Fly Ashes Used For Blended Portland Cement: Effect Of Grinding on Cement Quality
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FLY ASHES USED FOR BLENDED PORTLAND CEMENT: EFFECT OF GRINDING ON CEMENT QUALITY ERIK STOLTENBERG-HANSSON Norcem A.S, N-3950 Brevik, Norway Received 18 November, 1988; refereed ABSTRACT Tests have been performed with Class F fly ashes used for the production of interground 20% fly ash cement. Unground and ground fly ashes were mixed with a reference high fineness Portland cement and tested for strength in mortar (ISO/CEN method). The fly ashes were also tested for chemical composition, bulk density and specific gravity, fineness (Blaine) and particle size distribution (laser method). There are considerable variations in the specific weights of the asdelivered fly ashes. It is shown that even a small amount of grinding increases the specific gravity significantly, and improves and homogenizes the particle size distributions, resulting in higher strength. The strength increase corresponds to the decrease in air void content. Intergrinding of fly ash and clinker in large scale mills reduces the power consumption, giving the same 28-day strength as mixed fly ash cement with higher fineness. INTRODUCTION Norcem has for the past eight years been producing a 20% fly ash cement, MP30, as the main standard cement in Norway. This cement has as small a variation in strength as the former pure Portland cement. Figure 1 shows the standard grinding system used in the production of blended Portland fly ash cement. The fly ash is normally introduced in the first compartment of the mill [a] but receives a relatively small amount of grinding during its passage through the mill. The fly ash acts as a grinding aid in the finishing compartment of the mill [1,2].
Fly ash (c)
Finished
I Clinker Gypsum Fly ash (a)
Fly ash (b)
Figure 1. Grinding system used in the production of blended Portland-fly ash cement.
Mat. Res. Soc. Symp. Proc. Vol. 136. C1989 Materials Research Society
176
Table I Quality Data for Delivered Fly Ashes Sieve Res. Bulk p3 g/cm 45 lam
A120 3
Fe 20 3
MgO
CaO
S03
Available Alk. ASTM
LOI
49.76 54.13 52.57 51.82 52.92
31.23 31.13 35.14 33.2 31.26
5.31 5.05 3.60 4.69 6.17
2.23 1.12 0.71 1.21 1.10
8.09 3.7 5.27 5.11 2.95
0.39 0.21 0.22 0.25 0.16
0.24 0.40 0.17 0.23 0.36
3.65 3.60 2.90 3.70 3.83
31.0 25.6 16.0 22.6 26.0
6 52.26
27.16
7.93
2.26
4.45
0.27
0.40
4.90
27.4 20.8
0.94
8 79.06 9 74.79 10 61.12
14.73 16.78 24.04
2.91 4.07 6.02
0.30 0.70 1.00
0.44 1.07 2.78
0.08 0.17 0.36
0.12 0.20 0.30
2.28 2.21 3.40
23.1 22.6 15.9
0.72 0.79 0.98
11 12 13 14 15
61.05 59.00 50.94 51.53 48.94
21.54 30.43 31.16 30.64 29.19
7.54 3.83 3.48 5.26 5.99
1.74 0.92 1.62 1.44 2.33
2.99 3.92 7.57 4.74 6.96
0.43 0.21 0.35 0.34 0.41
0.54 0.23 0.25 0.91 1.04
4.50 3.20 3.55 1.84 4.07
27.1 22.4 18.0 23.2 16.0
1.06 1.02 0.94 1.02 0.94
16 17 18 19 20
51.75 51.07 55.53 52.18 51.95
26.68 29.59 29.79 33.40 25.14
7.35 5.98 3.36 6.41 8.23
2.63 2.30 0.95 0.79 3.08
4.86 4.88 5.59 2.05 5.01
0.45 0.48 0.39 0.13 0.66
0.52 1.27 0.18 0.37 1.88
2.66 1.95 1.80 2.16 2.02
18.4 22.0 19.4 23.4 28.0
1.03
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