Alternative cementitious binders, based on industrial side streams, characterized by a low carbon footprint, are profitably proposed to partially replace Portland cement. Among these alternatives, ...alkali-activated materials have attracted attention as a promising cementitious binder. In this paper, the chemical stability of the matrix, in fiber-reinforced slag-based alkali-activated composites, was studied, in order to assess any possible effect of the presence of the reinforcement on the chemistry of polycondensation. For this purpose, organic fiber, cellulose, and an inorganic fiber, basalt, were chosen, showing a different behavior in the alkaline media that was used to activate the slag fine powders. The novelty of the paper is the study of consolidation by means of chemical measurements, more than from the mechanical point of view. The evaluation of the chemical behavior of the starting slag in NaOH, indeed, was preparatory to the understanding of the consolidation degree in the alkali-activated composites. The reactivity of alkali-activated composites was studied in water (integrity test, normed leaching test, pH and ionic conductivity), and acids (leaching in acetic acid and HCl attack). The presence of fibers does not favor nor hinder the geopolymerization process, even if an increase in the ionic conductivity in samples containing fibers leads to the hypothesis that samples with fibers are less consolidated, or that fiber dissolution contributes to the conductivity values. The amorphous fraction was enriched in silicon after HCl attack, but the structure was not completely dissolved, and the presence of an amorphous phase is confirmed (C-S-H gel). Basalt fibers partly dissolved in the alkaline environment, leading to the formation of a C-N-A-S-H gel surrounding the fibers. In contrast, cellulose fiber remained stable in both acidic and alkaline conditions.
Porous ceramics were generated by direct foaming the alkali-activated unprocessed kaolin (impure kaolin, iK) with the addition of hydrogen peroxide (H2O2) and calcining at a low temperature of ...400 °C. Hydrogen peroxide, a blowing agent, decomposes producing oxygen gas bubbles forming the porous structure in the fresh alkali-activated iK paste. In the present study, three different molarity of alkali activator (5, 10, or 15 M NaOH) were employed. The dosage of blowing agent (H2O2) was varied between 0 and 2% with a constant dosage of 0.5% (wt. of binder) of surfactant. The gas bubbles in fresh-state geopolymer slurry are unstable with a tendency to coalesce. In such cases, surfactants are introduced to improve the stability of the gas-liquid interface. Two different surfactants: non-ionic and cationic ones were used to study the properties of alkali-activated porous material. Fresh properties such as viscosity, yield stress, foaming rate, and fresh density were compared between reference iK samples without surfactants and those with surfactants. The mechanical and microstructural properties of alkali-activated (AA) low-temperature porous iK ceramics were determined after calcination. Pore structures were characterized with electron microscope to understand the interaction of different parameters during fresh/hardened state and their relevance with the changes in the mechanical properties. Surfactants, irrespective of the type, highly influenced the fresh properties of the AA-iK samples, which in turn reflected on the compressive strength of the porous ceramics.
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•Low temperature (400 °C) was employed to produce alkali activated porous ceramics.•Non-calcined, un-processed kaolin responds to alkali activation with NaOH.•Presence of surfactants influence the fresh and hardened properties of kaolin foam.•Surfactants helps in foam stabilization and strength improvement.
Fly ash generation in fluidized bed combustion (FBC) is a critical issue in many countries due to its disposal is becoming increasingly restricted and expensive. Because of this, there is a demand ...for applications in which these types of fly ashes could be utilized efficiently. One promising use for FBC fly ashes is as a cement replacement material in mortar and concrete. The current concrete regulations do not allow the use FBC fly ash as a supplementary cementitious material, but it can be expected to be included in the standards in the future. The properties of FBC fly ashes typically do not fulfill the values set in the standards as such. This study aimed to establish whether the properties of fly ashes from FBC of peat, wood, and wastes can be modified by mechanical classification and grinding so that they meet the requirements of the standards. The sulfate and chloride content, the sum of the main components (Si, Al, Fe), and the fineness of material were analyzed before and after the classification and grinding processes. In addition, the mortar specimens were prepared by using the processed fly ash as a cement replacement material. It was found that air jet classification is an effective fractionating method for fly ashes that effectively removes sulfate and chloride into fine fraction. Classified and ground fly ashes are potential alternative cement replacement materials. It is possible to achieve 80% of the control sample’s compressive strength and 90% of the control sample’s flexural strength for mortars containing 20% of classified and ground FBC fly ashes.
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Green liquor dreg (GLD) is a side stream generated by pulp industry. Due to its complex physicochemical nature, it has been reported to be difficult material to utilize. Here, a novel approach ...towards utilization of moist and dry green liquor dreg as binder and filler in alkali-activated lightweight artificial aggregates was developed. Dried GLD and moist GLD were granulated with blast furnace slag (BFS) and Bioash in different mixtures using alkali activation. The effect of the GLD nature (dried and moist) on strength, microstructure and durability of the lightweight granules were determined and compared. Results show that the method used in homogenizing the moist GLD and other powders was efficient and improved the frost resistance. The reaction product identified in the granule’s includes calcium silicate hydrate, Mg–Al layered double hydroxides, and ettringite. These results demonstrate the potential of GLD as a binder and fillers in cementitious applications.
•Green liquor dregs an industrial residue was upcycled in alkali-activated binder as artificial aggregates.•The texture of the GLD plays a significant role in the strength development and microstructural properties of the aggregates.•GLD in the synthesis improves the reactivity and act as filler in the aggregates.•The granules showed considerable resistance to frost.
One-part alkali-activated materials: A review Luukkonen, Tero; Abdollahnejad, Zahra; Yliniemi, Juho ...
Cement and concrete research,
January 2018, 2018-01-00, 20180101, Letnik:
103
Journal Article
Recenzirano
Odprti dostop
Alkali-activated materials (AAM) are recognized as potential alternatives to ordinary Portland cement (OPC) in order to limit CO2 emissions as well as beneficiate several wastes into useful products. ...However, the alkali activation process involves concentrated aqueous alkali solutions, which are corrosive, viscous, and, as such, difficult to handle and not user friendly. Consequently, the development of so-called one-part or “just add water” AAM may have greater potential than the conventional two-part AAM, especially in cast-in-situ applications. One-part AAM involves a dry mix that consists of a solid aluminosilicate precursor, a solid alkali source, and possible admixtures to which water is added, similar to the preparation of OPC. The dry mix can be prepared at elevated temperatures to facilitate the reactivity of certain raw materials. This review discusses current studies of one-part AAMs in terms of raw materials, activators, additives, mechanical and physical properties, curing mechanisms, hydration products, and environmental impacts.
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The construction and demolition waste generation is increasingly evolving with the rapid urbanization, with more than a quarter of the produced waste being landfilled without further treatment or ...recycling strategy. Hence, sustainable management and valorization methods such as recycling in construction materials is becoming increasingly essential to tackle the economic and environmental burdens of landfilling waste. Construction and demolition waste recycling has been intensively studied. However, the present study proposes a promising solution for recycling construction and demolition wastes (CDWs) from the precast concrete waste sludge and ashes from paper mill sludge and biomass. Artificial lightweight aggregates were designed and produced by alkali activating a mixture of 50–90 wt% of dried and milled CDW with 3–25 wt% of ash and 5–35 wt% of blast furnace slag. The properties of the produced aggregates were assessed
via
density, water absorption, porosity, and crushing tests, in addition to microstructural characterizations using XRD and scanning electron microscopy SEM analysis. The optimum NaOH concentration was 8M with the highest mechanical properties and lowest efflorescence. The produced aggregates revealed a high crushing force of 82 N at 28 days with 50 wt% CDW, 15 wt% biomass ash, and 25 wt% blast furnace slag presenting a possible recycling pathway for such side-stream materials.
Aluminosilicate glasses are materials with a wide range of technological applications. The field strength of network-modifying cations strongly influences the structure of aluminosilicate glasses and ...their suitability for various applications. In this work, we study the influence of the field strength of network-modifying cations on the structure of (Na2O)1–x(MgO)x(Al2O3)0.25(SiO2)1.25 glasses. Due to the higher cation field strength of magnesium than sodium, magnesium prefers the role of network modifier, while sodium preferentially acts as a charge compensator. When magnesium replaces sodium as network modifier, Q3 silicon species are converted into Q2 species. The replacement of sodium with magnesium as charge compensator leads to the following changes: (1) the proportion of aluminum-rich Q4 species Q4(4Al) and Q4(3Al) decreases, while the proportion of aluminum-deficient Q4 species Q4(2Al) and Q4(1Al) increases; and (2) there is an increased tendency for phase separation between silica-rich and alumina-rich glasses.
The pulp and paper industry produces several calcite-rich by-products including Green Liquor Dregs (GLDs), lime mud, grits, sludges, etc. Presently, majority of these by-products are managed by ...landfilling. The GLD used in this study is mainly dominated by calcite (∼80 %) and Hydrotalcite like compounds (HTlc, ∼12 %). It is used to produced OPC clinkers by using them as 0 %, 5 %, 10 %, 15 %, and 20 % replacement of limestone used for clinker production. TGA-DSC analysis of the clinker raw meals up to 1350 ℃ indicates that increase in GLD leads to slight reduction in the decomposition temperature for the raw meals, and a slight change in the formation temperatures for C2S and C3S. The mineral phase compositions of all the clinkers are comparable with a slightly decreasing C3S and C2S with increasing GLD. Compared to the Bogue calculated compositions, C3S and C2S are slightly lower, while the C3A is significantly lower and C4AF is significantly higher. The environmental leaching of GLD and the clinkers are all within the limits set by EN-12457-2. The environmental impact of clinker production and effect of GLD is analyzed for cradle-to-gate scenario with system boundaries. This analysis shows that by using GLD as replacement for limestone can lower the impact on diversity as well as CO2 related to transportation can also be reduced.
•Clinker produced by replacing 5-20 % limestone with GLD waste from paper industry.•Slightly reduced decomposition temperature of raw meal and clinker phase formation.•Environmental leaching of clinkers was found within limits of EN 12457-2.•Biodiversity conservation: timely in Nordics with limited limestone mining allowed.
The recycling of steel plant side streams through cold-bonded briquettes has become quite common. However, Portland cement is mainly used as a binder in the briquettes, contributing significantly to ...the energy consumption, costs, and carbon footprint associated with the production of cold-bonded briquettes. This paper reports on a more sustainable method for side stream recycling that involves replacing cement with an ettringite-based binder. Ettringite binders develop early high strength and mainly consist of ladle slag, another side stream of the industry. Here, the ettringite-based binder is assessed in terms of its mechanical and thermal properties against a reference briquette made using the conventional technique. Three different briquette types are produced using several side stream materials and varying ettringite-based binder content. Briquettes produced using 15% and higher ettringite-based binder content exhibited excellent mechanical properties within a shorter curing period compared to conventional used binder. Moreover, the ettringite-based binder briquettes exhibited a better swelling behavior to conventional cement briquettes under conditions simulating a blast furnace.
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