186 



THE IRRIGATION AGE. 



year 1912, and in his report to the Hawaiian Sugar 

 Planters' Association for the year ending Sept. 30, 

 1912, H. B. Penhallow, Puunene, Maui, chairman of 

 the committee on cultivation, gives the first descrip- 

 tion of such work. His report is based upon a paper 

 presented to the Association by H. W. Collins, C. 

 E., who was in charge of this work for the H. S. 

 P. A. 



Mr. Collins emphasizes the fact that the lining 

 put on by the Cement-Gun process is far superior 

 to similar work done by hand. He states that they 

 have several miles of lining done by each method 



the water has been applied. I have seen them mix- 

 ing so much at one time that it would be impossible 

 to get it on inside of 30 to 40 minutes. This initial 

 set, especially with some cement on the market, is 

 considerable and is, of course, lost under these con- 

 ditions. The men repeatedly do this thing unless 

 watched, although explicit instructions to the con- 

 trary have been issued. This fault is entirely elimi- 

 nated with the gun method. 



"Comparative tests of mortar made by hand 

 and by the Cement-Gun have been made by a well- 

 known engineering company. These show that the 

 product of the Cement-Gun developed from 70 per 

 cent to 260 per cent greater tensile strength, and 

 from 70 to 720 per cent greater compressive strength 

 than the product of the same mixture when applied 

 by hand. These tests also showed that compared 

 with the most carefully prepared hand-made cement 

 mixture, 'Gunite' is far more impervious and water- 

 proof. 



"We have at this time finished 2J^ miles of 

 open ditch and three short tunnels, their respective 

 lengths being 250, 400 and 750 feet. The work has 

 been entirely satisfactory and very good results 

 have been obtained. On our larger ditch we have 

 averaged about 100 feet per day, a running foot 

 being equivalent to 18 square feet. All the labor 



o/ fla.tp Sec//o/? 



Fig. 2 Constructional detail of the cement gun. 



and find the gun work far more watertight and not 

 to contain any of the cracks found in hand work. 



After giving a brief description of the Cement- 

 Gun and the operation of the same, he makes the 

 following statements : 



"There is a marked difference between cement 

 mortar applied by hand and the product of the ma- 

 chine. The latter is shot under a pressure of ap- 

 proximately 40 Ibs. to the square inch, and leaves 

 the nozzle at a velocity of 200 feet per second ; con- 

 sequently it is far denser and of a much greater 

 tensile strength than that applied by hand. One 

 very .important point in favor of machine applied 

 mortar is that the combining of cement and water 

 takes place in transit, and the mixture does not have 

 to be moved after an initial set. This is one of our 

 worst troubles on concrete work in the islands. The 

 laborers generally employed here do not realize 

 the necessity of handling- the mortar quickly after 



on the job has been under contract, varying on this 

 larger ditch from 15 to 20 cents per linear foot. 

 This cost covers mudding where the section is un- 

 even, wiring, man for nozzle, men mixing sand and 

 cement and supplying the gun, a helper for the 

 engine, and all labor for moving the outfit. 



"The tunnel work has given us a good line on 

 what is possible with the gun. In all three tunnels 

 the engine and gun have been at least 100 feet from 

 the end of the tunnel. This in the long tunnel 

 would make an 850 foot delivery pipe or hose from 

 the gun to the nozzle. Working at this distance, 

 however, diminishes the output considerably, since 

 the air motor cannot be run wide open as when 

 working nearer. This means less material delivered 

 to the discharge pipe and consequently less work. 



"The following is the record of complete cost 

 of work' for a period of five weeks on a ditch of 18 

 feet cross section: 



