Workable and Robust Concrete using High Volume Construction and Demolition Waste in Sub Tropical Climate
Published at : 29 Apr 2018
Volume : IJtech
Vol 9, No 3 (2018)
DOI : https://doi.org/10.14716/ijtech.v9i3.1126
Yadav, N., Deo, S.V., Ramtekkar, G., 2018. Workable and Robust Concrete using High Volume Construction and Demolition Waste in Sub Tropical Climate . International Journal of Technology. Volume 9(3), pp.537-548
| Nishant Yadav | Department of Civil Engineering, SSIPMT, Raipur, India - |
| Shirish V. Deo | Department of Civil Engineering, National Institute of Technology, Raipur, Chhattisgarh, India |
| G.D. Ramtekkar | . Department of Civil Engineering, National Institute of Technology, Raipur, Chhattisgarh, India |
Full fledged use of construction
& demolition (C&D) waste in the construction industry is inevitable.
Concrete technologists across the world are engaged to scale its properties and
potential uses since last 65 years. The general consensus for the mechanical
property is to some extent is acceptable however the workability and durability
properties are still under a scanner and needs to be improved. The present
paper reports the optimistic results of series of experimental work carried out
using high range replacement of normal aggregates (NA) with recycled aggregates
(RA) (50-80%)
from C&D waste for producing sustainable and durable concrete (water cement
ratio 0.4) using C&D waste. Multiple strategies were used in research to
enhance workability and durability properties of concrete produced by using
C&D waste. Firstly the RA was used as an internal curing (IC) agent to
enhance the micro structure and Interfacial Transition Zone (ITZ) of concrete.
Secondly by apparently lowering the water cement ratio by using additional
low-lime fly ash similar to class F of ASTM C 618 mainly to improve
workability, packing of concrete, later age strength and durability. The
results show that water diffusion in concrete with RA being used as an IC agent
was delayed leading to decrease in shrinkage and micro cracks development; also
increase the hydration, compressive strength and improvement of durability
indexes such carbonation depth and electrical resistivity is seen. The Scanning
Electron Microscope (SEM) result illustrated the considerable improvement in
the microstructure. By adopting these strategies which are economical &
sustainable, mixtures show additional benefits that should permit their broader
application.
Concrete; Construction & Demolition (C&D) waste; Interfacial Transition Zone (ITZ); Internal Curing (IC); Shrinkage
Today land is a scarce commodity in the urban cities and to accommodate more population Floor Area Ratio is increased causing the demolition of existing structures for reconstruction. Good engineering practice advocates for recycling and reuse of materials. The reuse of Construction & Demolition (C&D) waste has potential to save a huge amount of natural resources, reduce CO2 footprint, reduce environmental impact, reduction of large space required for dumping sites, create space in urban areas, and also the creation of jobs and business opportunities (Yadav et al., 2017). The C&D wastes mainly consist of concrete, brick, ceramic and mortar which together constitute around 80%, but are in a complex mixed form and requires processing before being put to use. Un-engineered disposal and illegal dumping of these C&D waste is a threat and is causing environmental degradation. Huge heaps of C&D waste causes rise in flood levels of the rivers, scouring of the banks, depletion of resources, leaching out of hazardous material in the water causing an impact on aquatic life. Buried wastes cause the formation of an impervious layer which does not allow the growth of vegetation and prevents infiltration of rainwater. The other environmental impact includes deforestation, illegal mining of river beds for aggregates, air and water pollution, consumption of fossil fuels for transportation, topsoil loss etc. (Yadav et al., 2017).
The general wisdom on
the use of recycled aggregates for making concrete affects the workability,
strength, and durability of concrete. To sum up the experimental investigations
on concrete produced by using C&D waste aggregate, 0-100% replacement of natural aggregates has already been done and
reported. To scale the potential use of C&D waste it is unreasonable to
generalize all the results thus here the replacement is categorized into
a low replacement (up to 50%) and high replacement (more than 50%).
In low replacement, comparable compressive strength is achieved. At higher
replacement percentage of natural aggregates with C&D waste aggregate,
the compressive strength of concrete is
reduced (Brito & Saikia, 2013). The reason
attributed to this is poor Interfacial Transition Zone (ITZ),
(Medina et al., 2015). Concrete made with C&D waste aggregates have poor
workability and durability performance as compared to natural aggregates
concrete (Bravo et al., 2015). For 100% coarse recycled concrete aggregate
(RCA) in concrete,
Silva et al. (2015)
reported an increase in shrinkage by up to 80%. This high shrinkage
characteristic causes micro cracks within the concrete matrix and
leads to poor ITZ and durability issues in aggressive environments.
As per ACI-308, “Internal curing refers to the process by which the
hydration of cement occurs because of the availability
of additional internal water that is not part of the mixing water”
(Bentz & Weiss, 2011). Internal curing (IC) supplies the extra curing
water throughout the concrete mix thus maintaining the relative humidity and
avoiding self-desiccation and reducing autogenous shrinkage. IC also works well
with supplementary cementitious materials (SCM) like fly ash,
especially at higher dosage levels, due to increased water demand for SCM reaction
in later age. IC can address various age-old complex issues of
concrete like shrinkage, prominent ITZ, a considerable fraction of
un-hydrated cement due to lack of proper curing, and durability issues arising
from micro cracks due to various combinations of factors (Bentz &
Weiss, 2011). IC is an additional curing which supplements
conventional curing. The effectiveness of an IC agent depends on the
quantity of water IC agent can absorb and release in concrete. Brito and Saikia (2013)
reported that recycled aggregates adheres mortar around 16-17%, the water absorption capacity of recycled aggregate is also higher
compared to natural aggregate. Recycled aggregates marginally qualifies as an
IC agent and is not an effective IC agent because the pore size of
the mortar or paste coating on its surface is smaller or of similar size as
that of the mix around it. For proper functioning of IC mechanism pore size of
the IC agent acting as a water reservoir should be larger
than that of the mix around it. This is essential for the capillary pull of
absorbed water from IC agent to the desiccating mix around (Bentz & Weiss,
2011).
1.1.
Research
Objective
The primary objective of
the research is to reuse the C&D waste for producing concrete which is
viable from laboratory research scale as well as for field practical
implementation. To produce sustainable concrete using C&D waste as an IC
agent and hence to carry out a parametric study on the five
essentials of modern concrete – Workability, Strength, Durability, Micro Structure,
and Sustainability. The study also aims to address the contemporary
issues of the modern concrete mentioned in conclusion and to propose simple and
sustainable remedial measures to overcome limitations of using C&D waste in
concrete.
The constraints of using
C&D waste as coarse aggregate for making concrete: workability and durability issues have been
successfully dealt with by using multiple strategies. Higher DoH should result
in higher shrinkage, but in the present study, using multiple strategies the
shrinkage in the mix has been restricted successfully in spite of the increase
in DoH. Adjusting proportions of coarse aggregate fractions using maximum
density method and minimizing voids by using additional fly ash is highly
recommended for better strength and durability of concrete. Internal curing
should be applied for field applications especially in sub tropical regions it
is the grey area of
study and scope for future work are as follows: (1) The benefits of using
combinations of different size fractions of coarse aggregates, recycled
aggregates and fly ash are clearly seen in results of strength and durability.
However the evidence that which size fraction of fly ash precisely contributed
to which property of concrete in the present study could not be mapped. This
calls for a further specific study in some advanced research laboratory; (2) Smaller
fractions of coarse aggregate (4.75 mm - 10 mm) can be used
which might give some interesting results, as smaller recycled aggregates as an
IC agent will have better distribution across the mix. Three replacements (50%,
65% and 80%) using recycled aggregates are tried in the present study however
it is expected that even better results exist between 50% and 65% replacements.
Further, it is suggested to carry out a similar test using micro step increment
of fly ash dose between 5.26% and 11.11%.
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