EXPERIMENTAL STUDY OF THE COMPRESSIVE STRENGTH OF GROUTED CONCRETE BLOCK MASONRY BASED ON NONDESTRUCTIVE DETECTION METHOD

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1 11 th Canadian Masonry Syposiu, Toronto, Ontario, May 31- June 3, 2009 EXPERIMENTAL STUDY OF THE COMPRESSIVE STRENGTH OF GROUTED CONCRETE BLOCK MASONRY BASED ON NONDESTRUCTIVE DETECTION METHOD Jiang hongbin 1 and Li longei 2 1 Associate Proessor, Structural Engineering, School o Civil Engineering, Harbin Institute o Technology, Harbin, , China, @163.co 2 Master, Structural Engineering, School o Civil Engineering, Harbin Institute o Technology, Harbin, , China, alpha0335@163.co ABSTRACT The grouted concrete block asonry is coposed o sall size hollow concrete block, ortar and grout. To detect the copressive strength o grouted concrete block asonry, the convenient nondestructive detection easures that are used or concrete structures including: rebound ethod, ultrasonic ethod, pulling-out ethod and core drilling ethod, are proposed in this paper. In this paper, our types o detection tests on 25 grouted concrete block asonry speciens had been ade. Experiental results show that these detection ethods entioned above are applicable or grouted concrete block asonry. Based on test results and analysis the orulas o copressive strength or our types o detection easure have been derived respectively, and soe detection suggestions or concrete sall hollow block, ortar and grout or concrete sall hollow block have been given. KEYWORDS: grouted concrete block asonry; copressive strength; nondestructive detection INTRODUCTION The developent o sall concrete block asonry adequately shows its advantages o saving soil, saving energy and re-using waste. However, there is still no a reliable, convenient and practical detection syste, which accounts or the speciications and the actual construction conditions in dierent countries, and to rapidly and conveniently detects the copressive strength o the grouted concrete-block asonry in sall concrete block asonry structures that are in progress or already built. The purpose o this paper is to adopt existing non-destructive or icro-destructive detection ethods, to test coposed aterials o grouted concrete block asonry respectively, cobine these test results, and inally ind a reliable and coprehensive appraisal ethod o the copressive strength o grouted concrete block asonry. The existing non-destructive or irco-destructive test ethods explored are the rebound ethod, pulling-out ethod, and core drilling ethod. It is easible to use the above entioned detection ethods or testing concrete strength,

2 however using only one o the ethods can not resolve the proble due to the characteristics o the grouted concrete-block asonry itsel. Thereore, in this paper, according to suitability o various detection ethods and characteristics o grouted concrete block asonry, we consider rebound ethod to test block and ortar, the pulling-out ethod to test block strength; and the core drilling ethod to test the copressive strength o grouted concrete. DESIGN OF TEST SCHEME AND MATERIAL COMPOSITION Main actors aecting the copressive strength o grouted block asonry include block strength, ortar strength and grouted concrete strength. According to People's Republic o China national standards "Basic Standard Test Method o Basic Mechanical Properties o Masonry"(GBJ ), copressive speciens o sall concrete blocks can be ade. Main speciication o blocks is ,the speciication o secondary blocks is When testing, three categories o strength or blocks: MU10, MU15, and MU20 and three categories o strength or ortar: Mb10, Mb15, and Mb20. For grouted concrete, the three categories o strength level are: Cb20, Cb30, and Cb40 See Figure 1 or the specien, and Table 1 or cobination o specien aterial strength levels. Group Block strength Figure 1: Standard Specien Table 1: List o Specien Paraeters (each) Mortar strength Grouted Concrete strength Ultrasonic And rebound copressive Core Drilling ethod Pulling Out ethod Group1 MU10 Mb10 Cb Group2 MU15 Mb10 Cb Group3 MU20 Mb15 Cb Group4 MU15 Mb15 Cb Group5 MU20 Mb20 Cb Based on Table 1, speciens can be divided into ive groups, and every group contains ive speciens. As a result, there are 25 speciens in total. The irst three speciens o every group are tested with ultrasonic ethod and rebound ethod irst, then a copressive test is perored on the to directly obtain the copressive strength. The other two speciens are tested with core drilling ethod and pulling-out ethod respectively; and the copressive strength o the core colun concrete and the block is deterined respectively.

3 TEST RESULTS OF COMPRESSIVE STRENGTH OF STANDARD SPECIMENS In order to analyze and copare with nondestructive detection results, 5 groups o standard speciens including 15 speciens or copressive strength are tested. The actual values tested are listed in Table 2. Table 2: Actual Tested Values o Copressive Strength o Standard Speciens(MPa) Group Group1(MU10,Mb20,Cb20) Group2(MU15,Mb10,Cb20) Group3(MU20,Mb15,Cb30) Group4(MU15,Mb15,Cb30) Group5(MU20,Mb20,Cb40) REBOUND DETECTION OF SPECIMENS AND THE RESULTS The test includes rebound on the block and ortar. Using the rebound ethod to test copressive strength is rapid, siple, convenient, and applies to large area ield detection o strength. REBOUND OF THE BLOCK AND RESULTS The block rebound apparatus used is the ZC3-A type with a 2.207J standard energy and pointerdirect-reading type indication syste. When aking rebound tests o the block, 16 spots are tested in every test area. The representative rebound value o every test area should be the arithetic average o the reaining 10 rebound values ater eliinating the 3 largest and 3 sallest values ro the 16 rebound values o the area and expressed with R. When testing, the standard specien is placed vertically on the copressor and preload a orce o 100 kn is applied, (see Figure 2). Table 3 or contains the copressive strength values and rebound values o blocks o various standard speciens. Figure 2: Rebound o Block

4 Table 3: Copressive Strength and Rebound Values o Blocks No. Copressive Strength (MPa) Rebound Value R Carbonized Depth () A-1(MU10) A-2(MU10) A-3(MU10) B-1(MU15) B-2(MU15) B-3(MU15) C-1(MU20) C-2(MU20) C-3(MU20) D-1(MU15) D-2(MU15) D-3(MU15) E-1(MU20) E-2(MU20) E-3(MU20) In the Chinese Ministry o Construction standards "Technical Speciication or Inspection o Concrete Copressive Strength by Rebound Method" (JGJ/T ), the universal or o strength test curve is: 10 c B Cd cu = A R (1) In the regression equation o the universal strength test curve, the rebound value R and carbonized depth value d are taken as the ain variables. Fro Table 3, the strength testing orula can be derived ro the regression equation o the universal strength test-curve (Equation 1) by the rebound ethod as ollows: c cu R d = (2) According to the orula: the correlation coeicient r = 0.875, relative standard deviation e = 11.89% <12%, the average relative error δ=0.0071, the coeicient o variation = 11.92%. C v REBOUND TEST OF MORTAR AND THE RESULTS The ortar rebound apparatus used is the ZC5 type with a 0.196J standard energy and pointerdirect-reading type indication syste. A side o the specien is taken as one test area o the ortar rebound test. In every test area, 12 rebound spots are evenly set out. The axiu and the iniu are eliinated to get the arithetic average o the reaining 10-rebound values and are expressed with R. The rebound values ro tests o various speciens and the copressive strength value o standard copressive blocks o ortar let beorehand are

5 suarized, and then regression analysis is perored as per the principle o the least square ethod. The data used to it are listed in Table 4. Table 4: Mortar Copressive Strength and Rebound Data No. A-1 A-2 A-3 B-1 B-2 B-3 C-1 C-2 C-3 D-1 D-2 D-3 E-1 Copressive strength(mpa) Rebound value R Give the regression equation in the or o index: = A R c cu B (3) According to data in Table 5 and Equation 3, the index curve regression equation is: c cu R = (4) The correlation coeicient o the orula: r =0.861 > 0.85 which can eet the precision requireent. PULLING-OUT METHOD DETECTION AND THE RESULTS The principle behind the pulling-out ethod to test strength is ainly based on the correlation between concrete tensile strength and copressive strength. In Chinese Speciication " Technical Speciication or Inspection o Concrete Strength by Pull-Out Post-Insect Method" (CECS69: 94) speciies that: when testing concrete strength with the pulling-out ethod, the counterorce supporting the inner diaeter o the three-point type pulling-out test apparatus is d 3 =120, the anchoring depth o the anchorage h=35,the drilling hole diaeter d 1 =22, and the enlarged trough diaeter d 2 =30(see igure 3 or detailed diensions). The pulling-out device is the SHJ-40 odel ultiunction testing device anuactured by Beijing Chinese Coal Mine Engineering Copany Ltd. Insect sta Bearing ring 2α Figure 3: Sketch o Three-point Type Pulling-out Test Device

6 The pulling-out orces and block copressive strength obtained ro tests o various standard speciens were suarized and the itting data are listed in Table 5. As per the principle o the least square ethod, the regression analysis can be ade using straight line regression equation: = a F b (5) qk p + Where a, b =regression coeicient; qk =representative value o sall concrete blocks; F p =representative value o liit pulling-out orce. Thus, the linear regression strength testing orula o pulling-out ethod is as ollows: F (6) qk = p The correlation coeicient r = 0.966, the relative standard deviation e = 3.84%<12%, the average relative error δ=0.030, the coeicient o variation C v = 3.86%. Table 5: Block Copressive Strength and Pulling-out Force No. A-1 A-2 A-3 A-4 B-1 B-2 B-3 B-4 C-1 C-2 Copressive strength(mpa) Pulling-out orce(kn) No. C-3 C-4 D-1 D-2 D-3 D-4 E-1 E-2 E-3 E-4 Copressive strength(mpa) Pulling-out orce(kn) DATA TREATMENT AND ANALYSIS OF CORE DRILLING METHOD The HILTI DD130 drilling hole achine with 102 diaeter drilling bit was used. The core colun diension o grouted block asonry was ~ which eets the diension requireent o taking cores. In this paper, the stipulations in Chinese Speciication "Technical Speciication or Inspection o Concrete Strength by Core Drilling Method" (CECS03:2007) were adopted. The concrete copressive strength o core speciens can be calculated as per the ollowing equation: Fc, cor (7) A cu = Where cu, cor F c =concrete copressive strength o core speciens (MPa); =the axiu pressure ro copressive test o core speciens (N);

7 A =copressive section area o core speciens ( 2 ) The detailed calculation results o grouted concrete copressive strength and core specien copressive strength are listed in Table 6. Table 6: Grouted Concrete Strength and Core Specien Copressive Strength Design Value o Grouted Concrete strength Core specien copressive Strength (MPa) Grouted concrete Copressive strength (MPa) Core specien/grouted -core concrete Cb Cb Cb Fro the values in Table 6, it can be seen that the copressive strength o grouted concrete obtained by drilling core ethod well conors to the copressive strength o standard blocks o grouted concrete, and can relect real copressive strength o grouted concrete. Only the strength o the Cb20 concrete is higher than copressive strength o standard blocks o grouted concrete. The higher copressive strength ay have resulted ro the preparation process o standard blocks let beorehand. Thus, the drilling-core ethod is an eective ethod to test concrete strength directly and is easible or testing grouted concrete block strength. COMPARING AND ANALYZING OF COMPRESSIVE STRENGTH OF GROUTED CONCRETE BLOCK MASONRY In Chinese Code "Code or Design o Masonry Structures"(GB ), calculation orula or average copressive strength o grouted concrete block asonry is as ollows: g, =. 63α cu, ( (8) = ) K (9) Where g, =average copressive strength o grouted concrete block asonry. =average copressive strength o hollow concrete block asonry. cu, =copressive strength o concrete cubic block. 1 =average copressive strength o the block (N/ 2 ). 2 =average copressive strength o ortar (N/ 2 ). K =corrective coeicient o asonry strength, When 2 > 10MPa, K = α =rate o grouted cores; or tests in this paper, it is The results in Table 7 were obtained by putting the data outputs o copressive strength o blocks ro the pulling-out ethod, the data outputs o copressive strength o ortar ro the rebound ethod, and the data outputs o copressive strength o the core colun concrete ro the drilling-core ethod into the orulas (8) and (9), and then adopting the results ro copressive tests or the copressive strength o standard speciens.

8 No. Table 7: Coparative Analysis o Copressive Strength o Concrete Block Masonry 1 (MPa) 2 (MPa) K cu, g, (MPa) (MPa) (MPa) Actual copressive Strength (MPa) Copressive/(8) Pulling-out Rebound - (9) Drillingcore (8) Copressive A A A B B B C C C D D D E E E Fro Table 7 we can ind that when putting the corresponding testing data o copressive strength o coposed aterials o grouted concrete block asonry into Equations (8) and (9) to calculate the whole copressive strength, in the Table, the average ratio o actual copressive strength to the calculating value as per the speciications is 1.074,the standard deviation is 14.35%,and the variance coeicient is 14.35%. This shows that using this cobination o ethods o nondestructive or icro-destructive ethods to test the copressive strength o grouted concrete block asonry is easible, and the calculated copressive strength value well conors to the actual copressive strength value. CONCLUSIONS In this paper, the rebound, pulling-out and drilling-core nondestructive or icro-destructive detection ethods were used to test the copressive strength o 25 grouted concrete block asonry speciens. Large quantities o testing data on blocks, ortar, and grouted core concrete were obtained and a coparison and analysis with the copressive test results o standard speciens was ade. Finally a calculating ethod or the copressive strength o grouted concrete block asonry by nondestructive or icro-destructive detection ethods was deterined. The ain conclusions are as ollows:

9 1.The copressive strength o both concrete blocks and ortar can be tested by using the rebound nondestructive detection ethod. The copressive strength o blocks can also be tested by the icro-destructive pulling-out ethod. The testing results o the pulling-out ethod are better than those o the rebound ethod. In this paper, the strength testing orula or blocks and ortar respectively were set up. 2.It is convenient, easible, direct and reliable to use the drilling-core ethod in testing copressive strength o grouted concrete block. In this paper, data ro drilling-core ethod well conored well to the copressive strength obtained ro tests o standard blocks o core colun concrete. 3.The calculating ethod or the copressive strength o grouted block asonry is: Enter the copressive strength results ro the nondestructive or icro-destructive tests or blocks, ortar and core colun concrete into the calculating orula o average copressive strength in the asonry speciications to calculate the copressive strength o grouted concrete block. The calculated results copare well with the actual copressive strength. Through tests and analysis, it can be seen that under existing technical conditions, the nondestructive detection o the copressive strength o grouted block asonry can be deterined copletely. The data ro the nondestructive tests are accurate, and the calculated results are believable. We recoend incorporating the nondestructive detection ethods o copressive strength o grouted concrete block asonry into corresponding detection speciications. REFERENCES 1. Cui shuang-shuang. Experiental study on inspection o erchandise concrete strength by pull-out ethod.master's thesis in Harbin Institute o Technology WANG Yu-din. Test intensity o concrete by rear-extraction ethod & experiental research or local curve. Shanxi Architecture. 2005, (15) 3. SHI Cheng-ing, HU Xing-in, SHAO Shi-sheng, ZHANG ling. How to iprove the repercussion test accuracy o concrete copressive strength. Journal o Shanxi University o Technology (Natural Science Edition) 2007(03) 4. Han Jian-ping, Wang Fei-xing, Wang Zhi-hua. Discussion on Several Issues o Testing and Evaluating Concrete Strength by Drilling Core Method. Earthquake Resistant Engineering and Retroitting.2008(02) 5. Basic Standard Test Method o Basic Mechanical Properties o Masonry (GBJ ). China Architecture & Building Press Technical Speciication or Inspection o Concrete Copressive Strength by Rebound Method (JGJ/T ). China Architecture & Building Press Technical Speciication or Inspection o Concrete Strength by Pull-Out Post-Insect Method (CECS69: 94).China Planning Press Technical Speciication or Inspection o Concrete Strength by Core Drilling Method (CECS03:2007). China Architecture & Building Press Code or Design o Masonry Structures (GB ). China Architecture & Building Press.2002