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TAE MARINE. REVIEW 17 THE ACTION OF SEA-WATER UPON CONCRETE. BY W. J. SANDEMAN, M. INST. C. E. IN Engineering, LONDON. It has been known for a considerable time that chemical action takes place between the acids contained in sea-water and the lime contained in Portland cement; and that if Portland-cement concrete be made porous or permeable, so as to enable sea-water to act continuously throughout its mass, that the cement will gradually become disintegrated, and ultimately be destroyed by such action. This has happened, and is still happening, to a number of dock and pier works both in this country and abroad; and that such destruction has been due to the porosity of the concrete and the action of sea-water upon it has been proved by investigation of concretes in dock works that have failed. See "Notes from Reports upon Concrete, in Aberdeen Dry Dock" by Prof. Brazier, of Aberdeen University, and Mr. John Pattison, Northumberland County Analyst; also papers. by Dr. Michaelis, of Berlin, and R. Feret, of Boulogne. PROPOSED STANDARD PROPORTIONS FOR CONCRETES. TABLE I.--IMPERVIOUS CONCRETES FOR SPECIAL PARTS OF WORKS, SUCH AS AROUND GREENHEART DOCK SILLS AND GATE QUOINS.. NO. 2 CONCRETE IS ALSO ADAPTED FOR PIER WORKS NEAR LOW-WATER LEVEL WHERE EXPOSED TO WASH OF WAVES OR STRONG CURRENTS. Concrete without Displacers. -: Volumes. s A sis og OO ee Omg . StH [Unit Costs of Con- pee Gauged by Zget| 3s cretes per Cubic ele Meshes Ssuea| 368 q |Yard, taking No.6 go 2 3% In. Square. See oO Concrete as the Hoh a 4.8 aed @2e |Standard of Com- Zo, © WN > Ay mam © parison. : percent. 1 1 1% | 1% broken stone 1.75 100 141 Blah de 2egravel - 1.75 87.5 134 TABLE II.--IMPERVIOUS CONCRETES FOR MARINE WORK, SUCH AS SEA PIERS AND DRY DOCKS, ALSO RESERVOIR WALLS, ETC. Concrete without Displacers. Volumes. Sue cr So. ssog| 5°8 wee ert sgGe| aoa | BES oo| = Grayel Gauged by Meshes | & Eo) ots OF e so 2 3 | 1% In. Square and Bro- Mee] 2o pe g g zv Bue ° = Bie es 5 ken Stone by Meshes rae aoe ESO 7O|lo | wn 1 In. Square. Se wom les) oe es per cent 3 1 2 3 gravel 2.1 70 119 4 1 2 ae 2.1 60 117 5 1 2 broken st_ne 21 70 gis Conercie with Displacers. ooks OG -- | -- | -- | Gauged by | Displacers.| ---- 2k oe ---- Meshes 1% Ss £2 In. Square. moO ces ee s per cent. 6 1 2 3 gravel Y% cubic 2.1 48.8 100 . - yard Note.--For concrete deposited in situ under water, also near low-water level, where exposed to wash from waves or tidal currents, no displacers should be used. While the author has had experience of this destructive action of the sea-water has also had abundant proof of the permanent stability of dock and pier works which he has constructed in impervious concrete. PROPOSED STANDARD PROPORTIONS FOR CONCRETES. With the view to arrive at standard proportions for con- cretes which would enable them to permanently resist the action of sea-water, the author has carefully studied the question, and the following record if the results at which he has arrived is based on actual tests and long experience in the construction of dock and pier works in concrete; and although the proportions recommended, and the system of measuring sand and aggregates separately differ from or- dinary practice, yet the author contends that for sea works, and particularly for graving docks, should proportions be used other than those proposed in Tables I, and II. there would be risk of percolation by sea-water, which would certainly be followed by disintegration of the con- crete. TO MAKE IMPERVIOUS CONCRETE, Permeability in concrete is due either to the porosity or the insufficiency of the mortar, or to faulty manipulation of the materials. For impervious mortar the maximum pro- portion of sand must not exceed two parts to one of cement. For impervious concretes the volume of the mortar must be in excess of that of the maximum voids in the aggregate, so as to fill these and surround the aggregate. To effect this the most extreme conditions which can occur in practice must be allowed for--viz., maximum reduction in volumne of cement and sand when made into mortar; maximum voids in the aggregate; and unavoidable irregularities in manipulation of concrete. TABLE III.--ORDINARY CONCRETES (NOT IMPERVIOUS) FOR FOUNDATIONS, RETAINING-WALIS, ETC. Concrete without Displacers. ol . n Volumes SEES w,38 .| $82 6 : 0" Fn of Roe R23 nel Gravel Gauged by Meshes |8 4.584 |-3% RB 8 Oss g2| 2 | Z| 2% In. Square, and Broken |£# 9 an aS Ae] Soa qag| fl @ Stone by Meshes1% In. |O 65 5 BAS ey Boe 5o|5 | # Square. SBO o | Dy Zo a per cent, Moe 4 gravel 24 52.5 114 8| 1] 2% 5 Bs 2.45 49 107 0/7113 5 broken stone 2.8 56 108 10 ob 3 6 gravel 2.8. 46.6 102 Concrete with Displacers. oUn Gauged ae a g --|--| -- | Meshes 1 e hh. Displacers. | ---- | £888 | ---- Square. 2 2 3 m Boa } per cent. Wj 3 4 gravel Ycubicyard| 2.8 48.8 107 TABLE IV.--CHEAPER CONCRETES FOR WORKS IN WHICH NO GREAT STRENGTH IS REQUIRED. Concrete without Displacers. Volumes. wT ne 5 Sipe eee) 33 ; rd Z ne + | 4| Gravel Gauged by Meshes |§ tod |seed § o 2-3 S&| o| g| 2% In. Square, and Broken |E+ ® go SOShR 488 ga| 8| ®| Stone by Meshes 1% In. Soa3 est A 5 5Oo| & - Square. ASO o%8 5} 9 o a a per cent. 12);1 /4 7 broken stone 3.5 50 100 3/13) 4 8 gravel 3.5 43.7 97 Concrete with. Displacers. wSEe Gauged by : 4S 8 -- | -- | -- | Meshes 1% Tn: Displacers -- a8 os -- Square. a 5 2 a ' AoA per cent 14) 1] 4 5 gravel ¥4 cubic yard 3.5 48.8 86 For impervious concretes in which displacers are used it is necessary that the size of gravel be limited to what would be gauged by a sieve with meshes 114 in. square, and broken stone to what would be gauged by meshes % in. 'square. When gravel is above that size it separates from the mortar, accumulates together while being deposited, and causes voids in the concrete. The proportions of materials in Tables I and II are such as will fulfil the foregoing conditions, and (with proper manipulation) produce concretes which will perfectly resist the action of sea-water. VOIDS IN MATERIALS AND REDUCTION IN VOLUME. The author ascertained that the voids in gravel vary from 34 to 40 per cent of the volume of the gravel, and the voids