MECHANICAL PROPERTIES OF CONCRETE CONTAINING REACTIVE MgO UNDER ACCELERATED CARBONATION CURING

摘要

Concrete containing reactive MgO has potentially superior mechanical properties to conventional concrete under accelerated carbonation curing. Experiments were carried out to determine the influence of r-MgO replacement and accelerated carbonation on the mechanical properties of concrete containing r-MgO. Cylinders (dimensions of Φ50 mm x H100 mm and Φ100 mm x H200 mm) with an r-MgO replacement level of 30%, 50% and 70% were cast. Samples were demolded at 1 day for 30% and 50% r-MgO concrete, and on the 2~(nd) day for 70% r-MgO concrete. Demoulded cylinders were exposed to an ambient environment (temperature (20±3 °C) and a relative humidity (20±5%)) until day 5, and then the specimens were subjected to accelerated carbonation curing (temperature (20±3 °C), relative humidity (95±5%) and CO_2 concentration of 99%) for another 28 days. Mechanical properties, including compressive strength, bulk density, porosity and dynamic and static elastic modulus, were measured at 3, 5, 8, 12, 19 and 33 days after casting. The experimental results reveal that accelerated carbonation improves the mechanical properties of concrete containing r-MgO, especially in the first 3 days of carbonation. The mechanical properties of 30% r-MgO concrete are superior to those of 50% and 70% r-MgO concrete before carbonation, but are inferior after carbonation curing. This phenomenon is quantified by the relatively low carbonation depth of 30% r-MgO concrete, which results from the combined effect of water-to-binder ratio and differences in the precipitated carbonation product compared to the 50 and 70% r-MgO mixes.