Is electrodeless resistivity method suitable for monitoring the early-age reaction of Na2SiO3-activated slag? Mechanism and application

The Influence of Alkali Content on the Hydration of the Slag-Based Geopolymer: Relationships between Resistivity, Setting, and Strength Development

“…By combining with the resistivity model postulated in our previous study [ 15 ], the kinetic factor behind the change of curves in Figure 2 and Figure 3 could be preliminarily explained based on the model in Figure 4 . On the one hand, the high alkali content increased the concentration of Na + and SiO 4 4− ; on the other hand, to keep the total water-to-solids ratio unchanged, increasing the alkali content (namely a higher dosage of a water glass) reduced the additional water.…”

“…The electrodeless resistivity curves ( Figure 2 ) and differential curves ( Figure 3 ) clearly indicated the periodical change of the paste, in which five stages could be observed (located between O to A, A to B, B to C, and after C). The physical meanings of these inflection points could be pre-summarized based on our previous research [ 15 ], although the detailed profiles were different due to the change of alkali content, and further discussion on the discrepancy is carried out in the following sections: Stage I (OA): the sodium silicate activates the slag and causes it to disintegrate. Under the attack of OH − , the slag bond break and decompose into SiO 4 4− , AlO 4 5− , and Ca 2+ , and simultaneously the initial complex precipitate near the surface of the slag particles.…”

“…The detailed profiles of resistivity curves were different from the cases in varying water-to-solids ratios [ 15 ], implying the significant impact of alkali content on the hydration process of slag-based geopolymer pastes, especially in stages I/II/III/IV. The resistivity curves in Figure 2 indicated that the higher the alkali content, the shorter the time needed before the resistivity reaches the minimum point A, and the greater the A point value.…”

“…Due to the wide difference in electrical conductivity between the hardening product and pore solution, a higher resistivity value generally implies a higher reaction degree and superior strength, at least in the case of OPC or a slag-based geopolymer with the same alkali content [ 14 , 15 ]. However, it would be hasty to draw this conclusion herein, as the increasing alkali content complicated the situation.…”

“…Viewing from a larger scale, the hardening of geopolymer paste is somewhat similar to that of OPC, both of which require the dissolution of the raw materials and precipitation of the hydration products on the unhydrated particles, followed by phase boundary contact and reduced pore volumes of the geopolymers pastes [ 14 ]. In this process, owing to the consuming of reactant and traps of ions in pore spaces in the solidified hydration products, the early-age reactions of both geopolymers and OPC are apparently divided into four stages from the aspect of the reaction rate, namely the wetting, acceleration, deceleration, and steady periods [ 15 , 16 , 17 , 18 , 19 ], as identified by the heat release rate. Generally, this early-age heat releasing is completed within 24 h, which has been proven to relate to the setting behaviors and later-age strength developments (3 days~28 days) of OPC and geopolymers.…”