METHOD OF RECLAMATION OF AGGREGATES FROM WASTE HARDENED CONCRETE

Abstract

The present invention facilitates· a method for separating aggregates from waste hardened concrete, providing an eco-friendly and efficient technique to recycling construction materials. This method undergoes mechanically crushing hardened concrete to a uniform particle size of around 50 mm, proceeding with immersing the crushed material in a 5% concentration citric acid solution for I 0 days. This acid immersion provides the disintegration of the cementitious composites, enabling for the clean. separation of aggregates. The reclaimed aggregates subjected to comprehensive testing to evaluate their mechanical strength, water absorption, and specific gravity, ensuring their applicability for reuse in construction industry. This innovative method facilitates sustainability by lowering landfill waste and preserving natural resources, leading to the circular economy in construction.

Specification

Description:
Title: "Method of reclamation of aggregates from waste hardened concrete"
Field of the invention
The present invention relates to construction materials management,
especially the reclamation of aggregates from waste hardened ·concrete,
10 which tackles the environmental challenges of the construction industry is a
field known for significant generation ()f waste and resource depletion. As
concrete is one of the widely adapted construction material, significant
quantities of hardened concrete waste result from demolition and
construction activities, typically discarded in landfills. This method not only
15 · provides to environmental degradation but also necessitates the extraction of
virgjn aggregates, exacerbating ecological imbalances. The invention
enhances sustainability by providing novel methods for extracting and
repurposing aggregates, thereby lowering landfill waste and the need for
natural resources in new concrete production. Essential components of the
20 reclamation method include mechanical processing, chemical treatments by
using ecofriendly compounds like citric acid, and quality assessments of
reclaimed materials. This method coincides with sustainable construction
technologies and global circular economy principles, focusing on resource
conservation and waste reduction in the construction field .
25 : Background of the invention
The building sector is one of the wide users of natural resources and a
substantial contributor to global waste generation. Among the diverse
materials· employed, concrete stands out as the most substantially utilized
construction material, responsible for. approximately 70% of the total
30 material used in the construction sector. Nevertheless, the production and
disposal of concrete have significant environmental impact, in particular concerning carbon emissions, exhaustion of natural resources, and waste
management Throughout its lifetime, concrete engages extracting raw materials such as
sand, gravel, cement, and water, to produce fresh concrete. At the time of
construction and demolition process, considerable amount of hardened
concrete waste is produced, frequently leading to structural alterations,
building renovations, and decommissioned infrastructure. Conventionally,
10 · this waste is discarded to landfills, tends to several environmental problems,
including land degradation, increased greenhouse gas emissions, and the loss
of valmible resources that could otherwise be recycled.
The removal of concrete waste not only leads to ·landfill overflow but also
produces a cycle of resource consumption that is unsustainable. As urban
15 populations keep expanding and infras.tructure needs increase, the pressure
on natural aggregate resources escalates, leading to further ecological
disturbances. In addition, the acquisition of natural aggregates, typically
engages ecofriendly practices including quari-ying, which can interrupt local
ecosystems and facilitate to habitat destruction.
20 In light of these issues, there is an emerging need to improve sustainable
waste management technologies that enhance the reclamation and repurpose
of aggregates from hardened concrete. Reclaimed aggregates facilitate to a
suitable natural aggregates alternative and lowering the environmental
impact of construction projects while utilizing natural resources. The
25 capability ·to efficiently reclaim and process these aggregates can notably
diminish the burden on landfills and reduces the adverse effect of concrete
waste.
On account of the potential benefits, the reclamation of aggregates from
hardened concrete includes several challenges. Present methods typically
30 lack effectiveness, resulting to poor-quality reclaimed materials that could
fall short of the specified standards for reuse in construction field. Further,
the lack of innovative processing methods thresholds the overall recycling
efficiency of concrete wasfe.
This innovation aims to address these limitations by adapting novel methods
for the extraction, processing, and quality assessment ·of reclaimed
aggregates. Through the inclusion of eco-friendly chemical treatments, like
citric acid immersion, the novel method improves the reclamation process
and secures that reclaimed aggregates are of appropriate quality to be
. 10 restored into the construction material supply chain. This initiative not only
correspondence with the principles of sustainability but also facilitate to
wider efforts toward a circular economy, where waste is diminished, and
resources are reused effectively.
Objectives of the invention
15 The main objective of this invention is to develop innovative methods for the
effective reclamation of aggregates from waste hardened concrete, thus
fostering sustainability within the construction field. This involves
mechanically processing hardened concrete to attain a uniform particle size,
thereby employing eco-friendly chemic!ll treatments, like citric acid
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immersion.' to improve the reclamation of aggregates from the cementitious
composites. In addition, this invention is designed to assure quality and
applicability of reclaimed aggregates for reuse in construction industry via
comprehensive mechanical assessments. Finally, the main objective focusses
reducing landfill waste, preserving natural resources, and enhancing the
principles of a circular economy in construction materials management.
Brief description of prior art
EP4124609 AI (2023) discloses an .innovative method for removmg old
mortar from recycled coarse aggregate, eilhancing the material's quality for
use in recycled concrete. The process begins by crushing waste concrete to
·obtain the· aggregate, which is then saturated with water and subjected to
cyclic freeze-thaw experiments. These cycles utilize the frost heave force
generated by freezing water to break down the old mortar's microstructure
and weaken its bond with the natural aggregate. After completing the freeze-thaw process, high-speed stirring is used to further remove the ol~ mortar.
The remaining mortar content is assessed, and the process is repeated if
necessary until the old mortar content is reduced to 5% or less: This method
offers significant benefits by addressing challenges in recycled concrete mix
proportioning . and improving both the mechanical performance and
10 durability of the resulting material. By leveraging the natural forces of
. freezing to dislodge old mortar, ~the technique accelerates the adoption of
recycled concrete in construction, promoting sustainable engineering
solutions.
CN114853399B (2022) discloses a method for preparing high-performance
15 recycled concrete using construction waste. The process involves several key
steps: first, materials are sorted and raw materials are crushed to obtain
coarse·aggregate. Fine aggregate is modified by mixing machine-made sand
with a modifier in a ratio of 1-5:1000. The coarse aggregate is also modified
by combining it with attapulgite in a ratio of 1:20 to enhance its properties.
20 The modified fine and coarse aggregafes are then used to produce recycled
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30
. concrete using a direct water-adding method. This approach improves the
overall performance of~ the recycled concrete, addressing challenges ~ in
treating construction waste. By incorporating modifiers, the method
transforms waste into valuable high-performance concrete, promoting
sustainability and resource efficiency in construction.
CN113860822A (2021) describes a method for producing inorganic recycled
concrete· aggregate, focusing on enhancing mechanical strength. The process
involves using a mix of materials in specific parts by weight, including 280
parts cement, 100 parts fly ash, 150 parts mineral powder, 20-60 parts
recycled coarse aggregate, 950-1500 parts admixture, and 145 parts water.
The recycled coarse aggregate is~ produced by crushing, cleaning, grading,
and drying waste concrete blocks, followed by a pretreatment with a gelatin
solution and subsequent drying. The pretreated aggregate undergoes further
modification using hydrophobic silica sol to create the final recycled coarse aggregate. This method results in recycled concrete with improved
mechanical strength, promoting the use of recycled materials in concrete
production while maintaining - high performance, and addressing
sustainability challenges in construction.
CN113480216A (2021) describes a comprehensive system and method for
10 recycling waste concrete into fully regenerated concrete products. The
process begins with sorting and crushing waste concrete to obtain recycled
coarse-aggregate. This is followed by ball milling and separation to produce
regenerated stones and dry mortar. The dry mortar is further processed to
obtain recycled sand and cement. These recycled materials are combined
15 with additives and water, following a specified mix proportion, to create
fully recycled concrete. After the recycled concrete has completed its service
life, it is dismantled, and the process of sorting and crushing is repeated,
creating a continuous recycling loop. This method maximizes resource
recovery from construction waste, offering significant environmental
20 benefits, including reduced energy consumption, lower emissions, and
promoting sustainability through the production of high-quality recycled
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concrete components.
CN111393057B (2020) discloses a method for regenerating waste concrete
to produce high-quality recycled concrete aggregate. The process involves
pretreating the waste concrete, mixing it with modified micropowder, alkali,
and water, and allowing it to react for a preset time. The mixture is then
subjected to liquid-solid separation to obtain the final recycled concrete
aggregate. The patent also covers a method for preparing modified recycled
concrete · usmg this aggregate. The . resulting recycled concrete exhibits
reduced water absorption and enhanced strength, with performance
characteristics comparable to, and in some cases exceeding; ·those of
conventional concrete. This method offers a sustainable solution for
recycling waste concrete while producing high-performance materials
suitable for use in new construction projects.
CN111763026A (2020) discloses a process for preparing recycled concrete
aggregate, aimed at improving the quality and recovery rate of waste
concrete. The process begins with preprocessing, where collected concrete
blocks· are hammered, and steel bars and other impurities are removed. The
concrete blocks then undergo primary and secondary crushing treatments,
10 followed by screening to obtain recycled aggregate particles of specific
composite sizes. An air classification step is used to. grade the particles and
remove fine micropowder. This preparation method enhances the quality of
the recycled aggregate, significantly increases the recovery· rate of waste
concrete, and offers a highly economical and efficient process, promoting the
15 sustainable reuse of concrete materials in construction.
CNI10563370A (2019) describes a production process for. prepanng
recycled aggregate from· waste concrete, designed to enhance resource
utilization and energy efficiency. The process begins with pretreatment,
where waste concrete blocks undergo. wet spraying and epidemic prevention
20 treatment, followed by hammering to reduce the block size to under 50 mm.
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The pretreated blocks are then screened, crushed, and subjected to a
. strengthening treatment to improve the quality of the recycled aggregate. The
reinforced aggregate is finally conveyed to storage for later use. This method
effectively repurposes waste concrete, reducing resource waste while
optimizing energy use, and providing high-.quality recycled aggregate for
construction applications.
CN I 04261715A (20 14) discloses a comprehensive recycling technology for
construction waste, transforming it into valuable resources.· The process
involves grading, grinding, and sieving ·the waste to produce aggregates that
can replace natural sand and stones. These aggregates are used in various
applications such as premixed. mortar, cement mixtures, and concrete
. products. Any remaining aggregates are packaged and sold commercially for
use in concrete mixing plants, premixed mortar plants, or road foundation
backfilling. The process also converts the resulting powder into concrete products and utilizes the soil from the waste for greening purposes. This
technology effectively recycles construction waste into renewable resources,
· . offering significant economic benefits while preventing environmental issues
like dust pollution during transportation and addressing soil infertility from
waste burial.
10 EP2978724Bl (2014) discloses a method for extracting aggregates and
powdery mineral materials from source materials that contain hardened
mineral binders and aggregates, such as waste or demolition materials. The
process involves two main steps: first, treating the source material through a
disintegration process to break it down, and second, separating the treated
15 material based on a predefined cut-off grain size. This separation allows for
the retrieval of treated aggregates that meet or exceed the specified grain
size, as well as powdery mineral materials with grain sizes below that
threshold. This method enhances the recovery of valuable materials from
construction waste, promoting sustainability in material reuse and recycling
20 within the construction industry.
CN103086663A (2012) introduces a method for enhancing the physical and
mechanical properties of. recycled aggregates using water-soluble resins,
making the resulting concrete suitable for structural and high-performance
applications. The invention details a manufacturing process for recycled
25 aggregate structural concrete, which can incorporate various commonly used
cements. Key components of the admixture include water-soluble resins such
as polyvinyl alcohol (PYA) and white emulsion. The production method
involves mixing the water-soluble resin with water in a specified ratio,
followed by immersing the recycled aggregate in this mixture using dipping
30 or vacuum techniques. The treated aggregate is then air-dried to reduce water
absorption and improve its crush index. Finally, the cement, processed.
recycled aggregate, fine aggregates, and other mineral substances are
uniformly mixed according to a defined ratio, with the mixture transported to
construction sites for pouring. This approach significantly enhances the performance characteristics of recycled aggregate concrete, promoting its use in various construction applications.
EP2468695AI (2010) describes a novel method for recycling residual fresh
unset concrete by incorporating flash setting .accelerators and superabsorbent
polymers. The process involves adding these materials to the
10 residual concrete, which has not yef set, and blending the mixture until it
forms granular materials. This approach not only facilitates the effective
reuse of leftover concrete but also enhances the physical properties of the
· resulting granules. By integrating flash setting accelerators, the method
promotes .rapid hardening, while super-absorbent polymers contribute to
15 moisture retention, ultimately improving the performance and usability of the
recycled material. This innovative recycling technique offers a sustainable
solution for managing concrete waste in the construction industry.
US725873.7B2 (2005) outlines an innovative method for recycling concrete
~aste, consisting of several key steps aimed at efficiently recovering
20 valuable materials. The process begins by heating the concrete waste, which
increases its fragility and facilitates subsequent handling. Following this, the
heated waste is milled and sieved to separate the coarse aggregate from the
· concrete matrix. The remaining material is then further processed by milling
and sieving to distinguish between a cement-containing fraction and fine
25 aggregate. This method enhances the recovery of useful components from
concrete waste, promoting sustainability in· the. construction industry by
reducing waste and enabling the reuse of recycled materials in new concrete
applications.
Summary of the invention
30 The present invention . provides an innovative method for reclaiming
aggregates from waste hardened concrete, addressing the critical need for
sustainable practices in the construction industry. The process begins with
· the mechanical crushing of hardened concrete to achieve a consistent particle size of approximately 50 mm, facilitating efficient processmg for reuse.
Following this, an environmentally friendly citric acid immersion treatment
is . employed to leach the cementitious · matrix binding the aggregates,
enhancing their separation and· ensuring the quality of the reclaimed
materials. To verify their suitability for construction· applications,
10 comprehensive assessments are conducted such as tests for specific gravity,
water absorption and impact value. By effectively reducing concrete waste
entering landfills and decreasing the reliance on virgin aggregates, this
invention promotes resource conservation and enhances recycling potential,
contributing to sustainable construction practices and aligning with the
15 principles of a circular economy in materials management.
Detailed description of the invention
The present invention relates to a method for reclaiming aggregates from
waste hardened concrete, with ·the aim of enhancing sustainability and
lowering· environmental footprint within the construction application. The
20 reclamation method starts· with the mechanical crushing of waste hardened
concrete, which is employed to attain a uniform particle size of around 50
mm. This step is crucial as it facilitates the concrete to be processed
efficiently, ensuring that the aggregates can be effectively obtained for reuse.
Subsequent to mechanical. crushing, the invention engages a novel chemical
25 treatment using a diluted citric acid solution, especially at a concentration of
S%. The crushed concrete is immersed in this solution for a duration of about
I 0 days. In this period, the citric acid operates to leach the cementitious
composite that together binds the aggregates. This leaching phenomenon
offers the reclamation of clean aggregates by breaking down the hardened
30 cement paste, which is crucial for retrieving high-quality aggregates while
limiting damage to their structural performance.
To evaluate the quality and feasibility of the reclaimed aggregates, a set of
comprehensive tests are performed. · These · encompass mechanical
assessments like impact strength tests, which assess the structural integrity of
the reclaimed aggregates. In addition, water absorption and specific gravity tests are conducted to evaluate the porosity and density of the reclaimed
aggregates, offering critical data on their applicability for use in construction
industry.
This specific performance properties of the reclaimed aggregates are
compared with those of natural aggregates. For example, the specific gravity
10 of the reclaimed coarse aggregate is 2.52, demonstrating a suitable density,
whereas the water absorption rate is potentially lower as 0.206%. These
results highlight that the reclaimed aggregates meet or exceed industry
requirements, confirming their importance for effective reuse in construction
applications.
15 By means of this innovative method, the invention improves the efficiency of
aggregate reclamation as well as significantly lowers the volume of concrete
waste discarded to landfills. Through encouraging the reuse of reclaimed
materials, this method leads to the restoration of natural resources and aligns
with sustainable construction techniques. Finally, this invention facilitates a
20 possible solution to the limitations of concrete waste management, elevating
Q) a circular economy in the construction industry.
Claims:
I. The present invention offers a method for reclaiming aggregates from
waste hardened concrete, which includes a multi-stage process.
· Initially, the hardened concrete is mechanicillly crushed to a uniform
particle size of around 50 min, confirming it can be processed
effectively. Subsequently, the crushed concrete is immersed in 5%
· concentration of citric acid solution, where it remains for I 0 days.
This immersion in citric acid, offers the leaching of the cementitious
composites, permitting the hardened cement mortar to break down
and leading to the reclamation of clean aggregates. Upon completion
of this process, the aggregates are efficiently extracted from the
cementitious composites and ready for reus·e in construction industry.
2. Claim I, in which the water absorption rate of reclaimed coarse
aggregates is 0.206%.
3. Claim I, in which the specific gr~vity of the reclaimed coarse aggregate is 2.52.
4. Claim I, in which the impact value of the reclaimed coarse aggregate is 13.60.
5. Claim I, in which the method encouraging sustainable techniques in
the field of construction by employing reclaimed aggregates from waste hardened concrete.

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