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【多选题】
有关泵送混凝土的原材料和配合比的认识，下述正确的是（ ）。A.
为减小混凝土与输送管道内壁的摩阻力，应限制粗骨料最大粒径d与输送管道内径D 的比值，一般粗骨料为碎石时，d≤D／2．5，为卵石时d≤D／3
B.
水泥用量过少，混凝土易产生离析现象
C.
泵送混凝土的坍落度不应小于180mm
D.
混凝土的输送管道线应尽量直
E.
泵送混凝土中不能掺入外加剂
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