Innovative recycling approaches to enable new material loops for AAC

This paper shows different approaches to save mineral resources or energy for the production of autoclaved aerated concrete (AAC) using secondary materials. The goal is implement new recycling routes in building industry and establish material loops. It could be shown, that AAC can act as a sink fine fractions from rubble consisting waste calcium silicate masonry units (CSU) by replacing primary quartz sand. By choosing raw materials like rice husk ash with higher solubility than quartz, it even possible achieve desired properties at lower autoclaving temperatures. After end life, treated patented approach “ENSUBA,” wet-chemical washing procedure, which enables complete removal sulfate ions, usually cause problems AAC. this treatment easily brought back cycle example used cement production. Most importantly, ENSUBA combined sensibly carbon capture technique chilled ammonia process. process captures CO2 an solution, leading precipitation ammonium carbonate, needed Dieser Artikel zeigt verschiedene Ansätze zur Einsparung von mineralischen Rohstoffen oder Energie für die Herstellung Porenbeton unter Verwendung Sekundärmaterialien. Ziel ist es, neue Recyclingwege der Bauwirtschaft zu realisieren und Stoffkreisläufe etablieren. Es konnte gezeigt werden, dass als Senke Bauschutt-Feinfraktionen fungieren kann, indem man den primären Quarzsand durch Altbeton Kalksandstein ersetzt. Durch Wahl sekundären wie Reishülsenaschen mit einer höheren Löslichkeit Quarz es sogar möglich, gewünschten Eigenschaften bei niedrigeren Autoklaviertemperaturen erreichen. Nach Nutzungsphase kann dem patentierten Ansatz “ENSUBA” behandelt einem nasschemischen Waschverfahren, das eine vollständige Entfernung Sulfationen ermöglicht, normalerweise Probleme beim Recycling verursachen. dieser Behandlung können Porenbeton-Abfälle leicht Stoffkreislauf zurückgeführt beispielsweise Rohstoff Zementherstellung verwendet werden. Idealerweise lässt sich ENSUBA-Ansatz sinnvoll CO2-Abscheidungsverfahren gekühlten Ammoniakprozess kombinieren. Prozess fängt aus Zementproduktion Ammoniaklösung auf, was Ausfällung Ammoniumcarbonat führt, welches ENSUBA-Prozess benötigt wird. Recycled are aggregates obtained processing construction mainly road, earthwork, landfill [1]. They also recycled asphalt production, but only small proportion manufacture products equal value. due, among other things, composition constructional environmentally relevant Above all, form gypsum poses major problem subsequent recycling. Since relatively soluble, react components thus negatively influence damage when [2]. separation site type technology crucial better possibilities. Especially fraction waste, there still no suitable methods available, why landfilled. Every year Germany alone, about 5 million tonnes (<2 mm) accumulate, landfilled due their heterogeneous high content. Aerated sustainable material, impresses above all its combination low weight load-bearing capacity. Usually, natural concrete. In addition during returned manufacturing process, recent years industrial rich SiO2 CaO has increasingly been [3]. For example, fly cellulose [4], gasification residues [9], bottom coal-fired power plants [5], silica fume [3], blast furnace slags used. first part investigates whether these purpose, sand, serves concrete, replaced mixtures. These mixtures, proportions, contain synthetic well quartzitic calcitic aggregate. effects on compressive strength manufactured bodies examined conclusions substitute drawn characterizing overall chemistry mineralogy. characterization regard grain size distribution, chemistry, mineralogy work. aim such sand same time maintain quality second paper, focus reduction consumption previous study Fraunhofer IBP [6, 7] correlation between source temperature formation mechanical properties. (RHA) adapting formulation accordingly, reduce up approximately 30°C, directly leads consumption. third deals named remove ions completely routes, especially does not need deposited, meaningful Real inhomogeneous mixture includes accumulates demolition building. various bricks, clinker, units, ceramics, tiles, much more. order able investigate “ideal waste” investigations three components: aggregate, While commercially available used, common aggregate produced inhouse CEM I 42,5 N water/cement ratio 0.42. following, reasons simplicity, referred (ConQu) (ConCa). All were pre-crushed separately hammer, crushed jaw crusher, then sieved 1 mm sieve cut. analyzing phase given samples, X-Ray diffraction measurements made D2 Phaser device Bruker, based Bragg-Brentano method. carried out 2Θ step width 0.02° measurement duration 3 seconds per over total angle range 5–65°. qualitative evaluation measured spectra, program DIFFRAC.EVA V 4.2 uses PDF-2 structure database ICCD (International Center Diffraction Data). Rietveld analysis, quantitative evaluation, refinement DIFFRACplus TOPAS Bruker. analysis chemical Epsilon3XLE PANalytical, performed standard-free software Omnian. results X-ray fluorescence formed basis calculating mass attenuation coefficient. determination amorphous means external standards complement mineralogical samples XRD analysis. use AAC, mixtures produced. substitutes, each consists 100% (CSU), (ConQu), Calcium mixed 75/25, 50/50, 25/75 respectively. resulted nine compositions material. water-to-solid 0.7 have saturated steam autoclave IBP, applying pressure p = 12 bar T 190°C 6 h. class P4 bulk density 0.55 targeted. content 44 wt.% reference sample, 30% (LSS, ConQu, ConCa) according DIN EN 772-1 [8] four 10 × cm3 cubes. blocks cut into cubes band saw exact milling cutter. size, conditioning test specimens moisture crucial. stored oven 50°C several days until +/− 2 reached. A Zwick Roell Z 100 press strengths. Table materials, replace 30%. percentages, elements oxides. LOI loss ignition, after heating 1000°C h (Table 2). possess highest 74 lowest 15 wt.%. (∼57 wt.%) (∼22 wt.%). hand, ConCa 35 differs significantly 9 ConQu Slight differences seen Al2O3 3.6 contained followed 2.8 1.2 already quite substitutes proportions 0.1 1.6 wt.%, 3). sample tobermorite 56.7 constituents just below 54–56 solely 52 components, reach values 46–49 known dry densities compare other, dimensionless A-number represents parameter independent offers possibility densities. 4, sorted ascending A-number. An average value two identical bodies. There one clear trend observable: perform worst 800 860. containing somewhat 980 990. Mixtures 75/25 show best performance almost strengths ranging 1020–1060. respective block seems effect strength. determined hydroxylellestadite derived. noticeable increases increasing content, whereas decreases shown some works increase crystalline phases crystal [9-11]. tests showed minor changes severe losses Surprisingly, achieved while worst. factor most likely decrease decreasing However, appear concluded fact pure despite addition, correlations established. Thus, associated strength, anhydrite weakening show, point view feasible and/or 30 improves significantly, because generates hydrothermal condition under tobermorite, responsible formed. C-S-H generated through reaction dissolved alkaline ions. Lime (CaO) reactive component mixture. Hydration lime occurs initial mixing water. dissolution requires take place diffuse solution adequate extent. Therefore, dissolve generate [12]. implies if level required shorter applied. assumed advantage reducing time. way will influenced negatively. Accordingly, within (RHA), silica-rich quartz. mix similar industry, adjusted P4. Then substituted RHA study, kept constant investigated samples. conducted temperatures 134–192°C corresponding 2–12 bar. Quantitative (XRD) resultant hardened Additionally, density, A-value, drying shrinkage determined. (reference RHA-based AAC) temperatures, XRD-analysis detect (Tables 6). remarkable, typical 11 Å takes maximum 165°C. variations correlated reactions kinetics, types, hydration products. revealed improved those quartz-based deterioration observed. 7 variation 165°C 192°C. Afterwards, regarding shrinkage. large kinetics development minerals CSH-phases 165°C, led possibly caused promoting transition non-crystalline promotion always accompanied opposite pattern observed Applying 192°C suppressed increased source. reason above-mentioned transformation state derived change behavior [13]. assumed, initially Ca/Si comparison On literature, C/S short chains degree polymerization they rearrange more [14-16]. quantity compared shows, exist pathways favored <192°C. phases, is, sum bassanite quantities. might [12, 16]. Autoclaving suppression crystallization tobermorite. accordance result studies Mitsuda et al. [17] Chen [18] amount 1.1-nm crystallinity further autoclaving. probably < 192°C, beyond crystallization. decomposition did occur 152°C. remained unreacted resulting formation. mix, significantly. difference rather solid structures. agrees where changing affected specimens, occurred numerous [17, 19-22]. Moreover, A-value appeared existing simply since subtraction effect, comparison, strength-to-density spite distinct indicate determining Although many cases favors providing denser microstructure crystals, existence composed portion necessarily lead types binding microstructure. microstructure, morphologies interconnected affect considerably. line outcomes [19, 12] homogeneous distribution crystals obtain optimum Changing mixes. 59% expected widely reduces supporting well-crystallized 23-25]. demonstrated contrary behaviors regardless having C-S-H, respectively, exhibited According findings, controlled interconnection hydro-thermal factors. outcome Mesecke [26] reported function depends it's composition, <2 gypsum. landfills annually, causes re-use. concentration >5 wt. % damaging reactions, concete forming ettringite. 2030 coal close Germany, lack flue gas purification. great find innovative selectively, would enhance chances, remaining re-used. At so-called developed tackle challenge. Meanwhile procedure [27]. simple reaction. liquid carbonate contact solids sulfates, exchange means, Ca-ions remain solid, phase. applied mortar. project described, real first, mortar laboratory IBPs. commercial classes (350 kg/m3 500 kg/m3) cement. 196-1 32.5 III R standard curing autoclave, edge length cm crusher. crusher storage week. Both mm. analyzed (XRF) powder (XRD). produce powder, “XRD-Mill Mc Crone” Retsch. XRF measurement, compacts prepared binder wax (C38H76O2N2). As calibration, in-house calibration series CaCO3 AAC-based single-point XRD-diffraction tested 8). sulfates. room day. Figure 1a b before treatment. bearing detected calcite Based established re-use (see processed chamber filter separate fraction. Gypsum turn turns solution. agriculture fertilizer. But start adding recover >70°C precipitate recovered. fines de-sulphatized now very interesting economically viable solve companies avoiding cost-intensive landfilling waste. Instead, sold market (eg, fertilizer) producers. Thinking further, make sense combine future “chilled process.” Technical University Denmark [28] fact, CO2-from gases (e.g production) captured efficiently 10°C. product amounts obtained. substance baking course Meanwhile, plant scale installed premises should ready years. cycles siliceous reduced 30°C. ordinary ∼190°C achieved, remains unsolved scope research. promising approach, effectively temperature. opens authors wish acknowledge D. Wolfram, A.-L. Liesch K. Scherer, who conduct experiments lab project. Dr Oliver Kreft Xella Deutschland GmbH anonymous reviewer thanked reviewing article comments paper. research received public funding cooperation “BAUCYCLE”, institutes UMSICHT, IML IOSB involved. Open Access enabled organized Projekt DEAL.