Inorganic polymer cement from Fe-Silicate glasses: Varying the activating solution to glass ratio

Large volumes of Fe-silicate glasses - slags - are produced as residues of metal production and waste treatment processes. It would be interesting if these materials could become an alternative group of precursors for the synthesis of inorganic polymer (IP) cements. This paper investigates the polymerisation of Fe-silicate glasses of composition (in wt%) SiO2: 40; FeO: 30; CaO: 15; Al2O3: 8 and an activating solution of composition (in wt%) Na2O: 15; SiO2: 13; H2O: 72. The mass ratio of the activating solution to the glass (L/S) was varied from 0.3 to 1.0 and the effect on the IP chemistry, microstructure and properties was investigated. Despite the high Fe and low Al contents of the glass, an IP cement could be synthesised, resistant to water dissolution and delivering mortars of compressive strength >52 MPa after 28 days curing at room temperature when using a L/S ratio of 0.45. Lowering the ratio from 1.00 to 0.45 results in a significant improvement in compressive strength, a lower porosity and when immersed in water, Na dissolution is decreased and water pH is lower. Microstructural investigation indicates that when the amount of activating solution is decreased, the degree of glass dissolution is lower resulting in less IP formation and a more homogeneous IP chemistry. Compared to higher L/S ratios, the IP mortar has a more densely packed microstructure of partially dissolved glass and sand aggregates bound by the IP matrix. At lower L/S ratios, the formation of micro scale shrinkage cracks in the IP matrix is strongly reduced, while at higher L/S ratios, shrinkage cracking is more pronounced and individual micro-cracks connect to form more pronounced large scale cracks. At a L/S ratio of 0.45, the IP cement is composed of 90 wt% Fe-silicate glass and only 10 wt% Na-silicate (% of powder mix) and it is indicated that this percentage can still be reduced. As 90 wt% of this IP cement is composed of a waste material and as curing is performed at ambient temperatures, its production is expected to have important ecological and economic benefits.status: publishe

Properties of inorganic polymer cement from ferric and ferrous vitrified residues of plasma gasification

status: publishe

Use of bauxite residue slurry as single activator in a hybrid binder system

The use of bauxite residue (BR) slurry as an activator in a hybrid system is explored in this paper. The strong alkaline nature of the slurry, which is considered as a major barrier for most valorization routes, is beneficial in this approach, where it is used as single source of water and alkalis to activate a hybrid cementitious precursor blend. Moreover, the fineness of the solid fraction of the slurry is expected to improve the particle packing, enabling reduction of the water content and thus of the final system porosity. Experimentally, ≥ 33 wt% of BR slurry, was homogenized and subsequently mixed with either non-ferrous metallurgy slag or ground granulated blast furnace slag (GGBFS), ≤ 10 wt% of ordinary Portland cement (OPC) and minor additives. The raw materials were mixed and the resulting pastes were cured at ambient conditions. Satisfactory mechanical properties were reached, exceeding 35 MPa already after 3 d of curing at room temperature. The results are promising, also considering that the slag mix can be potentially replaced by a thermally processed BR, thus leading to a maximization of total BR content in the newly formed binder.status: publishe

Monitoring early-age crack formation in a Ca-Fe-Al-rich inorganic polymer

status: publishe

Fe-Si-glasses as geopolymer precursors: decreasing the amount of activating solution?

status: publishe

Inorganic polymer cement from Fe-Silicate glasses: Varying the activating solution to glass ratio

Large volumes of Fe-silicate glasses - slags - are produced as residues of metal production and waste treatment processes. It would be interesting if these materials could become an alternative group of precursors for the synthesis of inorganic polymer (IP) cements. This paper investigates the polymerisation of Fe-silicate glasses of composition (in wt%) SiO₂: 40; FeO: 30; CaO: 15; Al₂O₃: 8 and an activating solution of composition (in wt%) Na₂O: 15; SiO₂: 13; H₂O: 72. The mass ratio of the activating solution to the glass (L/S) was varied from 0.3 to 1.0 and the effect on the IP chemistry, microstructure and properties was investigated. Despite the high Fe and low Al contents of the glass, an IP cement could be synthesised, resistant to water dissolution and delivering mortars of compressive strength >52 MPa after 28 days curing at room temperature when using a L/S ratio of 0.45. Lowering the ratio from 1.00 to 0.45 results in a significant improvement in compressive strength, a lower porosity and when immersed in water, Na dissolution is decreased and water pH is lower. Microstructural investigation indicates that when the amount of activating solution is decreased, the degree of glass dissolution is lower resulting in less IP formation and a more homogeneous IP chemistry. Compared to higher L/S ratios, the IP mortar has a more densely packed microstructure of partially dissolved glass and sand aggregates bound by the IP matrix. At lower L/S ratios, the formation of micro scale shrinkage cracks in the IP matrix is strongly reduced, while at higher L/S ratios, shrinkage cracking is more pronounced and individual micro-cracks connect to form more pronounced large scale cracks. At a L/S ratio of 0.45, the IP cement is composed of 90 wt% Fe-silicate glass and only 10 wt% Na-silicate (% of powder mix) and it is indicated that this percentage can still be reduced. As 90 wt% of this IP cement is composed of a waste material and as curing is performed at ambient temperatures, its production is expected to have important ecological and economic benefits.status: publishe

A proposal for a 100% use of bauxite residue: The process, results on the novel Fe-rich binder and how this can take place within the alumina refinery

status: publishe

One-part inorganic polymers from residues only: Biomass ash activation of Fe-rich slag

The formation of inorganic polymers solely from industrial residues was investigated. Non-ferrous slag, an iron silicate precursor, was combined with biomass ash from electricity generation, which contains potassium, providing the alkalinity needed to dissolve and polymerize the slag. The reactivity in calorimetry was shown to be comparable with maize ashes, which have already proven in past research to provide strong geopolymers when combined with metakaolin. For optimised ash/slag and water/solid mass ratios of 0.9 and 0.15 respectively, the maximum compressive strength of pressed samples attained was 10.4 MPa. This low strength was associated with a low reaction extent, observed by attenuated total reflectance Fourier-transformed infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM), as well as with the formation of gypsum, observed using a combination of SEM and thermogravimetric analysis (TGA).status: publishe

The impact of curing conditions on heavy metal immobilisation of Fe‐rich inorganic polymers

status: publishe

Mix-design parameters and real-life considerations in the pursuit of lower environmental impact inorganic polymers

The environmental impact of inorganic polymer mortars from non-ferrous slag was assessed and compared to ordinary Portland cement (OPC) mortar based on a load bearing capacity of 10 MN of bricks of 0.1 m high. Two strategies to minimize the environmental impact of inorganic polymers were pursued. Activating solutions with a lower alkali content (H₂O/Na₂O = 16, 24, 32, 40, 48; constant SiO₂/Na₂O = 1.6) were investigated while keeping the water/slag mass ratio of the inorganic polymer mortar mix constant. Another synthesis route considered the complete replacement of the activating solution by maize ashes. These were blended with the slag in different ash/slag mass ratios (0.2, 0.4, 0.6) before adding water, producing a so called “one-part” inorganic polymer. A sensitivity analysis showed that the effect of compressive strength and transport distance is extensive. Because of this considerable transport distance dependence, several cities in Flanders were selected to perform a detailed LCA study. The optimal scores of the environmental impact were observed for Mol, the location of the sand supplier, and accounted for 23% with respect to OPC for the samples with the activating solution with a ratio of H₂O/Na₂O = 24 and 17% for an ash/slag ratio of 0.2.status: publishe