Which structural problem increasingly affected Roman concrete fortifications subjected to repeated freeze-thaw cycles during winter?

💡 Explanation

When water permeates the concrete, it freezes during winter, the resulting ice crystal formation causes expansive stress within the pores, leading to spalling. Therefore spalling damage results, rather than efflorescence, which requires salt migration; sulphate attack, which needs sulphate exposure; or carbonation, which proceeds slowly at warmer temperatures.

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