Practical aspects of correlation analysis of compressive strength from destructive and non-destructive methods in different directions

Ci a ion: Bada loo, B.; Lehne , P. P ac ical Aspec s o Co ela ion Analysis o Comp essi e S eng h om Des uc i e and Non-Des uc i e Me hods in Di e en Di ec ions. In as uc u es 2023,8, 155. h ps://doi.o g/10.3390/ in as uc u es8110155 Academic Edi o : Ma co Bonope a Recei ed: 28 Augus 2023 Re ised: 11 Oc obe 2023 Accep ed: 20 Oc obe 2023 Published: 24 Oc obe 2023 Copy igh : © 2023 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). in as uc u es Technical No e P ac ical Aspec s o Co ela ion Analysis o Comp essi e S eng h om Des uc i e and Non-Des uc i e Me hods in Di e en Di ec ions Bai ollah Bada loo 1and Pe Lehne 2,* 1Depa men o Ci il Enginee ing, Qom Uni e si y o Technology (QUT), Qom 37181-46645, I an 2Depa men o S uc u al Mechanics, Facul y o Ci il Enginee ing, VSB-Technical Uni e si y o Os a a, Lud íka Podéš ˇe 1875/17, 708 33 Os a a-Po uba, Czech Republic *Co espondence: pe [email p o ec ed] Abs ac : The esea ch p esen ed he e demons a es he p ac ical aspec s o he nume ical co ela ion o he esul s o he comp essi e s eng h es . The des uc i e es (DT) in a hyd aulic p ess and he non-des uc i e es (NDT) using a Schmid hamme in se e al p ocess a ia ions we e e alua ed. The aim was o e alua e he eal di e ences be ween he ool supplie ’s cu e and es ing. The e o e, 150 conc e e cube specimens wi h an edge leng h o 150 mm we e p oduced using a mix u e o h ee ypes o conc e e classes: C30, C35, and C40. The es was ca ied ou 7 and 28 days o age o he conc e e. The Schmid hamme es was ca ied ou in ho izon al ( θ = 0) and e ical ( θ = 90) di ec ions and using a se ies o 10 measu emen s. Fu he mo e, he es s we e pe o med in wo se s: i s , he sample was placed on he g ound, and second, unde a hyd aulic jack wi h a load o 50% o he maximum bea ing capaci y o speci ic conc e e. Then, eg ession analysis was pe o med on he da a se s o es ablish linea ma hema ical ela ionships be ween comp essi e s eng h and numbe o bounces. The esul s showed ha he co ela ion be ween he DT and NDT es s has a high alue o each g oup, bu he co ela ion equa ions a e di e en and mus be aken in o accoun . Keywo ds: comp essi e s eng h; conc e e; des uc i e es ing; non-des uc i e es ing; eg ession; Schmid hamme 1. In oduc ion Conc e e is one o he impo an cons uc ion ma e ials ha is widely used in building s uc u es due o i s a ailabili y, low cos , and wo kabili y [ 1 , 2 ]. Because conc e e unde load p essu e can ail, de e mining i s comp essi e s eng h plays a i al ole in judging i s quali y. Bo h des uc i e and non-des uc i e es ing me hods ha e been applied o es ima e comp ession s eng h. A conside able amoun o wo k has ocused on he comp essi e s eng h o conc e e. Rega ding des uc i e es ing (DT) me hods, such as he use o a hyd aulic jack, i should be men ioned ha he esul s ob ained om his me hod a e accu a e [ 3 – 7 ]. Howe e , his me hod su e s om d awbacks such as high cos , ene gy consump ion, labo , ime, and lack o abili y o measu e in si u conc e e. The e o e, non- des uc i e es ing (NDT) me hods a e now popula in ha hey a e ca ied ou wi hou des oying he conc e e specimen, while in DT me hods he specimen should be c ushed o ail [ 8 – 10 ]. These NDT me hods a e sui able o in si u measu emen s on exis ing s uc u es o o long- e m measu emen s, whe e i is necessa y o de e mine he changes in conc e e s eng h o e ime. NDT me hods can di ec ly e alua e he quali y o a building e en on-si e by es ima ing he comp essi e s eng h o he conc e e s uc u e, and he mos commonly used NDT me hod is he Schmid hamme [ 8 , 11 , 12 ]. Se e al au ho s ha e used he Schmid hamme o measu e conc e e s eng h [ 8 , 13 – 16 ]. A Schmid hamme , also known as a Swiss hamme o a ebound hamme , is a po able de ice ha measu es he elas ic p ope ies o he In as uc u es 2023,8, 155. h ps://doi.o g/10.3390/in as uc u es8110155 h ps://www.mdpi.com/jou nal/in as uc u es In as uc u es 2023,8, 155 2 o 14 s eng h o conc e e. Mo eo e , NDT me hods a e highly bene icial o measu ing di e en pa ame e s o conc e e, i.e., s eng h, du abili y, and homogenei y [ 9 ]. P e iously, some s udies ha e compa ed a des uc i e es ing me hod (co e es ing) wi h an NDT me hod. NDT me hods a e used o he analysis o conc e es o di e en basic ma e ials and di e en applica ions [10,17]. Acco ding o hei esea ch, he NDT me hod has he ollowing ad an ages in com- pa ison o DT me hods: (1) lowe cos , (2) simplici y, (3) educ ion in labo consump ion, (4) g ea e speed, and (5) e alua ion o conc e e p ope y wi hou damaging i [ 18 ]. The amoun o ebound depends on se e al conc e e pa ame e s, i.e., ha dness, coe icien o elas ici y, o e, wa e con en mo phology o he sample, su ace oughness, ype o agg ega ion, and conc e e ing edien [ 19 , 20 ]. Mo eo e , small es a eas, lack o equipmen , and es di ec ion should be conside ed as de e mining pa ame e s in NDT me hods [ 21 ]. Rega dless o he ad an ages associa ed wi h NDT me hods, his me hod is aniso opy in which di e en di ec ions o measu ing can a ec hei alue. Mo eo e , because he esul s ob ained om using a Schmid hamme can be a ec ed by se e al pa ame e s such as he amoun o po osi y, mois u e, ha dness, oughness, e c., he esul s a e mo e o an app oxima ion han a p ecise alue. Consequen ly, esea che s ha e ied o o e come his limi a ion by inding a co ela ion be ween DT and NDT alues o inc ease he accu acy o measu ing comp essi e s eng h. In ecen yea s, o he au ho s ha e also sea ched o he co ec co ela ion ela ions be ween NDT me hods and DT me hods, because hese co ela ions we e no de e mined on non-s anda d conc e es [ 22 , 23 ]. The e a e also s udies using machine lea ning me hods o p edic he dynamic comp essi e esponse o composi e ma e ials [24]. In he p esen ed esea ch, bo h DT (hyd aulic p ess machine) and NDT ( ebound hamme ) me hods we e p oposed o e alua e he comp essi e s eng h o C30, C35, and C40 o de ine a me hod mo e eliable and p ac ical. I should be no ed ha in o de o minimize e o s in in es iga ions, wa e con en , p ocessing, and a mosphe e empe a u e we e kep cons an . Then, a emp s we e made o compa e he esul s ob ained om he cube samples by eg ession o ind an accu a e ela ionship be ween he DT and he NDT da a in which he co ela ion coe icien is g ea e han 0.85. The esul s o a la ge numbe o es s we e used o e alua e he p ac ical use o he Schmid hamme in many aspec s. The s a is ical and nume ical e alua ion o accu a e measu ed da a in la ge quan i ies is o g ea impo ance o bo h academia and p ac ice, whe e he Schmid hamme is used and has signi ican alue. This is no he only eason why he esul s p esen ed and e alua ed a e placed in he con ex o cu en ends and habi s. 2. Ma e ials and Me hods 2.1. Mix u es and Samples Th ee ypes o conc e e wi h di e en equi ed s eng hs had o be p epa ed o he expe imen s. The conc e e composi ion is based on o dina y Po land cemen o he Teh an b and (OPC), po able wa e (as pe ASTM D1067 [ 25 ]), ine agg ega e (sand), and coa se agg ega e (g a el) om a local sou ce (Qom, I an). The design o he mix u es was ca ied ou in acco dance wi h ACI-211 [26], and he composi ion is shown in Table 1. Table 1. Mix u e design. Conc e e Sand (kg) G a el (kg) Cemen (kg) Wa e (li ) Slump Wa e /Cemen C30 950 852 400 228 7.5–10 0.57 C35 950 852 450 234 7.5–10 0.52 C40 950 852 500 240 7.5–10 0.48 These h ee ypes o conc e e we e selec ed because hey a e he mos commonly used in he cons uc ion indus y. The eason o he h ee ypes was o accoun o di e ences In as uc u es 2023,8, 155 3 o 14 in he case o s eng h. All conc e es had he same ine agg ega e and coa se agg ega e, bu di e en cemen and wa e con en s. This esul ed in di e en w/c a ios and hus di e en esul ing s eng hs. The manu ac u e o he conc e e was ca ied ou in acco dance wi h BS 1881: Pa 108:1983 [ 27 ]. In he p oduc ion o conc e e, he d y ing edien s we e mixed wi h each o he a ambien empe a u e, hen hal o he wa e was added, and all he ing edien s we e mixed o 2 min o o m a homogeneous mix u e. The es o he wa e was hen added and he ma e ials we e mixed o 2 min. The samples we e hen cas in o cube molds, compac ed, and le a oom empe a u e o 24 h; hey we e ans e ed o a ank o wa e and cu ed o 7 and 28 days. A o al o 150 cubic specimens (50 samples o each class) cubic specimens (150 mm × 150 mm × 150 mm) we e p oduced in 3 di e en classes. The e o e, each es se is based on 25 iden ical es samples. Thus, as shown below, i was es ed in wo di e en di ec ions, and a la ge s a is ical e alua ion was ob ained due o he numbe o 25 samples pe condi ion. 2.2. Expe imen al P og am Th ee es s we e p epa ed in he expe imen al p og am—non-des uc i e e ical hamme es , non-des uc i e ho izon al hamme es on a loaded specimen, and des uc i e p essu e es in a hyd aulic p ess machine. A 50% alue o he maximum p edic ed o ce was used o each ype o conc e e— o conc e e C30, i was 15 MPa, o conc e e C35 i was 17.5 MPa, and o conc e e C40 i was 20 MPa. All es s we e pe o med sequen ially on he same specimens o main ain a comple e co ela ion o esul s. Figu e 1shows he s eps o use a Schmid hamme . The i s pic u e is he calib a ion sample, he second pic u e is he es measu emen in a e ical way, and he hi d pic u e is he es measu emen in a ho izon al way. In as uc u es 2023, 8, x FOR PEER REVIEW 3 o 14 These h ee ypes o conc e e we e selec ed because hey a e he mos commonly used in he cons uc ion indus y. The eason o he h ee ypes was o accoun o diffe ences in he case o s eng h. All conc e es had he same ine agg ega e and coa se agg ega e, bu diffe en cemen and wa e con en s. This esul ed in diffe en w/c a ios and hus diffe en esul ing s eng hs. The manu ac u e o he conc e e was ca ied ou in acco dance wi h BS 1881: Pa 108:1983 [27]. In he p oduc ion o conc e e, he d y ing edien s we e mixed wi h each o he a ambien empe a u e, hen hal o he wa e was added, and all he ing edien s we e mixed o 2 min o o m a homogeneous mix u e. The es o he wa e was hen added and he ma e ials we e mixed o 2 min. The samples we e hen cas in o cube molds, compac ed, and le a oom empe a u e o 24 h; hey we e ans e ed o a ank o wa e and cu ed o 7 and 28 days. A o al o 150 cubic specimens (50 samples o each class) cubic specimens (150 mm × 150 mm × 150 mm) we e p oduced in 3 diffe en classes. The e o e, each es se is based on 25 iden ical es samples. Thus, as shown below, i was es ed in wo diffe en di ec ions, and a la ge s a is ical e alua ion was ob ained due o he numbe o 25 samples pe condi ion. 2.2. Expe imen al P og am Th ee es s we e p epa ed in he expe imen al p og am—non-des uc i e e ical hamme es , non-des uc i e ho izon al hamme es on a loaded specimen, and des uc- i e p essu e es in a hyd aulic p ess machine. A 50% alue o he maximum p edic ed o ce was used o each ype o conc e e— o conc e e C30, i was 15 MPa, o conc e e C35 i was 17.5 MPa, and o conc e e C40 i was 20 MPa. All es s we e pe o med sequen- ially on he same specimens o main ain a comple e co ela ion o esul s. Figu e 1 shows he s eps o use a Schmid hamme . The i s pic u e is he calib a ion sample, he second pic u e is he es measu emen in a e ical way, and he hi d pic u e is he es measu e- men in a ho izon al way. (a) (b) (c) Figu e 1. S eps o use a Schmid hamme : (a) placing he calib a ion elemen , (b) es ing e ically, (c) es ing ho izon ally. Be o e s a ing he es , he hamme should be calib a ed; he a e age o en eading numbe s should be conside ed as calib a ion be o e each es . Fu he mo e, he es su - ace should be smoo h, e en in he labo a o y o on si e. The specimen should also be held Figu e 1. S eps o use a Schmid hamme : ( a ) placing he calib a ion elemen , ( b ) es ing e ically, (c) es ing ho izon ally. Be o e s a ing he es , he hamme should be calib a ed; he a e age o en eading numbe s should be conside ed as calib a ion be o e each es . Fu he mo e, he es su ace should be smoo h, e en in he labo a o y o on si e. The specimen should also be held by a igid keepe o a oid shaking. I should be no ed ha he di ec ion o he hamme can a ec he ha dness alues. Acco ding o ASTM C805-02 [28], he hamme should i s In as uc u es 2023,8, 155 4 o 14 be kep e ical and hen he specimen placed on a hyd aulic jack o ake he numbe o opposi e aces o he cube specimen. An a e age o 10 eading numbe s o each su ace was conside ed as a hamme ebound numbe . I he measu ed alue de ia ed om he a e age by 20%, i was no included in he inal in es iga ion. Fu he mo e, i hese neglec ed eading numbe s we e mo e han 2 on each su ace, hen he es was no eliable and was cancelled. Finally, he specimen was des uc i ely es ed o de e mine he comp essi e s eng h o he hyd aulic p ess machine. The comp essi e s eng h o conc e e is a es ca ied ou on a cube, a cylinde , o a sui able piece o b oken beam, some imes on co e holes. A minimum o h ee bodies a e always es ed. Be o e he ac ual es , he geome y o he es body is e i ied. Specimens ha ail non-s anda dly a e excluded om he es . A eco d o each es and i s esul s shall be kep . 2.3. S a is ics The main aim was o ind a ela ionship be ween he DT and NDT esul s. These wo g oups we e i s co ela ed o all conc e es using Pea son’s co ela ion coe icien (PCC) [ 29 ]. The Pea son co ela ion coe icien is a desc ip i e s a is ic ha sums up he cha ac e is ics o a da a se . Speci ically, i desc ibes he s eng h and di ec ion o he linea ela ionship be ween wo quan i a i e a iables. Fo example, a PCC g ea e han 0.5 means s ong s eng h. The same se was hen analyzed using linea eg ession [ 30 ] and he de e minan R 2 [ 31 , 32 ]. R 2 is a s a is ic used in he con ex o s a is ical models whose main pu pose is o p edic u u e ou comes. This analysis p o ides a measu e o how well obse ed ou comes a e eplica ed by he model, based on he p opo ion o o al a ia ion o ou comes explained by he model. Linea eg ession analysis is used o p edic he alue o a a iable based on he alue o ano he a iable. The a iable you wan o p edic is called he dependen a iable. The a iable you use o p edic he alue o ano he a iable is called he independen a iable. This o m o analysis es ima es he coe icien s o a linea equa ion in ol ing one o mo e independen a iables ha bes p edic he alue o he dependen a iable. A linea eg ession co esponds o a line o a ea ha minimizes he di e ences be ween he p edic ed and ac ual alues o he ou pu . The e alua ion o co ela ion and linea eg ession indica es whe he wo pa ame e s ha e a e y high, high, mode a e, low, o no dependence. These nume ically ob ained linea co ela ion cu es we e aced wi h he no ma i e cu e o he Schmid hamme used. The cu es ob ained we e also desc ibed using he equa ion and he s a is ical pa ame e s desc ibed abo e. 3. Resul s and Discussion DT and NDT in es iga ions we e ca ied ou on h ee di e en g ades o conc e es, namely, C30, C35, and C40, o es ima e comp essi e s eng h wi h a good app oxima ion. Tables 2and 3p esen he a e age o 25 comp essi e s eng h measu es in MPa and 25 ebound numbe s in e ical and ho izon al hamme posi ions o conc e e cu ed o 7 and 28 days, espec i ely. Acco ding o he esul s, he comp essi e s eng h inc eased wi h inc easing conc e e g ade; wi h espec o samples cu ed o 7 days, he comp essi e s eng h inc eased om 31.7 MPa (C30) o 38.9 MPa (C40). Fu he mo e, o samples cu ed o 28 days, he comp essi e s eng h inc eased om 42.9 MPa (C30) o 51.1 MPa (C40). The e o e, by compa ing he esul s, i is ob ious ha inc easing he numbe o days ha conc e e samples we e cu ed in wa e led o an inc ease in comp essi e s eng h. Mo eo e , i can be unde s ood om Tables 2and 3 ha i he hamme posi ion changes om a ho izon al di ec ion o a e ical di ec ion, he ebound numbe dec eases. These obse a ions do no de ia e om he expec a ions and in o ma ion a ailable in he li e a u e [ 8 , 11 , 18 ]. E alua ion o he s anda d de ia ion shows ha in all cases he numbe s a e less han 10% o he mean, which co esponds o he es ic ion ha no esul had o be excluded om he s a is ical se . In as uc u es 2023,8, 155 5 o 14 Table 2. A e age comp essi e s eng hs in MPa and ebound numbe o di e en conc e e cu ed o 7 days. Age Class Tes Mean STD 7 days C30 Comp essi e S eng h 31.7 MPa 3.19 Rebound numbe (ho izon al) 28.5 2.81 Rebound numbe ( e ical) 23.1 1.22 C35 Comp essi e S eng h 37.5 MPa 2.74 Rebound numbe (ho izon al) 30.1 2.48 Rebound numbe ( e ical) 24.5 2.25 C40 Comp essi e S eng h 38.9 MPa 4.22 Rebound numbe (ho izon al) 33.2 2.14 Rebound numbe ( e ical) 26 1.75 Table 3. A e age comp essi e s eng h in MPa and ebound numbe o di e en conc e e cu ed o 28 days. Age Class Tes Mean STD 28 days C30 Comp essi e S eng h 42.9 MPa 4.82 Rebound numbe (ho izon al) 34.1 2.19 Rebound numbe ( e ical) 25.9 1.73 C35 Comp essi e S eng h 47.1 MPa 4.36 Rebound numbe (ho izon al) 35.5 1.19 Rebound numbe ( e ical) 28.6 2.36 C40 Comp essi e S eng h 51.1 MPa 3.68 Rebound numbe (ho izon al) 36.1 1.55 Rebound numbe ( e ical) 30.7 3.15 A compa ison be ween he s anda d de ia ion o he hyd aulic p ess measu emen and he s anda d de ia ion o he ebound es shows ha in his applica ion he ebound esul s ha e less a iance. This was obse ed o all h ee ypes o conc e e. To ind he co ela ion be ween Schmid ebound numbe and comp essi e s eng h, he c ushing conc e e s eng h in MPa e sus ebound numbe s is plo ed o 7-day-old conc e e and in ho izon al hamme posi ion o conc e e C30 (see Figu e 2), C35 (see Figu e 3), and C40 (Figu e 4). Simila ly, da a om e ical measu emen s a 7 days a e conc e ing we e analyzed. The esul s a e p esen ed oge he wi h he eg ession cu e in Figu es 5–7. Fu he mo e, da a a 28 days o all conc e es in he ho izon al di ec ion (see Figu es 8–10) and he e ical di ec ion o he hamme measu emen (see Figu es 11–13) a e p esen ed. Fi s , an e alua ion o he esul s measu ed 7 days a e he conc e e. The co ela ion be ween he ho izon al ebound hamme measu emen and he hyd aulic comp essi e s eng h o conc e e C30 shown in Figu e 2shows a PCC o 95%, demons a ing high ag eemen . E en he g aphical e alua ion o he linea co ela ion has a de e mina ion alue o o e 0.9. On he o he hand, in Figu e 3, whe e he same pai is co ela ed bu o C35 conc e e, a sligh ly highe PCC is seen, bu he linea eg ession has a be e i in his case. The equa ion o he cu e has a di e en basis bu a e y simila slope. Figu e 4 hen shows he conc e e C40, o which he co ela ion eg ession cu e has a nega i e in e cep alue on he y-axis, and so i can be seen ha he cu e is signi ican ly di e en . Unlike he i s wo conc e es (C30 and C35), he C40 conc e e has a no ma i e ins umen cu e wi h almos he same slope as he esul ing co ela ion cu e om he nume ical e alua ion. Figu e 5shows he co ela ion o he e ical ebound es expe imen and he com- p essi e s eng h o he p ess o C30 conc e e. The co ela ion o he esul s is a a e y high le el and he cu e de e mina ion is also e y high. The slope o he cu e does no co espond o he no ma i e cu e. Figu e 6 hen shows he same es s, bu o C35 conc e e. Again, we see high co ela ion coe icien numbe s and high ag eemen . Figu e 7shows In as uc u es 2023,8, 155 6 o 14 he same o C40 conc e e. Again, o his conc e e, he slope o he eg ession cu e is e y simila o he no ma i e cu e. In as uc u es 2023, 8, x FOR PEER REVIEW 6 o 14 Figu e 2. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C30. Figu e 3. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 7 days o conc e e C35. Figu e 2. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C30. In as uc u es 2023, 8, x FOR PEER REVIEW 6 o 14 Figu e 2. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C30. Figu e 3. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 7 days o conc e e C35. Figu e 3. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 7 days o conc e e C35. In as uc u es 2023,8, 155 7 o 14 In as uc u es 2023, 8, x FOR PEER REVIEW 7 o 14 Figu e 4. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C40. Figu e 5. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C30. Figu e 4. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C40. In as uc u es 2023, 8, x FOR PEER REVIEW 7 o 14 Figu e 4. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 7 days o conc e e C40. Figu e 5. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C30. Figu e 5. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C30. In as uc u es 2023,8, 155 8 o 14 In as uc u es 2023, 8, x FOR PEER REVIEW 8 o 14 Figu e 6. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C35. Figu e 7. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C40. PCC = 0.958 y = 2.4942x − 25.191 R² = 0.918 0 10 20 30 40 50 60 70 0 102030405060 Comp essi e S eng h [MPa] (DT) Schmid Rebound Numbe [-] (NDT) C35 - day 7 - e ical Expe imen s No ma i e Schmid cu e Linea - expe imen Figu e 6. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C35. In as uc u es 2023, 8, x FOR PEER REVIEW 8 o 14 Figu e 6. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C35. Figu e 7. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C40. PCC = 0.958 y = 2.4942x − 25.191 R² = 0.918 0 10 20 30 40 50 60 70 0 102030405060 Comp essi e S eng h [MPa] (DT) Schmid Rebound Numbe [-] (NDT) C35 - day 7 - e ical Expe imen s No ma i e Schmid cu e Linea - expe imen Figu e 7. Co ela ion o he ebound index o he e ical es and comp essi e s eng h a 7 days o conc e e C40. In as uc u es 2023,8, 155 9 o 14 In as uc u es 2023, 8, x FOR PEER REVIEW 9 o 14 Figu e 8. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 28 days o conc e e C30. Figu e 9. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 28 days o conc e e C35. Figu e 8. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 28 days o conc e e C30. In as uc u es 2023, 8, x FOR PEER REVIEW 9 o 14 Figu e 8. Co ela ion o he ebound index om he ho izon al es and comp essi e s eng h a 28 days o conc e e C30. Figu e 9. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 28 days o conc e e C35. Figu e 9. Co ela ion o he ebound index o he ho izon al es and comp essi e s eng h a 28 days o conc e e C35.