Materials Performance

APR 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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40 APRIL 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 4 COATINGS & LININGS quartz sand (fineness modulus of 2.3 and a density of 2.55 g/cm 3 ) and the coarse aggre- gate was crushed limestone (density of 2.69 g/cm 3 ) with particle sizes ranging between 5 to 15 mm in diameter. Concrete mixtures with a water-to-cement ratio of 0.4 were prepared. The concrete mixtures were cast in 100-mm cubic molds by compaction and vibration. They were demolded after two days and then cured for two weeks in water. Afterward, the samples were air-cured at 23 ±2 °C and 55 ± 5% relative humidity (RH) for an additional two weeks prior to prepa- ration for surface treatment application. The temperature and RH chosen for curing represent mean laboratory conditions. Specimen Preparation The concrete substrate surfaces were degreased with acetone and then placed in an air curing room at 23 ± 2 °C and 55% RH for three days. This dry condition provided an optimum surface for treatment. Then the silane emulsion was applied to the concrete specimens at coverage rates of 150 and 300 g/m 2 . These samples were identified as S1 and S2, respectively. For comparison, a commercial acrylic, identified as S3, was applied to similarly prepared samples. For a baseline reference, uncoated samples were included. Seven days after the application of the sealers, the specimens were tested. † Trade name. FIGURE 1 Results of the water absorption test. Characterization Water Absorption The water absorbed by capillary suc- tion was determined by weighing the speci- mens after different durations of immer- sion. The increase in weight after a period of 12 h was measured. Chloride Ion Resistance The method used to estimate chloride penetration depth and the chloride diffusion coefficient followed the procedure described by Luping and Nilsson, 9 which involved measuring the depth of color change in the direction of chloride flow using 0.1 M silver nitrate (AgNO 3 ) aqueous solution on a freshly broken concrete surface. 10-11 Carbonation Depth The carbonation test was performed under a controlled atmosphere (25 ± 5 °C, 70 ± 5% RH, and a carbon dioxide [CO 2 ] concentration of 20 ± 2%). After 7, 14, 28, and 56 days in the controlled climate box, the specimens were removed , cut, and immediately sprayed with an alcohol solu- tion of phenolphthalein. The carbonation depth was determined by measuring the depth of noncolored parts in the specimens using a vernier caliper, according to RILEM CPC-18. 12 Scanning Electron Microscopy The concrete surface was investigated via SEM ( JEOL JSM 5800 † ) carried out on an FEI Sirion 200 † field-emission SEM. The accelerating voltage was 25 kV. Results and Discussion Water Absorption Figure 1 shows the results of the water absorption tests. There was a significant dif- ference in water absorption between the nontreated and treated specimens. The results indicated, however, that the silane treatment is more effective in inhibiting water penetration in concrete than the acrylic product. The silane S1 and S2 con- crete specimens absorbed only 50% of water absorbed by the acrylic-coated concrete specimen (S3) after 12 h, and dramatically less than the uncoated reference. This shows that the silane treatment provided a greater hydrophilic barrier in the pores of the cement near the surface of the concrete. It should be noted that no significant dif ferences were obser ved between the S1 and S2 specimens in terms of the water absorption values. Visual evaluation of the hydrophobic efficiency of the silane protection systems tested is shown in Figure 2. The hydropho- bicity of the specimens with silane coatings is obviously distinguishable. The visual re sult s c onf irm ed th e si l an e c o atin gs reduce water absorption. Chloride Ion Resistance Figure 3 shows chloride diffusion coef- ficients (D) determined by the method pro- posed by Luping and Nilsson. The non- coated specimens presented the highest D values compared to the other three surface treatment systems. The acrylic treatment system reduced the chloride diffusion coef- ficient by more than 43%, indicating that this material greatly inf luenced chloride penetration. The concrete with silane treat- ments, however, showed even lower diffu- sion coefficients. These coatings provided the most efficient protection, reducing the chloride diffusion coefficient by 77%. The silane system, in addition to reducing the

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