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- Alkali-activation (3)
- Strength (3)
- Geopolymers (2)
- Monocarboaluminate (2)
- Wastepaper sludge ash (2)
- AFm (1)
- Bindemittel (1)
- Calcium carbonate (1)
- Cement (1)
- Concrete (1)
Organisationseinheit der BAM
A silica residue from waste treatment of chlorosilane production was used together with solid sodium aluminate to test its applicability for the production of one-part geopolymers. The blend was activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1, 3, and 7 days. The reaction products were analyzed by XRD and SEM/EDX. Until the third day of curing the degree of reaction of the residue reached 51 % and the strength was 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. Thus, the results confirmed that the residue may be used in the production of geopolymers. However, after 3 days of curing no further progress of reaction was observed and the strength slightly decreased, which was attributed to changes in the structure of the geopolymeric gel. It was further observed that even harsh vacuum drying left some water (presumably zeolitic water and surface hydroxyl groups) in the geopolymer.
Reaction products and strength development of wastepaper sludge ash and the influence of alkalis
(2014)
Wastepaper sludge ash (WSA) from a newsprint paper mill was investigated for its mineralogical composition and its reaction products and strength development after activation with water and sodium and potassium hydroxide solutions. The results showed the WSA to consist of calcite, free lime, gehlenite, tricalcium aluminate, belite, talc, quartz and probably a glassy phase. The principle reaction product was monocarboaluminate (CO3–AFm) for the water- as well as for the alkali-activated WSA. Formation of monocarboaluminate and strength gain was more rapid for the alkali-activated WSA until 1 day of curing. However, afterwards reactions proceeded much slower when alkali solutions were used, leading to an about twice as high compressive strength for water-activated WSA mortars after 28 days of curing. The observed behavior is tentatively ascribed to a less uniform microstructure of the alkali-activated WSA. Significant differences between NaOH- and the KOH-activated WSA were not observed.
Interactions between waste paper sludge ashes and superplasticizers based on polycarboxylates
(2016)
In many industrial nations, about two third of the paper demand is covered by recovered paper. A major process step within the treatment of waste paper is the de-inking. It is a floating process yielding paper sludge as a waste product. About 50 % of this residue is used as a fuel. In several cases it is burnt at temperature of about 850 °C and thereafter the accrued ashes are collected in the flue gas filter. During the combustion, kaolinite and calcium oxide generate gehlenite and larnite. Calcite is the main component of waste paper sludge ash (PA).The chemical and mineralogical composition of PA suggests using it as a supplementary cementitious material.
In modern construction materials technology, workability aspects gain importance, since for most modern materials the rheology and compaction ability are relevant for the operation at a hardened state. It was observed that PA significantly increases the water demand of powder systems, which can cause serious problems during the casting of mineral binder systems containing PA. It is therefore obvious that binder systems containing PA might demand for the use of superplasticizers. Superplasticizers are polymers with anionic backbone that cause electrostatic and steric repulsion effects upon adsorption on surfaces of particles and hydration phases.
In this paper interactions between superplasticizers and waste paper sludge ashes are discussed and analysed. Based on observations of changes in the zeta potential and the dispersion of the particle system, the influence of the charge density of superplasticizers is observed and time dependent effects are demonstrated.
Industrial wastes (bottom ash, crushed concrete fines, filter residue, paper ash and lignite fly ash) have potential for use in building materials, for instance as raw materials for clinker production, as supplementary cementitious materials (SCMs) or mineral additions in concrete. The properties of the products are dependent on the reactivity of the waste materials used, which can be classified as inert, latent hydraulic or pozzolanic. In this study, waste materials were first characterised. This was followed by theoretical considerations of the mentioned application options. Experiments were limited to evaluation of potential as SCMs and, for this purpose, activity index measurements and calorimetric and thermogravimetric analyses were performed. Finally, the synergetic effects of various waste materials were considered. Paper ash (calcium oxide source) and filter residue (amorphous silicon dioxide source) showed the best prospects for use as cementitious material components.
In paper recycling several types of waste sludges are produced, which contain organics as well as inorganic fillers of the recycled paper, e.g. kaolinite, calcite, talc, or titanium dioxide [1,2]. Part of these sludges is incinerated to recover energy and to reduce the volume of waste to be handled. The ashes generated in this process are commonly referred to as wastepaper sludge ash (WSA). The quantities of WSA produced are large and at present much of it is still landfilled or otherwise handled entailing costs.
Depending on the composition of the recycled paper and the conditions during processing and incineration, WSA can have cementitious properties. In the present investigation a CaC03-rich WSA was analyzed for reaction products and strength development after hydration with water, 2 M NaOH solution and 8 M NaOH solution. The rationale for activating the WSA with NaOH was to assess the behaviour of the WSA when alkalis are introduced to the System or when the WSA is used as addition in alkali-activated binders.
In paper recycling large amounts of waste sludge, containing organics as well as inorganic fillers of the recycled paper, are produced. A large fraction of these sludges is incinerated; the ashes generated in this process, often referred to as wastepaper sludge ash (WSA), have the potential to be used as binder material, either alone or as supplementary cementitious material. However, ashes from different paper mills differ in their Chemical and mineralogical composition, thus, the reaction products and the properties of the hardened binders may vary s i gn i fi cantley.
In the present study, a calcite-rich WSA was analyzed for reaction products and strength development. The WSA contained, besides calcite, hydraulic phases such as tricalcium aluminate (C3A) and belite (C2S), lime as well as inert phases. When activated with water, the WSA yielded a compressive strength of up to 12.3 MPa and the major hydration product was monocarboaluminate (C4A CO2 IIH2O or C4ACH11). Activation with 2M NaOH or 2M KOH solution caused a more rapid strength gain until one day of curing, but afterwards the strength development slowed down and the strength afiter 28 days was significantly lower than for the water-activated pastes. From TG analyses it is apparent that the higher strength of the alkaliactivated pastes after one day of curing was caused by a more rapid consumption of calcite and associated formation of C4ACH11. At later curing times the amount of calcite did not change substantially and consequently strength development almost ceased.
The results demonstrate the complex influence of alkaline conditions on the hydration of WSA and show that the reaction products, which determine the durability properties of the hardened pastes (and materials made from it), of the calcite-rich WSA differ from the products of other WS As, as discussed in the article.
European and Germany regulations demand an elaborate waste management to save natural resources, reduce waste volumes deposited at landfills and enhance sustainable development by recycling of various residues. Research into the use of these materials in the construction sector and other fields is a positive step forward in achieving these objectives. BAM shares its latest findings.
In Deutschland fallen jährlich 20 Millionen Tonnen Altpapier an. 75 % davon werden dem Recyclingprozess zugeführt. Dabei bleiben Prozessrückstände wie Deinkingschlämme, Sortierrückstände und Faserreststoffe übrig. Zusammengefasst als Papierschlamm verwerten die Recycler diesen Reststoff thermisch in dezentralen Heizkraftwerken. Die dabei anfallende Papierasche hat mit den Anteilen der Hauptoxide von 59 M.-% CaO, 22 M.-% SiO2 und 13 M.-% Al2O3 eine ähnliche chemische Zusammensetzung wie Portlandzement, wobei sich die Mineralphasen unterscheiden. Durch eine Aktivierung der Papierasche können jedoch hydraulisch aktive Phasen wie Mayenit (C7A12) und Belit (C2S) erzeugt werden. Die Mineralphase Mayenit reagiert schnell mit Wasser zu Calciumaluminathydraten, wodurch der Bindemittelleim schnell ansteift. Die festigkeitsbildenden Calciumsilicathydrate (CSH) in Bindemittelleimen entstehen bei einer späteren Reaktion von Belit mit Wasser.
Zur Aktivierung dient eine hydrothermale Calcinierung. Dabei wird Papierasche mit einer Aktivatorlösung (Wasser oder KOH) gemischt und bei 200 °C hydrothermal behandelt, wobei sich Hydratphasen ausbilden. Diese Zwischenprodukte dehydratisieren durch eine anschließende Calcinierung zu reaktiven Calciumsilicaten und Calciumaluminaten. Wie sich die Parameter des Aktivierungsprozesses auf die Mineralphasen auswirken, war Fokus der Untersuchungen. Mit thermogravimetrischen Analysen der Zwischenprodukte konnten die Reaktionsprodukte nach dem hydrothermalen Prozessschritt bestimmt werden. Den größten Einfluss auf den Mineralphasenbestand hat hierbei die Alkalität der Aktivatorlösung. Im zweiten Prozessschritt, der Calcinierung, ist die Temperatur der wesentliche Faktor für die Ausbildung reaktiver Phasen. Die Ergebnisse kalorimetrischer Untersuchungen an Leimen aus den calcinierten Proben dienten der Auswahl der optimalen Calcinierungstemperatur. Die gesamte Reaktionswärme war für die Proben, welche bei einer Calcinierungstemperatur zwischen 700-800 °C hergestellt wurden, am höchsten.