THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



3S 



But the blue Lias lime will not make g^sod mortar if mixed witli more than 

 two cubic feet of sand to one of lime. This opinion first formed by me from 

 analogy, and in consideration of the blue lias approaching- very nearly to a 

 water cement, proved on due enquiry to be borne out by, and exactly con- 

 formable to, the practice of the masons of Lyme Regis. But Captain Savage 

 of the Royal Engineers, who was employed professionally some years ago in 

 improving the Cobb or Pier of that little seaport, which was "done by tide 

 work, and in which no other kind of lime was used, assured me that he found 

 that a smaller proportion of sand than 2 to 1 made still better mortar. We 

 have sinceascertained by repeated experiments at Chatham, that 1 cubic foot of 

 blue lias lime from the kiln weighing 47lbs , mi.xed with 2 cubic feet of sand, 

 and about 3 quarters of a cubic foot of water, made mortar fit for use, but 

 which could not have borne more sand without becoming too short. The 

 average quantity produced was two cubic feet and one fifth, which contrary 

 to the result obtained with the purer limes, occupied more space than the sand 

 alone originally did. We found also that blue lias lime from the kiln, like 

 all the other limes that we e.xperimemed upon, tilled only about two thirds 

 of its original measure, when reduced by pounding to the state of quick lime 

 powder ; but one cubic foot of blue lias lime when slaked, only dilated into 

 one cub c foot and a third of slaked lime powder, not including about one 

 eighteenth part of a cubic foot of core, which we threw away. Hence it ex- 

 pands less by slaking than either chalk lime or Hailing lime." 



The Colonel very justly attributes the modern introduction of 

 concrete for foundations to Sir Robert Smiikc, who first used it at the 

 Penitentiary, Milbank, London. The Colonel remarks that : — 



Neither gravel without sand, nor sand without gravel can form good con- 

 crete. The large pebbles composing the former, if mixed with quicklime 

 powder and water would only be cemented together by lime paste, or as it is 

 technically termed //«;<> /y»//y, filling up the large interstices between tliem, 

 which is known to be the weakest form of lime. On the other hand, fine 

 sand alone would produce nothing better than a mass of common mortar, 

 which has very little sti-ength in itself, but is excellent for cementing larger 

 materials. The proportions of the gravel and sand used are of little imp°ortance, 

 provided that the former be rather large, and the sand sufficient to fiil up the 

 interstices in it, for which purpose a mi.xture of coarse and of fine sand is 

 better than one sort only. But no such mixtures are necessary, in using the 

 sandy gravel of many parts of the Thames, where it is found in the state most 

 suitable for making good concrete, and is employed both for this purpose, 

 and as ballast for shipping. 



It being known that clean gravel and sand when put dry into any measure, 

 will almost immediately settle to a lower level on the addition of a certain 

 quaritity of water, and it being a matter easily proved that no ramming can 

 possibly compress them afterwards, it appears to me, that the proportion of 

 Irme used in concr-ete should be just sufficient to combine with the gravel and 

 sand in this compact state ; that is after the violent action of slaking shall 

 have subsided, which causes a temporary expansion, that is counteracted 

 whilst in operation, but the usual process of treading down or ramming 

 concrete. 



Examples are given of several buildings in which concrete has been 

 applied in the formation of tlie external walls, and the Colonel shows 

 by their fallrne the impolicy of this mode of construction, however 

 strongly he recommends its ad"option for foundations. 



The composition, commonly called Roman cement, has witliin the 

 last few years been employed pretty extensively in the metropolis for 

 building purposes, and has certainly greatly contributed to the extension 

 of external decoration. A pi-cjudice, however, still exists asrainst its 

 application for ornaaient in our churches and public building's, which 

 may have arisen from an improper use of it, and from the frauds of 

 some of the manufactures, but the general result has been to convince 

 us strongly of its applicability for these purposes. In our O])iiiion, if of 

 good quality and properly worked in the mixture with sand, it is of 

 equal dii lability with Bath stone, and capable of employment for the 

 same objects. An unfortunate prepossession against its application to 

 ecclesiastical structures seems to prevail, even as if a mandate of inter- 

 diction were issued against if, although it would most certainly 

 materially assist the architect in giving some character and decoration 

 to these edifices. Neither would its expense be such as to call for a 

 great increase of the penurious allowances of the church commissioner^ 

 who show as niggardly a spirit in these respects as if tliey wished to 

 imitate the union workhouses. It would be well if the architects 

 generally could prevail upon the proper authorities to allow its intro- 

 duction, which we are sure could not fail to atford gratification to the 

 public. It is only necessary to guard against the application of inferior 

 preparations, and this could be fully secured by providing in the specifi- 

 cation that the cement should be procured from competent manu- 

 facturers, which the architect may appoint. 



We found by experiment at Chatham, that two thirds of a cubic foot of 

 calcined Sheppy cement powder, which is equivalent to one cubic foot of 

 cement from the kiln, would not bear much more than one cubic foot and one 

 third part of a foot of sand, without evidently becoming too short for building 

 purposes. This is equivftlent to a mixture of twQ lueasutes of siina to on« 



of cement powder. But experience has shown that even this proportion of 

 sand is too great in practice, for the builders of the metropolis, who have used 

 immense quantities of the Sheppy and Harwich cements for many years, a?ree 

 that more than 5 parts of sand to 4 of cement powder, or \\ measure of the 

 former to one measure of the latter, injures the cement, by retarding its setting- 

 and rendering- it loo friable, whether used as mortar for walls, or as stucco 

 for the fronts of houses; but they consider that equal parts of sand and of 

 cement powder, involving a smaller proportion of the former ingi-edie.it, are 

 still better. 



But not to lose sight of the just comparison between cement and lime, these 

 proportions, when stated in the same manner as we did in treaiinj; of lime, 

 imply that whilst one measure of cement from the kiln will not bear more 

 tlian two thirds or at the utmost five si.xths of a measure of sand without in- 

 jury, one measure of the various sorts of lime from the kiln, according- to its 

 quality, will bear two or three measures of sand or even more. 



There are two properties of cement, which ought to be thoroughly 

 understood. 



First. It only sets rapidly when made up into small balls or in very thin 

 joints. In largo masses or in thick joints, the rapid induration lakes pl.ice 

 near the surface only, from whence it extends towards the centre so very 

 slowly, that the cement there may remain in an inrperfect .state for a very hirig- 

 lime. This property it has in common w-ith lime mortars and concrete, which 

 when in mass .set more slowly at the centre than at the surface, in the like 

 proportion (33). 



Secondly. As was before remarked in article 42, cement is alwa' 3 

 weakened by sand, no matter how small the proportion of that ingredient may 

 be, so that if both materials were equally cheap, it would be be»t to dispense 

 with sand altogether in using cement as mortar for building walls, but not in 

 using itas stucco for plastering the fronts of houses. 



Numerous experiments have convinced me of the truth of these maxims, 

 which any of my readers may easily verify. In respect to the hatter in par- 

 ticular, take a small quantity of the best cement powder, mix it with three or 

 four times its bulk of fine sand and make it up into a ball with water, and 

 you will find that instead of setting, it «ill either remain quite friable or 

 crumble to pieces, both under water and in air. 



Upon the whole cement sets most quickly, and unites itself most powerfully 

 to bricks or stones, when it is perfectly pure or unmixed with sand, provided 

 only, that the joints be thin, I should say not exceeding half an inch in thick- 

 ness. For this reason, in forminj^ cement into chimney pots, copings, &c., 

 where the general thickness mwch exceeds the above dimension, and con- 

 sequently where pure cement alone would not make sound work, insiead of 

 frittering aw;iy its strength with sand, I would recommend fragments of broken 

 tiles or gravel, to he mixed with it, the interstices of which are such as to 

 allow the pure cement which fills them, sufficient body to attain a due degree 

 of strength, without being quite so large as to retard its setting, and thereby 

 cause weakness in the central parts of those spaces. 



Among other interesting illustrations of the powers of cement, tiie 

 Colonel has fully proved its great strength when applied as a joint for 

 stone-work. One of these experiments was made upon two blocks of 

 Bramley-fall stone, each 39 inches long, 29 inches broad, and 26 inches 

 deep, weighing about •26(32 lbs. The beds or contact surfaces of the 

 stones at the joints were roughed over by picking down the surface; 

 they were then united with some of Messrs. Francis & Son's best Roman 

 (English) cement, composed of a mixture of Sheppey and Harwich 

 cement stone. Six weeks after, the experiment was continued by sus- 

 pending the upper stone, and loading the under one with weights, to the 

 enormous extent of 36,544 lbs. without breaking the joint. This was 

 then split by means of a mallet and chisel, when, to the Colonel's asto- 

 nishment, it was found that witli the exception of the outer part of 

 the cement, which had been exposed to the air, and was extremely 

 hard, the whole interior of the cement joint was sof'tisli, and 

 neither resisted the action of the thumb-nail nor of a sixpenny piece on 

 edge, which scored the surface to the depth of nearly a sixteenth of an 

 inch. From this and other experiments, the Colonel deduces the im- 

 portance of the "application of cement in masonri/, even in the union of 

 the largest stones.'' ^ 



The author gives some experiments on the strength of stone, which 

 we think will be found serviceable to the architect and engineer in the 

 choice of this material : — 



As the value and importance of artificial stone used for the walls of build- 

 ings, or for those of wharfs or docks, must depend upon its strength in opposi- 

 tion to a breaking- weight, it now appeared desir,able to ascertain its resistance 

 in competition with that of the common building stones of this country, as 

 well as with that of bricks and of pure chalk from the quarry, for which pur- 

 pose I caused a number of similar small prisms, eai-h four inches long and 

 two inches square, to be cut out of all those substaucos, which beirrg sub- 

 jected to the proper breaking .apparatus, yielded the results contained in 

 another Table, No. Vlll., and, in order to render this more complete, the 

 cohe^iveness of the same stones has been repeated from Table HI., whilst 

 that of well-burned bricks and of inferior bricks has been estimated, from 

 the average of the strongest ftud some of the weakest results, vccorded in 

 Tables I, and II. 



