LII. T. W. SEAVER. 



In the ordinary specifications for concrete, the measured 

 amounts of the materials are stated, but it may happen in 

 some cases that the quantity of mortar is not sufficient to 

 fill the voids in the aggregate. This subject is thoroughly 

 discussed by Lieut. Sankey, R.E., in Engineering for Sep- 

 tember last ; he proposes the following as a specification 

 for concrete: — "The percentage of voids in the selected 

 aggregate is to be found, and sand and cement are to be 

 added to make sufficient cement mortar of the quality x 

 sand to 1 cement to fill the voids -f- 20°/°." 



One point to which I should like to draw special atten- 

 tion is that of the grading of sand for concrete purposes; 

 this is already done in the manufacture of concrete pipes, 

 some of which, with sides only If inch thick, will permit 

 of no leakage under a head of 140 feet. From experiments 

 made by Trautwine it appears that ordinary pure sand from 

 the sea shore weighed 97fbs. per cubic foot, and its voids 

 were 0*41 of the whole. Some very fine sand weighed 82tbs. 

 per cubic foot, and the voids amounted to 0*5 of the mass. 

 From the above we learn that coarse grained sand should 

 be used for making concrete, if however, we mix both 

 together, the voids disappear and the weight increases, 

 from which it follows that the amount of cement can be 

 reduced. 



Some interesting experiments were made as to sand 

 grading in concrete by F. Latham, m. inst. c.b., during the 

 last year, and were referred to by him in a paper read 

 before the Society of Engineers in London. These tests 

 were made in connection with the Penzance sea wall and 

 from the materials used ten briquettes were made. In 

 some cases, the materials were carefully measured accord- 

 ing to the stereotyped specifications 1 of cement to 4 of 

 sand &c, and in others care and judgment were used 

 placing a little finer sand to the mixture and a larger pro- 



