Use of Hydrophobic Agents as Concrete Admixtures


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Title: Use of Hydrophobic Agents as Concrete Admixtures

Author(s): G. Moriconi and F. Tittarelli

Publication: Special Publication

Volume: 212


Appears on pages(s): 279-288

Keywords: concrete admixture compatibility; hydrophobic admixture; water absorption

Date: 6/1/2003

The environmental attack on reinforced concrete structures can he reduced by preventing water penetration into the concrete pores using hydrophobic agents as concrete admixtures. In order to point out problems related to their practical use, the effectiveness of hydrophobic admixture on cement pastes with different w/c, and in the presence of other commonly used chemical admixtures, was studied. Capillary water absorption and the contact angle between water drops and the cement paste surface were evaluated. Changes in the cement paste porosity due to the hydrophobic admixture were studied by porosimetric analysis. The results obtained show that the hydrophobic admixture is able to reduce the prolonged capillary water absorption in all cement pastes by about 70%. regardless of how it is added. The hydrophobic agent appears even more effective during the initial phase of water absorption, especially with increasing w/c. The simultaneous presence of either plasticizing or air-entraining admixtures does not negatively affect the effectiveness of the hydrophobic agent even if different ways of addition are used. An appreciable increase in the cement paste porosity, related to an ex- pected reduction in mechanical strength, is observed only for cement paste with the highest w/c (0.50).