Alkali-activated concretes based on fly ash and blast furnace slag: Compressive strength, water absorption and chloride permeability

Abstract

Concretes based on alkaliactivated binders have attracted considerable attention as new alternative construction materials, which can substitute Portland Cement (OPC) in several applications. These binders are obtained through the chemical reaction between an alkaline activator and reactive aluminosilicate materials, also named precursors. Commonly used precursors are fly ash (FA), blast furnace slag (GBFS), and metakaolin. The present study evaluated properties such as compressive strength, rate of water absorption (sorptivity), and chloride permeability in two types of alkaliactivated concretes (AAC): FA/GBFS 80/20 and GBFS/OPC 80/20. OPC and GBFS/OPC* concretes without alkaliactivation were used as reference materials. The highest compressive strength was observed in the FA/GBFS concrete, which reported 26,1% greater strength compared to OPC concrete after 28 days of curing. The compressive strength of alkaliactivated FA/GBFS 80/20 and GBFS/OPC 80/20 was 61 MPa and 42 MPa at 360 days of curing, respectively. These AAC showed low permeability to the chloride ion and a reduced water absorption. It is concluded that these materials have suitable properties for various applications in the construction sector.

Transport properties of fly ash-slag-based geopolymer concrete with 2M sodium hydroxide combined with variations in slag percentage, Al/Bi ratio, and SS/SH ratio

“…This gel fills the voids in the paste and interfaces between the paste and the aggregate, leading to a denser material. The C-A-S-H gel is associated with greater densification and compactness, due to Slag 10% Slag 20% Slag 30% Slag 40% Slag 50% OPC 0,0 Slag 10% Slag 20% Slag 30% Slag 40% Slag 50% OPC 0,0 the fact that fly ash/slag concrete has fewer porous capillaries or pores (9). In addition, the less porous matrix is also associated with a smaller slag particle size than the fly ash particles which develops a micro filler effect (22).…”

“…The matrix and strength of this type of cement does not require the formation of hydrated calcium silicate (C-S-H) gel, as with ordinary Portland cement concrete (OPC), but instead relies on aluminosilicate polycondensation (8). When a low calcium precursor is used to create geopolymer binder, a sodium aluminum silicate hydrate (N-A-S-H) gel with a three-dimensional structure is produced (9).…”

The Obstacles to a Broader Application of Alkali-Activated Binders as a Sustainable Alternative—A Review

“…GGBFS [17,23,[27][28][29]33,35,41,42,45,46,48,49,[51][52][53][54][55][56]59,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86] Ground granulated blast furnace slag (GGBFS) is a by-product of the iron-making process.…”

“…It can be used as a single precursor in AABs [31,34,36,38,39,42,56,[61][62][63][64][65][66]. It was also utilised as a part of binary and ternary blended precursors with a variety of conventional and/or alternative precursors [17,22,28,30,32,33,35,37,40,41,[43][44][45][46][47][50][51][52][53][54][55][57][58][59][60]. The ternary mix of waste brick powder (WBP), waste ceramic powder (WCeP), and waste concrete powder (WCP) was examined together with integrating FA in the precursor and activating it using a mix of SH and SS [48].…”

Fractional-order numerical modeling to study chloride ion transport in concrete with fly ash or slag additions

“…There are already many practical and environmentally friendly methods to improve the durability of reinforced concrete. These methods include: changing the formulation of concrete to manufacture new types of concrete [ 4 , 5 ], coating concrete reinforcement with protective layers [ 6 , 7 ], and adding polymer modifiers [ 8 – 11 ], rubber [ 12 ], and minerals [ 13 , 14 ] to concrete. The use of Class F fly ash or finely ground blast furnace slag as admixtures in concrete is convenient, relatively low-cost, and environmentally friendly [ 15 ].…”