摘要
基于再生卵石混凝土直剪试验,研究了再生卵石骨料取代率和试件尺寸对再生卵石混凝土剪切力学性能的影响.结果表明:与天然卵石混凝土相比,再生卵石混凝土的抗剪强度有较大提升,再生卵石骨料取代率为50%时抗剪强度提升最大,提高幅度最大为47%;峰值位移随着再生卵石骨料取代率的增大而增大,最大提高了115%;再生卵石骨料取代率和试件尺寸对混凝土剪胀性能影响较小;最后,给出了尺寸换算系数,建立了再生卵石混凝土抗剪强度尺寸效应律公式,计算值和实测值吻合良好.
卵石具有强度高、耐腐蚀等优点,是沿江地区主要的混凝土骨料之
抗剪强度是混凝土力学性能的主要组成部分之一,对混凝土构件的整体性能和破坏起着重要的作用.王建民
本文通过改变再生卵石骨料取代率和试件尺寸,研究再生卵石混凝土的抗剪性能及其尺寸效应,并建立再生卵石混凝土抗剪强度尺寸效应律公式,以期为再生卵石混凝土抗剪强度预测和工程设计提供参考.
再生卵石骨料(RPA)由某市环江旧城改造的建筑废弃混凝土经颚式破碎机破碎、筛分、清洗后获得,粗骨料粒径为5~20 mm,再生卵石骨料及天然卵石骨料(NPA)的形貌见

图1 再生卵石骨料及天然卵石骨料的形貌
Fig.1 Morphology of RPA and NPA
Aggregate type | Moisture content(by mass)/% | Water absorption rate(by mass)/% | Apparent density/(kg· | Bulk density/(kg· | Crush index(by mass)/% |
---|---|---|---|---|---|
NPA | 0.06 | 0.26 | 2 619 | 1 615 | 12.02 |
RPA | 0.26 | 1.08 | 2 573 | 1 508 | 16.92 |
混凝土设计强度为C30,再生卵石骨料取代
r/% | Mix proportion/(kg· | ||||
---|---|---|---|---|---|
Cement | Water | Sand | NPA | RPA | |
0 | 353.9 | 195.0 | 666.4 | 1 184.7 | 0 |
50 | 353.9 | 195.0 | 666.4 | 592.4 | 592.4 |
100 | 353.9 | 195.0 | 666.4 | 0 | 1 184.7 |
试验采用基于RMT‑301岩石与混凝土力学试验压力机自行研发的剪切加载装

图2 加载装置
Fig.2 Test setup
试件的破坏形态如

图3 试件的破坏形态(剪切破坏面)
Fig.3 Failure modes of specimens(shear failure surface)
试验实测特征点参数见
Specimen | Fτp/kN | τp/MPa | Sp/mm |
---|---|---|---|
S‑0 | 44.95 | 2.00 | 0.57 |
S‑50 | 57.83 | 2.57 | 1.03 |
S‑100 | 50.63 | 2.25 | 1.10 |
M‑0 | 52.47 | 1.75 | 0.37 |
M‑50 | 77.41 | 2.58 | 0.65 |
M‑100 | 59.12 | 1.97 | 0.78 |
L‑0 | 61.95 | 1.55 | 0.33 |
L‑50 | 86.96 | 2.17 | 0.45 |
L‑100 | 74.47 | 1.86 | 0.71 |

图4 混凝土的荷载-位移曲线
Fig.4 Load‑displacement curves of concretes

图5 混凝土垂直位移-剪切位移曲线
Fig.5 Vertical displacement‑shear displacement curves of concretes

图6 再生卵石骨料取代率对混凝土抗剪强度的影响
Fig.6 Effect of RPA replacement rate on concrete shear strength

图7 再生卵石骨料取代率对混凝土峰值位移的影响
Fig.7 Effect of RPA replacement rate on peak shear displacement of concretes
根据上述荷载-位移曲线及破坏形态分析可得,再生卵石混凝土试件的破坏过程主要分为弹性阶段、弹塑性阶段、破坏阶段和残余阶段.从弹塑性阶段开始,试件的荷载-位移曲线呈现非线性增长,说明直剪作用下再生卵石混凝土试件存在一个损伤演变的过程.基于损伤力学理论,引入损伤变量D来描述再生卵石混凝土的损伤过
(1) |
式中:E0为材料初始变形模量,取值为0.4Fτp处的割线模量;E为材料割线模量.

图8 试件的损伤曲线
Fig.8 Damage curves of specimens
各规格试件尺寸换算系数按照下式计算:
(2) |
式中:Ci为尺寸换算系数,i取M、L;τpS是尺寸为S的试件抗剪强度;τpi是尺寸为i的试件抗剪强度.
各再生卵石骨料取代率下试件的尺寸换算系数如

图9 各再生卵石骨料取代率下试件的尺寸换算系数
Fig.9 Size conversion coefficient of specimens under different RPA replacement rates
基于Bazant能量释放准
(3) |
式中:As为试件剪切破坏面的面积,c

图10 抗剪强度和剪切面面积的关系
Fig.10 Relationship between shear strength and area of shear plane
(4) |
(5) |
(6) |
(7) |

图11 抗剪强度计算值与实测值对比
Fig.11 Relationship between τp,c and τp,t
(1)随着再生卵石混凝土试件尺寸的增大,试件破坏时的剪切位移逐渐减小;试件剪切破坏面的骨料脱落程度随着再生卵石骨料取代率的增大而减小.
(2)再生卵石骨料取代率r对试件的抗剪强度、峰值位移影响显著.与r=0%的试件相比,r=50%、100%的试件抗剪强度最大提高幅度分别为47%、20%,峰值位移的最大提高幅度分别为81%、115%.
(3)再生卵石混凝土的尺寸效应要弱于普通混凝土,但强于天然卵石混凝土.随着再生卵石骨料取代率的增大,再生卵石混凝土的尺寸换算系数先减小后增大.尺寸为150 mm×150 mm×200 mm、200 mm×200 mm×200 mm的试件尺寸换算系数平均值分别为1.09、1.23.
(4)基于Bazant能量释放准则,提出了再生卵石混凝土抗剪强度与试件尺寸、再生卵石骨料取代率的计算关系式,计算值与实测值吻合较好,可用于预测不同尺寸、不同再生卵石骨料取代率下再生卵石混凝土的抗剪强度,供工程结构设计和分析时参考.
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