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Optimisation
of high early strength steam cured concrete mixtures
using central composite design
C.
Ramesh Babu and Manu Santhanam
Steam
curing is a useful technique for accelerating strength
gain in concrete. It increases the initial rate of
strength development by accelerating the chemical
reactions of hydration. Proper selection of delay
period and curing temperature is required to achieve
the early strength without affecting long-term performance.
In the present investigation, steam-curing technique
was adopted to achieve high early strength of 30 MPa
in 24 hours. Central composite design, an augmented
factorial design, was used for analysis. The effects
of cement content, water-cement ratio (w/c), curing
temperature and delay period on the one-day compressive
strength of steam cured concrete mixtures were investigated.
Based on the experimental results, optimised conditions
of steam curing to achieve the desired strength were
proposed.
Phenomenological
model for assessment of strength development in CLSM
T.S.
Nagaraj, B.C. Udayashankar, A. Shashishankar, and
H.R. Pradeep
Controlled
low-strength materials (CLSM), also known as flowable
fills are self compacting cementitious slurries capable
of developing required low levels of strength in the
range of 1 to 10 MPa. These are essentially cement-based
materials along with combination of fly ash and ground
granulated blast furnace slag (GGBS). The fine aggregate
constitutes, apart from sand, other marginal materials
such as rock dust, foundry waste sand, ponded or bottom
ash and such other materials. The water-cementitious
materials ratio varied from 0.7 to 2.5 with intermediate
values being 1.0 and 1.6. In this investigation a
phenomenological model is formulated within the basic
framework of Abrams' law for cement and fly ash as
cementitious materials. This model is validated with
another independent set of experimental data for tertiary
combination of cement, fly ash and GGBS as multi-component
cementing materials. The fine aggregate used in all
the cases was rock dust. The specific advantage of
this phenomenological model is to get the range of
water-cementitious materials ratio required for the
wide spectrum of strength requirement with the input
strength data at a reference value of water-cementitious
materials ratio.
Concrete
composites with ground granulated blast furnace slag
Subhajit
Saraswati and Prabir C. Basu
Concrete
composites incorporating high volume of ground granulated
blast furnace slag (GGBS) as cementitious mineral
admixture is being increasingly used in the construction
of structures for large projects in many countries.
Use of ground granulated blast furnace slag concrete
(GGBSC) has a positive effect in disposing GGBS in
environmental-friendly way and preserving resources
and above all in producing concrete of better quality.
Though the use of GGBS in the form of Portland slag
cement is not uncommon in India, experience of using
GGBS concrete in India is scanty. Experimental studies
were conducted to develop and examine the performance
of concrete mixes using GGBS as cement replacing admixture
and mixing it at the batching plant. Commercially
available GGBS, ordinary Portland cement (OPC) and
other ingredients were used. The present paper discusses
the effects of GGBS in concrete and includes the outcome
of experimental trials to develop GGBS concrete.
Modelling
of low-rise shear walls for push-over analysis of
buildings
P.
Gajalakshmi and Amlan K. Sengupta
For
the push-over analysis of a building with a shear
wall, modelling of the shear force versus drift behaviour
of the shear wall is necessary. This paper presents
a method for predicting the behaviour of a low-rise
framed shear wall. The method is based on the softened
truss model. The in-plane normal stress and strain
generated in the wall in presence of boundary elements,
were evaluated based on finite element analyses of
walls. The method of solution by the softened truss
model was modified to incorporate the effect of boundary
elements. The predicted non-linear shear force versus
drift curve was simplified to generate the shear hinge
property of a wall.
Heat-cured,
low-calcium, fly ash-based geopolymer concrete
B. Vijaya Rangan, Steenie Wallah, Dody Sumajouw
and Djwantoro Hardjito
The paper
presents the results of an extensive research programme
on heat-cured, low-calcium, fly ash-based geopolymer
concrete. Both short-term and long-term properties
of geopolymer concrete along with the behaviour and
strength of reinforced geopolymer concrete structural
members are described. Heat-cured, low-calcium, fly
ash-based geopolymer concrete offers many advantages
such as excellent structural properties, low creep,
very little drying shrinkage, excellent resistance
to sulphate attack, and good acid resistance.
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