118 REIBLING. 



Tropical climatic conditions enhance its value, for in our climate it is 

 never subjected to low temperatures. It is absolutely impervious to the 

 ravages of white ants. The local high temperature, heavy rains, and 

 alternate humid and dry atmosphere, although rapidly destructive to 

 iron and steel and their protecting coatings, are actually beneficial to 

 good concrete, adding to its strength, hardness, and durability. 



Properly constructed concrete will resist earthquake shocks and it 

 can be made fire and water proof. It protects iron or steel rods, beams 

 or girders from rusting. It is sanitary and clean. The materials can all 

 be shipped in small parcels no matter how massive the desired structure, 

 thus eliminating many of the difficulties of inferior or limited trans- 

 portation facilities. 



However, these influences are advantageous only to good concrete. For 

 instance, a bad mixture resulting in a permeable concrete will not 

 protect the reinforcement from atmospheric influences, and the iron 

 work may rapidly rust away. Cement expands when wet and contracts, 

 on drying. Therefore, the concrete exposed to sun and rain should be 

 homogeneous and its mortar not too rich, otherwise surface cracking 

 will result. It must also be remembered that the same raAv material 

 and identical process of manufacture may result in a 25 per cent difference 

 in the ultimate strength of the exposed concrete if made before, during, 

 or after the rainy season. Under the present conditions a high factor 

 of safety is our only recourse to assure permanent structures. 



The same conditions existed in tbe United States only a few years 

 ago. Concrete construction was taking tremendous strides, but the 

 demand for the more economical use of cement was heard from all sides. 

 More reliable construction, better workmanship, more practical building 

 laws, and a better knowledge of the value of the natural resources of 

 sand, gravel and stone was demanded. As a result, builders, engineers, 

 architects, chemists and' cement testers carried on experimental work and 

 the Government aided the inquiry. The Structure-Material Testing 

 Laboratory at St. Louis which is devoted entirely to testing concrete 

 material has an annual appropriation of $100,000. Similar work is 

 necessary in the Philippine Islands, and fortunately it can be undertaken 

 without excessive extra expense, as we already have a fully equipped 

 cement-testing laboratory at the Bureau of Science. 



THE SAND USED IN CONCRETE CONSTRUCTION. 



The importance of thoroughly testing sand and gravel has been fully 

 set forth in the literature on concrete construction. 



"Upon large or important structures it pays from an economic standpoint to 

 make very thorough studies of the materials of the aggregates and their relative 



