Absorption, porosity, capillarity and chloride diffusion in ultra high performance concretes

Abstract

Concrete durability performance can be assessed by a number of parameters, among which permeability properties are key. In this experimental work, the permeability to water and the diffusion of chlorides in Ultra High Performance Concrete (UHPC) are studied. To this end, three types of concrete were made: Two Ultra High Performance (one with fibers and one without fibers) and a Conventional Concrete (CC) of w/c ratio equal to 0.5. The compressive strength of Ultra High Performance Concretes was 130 MPa, and that of conventional concrete was 50 MPa. All of them were cured at a temperature of 20°C and RH greater than 95% until the age of 28 days. In the case of UHPCs with fibers, some of the specimens were not placed in the curing chamber but were allowed to air dry in a laboratory environment in order to study the influence of curing on this type of concrete. The results show that UHPCs have remarkably lower water permeability than CC, with the water absorption and water porosity being in the order of 8 times lower, the water absorption by capillarity being in the order of 30 times lower, and the non-steady-state chloride migration coefficient more than 100 times inferior. The values recorded of absorption and capillarity in UHPCs with and without fibers were very similar. However, the permeability to chlorides was somewhat higher in concretes with steel fibres. With regard to the influence of curing, in air-dried UHPCs there was a significant increase in permeability to both water and chlorides. Despite this, the chloride migration coefficient registered remained very close to the values proposed by some recommendations for very high durability concrete. © ICDCS 2018. All rights reserved.