ABSTRACT
Fig. 4. a) Calculated thermal and nonthermal deformation based on the measurement of the total deformation of an unrestrained concrete specimen. Development of stress b) and Young's modulus c) for the same concrete mix under full restraint in the TST machine
the beginning of the hydration. This is because the concrete was not able to built up stresses due to its plasticity. Only after the Young's modulus started to increase the concrete could build up compressive stresses during the subsequent temperature increase. Additional compressive stresses were caused by the p r i m a r y c h e m i c a l s w e l - l i n g . This swelling corresponds, depending on the cement, to an estimated temperature increase of about 2.5 to 8 K. The short-term intensive s e c o n d a r y autogenous s h r i n k a g e which occurred after the primary chemical swelling caused the compressive stress curve to flatten although the temperature increased continuously during this period. The following s e c o n d a r y s w e l l i n g corresponds to an estimated temperature increase of about 1.5 to 5 K. This swelling continued to some extent during the first hours of the cooling stage. Because the Young's modulus had already reached a relatively high value, the reduction of the compressive stress due to the cooling was retarded by the secondary swelling or was strengthened by the autogenous shrinkage. The tensile stress which developed on further cooling was partly strengthened by the t e r t i a r y autogenous s h r i n k a g e . This intensified the risk of cracking.
