own or of others, or the initial investment required will in many cases influence him in a decision. In a general way the difference in the three processes is chiefly in the amount of water used in the mixture of materials which go to make the concrete. A little more, a little less water in the mix, and the limitation has been found for any one of the three ways of molding concrete. The consistency of the mixture determines the way in which that mixture must be manipulated. Not only is it true that a higher or a lower percentage of water in the mixture finds one of the chief points of difference among the three lines of equipment, but it is also true that a little less water than can be successfully manipulated in the equipment of the line which uses the least water is almost sure to result in a poor concrete product, and a little more water than should be used in the process requiring the most water will likewise give an unsatisfactory result. However, the matter of consistency of mixture is properly considered in connection with the materials which make up the mixture and these subjects are taken up in the succeeding chapter.

The prospective manufacturer, having decided upon a suitable location for his factory, and having at least a general idea as to what the nature of his product is to be, must consider the plan and the extent of his factory. The plan or layout will, in great measure, depend upon the process of manufacture and the type of equipment to be utilized. The whole scheme centers in the molding equipment. The choice must be among these three : The so-called "dry-tamp" machine; the pressure machine, each of which involves the use of a small number of mold boxes in which the mixture is quickly molded and quickly released to be taken away to "cure;" or the poured process, involving a relatively large number of molds in which the concrete unit must remain until the cement has set so that the unit can be handled.

Good building units, suitable for creditable construction and showing qualities under tests for both strength is

TYPES OF EQUIPMENT and absorption which are satisfactory under rigorous building regulations, can be made and are made with each one of the three types of equipment. Not only are products by all three processes showing structural value, but they all have architectural merit. These statements do not hold for all the products of all three types of equipment^ nor for all the products of any one of the three. Nor can it be said that all the equipment offered the public in any one of these lines is equally desirable.

If the prospective manufacturer has convictions as to the desirability of a concrete mixture of a certain consistency, he should not proceed in the selection of equipment with the idea that all the equipment in one line has precisely the same limitations in the manipulation of that mixture of concrete. Wetter concrete can be used in some machines of the dry-tamp class than in others. Further, he should consider the fact that a given consistency will be obtained with more or less water, depending upon the materials used. Crushed stone usually takes more moisture for a given degree of plasticity than gravel and this is but one of the variations to be encountered in the consistency of mixture.

Eventually each products manufacturer must face the truth: that having exercised reasonable care in the selection of equipment of any general type, it is up to his ability and his integrity to produce sound concrete units.

A block machine or a machine for the production of any of the standard building units is designed to attain a few simple results. The machine must provide a box in which the product is molded, holding the concrete mass rigidly in shape while pressure is applied or blows dealt by a tamper. The machine must also attain a simple release of the product from the mold without injury when the compacting is completed. These are the two chief requirements of molding machinery.

Machines are utilized in producing units which are either tamped or pressed. Tamped products are also produced in commercially standard molds of metal or in special molds of metal, wood or plaster.

"Block machines" as commonly understood are not involved in wet process manufacture. The wet process

DRY-TAMP EQUIPMENT makes use of molds of metal, wood, plaster, gelatin and sand.

Dry-Tamp Equipment

The dry-tamp equipment has been in most general use. That it has been abused ean scarcely be too often repeated. That its use has been many times misrepresented by its salesmen cannot be denied. That its improper use is frequently due to the failure of some users to grasp and apply the first essentials of good concrete, is still evident. Its operation requires that the concrete mixture be placed in the mold box and tamped to a condition of maximum density. The tamping may be done by hand, or with pneumatic tools, or by power-driven machinery mounted above the mold box.

Hand Tamping — In hand tamping everything depends upon the operator. The point is frequently made that

Fig. 8 — Common Type of Double-End Hand Tamp in hand tamping the work is thoroughly done in the morning and not so thoroughly done in the afternoon. It is only natural to suppose that the operator will relax slightly as the day grows old, that his blows are less frequent, and that not only does his output decrease but its quality shows some loss. It cannot be denied, however, that a good workman forms a certain habit in his manipulation of the tamper and that the force of this habit is in the main strong enough in many cases more than to make up the difference between the morning freshness and the afternoon weariness.

A man wielding a hand tamp at maximum efficiency may do good work, and with the exercise of unusual judgment in his work, can do work as well as a machine, though considerably less of it.

Pneumatic Tamping — Pneumatic tampers are used in products manufacture. Their use is probably more common in Europe than in this country. Manufacturers

MACHINE TAMPING using them find that operators must become accustomed to their continuous jarring and vibration, which because of great rapidity of action are at first very tiring. Accustomed to their use, the operator has in a degree acquired some of the unrelaxing quality of a machine and may be expected to accomplish as much and accomplish it as well at the end as at the beginning of the day.

Fig. 9 — Power Tamper Operating in Connection with Brick Machine, Equipped with Device for Handling Facing Material

Machine Tamping — Machine tamping with well built equipment is the same in the afternoon as in the morning. Its work is uniform, its capacity undiminished by fatigue, and its output is rapid. Tampers have several feet at the ends of plungers so arranged as to fit the type of machine in use, striking the concrete blows of equal force and compressive value over the entire open area of the mold. The plungers are so adjusted as to be responsive to the depth of material in the mold box, the length of stroke varying as the mold box is filled.

PRESSURE MACHINES

Pressure Machines

The application of pressure in compacting concrete is accomplished in both hand and power-driven equipment. Pressure machines are made for the exertion of mechanical pressure by hand or power and other machines are hydraulic in their application of pressure.

Fig. 10 — Hand Operated, Double End, Pressure Block Machine

When the mold box is in position as at right, it is filled; if a faced block is to be made, the backing material is struck off to a depth of and the facing material put in and struck off. The box is then rolled to the center under the pressure head, and the pressure is applied by means of the toggles, operated by a hand lever; the levers are released, the box is rolled back to its first position, a pallet applied on top and clamped and the box turned over. It is shown turning at the left end of the machine in the illustration. It is released face downward on a pallet, and supported by the framework shown under the mold box, from which it is carried away

In their operation it is generally possible to use a wetter mixture than can be successfully manipulated under most machines which rely upon tamping in securing density. Too wet a mixture in a dry-tamp machine will be displaced by tampers rather than compacted. In pressure machines the compacting force is exerted evenly over the entire area of the mold box^ and displacement is impossible. Opponents of pressure equipment maintain that in applying this pressure evenly over the entire

WET PROCESS area of the mold box, the sand, cement and aggregate are hindered in slipping into the most dense condition, by an arching action between pieces of aggregate. This claim is based chiefly upon theory and proof by satisfactory tests is lacking. The tendency in this direction would, undoubtedly, vary with the nature of the materials used, as for instance, rounded pebbles are in most cases less likely to set up an arching action than crushed stone. The consistency of the mix and the percentage of excess of mortar over voids in the aggregate would in great measure be controlling factors. The proponents of pressure machinery maintain that the tremendous mechanical or hydraulic force exerted drives the cement, sand and aggregate into a mass more dense than can ordinarily be obtained under tamping.

Wet Process

There is no denial from makers of any of the types of block machines that more water than is used in mixtures either under tamping or under pressure has a remarkable tendency to obtain density in the concrete product. Water causes the materials in the mix to flow together so that each small particle seeks out the space of smallest compass in which it can be contained. Yet too wet a mix with no means for removing the excess makes a porous concrete. The manufacturing problems, however, among which choice is to be made, place upon the side of the tamp and the pressure processes, rapidity of operation with a minimum of molds. The molded product is momentarily released and the mold is ready to repeat the operation. The molding equipment Is in small area and the products are carried away from the equipment almost immediately.

The wet process involves either the use of a very large number of individual molds in which the product must remain scattered over a large casting area for from 12 hrs. to 48 hrs. or else it involves the use of molds set up in such a way that they may be conveyed to a curing place when they are filled. In the method first mentioned the mixed concrete must be moved about over a

TYPES OF PRODUCT

%3 relatively large shop area and in this case the manufacturer must ordinarily resort to the use of some means of keeping the wet mixture constantly agitated to prevent a separation of cement from sand or mortar from stone. It is obvious that the tendency in a very wet mixture at rest in any kind of container would be for the stone to settle, so that when poured out of the receptacle it would lack homogeneity, the stone and sand and cement in extreme cases being deposited in layers. A means for agitating the mixture, in fact a means for supplemental mixing after the concrete has been discharged from the mixer proper, is generally regarded as essential.

This is obviated only when a means is provided for conveying the molds to the mixture, filling them as the mixer is discharged, and moving the molds away again when they have been filled. It should not be lost sight of that whatever means is adopted to secure density, subsequent to combining and mixing the materials — whether by tamping or pressing or pouring into molds, no amount of tamping or pressing or care in pouring and puddling will give a dense product unless the most scrupulous care has been exercised in the choice, the grading and the mixture of materials. The most skilfully designed block machine, the most vigorous and thorough tamping, the most powerful exertion of pressure, are quite useless in the manufacture of a good product if the mixture put into the mold is lacking in those qualities (considered in the succeeding chapter) which make for density and strength. No concrete block machine has yet been devised which is fool-proof.