12. Concrete slabs of length 25 m are laid end to end to form a road surface. What is the width of the gap that must be left between adjacent slabs at a temperature of -150C to ensure they do not buckle at a temperature of +450C.Coefficient of thermal expansion for concrete a = 12x10-6 0C-1 13. The main span of San Francisco's Golden Gate Bridge is 1275 m long at its coldest. The bridge is exposed to temperatures ranging from -150C to 400C. What is its change in length between these temperatures? Assume that the bridge is made entirely of steel.