Blast furnace slag-Mg(OH)₂cements activated by sodium carbonate

Abstract

Novel cements can contain up to 50 wt% Mg(OH)2, offering a new route to immobilisation of this nuclear waste constituent.

Effect of Sodium Disilicate and Metasilicate on the Microstructure and Mechanical Properties of One-Part Alkali-Activated Copper Slag/Ground Granulated Blast Furnace Slag

“…BSE imaging of the GGBS disilicate systems shows a reaction rim around the grains, indicating clearly that the GGBS actively dissolves ( Figure 12 a). This is also evident for slag fines that have been completely reacted and leave behind a darker gray-scale patch in the matrix [ 38 ]. When replacing 25 wt% of the slag by CS, this reaction rim and patches are present for GGBS ( Figure 12 a).…”

“…EDS-SEM analyses of the metasilicate GGBS systems show a higher Mg- and Al-content and lower Si- and Ca-content within the rim ( Figure 13 ; cf rim in Figure 12 a,b). This is typically observed within slag cements that are activated with Na, with hydrotalcite and AFm phases in the rims ([ 38 , 39 ] and the references therein). With respect to the matrix, it has a lower Na-content.…”

Influence of cellulose nanofibrils on the rheology, microstructure and strength of alkali activated ground granulated blast-furnace slag: a comparison with ordinary Portland cement

“…The replacement of Portland cement with alkali-activated ground granulated blast-furnace slag (GGBS) does not only reduce CO 2 emissions, but is more economically viable and environmentally sustainable in terms of reduction of primary raw materials and of disposed waste. The efficiency, both technical and environmental, of the alkali activation can be limited depending on the composition of the slag and the type and concentration of the activator [7][8][9]. The use of alkali hydroxide or silicate solutions raises concerns about their corrosive properties and the related health and safety on the working sites [10].…”

Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2

“…The solid activators used in this work included the reagent-grade Na 2 CO 3 , Ca(OH) 2 and Mg(OH) 2 . The dosage of Na 2 CO 3 was fixed as 10 wt% of slag [ 19 , 25 , 33 ]. The blended Ca(OH) 2 and Mg(OH) 2 were used as the auxiliary activators with the purpose of expediting the kinetics of alkali activation [ 32 ].…”

“…The Ca 2+ dissolved from slag initially react with the CO 3 2− to precipitate as CaCO 3 , and the formation of the C-A-S-H gel phase occurs after the CO 3 2− ions are exhausted, accounting for the prolonged hardening process [ 18 , 19 , 22 ]. For the purpose of serving the one-part Na 2 CO 3 -activated slag binders as practical cementing materials in general applications, recent studies are extensively focused on the use of auxiliary activators to accelerate the kinetics of alkali activation [ 23 , 24 , 25 , 26 , 27 , 28 ]. Kovtun et al [ 29 ] enhanced the 1 day compressive strength of Na 2 CO 3 -activated slag concretes cured at ambient temperature up to 25 MPa via the additions of slaked lime (Ca(OH) 2 ) and silica fume.…”