回复:c20c30c40混凝土配合比设计计算步骤
原始资料:ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
1、混凝土设计强度等级为C30(空心板)无强度历史统计资料,桥梁所在地区属寒区。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
2、组成材料:PO42.5等级牡丹江牌水泥,密度PC=3.1×103Kg/m3,富裕系数=1.13,砂为中砂表观密度P'S=2.65×103Kg/m3,碎石最大粒径dmax=40mm,表观密度P'g=2.75×103Kg/m3,水为一般饮用水。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
设计步骤:ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(一)设计初步配合比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
1、确定混凝土配制强度(Ryp=Ry+1.65б=30+1.645×5=38.2MPaÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
2、计算水灰比(w/c)ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(1)按强度要求计算水灰比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Rs=RCRb=1.13×42.5=48MPaÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(2)计算混凝土水灰比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
w/c=ARs/Ryp+ABRs=0.48×48/38.2+0.48×0.52×48=23/50.1=0.46ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(3)按耐久性校核水灰比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
根据混凝土所处环境属于寒区允许最大水灰比为0.55.按强度计算水灰比是0.46。符合耐久性要求,采用计算水灰比0.46。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
3、选定单位用不水量(Mwo)ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
由于碎石最大粒径40mm,选用混凝土用水量:Mwo=175Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
4、计算单位用灰量(Mco)ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(1)按强度计算单位用灰量ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mco= Mwo/ w/c=175/0.46=380 Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(2)按耐久性校核单位用灰量ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
根据混凝土所处环境属寒区配筋混凝土,最小水泥用量不低于300 Kg/m3,按强度计算单位用灰量380 Kg/m3,符合耐久性要求,采用单位用灰量为380 Kg/m3。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
5、选择砂率(βs)ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
胜根据碎石最大粒径40 mm及水灰比w/c=0.46,选定混凝土砂率取βs=32%。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
6、计算砂石用量ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(1)采用质量法ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
已知:单位用灰量Mwo=175 Kg/m3,砂率βs=33%ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mso+Mgo=Pcp-Mco-MwoÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mso/Mso+Mgo=0.33ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
假设混凝土混合料湿表观密度Pcp=2400 Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mso+Mgo=2400-380-175ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mso/Mso+Mgo=0.33ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
解得砂用量Mso=609 Kg/m3,碎石用量Mgo=1236 Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
按质量法计算初步配合比:ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mco : Mwo : Mso : Mgo =380 : 175 : 609 : 1236ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
即: 1 : 0.46 : 1.6 : 3.25 w/c=0.46ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(二)试拌混凝土,提出基准配合比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
1、按计算初步配合比试拌15L混凝土拌后物,测定其坍落度为2.5cm,满足施工和易性要求,其粘聚性和保水性亦良好。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
2、提出基准配合比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Mca :Msa :Mga=1 :1.6 : 3.25, w/c=0.46ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
(三)检验强度,测定试验室配合比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
1、检验强度ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
采用水灰比分别为(w/c)A=0.41 B=0.46 C=0.51拌制三组混凝土拌和物。砂、碎石用量不变,用水量亦保持不变。三组配合比经拌制成型,在标准条件养护28d后,A组抗压强度为41.5MPa,B组抗压强度为34.0MPa,C组抗压强度为28.5MPa。ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
绘制混凝土配制强度Ryp=38.2MPa的灰水比c/w2.38关系曲线即水灰比w/c=0.42ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
2、确定试验室配合比ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Msb+Mgb=2400-417-175ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
Msb/ Msb+ Mgb=0.33ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
即Msb=596,Mgb=1213ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
修正后配合比Mcb:Msb:Mgb=417:596:1213=1:1.43:2.91ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
水灰比Mwb/Mcb=175/417=0.42ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
计算湿表观密度Pcp=417+175+596+1213=2401 Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
实测湿表观密度P'cp=2400 Kg/m3ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
修正系数б=2400/2401=1ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´
因此试验室配合比为Mcb':Msb':Mgb'=1:1.43:2.91, w/c=0.42ÅH»¬NpYbbs.3c3t.comMGNacR¥Ò´