86 Fir.E-Kl-:SJ STING liLMLDlNGS. 



5. Burnt ballast and cement, mixed 5:1 and 5/^" thick. 



6. Furnace clinker, sand and cement, mixed 3:2:1 and Sj^" 

 tliick. Became red hot. 



7. Thames ballast, sand and cement, mixed 3:2:1 and 5/1" 

 tdiick. Became red hot. 



The general result was in favour of Nos. i. 5 and 6, and 

 details of the gauge of aggregates, quantity of water, and 

 method of mixing and depositing can be ascertained by referring 

 to the committee's literature and reports. It is thus evident 

 that burnt aggregates should be used, and materials containing 

 latent heat avoided. 



The committee's experiments with timber gave the follow- 

 ing results, though, of course, the varying bulk or dimensions 

 ■of the specimens render them comparatively valueless. 



Karri Wood : 2 hours' exposure — maximum temperature 

 1,800° F., charred depth 3//'. 



Jarrah Wood: 2 hours" exposure — maximum tem])erature 

 2,000° F., charred depth y^" . 



Fir: 2 hours' exposure — maximum temperature 2.000" F., 

 charred de])th 2". 



Oak: 4/ minutes' exposure of 23-I" boards in a horizontal 

 position at a maximum temperature of 2,000° F., consumed 

 them. 



The Karri and Jarrah wood was proljably specially selected 

 for the tests. 



Causes of Failure. — When not caused by earth([uakes, explo- 

 sions, lightning or other shocks, which may be classed as 

 " unavoidable causes," failures are due to more or less '" pre- 

 ventable causes," and, as a rule, can be attributed to carelessness 

 or incompetence in the design or execution of the work. 



Failures due to Materials. — Failures due to the careless 

 selection or manipulation of materials are commonly found to 

 come under one or other of the following heads: — 



(a) The use of inferior, unaerated. damaged or too 

 f|uick setting cement. 



(b) The use of unsuitable or inferior aggregates, such, 

 for instance, as contain only very coarse material, 

 or have been insufficiently graded or carry too 

 much sand or loam, or by the presence of free 

 lime in the stone. 



( e) The use of water containing clay or injurious 

 chemical constituents. The use of too much or 

 too little water in the process of mixing or the 

 imeven application of same. 



Failures due to other Causes. 



( (/) Carelessness in the proportioning or mixing of 



the aggregate with the cement. 

 {e) Disturbance of the concrete after the "setting" 



has progressed. 



