9 research outputs found
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Development of ambient-cured geopolymer mortars with construction and demolition waste-based materials
YesDegrading infrastructure and applications of structural demolition create
tremendous amounts of construction and demolition waste (CDW) all around
the world. To address this issue in an effective way, recycling CDW in a most appropriate
way has become a global concern in recent years. To this end, this study
focused on the valorization of CDW-based materials such as tile, bricks, glass,
and concrete in the development of geopolymer mortars. CDWs were first collected
from demolition zone and then subjected to crushing-milling operations. To
investigate the influence of slag (S) addition to the mixtures, 20% S substituted
mixture designs were also made. Fine recycled concrete aggregates (FRCA) obtained
from crushing and sieving of the waste concrete were used as the aggregate.
A series of mixtures were designed using different proportions of three distinct
alkali activators such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3),
and calcium hydroxide (CH; Ca(OH)2). To improve their applicability, the mixtures
were left to cure at room temperature rather than the heat curing which
is frequently applied in the literature. After 28 days ambient curing, the 100%
CDW-based geopolymer mortar activated with three different activators reached
a compressive strength of 31.6 MPa, whereas the 20% S substituted geopolymer
mortar showed a 51.9 MPa compressive strength. While the geopolymer mortars
activated with only NaOH exhibited poor performance, it was found that the
use of Na2SiO3 and CH improved the mechanical performance. Main geopolymerization
products were related to NASH (Sodium alumino-silicate hydrate),
CASH (Calcium alumino-silicate hydrate), and C(N)ASH gel formations. Results
demonstrated that mixed CDWs can be employed in the manufacturing
geopolymers, making them potential alternatives to Portland cement (PC)-based
systems by being eco-friendly, energy-efficient, and comparable in compressive
strength.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100
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Characterization and life cycle assessment of geopolymer mortars with masonry units and recycled concrete aggregates assorted from construction and demolition waste
YesDeveloping a fast, cost-effective, eco-friendly solution to recycle large amounts of construction and demolition waste (CDW) generated from construction industry-related activities and natural disasters is crucial. The present investigation aims to offer a solution for repurposing CDW into building materials suitable for accelerated construction and housing in developing countries and disaster-prone areas. Feasibility of recycled concrete aggregate (RCA) inclusion in geopolymer mortars constituted entirely from CDW (masonry elements) was investigated via an environmental impact-oriented approach by addressing the composition related key parameters. Mechanical performance was evaluated through compressive strength tests, and scanning electron microscope (SEM) imaging with line mapping analyses were carried out to monitor the interfacial transition zone (ITZ) properties. To investigate the environmental impacts of the geopolymer mortars and highlight the advantages over Portland cement-based mortars, a cradle-to-gate life cycle assessment (LCA) was performed. Findings revealed that roof tile (RT)-based geopolymer mortars mainly exhibited better strength performance due to their finer particle size. Mixtures activated with 15 M NaOH solution and cured at 105 °C achieved an average compressive strength above 55 MPa. RCA size was the most influential parameter on compressive strength, and a smaller maximum RCA size significantly increased the compressive strength. Microstructural analyses showed that the ITZ around smaller RCAs was relatively thinner, resulting in better compressive strength results. LCA proved that CDW-based geopolymer mortars provide the same compressive strength with around 60% less CO2 emissions and similar energy consumption compared to Portland cement-based mortars.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100. The authors also wish to acknowledge the support of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under project: 117M44
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Development of ambient-cured geopolymer mortars with construction and demolition waste-based materials
YesDegrading infrastructure and applications of structural demolition create tremendous amounts of construction and demolition waste (CDW) all around the world. To address this issue in an effective way, recycling CDW in a most appropriate way has become a global concern in recent years. To this end, this study focused on the utilization of CDW-based materials such as hollow brick (HB), red clay brick (RCB), roof tile (RT), glass (G) and concrete (C) in the production of geopolymer mortars. These materials were first collected from an urban transformation area and then subjected to an identical two-step crushing-milling procedure to provide sufficient fineness for geopolymerization. To investigate the influence of blast furnace slag (S) addition to the CDW-based mixtures, 20% S substituted mixture designs were also made. Fine recycled concrete aggregates (FRCA) obtained from crushing and sieving of the waste concrete were used as the aggregate. A series of mixtures were designed using different proportions of three distinct alkali activators such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2). To improve their applicability, the mixtures were left to cure at room temperature rather than the heat curing which is frequently applied in the literature. After 28 days of ambient curing, the 100% CDW-based geopolymer mortar activated with three different activators reached a compressive strength of 31.6 MPa, whereas the 20% S substituted geopolymer mortar achieved a compressive strength of 51.9 MPa. While the geopolymer mortars activated with only NaOH exhibited poor performance, it was found that the use of Na2SiO3 and Ca(OH)2 improved the compressive strength. Main geopolymerization products were related to NASH, CASH, and C(N)ASH gel formations. Our results demonstrated that mixed CDW-based materials can be employed in the manufacturing geopolymers, making them potential alternatives to Portland cement-based systems by being eco-friendly, energy-efficient, and comparable in compressive strength.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100
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Development of Concrete Mixtures Based Entirely on Construction and Demolition Waste and Assessment of Parameters Influencing the Compressive Strength
YesDemolition and reconstruction of degrading structures alongside with the repetitive repair, maintenance, and renovation applications create significant amounts of construction and demolition waste (CDW), which needs proper tackling. The main emphasis of this study has therefore been placed on the development of concrete mixtures with components (i.e., aggregates and binder) coming entirely from CDW. As the binding phase, powdered CDW-based masonry units, concrete and glass were used collectively as precursors to obtain geopolymer binders, which were then incorporated with CDW-based fine and coarse concrete aggregates. Together with the entirely CDW-based concretes, designs were also proposed for companion mixtures with mainstream precursors (e.g., fly ash and slag) occupying some part of the CDW-based precursor combination. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2) were used at various concentrations and combinations as the alkaline activators. Several factors that have impact on the compressive strength results of concrete mixtures, such as mainstream precursor replacement rate, al-kaline molar concentrations, aggregate-to-binder ratios and curing conditions, were considered and these were also backed by the micro-structural analyses. Our results showed that through proper optimiza-tion of the design factors, it is possible to manufacture concrete mix-tures entirely out of CDW with compressive strength results able to reach up to 40 MPa under ambient curing. Current research is believed to be very likely to promote more innovative and up-to-date techniques to upcycle CDW, which are mostly downcycled through basic practices of road base/sub-base filling, encouraging further research and increas-ing the awareness in CDW issue.The full-text of this paper will be released for public view at the end of the publisher embargo on 1 Jul 2024
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Characterisation and standardisation of different-origin end-of-life building materials toward assessment of circularity
YesConstruction and demolition waste (CDW) management and recycling practices are crucial for transitioning to a circular economy. This study focuses on the detailed characterization of CDWs, including hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete (C), and glass (G), collected from seven different sites. The CDWs were characterized based on particle size distribution, chemical composition, and crystalline nature. Pozzolanic activity was evaluated through compressive strength measurements of cement mortars with 20% cement replacement by CDWs at 7, 28, and 90 days. The results showed that clayey CDWs exhibited similar physical/chemical properties and crystalline structures. Compositions of Cs varied significantly based on their original materials. CDWs satisfied the minimum strength activity index for supplementary cementitious materials, with pozzolanic activity influenced by fineness and SiO2+Al2O3 contents. The average strength activity indexes for HB, RCB, RT, C, and G were 84.5%, 86.3%, 83.4%, 80.7%, and 75.8%, respectively. Clayey CDWs contributed to mechanical strength development, while Cs' contribution was related to hydration of unreacted cementitious particles. G exhibited the weakest pozzolanic activity due to its coarser particle size. Overall, CDWs demonstrated suitable properties for use as supplementary cementitious materials in PC-based systems
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An Investigation into Durability Aspects of Geopolymer Concretes Based Fully on Construction and Demolition Waste
YesThe focus of the construction industry has shifted towards the development of al-ternative, eco-friendly and green construction materials due to the energy-inefficient and carbon-intensive nature of Portland cement (PC) production and aggregate quarrying. Meanwhile, increased number of repetitive re-pair/renovation/maintenance activities and demolition operations for the end-of-life buildings generate significant amounts of construction and demolition waste (CDW). For the purposes of sustainability and upcycling wastes into high-value-added materials with improved greenness, components from CDW streams can be used in producing geopolymer concretes without using PC and natural aggre-gates, given the rich aluminosiliceous nature of CDW components. The focus of current work is therefore on the analysis of durability of aspects (i.e., drying shrinkage and resistance against sulfate attack, cyclic freezing-thawing, and chlo-ride penetration) of geopolymer concretes made entirely of CDW. Different types of bricks, tile, concrete, and glass were used in mixed form as precursors for ge-opolymerization while different-size grains of waste concrete were used as recy-cled aggregates. As alkali activators, sodium hydroxide, calcium hydroxide and sodium silicate were used. In a companion mixture, CDW-based precursors were replaced with slag and class-F fly ash. Results showed that sulfate and cyclic freeze-thaw exposure did not cause any noticeable weight and compressive strength loss in CDW-based geopolymer concretes, while chloride penetration was found comparable to PC-based concrete. While drying shrinkage was found high in entirely CDW-based geopolymer concrete and resulted in surface mi-crocracks, it was possible to lower the drying shrinkage substantially via substi-tution of CDW-based precursors with fly ash and slag.The authors also wish to thank the support of Scientific and Technical Research Council (TUBITAK) of Turkey provided under projects: 218M102 and 117M447.The full-text of this article will be released for public view at the end of the publisher embargo - 12 months after publication
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Structural performance of construction and demolition waste-based geopolymer concrete columns under combined axial and lateral cyclic loading
YesConstruction and demolition waste (CDW) has reached severe environmental and economic dimensions due to its
large volume among all solid waste, highlighting the importance of local actions to manage, recycle, and reuse
CDW. Ductile demountable connections are necessary to disassemble and reuse the concrete structural members
and fast assembly of precast structures in seismic regions without generating waste. In this study, the seismic
performance of CDW-based reinforced geopolymer concrete columns has been investigated. Six ½ scaled columns
(half of which were demountable and the other half monolithic) were experimentally tested under reversed
cyclic lateral displacement excursions, considering three different levels of constant axial loading to determine
failure mechanisms, load–displacement responses, ductilities, energy dissipation capacities, stiffness degradation
relations, and curvature distributions. The obtained test results were used to determine the performance of CDWbased geopolymer concrete columns and compare the performances of the demountable connection with the
monolithic connection. The test results showed that the novel demountable connection for precast concrete
frames exhibited better seismic performance in terms of maximum lateral load capacity, initial stiffness, energy
dissipation capacity, and maximum curvature than their monolithic counterparts. Besides, increasing the axial
compression ratio on the columns caused an increase in lateral load capacity, energy dissipation capacity, energy
dissipation ratio, and initial curvature stiffness; however, it decreased the ductility. Finally, the capacity predictions of current codes, i.e., TS500 and ACI318, were conservative when compared with experimental results.This publication is a part of doctoral dissertation work by the first author in the Academic Program of Civil Engineering, Institute of Science, Hacettepe University. The authors gratefully acknowledge the financial assistance of the European Union’s Horizon 2020 research and innovation program under grant agreement No: 869336, ICEBERG (Innovative Circular Economy Based solutions demonstrating the Efficient recovery of valuable material Resources from the Generation of representative End-of-Life building material). This work was also supported by Newton Prize 2020. The fifth and seventh authors acknowledge the financial support received from the European Union’s Horizon 2020 research and innovation program under the Marie SkłodowskaCurie grant agreement No 894100.The full-text of this article will be released for public view at the end of the publisher embargo on 4th Oct 2024
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A comprehensive study on the compressive strength, durability-related parameters and microstructure of geopolymer mortars based on mixed construction and demolition waste
YesAs a viable option to upcycle construction and demolition waste (CDW) into value-added materials, geopolymer technology is emerging. Most studies investigate CDWs in a separated form or in combination with mainstream pozzolanic/cementitious materials focusing only on fundamental properties of geopolymer pastes, not considering to scale such materials to the level of their application in the forms of structural mortars/concretes or to characterize long-term performance/durability. This study investigated the development and characterization of ambient-cured mortars with mixed CDW-based geopolymer binders and untreated fine recycled concrete aggregates (FRCA). Mixture of CDW-based roof tile (RT), red clay brick (RCB), hollow brick (HB), concrete (C), and glass (G) was used as the precursor, while ground granulated blast furnace slag (S) was used in some mixtures to partly replace CDW precursors. Compressive strength, durability-related parameters including drying shrinkage, water absorption, and efflorescence, microstructure and materials sustainability were evaluated. Results showed that 28 d compressive strength results above 30 and 50 MPa is achievable with the entirely CDW-based and slag-substituted mortars, which were found improvable to have entirely CDW-based structural concretes. Drying shrinkage of the mortars is slightly higher than that of conventional cementitious/geopolymeric systems although it can be minimized significantly through mixture optimization. Water absorption values remain comparable with the literature. CDW-based geopolymer mortars outperform Portland cement mortars in terms of CO2 emission and energy requirement. Our findings show that via utilizing CDW-based constituents in mixed form as precursor and waste aggregates, it is possible to develop greener construction materials with acceptable strength and long-term performance.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100. The authors also wish to acknowledge the support of the Scientific and Technical Research Council (TUBITAK) of Turkey provided under project: 117M447
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Fully demountable column base connections for reinforced CDW-based geopolymer concrete members
YesCDW-based concrete requires alkali-activators to generate geopolymerization process. These alkali-activators are difficult to be handled at the construction site and one of the rational ways to built reinforced geopolymer structures is the prefabricated construction. The connection of the precast structures is the most vulnerable component under the effect of seismic actions. Proper detailing and design of connections are crucial for sufficiently-ductile performance under seismic loading. Additionally, to achieve the disassembling and reusing of structural members, a demountable connection, i.e., dry connection, should be used instead of a wet connection.
In this study, four novel fully-demountable connections for reinforced construction and demolition waste-based (CDW) geopolymer concrete members are developed. Seismic performances of these different demountable connections and one reference monolithic connections are experimentally investigated. The connections are subjected to reversed cyclic lateral displacements under constant axial loading. Comparisons are made referring to observed damage patterns, connection strengths, moment–curvature relations, initial stiffnesses, plastic hinge lengths, and energy dissipation characteristics of the proposed demountable connections and the monolithic connection. The results of the experimental study indicate that one proposed demountable connection exhibited larger lateral capacity and better seismic performance than its monolithic counterpart, whereas the other three proposals showed less performance than the monolithic counterpart.The authors gratefully acknowledge the financial assistance of the European Union’s Horizon 2020 research and innovation programme under grant agreement No: 869336, ICEBERGThe full-text of this article will be released for public view at the end of the publisher embargo on 31 May 2024