|
Cement-superplasticiser
compatibility and method of evaluation
A.K.
Mullick
Instances
of particular cement and superplasticiser combination
not resulting in optimum performance are common. National
specifications draw attention to the possibility of
such incompatibility. However, methods of evaluation
of a particular combination for compatibility are
not prescribed. This paper traces the mechanisms of
action of superplasticisers in concrete mixes and
suggests a procedure to ensure compatibility, especially
for low water/cement ratio, high strength concrete
mixes.
Computer
aided non-linear simulation of brick masonry reinforced
concrete infill frame under in-plane lateral load
P.L.
Pradhan, C.V.R. Murty, K.V. Hoiseth and M.P. Aryal
Analytical
and experimental studies are carried out on the effect
of central window opening with different sizes in
one-bay one-storey brick masonry infill frames subjected
to in-plane lateral loads. In the analyses, the brick
elements are modelled using plane-stress elements,
and mortar joints by link elements. The parameters
investigated include lateral deflection and lateral
stiffness of infill frame. Analytical and experimental
results are compared. Overall results showed that
wall panel significantly reduces performance of infill
frames with the increase in opening size, whereas
the infill walls possess remarkably high lateral stiffening
capacity in comparison to the bare frames.
Wood
ash from forest waste for partial cement replacement
in mortars
Maria
da Luz Garcia and Joana Sousa-Coutinho
Renewable
energy sources are being used throughout the world
and one of these is forest waste. Resulting wood bottom
ash, waste with no application, is currently being
tested for use as partial cement replacement in structural
concrete. The first stage of this study was carried
out on mortars with 0% (control), 10% and 20% Portland
cement replacement by weight, with ground wood ash
(WA). Tests considered were mechanical strength, pozzolanic
activity, chloride ion penetration, carbonation, resistivity
and capillary absorption but no improvement from WA
was observed because of insufficient fineness. Research
is presently underway using finer material.
Evaluation
of drying shrinkage and residual stresses of a high
strength concrete using restrained ring test
A.
Sivakumar and Manu Santhanam
Volume
changes in concrete start at early ages (plastic shrinkage)
and continue after hardening as a result of drying
shrinkage. When restrained, these volume changes cause
cracking because of the poor tensile strength of concrete.
The present investigation was aimed at mitigating
drying shrinkage cracks in high strength silica fume
concrete by the addition of a combination of metallic
(steel) and non-metallic fibres (polypropylene, polyester
and glass). The relative performance of the plain
and fibre reinforced concrete mixtures was quantified
in terms of the residual stresses generated upon drying.
Residual stresses were calculated from the measured
strain in a steel ring using a restrained ring test
set-up. The experimental results showed that drying
shrinkage cracking occurred earlier in the plain concrete
specimen compared to fibre reinforced concrete specimens.
The hybrid combinations of steel and non-metallic
fibre performed better than the steel fibre reinforced
concrete, possibly due to the increased fibre availability
resulting from the addition of non-metallic fibres
(which have lower specific gravity and higher aspect
ratios compared to steel fibres). Among the three
hybrid fibre combinations, the steel-polyester combination
showed the lowest drying shrinkage cracking potential.
|