A.混凝土運(yùn)輸時(shí)間長(zhǎng)、轉(zhuǎn)運(yùn)次數(shù)多 B.振搗過(guò)渡 C.摻入的外加劑過(guò)多
A.人工砂 B.河砂 C.山砂
A.30minB.35minC.45min