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Christopher HallDe~artment f Bulldlnq I On the Historv o i Portland after.niversity of ManchesterInstitute of Science and Technology 1 150 Yearsanchester. England M60 1QD

Cementitious building materials have a long history, andth e date 1824, traditionally taken as the origin of portlandcement, is in fact only the date of a patent ( I ) granted toJoseoh Asodin (1778-1855) of Leeds. Eneland. who mavnot at that'time have made portland cemei t at all. ~ o d a y ;cement is the successor to a line of materials with a historvreaching hack t o the ancient world; it has a chemistry o?perhaps unsurpassed complexity amongst major inorganicindustrial materials and is still the subject of intense study.At some ~ o i n tn the second quarter of the 19th century,abou t 150 ago, the cement as we know it now was fir&produced.

Th e very simplest of the mineral cements are those basedon gypsum, hydrated calcium sulfate. Gypsum loses itswater of crystallization easily on gentle heating to yieldvarious olasters. These dehydrated suhstances when mixedwith water reform a crystalline mass of synthetic gypsum,which however is mechanically weak an d is slowly dissolvedhv water. The re is evidence tha t the an cien tEev oti ans.mixed burnt gypsum with sand to make masonry mortars12).Such mortars were unsuited to less arid climates. andthe early bu~ldrrs II [he nurthtm shores of the Xlediterra-nean dt.wlc>oed the ; k ~ l l ; of lime-hurninr ,conversion ofcalcium carbonate to the oxide). The quickkme produced isslaked with water to yield a lime putty, to which can headded sand to produce a mortar or coarse mineral to pro-duce a concrete. Such pure lime mortars and concretesharden slowly and often incompletely by reaction with thecarbon dioxide of the air to give calcium carbonate oncemore. The Roman builders could achieve supe rb quality inpure lime mortars of thi s kind-many examples remaintoday-hut these materials did not set from within themass of t he paste, nor did they have the quality of hydraul -icily: t he capacity t o set in contac t with water, so valuahlein many engineering situations.

Hydraulic limes were produced by hoth Greeks and Ro-mans by adding to the lime putty fine volcanic ash orcrushed volcanic minerals, the Romans using the depositsat Pozzuoli, so that now all such materials are known aspozzolanas. Th e Romans also discovered tha t crushed tilescould act as artificial pozzolanas. Both natural and artifi-cial pozzolanas are composed chiefly of silica with somealumina in forms which on mixing with water will reactreadily with calcium hydroxide from the lime to give hy-drated calcium silicates and aluminates. These importantsuhstances are closely similar to the cementing compoundsin por tland cements themselves. Because hoth the pozzola-na and the lime are present in the mortar, the setting pro-ceeds from within the mass; the extreme insolubility anduseful strength of these hydrates leads to the property ofhydraulicity. Lime-pozzolana cements were the only ce-ments available for work in contact with water from theRoman period until as late as th e 19th century ( 3 ) .

In the 18th and 19th centuries, we see the beginnings ofan understandine of whv it is th at lime-oozzolana mixturesIln\,e t h rw rcmarknhle hydraulic pr,,ptrries, and !he ;tartof .a I,?horwus ernoiricnl itrun~lp 0 make Iwtter and hertercements. B ut t h e understanding was a long time coming,and the early pioneers had very little help from the chem-ists of the day. In 1757 the great engineer John Smeaton

began to build the third Eddystone lighthouse off thesouthwest coast of Britain ( 4 ) , pparently a labor of Hercu-les in the absence of a good hydraulic cement. Smeaton, ap-preciating the need to obtain the best component materialsfur the lime-pozzolana cement he intended to use, exam-ined a number of mixtures, and found that the quality de-pended on the limestone (5).He made the important dis-covery that the best mortars were made from limes con-taining clay impurities. We recognize now that the alumi-nosilicate clay minerals are closely related to those in thepozzolana, with this essential difference: that they areburned intimately with the lime in the calcining process. I tsoon emerged that certain heavily clay-bearing limestoneswere hydraulic in the absence of the pozzolana (6). uchmaterials became known as Roman cements. Various natu-ral cements of this kind (whose properties depended in anerratic way on the composition of the mineral taken fromthe ground) achieved prominence in various places in theearlv vears of the 19th centurv. Th e essential roles of limeands ik ca in producing hydra;lic cements were establishedsome time before 1818 hv the Frenchman Vicat in his sci-entific studies of innumerable artificial mixtures of lime-stones and clays (7 ) .Th us abo ut the year 1824, a good many people in severalEuropean countries were interested in trying to make theirfortunes by perfecting these cements. Some were spurredon by the belief th at the Romans had had a secret for mak-ing fine cement which had been lost, and many unlikelysubstances were added in the hope of stumbling upon amissing ingredient. Lacking any clear notion of the natureof the cementing reactions and using the most variable ofraw materials. thev labored lareelv in the dark. Scientifical-. u Aly speaking the nature of portland cement did not emergeuntil well into the second half of the 19th centurv. Todav'scement is made by heating an intimate mixture of finelyeround limestone and clav (in ~ ro uo rt io ns arefullv adiust-. . . " -ed by reference to analyses of raw materials) to a tempera-ture sufficientlv high for oartial meltine to occur (8). he. "cooled granular product, a complex multiphase clinker, isground to a powder of large surface area. Thi s is portlandcement. It consists primarily of a number of calcium sili-cate and aluminate comoounds. When mixed with water itforms a hydraulic paste which sets and hardens to a strongsolid, larpelv com~osedf hydrates of calcium silicates butwith a remarkahfy intricate physical microstructure. Thecritical variables closely controlled in manufacture are t hecomposition of the feed (chalk:clay, 7525) and clinkeringtemperature (over 1400C). Neither Aspdin nor anyoneelse for a long time after 1824 fully understood these basicfacts. What then is the basis of Aspdin's claim to be the in-ventor of portland cement?

On November 6, 1824, the gossip column of the newspa-per the Leeds Mercury was preoccupied with its usualbusiness of warning t he honest citizens about the dishonest("Last Saturdav. three females. handsomelv dressed. and.having the appearance of respectable ladies, paid a five~ o u n d. hnnknote.. . o a haberdasher in Leeds, which isnot worth a farthing") and gave only a single passing sen-tence to Aspdin's news. "We hear that Joseph Aspdin,bricklayer of this town, has obtained a pa ten t for a superior

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sign (12).The understandine of the nature of the cementement representing Portland stone." His paten t BP 5022:1824, "An Improvement in the Modes of Producing an Ar-tificial Stone" consisted of two hrief pages and the rough-ness of his manufacturine methods is apparent . His Drocesscalls for the use of a "specific qu an tit yG f limestoneand ofclav hut sadlv thev are not specified. Information abou t the.burning temperature is of course also absent, as are all de-tails of the kiln which might have helped to establish this.However, Aspdin did introduce the name por tlan d cement,a shrewd idea to link the unproven qualities of his new ce-ment with those of a fine building stone. Unfortunately lit-tle is known of Aspdin's manufacturing activities at thistime. The scanty records have been examined with greatcare by Halstead (6,9). spdin was carrying on business aspatent portland cement manufacturer at times during thenext ten years both in Leeds and Wakefield, and certainlylater in Wakefield, hut few details have come to light. Hisson William entered the business, and sp ent the re st of hisrather short life in the cement industry, moving from oneventure to the next without ever apparently really prosper-ing (10).The question of whether what Aspdin made in the earlydavs of his business. sav from 1824 to 1830. should be re-ga;ded as a true portland cement is a debated but still openauestion. No specimens appear to he available, though itmay yet he to establish his connection with someexisting building of that period. His product may simplyhave been yet another artificial hydraulic lime (excesslime) or Roman cement (excess silica). No record has beenfound of his early kiln, hut th e claim made by a commenta-tor much later in the century that he used a glass-makingkiln rather than th e cooler lime-hurnine kiln at least holdsout the possihility tha t he attained the temperatures neces-sarv for clinkerine (that is. for more complete reaction of.lime and clay), today regarded as essential to cement for-mation.Other evidence which bears on whether Aspdin's earlycement should be considered a portland is inferential. Pro-fessor Skempton's detailed studies (11) of the cements ofthe middle of the 19th century (including those producedby William Aspdin) provide the basis for making a casethat Joseph Aspdin had stumbled upon the essential factsof manufacture. Briefly the argument is this. In 1841 Wil-liam Aspdin entered into an agreement with a firm ofRoman cement manufacturers, Maude, Son & Co., of Roth-erhithe, in East London to make the Aspdin cement. Thereis no suggestion that the son made any innovations to hisfather's process. At this time work was under way on thebuilding of the new Houses of Parliament following the fireof 1834 and in 1843 the contractors carried ou t tests tocompare Maude's new cement with th e available Romancement. The results of these tests seem definitely to showthat the new cement was almost twice as strong in com-pression as the finest Roman cements available, compellingevidence that this was indeed a true portland cement. IfWilliam Aspdin's Rotherhithe cement i n 1843 was a port-land, there can be little doubt that Joseph Aspdin's prod-uct at that time was also. However, whether this was thesame cement as that which he was producing as earlv as1824 we cannot a t present say.Once the comparative tests of the 1840's showed publiclythe superiority of portland cements over the other calcare-ous cements production began in a number of places in Eu-rope and the gradual empirical improvement of the processand the material gathered speed. The development ofsound test methods, especially for streng th, played a n im-portant part in this, as did the refinement of methods ofchemical analysis of raw materials and changes in kiln de-

- . . wreactions-both the composition and phase relationships inthe clinker and the details of the hvdration reactions-have been more recent, and the materials science of cementand concrete remains an active and important area ofstudy.Advances in knowledae have been brought about by anumber of modern experimental methods,-such as X-raydiffraction techniques for compound identification, opticaland electron micr&copy, d iffeiential thermal analysis, ad -sorption isotherm techniques, and so on (13).

There is no doubt tha t for the first few decades the pro-duction of portland cement was a primitive manufacturingenterprise, even by the standards of the day. The materialtook a considerable time to penetrate into constructionaland civil eneineerine nractice. and indeed not unt il the de-.velopment of the techniques and s tructural theory of rein-forced concrete construction were its full potentialities re-alized.These facts help explain why portland cement was notproduced in the US until 1871 when David 0. Saylor waseranted his US patent (14). The earlv American portlandcement manufac&ers had to face strong dual competitionfrom the natural cement industry and from the portlandcements imported from Europe. ~ a t u r a lydrauliE cementhad been discovered as earlv as 1818 in New York State,and la ter in a number of other Eastern seaboard states , andKentucky and Illinois. The natural cement rocks werefound much more abundantly in these areas than in Eu-rope and many of the products established good reputa-tions in the middle of the 19th century. They were used inhuge quantities in the great canal construction projects ofthose years-starting with the Erie Canal in the 1820's.The importation of European portland cements startedin the later 1860's. The trade was viable only because thecement could travel free of charge westwards across the At-lantic as ballast in tramp careo ships seekine erain or cot-ton cargoes. The ~ ur op e an ndustry at t his dat e was wellestablished. The product was reliable and auicklv earned agood name. By thk 1890's however the ~ m e ri c a n arket forcements was expanding so rapidly that the indigenousportland cement industry was able to establish dominance.Literature Cited

i l l As p d in . J. ,"An lmprovemenlin the Modes of Produeinpan Art if~eial tone." Br it ~irh Patent 5022:1824.(21 Lea. F. M., "The Chemistry of Cement and Concrete: 3rd Ed.. Edward ArnoldLtd.. London. 1970.(31 D ~ ~ ~ ~ :., S& Enainaar. 52,193 (197").(41 Smeaton. J.. ',A narrative of the buildins and a description of the construction ofthe Edystone 1i~hthou~e: 'C.NICOI. ~ n d m .791. .(51 For a life of Smeaton. see Smiles, Samuel, '"Livesof the Engineers: vol. 2, pl, 6. re-print of the 1862 ed., David and Charles. Newton Abbot. E ngland, 1968; Turner.T.. Endenuour, 33.29 (19 74 .(61 Halstead. P.. T r o w Necueomen Sor , 3 4 3 7 (1861.2) .(71 Vicat. L. J., "Treatise on Calcareous Mortars and C ements," John Weale. London.1837.I81 Fo r a de~ crip tion f the modern manufacturing process, see Pollitt. H. W. W., inTsylor. H. F.W.. "The Chemistrv of Cements.'' Academic Presi. Landon and~ & Y o r k . Sbd, p. 27.(91 Goading, P.. and Halstead, P. E.. P i o r Thirdlnl i . Symposium on th e Chemistry ofCement. London. 1962. Cement and Concrete Annociation, London. 1954.

(10) Much interesting information an the history of the Aspdin iamily, especialiy thesuns .lamer and William. has been eathered toeether in a recent ertic1e bv Bar-i0ot.R. .I.,Conemla. R, 18i1974).(11) Skempton. A. W. . T r o ns . N ~ w c o m s n oc., 35,117 11962).112) A v i e r of the sa te of cement msnufaeture at the heginning of this century is pro-vided by Butlor , D. , "Portland Cem ent: its Manufacture, Testing and Uses."Soon. Ltd. .Londonand New York. 1905.

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