Interrelations between cement and concrete properties, part 4 :

Abstract

The relationship between cement properties and drying shrinkage of partially hydrated neat cement pastes of normal consistency made of a large number of portland cements of different types and composition were studied by fitting multivariable regression equations with the aid of a digital computer. The time of cracking of annular specimens restrained from shrinking by a steel core varied from 0.1 to more than 40 hours. The principal variables which appeared to have the greatest effect were the fineness and K2O and C4AF contents of the cements. The fineness and K2O contents of the cements appeared to have the greatest effect on the nonrestrained shrinkage of prisms at the time of cracking of the annular specimens. The shrinkage of neat cement bars after 1, 6, 27 days, and 6 months in laboratory air differed greatly with different cements. The principal variables appeared to be the C3A, SO3, and C3A/SO3 ratios. Other commonly determined variables were associated with each of the above test values. The trace elements, other than Na20 and K2O, were not generally associated with the shrinkage or cracking characteristics. Keywords: Chemical composition of portland cements; cracking of portland cements; cracking resistance of cements; portland cement; shrinkage of Portland cements; trace elements. Page 1. * Included among those notations etc. are the use of C3A, C3S, CzS, and C4AF for the calculated potential compound composition of the cements, viz, tricalcium aluminate, tricalcium silicate, diealcium silicate and tetraealcium aluminof errite. Also used are Loss for loss on ignition, Insol for insoluble residue, and APF for airpermeability fineness. Also used are AE + NAE to designate airentraining plus non-air-entraining cements and NAE for the nonair-entraining cements. The compressive strength in psi of 1:2.75 (cement to sand) mortars cured for 1, 3, 7, 28 days, and 1 year are designated by STOl, ST03, ST07, ST28, and STIY respectively. * Note (1) Ratio of number of plotted points in pairs of diametrically opposite quadrants. Note (2) General trend of lines drawn through plotted points. Note (3) Apparent nature of relationship. L = linear; NL =: nonlinear; NO = no apparent relationship; and L? = nature of relationship not determinable. (Note (4) Quadrant sum in corner test (see reference 5). * Note (1) Ratio of number of plotted points in pairs of diametrically opposite quadrants. Note (2) General trend of lines drawn through plotted points. Note (3) Apparent nature of relationship. L = linear: NL = nonlinear; NO = no apparent relationship; and L? = nature of relar tionship not determinable. Note (4) Quadrant sum in corner test (see reference 5).

Interrelations between cement and concrete properties, part 3 :

“…No measurements were made of the quantity of air entrained in the 1 :2.75 mortars. It was therefore necessary to use the air-content values in the 1 :4 (cement to [20][21][22][23][24][25][26][27][28][29][30] Ottawa sand) mortars as an independent variable even though the relation between the entrained air in the 2 mortars is far from perfect.…”

“…Equations relating the 1-year compressivestrength values of the moist-air stored specimens to combinations of the various independent variables are presented in table [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] for the AE+ NAE cements, and in table [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] for the NAE cements. Equation 1 of table [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] indicates the relationship to commonly determined variables all of which were found to be significant except SO3, and eq 2 indicates the relationship with the addition of the trace elements which were found to be promising. The S.D.…”

“…The contributions of the independent variables to the compressive-strength values of the 1-year air-stored specimens were calculated from the coefficients of eq 4, table [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] [8].) ; **Stored in moist air for 24 hrs., then water for 6 days, then in laboratoi-y air at 23°C, 60 percent RH for 49 weeks, then water for 2 weeks.…”

“…The Portland cements used for the series of tests reported in this section have previously been described [20,21,22]. Some of the cements Avere not tested as Avill be indicated in the next sub- The mix-proportion was 1 part of cement to 3.525 parts of silica by weight.…”

“…The statistical treatment of the compressive strength data obtained was the same as that used in previous sections of this series of articles. It was described in detail in Part 1 section 1 [20]. Briefly it consisted of determining which of the available independent variables appeared to have a significant relation to the dependent variable, and should be tried in the equations.…”