Table A-1. Compressive Strength Data on Effect of Drilling Cores 



Investigator 



Size of 



Specimen 



(in.) 



Type of 

 Cement 



No. of 

 Specimens 



Compressive 

 Strength 

 at 28 Days 

 for Standard 

 Laboratory 

 Conditions, 

 fc (psi) 



Test 

 Age 

 (days) 



Compressive 

 Strength, f^^ 

 (psi) for - 



Core/Cast 



Coefficient 



of 



Variation 



(%) 



Cast 

 Cylinders 



Cores 



Bloem 



4x6 



Type 1 





3,730 













(Ref 11) 







3 

 3 





3 

 7 



1,750 

 2,310 



1,700 

 2,290 



0.971 

 0.991 











3 





28 



3,210 



3,040 



0.947 











3 





91 



3,420 



3,370 



0.985 











3 





364 



3,450 



3,025 



0.877 

 avg 0.954 



4.9 



4x6 



Type III 





5,490 



















3 





3 



3,710 



3,250 



0.876 











3 





7 



3,770 



3,510 



0.931 











3 





28 



4,160 



3,640 



0.875 











3 





91 



4,440 



4,130 



0.930 











3 





364 



4,270 



3,500 



0.820 

 avg 0.886 



5.2 



4x6 



Type III 





4,150 



















3 





1 



2,980 



2,770 



0.930 











3 

 3 





3 



7 



3,110 

 3,280 



2,910 

 3,020 



0.936 

 0.921 











3 





28 



3,340 



3,060 



0.916 











3 





91 



3,540 



3,180 



0.898 











3 





364 



3,390 



2,850 



0.841 

 avg 0.907 



3.9 



Campbell 



6x12 



Type II 





4,515 













and Tobin 







4 





28 



4,150 



3,850 



0.928 





(Ref 12) 







4 





56 



4,195 



4,140 



0.987 











4 





84 



4,660 



4,095 



0.879 

 avg 0.931 



5.8 



6x12 



Type II 





5,870 



















4 





28 



5,280 



5,345 



1.012 











4 





56 



5,460 



5,390 



0.987 











4 





84 



6,000 



5,695 



0.949 

 avg 0.983 



3.2 



overall avg 0.932 



38 



