Durability characteristics of fly ash concrete containing lightly-burnt MgO

• We examine the effect of lightly-burnt MgO on durability characteristics of fly ash concrete.
• The resistance of MgO concrete to carbonation, chloride attack, and sulfate attack increased in the long-term age.
• The freezing–thawing resistance was slightly affected by the use of MgO.
• The durability of MgO concrete in the long-term age slightly improved by the reduction of the total porosity.

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 °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.