|
SCC
mixes with limestone and chalk powder - The Indian
experience
Bhupinder
Singh, Rajesh Kumar and Abhishek Singh Mukati
The
use of limestone powder and chalk powder as fillers
in self-compacting concrete (SCC) was investigated.
Flow and strength characteristics of the concrete
mixes prepared using these materials were studied.
With minor adjustments in the superplasticiser dosage,
it was possible to develop concrete mixes with suitable
self-compactability by using limestone powder. The
morphology of the powders had a significant influence
on flow behaviour and the best deformability was obtained
in the SCC mixes containing the fine limestone powder
whereas the coarser chalk powder gave poor performance.
Besides particle size, the shape of the powder particles
also had a significant influence on deformability.
The deformability of the SCC mix with the coarser
but spherically shaped fly ash particles was comparable
to that of the SCC mixes with the much finer but irregularly
shaped limestone particles. The slump flow retentivity
of the SCC mixes with the Glenium 51 superplasticiser
was checked over two hours after casting and was found
to be satisfactory except in the mixes with the coarser
chalk powder. However, the plastic viscosity of the
mixes with higher powder addition levels was found
to increase rapidly with time. The compressive strength
of the SCC mixes containing the fine limestone powder
was significantly greater than that of the control
SCC mix with the same powder content.
Impact
of aggregate sizes on fresh & hardened states
of concrete
Subrato Chowdhury,
Sandeep Kadam, Satyaki Sarkar and Partha P. Biswas
There
is a general view that the size of coarse aggregate
affects only the properties of fresh concrete and
its impact on hardened properties is insignificant.
This paper presents the results of a series of tests
on concrete mixtures to examine the impact of different
sizes of coarse aggregate on fresh and hardened properties
of concrete. While slump cone test evaluated the fresh
concrete properties, compressive strength test and
rapid chloride penetration test (RCPT) determined
the hardened state properties. Concrete mixtures were
proportioned with three types of cements; Ordinary
Portland Cement (OPC), Portland Pozzolana Cement (PPC)
and Portland Slag Cement (PSC). Graded coarse aggregates
with maximum aggregate size (MSA) as 12.5, 16 and
20 mm; and water-binder ratios of 0.3 and 0.4 were
selected for this experimental programme for each
cement. The results show that while the coarse aggregate
size influences the slump, it is not relevant to compressive
strength and RCPT. The latter properties are governed
by (w/b) ratio, cement type and cement content.
State
of stress and ultimate strength of multi-layered RC
sections subjected to combined bending and tension
Saptarshi Sasmal
and K. Ramanjaneyulu
Combined
bending and high tensile axial loads are common in
walls of silos and tanks, nuclear power plant structure
and in other special types of structures, yet handbooks
and the codes have not dealt with these design aspects
in detail. With different types and magnitude of loading
and the possibility of reversal of loading, structural
members have layers of reinforcement. This makes section
analysis complicated. For example, design checks for
the adequacy of the reinforcement, thickness of the
concrete section and the orientation of the reinforcement
through the calculation of the state of stress at
different layers of reinforcement are needed. This
paper discusses different possibilities of tension
and bending, and proposes a methodology to calculate
the strength and the state of stress at a section
with multi-layers of reinforcement subjected to tension
and bending.
|