Some favorable properties of lightweight aggregate concrete are shown to originate from its internal structure, which combines relatively flexible aggregate with more rigid cement paste matrix. Scanning electron microscopy (SEM) was used to analyze the cracking pattern which developed under cyclic loading. The cracks appear to originate in the hard brittle matrix and progress into the aggregate. At low load levels, some cracks seem to deflect and lose energy as they penetrate the aggregates, with many never emerging from the other side or emerging as thinner cracks. A process of healing of cracks through the formation of new products appears to restore integrity and enhance strength of a previously cracked concrete which was allowed to rest for a long period after cracking. Micrographs of the healed cracks are presented.

No abstract