Enhancement of Material Properties of Lime-Activated Slag Mortar from Intensified Pozzolanic Reaction and Pore Filling Effect

Abstract

To utilize alkali-activated materials widely, this study investigates the effects of an intensified pozzolanic reaction and pore filling by silica fume on various material properties of lime-activated slag mortar. Although ground-granulated blast-furnace slag is classified as a cementitious material, it commonly requires an activator to enhance the performance of structural materials. In the first step of the improvement strategy, slag reaction is activated by hydrated lime. Next, silica fume is added to densify the microstructure by the physical pore filling effect and/or the pozzolanic reaction that additionally forms hydration products. This increased the compressive strength by 18% at 28 days and by 25% at 91 days under ambient curing condition, mainly due to the physical effect. Moreover, elevated temperature curing for three days was highly effective to further improve the strength, and to accelerate strength development. This is because both the physical effect and the chemical reaction are effective at the high temperature curing condition. The conducted microstructural investigation provided the evidence for the intensified pozzolanic reaction and pore filling effect, both of which are closely related to the mechanical properties. It is also found that the use of silica fume positively contributes to the dimensional stability. Since the developed material exhibits high strength (>40 MPa after 14 days) without Portland cement or highly toxic chemicals, it can be practically used as an eco-friendly structural mortar.

Quantitative Analysis of CO2 Uptake and Mechanical Properties of Air Lime-Based Materials

“…On the other hand, when the w/b increased from 0.4 to 0.6, both compressive and flexural strengths decreased by 29%. The enhancement of the mechanical properties by the addition of silica fume can be explained by the pore-filling effect (i.e., the capillary pores are filled with ultrafine particles) and the pozzolanic reaction [41,42]. This positive effect of the silica fume addition was more pronounced in compressive strength than in flexural strength, as reported previously [43].…”

A Review of Durability and Strength Characteristics of Alkali-Activated Slag Concrete

“…There is a striking similarity between the effect of silica fume on OPC concrete and the effect of AAS concrete in terms of enhancing compressive strength up an optimum percentage of silica fume. Kwon et al [27] tested mortar samples that use slag as binder and activated using Ca(OH) 2 . Mortar sample that contained 15% silica fume developed higher compressive strength and elastic modulus compared to mortars that contained only slag after 1, 3, 7, 14, 28, 56, and 91 days of curing.…”

“…In OPC concrete, autogenous shrinkage occurs during the first 24 h, most dominantly in high strength concrete where w/b ratio is less than 0.4. However, in AAS concrete, autogenous shrinkage was shown to continue until 91 days [27]. This is due to the continuation of slag reaction and consumption of moisture in AAS concrete for a longer time compared to OPC concrete [27].…”

Evaluation on Strength Properties of Lime–Slag Stabilized Loess as Pavement Base Material

“…Moreover, these reactants acquire high reactivity due to alkaline environment provided by the existence of enough lime for the pozzolanic reaction of slag, which was to produce more calcium silicate hydrate and calcium aluminate hydrate [26,56]. Thus the product of pozzolanic reaction was the main contribution factor to enhance the strength of the mixture [36]. [6,7,26].…”

“…However, the early-stage strength of lime stabilized soil tends to be quite low due to the slow pozzolanic reactions [20][21][22][23][24][25][26]. Many of the aforementioned studies demonstrate that lime can be used as an activator for industrial by-products, such as ground granulated blast furnace slag in engineering applications [27][28][29][30][31][32][33][34][35][36]. The utilization of lime-slag mixture to improve the mechanical characteristics of soils is expedient for pavement engineering and some other geotechnical applications [37][38][39][40][41].…”