acoustic strain gauges and thermocouples were placed in a reinforced concrete cantilever of the chiswick-boston manor viaduct (m4) during 1964 with a view to providing information on the creep and shrinkage of a normal reinforced concrete construction. readings have been taken over 5 years following casting. the gauges indicated a strain variation of plus or minus 100 x 1/1000000 across the section during the setting of the cement. tensile strain changes occurred on the outside of the cantilever on heating up and on the inside on cooling down. this offers an explanation for the cracking that occurs in large concrete members soon after casting. the total measured movement in the compression flange of the cantilever, inclusive of creep, shrinkage and elastic strain, was less than 200 x 1/1000000 in 5 years, which is less than the value for shrinkage alone specified in cp 115. the recorded shrinkage due to moisture loss was small. it is estimated to be about 30 x 1/1000000 in 5 years. creep factors, measured as the ratio of creep to elastic strain after 5 years. were 0.67 and 1.02 and creep appears to have stabilised. they compare with a range of values of 1.0 to 2.0 measured in other concrete structures recently.(a).

Want to know more about this project?