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Location: Naples, Florida

Structure

Three balconies at the Shipp’s Landing Condo, Marco Island, Florida, were selected by the Board and their engineering consultant, for a demonstration of the SURTREAT® concrete reinforcing steel corrosion evaluation and inhibition processes.

Problem

The balconies were selected for the evaluation program due to some delamination indicating the presence of corrosion.

Solution

SURTREAT® is a proprietary, water based, environmentally friendly solution of activators and migratory aids that inhibits rebar corrosion, increases strength and reduces porosity in reinforced concrete.

 

SURTREAT® Solutions

  • Inhibits salt, water, air and contaminates from penetrating the concrete and forms a better seal in the pores and micro cracks
  • Controls pH and maintains the high alkalinity in the  concrete and is highly acid resistant
  • Migrates to the rebar in liquid and ionic phase and reacts to form a very stable passivating film – more stable than in new concrete
  • Converts rust to a stable, inert compound – and increases compressive, flexural, and tensile strength. Also increases hardness and abrasion resistance

Scope of Work

Each balcony was prepared by removing the surface coating and removing and replacing spalled concrete. A small section of rebar was left exposed for making half-cell corrosion measurements.

Per the described plan, concrete samples were taken for chloride and pH measurements. The half-cell potential was measured in the area surrounding the exposed rebar, and the concrete strength was measured using an impact hammer. The results of these tests are recorded in Table I.

After testing, TPS-II was applied to the three balconies along with water to aid in penetration. The quantity of TPS-II applied is recorded in Table I.

Evaluation and Conclusions

Impact hammer measurements showed that the balcony concrete was in the 5000-7000 psi range, which means that it has a low cement porosity. This coincides with the high pH (12) measurements at the surface and the relatively small amount of TPS-H required to saturate the cement phase.

Chloride analysis shows that the lower level balconies (1023) have a higher chloride content (1900 ppm at 2.4 cm) in comparison to the higher level balconies such as 1920 with only 80 ppm at 2.4 cm). The chloride content of balcony 1023 is within the corrosion activity range, while balconies 1420 and 1920 are at what can be considered as background levels.

Half-cell measurements were made on balconies 1023 and 1420 and were just above the silver chloride half-cell corrosion threshold level of —250 mV. There is, though, a significant difference between the high and low readings (-250 mV vs. 45mV) for balcony 1420, which means that there are anode cathode differentials which could be indicative of corrosion.

The first application of TPS-II was made to balcony 1023. When the application of 4 gallons at a rate of 137ft/gallon was completed, it was realized that this was an excessive amount in relationship to the concrete porosity, since there was excess TPS-H on the surface which had to be removed. The rate and method of application were modified for balconies 1420 and 1920, reducing the application rate down to 245 ft2/gallon and 366 ft2/gallon respectively, and applying water first to prime the surface.

When TPS-II was applied, a network of cracks became visible on the surface as a result of significant product penetration in these areas. These cracks can be seen by examining Photos 3 and 4. All of the balconies showed the same micro-cracked condition.

It is concluded that water, salt and air are penetrating the balcony surfaces primarily through these micro-cracks and creating spot conditions conducive to rebar corrosion. This was confirmed by the half-cell measurements showing small isolated corrosion “hot spots.” Most of the TPS-II penetration is through these cracks which is where it is needed.

Testing if Applicable

Preliminary Proposal for TPS-II Application to Balconies

Based in physical examination and the present test results, there is a definite need to take action to prevent further rebar corrosion-related deterioration. Low-level ocean front balconies which have a higher chloride content are prime candidates for immediate attention. Since most penetration in through the network of micro-cracks, the TPS-ll application rate will be modest. Higher rates should be used on lower-level balconies (floors 2-10) versus higher level (10-20).

It is recommended that TPS-II be applied to balconies at levels 2-10 at the rate of 200 ft2/gallon and at the rate of 250 ft2/gallon on balconies at levels 11-20, using the following application procedure.

The balcony surfaces should be pre-wet with water to dampen them. Apply TPS-II at the prescribed rate just after the surface has dried from pre-wetting. When the TPS-H application has just become dry, make one application of water at a rate similar to TPS-ll and let the surface dry overnight. Inspect the balcony surfaces for TPS-II residue and impurities purged to surface. Wash the balcony surfaces with water to remove residues. Avoid allowing TPS-II or water to pond or flow over balcony edge unless in the washing step. It is recommended that the prescribed amount of TPS-II be placed on the balcony surface in increments and spread using a soft-bristle broom.

concrete-and-rebar-corrosion-properties

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