Page 143 - Handbook of Thermal Analysis of Construction Materials

126 Chapter 3 - Formation and Hydration

Table 6. Effect of Curing Procedures on Mg(OH) Produced
2

Curing Procedure Cement A Cement B

Autoclaved 2 MPa, 3 hrs 4.9 4.3

Boiling, 8 hrs 2.0 1.0
Boiling, 2 hrs 4.6 3.4
Steam Curing, 1 day 3.1 2.4
50°C, 2–3 days 0.0 0.0

9.3 High Temperature Effects

Concrete, having a relatively low thermal conductivity and high
specific heat, provides protection to the steel against fire. At low tempera-
tures concrete expands and by 300°C contraction due to the water loss
occurs. Aggregates continue to expand and create stresses in the concrete.
Quartz expands sharply at 573°C due to phase transition and decomposition
of calcite leads to contraction. During the cooling period, calcium oxide
begins to hydrate and causes expansion. Accidental fire causes damage to
structural concrete elements. Assessment of the condition after a fire is
important for recommendations for rehabilitation of concrete. DTA/TG
techniques are useful to assess the temperature ranges to which the elements
could have been exposed. [75] Damaged concrete (at different depths) has
been analyzed by DTA/TG. The damaged concrete did not exhibit
dehydroxylation peak of Ca(OH) indicating that such concrete was ex-
2
posed to temperatures above 500°C. The undamaged concrete contained
Ca(OH) as evidenced by the endothermal peak. A new thermal technique
2,
has been devised to monitor thermal expansion of cementitious materials as
a function of temperature. [76] Higher temperatures also chemically alter the
concrete performance.
Fiber reinforcement is an established means of improving the
mechanical properties of a variety of matrices. Sarvaranta, et al., [77]
studied by TG/DSC the thermal behavior of polypropylene and two
types of polyacrylonitrile fibers. A DSC examination revealed that the