CMA

14 Some accelerated test methods introduce an external electrical potential difference that increase the rate of migration of chlorides into the concrete pores structure. Exposure of concrete surfaces with chloride containing solutions (whether ponding test or multiple splash method) lead to diffusion of chloride but these tests take usually more time. The method used to initiate and accelerate chloride ingress may have an impact on the results of the study. Ponding the surface of concrete specimens with sodium chloride solution requires longer testing period, but enables proper testing of the effect of the concrete impregnation on water absorption (and chloride ingress) by capillary action [16]. Soaking of concrete specimens in chloride solution and application of an electrical potential induces migration of chloride. Previous studies have confirmed that the evaluation of chloride may depend on the test method (the immersion test and the electrophoresis test) and depend on the type of surface impregnating material [15]. The protocol of testing the coefficient of chloride ingress by electrophoresis implies the vacuum impregnation of the concrete specimens (specimens under vacuum followed by saturation with water. The forced impregnation of concrete specimens makes that the potential benefit of integral water repellent cannot be evidenced. Therefore, the results of this test will not be reported here in order to avoid misleading conclusions. Build up of chloride into cement matrix upon solution exposure In order to assess chloride ingress in the cement matrix, some light mortar (made with lime and a foaming agent to decrease density and therefore voids space), unmodified or modified with the microencapsulated silicone resin or the silane emulsion were place in contact (enable capillary absorption) with a saturated sodium chloride solution for 7 days (see figure 3). Each block was weighed before and after the exposure to the sodium chloride solution (following a drying step of the blocks). Weight increase, reported as % of initial weight of the different mortar blocks are reported in figure 3. It can be seen that the weight of the reference blocks is increasing significantly. Weight of the blocks modified with MIC-RES and SIL-EM (@ 0.19 and 0.3% of the additive vs the full mortar weight) increases only very moderately, demonstrating very good control of salt ingress within the modified blocks. Figure 4. Weight increase (as % of initial dry weight) of mortar blocks modified with different integral water repellents, after 7 days contact time with a saturated sodium chloride solution. This test is not intended to provide a model for long term to sodium chloride exposure, but it illustrates the fact that strong reduction of capillary water absorption does lead to reduce chloride ingress into the treated cement matrix [17]. Conclusions The study explored the benefit of a new integral water repellent based on a microencapsulated silicone resin in concrete. Effectiveness of the additive to reduce water penetration at the surface or in the bulk of modified concrete was demonstrated. The microencapsulated silicone resin was demonstrated to much improve resistance of modified concrete to freeze thaw cycles and to salty water absorption. Impact of the additive on the mechanical properties is very limited. References 1a. Meijers, S.; Bijen, J.; de Borst, R.; Fraaij, A. (2005) Computational results of a model for chloride ingress in concrete including convection, drying-wetting cycles and carbonatation, Materials and structures, 38: 145‒154. b. Neville, A. (1995) Chloride attack of reinforced concrete: an overview, Materials and Structures, 28: 63‒70. 2. Chloride penetration in RC-structures in marine environment ‒ Long term assessment of a preventive hydrophobic treatment, Luc Schueremans, DionysVan Gemert, Sabine Giessler, Construction and Building Materials, Volume 21, Issue 6, June 2007, Pages 1238-1249 0.0% 5.0% 10.0% 15.0% 20.0% Reference SIL-EM @ 0.19% SIL-EM @ 0.3% MIC-RES @ 0.19% MIC-RES @ 0.3% Salt