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INFLUENCE OF CHEMISTRY AND MICROSTRUCTURE
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INFLUENCE OF CHEMISTRY AND MICROSTRUCTURE
ON PORTLAND CEMENT CLINKER GRINDABILITY

C.E. BUCHANAN JR., ROAN INDUSTRIES INC.
H.J. BAYLES, COPLAY CEMENT COMPANY

ABSTRACT

A simple test is presented which can detect differences in clinker grindability. The results obtained correlate fairly well with clinker chemistry and with the clinker structure as determined by the scanning electron microscope.

INTRODUCTION

A simple test was needed to evaluate various materials for efficiency as grinding aids. From this evolved the current test procedure which can be used to predict the relative grindability of Portland cement clinkers.

PREVIOUS TESTS

In all probability soon after man broke his first rock, he began wondering how much energy was required to split it, and why some rocks split easier than others. It was not until 1867 however that Rittinger proposed that the new surface produced was directly proportional to the work input, and thus began the first quantification of these relationships. In 1885, Kick stated that the reduction in volume of the particles was directly proportional to the work input. In 1951, the Hardgrove-Machine method, developed by the Babcock & Wilcox Company, was accepted by ASTM as a standard for coal grinding. (1) The Hardgrove-Machine is now used for a variety of materials, with an index of from 26 to 50 being reported for 23 Portland cement clinkers with an average of 37.8. Also in 1951 Mr. Fred Bond of the AllisChalmers Co. proposed his third theory of communition which states that "The work input is proportional to the new crack tip length produced in particle breakage and equals the work represented by the product minus that represented by the feed." (2) From this theory, Mr. Bond developed his work index (Wi), which is used extensively today. Eight Portland cement clinkers showed a low of 10.8 a high of 18, with an average of 13.2.

DEVELOPMENT OF PROCEDURE

Both of these tests are good and have been used extensively to determine clinker grindability and in turn to size finish mills when commercial grindability was not available. However, they are relatively expensive, require a considerable equipment investment, need a large sample, and are time consuming. Needing a quick method of evaluating a series of materials to determine their relative worth as a grinding aid, I decided to investigate the Bleuler mill. This mill uses a small sample size, produces Portland cement fineness in a short period of time, and is available to most Portland cement laboratories.

The first attempt was to use a fixed grinding time. It soon became apparent that a precise grinding time could not be achieved and that only one fineness level was reported. It was then decided to use four different times, each of approximately the same duration, but with the actual time measured accurately. The first times selected were 1,2,3 and 4 minutes. After evaluating the data, it was apparent that the 1 and 4 minute time were higher than anticipated. An examination of the procedure showed that the 3 and 4 minute grinds were sticking to the mill, and for clean out, sand with a good amount of grinding aid was being used. Apparently there was enough residual grinding aid in the container to influence the result of the following grind. The procedure was then changed to 15, 30, 60 and 120 seconds. The mill is cleaned after 120 seconds but with sand only.

Consequently, the procedure used is to take 47 grams of clinker which has been passed through a jaw crusher, add 3 grams of gypsum, grind for the prescribed time, measure the time accurately, and determine Blaine surface area. A typical work sheet is shown in Table 1. A simple program has been written for a Hewlett-Packard Model 86 computer using VisiCalc in which the grinding time in seconds, and Blaine surface area are entered for the four grinds. The natural logarithm of the grinding time is calculated, and linear regression computed. Blaines are then calculated at exact grinding time of 15, 30, 60 and 120 seconds. An evaluation is made principally on the basis of the correlation coefficient being above .985 of whether additional grinds are needed or not.

TEST RESULTS

Thirty three clinkers have been tested in this program. The grindability data is shown in Table 2 with the calculated Blaine results at 15, 30, 60 and 120 seconds, the slope of the regression curve (A1), the standard error of estimate (SY.X), the correlation coefficient (r), and the coefficient squared (R), being given. It can be noted that a very good relationship was obtained between the natural log of grinding time and Blaine, with an average SY.X of 80 and a maximum of 154 Blaine points being obtained. The data for sample A190 is shown on figure 1, along with the regression lines for the easiest, hardest and average grinding clinkers.

The chemical analyses are shown in Table 3 with their potential composition being given in Table 4. These show a wide variation in chemical composition as well as being manufactured in wet kilns, grate and four stage preheaters, and flash calciners. The compound composition was calculated using the equations found in ASTM C-114, the lime saturation factor (LBS..) from the formula CaO-(1.65 x A12O3 + 0.35 x Fe2O3 + 0.7 x SO3) x 100 all divided by 2.8 x SiO2. (3) The percent liquid was calculated using 2.95 x A12O3 + 2.2 x Fe2O3 + MgO -- alkalies. The silica ratio (S.M.) was simply, the silica divided by the sum of the A12O3 and Fe2O and the (A.M.) was the alumina divided by the iron.

Simple correlation is shown on the 32 clinkers in Table 5. It is interesting to note that when grinding time is considered, A12O3, Fe2O3, CaO, Loss, Free CaO, and C3S all had increasingly positive coefficients with increased grinding times while SiO2, MgO, SO3, K2O, and the S.M. all had increasingly negative ones.

Multiple regression was then run on the data, using up to 22 independent variables. It soon became apparent that sample A254did not fall on the regression curves. Consequently it was dropper from the regression and 32 observations used. This can be justified because A254 was clinker dust from a clinker cooler dust collector rather than straight clinker. The 120 second grinding time gave the best model fit and it was used to draw all of the conclusions concerning hardness of grind. A summary of the stepwise multiple regression is shown in Table 7. In addition the 15 second grind summary is shown in Table 6, and the slope, (Al), is shown in Table 8.

In this particular program, a F to add and a F to delete is given and the program continues until no more independent variables can be added or deleted.

If you observe Table 7, you can note that the S.M. correlated best, with the Loss, Fe2O3, SO3, K2O, L.S.F., CaO, Liquid, A.M. and MgO following. The last step then eliminated the Fe2O3 from the model. The best model however probably would use just the S.M., Loss, and the Fe2O3.

Consequently, conclusions can be drawn that there is a definite relationship between grindability and chemistry, that it improves as the Blaine surface area increases, and that Type I fineness approximately 65% of the variation can be explained by the chemical analyses.

S.E.M. RESULTS

In order to see if the clinker structure and physical appearance played a part in grindability, five clinkers were selected for examination by the Scanning Electron Microscope (S.E.M.) based on the grindability data determined above. The two samples with hardest grindability and the two easiest grinding samples were selected as well as a fifth sample located between the hardest and the softest grinding ones. Specimens were studied at 20x, 200x, 300x, and 1300x.

Figures 2a, through 2e illustrate the 20x series arranged from easiest to hardest grinding. We can observe more porosity and a more prominent structure in the harder grindability compared to the easier one.

Figures 3a through 3e at 200x illustrates more dramatic differences with the harder grindability exhibiting a well formed prominent crystal structure compared to the easier one which shows less apparent and poorer defined crystals.

Figures 4a through 4e at 300x illustrates the same relationship of crystallinity as does the 200x.

Figures 5a through 5e at 1300x gives the closest look at the relationship of crystal structure and grindability for these samples.

CONCLUSIONS

In conclusion, a simple grinding test is presented that can correlate clinker hardness to crystal structure and appearance as seen in the S.E.M. and chemistry as shown by multiple regression analysis.

REFERENCES

(1) Pit & Quarry Handbook, Seventy Third Edition, 1980-1981, page B-86

(2) Don Olson, Grinding Mill Theory, Portland Cement Association Mill Grinding Short Course, Paper No. 2, 1977

(3) A.K. Chatterjee, Cement Raw Materials and Raw Mixes, Pit & Quarry, September 1979, page 103

 

 

FIGURE 1, SAMPLE A190 COMPARED TO OTHER CLINKERS

 

 

TABLE 1-WORK SHEET FOR REGRESSION CALCULATIONS

SAMPLE NO. A190
INTERCEPT (Ao) -2681.0
SLOPE (A) 1429.30
SY.X2 2586.96
SY.X 50.86
r .998935
SUMS 10631 14.94 3.312E7 58.18 43102.4
ST DEV 1272.92 .889637 6747467 6.67 7120.84
SECONDS (X) BLAINE (Y) LN(X) X*X Y*Y LN(X)*Y Y CALC Y-Y CALC
14.94 1158 2.70 1340964 7.31 3131.28 1183.94 -25.94
29.63 2160 3.39 4665600 11.48 7319.78 2162.65 -2.65
58.9 3227 4.08 1.041E7 16.61 13152.7 3144.66 82.34
118.16 4086 4.77 1.670E7 22.77 19498.6 4139.74 -53.74
SECONDS 15 30 60 120
BLAINE CALCULATED 1164 2180 3171 4162

 

 

TABLE 2-SUMMARY OF GRINDING RESULTS

  GRINDING TIME, SECONDS  
15 30 60 120
Lab# *********BLAINE********* Ao A1 SY.X r R
A177 1004 2006 3007 4008 -2908 1448 48 .9963 99.26
A190 1164 2180 3171 4162 -2681 1429 51 .9989 99.78
A205 1148 2035 2923 3811 -2320 1280 127 .9912 98.25
A207 1139 1926 2712 3500 -1936 1135 36 .9992 99.84
A208 1320 2208 3096 3983 -2148 1281 64 .9977 99.54
A209 1196 2098 2999 3901 -2326 1301 21 .9998 99.96
A224 1339 2112 2885 3658 -1681 1115 28 .9995 99.90
A226 1146 2159 3172 4185 -2831 1462 124 .994 98.80
A227 1117 2094 3072 4050 -2703 1410 146 .991 98.21
A228 596 1460 2324 3188 -2782 1247 142 .9929 98.59
A229 1162 2011 2860 3709 -2154 1224 112 .9929 98.59
A239 1315 2235 3155 4075 -2280 1328 57 .9984 99.68
A240 985 1987 2990 3991 -2930 1446 49 .999 99.80
A241 1175 1965 2753 3542 -1908 1138 87 .9954 99.08
A254 912 1667 2422 3178 -2039 1090 103 .9926 98.53
A259 1335 2291 3248 4204 -2401 1380 111 .9949 98.98
A260 1297 2283 3270 4257 -2557 1423 46 .9991 99.82
A261 1301 2091 2881 3671 -1784 1140 99 .994 98.80
A262 923 2007 3091 4175 -3311 1564 154 .992 98.41
A263 1056 2187 3317 4447 -3360 1631 56 .999 99.80
A264 1225 2114 3002 3890 -2497 1282 12 .9999 99.98
A270 1630 2383 3137 3890 -1313 1087 62 .9975 99.50
A307 801 1753 2704 3657 -2920 1374 118 .9937 98.74
A308 753 1776 2799 3822 -2344 1476 198 .9851 97.04
A310 1110 1913 2716 3519 -2026 1158 156 .985 97.02
A311 1174 2090 3006 3921 -2403 1321 56 .9984 99.68
A312 999 1812 2625 3438 -2178 1173 85 .9956 99.12
A313 964 1824 2685 3546 -2399 1242 100 .9944 98.88
A315 1156 2102 3046 3991 -2536 1363 84 .9957 99.34
A316 1096 2002 2909 3815 -2445 1308 51 .9987 99.74
A321 1282 2226 3169 4112 -2403 1361 26 .9997 99.94
A326 1529 2297 3064 3832 -1470 1107 132 .987 97.42
A332 607 1497 2388 3278 -2871 1284 122 .9922 98.45
 
MEAN 1125 2030 2933 3837 -2414 1304 88 .99509 99.02
MAXIMUM 1630 2383 3317 4447 -1313 1631 198 .9999 99.98
MINIMUM 596 1460 2324 3178 -3360 1087 12 .985 97.02
RANGE 1035 923 993 1269 -2047 544 186 .0149 2.96
ST DEV 226 219 251 311 -490 139 46 .00415 0.82

 

TABLE 3-CHEMICAL ANALYSES OF CLINKERS STUDIED

Lab # Si02 A1203 Fe2O3 CaO MgO S03 Na2O K20 Loss Total
 
A177 20.80 5.60 2.80 65.50 4.00 0.10 0.31 0.13 0.60 99.84
A190 21.20 4.50 3.40 63.50 4.30 1.20 0.22 0.96 0.50 99.78
A205 22.30 5.00 3.60 66.70 0.90 0.40 0.20 0.43 0.50 100.03
A207 21.80 4.80 2.50 65.70 2.70 1.00 0.23 0.70 0.70 100.13
A208 21.9_ 4.70 2.00 65.40 3.50 0.50 0.26 0.76 1.10 100.12
A209 22.20 4.10 4.10 63.40 3.90 0.40 0.22 0.68 0.70 99.70
A224 22.50 4.50 3.30 66.60 1.00 0.70 0.23 0.68 0.40 99.91
A226 22.00 5.00 3.70 66.80 0.80 0.20 0.28 0.50 0.70 99.98
A227 21.60 4.00 6.10 65.90 0.70 0.20 0.24 0.38 0.60 99.72
A228 22.60 3.90 2.60 65.30 3.10 0.90 0.09 0.67 0.90 100.06
A229 21.10 5.00 2.90 66.70 2.90 0.20 0.29 0.48 0.60 100.17
A239 21.90 4.80 2.90 67.00 1.30 0.30 0.29 0.28 1.20 99.97
A240 22.30 5.00 3.10 65.50 1.20 0.10 0.08 0.12 0.60 100.00
A241 23.20 4.50 2.90 66.80 1.00 0.50 0.06 0.43 0.60 99.99
A254 22.30 4.50 3.10 68.10 1.00 0.20 0.16 0.27 0.40 100.03
A259 21.80 4.80 3.50 67.60 0.90 0.10 0.14 0.13 0.50 99.47
A260 22.40 4.90 3.60 66.10 0.90 0.40 0.09 0.34 1.00 99.73
A261 22.60 4.80 3.70 66.30 0.90 0.30 0.08 0.25 0.80 99.73
A262 20.30 4.40 6.10 66.40 0.80 0.20 0.11 0.31 1.30 99.92
A263 21.70 5.30 2.20 67.50 1.10 0.40 0.12 0.75 0.80 99.87
A264 21.20 4.70 5.50 64.50 1.00 1.30 0.29 0.75 0.70 99.94
A270 21.70 5.10 1.90 63.60 4.00 0.70 0.25 1.03 0.70 98.98
A307 22.30 4.90 3.30 67.00 0.80 0.50 0.21 0.33 0.40 99.74
A308 20.90 5.90 2.60 66.40 0.90 1.00 0.13 0.90 0.40 99.13
A310 20.90 4.30 4.00 65.20 3.30 1.00 0.29 0.96 0.30 100.25
A311 21.10 5.10 3.50 68.50 0.30 0.10 0.06 0.13 0.50 99.29
A312 21.50 4.60 3.10 64.20 3.90 1.00 0.09 0.64 0.50 99.53
A313 21.30 4.40 3.70 64.00 4.20 0.80 0.11 0.64 0.30 99.45
A315 21.90 5.70 2.40 66.20 0.80 0.50 0.11 1.44 0.70 99.75
A316 21.20 5.20 1.90 64.10 4.10 1.50 0.26 1.10 0.30 99.66
A321 21.20 4.40 3.20 63.60 5.30 0.60 0.19 0.56 0.90 99.9'5
A326 21.40 4.70 3.50 62.80 4.60 1.30 0.25 0.99 0.50 100.04
A332 22.80 4.20 2.20 65.90 2.90 0.80 0.09 0.84 0.30 100.03
 
MEAN 21.75 4.77 3.30 65.78 2.21 0.59 0.18 0.59 0.64 99.81
MAXIMUM 23.20 5.90 6 10 68.50 5.30 1.50 0.31 1.44 1.30 100.25
MINIMUM 20.30 3.90 1.90 62.80 0.30 0.10 0.06 0.12 0.30 98.98
RANGE 2.90 2.00 4.20 5.70 5.00 1.40 0.25 1.32 1.00 1.27
ST DEV 0.66 0.46 1.03 1.49 1.54 0.40 0.08 0.33 0.26 0.29

 

TABLE 4-POTENTIAL COMPOSITION OF CLINKERS STUDIED

Lab # F CaO C3S C2S C3A C4AF L.S.F. Liquid S.M. A.M.
 
A177 0.70 66.66 9.34 10.10 8.52 94.80 27.12 2.48 2.00
A190 0.40 58.87 16.37 6.17 10.35 91.05 26.24 2.68 1.32
A205 0.60 62.18 17.03 7.16 10.95 91.14 24.20 2.59 1.39
A207 1.50 63.11 14.89 8.49 7.61 92.08 23.29 2.99 1.92
A208 2.30 63.94 14.55 9.07 6.09 92.29 22.79 3.27 2.35
A209 0.80 54.83 22.28 3.93 12.48 88.35 25.92 2.71 1.00
A224 0.60 63.18 16.84 6.34 10.04 91.32 22.45 2.88 1.36
A226 1.40 65.29 13.82 6.99 11.26 92.72 24.47 2.53 1.35
A227 1.10 67.95 10.66 0.28 18.56 94.29 26.54 2.14 0.66
A228 1.20 61.59 18.33 5.94 7.91 90.59 21.09 3.48 1.50
A229 0.90 72.87 5.52 8.34 8.82 96.98 24.80 2.67 1.72
A239 1.10 69.07 10.68 7.81 8.82 94.35 22.41 2.84 1.66
A240 0.30 67.00 13.39 8.00 9.43 93.04 22.97 2.75 1.61
A241 0.40 59.82 21.39 7.02 8.82 89.30 21.15 3.14 1.55
A254 0.50 72.52 9.22 6.68 9.43 95.21 21.53 2.93 1.45
A259 0.50 71.98 8.20 6.80 10.65 95.65 23.03 2.63 1.37
A260 0.30 59.65 19.22 6.89 10.95 90.04 23.71 2.64 1.36
A261 0.30 59.75 19.72 6.46 11.26 89.88 23.53 2.66 1.30
A262 2.10 77.18 -0.03 1.34 18.56 100.04 27.62 1.93 0.72
A263 1.40 69.98 9.42 10.32 6.69 94.97 22.45 2.89 2.41
A264 0.90 58.31 16.79 3.15 16.74 90.82 28.01 2.08 0.85
A270 0.60 55.02 20.71 10.30 5.78 88.92 24.51 3.10 2.68
A307 0.70 64.21 15.49 7.40 10.04 91.94 23.06 2.72 1.48
A308 1.90 65.27 10.68 11.24 7.91 94.08 25.06 2.46 2.27
A310 0.40 69.13 7.77 4.63 12.17 95.70 26.04 2.52 1.08
A311 1.10 78.95 0.93 7.59 10.65 99.51 23.24 2.45 1.46
A312 0.40 59.77 16.55 6.94 9.43 91.07 25.02 2.79 1.48
A313 0.40 61.53 14.65 5.40 11.26 92.03 26.07 2.63 1.19
A315 0.90 59.91 17.59 11.04 7.30 90.68 24.45 2.70 2.38
A316 0.80 57.90 17.10 10.57 5.78 90.64 24.98 2.99 2.74
A321 1.50 61.95 14.05 6.25 9.74 92.32 26.07 2.79 1.38
A326 0.70 52.73 21.57 6.53 10.65 88.30 27.41 2.61 1.34
A332 0.40 61.36 19.08 7.41 6.69 90.29 21.06 3.56 1.91
 
MEAN 0.88 64.05 14.05 7.05 10.04 92.56 24.31 2.73 1.58
MAXIMUM 2.30 78.95 22.28 11.24 18.56 100.04 28.01 3.56 2.74
MINIMUM 0.30 52.73 -0.03 0.28 5.78 88.30 21.06 1.93 0.66
RANGE 2.00 26.22 22.31 10.96 12.78 11.74 6.95 1.63 2.08
ST DEV 0.53 6.22 5.60 2.51 3.13 2.91 1.97 0.35 0.52

 

TABLE 5-SIMPLE CORRELATION BETWEEN VARIABLES STUDIED

  Si02 Al2O3 Fe2O3 CaO MgO S03 Na2O K20 Loss FCaO C3S C3A L.S.F Lqd S.M. A.M. 15 30 60 120 A1  
Si02 1.00 -.24 -.28 0.24 -.28 -.16 -.35 -.11 0.00 -.37 -.37 0.07 -.27 -.75 0.61 -.05 -.09 -.16 -.26 -.31 -.30 Si02
A1203   1.00 -.43 0.32 -.25 -.12 0.04 0.09 -.08 0.13 0.11 0.78 0.17 0.02 -.15 0.64 0.05 0.24 0.33 0.36 0.30 A1203
Fe2O3     1.00 0.00 -.31 -.17 0.06 -.34 0.16 0.03 0.24 0.90 0.27 0.59 -.80 -.88 -.01 0.09 0.16 0.20 0.22 Fe203
CaO       1.00 -.84 -.67 -.32 -.56 0.10 0.11 0.73 0.16 -.30 -.54 -.09 0.02 -.24 -.07 0.08 0.18 0.35 CaO
Mg0         1.00 0.49 0.32 0.40 -.15 -.08 -.46 0.10 -.33 0.31 0.34 0.19 0.18 -.02 -.16 -.24 -.34 MgO
S03           1.00 0.18 0.72 -.37 -.09 -.60 0.07 0.41 0.20 0.21 0.17 -.04 -.25 -.37 -.42 -.37 S03
Na2O             1.00 0.18 -.02 0.16 -.10 -.02 -.13 0.42 -.17 0.04 0.24 0.32 0.24 0.15 -.12 Na20
K20               1.00 -.25 0.07 -.54 0.28 0.45 0.13 0.28 0.44 0.11 -.05 -.14 -.19 -.24 K20
Loss                 1.00 0.53 0.18 -.15 -.49 -.01 -.06 -.07 0.23 0.34 0.42 0.43 0.28 Loss
FCaO                   1.00 0.36 0.04 -.11 0.09 -.11 0.17 -.06 0.04 0.19 0.28 0.39 FCaO
C35                     1.00 -.11 -.16 -.08 -.36 -.16 -.17 -.03 0.15 0.27 0.45 US
C3A                       1.00 0.27 -.40 0.48 0.92 0.03 0.05 0.05 0.03 0.00 C3A
L.S.F                         1.00 0.09 0.10 0.28 -.20 -.22 -.29 -.03 -.22 L.S.F
Lqd                           1.00 -.76 -.38 0.20 0.26 0.30 0.30 0.17 Lqd
S.M.                             1.00 0.56 -.08 -.29 -.42 -.46 -.39 S.M.
A.M.                               1.00 0.05 0.03 0.02 0.01 -.02 A.M.
15                                 1.00 0.81 -.03 0.38 -.31 15
30                                   1.00 0.60 0.77 0.06 30
60                                     1.00 0.96 0.45 60
120                                       1.00 0.69 120
A1                                         1.00 A1

 

TABLE 6-STEPWISE MULTIPLE REGRESSION 15 SECONDS
GRINDING TIME DEPENDENT VARIABLE

STEP # VARIABLE ADDED VARIABLE DELETED STANDARD ERROR R SQUARED F F@90% F/F@90%
1 Na20   293 .057 1.83 2.88 63.54
2 Loss   289 .115 1.86 2.49 74.70
3 F CaO   281 .19 2.19 2.28 96.05
4 K20   280 .229 2.00 2.14 93.46
5 S03   281 .247 1.71 2.05 83.41
6 Si02   282 .27 1.54 1.98 77.78
7 L.S.F.   285 .288 1.39 1.93 72.02
8 C3S   287 .309 1.29 1.88 68.62
9   Na2O 283 .299 1.46 1.93 75.65
10 Liquid   284 .323 1.37 1.88 72.87

 

TABLE 7-STEPWISE MULTIPLE REGRESSION 120 SECONDS
GRINDING TIME DEPENDENT VARIABLE

STEP # VARIABLE ADDED VARIABLE DELETED STANDARD ERROR R SQUARED F F@90% F/F@90%
1 S.M.   265 .217 8.29 2.88 287.85
2 Loss   240 .378 8.81 2.49 353.82
3 Fe2O3   218 .506 9.5E 2.28 419.30
4 S03   214 .538 7.86 2.14 367.29
5 KwO   214 .556 6.51 2.05 317.56
6 L.S.F.   212 .581 5.78 1.98 291.92
7 CaO   214 .591 4.95 1.93 256.48
8 Liquid   214 .608 4.46 1.88 237.23
9 A.M.   215 .623 4.04 1.85 218.38
10 mgO   213 .634 3.79 1.82 208.24
11   Fe2O3 208 .644 4.42 1.85 238.92

 

TABLE 8-STEPWISE MULTIPLE REGRESSION A1 (SLOPE)
DEPENDENT VARIABLE

STEP # VARIABLE ADDED VARIABLE DELETED STANDARD ERROR R SQUARED F F@90% F/F@90%
1 C3S   124 .205 7.75 2.88 269.10
2 S.M.   121 .267 5.29 2.49 212.45
3 F CaO   118 .327 4.54 2.28 199.12
4 A1203   117 .366 3.89 2.14 181.78
5 Na20   116 .404 3.52 2.05 171.71
6 LBS..   114 .444 3.33 1.98 168.18
7 Liquid   114 .462 2.94 1.93 152.33
8   S.M. 112 .461 3.57 1.98 180.30

 

Grindability
Magnified By:
20x 200x 300x 1300x

 

 
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