CONCRETE CONSTRUCTION IN THE PHILIPPINE ISLANDS. 119 



proportions. This fact has been seriously overlooked in the past and thousands 

 of dollars have sometimes been wasted on single jobs by neglecting laboratory 

 studies, or by errors in theory." 1 



The experience of Spackman 2 and Lesley, 3 described in their report 

 read before the Eleventh Annual Convention of the American Society 

 for Testing Materials, is also of special interest. 



These authors found that cement which would harden with one sand, would 

 not do so with another, and that great variations of the strength of cement mortar 

 were produced by washing the sand. These variations are shown in the following 

 table. 



Comparative test of sand "A," washed and unwashed, Ottawa sand, and normal 



cement. 



Age. 



"A" un- 

 washed. 



"A" 

 washed. 



Ottawa 

 sand. 



7 days. . 



28 davs. - .. 



Pounds. 

 21 

 130 



Pounds. 

 172 

 228 



Pounds. 

 250 

 438 









However, Spackman and Lesley state that — 



"such extreme cases are not frequent and from the engineering standpoint are 

 less dangerous than where the lack of strength due to the sand is less marked. 

 When the failure to harden is complete, the effect is so obvious as to insure the 

 taking out of the defective material; but where the failure to harden is only 

 partial, it may not be discovered during construction, in which event the latent 

 weakness in the structure may in time of unusual stress cause failure and 

 consequent grave disaster." 



In another report 4 we find the following : 



"Sand, or the fine aggregate shall be suitable siliceous material passing the 

 one-fourth inch mesh sieve, and containing not over 10 per cent of clean, un- 

 objectionable material passing the 100 sieve. A marked difference will be found 

 in the value of different sands for use in cement mortar. This is influenced 

 by the form, size, relative roughness of the surface of the sand grains, and the 

 impurities, if any, contained. Only a clean, sharp, gritty sand, graduated in 

 size from fine to coarse, and free from impurities can be depended upon for best 

 results. Soil, earth, clay, and fine 'dead' sand are injurious to the mortar, and 

 at times extremely dangerous; and they also materially retard the hardening 

 of the cement. An unknown or doubtful sand should be carefully tested before 

 use to determine its value as a mortar ingredient." 



1 Taylor and Thompson. Concrete, Plain and Reinforced. 

 183. 



2 M., Am. Soc. Testing Materials. 

 1 Assoc. Am. Soc. C. E. 



'Eduard S. Lanied. Cement Age (1907), 4, 2. 

 93217 5 



New York. (1907), 



