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• W3137177598 abstract "The world is going through a transition from a GDP (gross domesticproduct) oriented to a sustainable development-oriented way of life. Hugeamounts of wastes are generated each day, and smart management of thesewastes is an important issue for attaining sustainability. Incineration is aneffective method to handle huge quantities of municipal solid wastes whichcannot be reused or recycled. This process generates huge amounts ofresidues which are currently landfilled or used for low value applications suchas in construction of road subbases. The municipal solid waste incineration(MSWI) ashes have been widely investigated as a replacement for aggregates,and many studies concluded that this posed the possible risk on alkali silicareaction, which indicates the presence of reactive silica. Having a chemicalcomposition similar to that of coal combustion fly ash, and having gonethrough heat treatment, these MSWI ashes have the potential to be used as asupplementary cementitious material. Furthermore, they can be used as acorrective agent in raw meal for clinker production. Very few studies inliterature have explored these options. One of the main obstacles forimplementation as supplementary cementitious materials is the presence ofelemental aluminium. The main treatment proposed in literature forelemental aluminium removal when the ashes are used as aggregate, istreatment with NaOH. However, this has the disadvantage of introducingalkali into the ash when treated after grinding, which could alter the hydrationkinetics of the binder when the ashes are used along with cement. When ashesare treated before milling, the treatment risks to be slow or ineffective.Three fractions (6/15(50) mm, 2/6 mm and 0/2 mm) of bottom ash from aBelgian incinerator were collected. Visual sorting of the 6/15 fractionrevealed the components to be predominantly glass and stone objects,including also ceramics, bricks, metal parts and organics. The 6/15 and 2/6fractions are predominantly amorphous in nature. Two kinds of treatmentswhich are simple and effective are proposed in this thesis for removal ofelemental aluminium and other unwanted residues. One is submerging themilled ash in water (L/S ratio 1:5 was used here) and subjecting the slurry toa temperature of 100°C until the ash is dry. The second type of treatmentconsists of slow grinding of ashes and subsequent sieving out of the coarsefraction >142.5 µm containing a major portion of the elemental aluminium(which is less easy to grind). Various effects of the first treatment methodwere investigated in laboratory, including the effect of partial replacement ofxviPortland cement by MSWI ashes on expansion, strength, hydration kinetics,setting time and workability of cement-bound material. Expansion of mortarreduced considerably after the ash pre-treatment, while strength increased.Workability of mortar with ash replacement reduced slightly on treatment ofthe ash. Initial setting time increased on replacement of cement with bothtreated and untreated bottom ash, with treated ashes leading to shorter settingtimes than untreated ashes. This could be due to a prolongation of theinduction period which can be observed also in calorimetry curves. From thepreliminary tests, the 2/6 fraction was selected for further investigation at theconcrete level and was treated at larger volumes, for which the second typeof treatment; the bulk treated ash is named as 2/6 NB.Reactivity tests on the treated ashes showed low to moderate reactivity of theashes. The 2/6 fraction ashes passed the strength activity index test at both28 and 90 days, and therefore were selected for further tests at the concretelevel. The R3 calorimetry test on ashes indicated that aged ashes (stockpiled)have lower reactivity than young ashes. The compressive strength of mortarsafter 28 days of curing had good correlation with the cumulative heat releasedby bottom ash in cement paste during 7 days of hydration at 40°C asdetermined by isothermal calorimetry, while the correlation with heat releasein the R3 paste at 40°C was lower. This indicates that the dominant effect oncompressive strength put forth in the paste by bottom ash is not thepozzolanic reaction, but rather an improvement in the hydration of alite. Thiswas confirmed via XRD with Rietveld refinement, on pastes of water-tobinder ratio 0.5 with CEM I 52.5N reference and blended cement with 25%CEM I 52.5 N replaced with 2/6 NB, showed an increase in degree ofhydration of alite with ash replacement. Portlandite consumption determinedby TGA was minimal. However, this determined value is interfered by theadditional portlandite formed due to increased reaction of alite, and theinherent mass loss in that range (400-500˚C) in the ashes.Concrete level tests were conducted on mainly four mixes namely Mix 1, 2,3 and 4. Mix 1, 2 and 3 had same relative proportions of materials, differingonly regarding the binder, CEM I 52.5N (Mix 1), CEM II B-V 32.5R (Mix 2)and 75% CEM I 52.5N + 25% bulk treated ash (Mix 3). Mix 4 was designedusing various trial mixes to have similar strength at 28 days as that of Mix 1and had 80% CEM I 52.5 R with 20% bulk treated bottom ash as binder. Italso had a water-to-binder ratio which was reduced by 0.05 compared to thefirst three mixes. At 28 days, Mix 2 and Mix 3 had comparable strengths, andMix 1 and Mix 4 had comparable strengths. However, Mix 2 gained morexviistrength than Mix 3 and Mix 4 gained more strength than Mix 1 from 28 to90 days. At 90 days, Mix 4 had better strength than Mix 1. In terms ofdurability tests performed (open porosity, capillary imbibition, airpermeability, chloride ingress and freeze thaw), both Mix 2 (concrete mixwith mainstream fly ash) and Mix 4 (optimized concrete mix with bottomash) performed the best. Similar to most durability phenomena tested, Mix 2performed best in creep and shrinkage, followed by Mix 4, and Mix 3performed the worst. While judging based on these results, it is to be kept inmind that Mix 2 and Mix 1 are concrete mixes with commercially availablecements that are optimised in particle size distribution and packing density.This contrasts with Mixes 3 and 4, where the addition of bulk treated ash wasdone by simple blending during concrete mixing.The prospect for second life of MSWI ash concrete was evaluated by using itas recycled aggregate in new concrete. Concrete Mix 5 was produced with thesame basic mix design as that of Mix 1 with around 26 mass-% of theaggregates replaced with crushed concrete from Mix 4 trials. Compressivestrength and pore structure of Mix 5 were found to be better than for Mix 1,which could be attributed to a large extent to the fact that the parent concretefrom which recycled aggregate was produced, was of a better strength classthan the recycled aggregate concrete.Further, trials on production of cement clinker with MSWI bottom ash wereconducted. Three raw meal mixes were formulated with around 5% of eachof the three fractions of bottom ashes and were fired to obtain three clinkers.The resulting clinkers had comparable mineralogy and hydration kinetics asthat of commercial Portland cement. SEM-EDX analysis was also conductedon clinkers and trends visible in presence of minor elements along with majorphases were interpreted. Mg and Ti were found to be prominently spottedalong with C3A and C4AF phases.Overall, the results of this research exhibit the potential use of bottom ash inconcrete as cement replacement and form a basis for further research tooptimize and standardise its use for commercial applications." @default.
• W3137177598 created "2021-03-29" @default.
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• W3137177598 date "2021-01-01" @default.
• W3137177598 modified "2023-09-23" @default.
• W3137177598 title "Processed bottom ash based sustainable binders for concrete" @default.
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