Civil Engineering Reference
In-Depth Information
5.7
Particles of quartz in cogenerated sugar cane bagasse ash.
may be present in the ashes as crystalline compounds. When the calcining
temperature was raised to 1000 °C, however, cristobalite was detected as a
result of the recrystallisation of amorphous to crystalline silica.
Activated paper sludge (APS).
The paper industry, which uses recycled paper as a raw material, generates
great volume of paper sludge wastes, which presently constitutes an alternative
source of metakaolinite, a highly pozzolanic product classified in class Q
in European legislation (Bai et al. 2003). Europe generates on the order of
2.5 Mt of such sludge yearly, and Spain alone 800 000 t. The dry sludge
(35-40% moisture) consists primarily of organic matter (30%), calcite (35%)
and kaolinite (20%) (Fig. 5.8).
Recent studies conducted by Frías et al. (2008a, 2008b, 2010a), García
et al. (2007) and Vigil et al. (2007) established the scientific, technical and
environmental basis for its reuse as a new artificial pozzolan. These authors
showed that the optimum activation conditions to eliminate all the organic
matter and completely convert the kaolinite into reactive metakaolinite
consisted of calcination at 650-700 °C for two hours. The product obtained
is depicted in Fig. 5.9: its particles are normally smaller than 90 mm with
luminosity (whiteness index) of over 90%, an important property for the
manufacture of white blended cements. Chloride ions (<0.02%)
may or
may not be present in paper sludge, depending on the industrial bleaching
process used by each individual paper manufacturer (Frías et al., 2011a).
The
chemical composition of this activated sludge may vary substantially with
