ASTM C78/C78M:18 pdf free download – Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading).
10.1.8 11 specimens were capped. ground. or if leather shims wei used.
10.1.9 Whether sawed or molded and defects in specimens.
10.1.10 Age of specimens.
II. Precision and Bias
II. I Precision:
11.1 . I Singk-Operawr Precisicrn—The single operator standard deviation for Lest determinations has been tound to be 0.25 MPa 137 psil and to be indcpcndcnt of thc beam sizes used in the interlaboratory study (11$) (Note 7). Therefore, the modulus of rUpture from two properly conducted tests by the same operator on specimens of the same material (sanw batch of concrete), using the same size specimen (100-mm (4-in.J or I 50-,nm (6-in.j deep beams). is not expected to ditler by more than 0.72 MPa 1104 psiJ.
11.1.2 Mulii.Laboratorv Precision—The multilaboratory coefficient of variation for test determinations has been found to be as shown in the third column of Table I. The coefficient of variation was found to be similar for both specimen sizes used in the ILS for modulus of rupture between 4.2 and 5.5 MPa 16(X) and 800 psil. A higher multilaboratory coefficient of variation was observed for 100-mm L4-in.I deep beams 11’r modulus of rupurc near 6.9 MPa I l(X)O psil. Therefore. the modulus of rup(ure from two properly conducted tests by two different laboratories on specimens of the same material (same batch of concrete) and beam size arc not expected to differ from each other by more than the value in the fourth column of Table I. The acceptable difference between two test deterniinations is expressed as a percentage of their average.
Nrii 7—Thc preCision of this test method was deiennincd from an inierlaboraoy study conducted in 2016 The study insolsed three concrete mistures with modulus of rupture value’, of approsimately 4.1
MPa 1600 pil. 5.5 MPa 1800 psil antI 6.9 MPu 11000 pil. Two betm sues were used: 1(8) by 100 by 355 mm 14 by 4 by 14 in.l and ISO by ISO by 533 mm 16 by 6 by 21 in.J. Three cst determinations were conducted for each combination of specimen size and concrete mixture. The number of laboratories used br dclennining the precision ‘.aned from It) to 17 depending on the concrete mixture and beam size. The data used to develop the precision statement were obtained using the inch.pound
This number represents the difference limit td2s as dcscntwd in Practice C670.
Note 8- -The results for each test condition (specimen size and concrete strength) include data from 3 to 5 laboratories that used hand operated testing machines with paper charts for reading the ultimate force.
For the 100-mm [4-in.] deep beams, these machines resulted in higher single operator variability in mixtures with strengths between 4.1 to 5.5