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Mix
design and production of flyash based geopolymer concrete
B.
Vijaya Rangan
The
global use of concrete is second only to water. As
the demand for concrete as a construction material
increases, so also the demand for Portland cement.
It is estimated that the production of cement will
increase from about from 1.5 billion tonnes in 1995
to 2.2 billion tonnes in 2010. On the other hand,
the climate change due to global warming has become
a major concern. The global warming is caused by the
emission of greenhouse gases, such as carbon dioxide
(CO2), into the atmosphere by human activities. Among
the greenhouse gases, CO2 contributes about 65% of
global warming. The cement industry is held responsible
for some of the CO2 emissions, because the production
of one tonne of Portland cement emits approximately
one tonne of CO2 into the atmosphere. Several efforts
are in progress to supplement the use of Portland
cement in concrete in order to address the global
warming issues. These include the utilisation of other
cementing materials such as flyash, silica fume, granulated
blast furnace slag, rice husk ash and metakaolin,
and the development of alternative binders to Portland
cement. In this respect, the geopolymer technology
proposed by Davidovits (1988; 2008) shows considerable
promise for application in concrete industry to develop
an alternative binder to the Portland cement. In terms
of global warming, the geopolymer technology could
significantly reduce the CO2 emission into the atmosphere
caused by the cement industries as shown by the detailed
analyses of Gartner.
Improvement
of IS 1343 procedure for estimation of ultimate moment
capacity of PSC sections with bonded tendons
Shinto
Paul and Devdas Menon
The
prevailing version of IS 1343 (1980) needs improvement
with respect to the procedure for estimating the ultimate
moment capacity of prestressed concrete (PSC) sections.
There is a lack of clarity in the specified typical
stress-strain curves for two different types of tendons
specified in the code especially with regard to the
manner in which the specified partial safety factor
has to be applied. The code also suggests a simplified
method in Appendix B, as an alternative to more rigorous
strain compatibility method for estimating the ultimate
moment capacity. However, it is seen that the IS 1343
simplified procedure invariably fails to satisfy the
condition of force equilibrium and also overestimates
the moment capacity. These shortcomings in the code
are examined and reviewed in this paper, and suitable
modifications are proposed in the form of modified
stress-strain curves and simplified tables for incorporation
in the forthcoming revision of the code.
Thermal
properties of high volume flyash concrete
M.
Shahiq Khan, J. Prasad and B.M. Suman
This
paper describes the influence of admixture especially
flyash on thermal properties of concrete. Flyash was
added as replacement for cement by decreasing the
cement weight in the ratios of 40, 50 and 60% by weight.
The binder dosage was kept constant at 340 kg/m3 throughout
this study. The amount of superplasticiser used was
1.176% by weight of cement along with crushed aggregate
(12 mm). The obtained results showed that thermal
conductivity and thermal transmittance decreased with
the increase of flyash as replacement for cement whereas
thermal resistance increased with the increase of
flyash. The compressive strength increased upto 50%
flyash replacement after heating to 200°C.
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