Influence of curing conditions on the mechanical properties and durability of cement mortars

Abstract

Real structures are hardened in conditions different from the optimum laboratory conditions, where materials are usually tested. The different temperature, and especially the different relative humidity present in the environment, may cause a different microstructure and, as a consequence, different service properties. In this work mortars made with two different cement types are tested in laboratory conditions and at a lower relative humidity. These new environmental conditions cause a slower microstructural development and different durability and mechanical properties at early hardening ages.

Influencia de diferentes condiciones de curado en la estructura porosa y en las propiedades a edades tempranas de morteros que contienen ceniza volante y escoria de alto horno

“…El descenso más tardío de la porosidad total podría estar relacionado con la humedad relativa más baja de este ambiente, ya que al haber menos agua disponible en el ambiente para el desarrollo de las reacciones de hidratación del clínker y escoria, éstas se producirían más lentamente (31). El menor descenso de la porosidad total entre 28 y 90 días que mostraron los morteros de CEM II, así como el menor grado de refinamiento de su microestructura en comparación con los de CEM I, puede estar relacionado nuevamente con el retraso en el inicio de la reacción puzolánica de la ceniza (7), cuyo grado de desarrollo parece ser muy escaso después de 90 días de exposición al ambiente C.…”

“…The later decrease of total porosity could be related to the lower relative humidity of this environment, because if there is less water available in the environment for the development of hydration reactions of clinker and slag, these would be produced more slowly (31). The lower decrease of total porosity between 28 and 90 days for CEM II mortars, and the lower refinement degree of their microstructure in comparison to CEM I ones, could be related again to the delay of the beginning of fly ash pozzolanic reaction (7), whose development degree seems to be very low after 90 days of exposure to environment C.…”

Effects of Environment in the Microstructure and Properties of Sustainable Mortars with Fly Ash and Slag after a 5-Year Exposure Period

“…This result agrees with the total porosity results already discussed. The high water availability in this environment, combined with a high enough temperature, would facilitate the development of clinker and slag hydration, as well as the fly ash pozzolanic reactions, producing a fast new solid formation, which would reduce the size of the pores of the sample [30,44,48]. In addition to this, it is important to indicate that mortars with fly ash and slag showed a more refined microstructure than CEM I ones.…”

“…For environment A, generally this parameter decreased with time for all of them. This result could be related to the high relative humidity (100%) combined with a high enough temperature (20 • C) of this optimum environment, which allows an adequate development of clinker and slag hydration [30,44] and fly ash pozzolanic reactions [44,48], whose products would entail a rise of samples solid fraction and consequently a porosity reduction. The lowest total porosities for environment A corresponded to CEM III mortars, while this parameter was very similar for CEM I and II mortars and a little higher for CEM IV ones, which would be in keeping with other authors [7].…”

“…The fact that this parameter showed slight modifications could be related to the low environmental relative humidity (65%), although it is combined with an optimum temperature (20 • C). This optimum temperature would permit a suitable development of hydration and pozzolanic reactions [30,36] but the relatively low environmental relative humidity would make it difficult [44,48,50], causing a smaller new solid phases formation. Once again, the mortars prepared using sustainable cements with slag and fly ash hardened in the environment C, also showed lower or similar total porosities in the very long-term compared to CEM I mortars.…”