Figure II-16

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Figure II-16: Flowchart. Flowchart for assessing the condition of the concrete paste and air. This flowchart can be used to assist with assessment of the paste and air-void system and identify any problems in the concrete.

The following scenarios show the symptoms for various concrete problems associated with the paste and air-void system.

Symptoms of corrosion of embedded steel include the following:

• Cracks in the paste and rust stains around embedded items.

Symptoms of a possible paste freeze thaw include the following:

• Cracks in the paste, corrosion of the embedded steel, a freeze thaw occurs, and the original (unfilled) air-void system is inadequate.
• Cracks in the paste, corrosion of the embedded steel, a freeze thaw occurs, the original (unfilled) air-void system is adequate, and the air void spacing factor is greater than 0.20 millimeters due to infilling.
• Cracks in the paste, corrosion of the embedded steel, a freeze thaw occurs, the original (unfilled) air-void system is adequate, the air void spacing factor is less than 0.20 millimeters due to infilling, and the air-void system in the concrete near the road surface is inadequate.
• No cracks in the paste but evidence of paste softening or degradation, gypsum corrosion leading to a possible sulfate attack or no gypsum corrosion, calcium hydroxide depletion near the joints leading to a deicer attack or no calcium depletion, gaps around the aggregates where the gap width is not proportional to the aggregate size but the gaps are nonuniform around coarse aggregates.
• No cracks in the paste or paste softening or degradation, but evidence of gaps around the aggregates with gap width is not proportional to aggregate size and there are nonuniform gaps around the coarse aggregates.

Symptoms of possible aggregate freeze thaw including the following:

• Cracks in the paste, corrosion of the embedded steel, a freeze thaw occurs, the original (unfilled) air-void system is adequate, the air void spacing factor is less than 0.20 millimeters due to infilling, the air-void system in the concrete near the road surface is inadequate, and a paste freeze-thaw occurs.
• Cracks in the paste, corrosion of the embedded steel, a freeze thaw occurs, the original (unfilled) air-void system is adequate, the air void spacing factor is less than 0.20 millimeters due to infilling, the air-void system in the concrete near the road surface is adequate, and cracks extend through the aggregates into the paste. Note that if all of the previous conditions are met but the cracks do not extend through the aggregates into the paste, an aggregate freeze-thaw is probably not the problem.

The next step would be to identify whether the cracks or voids are filled. If they are filled, identify the filling material, look at other problems as a source of distress, and proceed as if there are no cracks in the paste. If they are not filled then the sample might be poorly prepared or have shrinkage cracks and symptoms of other problems should be evaluated as the source of distress. Proceed as if there were no cracks in the pavement.

Note also that cracks or voids should be evaluated to determine if they are filled even if the cracks extend through the aggregates and an aggregate freeze-thaw occurs.

Symptoms of a sulfate attack include the following:

• No cracks in the paste but evidence of paste softening or degradation and gypsum corrosion.
• No cracks in the paste, gypsum corrosion, or calcium hydroxide depletion near the joints, but evidence of paste softening or degradation and unfilled gaps around the aggregates with gap width proportional to aggregate size. If the gaps are filled, then the infilling material should be identified.

Symptoms of a possible de-icer attack include the following:

• No cracks in the paste but evidence of paste softening or degradation, gypsum corrosion, and calcium hydroxide depletion near the joints.
• No cracks in the paste or gypsum corrosion, but evidence of paste softening or degradation and calcium hydroxide depletion around the joints.

The aggregates should be examined if any of the following occur:

• If a possible sulfate attack is caused by unfilled gaps.
• If a de-icer or sulfate attack occur but there are no gaps around the aggregates or if the gaps around coarse aggregates are uniform.
• If a paste freeze-thaw occurs caused by nonuniform gaps around coarse aggregates.