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Processed bottom ash based sustainable binders for concrete

(2021)
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(UGent) and (UGent)
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Abstract
The world is going through a transition from a GDP (gross domestic product) oriented to a sustainable development-oriented way of life. Huge amounts of wastes are generated each day, and smart management of these wastes is an important issue for attaining sustainability. Incineration is an effective method to handle huge quantities of municipal solid wastes which cannot be reused or recycled. This process generates huge amounts of residues which are currently landfilled or used for low value applications such as 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 silica reaction, which indicates the presence of reactive silica. Having a chemical composition similar to that of coal combustion fly ash, and having gone through heat treatment, these MSWI ashes have the potential to be used as a supplementary cementitious material. Furthermore, they can be used as a corrective agent in raw meal for clinker production. Very few studies in literature have explored these options. One of the main obstacles for implementation as supplementary cementitious materials is the presence of elemental aluminium. The main treatment proposed in literature for elemental aluminium removal when the ashes are used as aggregate, is treatment with NaOH. However, this has the disadvantage of introducing alkali into the ash when treated after grinding, which could alter the hydration kinetics of the binder when the ashes are used along with cement. When ashes are 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 a Belgian incinerator were collected. Visual sorting of the 6/15 fraction revealed the components to be predominantly glass and stone objects, including also ceramics, bricks, metal parts and organics. The 6/15 and 2/6 fractions are predominantly amorphous in nature. Two kinds of treatments which are simple and effective are proposed in this thesis for removal of elemental aluminium and other unwanted residues. One is submerging the milled ash in water (L/S ratio 1:5 was used here) and subjecting the slurry to a temperature of 100°C until the ash is dry. The second type of treatment consists of slow grinding of ashes and subsequent sieving out of the coarse fraction >142.5 µm containing a major portion of the elemental aluminium (which is less easy to grind). Various effects of the first treatment method were investigated in laboratory, including the effect of partial replacement ofxvi Portland cement by MSWI ashes on expansion, strength, hydration kinetics, setting time and workability of cement-bound material. Expansion of mortar reduced considerably after the ash pre-treatment, while strength increased. Workability of mortar with ash replacement reduced slightly on treatment of the ash. Initial setting time increased on replacement of cement with both treated and untreated bottom ash, with treated ashes leading to shorter setting times than untreated ashes. This could be due to a prolongation of the induction period which can be observed also in calorimetry curves. From the preliminary tests, the 2/6 fraction was selected for further investigation at the concrete level and was treated at larger volumes, for which the second type of treatment; the bulk treated ash is named as 2/6 NB. Reactivity tests on the treated ashes showed low to moderate reactivity of the ashes. The 2/6 fraction ashes passed the strength activity index test at both 28 and 90 days, and therefore were selected for further tests at the concrete level. The R3 calorimetry test on ashes indicated that aged ashes (stockpiled) have lower reactivity than young ashes. The compressive strength of mortars after 28 days of curing had good correlation with the cumulative heat released by bottom ash in cement paste during 7 days of hydration at 40°C as determined by isothermal calorimetry, while the correlation with heat release in the R3 paste at 40°C was lower. This indicates that the dominant effect on compressive strength put forth in the paste by bottom ash is not the pozzolanic reaction, but rather an improvement in the hydration of alite. This was 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 of hydration of alite with ash replacement. Portlandite consumption determined by TGA was minimal. However, this determined value is interfered by the additional portlandite formed due to increased reaction of alite, and the inherent 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, differing only 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 designed using various trial mixes to have similar strength at 28 days as that of Mix 1 and had 80% CEM I 52.5 R with 20% bulk treated bottom ash as binder. It also had a water-to-binder ratio which was reduced by 0.05 compared to the first three mixes. At 28 days, Mix 2 and Mix 3 had comparable strengths, and Mix 1 and Mix 4 had comparable strengths. However, Mix 2 gained morexvii strength than Mix 3 and Mix 4 gained more strength than Mix 1 from 28 to 90 days. At 90 days, Mix 4 had better strength than Mix 1. In terms of durability tests performed (open porosity, capillary imbibition, air permeability, chloride ingress and freeze thaw), both Mix 2 (concrete mix with mainstream fly ash) and Mix 4 (optimized concrete mix with bottom ash) performed the best. Similar to most durability phenomena tested, Mix 2 performed best in creep and shrinkage, followed by Mix 4, and Mix 3 performed the worst. While judging based on these results, it is to be kept in mind that Mix 2 and Mix 1 are concrete mixes with commercially available cements that are optimised in particle size distribution and packing density. This contrasts with Mixes 3 and 4, where the addition of bulk treated ash was done by simple blending during concrete mixing. The prospect for second life of MSWI ash concrete was evaluated by using it as recycled aggregate in new concrete. Concrete Mix 5 was produced with the same basic mix design as that of Mix 1 with around 26 mass-% of the aggregates replaced with crushed concrete from Mix 4 trials. Compressive strength 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 concrete from which recycled aggregate was produced, was of a better strength class than the recycled aggregate concrete. Further, trials on production of cement clinker with MSWI bottom ash were conducted. Three raw meal mixes were formulated with around 5% of each of the three fractions of bottom ashes and were fired to obtain three clinkers. The resulting clinkers had comparable mineralogy and hydration kinetics as that of commercial Portland cement. SEM-EDX analysis was also conducted on clinkers and trends visible in presence of minor elements along with major phases were interpreted. Mg and Ti were found to be prominently spotted along with C3A and C4AF phases. Overall, the results of this research exhibit the potential use of bottom ash in concrete as cement replacement and form a basis for further research to optimize and standardise its use for commercial applications.

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MLA
Joseph, Aneeta Mary. Processed Bottom Ash Based Sustainable Binders for Concrete. Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur, 2021.
APA
Joseph, A. M. (2021). Processed bottom ash based sustainable binders for concrete. Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur.
Chicago author-date
Joseph, Aneeta Mary. 2021. “Processed Bottom Ash Based Sustainable Binders for Concrete.” Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur.
Chicago author-date (all authors)
Joseph, Aneeta Mary. 2021. “Processed Bottom Ash Based Sustainable Binders for Concrete.” Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur.
Vancouver
1.
Joseph AM. Processed bottom ash based sustainable binders for concrete. Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur; 2021.
IEEE
[1]
A. M. Joseph, “Processed bottom ash based sustainable binders for concrete,” Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur, 2021.
@phdthesis{8694932,
  abstract     = {{The world is going through a transition from a GDP (gross domestic
product) oriented to a sustainable development-oriented way of life. Huge
amounts of wastes are generated each day, and smart management of these
wastes is an important issue for attaining sustainability. Incineration is an
effective method to handle huge quantities of municipal solid wastes which
cannot be reused or recycled. This process generates huge amounts of
residues which are currently landfilled or used for low value applications such
as 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 silica
reaction, which indicates the presence of reactive silica. Having a chemical
composition similar to that of coal combustion fly ash, and having gone
through heat treatment, these MSWI ashes have the potential to be used as a
supplementary cementitious material. Furthermore, they can be used as a
corrective agent in raw meal for clinker production. Very few studies in
literature have explored these options. One of the main obstacles for
implementation as supplementary cementitious materials is the presence of
elemental aluminium. The main treatment proposed in literature for
elemental aluminium removal when the ashes are used as aggregate, is
treatment with NaOH. However, this has the disadvantage of introducing
alkali into the ash when treated after grinding, which could alter the hydration
kinetics of the binder when the ashes are used along with cement. When ashes
are 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 a
Belgian incinerator were collected. Visual sorting of the 6/15 fraction
revealed the components to be predominantly glass and stone objects,
including also ceramics, bricks, metal parts and organics. The 6/15 and 2/6
fractions are predominantly amorphous in nature. Two kinds of treatments
which are simple and effective are proposed in this thesis for removal of
elemental aluminium and other unwanted residues. One is submerging the
milled ash in water (L/S ratio 1:5 was used here) and subjecting the slurry to
a temperature of 100°C until the ash is dry. The second type of treatment
consists of slow grinding of ashes and subsequent sieving out of the coarse
fraction >142.5 µm containing a major portion of the elemental aluminium
(which is less easy to grind). Various effects of the first treatment method
were investigated in laboratory, including the effect of partial replacement ofxvi
Portland cement by MSWI ashes on expansion, strength, hydration kinetics,
setting time and workability of cement-bound material. Expansion of mortar
reduced considerably after the ash pre-treatment, while strength increased.
Workability of mortar with ash replacement reduced slightly on treatment of
the ash. Initial setting time increased on replacement of cement with both
treated and untreated bottom ash, with treated ashes leading to shorter setting
times than untreated ashes. This could be due to a prolongation of the
induction period which can be observed also in calorimetry curves. From the
preliminary tests, the 2/6 fraction was selected for further investigation at the
concrete level and was treated at larger volumes, for which the second type
of treatment; the bulk treated ash is named as 2/6 NB.
Reactivity tests on the treated ashes showed low to moderate reactivity of the
ashes. The 2/6 fraction ashes passed the strength activity index test at both
28 and 90 days, and therefore were selected for further tests at the concrete
level. The R3 calorimetry test on ashes indicated that aged ashes (stockpiled)
have lower reactivity than young ashes. The compressive strength of mortars
after 28 days of curing had good correlation with the cumulative heat released
by bottom ash in cement paste during 7 days of hydration at 40°C as
determined by isothermal calorimetry, while the correlation with heat release
in the R3 paste at 40°C was lower. This indicates that the dominant effect on
compressive strength put forth in the paste by bottom ash is not the
pozzolanic reaction, but rather an improvement in the hydration of alite. This
was 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 of
hydration of alite with ash replacement. Portlandite consumption determined
by TGA was minimal. However, this determined value is interfered by the
additional portlandite formed due to increased reaction of alite, and the
inherent 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, differing
only 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 designed
using various trial mixes to have similar strength at 28 days as that of Mix 1
and had 80% CEM I 52.5 R with 20% bulk treated bottom ash as binder. It
also had a water-to-binder ratio which was reduced by 0.05 compared to the
first three mixes. At 28 days, Mix 2 and Mix 3 had comparable strengths, and
Mix 1 and Mix 4 had comparable strengths. However, Mix 2 gained morexvii
strength than Mix 3 and Mix 4 gained more strength than Mix 1 from 28 to
90 days. At 90 days, Mix 4 had better strength than Mix 1. In terms of
durability tests performed (open porosity, capillary imbibition, air
permeability, chloride ingress and freeze thaw), both Mix 2 (concrete mix
with mainstream fly ash) and Mix 4 (optimized concrete mix with bottom
ash) performed the best. Similar to most durability phenomena tested, Mix 2
performed best in creep and shrinkage, followed by Mix 4, and Mix 3
performed the worst. While judging based on these results, it is to be kept in
mind that Mix 2 and Mix 1 are concrete mixes with commercially available
cements that are optimised in particle size distribution and packing density.
This contrasts with Mixes 3 and 4, where the addition of bulk treated ash was
done by simple blending during concrete mixing.
The prospect for second life of MSWI ash concrete was evaluated by using it
as recycled aggregate in new concrete. Concrete Mix 5 was produced with the
same basic mix design as that of Mix 1 with around 26 mass-% of the
aggregates replaced with crushed concrete from Mix 4 trials. Compressive
strength 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 concrete
from which recycled aggregate was produced, was of a better strength class
than the recycled aggregate concrete.
Further, trials on production of cement clinker with MSWI bottom ash were
conducted. Three raw meal mixes were formulated with around 5% of each
of the three fractions of bottom ashes and were fired to obtain three clinkers.
The resulting clinkers had comparable mineralogy and hydration kinetics as
that of commercial Portland cement. SEM-EDX analysis was also conducted
on clinkers and trends visible in presence of minor elements along with major
phases were interpreted. Mg and Ti were found to be prominently spotted
along with C3A and C4AF phases.
Overall, the results of this research exhibit the potential use of bottom ash in
concrete as cement replacement and form a basis for further research to
optimize and standardise its use for commercial applications.}},
  author       = {{Joseph, Aneeta Mary}},
  isbn         = {{9789463554541}},
  language     = {{eng}},
  pages        = {{xxii, 338}},
  publisher    = {{Universiteit Gent. Faculteit Ingenieurswetenschappen en Architectuur}},
  school       = {{Ghent University}},
  title        = {{Processed bottom ash based sustainable binders for concrete}},
  year         = {{2021}},
}