The Effect of Heat Treatment on Alkali Activated Materials

Abstract

The primary object of the present research was to investigate the porous low calcium alkali activated material (AAM). Traditionally Na+ ions for alkali activation solution ensure highly alkaline media which enhances the dissolution of amorphous phase in the raw materials forming solid cementitious material with sodium aluminosilicate hydrate (N-A-S-H) structure afterwards. Almost all alkali ions are partially hydrated filling the pores in the gel structure (N-A-S-H gel, type zeolite precursor) and neutralizing the charge on Al(OH) -4 groups. These alkali ions are available for leaching in water environment. Due to this property the application of porous AAM in this research is related to the water treatment systems similar to those of natural zeolites which are considered as effective sorbent because of their porous structure, high specific surface and ion exchange. Porous AAM was obtained from metakaolin, sodium silicate glass, modified sodium silicate solution with Ms = 1.68 and diethylene glycol (DEG) aluminium paste as pore forming agent. The density of AAM was 1150 ± 12 kg/m 3 and compressive strength fc > 12 MPa. The effect of heat treatment to microstructure and structural properties of AAM was investigated. Heat treatment is an effective method for changing the alkali leaching kinetic form AAM structure.

Low-Calcium, Porous, Alkali-Activated Materials as Novel pH Stabilizers for Water Media

“…It focused on the changes detected between 25 • C and 200 • C. The peak maximum of the DTG curve at 98 • C temperature represented the water loss of FA_0, which constituted 5.2% of the weight loss, while MK_0 at 129 • C and MK + FA_0 at 127 • C constituted 11.5% (MK_0) and 8.9% (MK + FA_0), respectively. The weight loss of pAAM between 25 • C and 150 • C was associated with the evaporation of physically bonded water from the pore structure [28] as well as with different L/S ratios used for sample preparation ( Table 2). The paste of MK_0 had 2.0 times more water coming from the activator in its composition than sample FA_0 and 1.5 times more than sample MK + FA_0.…”

“…Zeolites in the structure of AAM could improve the effectiveness of contamination sorption from wastewater, such as heavy metals [24][25][26], ammonium [27], calcium [25], and fluoride [18]. Due to relatively weakly bonded alkali atoms in the N-A-S-H gel structure (similar to zeolites) it is possible to provide a Na + and OH − ion exchange in water media [28].…”

“…Alkali-activated materials with high porosity could be used for water treatment systems as pH adjustment materials due to its stable alkali leaching rate in time as well as its intensity of ion exchange due to a high specific surface. There are different foaming agents that can be used to produce porous alkali-activated materials (pAAM): Hydroxide peroxide [5,29]; an aluminum paste [3,28,30] foaming agent, for example, sodium dodecyl sulphate [31,32]; aluminum containing, for example, aluminum scrap recycling waste [33]; Na-perborate monohydrate [34]; and others. The high pH buffering capacity of pAAM in water media has been reported by Novais et.al.…”

“…Porous monolithic materials and granules were produced for the planned tests. To determine the effect of thermal treatment considered as an effective treatment for the changing of alkali leaching ability and its ability to ensure stable pH over time in water media [3,28], some samples were treated at 200 • C for 3 h.…”

Alkali-Activated Metakaolin as a Zeolite-Like Binder for the Production of Adsorbents

“…Zeolites in the structure of an AAB might improve contaminant sorption effectiveness, i.e., in removal of heavy metals from wastewater [9,10], as well as removal of NH 4 + [11], Ca 2+ [10], and F − [12]. Due to relatively weakly bonded sodium and potassium ions in the N(K)-A-S-H gel structure (similar to zeolites), it is possible to provide alkali and H + ions exchange in water media [13].…”