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Concrete
pavements - Need to review Indian specifications
Santhosh
Kumar and Sudhir Misra
Concrete
has been used in pavement construction in different
parts of the world for the last several decades. Several
countries and professional organisations have developed
relevant design methodologies and construction methods
to suit local conditions. Construction of rigid pavements
is relatively recent in India, and studies need to
be carried out to update the Indian documents dealing
with various aspects of design and construction of
concrete pavements to make them more relevant to the
local conditions and ensure economy. A model design
exercise carried out with a set of input parameters
showed that the design thickness is the highest with
the Indian codes, even though the design traffic load
is the least. The study highlights the need for engineers
specialising in diverse areas such as transportation,
geotechnical, structural and concrete engineering
to work together for achieving the best results.
Application
of particle packing to produce roller compacted concrete
Inian
Rajasekaran and Manu Santhanam
Roller
compacted concrete is used in mass concreting applications
like dams and pavements due to certain advantages
such as use of low cement content, made possible by
blending with mineral admixtures like fly ash and
adopting innovative placement methods. In this context,
particle packing models help in selection of appropriate
size and proportions of particulate materials to get
suitable combination for optimum packing. In this
article, control mixtures of M10 and M20 grade roller
compacted concrete were designed based on US Army
Corps of Engineers method. These mixtures were then
redesigned by replacing cement with fly ash conventionally
by conducting trials and also by using software based
on a particle packing model. These modified mixtures
were then compared with control mixtures for strength
and durability parameters. It was found that concrete
mixtures that were designed based on particle packing
model using fly ash as cement replacement material,
had better strength characteristics and superior durability
performance than control mixtures and cement replacement
mixtures at very low cement content. The proportion
by which cement is to be effectively replaced by fly
ash can be determined by particle packing approach,
rather than conventional trial mixture procedures,
which are time consuming.
Proposed
draft for IS 1893 on design of non-structural elements
Goutam
Mondal and Sudhir K Jain
Seismic
safety of non-structural elements is no less important
than that of supporting structures as their survival
is essential to provide emergency and recovery services
in the aftermath of an earthquake. Therefore, non-structural
elements should be designed to resist the seismic
forces or seismic relative displacements depending
on their nature. Indian seismic code IS 1893 (Part
1): 2002 does not have specific provisions on design
of non-structural elements and their connections or
attachments. A companion paper1, published earlier,
reviewed the design philosophy and design provisions
on non-structural elements contained in several international
seismic codes. This paper contains proposed provisions
for inclusion in IS 1893, detailed commentary of the
proposed clauses as well as some solved examples of
the seismic design of non-structural elements.
Proportioning
of recycled aggregate concrete
B.
Rajkumar, B. Vijay Kalimuthu, R. Rajkumar and A.R.
Santhakumar
The
authors present an experimental study comparing the
properties of M20 grade concrete using conventional
and recycled aggregates. The study concludes that
with appropriate care in mixture proportioning recycled
aggregate concrete (RAC) can be used for structural
concrete and it is also cost-effective. However, the
water demand is more for RAC.
Empirical
correlations between rheological properties of cement
pastes from various models
M.A. Rahman and M. Nehdi
Empirical
correlations were established between rheological
properties of cement pastes estimated by various rheological
models from flow curves obtained using various test
accessories on cement pastes incorporating different
mineral additions and chemical admixtures. The Bingham,
Modified Bingham, Herchel-Bulkley and Casson models
were used to estimate yield stress, while plastic
viscosity was estimated using the Bingham, Modified
Bingham and Casson models. It was found that rheological
properties of cement pastes varied significantly not
only with their mixture composition, but also with
the change of test geometries used to obtain flow
curves and the rheological models employed to fit
such flow curves. Depending on the type of test geometry
used, correlations between rheological properties
of cement pastes estimated using various rheological
models were found to be linear, parabolic, logarithmic
or exponential. The empirical correlations thus established
allow expressing the rheological properties of cement
pastes calculated using various rheological models
from flow curves. The flow curves were generated using
various test accessories based on the results of a
particular test accessory-rheological model combination.
Correlations between standard errors of various rheological
models can facilitate prediction of as to which model
will be more accurate in fitting a flow curve generated
by a specific test geometry.
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