Fig. 3.38. Development of compressi

Fig. 3.38. Development of compressive strength (in percentage) for 90 day value of mortars
with a binder consisting of mixtures of 70 wt.-% cement and 30 % further thermally treated
MSWI-slag, quartz (QZ), fly ash (SFA), blast furnace slag (HS), and pure cement
In Figure 3.38 the strength development from the 90 day values is indicated in
percentage. At 7 days, approximately 50 to 70 % of the total 90 day strength for
the further thermally treated MSWI-slag samples is already reached. Between 28
and 90 days a further strength increase of about 20 to 40 % takes place. The relative strength development (over time) of the further thermally treated MSWI-slag
is similar to that of fly ash from coal-fired power plants and blast furnace slag
from iron industry; lower compared to quartz powder (Fig. 3.38). Samples with
further thermally treated MSWI-slag CTU-H showed the lowest compressive
strength and samples with further thermally treated MSWI-slag CTU-W showed
the highest strength increase after 28 days. In general, for further thermally treated
MSWI-slag, hardly pozzolan reactivity can be assumed.
Further experiments were carried out in order to study the use of further thermally treated MSWI-slag for stabilisation of MSWI ash. As binder for stabilisation purposes, cement and lime have been used and served as references. Further
samples were made with mixtures consisting of cement, lime and further thermally
treated MSWI-slag (PECK-M 2500, PECK-M 4000, PECK-K 2500, PECK-M
4000). In those mixtures, 15 % (by weight) of the cement was replaced by further
thermally treated MSWI-slag. The compressive strengths of the stabilised MSWI
fly ash are shown in Figure 3.39. The strengths of all samples are similar at 7
days. At 35 days the samples consisting only of cement as binder showed significantly higher strength. Nevertheless, the strength of the samples with further
thermally treated MSWI-slag is sufficient.