Alkali Activated Cementitious Materials: An Overview
- PDF / 1,574,069 Bytes
- 12 Pages / 420.48 x 639 pts Page_size
- 40 Downloads / 254 Views
ALKALI ACTIVATED CEMENTITIOUS MATERIALS: AN OVERVIEW D.M. ROY and M.R. SILSBEE, The Materials Research Laboratory, Pennsylvania State University, University Park, PA 16801
The
ABSTRACT Alkali-activated cementitious materials have considerable potential, with properties ranging from very high early strength to very high long term strength and low porosity. The role of alkalis in activating industrial by-products such as ground granulated (glassy) blast-furnace slag, ultra-fine silica fume or other by-product silicas, glassy fly ashes, and other amorphous materials is discussed. These by-product materials are activated by alkali additions which break the strong silicon oxygen bonds in the silicate or alumino-silicate network, accompanied by the formation of new reaction products. The role of the different components in multi-component activated cements on the reactivity and the nature of the resultant products is discussed. Characterization of starting materials and reaction products by XRD, SEM (including environmental SEM), chemical, and particle characterization techniques has been made. Additional results include investigation of pore solution chemistry as a function of time. Some inferences for long term durability are discussed.
INTRODUCTION AND BACKGROUND The use of alkaline activators to stimulate the latent pozzolanic properties of materials has a long history; in fact the initial use dates from at least the time of Nebuchadnezzar. Bricks in the city of Ur of the Chaldees have been found to have been produced from a mixture of lime and ashes. Studies of the alkali activation of glassy blast-furnace slag have a long history in the Soviet Union and in Scandinavia[l]. The Trief cements and F-cements from the Scandinavian countries[2,3] and alkali activated blended cements (sold under the trade name Pyrament) are more recent examples[4-6]. In recent years particular emphasis has been placed on the utilization of industrial-by products in chemically bonded ceramics[4,7].
Blended Cement Systems Wu et. al.[8] examined the ability of alkaline admixtures to increase the rate of strength development in slag-portland cement blends (see Figure 1). While all the admixtures resulted in at least a small increase in the observed compressive strengths at short times (3 days), some reduced the long term (28 days) strengths. They cautioned that only small additions of alkalis, in this case Na 2 SO 4 and alum, were needed and that higher levels might be detrimental to the long term performance in these blended systems. Mat. Res. Soc. Symp. Proc. Vol. 245. '1992 Materials Research Society
154
154
a
S...
C;(2) TW594(2)+3(•
MNa2SO4(2)tSP(1)
74
...rrrr..Na2SO4(0.5)+ALUM(o.5)sP(Cs.5)
64
6 5-•;;•:•== HAC (4) x~ ~ ~~~~ 4 ............ ...... ~1 sP (1)
z
.N02S04(2)
..
.
3
NTROL SLAG-MC
2 .CO....... I . . .•.l,,, 1000 2000 0
S3
T PASTE
.. '" ' CO TROL CEMENT" PASTE 3000 4000 5000 6000 7000 8000 '9000 '10000 Compressive Strength (PSI)
DAYS M 7DAYS Mf 28 DAYS
Figure 1 - Compressive strengths in activated slag-cem
Data Loading...
