Page 7 - Open-Access-May-2020

TECHNICAL PAPER

at the compressive strengths of inner and jacket concrete. corresponding to HSSCC and NSSCC with target strengths of
th
Inner portion concrete had a 30-day gap between 28 day and 70 MPa and 40 MPa respectively, were adopted from a previous
test day. The specimens were tested on 28 days age of jacket study [17] . The flowability through the narrow space in the
concrete. formwork without segregation or bleeding is necessary during
jacketing. The self-compactibility was achieved by limiting the
4.2.1 Conventional Concrete for the Inner coarse aggregate content (which reduced the internal stresses
Portion due to aggregate particle friction) and using superplasticizer.
The SCC was mixed in a pan-type tilting mixer machine, poured
The inner portion concrete consisted of ordinary portland in a mould and allowed to set without any compaction (Figure 3).
cement, fine aggregate (river sand), coarse aggregate of
nominal size 20 mm and water as the constituents. Mineral
or chemical admixtures were not added. The concrete was
prepared in a conventional drum-type mixer machine of 100
litres capacity. It was placed in a mould and compacted using
a needle vibrator. The target strength of the inner portions of
jacketed specimens was 20 MPa. This was similar to that used in
existing buildings.

4.2.2 SCC for the Jacket Portion

The SCC had portland pozzolana cement, fine aggregate (river
sand), coarse aggregate of nominal size 8 mm, superplasticizer
and water as its constituents. The superplasticizer was poly-
carboxylic ether based, with low viscosity and high performance (a) (b)
quality. In the trial mixes, these constituents were adjusted such Figure 3: Preparation of SCC (a) Mixing of ingredients and
that the concrete flowed under its own weight. The mix ratios (b) Casting of cubes

Table 1: Details of Concrete Mix Design and Salient Measures of Compressive Strengths

mix ratio →
cement : fine aggregate : comPreSSive comPreSSive
SPecimen coarSe aggregate : Water : target StrengtH StrengtH StrengtH
iD (mPa) at 28 DayS at tHe Day of teSt
SuPerPlaSticizer (mPa) (mPa)
(% of cement)
inner Jacket inner Jacket inner Jacket inner Jacket
HSSCC 1A
HSSCC 1B

HSSCC 2A 1 : 1.7 : 1.3 : 70.0
HSSCC 2B 0.3 : 1.0% 20.4 69.1 22.6 69.1

HSSCC 3A
HSSCC 3B 1 : 3.2 : 4.9 :
NSSCC 1A 0.7 : Nil 20.0

NSSCC 1B
NSSCC 2A 1 : 1.8 : 1.4 : 40.0 19.8 43.7 20.3 43.7
NSSCC 2B 0.4 : 0.4 %

NSSCC 3A
NSSCC 3B

8 The IndIan ConCreTe Journal | MaY 2020