Rebound Hammer Test: An Investigation into Its Reliability in Applications on Concrete Structures

&eissueofconcretestrengthoftenarisesincivilengineeringpractice,eitherduetoqualitycontrolofnewconstructionsorduetothe assessment of existing structures. To this aim, one of the most widely spread techniques is the rebound hammer (Schmidthammer) test,forwhichcalibrationisstillrelatedtothe originalSchmidt curvedating back totheearly 50’s.Inspite ofthelargeamount of research work performed in the last decades, the uncertainties of the rebound test are still not clearly quantified andopento further insight.&is paperpresents anddiscussesawideresearchcampaign onlaboratoryspecimensandonthird-partyspecimensdeliveredtotheLaboratoryforBuildingMaterialsoftheUniversityofGenoa,Italy,forstandardqualitycontrols.Whileitiswellknownthatmoisturecontent,surfacefinishing,andconcretematuritystronglyaffectthetestresult,theeffectofthestressstatehasnotyetbeenstudiedandisfoundinthisresearchtobeafurtherparameteraffectingthetestreliability.&efinaloutcomeofalltheuncertaintiesisvariabilityinestimatedconcretestrengthaslargeas±70%;additionally,someissuesarediscussedontheintrinsicuncertaintyofthistest.Asalreadydemonstratedbymanyauthors,theresultsofthisresearchalsoshowthatauniversalcalibration curve to be used for any concrete, in any condition, conceptually does not exist.