1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



The lime is to be used in a hot state when slacked, and to be imme- 

 diately mixed, using no more water than is sufficient to incorporate 

 them. After being twice turned, it is to be wheeled on to a stage 

 10 feet high, and let fall into the trench ; it is not to be puddled or 

 disturbed in any way until perfectly set. — No. 3. All concrete must 

 be composed of gravel perfectly clean, and mixed with fresh well- 

 burnt lime in the proportion of 6 of gravel to 1 of lime. The lime and 

 gravel to be mixed in a dry state, and a sufficient quantity of water 

 afterwards added. — No. 4. Concrete to be composed of good lime, 

 gravel, and sand, in the proportion of y to ~ of lime, and it should be 

 laid in about 12 inch layers or courses, and pitched from a height of 10 

 to 12 feet, neither should it be disturbed until properly concreted and 

 set. 



In the above five opinions, including that of Sir Robert Smirke, we 

 have the relative proportions of gravel and lime, varying from 3 to 9 . 

 and No. 1 states the lime and water to be first mixed, in which No. 2 

 nearly coincides, whilst No. 3 insists on the gravel and lime being first 

 mixed, and then the water added ; Nos. 4 and 2 coincide that the 

 concrete is not to be disturbed after it is thrown into the trench, 

 whilst Sir Robert Smirke expressly states that parties are to be em- 

 ployed puddling the mass. The whole are agreed in specifying that 

 the material is to be thrown from a height. From considerable prac- 

 tice and experience in the mixing of concrete, I think that the lime 

 need not be ground, but simply mixed with the gravel, and then, by 

 the addition of water, it will fall to an impalpable powder, also that 

 it is unnecessary to be at the expense of puddling the mass after being 

 deposited in the trenches, neither is there any advantage to be derived 

 from discharging the mixture from a height, both of which operations 

 increase the expense of the concrete, and as the concrete in the act 

 of setting expands in bulk, I think that alone a sufficient proof of the 

 inutility of both of the above mentioned operations, their tendency 

 being to condense the mass, whilst its own natural tendency is to 

 expand. With respect to the proportion of lime and gravel, I think 

 the less lime the better will be the concrete, and that the proportion 

 of 8 to 1 of lime is decidedly better than 3 of gravel to 1 of lime. As 

 to the quality of materials employed, the lime must be stone lime, 

 fresh from the kiln ; that from chalk will not do, and hydraulic or lias 

 lime is to be preferred to stone limes. With respect to gravel, if ob- 

 tained from a pit, the ochereous or ferruginous is to be preferred, and 

 if loam is present, so as to soil the hand, the gravel must be washed, 

 if the gravel be obtained from rivers by dredging, alluvial and vege- 

 table deposits are to be avoided; and if the gravel contain vege- 

 table refuse, it must be screened or washed. Shelly sharp gravel is 

 the best, the proportion of small or large pebbles, and the due quan- 

 tity of sand, is soon learned with a little practice. 



As to the uses of concrete, it is principally adopted as an artificial 

 foundation, and from four to six feet is a sufficient depth, and ex- 

 tending two feet beyond the space to be occupied with the building. 

 The following testimony of the utility of concrete, is from Weale's 

 Bridges, page 31. "Piling will probably never be found more safe 

 than a body of concrete ; the latter cannot be too much esteemed, for its 

 durable and almost imperishable nature, besides being quite as safe and, 

 perhaps, more durable than piling;" and from the paper of Lieute- 

 nant Denison, before alluded to, we have the following ratification of 

 its uses. "Concrete cannot be advantageously employed as a build- 

 ing material." " It may be employed with advantage in backing 

 retaining walls." I. K. Brunei, Esq., C. E., has used concrete as a 

 foundation, nearly exclusively and universally in the bridges on the 

 Great Western Railway; and in the celebrated bridge of Maiden- 

 head, the land arches are backed with concrete, to the depth of 10j 

 feet, and the abutments of the large arches are also backed with 

 concrete. In culverts underneath embankments, the same able engineer 

 has extensively used concrete as a backing material, the brickwork 

 being kept thin, and then enveloped in a mass of concrete, in the 

 form of a polygon, of six sides, or, of the form of two truncated 

 cones, with their bases joined. 



Concrete was used on the Great Western Railway, wherever it could 

 be employed, as a backing material ; its use is now rapidly extending 



47 



to the provinces, and bids fair to supersede all other means now em- 

 ployed for making a foundation; it is much improved by being mixed 

 with oxide of iron, smith's scales, and roasted iron stone, or any ma- 

 terial containing iron. As regards the comparative expense, brick- 

 work being the most common building material, has been taken as the 

 standard of comparison with concrete for price, and its cost in most 

 districts will be found from one-third to one-sixth the price of brick- 

 work, taking a cubic yard as the quantity of each material, the latter 

 will cost 5s. and the former 21s, both, to a great extent, bein* regu- 

 lated by the vicinity of brickyards, and the facility of obtaining 

 gravel. I have known concrete executed at3s.3rf., 3s. Gd., 4s., 4s. Gd., 

 5s.,7s.Gd., 8s. Gd., and lis. Gd. per cubic yaid, although the most 

 common price is 7s. Gd.; as to brickwork, the general price is 21s., 

 and the range is from 14s. to 27s. Gd. per cubic yard. The London' 

 price being 25s. per cent, dearer than the country. The facility of 

 obtaining lime regulates the cost of concrete ; the price of lime per 

 cubic yard, measured dry in clots, at Dorking in Surrey, is 11*.-, 

 Barrow in Leicestershire 21s.; Bulwell in Nottinghamshire 9s. Gd.- 

 Breadon in Derbyshire 15s. Gd; Harefield in Buckinghamshire 16s'. 

 Gd. ; Fulwell, Durham County 9s. The measures of lime, also, vary 

 much ; in some places it is sold by the cubic yard, measured dry, 

 which is decidedly the best method adopted ; it would be desirable if 

 it was universal. It used to be sold in London by the hundred, as it 

 was called, not of weight, but a measure, a yard square, and a yard 

 and one inch deep, which will be equal to 16 or IS bushels, but it is 

 now sold by the cubic yard. The Fulwell and Barrow lime is sold 

 by the quarter, eight of which make a ton and a half. Lime is also 

 sold by the boll and chaldron; a chaldron will be about 3A tons, a 

 single horse cart about six bolls. In agricultural districts, the bushel, 

 boll and quarter are used ; in colliery districts, the chaldron and ton are 

 the standard of measure. With respect to the cost of gravel, pro- 

 vided it can be obtained on ground belonging to the company, the 

 getting, screening, and cartage will cost Is. 6d. to 2s. per cubic yard; 

 if it be obtained from the gravel pits of the country, the charge will 

 be per ton, from 2s. Gd. to 2s. 9J., if screened 3s. 3d. to 3s. I0d., if 

 broken Gs. lOd. A cubic yard will weigh from 24 to 27 cwt. If the 

 gravel is dredged or brought from the shores of a river, the cost will 

 be 2s. Gd. per yard, or nearly the same as from the pit. The prices 

 of the various operations of getting, screening, and washing gravel 

 are respectively 10d. and 12d. per cubic yard. The price of excava- 

 tion is also included in the price of concrete in all railway specifica- 

 tions, which will be about 4d. per cubic yard, as generally the exca- 

 vation is of limited extent, and consequently more expensive than an. 

 extensive excavation, and when the gravel is obtained on the ground 

 of the Company or proprietor, the excavation is a double operation, 

 the hole having to be refilled with other materials in lieu of the gravel 

 obtained. From the experience of several thousands of yards and 

 variety of situations, I find the cost of mixing the materials, or as it is 

 termed concreting, to be Is. per cubic yard, and taking the proportion 

 of material at 5 to 1, the following will be a fair estimate of the cost 

 of concrete : — 



s. d. 

 1 cubic yard of lime - - 12 6 



5 do of Gravel at 2s. Gd. • 12 6 

 Labour mixing at Is. per yard - GO 



G yards of excavation at id. - 2 



Waste, contingencies and profit, at Is. 6 



6 cubic yards, at Gs. Gd. - =: 39 

 Concrete will set in 24 hours; the specific gravity is 125, or about 

 the same as brickwork, although brickwork is sometimes 1G5 lb. per 

 cubic foot. Lieutenant Denison gives the strength of concrete S = 

 IW 

 Abd- 

 paving, tlie proportion is as 1 to 13. 



The following works may be consulted ; Colonel Pasley, on Calca- 

 reous Cement: Weale, 1839; — Aikin on ditto, in Transactions of So- 



The constant S being 9-5, and comparing concrete to York 



