Research On The Evaluation Of Strength For Normal Concrete Hollow Block In Existing Masonry Structures By Rebound Method

Rebound Method is a method to estimate the compressive strength o f concreteand bricks by us ing a spring-driven ha mmer to hit the surface of materia ls andmeasure the rebound value (the ratio of the initia l length of the rebound from thespring) as a strength parameter. This nondestructive, s imp le, fast, and widely usedmethod has been cons idered to be an idea l site detection method of masonry. With theincreasing wide applicatio n of rebound method, it has become a mature technolo gy toevaluate the strength of the concrete, fired brick and mortar. The Chinesegovernme nt has formulated releva nt regulations. Many provinces and c ities a lso haveestablis hed rebound strength curves for application in the respective regio ns. However,a non-fired brick rebound strength formula has not been inc luded in these regulations.Besides that, in order to protect the environment and arable la nds, save energy, anddeve lop lightwe ight, high strength, and hollow chunks of wall materials, theapplication o f concrete hollow b lock has been increasingly widespread. Yet, there isno corresponding rebound method standard for detecting compressive strength of theblocks. Thus, it is necessary to establis h a unified rebound strength curve for concretehollow block in masonry. This research emp loyed a co mparison of the existingreleva nt standards, experime nts, and the mathe matica l statistics method to estabilis h arebound strength curve for concrete hollow blocks in existing masonry. The ma inworks of this thes is are summarized as fo llows:(1) The research processes, deve lopments and characteristics of the concreteblock and concrete block build ing has been introduced. The basic princip les and keyinflue nc ing factors of rebound method to detect the block strength in exiting masonryare summarized. The influences of d ifferent vertical pressure, test methods and thepresence or absence of grouted to the rebound va lue are stud ied in the experime nt ofnine specime ns by Huna n Univers ity. In additio n, based on the test of60blockschosen fro m three walls by Sichuan institute of Build ing Research, the differences ofthe rebound value for d ifferent options of rebound ha mmers and blocks with orwithout ribbed position has been investigated in this research.(2) This research utilised the Origin software to curve fitting. The rebound testadopted Silver Schmidt concrete rebound ha mmer and compressive strength tested sixstandard block masonry specimens and79norma l concrete hollow b lock specimens. 91data of R-f were obta ined fro m the Rebound Test and the compressive test. Thedata were divided into23groups with the group interva l o f0.5. The a verage va lue ofrebound va lue and compressive strength in each group were calculated. The reboundtest adopted ZC3-A concrete rebound hammer and compressive strength tested sixstandard block masonry spec imens, an experimenta l masonry wall from Nanchongcity, and79norma l concrete hollow block specimens.101data of R-f are obtainedfro m the Rebound Test and the compressive test. The data were divided into33groups.The average value of rebound va lue and compressive strength in each group wereca lculated. The data of R-f obtained fro m the two different rebound hammers wasfitted with the Least Square Method in the style of power function. The regress ionanalys is was also conducted. Consequently, the ZC3-A concrete rebound hammerstrength calculatio n formula in the style of power function for the concrete hollowblock in the existing masonry is obtained.Confirmatory experime nta l results demo nstrated that the degree of accuracy ofthe rebound strength curve for concrete hollow b locks in existing masonry establis hedin this thesis is high. As a result, it can provide some essentia l bases for revis io n ofindustry standard The method of eva luat ing the non agglo meratio n brick strengthgrading by rebound method.