CMA

13 Table 6. Compressive strength of reference and modified concrete specimens. Compressive strength of reference / compressive strength of modified specimens ratio Impact of freeze thaw cycles on concrete elastic modulus Measurement of the relative dynamic elastic modulus of concrete specimens was used to assess the impact of freeze thaw cycles on reference or modified concrete specimens. Relative dynamic elastic modulus of concrete specimens modified with the addition of 0.2, 0.5 and 0.7% of the microencapsulated hydrophober (MIC-RES) or 0.5% of the silane emulsion (SIL-EM) was measured as a function of the number of freeze thaw cycles to which concrete specimens were submitted. Table 7 shows the relative dynamic elastic modulus after 300 cycles when the initial relative dynamic elastic modulus is used as a reference and set to 100. Figure 3 shows that a limited reduction of relative dynamic elastic modulus is observed when concrete specimens are modified with 0.2 or 0.5% of the microencapsulated silicone resin (MIC-RES). Concrete specimens modified with 0.7% of the microencapsulated hydrophober are showing a somewhat larger drop of the relative dynamic elastic modulus although the drop is never larger than 30% of its initial value after 300 cycles. According to ASTM C666 - Proc. A (2003), concrete is considered to be frost resistant if the reduction of the dynamic modulus of elasticity is lower than 40% after 300 cycles. Concrete specimens modified with 0.2, 0.5 or 0.7% of microencapsulated hydrophober satisfied this index. On the other hand, concrete specimens modified with 0.5% of the silane emulsion (SIL-EM) experiences a sharp decrease of the relative elastic modulus even after a limited number of freeze thaw cycles. It became impossible to measure relative elastic modulus after 51 cycles. It has been shown that addition of silane emulsion can impact hydration of cement [15] but also may induce some extra porosity. Size of the pores might be too small to improve freeze thaw resistance. Table 7. Ratio of elastic modulus of reference and modified concrete specimens before and after 300 freeze thaw cycles Figure 3. Relative elastic modulus of concrete specimens modified with microencapsulated hydrophober (MIC-RES) or silane emulsion (SIL-EM) as a function of number of freeze thaw cycles Measurement of the diffusion coefficient of chloride ion into concrete Chloride can ingress into concrete by different mechanisms. Water containing dissolved chloride can be absorbed due to capillary action into concrete pores, leading to transport of chloride into the concrete matrix. Concrete can be transported by diffusion under the influence of a concentration gradient. Diffusion can take place when the concrete pore structure is saturated enough with water. Chloride can also ingress concrete under the influence of an electrical field and move by a migration phenomena [14]. The evaluation of chloride penetration in concrete can be carried out by different test methods, which provide some information on the resistance of concrete to chloride penetration. Specimens Compressive strength (N/mm²) Compressive strength ratio (%) Control 26.1 100 MIC-RES (0.2%) 27.4 104 MIC-RES (0.5%) 27.9 107 MIC-RES (0.7%) 29.5 113 SIL-EM (0.5%) 29.8 114 Specimens Elastic modulus ratio (%) Control 95.9 MIC-RES (0.2%) 93.3 MIC-RES (0.5%) 85.9 MIC-RES (0.7%) 62.3 SIL-EM (0.5%) NA Control MIC-RES (0.2%) MIC-RES (0.5%) MIC-RES (0.7%) SIL-EM (0.5%) 0 10 20 30 40 50 60 70 80 90 100 0 30 51 77 103 139 160 186 211 245 278 300 lRelative elastic modulus (%) Cycle (Times)