Concrete is the most important construction material in terms of volume and turnover. Its success comes, among other reasons, from its amazing versatility and its availability in most parts of this planet, being essentially a local material. However, this XXIst century sees humanity facing its most difficult challenge since its appearance on this planet: how to keep it livable for the next generations, with a population approaching ten billions of inhabitants, and a general shortage of non-renewable resources? Most informed people agree nowadays with the necessity of turning from linear to circular economy. Concrete cannot miss this major paradigm change.
The British Standards Concrete Committee wished to introduce
provisions for recycled aggregates into its concrete standard
(BS8500-2), but before it could do so a number of questions needed to be
answered. Research undertaken at the University of Dundee provided
answers to the questions raised by British Standards Institution (BSI)
and this led to the introduction in 2002 of a full specification for the
product and use of coarse recycled concrete aggregates (RCA) and a
partial specification for other types of coarse recycled aggregates
(RA).
The reason for the high use of RCA in the UK and the
Netherlands is that the Governments took measures to make the use of RCA
competitive with primary materials. One key measure was the
introduction of landfill taxes. This would be an effective measure in
India to reduce the volume of construction and demolition waste provided
‘fly tipping’ can be minimised.
Since 2002 the requirements for
the use of coarse RCA and RA have only had very minor changes, but the
requirements for the composition of the aggregate and the test method
have been transferred from the BS8500-2 to the European aggregates
standards.
Most studies have paid attention to the analysis of concrete with
recycled aggregates (RA) that come from one source only. In some of
them, recycled concrete aggregates (RCA) were used whereas in others RA
from construction and demolition waste (CDW) were employed. However, in
both cases, aggregates from different sources are not used, which does
not allow evaluating the variation of the results.
With this
research, one of the main objectives is to evaluate the variation of the
properties of concretes when incorporating (fine and coarse) RA from
five different CDW recycling plants.
Also, the properties of the
natural and recycled aggregates used in the production of the concrete
mixes are analyzed. For this purpose, composition, chemical and physical
tests were performed.
In order to evaluate the concrete
produced, compressive and tensile strength, modulus of elasticity,
resistance to wear, immersion and capillary water absorption, resistance
to chloride ions penetration and carbonation and shrinkage tests were
carried out.
The analysis allowed concluding that the results
significantly varied according to the RA family used, mainly when the
fine aggregates were replaced. Furthermore, it was found that the great
majority of the properties of recycled aggregate concrete (RAC) are
lower than those of the corresponding (reference) natural aggregate
concrete (NAC).
Several successful demonstration projects have been conducted in the
past 20 years in order to verify the practical, technical and
environmental applicability of recycled aggregates. One example is
Sørumsand High School where 37% of the natural coarse aggregates were
replaced by recycled concrete aggregates. The project was well-planned
with solid documentation of the recycled materials as well as the fresh
and hardened concrete properties. The experiences obtained were that the
project was competitive to the regular project with natural aggregates
with regard to costs, technical performance, practical handling and
environmental properties. Furthermore, recycled aggregates are included
for use in nearly all of the European (EN) aggregate standards, though
at varying implementation level. In India, a large deficiency of
treatment and recycling capacity of C&D waste exists. Recycling by
the wet process technology seems to increase, due to the highly complex
heterogenic waste received at the stationary plants. Heterogeneity
should be tackled by increased source segregation, pre-mixing of
feedstock materials and a daily control of the recycled products.
Homogenous feedstock source of concrete waste is highly applicable to
recycle into RCA.
One of the challenges of concrete technology is to minimize cement
clinker, responsible for 8% of the manmade CO2emissions globally and
maximize other constituents emerging from waste, such as recycled
aggregates, which belong to the construction, demolition and excavation
waste (CDEW) stream or fly ash, which belongs to the industrial waste
stream, according to European regulations. There is another form of
waste, however, that has received limited attention, so far, and this is
namely marble dust and solids. This waste stream is either derived from
demolition and crushing of architectural parts made of marble and
therefore belongs to the CDEW waste stream or it is produced during the
cutting and shaping of marble in industrial units and can be found in
the form of dust (water marble dust - WMD) or slurry. The present paper
offers a new perspective of the waste stream classification and a review
on the re-use and recycling methods and case studies suggested by
scholars. Lastly, at the same time, potential extensions to the current
state-of the-art in the field of valorization of the waste stream of
marble dust, solids or slurry are discussed.
This paper presents the effects of supplementary cementitious
materials (SCMs) (Fly ash, slag and silica fume) and emerging nano- and
ultrafine-materials (nano silica and ultrafine fly ash) on mechanical
properties of concrete containing 50% recycled coarse aggregate (RCA) as
partial replacement of natural coarse aggregate. The RCA are mixed
construction and demolition (C&D) waste consisted of concrete,
masonry and other materials. In the first part, the effects of 50% slag
or 50% fly ash as partial replacement of ordinary Portland cement (OPC)
in concrete containing 50% RCA is evaluated, while in second part the
effects of 5, 10 and 15% silica fume on above recycled aggregate
concrete containing 50% slag or 50% fly ash are evaluated. In third
part, the effects of 2% nano silica (NS) and 10% ultrafine fly ash
(UFFA) on concrete containing 50% RCA are evaluated. The above results
are compared with control concrete containing 100% and 50% natural
coarse aggregate. Water-to-binder ratios of all concrete are kept
constant, however, superplasticizer is added in the mixes containing
silica fume, nano silica and ultra fine fly ash to improve the
workability. The compressive and indirect tensile strengths of all
concrete are measured at 7, 28, 56 and 91 days. The results show that
due to addition of 50% RCA the compressive strength of concrete at all
ages is reduced significantly compared to control concrete containing
100% natural coarse aggregates. The addition of high volume fly ash and
slag further reduced the compressive strength of recycled aggregate
concrete at all ages, where high volume fly ash shows more reduction in
compressive strength than high volume slag. The addition of silica fume
is, however, recovered the compressive strength reduction of both high
volume fly ash and slag concretes containing 50% RCA. The addition of
nano silica and ultrafine fly ash also improved the compressive strength
of recycled aggregate concrete. Similar results are also observed in
the case of indirect tensile strength. The carbon footprint of recycled
aggregate concrete is slightly higher than the control concrete.
However, the addition of SCMs reduced the carbon footprint
significantly.
Inkjet (Powder-based) three-dimensional printing (3DP) shows
significant promise in concrete construction applications. The accuracy,
speed, and capacity to build complicated geometries are the most
beneficial features of inkjet 3DP. Therefore, inkjet 3DP needs to be
carefully studied and evaluated with construction goals in mind and
employed in real-world applications, where it is most appropriate. This
paper focuses on the important aspect of curing 3DP specimens. It
discusses the enhanced mechanical properties of the mortar that are
unlocked through a heat-curing process. Experiments were conducted on
cubic mortar specimens that were printed and cured in an oven at a range
of different temperatures (40, 60, 80, 90, 100°C). The results of the
experimental tests showed that 80°C is the optimum heat-curing
temperature to achieve the highest compressive strength and flexural
strength of the printed mortar specimens. These tests were performed on
two different dimensions of the cubic specimens, namely, 20x20x20 mm,
50x50x50 mm and on prism specimens with dimensions of 160x40x40 mm. The
inkjet 3DP process and the post-processing curing are discussed. In
addition, 3D scanning of the printed specimens was employed and the
surface roughness profiles ofthe 3DP gypsum specimens and cement mortar
are recorded 13.76 µm and 22.31µm, respectively
Estimates of Construction and Demolition (C&D) waste generation
in India range between 150 to 716 million tonnes/year. C&D debris
recycling, one of the sustainable solutions for managing this sector of
waste, is gaining popularity worldwide. However, very few recycling
facilities are available in India presently to handle C&D debris.
Several barriers, such as inadequate regulations, lack of incentives and
awareness about recycling techniques, and unavailability of guidelines
have been reported to hinder setting up recycling facilities in India.
However, the influence of human factors, such as attitude and industry
norms, have been overlooked in the existing literature. The primary
objective of this paper is to evaluate the viability of a business model
in the construction materials market in India for recycling operations
and products. Different stakeholders of C&D waste recycling
operations, such as construction & demolition contractors (waste
generators), government engineers, architects and RMC producers were
interviewed to understand their perspectives towards recycling and
recycled products. A total of 67 open-ended semi-structured interviews
across six major cities comprise part of the primary evidence. The
customer discovery process of the lean startup methodology and related
tools were employed to analyze the qualitative interview data. It was
found that rewards in the industry for green products and services are
negligible and inconsistent. The stiff competition offered by natural
aggregate-based products necessitates price restrictions on any new
entrants. Supply chain costs of waste acquisition and processing pose a
big challenge owing to the lack of stringent regulations and
enforcement. Quality concerns and usage restrictions might make direct
selling of recycled aggregates unattractive. Value-added products, such
as paver blocks made of recycled aggregates, present an attractive
channel for recycled materials to enter the market. Challenges hindering
the adoption of recycled aggregates and the ways in which government
support could benefit recyclers by off-setting supply chain costs to
make recycled products competitive are discussed.
December 2024
Volume - 98
Number : 12
November 2024
Volume - 98
Number : 11
October 2024
Volume - 98
Number : 10
September 2024
Volume - 98
Number : 09
August 2024
Volume - 98
Number : 08
July 2024
Volume - 98
Number : 07
June 2024
Volume - 98
Number : 06
May 2024
Volume - 98
Number : 05
April 2024
Volume - 98
Number : 04
March 2024
Volume - 98
Number : 03
February 2024
Volume - 98
Number : 02
