Effect of drying under service environment on the mechanical properties of structural lightweight concretes

Abstract

In this paper the effect of the ambient relative humidity at service on the compressive and splitting strengths and in the modulus of elasticity of structural lightweight concretes is evaluated. Also, relationships are proposed allowing estimating these properties as a function of the ambient relative humidity and drying time. The concretes were made with two types of coarse lightweight aggregates, pumice and fly ash pellets, and with normal density fine aggregate. The concretes were subjected to two different environmental service conditions: 90% relative humidity and curing at 90% relative humidity during the first seven days and then to 50% relative humidity until the age of testing. The samples were tested at 7, 28, 60 and 90 days of age. An important deterioration of the measured properties due to the effect of the drying conditions was observed; at 83 days of drying, the compressive and splitting strength losses were on average of 20% and 15%, respectively, and of the modulus of elasticity of 40% with respect to concretes at 90% relative humidity. It was concluded that there are two main variables that can explain the loss of strength of lightweight concrete due to the effect of a dry environment. The first of them is the water-cement ratio which controls, among others, the permeability of the mortar or resistant phase. The second one is the relative content of lightweight aggregate in the concrete.