Page 166 - New Trends in Eco efficient and Recycled Concrete

138 New Trends in Eco-efficient and Recycled Concrete

Figure 5.6 Workability behaviour (FTS values) for SSA-CEM I 42.5 R blended cements
containing 0% 40% of SSA replacement. SSA, Sewage sludge ash; FTS, flow table spread.
From Garce ´s, P., Pe ´rez Carrio ´n, M., Garcı ´a-Alcocel, E., Paya ´, J., Monzo ´, J., Borrachero, M.V.,
2008. Mechanical and physical properties of cement blended with sewage sludge ash. Waste
Manage. 28 2495 2502. Available from: https://doi.org/10.1016/j.wasman.2008.02.019.

substitution met established standards. As can be seen in Fig. 5.6, the loss of work-
ability was very important for substitution percentages greater than 10%.
The porous and rough nature of SSA can be the cause of this workability loss.
This conclusion was corroborated by Chen and Poon (2017a) as their results indicated
that milled ash had better performance than the original in terms of workability. The
same conclusion was reached by Kappel et al. (2017). The authors confirmed that
pre-treatment with milling improved the performance of mortars with SSA.
Li et al. (2017) suggested that the loss of workability was due to increased water
absorption, which may be an advantage to obtain mortars with lower segregation.
Stirmer et al. (2016) studied the influence of the calcination temperature on the
fresh properties of mortars with SSA. They concluded that a greater calcination
temperature produced mortars with less air content and better workability. For

example, the ashes calcined at 1000 C had a lesser absorption of water than the
ashes calcined at 800 C. However, the high temperature treatment reduced the

pozzolanic properties.
Vouk et al. (2017a) observed that the air content in concrete was increased with
the use of SSA, especially for ashes with added lime. It was also noted that a higher
temperature treatment at 1000 C reduced the air content because it increased the

specific density of the ashes.

5.6 Mechanical and durability properties of concrete
containing sewage sludge ash

Many studies indicated that SSA can be used in mortars or concrete preparations
because of its reactivity and size distribution.