A minimum compressive strength of at least 4500 psi, after 180 days of curing (aging), is specified for concrete used in a bridge deck project. It is further specified that a water-cement ratio of 0.5, a slump of 3.5 in, and air entrainment of 4% are to be used. To provide a curing protocol that will produce the required compression strength, the concrete should first be moist cured and then cured: a. In air for 3 days.
b. In air after 7 days.
c. In air after 14 days
d. A compressive strength of at least 4500 psi cannot be attained.

An engine, weighing 3000 n, is supported on a pedestal mount. it has been observed that the engine induces vibration into the surrounding area through its pedestal at the maximum operating speed. determine the stiffness of the dynamic vibration absorber spring in (n/m) that will reduce the vibration when mounted on the pedestal. the magnitude of the exciting force is 250 n, and the amplitude of motion of the auxiliary mass is to be limited to 2 mm note: in this question type-in right numbers, no decimals, no fractions, no unit. approximate to right number if needed