30 BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 
CONCLUSIONS, BASED ON EXPANSION AND CONTRACTION 
MEASUREMENTS. 
1. Xeat cement when allowed to dry, first contracts rapidly, then 
more slowly. The amount of contraction seems to vary with the 
cement, size of specimen, and condition of atmosphere in which 
drying takes place. The amount at 28 days is about 0.1 per cent 
and at 6 months about 0.2 per cent. 
2. Mortar contracts on hardening in air and expands on hardening 
in water. The contraction in warm, dry air at 28 days is about 0.01:5 
per cent for 1:2 and 1:3 mortar and at 6 months is 0.0T8 for 1:3 
mortar and 0.085 for 1 : 2 mortar. The expansion in water is 0.01 per 
cent for 1 : 3 and 0.017 for 1 : 2 mortar at 28 days, and at 6 months 
0.013 for 1 : 3 and 0.02 per cent for 1 : 2 mortar. 
3. Both 1:2:4 and 1:3:6 concrete contract on drying in warm, dry 
air from 0.02 to 0.04 per cent at 28 days and from 0.04 to 0.07 per 
cent at 6 months. When hardening in water an expansion of about 
0.01 per cent takes place at 28 days and 6 months in 1:2:4 and 1:3:6 
concrete. 
4. The richness of the mix of concrete seems to exert a small in- 
fluence on the contraction ; the richer the mix the greater the change 
in length. 
5. Concrete alternately wetted and dried may be made to expand 
and contract owing to these causes. The expansion due to wetting is 
more rapid than the contraction on drying. The thoroughly dried 
specimens of concrete do not recover their original wet length when 
immersed. 
6. Concrete stored in the outer air and exposed to the weather does 
not contract to the same extent as the above described specimens ex- 
cept under very dry conditions. 
7. A waterproof covering, such as coal tar, prevents the rapid 
change in moisture content and greatly retards the expansion and 
contraction. 
8. Reinforcement decreases, but does not prevent, the shrinkage 
and expansion of concrete clue to drying and has no effect on tempera- 
ture changes. Reinforcement can not, therefore, entirely prevent 
cracks, but seems to distribute them and keep them small. 
9. Concrete roads are affected by both temperature and moisture. 
When the drainage is good and the sub-base not wet, the temperature 
effects seem to be most important. A wet sub-base may add to the 
temperature expansion by about 0.01 to 0.02 per cent. The restrain- 
ing effect of friction at the base seems to be almost negligible when 
figuring temperature and moisture expansion and contraction. In 
very dry climates shrinkage due to drying must be added to contrac- 
