5.1 : חוסר עמידות של אגרגטים כתוצאה משינויי נפח

Consider a lightweight aggregate with a porous structure. Water entering these pores expands in volume upon freezing, generating hydraulic pressure within the aggregate pores.

This pressure eventually disintegrates the aggregate, rendering it unsound due to permanent volume changes.

The size and continuity of the pores in aggregates are crucial in frost damage as they control the water's movement within the aggregate.

Similarly, salt crystallization within the aggregate pores due to wetting and drying cycles also results in permanent volume changes.

The soundness of aggregates is tested by subjecting graded and weighed aggregates to cycles of immersion in a sodium or magnesium sulfate solution followed by drying in an oven.

Salts crystallize within the aggregate's pores in this process, creating stresses that might disintegrate the aggregate. This results in a reduction in particle size and weight loss, which indicates its soundness.

Other laboratory tests for soundness involve subjecting loose aggregates and aggregates embedded in concrete to cycles of freezing and thawing that are likely to be encountered in practice.

Generally, pop-outs, scaling, and surface cracking occur in concrete with unsound aggregates.