Performance and sustainability overview of sodium carbonate activated slag materials cured at ambient temperature

Accelerating the Reaction Kinetics of Na2CO3-Activated Slag Mortars by Calcined Recycled Concrete Fines

“…This promoted the breakage of Ca-O and Mg-O, as well as Al-O and Si-O, in GBFS and induced the production of the strength-giving phase (C-(A)-S-H). The remaining CO 3 2− would continue to be consumed by forming carbonates such as calcite (Equation (2)), gaylussite (Equation (3) [ 1 ]), Ht (Equation (5) [ 16 ]), Mc (Equation (6) [ 43 ]), and Hc (Equation (7) [ 43 ]), as identified in the XRD patterns. It should be noted that the gaylussite, as a transient phase, can be decomposed (Equation (4)) in an environment of low CO 3 2− concentration or high OH − concentration, and the CO 3 2− could be stored in other carbonates (Ht, Hc, and Mc) [ 44 ].…”

“…Ordinary Portland cement (OPC) is the most extensively applied cementitious material for concrete production. The high CO 2 emission and consumption of raw materials, however, are created by OPC production, which results in serious environmental problems such as rising sea levels and global warming [ 1 , 2 ]. To relieve the increasing pressure in OPC production and thus reduce CO 2 emissions, the alkali-activated slag (AAS) binders produced by the reaction between alkaline activators and granulated blast furnace slag (GBFS) have been rapidly developed in the last few decades.…”

“…This has been the most popular and promising way to develop sustainable AAS mortars, as the Na 2 CO 3 can not only easily be obtained from trona ore but is also 2–3 times cheaper than the Na 2 O·nSiO 2 as well as NaOH [ 10 ]. In addition, Na 2 CO 3 , as a near-neutral salt, is less harmful to the handler than strong base activators and releases a lower carbon footprint [ 1 , 11 ]. However, compared to the NaOH and Na 2 O·nSiO 2 , Na 2 CO 3 provides a relatively weak alkaline environment for the dissolution of GBFS, and, therefore, a slow hydration process with a very long induction period and low early-age strength development can be observed in one-part Na 2 CO 3 -activated GBFS binders [ 12 , 13 , 14 ].…”

C-S-H Seeds Accelerate Early Age Hydration of Carbonate-Activated Slag and the Underlying Mechanism

“…Low alkalinity, ease of operation, and good performance are the advantages of carbonate activation, which has drawn significant attention from the academic and industrial fields in recent years [ 1 , 2 , 3 ]. The long setting time caused by slow hydration is the major challenge that is still to meet the basic requirements for in situ applications [ 4 , 5 ].…”

“…Incorporated extra agents increase the alkalinity of activators, promote the dissolution rate of elements of Si, Al, and Ca from slag particles, and accelerate the formation of hydration products, such as Al-substituted calcium silicate hydrates (C-A-S-H gel) and carbonate-containing phases. The hardening process of carbonate activation is accelerated; however, reductions in strength or issues of durability are also often reported [ 1 , 6 , 9 , 10 ]. Importantly, increasing alkalinity also raises the risk of storage, operation, and costs, limiting their wide application in in situ constructions.…”