7 
Buarr.—On the Building Materials of Otago. 155 
retard the setting of cement by a mixture of ordinary lime, or by prolonged 
mixing, than omit the operation. 
The large French works that I have mentioned are all built of a conerete 
invented by Mon. F. Coiquet, and known as “betou agglomeré ;” the com- 
position being as follows :— 
Hydraulic lime ... dev bie vis re | 1 
Portland Cement ses 1-5} or,4 
Sand, or gravel, not taieed Shot 8 a pea ee 4 
This has been the most successful application of concrete to ordinary 
building purposes hitherto recorded, and the result is due almost entirely to 
careful manipulation. 
In addition to the essentials of a proper adjustment of the ingredients, 
and thorough mixing with the minimum quantity of water, great stress is 
laid on the necessity for heavy ramming. The concrete is spread in thin 
layers, and hammered with iron-faced beaters till each layer is compressed 
to a third of its original thickness. The surface is then raked to form a 
bond with the next layer, and so the work is carried on continuously to the 
end. The result of this careful treatment is that ‘‘betou agglomere ’’ is one 
of the most compact, impervious, and durable building materials at present 
in ordinary use. 
General Gillmore, of the United States Army, in reporting to his 
Government on the question, made some experiments to determine the 
relative strength of concrete prepared in the usual way, and in the method 
adopted by Mon. Coiquet. I give a few of the results :-— 
Compressive strength.—Crushing weight of Portland cement pure and 
mixed with sand, in pounds per square inch, on blocks seven days’ old :— 
Rammed. Loose. 
Pure cement... 28463 (not sng 2597 
1 of cement to 1.7 of aes 28044 1038 
1 to 3.4 ... es ae 931 Sa 727 
TOs 3s at =. 519 ora 2594 
1 to 6.8. s 2594 re 1042 
Tensile strength eam the same sone: 
20034 55: ive ae 138 os 109 
140 6: in see 66 oye 33 
1t0 6.8. 5 39 24 
Independent of dba Giparoanis. the defects of the loose method of 
depositing concrete in buildings is apparent to any observer. The cavities 
occasionally amount to a third of the whole, consequently a nine inch wall 
is no stronger than one of six inches in which the materials are compressed 
into a solid mass, and the porosity of the structure must be proportionately 
