DURABILITY PROPERTIES OF ORDINARY, SLAG BLENDED AND ALKALI-ACTIVATED SLAG CEMENT MORTARS

摘要

The presence of sulfate and chloride ions in soils and marine environments causes deterioration of reinforced concrete structures due to reinforcement corrosion and sulfate attack into concrete. The phase of the hardened cement paste, tricalcium aluminate (C_3A), that binds chloride ions and reduce its action is the same that can react with sulfate ions to form ettringite or gypsum and attack the concrete causing expansion and strength reduction. Several supplementary additions -as silica fume, fly ash, slags- are being used with Portland cement in order to reduce the permeability and increase the resistance to the ingress of aggressive ions. Recent advances have made possible to develop new high performance cementitious materials, as the chemically bonded ceramics, for example alkali-activated slag mortars. The purpose of this study was to evaluate the durability properties of Portland cement mortars made with addition of a Colombian ground granulated blast furnace slag (GGBS) and with the same GGBS but alkali-activated with 4% Na_2O waterglass (Na_2SiO_3.nH_2O + NaOH). The proportion of GGBS added ranged from 0 to 80% (w/w). Properties of compressive strength, water absorption, chloride ion penetration and sulfate resistance were determined. The obtained results were compared with those from a Spanish GGBS. In general the GGBS improves resistance to chemical attack of mortar by sulfates and reduce the diffusion of chloride ions. The diffusion rate can be decreased up to 95% compared to that of ordinary cement mortar. In presence of high levels of chlorides or sulfates 70% GGBS is recommended. The results also indicate that the resistance to chloride and sulfate ion penetration increase in alkali-activated slag mortars. These findings permit to conclude that the process of slag activation with waterglass improves the properties if compared with ordinary cement and slag mortars. Only when the slag addition is higher than 50% (w/w) its behavior properties are comparable than those obtained with alkali-activated GGBS.