EXPANSION AND CONTRACTION OF CONCRETE. 23 



reading on the instrument. The total contraction over the uncracked 

 portions of the pavement equaled 0.462 inch in a total length of 230 

 feet, or 0.00017 inch per inch of length. The calculated contraction 

 for the fall in temperature between the initial reading (82°) and this 

 reading (50°) equals 0.000176 inch per inch of length, almost iden- 

 tical with the actual measured contraction. 



On March 4, when the temperature of the pavement was 30° F., 

 another set of readings was taken. In the interval the pavement 

 had been subjected to the extreme cold of the winter. Here again is 

 seen the effect of change in temperature upon the concrete. That 

 part of it which remained free from cracks contracted 0.000307 inch 

 per inch of length. The decrease in temperature during this period 

 was 52°, and hence the theoretical contraction would be equal to 

 0.00029 inch per inch of length, so that here again the temperature 

 influence seems to be borne out by actual nieasurement. It will be 

 seen that the cracks and expansion joints in this section opened con- 

 siderably, and the colder the weather the greater the openings be- 

 came. 



In June, 1915, not quite a year after the road was constructed, 

 another set of readings was made and gave the results shown on the 

 curve. The warm weather had decreased the contraction of the con- 

 crete below the amount shown in the preceding March. This section 

 was laid in warm weather when the temperature exceeded 82° and 

 the temperature for the pavement on June 19 was only 68°, so that 

 some contraction of the uncracked concrete should be expected. This 

 amounted to 0.0167 inch, or 0.00006 inch per inch of length. The 

 theoretical contraction for this fall in temperature is 0.000077 inch, 

 just a little more than the actual measured contraction. A feature 

 of this measurement is the great contraction at some of the expansion 

 joints and a very large expansion at another joint and at two of the 

 cracks. The large contraction or closing of some of the joints and 

 the large opening at one may be accounted for by the relative move- 

 ments of the slabs due to inequalities in the sub-base and to the fact 

 that the section under test is at the bottom of a long 4 per cent grade. 



In February, 1916, the last set of measurements was taken in cold 

 weather. Here again the contracting effect of low temperatures is 

 seen on that part of the concrete which has remained intact. A con- 

 traction of 0.00023 inch per inch of length occurred by actual meas- 

 urement, whereas the figured temperature contraction was 0.000264 

 inch per inch of length. Temperature again has played a prominent 

 part in influencing the length of the concrete. Note that the 100-foot 

 length cracked in two places, whereas the sections of smaller length 

 did not crack. 



