Effect of sodium content as an activator in alkali-activated cement on cement dosage: Evaluation of cement, concrete, and Abrams’ law applicability

Although research on alkali-activated cements has progressed, large-scale application remains challenging due to a lack of established companies, despite the current interest in the development of one-part alkali-activated cements for different applications. Scale-up production also depends on validating the mechanical and durability properties of the associated raw materials, and the understanding of dosage parameters and physical behavior is a key factor for the advancement of technology. One-part alkali-activated cements typically consist of ground granulated blast furnace slag as the precursor, with the alkaline activator in solid form, finely ground and mixed with the slag. The solid activator is a decisive factor in the reactivity of the cement, rheological properties in the fresh state, and in the strength development over time in the hardened state. For its widespread application in the construction industry, the alkali-activated cement must be easily used in the production of concrete with different strength levels. Portland cement concrete mix design, a well-known concept widely applied in structural design, is based on Abrams’ law, which correlates mechanical strength with the water-to-binder (w/b) ratio. Although the water content also plays a role in the strength of alkali-activated concrete, the concentration and type of activator make this correlation even more complex. The objective of this study is to evaluate the effect of mixing water content on concrete produced with three different types of one-part alkali-activated cements. These three cements were manufactured in a pilot-scale plant, where the activator was adjusted to achieve different alkali concentrations. The alkali content directly influences the strength and reaction rate both in cement and concrete. The behavior of alkali-activated cement is different from ordinary Portland cement in relation to the Abrams’ curve, mainly in terms of the inclination of the curve with respect to the w/b ratio; however, for adequate design of this type of concrete, other information such as Na₂O content and H₂O/Na₂O ratio must be considered.