Durability characteristics of fly ash concrete containing lightly-burnt MgO

There is a growing interest in the use of by-products in concrete for cost-reduction and performance enhancement. In China, lightly-burnt MgO (magnesium oxide), a by-product, has been used in dam concrete. Since lightly-burnt (850-1000 degrees C) MgO tends to expand due to the hydrated product Mg(OH)(2), and the hydration progresses at a lower rate than in cement, it can effectively compensate for concrete shrinkage. Many studies have been conducted to investigate the hydration and expansion properties of MgO, but few have attempted to examine the durability of concrete containing MgO. This study aims to investigate the durability properties of fly ash concrete containing 5% MgO by mass of binders as an expansive additive. To achieve this, the carbonation, freezing-thawing, chloride penetration, and sulfate resistance were tested on specimens cured for 28 days or for 360 days. In addition, MIP (Mercury Intrusion Porosimetry) analysis on the concrete specimens cured for up to 360 days was conducted, and XRD (X-ray Diffraction) analysis of mortar containing 5% MgO and 20% fly ash was also carried out from 7 to 360 days, to observe hydration products. The test results revealed that the compressive strength and durability characteristics of concrete in the long term age were slightly improved by the reduction in the porosity of the concrete due to the replacement of MgO. (C) 2014 Elsevier Ltd. All rights reserved.