Investigation Of Effect Of Sodium Carbonate On Properties Of Alkali-Activated Slag Cement

Alkali-activated slag cement?AASC? is a new type of cementitious material with better physical mechanics and durability property. The most widely used activators are Na OH, water glass?sodium silicate?, and a combination of both. These activators, however, would cause the AASC to harden more rapidly than what is desirable and need to be solution before applying. It is a big barrier for practical application of AASC. In addition, these activators are a source of concerns because they are the most expensive component in the system. Meanwhile, retarders for these activators are expensive, that limit the use of AASC. However, the researches on solid alkaline component with retarding effect of AASC are difficult to find up. Setting time, slump and compressive strength of AASC with Na₂CO₃, water-glass and Na OH were studied in my work. The ratio of water to slag was 0.45. TAM air calorimeter was used to study the effect of Na₂CO₃ on the hydration process of SAAS. The hydration products of AASC with Na₂CO₃ were been analyzed by XRD and SEM. The result shows that:?1? the setting time of AASC was depended on the Na2 O ratio of Na₂CO₃ and Na OH?or water glass? when the Na2 O equivalent was constant. With the increasing of Na₂CO₃, the setting time of AASC first delayed and then decreased and existed a peak. The peak of setting time AASC appeared when the Na2 O equivalent ratio of Na OH and Na₂CO₃ was 1:1,or the Na2 O equivalent ratio of water glass and Na₂CO₃ was 3:2. Meanwhile, as the addition of Na₂CO₃, the compressive strength of AASC activated by Na OH can be improved during the late curing age.?2? maintaining always a constant concentration of Na OH by Na2O?3% by mass of slag?, the influence law of dosage of Na₂CO₃ on setting time of AASC under the condition of 30 ?was the same with room temperature. However, there is a little deviation on the peak, and the peak of setting time appeared when the ratio of Na OH and Na₂CO₃ was 1:1.17.?3? maintaining always a constant concentration of Na2 O by 5%, the hydration heat release behavior of AASC can be impacted significantly by the addition of Na₂CO₃. In the system of Na OH-slag, with the increasing of Na₂CO₃, the rate of hydration heat release of AASC decreased and the hydration heat release peak moved to the right. When the dosage of Na₂CO₃ was less than 2%, there was almost no effect on the rate of hydration heat release in the system of water glass-slag; when the dosage of Na₂CO₃ was more than 2%, the influence law is the same with the system of Na OH-slag.?4? the hydration products of AASC is related to the relative contents of activators in the system. And the formation of gaylussite or pirssonite at early time of reaction in the hydration products may be the reason why the peak of setting time appeared in AASC.