The　panel　spalling　test　was　conducted　on　refractory　castables　for　steel　ladle　linings　to　examine　the　effect　of coarse　aggregate　addition　on　thermal　spalling　resistance． 　Thermal　spalling　cracks　extend　almost　straightly　in　castables　which　include　no　coarse　aggregate．The　cracks in　castabIes　which　include　coarse　aggregates，however，deflect　or　branch　due　to　the　collision　of　cracks　with coarse　aggregates．Such　deflecting　or　branching　of　cracks　are　effective　to　improve　thermal　spalling　resistance of　castables． 　Size　and　amount　of　coarse　aggregates　in　castables，regarded　as　dominant　factor　for　collision　frequency　of cracks　with　coarse　aggregates，influence　consequently　thermal　spalling　resistance　of　castables．The　collision frequency　o｛cracks　with　coarse　aggregates　can　be　quantitatively　evaluated　by　the　collision　probability　calculated　from　cross　section　and　density　of　coarse　aggregate　included　in　a　castables．

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