Page 142 - Handbook of Thermal Analysis of Construction Materials
P. 142
Section 9.0 - Durability Aspects 125
Figure 38. Effect of different amounts of MgO on the autoclave expansion of cements.
Under exceptional situations the aggregates may be contaminated
with MgO. A contaminated coarse aggregate containing dead-burnt CaO
and MgO was inadvertently added to concrete. After a few years the
concrete exhibited large pop outs. DTA could be used to estimate the
amount of Mg(OH) present in the samples. [72] In another example, DTA [73]
2
was applied to estimate the amount of unhydrated MgO present in a fifteen
year old concrete. The amount of Mg(OH) was determined by the
2
endothermic peak at 400°C. By estimating the amount of Mg(OH) before
2
and after autoclave treatment, the amount of unhydrated MgO present in the
sample could be computed.
