Reinforced concrete buildings; a treatise on the history, patents, design and erection of the principal parts entering into a modern reinforced concrete building

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Preface

This little volume is presented to the engineering profession for the purpose of showing what reinforced concrete is, and how it came to be what it is. In deciding upon the scope of the book, the authors have endeavored to select matters of interest to the mature and experienced engineer, and for that reason the ultimate result of the analysis has been treated in greater detail than the derivation itself.

Many books on reinforced concrete have been written principally for the practical man or even for the untrained man; those :\ who approve of that tendency will not approve of this book, in ^ which all references to weights and dimensions, earth pressure, etc., have been avoided. The practicing engineer, the contractor, or even the college student should look for such matters in special '^"pocket books," and he must not expect the reinforced concrete book to furnish a complete encyclopedia on civil and hydraulic engineering.

On the other hand, much matter has been included in this book which will be looked for in vain in other works, and this is especially true of Part I, where an account of the history of reinforced concrete has been given, with special reference to the patents granted by the United States. Naturally, a selection of the more important or interesting patents is a difficult matter, and most likely some readers will find that too much has been included, and others that not enough has been included. However this may be, the records of the patent office contain on the whole more and better information than any other source, and the engineer who is striving to attain perfection cannot afford to relegate the most valuable thoughts tod results of his predecessors to the scrap heap. It is also hoped that inventors and patent attorneys may find matters of interest in the necessarily brief descriptions given; anybody wishing full information in regard to any patents may obtain copies for

• • Vll viii PREFACE

a nominal sum by addressing the Commissioner of Patents, Washington, D.C.

The theoretical analysis in Part II has been made as brief and concise as seemed consistent with its purpose; — the solutions of equations, etc., have usually been given after the premises have been stated, omitting all the intermediate steps. If this book should find its way into the classroom, the teacher can easily supply what is omitted; — the practical engineer would not stop to read a treatise on mathematics, in any case. The author believes that much of this is new and original, especially the use of two constants in the bending problem; the further development in Articles 34, 35, and 49, where the effect of an increase in depth of beam is discussed, and the analysis of stresses in given beams.

The entire chapter on Transverse Stresses and U-bars is original, and avoids the use (or mis-use) of the word ''shear." In reinforced concrete the steel is supposed to act in tension, and the U-bars must follow this general rule.

Part III is devoted to the practical construction. Here again more attention has been given to the useful facts not generally known, than to those that are matters of common knowledge. There is no necessity today for describing at great length the various types of buildings, or their component parts; an exception has however been made in regard to ''Unit Construction" which appears to be coming rapidly to the front. No effort has been made toward giving the details of form design, but the general principles have been stated with great care. The chapters on fireproofing and repairs should be of interest, and the superintendents' specifications have proved their own value on a number of large contracts. Immediately preceding this chapter we have placed a short account of some bad failures; while we have not been able to throw new light on the causes, we hope that the perusal of the chapter on "accidents" may put the reader in the proper frame of mind to not only read, but also follow, the instructions given in the last chapter.

It has been customary with other writers to describe in more or less detail the tests made on reinforced concrete beams. As a general principle we have avoided such discussions, partly because the plan of this book did not allow us to devote the required large number of pages, and partly because the vast majority of tests are of little value, not from want of ability or

PREFACE ix

care in the experimenters, but because the tests were not systematized, that is, every group should first demonstrate one general fact, and then individual test specimens should be so designed that they vary in only one feature from the standard, so that the effect of the variation at once becomes evident. The groups of tests so made are few indeed, and only during the last few years have clear photographs of the broken specimens been pubUshed. However, where a given problem requires the illustration of a test, the best available source has been referred to.

In this book an earnest effort has been made toward stating the truth when it was known, and to make it clear and evident that the truth is not known in a number of cases. The chapters relating to the mathematical design are so arranged that everyone can readily assure himself of the correctness, but in regard to such matters as cement testing, rolling of concrete floors while setting, and numerous other practical or general propositions where the authors have taken issue with prevailing ideas, and gone contrary to accepted practice, our statements must either be rejected as heresy or accepted as doctrine.

The authors desire to acknowledge their indebtedness to various papers published in the Engineering Record, the Engineering News, the American Machinist, and the Cement Age. Information has also been gained from a paper read by Geo. W. Percy before the San Francisco Chapter of the A.I.A. (Feb. 9, 1894); from C. W. Pasley's "Observations on Limes" (1847), from Hyatt's "Account of some Experiments" (1877); from papers by Scott, Bernays, and Grant, edited by James Forest as a separate volume under the name "Portland Cement" (1880); from "Reinforced Concrete in Factory Construction" by the Atlas Portland Cement Co., and in regard to theoretical questions, from works by Consid^re and Morsch. The author of Part II desires to emphasize the inspiration received from the study of these two authorities, who have contributed so much to the knowledge of the subject. The discovery of the *' water-marks" by Professor Turneaure has perhaps influenced the U-bar theory here advanced more than any other tests on record have.

The authors are greatly indebted to Professor L. J. Johnson, M. Am. Soc. C. E., for certain data relating to reinforced concrete beams tested at Harvard University. The results obtained are extremely important and will undoubtedly revolutionize

X PREFACE

current practice in regard to the simultaneous manufacture of beam and slab. Moreover, these tests confirm in a remarkable manner the theories advanced in Chapter VII, which were conceived and printed long before the test beams were designed.

Part I Contribution To The History Of Reinforced

CONCRETE CONSTRUCTION

CHAPTER PAGE

I Personal Reminiscence by Ernest L. Ransome ... 1

The invention of "Ransome Stone" in England, 1844. — Introduction in America in 1870. — Early work in Portland Cement Concrete on the Pacific Coast. — The invention of twisted bars (1884). — Reinforced Concrete Buildings in and near San Francisco. — Their behavior in the Earthquake. — The first "ribbed" floors (1889). — Effect of retempering of mortar and of continued mixing. — Rolling the floors. — Development of Sidewalk Lights. — Joining new and old concrete. — Concrete made fireproof by adding salt, waterproof by adding lime; effect of clay in the aggregates. — The Reinforced Concrete Belt Course, its use and advantages. — The Coil Joint for joining Lapping Bars. — Notes on falsework, the importance of standardization; floor core boxes; unit construction. — "Wet" and "Dry" concrete. — Injurious Agencies. — The growth of Reinforced Concrete Construction.

II Basic Patents, and a Short Survey of the Early History

OF THE Art by Alexis Saurbrey 18

Elements of invention. — Ancient use. — Early ideas of the properties of lime. — Smeaton's chemical analysis. — Discovery of "Roman Cement" and "Portland Cement."

The Period of Discovery 19

Cement testing a necessity. — Brunei's Reinforced Brick Arches (1834-1838) and Beams. — Pasley's Beams. — Ranger's patent and early works. — Early English patents. — Edward's Analysis and Patents. — Use of Reinforced Concrete in England, in Germany, in Holland, in France. — Early American patents. — Hyatt's patent of 1878.

The Period of Improvement 35

Recent Patents 40

xi xii CONTENTS

Part II Rational Design Of Reinforced Concrete Buildings

BY ALEXIS SAURBREY

CHAPTER PAGE

III Introduction 51

Definition; homogeneity; mutual relation of steel and concrete; assumptions; principles; thenecessity of "bond."

IV Adhesion 54

Laws; anchorage in beams; diameter of rod.

V Compression and Lateral Expansion 57

Laws; effect and necessity of hooping; calculation of plain and hooped columns; least diameter; practical considerations.

VI Bending 66

Notations. — Assumptions. — Design. — Slab Formulas. — T-beams. — Tile-Concrete-Construction. — Simplified Formulas for flat slabs. — Discussion of the tables; numerical examples. — Analysis of given beams; numerical examples.

VII Transverse Stresses 92

Is a concrete beam solid? — Effect of hair cracks. — Effect of large cracks. — Adjustment of stresses to meet the new condition in a cracked beam. — The U-bar as cantilever reinforcement. — Calculation. — Same result obtained in a simpler but less convincing manner. — The equilibrium curve must be approximated. — Moving and stationary loads. — How many bars should be bent up? — Anchorage a necessity for rational calculation. — Spacing of U-bars. — Shear must be considered as a component stress resulting from tension and compression acting simultaneously. — Frictional stresses. — Beams and slabs not monolithic. — Angle of friction. — That the same rule should be used whether beams are ca^ in one piece with the slab or not. — Tensile stresses disregarded. — The true assumption. — Details of reinforcement; the elements combined to one beam.

VIII Applications of the Bending Theory 109

Continuity. — Moment of Inertia; double reinforcement; Combined Bending and Compression ; a simple chimney formula; footings ; circular reinforcement in plates ; theory of plates.

DC Initial and Allowable Stresses 126

Setting in air; in water; wetting dry concrete; shrinkage; temperature stresses; expansion joints. — Assumptions; factor of safety; allowable stresses fixed by custom. — Columns, floors; other structures; actual safety.

CONTENTS xiii

Part III

PRACTICAL CONSTRUCTION BY ERNEST L. RANSOME

AND ALEXIS SAURBREY

CHAt»TER PAGE

X Materials of Construction 137

Cement : tests not reliable. — Storage and use. — Quick setting cement. — Samples; field tests of concrete. — Sand : tests; standard sand; specifications. — Stone: dust; run of crusher; separate piles; sizes used; furnace slag; boiler cinders, lime stone; sand stone; brick; shale; conglomerate. — Steel : plain bars; rerolled bars; deformed bars; wire mesh. — Tiles. — Concrete: Mixing; water used; deposited in forms; supervision; joints; cold and heat.

XI Floor Systems 152

Monolithic vs. Unit. — Design. — Monolithic Work. — Forms; reinforcement. — Unit Work. — Where used; the Ransome System.

XII Foundations 171

Brief description; piling.

XIII Finishing Operations 176

Corners; flat surfaces; plastering; brick and terra cotta; improved surfaces; tooling; rubbing; brushing; left unfinished. — Floor finish.

XIV Fireproofing AND Fires 183

Smoke and water. — Insurance. — Behavior of concrete; thickness required; protection of corners. — Salt retards attack of fire. — Bayonne fire. — Pittsburg, Baltimore, San Francisco. — Comparison between different methods.

XV Repairs to Existing Buildings 188

Cracks in floors; in beams; repairs of columns; cutting concrete; laitance; settling of footings; hardening soft concrete.

XVI Accidents 191

South Framingham; Long Beach; Rochester; Philadelphia; Annapolis; Saybrook; Cleveland. — Defective column- design. Three good rules.

XVII Superintendents Specifications 195

General; temporary offices and buildings, setting up plant, etc.; excavating and grading; molds; concrete; steel; finishing; acid joint.

xiv CONTENTS

XVIII The Engineer 200

Reinforced Concrete manufactured in situ. — Necessity for skillful manipulation. — Building Ordinances; in Cleveland; in Boston. — Uniform Regulations. — Injurious influences. — " Cost plus profit" Contract. — Lump Sum Contract. — Monthly estimates. — Qualifications of the Engineer. — Patents.

XIX The Theory of Beams as Illustrated by Tests . . . 207

Extensibili ty . — Shear Resistance . — Stirrups . — German Tests on T-Beams. — Author's Tests at Case School. — Professor Johnson's Tests at Harvard.

INDEX 233

Part I

A CONTRIBUTION TO THE HISTORY OF REINFORCED CONCRETE rp:ixforced concrete buildings

Chapter I Persoxal Remixiscexce

BY ERNEST L. RAXSOME

Whex, in 1859, I entered as an apprentice in my father's factory in Ipswich, England, the concrete industiy was in its infancy, and was confined largeh' to the manufacture of artificial stone for ornamental purpose. .One of the earliest applications of the new industry was invented in 1844 by my father Frederick Ransome, who was then engaged as superintendent of the well-kno\^Ti Iron Works of Ransomes and Sims at Ipsi^-ich. Noticing one daj' the waste of good hard stone in the dressing of mill-stones, he conceived the idea of cementing hard, selected pieces together, and so to manufacture a superior grade of burrstones. The first diflSculty was in finding a proper cementing substance: plaster of paris, shellac, glue, isinglass, lime with bullock's blood, mastic, etc., were tried and discarded. Among the numberless ingredients tried were also common glass, but it was not until experiments with soluble glass were made that success became probable. It occurred to him that if he took flint stones with a moderate amount of caustic alkali in solution, and subjected them to heat in a Papin's digester under high pressure, he might be able to concoct a soup from flint, as Papin had done from bones. But the result was apparently a disappointment, and in order to increase the heat, he finalh' tied the safety valve with a piece of \i4re, and forced the fire until the boiler became overheated. Fearing, however, that the boiler would blow up, he threw it out into a cistern \iith cold water, and the boiler, as might have been anticipated, was broken to pieces — and there, inside, was the glazy, syrupy mass of dissolved glass. The portions next to the walls of the boiler were baked to a flinty hard stone; in one word, the problem was solved.

Step by step, a process was now evolved whereby a cementing substance was had, as above described; and based upon this process, a large business was developed. Before long, the parent Company, ** Patent Concrete Stone Co.,'' was selling its product in all parts of the world, especially after methods had been invented whereby the stones were made not only hard but also weather-proof. This process consisted originally in the application of a solution of chloride of calcium to the silicate of soda previously used, whereby insoluble silicate of lime, and soluble chloride of sodium were formed by double decomposition. The latter is common cooking salt and was easily removed by washing.

A further experiment disclosed the fact that powdered magnesian limestone, mixed^ with a small quantity of silicate of soda, formed a very hard substance when submerged in a solution of chloride of calcium, in a very short time.

In America, the new process was introduced in 1870 by the Pacific Stone Company of San Francisco, of which Company I was the superintendent for four years. About this time, the concrete industry was in slow development on the Coast, based upon the use of imported Portland Cement; in 1874 I remember to have paid as much as nine dollars per barrel of cement. But even as late as 1882, the concrete construction was mainly utilized in foundations and arches suspended between iron beams. In the latter type of construction some trouble was experienced with the cracking of the concrete over the beams, and to overcome this tendency I patented, No. 263,579 (Figure 1), a con-

FlGURE 1.

struction in which an expansion-joint feature was introduced, and several sidewalks have been built over cellar areas in this manner.

Before long, I was called upon to devise a cheaper method of self-supporting sidewalks for the Masonic Hall at Stockton, Cal., and this I accomplished by using, instead of the I beams, a 2*^ round tie-bolt to carry the tension, while the concrete carried the compression. The rods had upset ends and large cast-iron washers at each end, and I soon found that the upsetting and threading of the ends, the nuts and washers, etc., made the cost of the finished rod exactly twice that of the plain rod. I looked around for means whereby a continuous tie or bond could be developed along the length of the rod, and even contemplated cutting a spiral groove in the rod, when suddenly the idea of twisting a square or rectangular bar entered my head. I happened to have a rubber band in my pocket, and the spiral thread became at once evident when the rubber band was twisted in the hand. My patent. No. 305,226 (Figure 2), was granted in 1884, and the mills were soon turning out twisted bars up to one inch square, at a cost of about ten dollars per ton for twisting. Larger bars they positively refused to tackle under the plea that the common lathes used for the purpose did not have the requisite strength. I had, however, in my yard an old concrete mixer equipped with a worm and wheel, and by modifying this arrangement I soon succeeded in twisting 2*^ square rods, using hand power. The cost did not exceed seventy-five cents per ton, and from that date until a more recent period, all the twisting was done in my own yards.

However, the introduction of the twisted iron was no easy matter, and when I presented my new invention to the technical society in California, I was simply laughed down, the concensus of opinion being that I ^ injured the iron. One gentleman kindly suggested that if I did not twist my iron so much I might not injure it seriously, in spite of all my references to the twisting of ropes and similar devices. This argument I based upon the supposed fibrous or laminated structure of the iron.

But all this criticism led to exhaustive tests, and when the professors found that my samples stood up better than the plain bars, one even went as far as to suggest that I had doctored my samples. This led me to twist half of each test rod only, and the superior strength of the cold twisted iron was finally admitted, and in due time, when steel became common, even better results were had with cold twisted steel. Even at this present time, I do not believe that the increase in strength due to the twisting has been accounted for. In this connection 1 call attention to an interesting fact first discovered by Professor Hesse, and that is, that bars tested at once after twisting do not give as good results as those tested five or more days after twisting, showing that a certain slow change takes place in the structure of the iron.

From the earliest time of my career I have experimented extensively with concrete mixers and other machinery, and the Ransome mixer is now a standard article. However, a description of these experiments would carry us too far, and might not interest the reader. Suffice it to say that my first patent for a concrete mixer was granted in 1884, to be followed by many more.

Up to about 1888 my work in reinforced concrete was largely confined to what we now term small and unimportant structures. The Bourn & Wise wine-cellar at St. Helena, Cal., was erected in 1888; the building is 75' X 400', three stories high, with stone walls. The main floor only was of reinforced concrete resting upon iron columns. The design is shown in Figure 3. The next floors were erected for the Calif ornian

Academy of Sciences in San Francisco, Figure 4; during construction these floors were subject to much adverse criticism from many architects, builders, and members of the Society, and efforts were made to have the fire wardens condemn the work. However, inspectors from the fire department found nothing about the construction that could be injured by fire, and having sense enough to perceive its great strength, they declined to take any action in the matter. To satisfy all skeptics in regard to the strength, a section of the second floor 15' X 22' was uniformly loaded with gravel to 415 lbs. per square foot; the deflection was 1'^. For the further satisfaction of the doubtful the load was left on for four weeks, but very few availed themselves of invitations to examine the work a second time. The few who came were, however, convinced.

The Leland Stanford Jr. Museum, at Palo Alto, Cal., was

M

* 1 fhfW^~^

V

Figure 4. — Academt of Sciences, San FBANCiaco

Reinforced Concrete Floors, Cast Iron Columna

Erected by Ernest L. Ransome

erected about this same time, and the entire wall and floor construction was of concrete, the walls having superficial joint lines as indicated in my patent, No. 405, 800, of 1889 {Figure 144A). The outside surface was partly tooled, and the whole was luilt in the classical design originally made for sand stone. The greatest innovation was, however, the roof, and this was probably the first instance on record where a finished and exposed roof was made entirely of concrete. The root was supported on iron trusses 10 ft. on centers and the concrete construction rested upon the iron rafters, as shown in Figure 5. The roof over the central pavilion is quite flat and is 46' X 56' in plan, reinforced with 2" twisted bars 60 ft. long and with a flat reinforced concrete dome panelled with 1' thick glass. In the same location the Girls Dormitory of the Stanford University was erected soon afterwards, and its three stories were completed in ninety days from the time the plans were ordered.

When, on April 18, 1906, San Francisco was destroyed by the earthquake, the buildings at Palo Alto suffered severe damage, in many cases beyond repairs. However, the old reinforced concrete buildings referred to above stood the test with little if any damage; see Bulletin No. 324 of the United States Geological Survey, pages 22, 23, 24, 75, 112-1 14.

It may be worth while to note that the addition to the Borax Works at Alameda, Ca!. (1889), was the first instance of the ribbed floor construction erected; it will be seen from Figure 6 that the construction is identically the same as used for that kind of floors today. The columns were also of concrete, probably the first ever erected.

I desire to express here my sincere gratitude to the men who, in those early times, had the confidence and foresight to r^lize the technical and commercial importance of the novel construction, often in the face of severe criticism and bitter attacks. Chief amongst these are my associate for many years, Mr. Frank M. Smith, Architect Percy and Governor Stanford, deceased.

Additional ' information in regard to the preceding buildings may be found in a paper " Concrete Construction," read by George W. Percy before the San Francisco Chapter of the American Institute of Architects, February 9, 1894.

In this paper reference is also made to my tests on delaying the placing of 1:2 mortar; the results are really astonishing. The tensile strength of briquettes made with Knight, Bevan, and Sturgess cement was as follows:

Delay in hours 1 2 2S 31 4i showing that a delay of 2\ to 3^ hours really gave the highest results. Similar tests with White's cement gave the best results with a delay of 1^ hours, after which the strength fell rapidly. In all these cases, the concrete was worked up again as soon as it stiffened. Unfortunately, these tests have never been extended to modem cement. However, in my address to the Society of American Architects, October 17, 1894, I called attention to the truly remarkable results obtained by Mr. Spencer Newberry, who found that a mixture 1 : 3 which, when worked for one minute with a trowel, developed a tensile strength of 87 lbs. in seven days, developed a strength of 240 lbs. in the same period after being worked with a trowel for five minutes. I also made experiments with continued mixing, keeping the concrete in the mill for as many as 1000 revolutions. I found that within this limit the strength of the concrete increased with the number of revolutions, so that concrete given 1000 turns in the mill was stronger than when it had had 700 revolutions only.' These observations led me to believe in the continued working of the concrete while it is settmg that is when makmg a slab I put men on with rollers who were instructed to keep the rollers going for se\eral hours The slab is laid on the forms m the usual manner as soon as the concrete is hard enough to carry a man the rolhnK begins and is earned on with two or

Figure 7. three sets of rollers of increasing weight until the rollers make no impression. A more handy method is to use hollow iron drums

filled with increasing amounts of water. It is important that the floors be not allowed to dry out too quickly, for which reason they may be sprinkled if necessary during rolling and kept moderately wet for at least one week more.

The construction of "illuminating panels" in concrete floors, or, as they are more commonly called, sidewalk lights, has captured the attention of inventors for many years. But owing to the unequal expansion of glass and iron, the great majority of such constructions embodying a combination of these two elements have not been satisfactory. My patents, No. 448,993 (1891), Figure 7, and 518,045 (1894), Figure 8, aimed to avoid

' It must here be noted that the mill used for this experiment was of a different type from those used today, the modem machines having a much more severe action. The danger in ovennixing is that the aggregate is ground very fine, thus giving a mortar with an excess of sand.

the use of the iron plate by setting the glasses in a body of reinforced concrete, and this was accomplished with great success. The Ransome Sidewalk Lights may be seen in every large city of the country, amongst other places the New York Subway, and my patents formed during their terms the basis for a large and prosperous industry.

One of the problems most troublesome to the reinforced concrete engineer is encountered in joining new concrete to old. A more or less suitable joint may be had in a number of ways, and from time to time I have given this problem much thought. A purely mechanical bond is created by bedding an open coil half way in the old concrete surface, so that the other half is caught in the new concrete, subsequently molded against the old surface, Patent No. 647,904 (Figure 9). This principle is utilized in the " unit " construction of reinforced concrete buildings according to my patent No. 694,577 (1902), Figure 10, and the tie thus made is so eflScient that the subsequently

/V iuuu\s molded slab may serve as the compression flange for the beam or girder erected ahead of the slab. The first application of this principle was in connection with the office building erected for the Foster-Armstrong Company at East Rochester, N. Y. (1904-5), and it has since been extensively used. Honeycomb slag may also be utilized in a similar manner, Patent No. &94,578 (1902), especially for large surfaces, but here I prefer my later invention, the removal of the surface skin with hydrochloric acid. The surface is next washed with water, and the finish coat is then placed in the usual manner, Patent No. 800,942 (1905).

This latter method, " the acid joint,*' has been tried in practice with excellent results. Fresh bases were welded to old concrete cylinders, the mass allowed to set, and in all cases the concrete would split apart from the joint when tested. One of my superintendents found himself unable to believe in the superiority of the new joint, and I had therefore a slab, about 4' X 4', set aside, letting him finish one half by any method desired, and reserving the other half for my acid joint. Try as he would, he never succeeded in making an unbreakable joint. A reward of ten dollars was promised to any man on the job who could separate the finish from the base on the half treated with acid, and while many of the men availed themselves of the opportunity, the reward is as yet unearned.

The Pacific Coast Borax Co.'s building, at Bayonne, N. J., erected in 1897-98, in a measure marks the closing of the oldtime construction of reinforced concrete buildings, constructed more or less in imitation of brick or stone buildings, with comparatively small windows set in walls (Figure 11). This building, however, occasioned the discovery of an important fact, that of the greatly improved fire-resistance of concrete mixed with salt. Before that time, salt had been known and used as a frost preventative, and as this building was constructed in the winter, I desired to use salt. I had some doubts as to the strength of concrete so made, and I also anticipated some trouble with efflorescence. A number of test cubes were made with salt, some mixed by hand, others by mill, and to my surprise I found that the hand-mixed specimens showed efflorescence while the machine-mixed specimens did not. I am unable to explain this difference. As to the strength, I found it was not impaired by the salt, when salt to the extent of one to five per cent, of the weight of the cement was added; I also found that the specimens without salt showed air or hair cracks, while those with salt did not. It now occurred to me that salt might have the same or similar effect on concrete that it has on clay; it is well known how clay pipes, etc., are glazed by being burned with salt. Test cubes with and without salt were heated in the boiler furnace to a red heat, and then plunged into cold water; the specimens without salt had a soft surface easily picked to pieces with the bare fingers, while those with salt were intact, and the compressive strength appeared to be unchanged. I had then the belief that different brands of cement were affected in different ways by the addition of salt, but I have so far never found a Portland Cement that was injured in the least by addition of the quantities indicated.