CON
187
CON
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®ece Ssa atter no more should be used than is absolutelySot to e ffect a perfect mixture of the ingredients.
Tjjg er accelerates the induration,brick ® x Pediency of using concrete as a substitute for stone,v °^ er materials for building, or constructions above°Piniori i, 38 ' Jeen mu ch discussed, and a great variety ofu p°n (h P re vailed on the subject. In the “ Prize Essay( }°n t 0 ^., a ^ u re and Properties of Concrete and its Applica-lXi Wr aii ^ >nstrUc ^ on ” Mr- Godwin has given much valuable88 to th IOn ’ bu ^ we think the opinions he has there venturedhy arch^ USe concrete for walls, &c., will hardly be adoptedgenerally. “ A prudent man,” says Mr. Bar-°f coa cr ’ w ill not heap up walls a second time, altogether,r| ort ar He will not exchange masonry of good strongttiortar ® 00< ^ strong stone or brick, for a heap entirely^'il! fl- > Und that “ tres maiare .” A /»nrofnl PYaminntimi
C c% '" -
the .. bee n
Ulg ar, d that “ tres maigre.” A careful examinationa Ve er that in every instance in which concrete walls^ l; nt „? Use< l, more or less of instant ruin has occurred,, s over the apertures of the first story giving
'vlien > even those of the second story have been laid;
„ .....
'^Pearecj 1 . tbose breaches have been repaired, they have re-? t5s tantlv ’ an<b even through the solid walls, rents haveI, an ( j ° cc urred: experience proves that gravel lying in aere growing, as it were, without the means of flow
o r
it wcic, wiwuuc me iucuuo ui iiuw
3 fubri e • k Su fHcient to support the most enormous weightSn to ’ „ u t the same gravel detached, cannot be piled up,i, °rm either solid upright walls, or horizontal
as
l. 11 klocljg 6 ^ bas been also used both as “ rough concrete,” andbee ex * ens ‘ ve works, as river-walls, breakwaters, &c.
0f this u n S>neers,”
recommended for such purposes by engineersIn the “ Professional Papers of the Corps ofV Ulls kind * ccrS ’.” ^uptam Denison describes some worksB Messing ’ anc *’ the experiments he had the opportunity offy^t'cal a ’ S ? me very instructive results are obtained as to the*s at \y | lca t' on of concrete to the construction of river-
W “> It >!? f I lwich and Chatham. In one instance at Wool-? tr Uct eH ,aa oee«both tK
Cfet e ae oth ei
( e en applied in mass, the wall having been con-• 8ame manner as the Brighton sea-wall; into "'as fby 1 * instan ces at Woolwich and Chatham, the con-atl d h ' nto blocks, which were allowed ample timean ’ ^-t W i before they were built into the face of theh . pil es . °°* w >ch, the river-wall is for the most part founded1 s height above the piles is about 24 feet ; the
?fr,
K o uic puco io auuut icok > ujo
a T ? 11 ^ of q 9 feet, at top 5 feet, with a slope or batter
th e ^°cks l a j^ * Q ^2. The face of the wall is composed of
6j flea ders 111 ce ment, in courses 18 inches in height;I att c kes l on a _ stretchers in the course being each 2 feetbav e mjl ” le f° rmer having a bed of 2 feet, while the^Un tbro Wn ; ^ b f° ot > behind the facing, the rough concreteter -fort s n J; 0 complete the thickness of the wall andbr 0| }>d 0 p j. Doth the blocks and the rough concrete wereth e Jjkt to and gravel, in the proportion of 1 to 7 andVe Wep 6 f >r °P er consistence with boiling water; butklooi b *° I 'kirur v ° r Ou obt to have been, made with AberthawMii| 8 "’ere ca ID - e be ’ n o us cd for the rest of the work. Thefor Se tti n< , , 8t In moulds, and were submitted to pressureby (■ 8a ke < of a Coat ’ n g of finer stuff being given to the facea bPearance. The whole of the wall was built"iti, t , c °Hcr e ( e a v <a ,' n tbe lower part therefore the backing ofki Ift tirl,. . . hardly time to set before it was covered
the
-* a f ' ~ Water , however, in this instance appeared
i"d le r e fbe mass only, the interior at the depth, I)^? 8 ' Wh ei . a PP ea ring dry, and of a moderate degree ofv i ft lri S th e exa mined after the retiring of the tide.
^ay ^ ag tnmer months, the action of the water fromnot perceptible ; the surface still remained
tolerably hard; occasionally portions of the fine facing separatedfrom the rest of the block, owing, it was said, sometimes to ‘want of care in the original construction, sometimes to injuriescaused by boats or vessels striking the wall ; in these cases,however, a new facing of cement was applied, and before thewinter, the general appearance of the wall was to a certainextent satisfactory.
During a hard frost, however, evidences of failure began ,to show themselves ; and as soon as the thaw allowed a thorough jinspection of the face of the wall to be made, it was found that jhardly a single block had escaped damage; in many instances, |the whole face had peeled off to the depth of half an inch ; atone spot, where a drain discharged itself into the river froma height of about six or eight feet, the back action of thewater after its fall, had worn away the lower courses to thedepth of some inches. These were the evidences of the action jof frost and water combined, upon the best constructed wall !at Woolwich. At Chatham, they were of the same character, ibut the damage done to the wall was much greater, :
The portion of river-wall at Woolwich, which was built withrough concrete, was severely injured by the common action iof the water before frost, and the same result was observedin the walls of a school near Blackheath, which were built of ;concrete some years ago : at the ground-line, where the drip 'of the water had acted, the concrete was soft, and yielded easilyto any force applied, while the walls above were very fairlyhard, and seemed to have stood very well. The results of the ;observations made at that time, on the use of concrete in con- :structions of a kind similar to those above mentioned, aresummed up by Captain Denison in the opinion “ that inclimates like ours, in situations exposed to the alternate actionof water and air, concrete cannot be advantageously used usa building material, the apparent economy, caused by thecheapness of the material employed, being more than compen- jsated for by the frequency of repairs. ”
In the report (dated 1846) and evidence of the “ Committee 'on the Harbour of Refuge to be constructed in Dover Bay,” ja great deal of valuable information is afforded on the use ofconcrete. Amongst the various plans submitted to the com-mittee, Captain Denison, Colonel Jones, and Mr. Vignolesproposed to construct breakwaters of blocks of concrete.
The first of these gentlemen recommended that the blocksshould be manufactured at Dungeness, and thence floated toDover by means of camels. The French adopted a similarplan in their works at Algiers , where large blocks of biton,or hydraulic concrete, were floated out to the required spot, jand then allowed to drop into their places from slings. These j !blocks were rectangular in form, and measured 324 cubic j jfeet. At the works at St. Joilette, at Marseilles , also, | ;immense blocks of concrete, 13 yards cubic measure in size, ; ihave been sunk for the foundation. The form suggested by iCaptain Denison was that of an hexagonal prism, and it was jconsidered each block would weigh from 20 to 30 tons. The i jconcrete would be made in the following manner:—the i
gravel of sea-beach to be mixed with the best hydraulic lime ; Iin the proportion of ten or twelve parts of gravel to one of i jlime ; and with the view of causing it to set more speedily Iunder water, a proportion of puzzolana should be added,varying in quantity according to its quality; half the quail- jtity of puzzolana to that of lime would make very hard,sound concrete, which would set rapidly ; but if desirable to jmake it set very quick, the quantity of puzzolana might be !increased till it equalled that of the lime. The concrete usedby Mr. Ranger at Woolwich was nearly the same, except thathe used no puzzolana.
In the course of Captain Denison’s evidence he refers tothe works at Chatham and Woolwich, to which we have