Conclusions > Flaws are the source of cracking > Concrete compressive strength is primarily depend on the water/cement ratio > Concrete in the 'critical'zones of compression always fail by 'splitting'--- never by 'crushing > Transverse confine can greatly increase axial compressive strength
Ø Flaws are the source of cracking Ø Concrete compressive strength is primarily depend on the water/cement ratio Ø Concrete in the ‘critical’ zones of compression always fail by ‘splitting’ --- never by ‘crushing’ Ø Transverse confine can greatly increase axial compressive strength
Uniaxial compressive strength of three types of specimens:fou,fc,f' b=150 feu=20N/mm2 100%
Cube strength fcu (位方体强度) The dimension of cubic specimen is 150*150*150mm(0r100*100*100mm) >The test result of Cubic specimen is the base of strength grade(强度等级c2o;c3o)of concrete The frictional forces develop between the plates of the testing machine and the contact faces of the test specimen.These end forces produce a multiaxial stress state which increases the compressive strength of the concrete
Cube strength fcu (立方体强度） Ø The dimension of cubic specimen is 150*150*150mm （or 100*100*100mm ） Ø The test result of Cubic specimen is the base of strength grade （强度等级 C20；C30….）of concrete Ø The frictional forces develop between the plates of the testing machine and the contact faces of the test specimen. These end forces produce a multiaxial stress state which increases the compressive strength of the concrete
Prism strength fc (棱柱体抗压强度) >Specimen 150*150*450 mm prism >f。=0.8fcu regions influenced by local stress 1.0 0.9 6=100mm uniform axial stress region 岂ag =150mm 0.7 0.6 1 2 3 4 h/b (b) (a) fig.Uniaxial compression test for prism specimen
Prism strength fc （棱柱体抗压强度） ØSpecimen 150*150*450 mm prism Øfc =0.8fcu fig. Uniaxial compression test for prism specimen
Cylinder strength f(In ACI,CEB) >Specimen d=150mm,H=300mm cylinder >f。'=0.79fcu In the cylinder or prism,the height/width ratio is sufficiently large for the mid- height region to be reasonably free from the multi-axial stress The cylinder or Prism strength may be taken as the uni- axial compressive strength of concrete f。轴向抗压强度 fcu强度等级
Cylinder strength fc ’ (In ACI, CEB) ØSpecimen d=150mm, H=300mm cylinder Øfc ’=0.79fcu In the cylinder or prism, the height/width ratio is sufficiently large for the mid- height region to be reasonably free from the multi-axial stress . The cylinder or Prism strength may be taken as the uni- axial compressive strength of concrete fc 轴向抗压强度 fcu 强度等级