Table Xiv

TABLE XIV Materials for One Cubic Yard of Concrete Quantities per Cubic Yard. Any table giv ing the quantities to be used in mixing concrete by the cubic yard, can be only approximate. Varying fineness in the sand, or varying com pactness in the concrete due to ramming, may affect the quantities by 10 per cent in any direction.

Table XIV, showing the number of barrels of cement, sand, and gravel required for one cubic yard of concrete of different mixtures, will therefore serve a useful purpose only for estimating roughly the quantities and cost of materials.

A more nearly accurate determination can be made by referring to Table XV, which indicates the number of barrels of Portland cement, and the fraction of a cubic yard of both sand and stone, required for making one cubic yard of rammed concrete of variously proportioned mixtures with different coarse aggregates.

Measuring According to Voids.

As an ap proximate guide to the use of Table XV and other tables, where a determination of voids has been made, it may be pointed out that 45 per cent voids in the coarse aggregate would indi cate the average conditions, and would be about what is found in broken stone with dust screened out; 40 per cent voids would correspond to gravel or mixed stone and gravel; 50 per cent voids would indicate poor grading, as in an aggregate screened to uniform size; while 30 per cent voids and under would indicate an aggregate graded with great care.

Where voids have been determined in both sand and coarse aggregate, the upper part of Table XVI, which may be taken as representing average conditions, will be found useful.

Where the voids are the same as in the upper part of Table XVI, but the cement is measured loose in a box after dumping from a barrel, the quantities should be determined from the lower part of the table, as under such conditions a bar rel of cement yields 4.4 cu. ft. of loose cement: From the above table it will be seen that the following rule can be deduced: Add together the number of parts, and divide this sum into 10; the quotient will be approximately the number of barrels per cubic yard. Thus, for 1:2:5 con crete, the sum of the parts is 8, and 10---8=1.25 barrels of cement per yard, which is approxi mately equal to 1.30, the amount called for by the table.