Influence of environmental conditions on the mechanical properties and durability-related characteristics of slag and fly ash cement mortars

摘要

The use of mineral admixtures in the cement manufacture has many environmental benefits. The main advantages are the reduction of CO2 emissions and the lower energy consumption during the cement production, as well as the use of an industrial waste. Many studies show that in laboratory conditions this kind of materials with partial substitution of clinker by ground granulated blast-furnace slag and fly ash have good service properties, even better than Portland cement. Real structures are usually hardened in different environmental conditions depending on their geographical location. The different temperature and specially the different relative humidity present in the environment may influence the service properties of concretes and mortars made with slag and fly ash cements. In this work, the behaviour of mortars made with three different cement types, an ordinary Portland cement, a fly ash cement (with a content of fly ash between 21-35% of total binder) and a ground granulated blast-furnace slag cement (content of slag from 66 to 80%) have been tested. These mortars were exposed to two different environmental conditions during their hardening, an optimum laboratory condition (20oC and 100% RH) and a Mediterranean climate environment with lower relative humidity (20oC and 65% RH). The development of their microstructure has been studied using mercury intrusion porosimetry. In order to study their durability, the capillary suction coefficient and effective porosity of the mortars have been determined too. Their changes in chloride ingress resistance have also been studied through a forced migration test and with the steady-state diffusion coefficient obtained from saturated sample’s resistivity, determined using impedance spectroscopy. Finally, compressive and flexural strengths were studied too. The different mortars were tested at different hardening ages until 180 days. The mortars made with slag and fly ash cements have shown a good behaviour compared with ordinary Portland cement mortars. The relative humidity has an influence on materials properties, and this influence is higher in mortars containing slag and fly ash cements than in those made with ordinary Portland cement. The improvement of durability is delayed in environments with relative humidity lower than 100% but after 180 days hardening these properties have reasonable good values. Compressive and flexural strength increased with the age in the majority of the samples studied. Then, cements with slag and fly ash, hardened under environmental conditions of Mediterranean climate, can have good service properties in the long term.