BOULDERThe concrete block of Boulder D a m is so huge that serious overheating would have occurred deep within its mass i f only common Portland cement had been used as a binder in its construction. B y reduction of the aluminate and increase of silicate in the cement, the production of chemical heat, particularly at early dates, was sharply reduced. Such items as grouted contraction cracks, refrigeration, particle size, and control of aggregate size have featured the studies leading to the final production of a n extremely secure monolithic block.
G. ROSS ROBERTSON University of California at Los Angeles RIGGER-RODNAN WORKIXG WITH TOPOGRAPHY SURVEY PARTY IS BLACK CANYOVON THE NEVADA SIDE
Al
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S THESE words are ritten, the Six Companies, Inc.,
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sion. Striking descriptions of these engineering features are given in articles by government and consulting engineers (6, 7). Of the vast financial expenditure at Boulder Dam, a substantial part goes for Portland cement. While the aqueduct will utilize much of this cement, it is the huge monolith of the dam which has been commanding the greatest interest in cement research. Figure 1, a cross section of Boulder Dam, shows that the thickness-not the length-of the block a t its base would just span a standard 220-yard straightaway running track. The height is greater, 727 feet, and the length around the curve is about one-quarter mile. In designing this colossal block (6) the United States Bureau of Reclamation sought as an ideal a single monolith weighing about 7 million tons. It is this vast size, and more particularly the compact form, which primarily introduced a series of chemical problems which do not arise in the construction of a sidewalk or culvert.
supercontractors, expect to pour the last bucket of concrete upon the main central block of Boulder Dam about March 1, 1935-two years ahead of time. For this colossal achievement not only the engineer, but also the chemist deserves a substantial share of credit. By predepression standards of public expenditure, the figures for the Colorado River program are impressive : Boulder Dam, poaer plant and All-American Canal Poner transmission line to Lo0 Angeles Metropolitan Aqueduct ( t o Southern California)
$165,000,000 22,~00,000 220,000,000
$407,800,000
Most of the above reckoning is primarily for the benefit of five or six counties of Southern California. By the time Arizona, Nevada, and Utah enter the field seriously, the public wallet should be out, roughly speaking, a half-billion dollars. As a result of this huge outlay a project of truly superlative proportions lies before the visitor’s eyes. At Black Canyon one may watch the great aerial hoist, spanning the entire chasm from KeT-ada to Arizona with six 3-inch wire ropes, pick up a 50-ton pipe section and deposit it gently upon the river bed 900 feet below. Such a pipe, 30 feet in diameter, is far too large to pass through railway tunnels. It was necessary to build a steel fabrication mill a t the job to effect its manufacture. Spill\\-ays resembling great highway underpasses, giant valves, colossal tee joints, elbows, monster turbogenerators-these and a thousand other structures, appliances, engines, gadgets exhaust one’s synonyms for great size and go hopelessly beyond the scope of this discus-
HEATOF HYDRATION
When ordinary Portland cement is mixed with water, the resulting hydration generates about 100 gram-calories of heat. This evolution of heat requires considerable time, and there is considerable variation per gram of cement as the composition is changed. During the setting of a concrete structure of ordinary size With so this .~ heat escaDes freelv and causes no concern. great a mass as that of Boulder Dam, engineers a t once realized that the heat, unable to escape would raise the temperature of the interior concrete to intolerably high values just as
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t,be major part OS the hardening process was occurring. 0 1 1 $,heother Land, the external portions of the mass, rvitliiii a rery few Seet of the siiriace, would radiate their chemical lieat promptly and harden as usual at loiv temperatures. Obviously this combination of expanded and contracted concrete would not hold together u-lien all finally became cool. The mass would crack and lose its stability iii future service. Two logical modes of attack on the problem TTere considered and both adopted---namely, prevention by ehrniical means, ;and ineclianical refrigeration. Long before the Boulder Uarii project wax lwiniehed, Woods, Steinour, and St.arke (14, 16, 16j investigated the heat-producing capacities of cements of several different compositions. Their report showed that striking reductions could be made froin the ordinary calorific values by alterations in cement compositions to proportions which were still consistent with engincoring standards and manufacturing economy. It indicated, furtherniorc, that the time schedule of cooling was of great engineering importance. Specifically, a reduction in heat eenerrited diirine the first meek from valuos srorind 80 calories to 45 or 50 mas entirely feasible. Encouraged by this pioneer investigation, the Bureau of Kcclamation, with the aid of the Department of Civil Engineering of the University OS California, laiinched a formidable cement research program nnder the direction of ltaymond E. Davis. An extensive laboratory with unique equipment was established at Berkeley. The fnll report of this invcstigation, in about nine volumes of government bulletin type, is promised Sor the nea.r Suture. A t present only a general abstract oi results ( 1j is available. Coincident with this program came the exhaustive labors of tho Portland Cement Association under the leadership OS McMilbn and Gonnerman. Condensed reports of this work mere given recently by Gonneman (3). The pioneer work of the Bureau of Standards, of which the report of Bogne (B) is an outstanding illustration, laid invaluable foundations for the later investigations, all of which indicated the possibility of combining ninny other desired qualifications in cement with the heat specification. I n a s m u c h as large-scale commercial equipment was needed, four leading Soutliern California cement companies (Riverside, Southw e s t e r n , California, and M o n o l i t h j were invited t o join i n t h e research, each furnishing certain synthetic or analytic services as needed by the bureau and the uni.. v e r s i t y . Later when the FIGUREI. Cnoss S E C T ~ ~ government contracts were OF h U L D E R D A M awarded, these concerns, as Dow,,atreem to the E++W lowest bidders. were able to furnish thc new special cement required. Later a small part of the cement reqairement came from concerns in Utah and vicinity. Since the first specifications were announced, slight changes have been made. Furthermore, in view of minor differences in the cement products from the four h s , especially in color, it was decided to blend the cements before running into the mixers. Irregularities both in appearance and sctting behavior of the darn were thus avoided.
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CEMENT CRE.MISTRY Ttic significance of this program is perhaps best realized lly a consideration of the fundamental chemistry of cement.
Mmm.1: SECTION OF -PWE DOWNSTREAM FACEOF B O I J L DDAM E~ (:OOLIND SYSTEX NEAIIER SLOT ,ANDI ~ F ; A L ~ I I Prlws
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T o be sure, m e may turn back two t.liuuaand years or more, and find that even ancient man knew of the scheme of mixing
clay with the lime whicli he burned for mortar to hold tllc Roman temples togctlier. I n this way 5 certain degree of waterproofing was obtained. In modern years it has been the costom t o inform t.he lay reader that Portland cement is a calcium silicate-aluminat+~ mixture oS uncertain composition and uncertain reaction hehavior. It has remained for Bogue (Bj in his recent, but now almost classical, paper to cryst.allise and present the idea that cement is substantially a physical mixture of fonr definite solid compounds. These are the following.: c"inp""ad 'Tetra1:aleiurn ulus,ieofeiiita Trinaloium niirmiiiatr Diealrillrn niiietit,e Tricaioiun, eiiieam
FDrrnWN
Cundeneed Borinuln" CidF CS\
CIS
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Other substances, notably t.he inipurity magnesia, and calciunr sulfate addcd for retardation of setting, do not takc part iu the principal chomical rolas OS tire four csccntiala. On the other hand, ;my one of the Sow comlioiients, separate1 ryntlmsized, is of itscli a "hydraulic" cement, more or le siiitaiilc for ntortnr purposes. Ry it,seli, however, s11c1i :I single compriund is likely to Sal1 short. of cine or mire of tlre varicd requirements related to time, teniperaturc, strcngt,l,, economy of manufacture, etc. For pi~rposesof syiitlietic specification, one may without r
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practical error assunie tirst that the calcite, clay or ironbearing silicate, and quartz behave in the kiln as though the equivalent quantities of calcium, aluminum, silicon, and iron oxides had been furnished in separate form. That is, the particular way in which the oxides are gri~opedcliemically in the ingredients of tho raw mix has no bearing upon the relative quantities of the four comporinds expected in the iiroduct. Furthermore, these oxides behave as thougli thc four cemeiit compounds >%-ere required to be made in succession in an illvariable order. Tlie sequence is best illustrat,ed by an ideal cement synthesis in which small quantitics of iron and a,linninum oxides are heated with a large proportion of silica and a still larger proportion of lime.
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Assuming successive reactions, tlie C , A, and F unite until the maximum possible yield of CAF has been produced. As soon as the oxide present in least adequate quantity (F) is exhausted, the production of CAF stops. A11 of the excess alumina is now diverted to produce C A . When A rims out, there is still left a great excess of C. Only calcium and silicon oxides remain. Continuing the sequential assumptions, all of the silica now unites with t.hc proper quantity of calcium oxide t o form the third compound C2S. Finally the residual calcium oxide combines with just. the proper amount of the newly made C2Sto yield Cas. Any magnesium, potassium, manganese, or calcium oxides in excess of the above requirements stands aside as unreacted impurity, or in combinations as yet unknown.
March, 1935
I S U I I S T IU5ffiIkL A\I>
EYGINEEKING CHEMISTRY
Vol. 27, No. 31
Wi
ABOVE: ROUI.DERDAnr FROM TIIT NEVADAh n s , JANUARY, 1935, SBHDWING TNE CENTRAT, SLOT A N D CONTROL T O W E R
L‘niortunately the statement has been made iu certain recent literature of cement technology that the low hea.t values are obtained by virtue of a cement blending process. Such a d e d u c t i o n is e n t i r e l y erroneow, and the blending is merely a concession to engineering and artistic uniforniity in construction. Incidentally Boulder Dam whcn finished will be a tieautiful example of the art as well as the science of pouring concrete. The low lieat values noted in case b during the first few weeks of the hardening process arc of principal interest t,o the engineers, sirlee the rate of heat production a t the early dates is likely to run high. These reductions have meant an enormous saving in constructional cost, covering tlre expense of the research several times over. n’evertheless the suhstantial values of 42 to 47 have necessitated a refrigeration system of good size. During the winter the setting of low-heat cement hss proved t.o be somewhat too slow, so that the plan vas adopted of mixing a small proportion of ordinary cement with the standard concrete batches. This modification of technic allows of uniformity in behavior, suminer and winter. When the thermometer reaches 120” F. in the summer, as the workmen know only too well, straight low-beat cement is used. COOUNGSYSTEM For this purpose about 300 miles of light-weight, one-inch pipe have been embedded in the concrete mass, and these arc served by an external system of nearly the same length of other pipe. Through these pipes refrigerated water or brine is passed. Desilted river water is first cooled as far as economy permits in a water tower. Although the suminer temperature at the river bed is high, the low humidity gives the natural compensation whioh is of much value. An ammonia plant, capacity 825 tons daily (refened to melting ice), then
acts as a second stage, delivering the necessary cold water to the pipes in the concrete. Engineering details are given in a series of articles hy Mead and associates (7) and by Steele (10). Eventiidly the pipes in the block of the dam will he filled with neat cement,, thus adding to the compactness of the structure. The slight reenforcing value given by these pipes is not considered to be of consequence. Early calculations showed that any significant amount of reenforcing steel would have entailed unwarranted expense. It wss better for the outlay to he spent in additional mass concrete. CONCRETE MIXING
At the immense “Himix” concrete plant, perched upon the rocky cliff of the canyon a few hundred feet from the dam
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Vol. 27, No. 3
site, a respunsible employee watches seven automatic pens and also a wide central \lot for the temporary accommodation which write before his eyes a continuous report showing that. of pipe headers, etc. The pouring of concrete is carried out to the depth of sevexactly the correct weight.; of seven components are passing into one or another of thc huge mixer units. Along with the eral feet at one run, in alternate blocks, after which the forms are elevated out of the way and the intervening spaces BIed. carefully measured cement and water, the aggregate-sand, gravel, rock--is supplied in five sizes appropriately balanced A few hours after a given block is poured, workmen with highso as to give minimum waste internal spaces. The formula is pressure water service wash the top of the block. Surface 7.1 parts coarse material, 2.4 parts sand and gravel, and 1 part cement, which has scarcely bad time to set, is thus washed .VWBY, leaving a rough but clean cobblestone surface which is cement. The coarse aggregate is natural river-worn cohblestones w&pableof gripping tho next batch of concrete with full from the river valley cohesive strength. upstream. It is of The f l u t e d side walls of the block, beexcellent q u a l i t y , abounding in granite, ing still p r o t e c t e d wvth forms, receive tough compact breccia, Iiasalt, and no such scouring. As a result they set the like. Except lor hard and smooth in small amounts the manner of ordic r u s h e d t o give nary f i n i s h e d conproper size amounts, crete. Finally, when it is n o t b r o k e n . t h e next pouring The l a r g e s t size is 9 inches in dimenoccurs in the space between blocks, no sion, which explains form is needed. On t.he f a c t t h a t t h e the other hand, the men working at the new concrete does not point of actual constick tightly to the crete p o u r i n g wear side wall oE the older "tin hats" much like mass. h-ow comes those seen in France the expected contracin 1918. If a bucket tion upon s e t t i n g . of concrete, hanging This reaction merely from a cable far above inills the new block a t,he f o r m s , shoutd small fraction of an happen to drop someinch away from the thing about the size SPILLW.~Y AT BOULDER DAM older s u r r o u n d i n g of a cantaloupe upon blocks, and strain is the scene, one would ' thiw n vnidd -."."ll. appreciate a substanIt is now necessary, tbfter contraction has taken place, t.o tial helmet. In due fairnes6 to the Six Conipanies it slirdd be added that extreme safety precautions have been taken in bond together the mighty concrete blocks. This is accomplished with the aid of extremely fine grouting cement forced the design of the buckets. The buckets, each holding 16 tons of concrete, have heen into the cracks at high pressure. A special sifting plant a t the traveling now for 20 months, back and forth, day and night, dam provides cement for this purpose, all of which passes a a t this one task. Every three to four minutes a loaded 2Wmesh sieve. Finally the wide central slot of the dam is bucket is swung uul over the abyss and dumped neatly and filled with concrete. When all of these operations are completed, one may fancy accurately into the proper form. To keep this delivery going steadily requires three train services in constant operation: Boulder Dam as a grand masonry structure, in which huge bulk cement by the trainload from Las Vegas, cobbles and quadrangular pillars of artificial conglomerate are set upon gavel from the river Ired, and a busy electric train service end and bound together just where fabricated. Smce the whole mass of blocks is not only bound together tightly by plying between the mixer and the hoist. So high is the speed of performance that the concrete the grouting cement but is obviously heystoned against d a m technologist cannot wait for the ordinary setting of his routine stream pressure, its strength is beyond question. test cylinders at normal temperatures. Instead he pours a concrete sample into a steel vessel which is immediately FUTURE CHEMICAL PROBLEMS placed in a heating device suggestive of a fireless cooker. The fineness requirement in the government cement specifiWithin eight hours the sample has set sufficiently to permit cations is not so n-ell understood as the heat limitations. strength tests ordinarily ohtained only after many days. Until recently most purchasing anthorities were satisfied to specify that a certain high percentage of a cement must pass a CoNTR.4cTloN CRACKS ZOO-mesh sieve, and that all must paas certain coarser sieves. Sieve specifications, satisfactory for coarse powders, fall Despite all the synthetic and analytic ctiemi(:al aid and the refrigeration program, the government engineers have never down seriously at values oE 2M) per inch and above. At such assumed that so vast a block could be produced without high fineness ratings the sieve gives an extremely poor record cracks. Wherefore, cracks being in order, they may as well of the distribution of sizes. I n the government specifications be planned in orderly fashion and included. This account,s for Boulder Dam, accordingly, the sieve has been displaced for the block system (9)oE pouring shown in some of the by the turbidimeter of Wagner (19), which gives an optical photographs of the project. Both radial and circumferential determination of particle size. Thanks to Knapp (4, 6),a new instrument has been dei)assages are provided, running the entire height of the dam,
March, 1935
I N D U S T R I A L -4ND E N G I N E E R I N G C H E M I S T R Y
vised, based virtually upon Stokes's law. Cenient powder is mixed with a suitable anhydrous liquid, such as petroleum naphtha of low viscosity, and is allowed to settle. A photographic determination is then made of the rate of settling. A diagram is then plotted, showing the fraction of the cement present in each of several brackets from 0 to 10 microns up to 80 to 90 microns, or as high as desired. Somewhat similar apparatus, developed independently a t the Berkeley laboratory, gives results fairly concordant with those of Knapp. This will doubtless be described in the government reports. Although both of these devices are the result of the special western research, they hare not been used officially. While the probleiii of actual determination of particle size is thus well along toward a satisfactory solution, there is still an uncertain question as to the meaning of such specification in actual use of cement. The present Boulder Dam specifications merely call for limits of surface area of particles. So far there seems to be no definite idea whether a cement of even distribution of sizes, one of much fine and much coarse, or one of uniform size is most desirable. Any of these options would pass the present regulations. Naturally the habits of the ball mill or other crusher may have to be consulted in any case, lest the cost of production be raised unduly by arbitrary requirements.
SAFETYFACTOR Knowing the tremendous expanse of rich agricultural territory absolutely dependent upon the security of Boulder Dam, the engineer is interested in the factor of safety. Such R factor is difficult t o calculate accurately, but a pessimistic semi-engineering pue~syields a value of 4. In all prohahility
249
it would take considerably more than four times the stress of a full lake to cause failure of the dam. This leaves only the earthquake problem. Here, however, the geologists agree that they can find no faults or evidence of quakes which have occurred since the Colorado River cut through the last thousand feet of hard rock. How many scores of thousands of years are involved in that last geographical phase nobody knows. Apparently Boulder Dam is a permanent fixture.
ACKNOWLEDGMENT The photographs were supplied through the cooperation of the U. S . Biireau of Reclamation and the Six Companies, Inc. IJTERATURE CITED
(1) Blanku, K . E'., Eng. IYews-Record, 113, 648 (1934). (2) Bogue, R . H.. IXD.EKG.CHEW.,A4nal.Ed., 1, 192 (1929).
(3) Gorinerman, H. F., Eng. .l-ews-Record, 113, 651 (1934). (4) Knapp, R. T., IKD. ESG. CHEnr., Anal. Ed., 6 , 66 (1934). (5) Knaljp, R . T. (to Riverside Cement C o . ) , U. S. Patent 1,838,628 (Dee. 29, 1931). (6) Mead. E.. E m . .Vews-Recod. 109. 724 11932). (7) Mead; E . , a n i associates, Ib;.d., ill, 733 (1433). (8) Savage, J. L., Ibid., 109, 558 (1932). (9) Steele, B. W., Ibid., 111, 737 (1933). (10) Ibid., 113, 451 (1934). (11) Thorvaldson, T., Brown, W. G., and Peaker, C. R., J . Am. Chem. Soc., 52, 3927 (1930). (12) Wagner, Proc. Am. SOC.Testing Materials, 33, Pt. 11, 553 (1933). (13) Walter, R. F.. Env. iVews-Record, 111. 736 (1933). (14) Woods, H., and Steinour, H. H., J . Am. Concrete Inst., Nov.. 1931, 195. I., Starke, H. R., Eng. News(153 TToods, H., Stemour, H. €and Record, 109, 404, 435 (1932). (16) Woods, H., Steinour, H. H., and Starke, H. R., IVD. ENG. CHEM.,24, 1207 (1932) RECEIVEDFehrnnrv 4, 1934
UPSTREAM FACEOF DAMAND INTAKE TOWERS,AS SEENFROX
THE
ARIZONASIDEOF BLACKCANYON
