Page 5 - Open-Access-May-2020

TECHNICAL PAPER

does not carry gravity load, the chance of delamination of the stiffness were observed in column specimens jacketed with
jacket under service load, due to differential creep of the inner concrete of strength 24 MPa, even if the interface was not
concrete and jacket, is minimal. However, the performance (any treated . Predicted increase in flexural capacity and ductility
[6]
delamination of the jacket and reduction in ductility) under were observed in column specimens jacketed with 43 MPa self-
increasing lateral drift, needs to be investigated. compacting concrete (SCC) [7, 8] .
An essential component in HSC is the admixture, which shall
improve its performance in parallel with the strength. For 2.2 Tests on Concrete Jacketed Beams
instance, most of the HSC mixes have reduced water-to-cement Flexural failure mode was predominantly observed in beam
ratios, and hence higher compressive strengths. The use of a specimens jacketed with preplaced aggregate concrete of
suitable admixture aids to improve the workability along with [9]
strength. The use of admixture requires early and adequate strength up to 50 MPa . Beam specimens tested till the yielding
curing of concrete. Considering these conditions, the important of longitudinal bars were jacketed with 23 MPa concrete and
aspect in the HSC is the quality control, which is to be strictly re-tested [10] . Slightly improved behaviour was observed. Shear-
maintained to achieve the desired properties. Of course, use of dominated beam specimens tested to brittle failure were
higher quality materials increases the material cost. jacketed with SCC of strength 40 MPa and re-tested to observe
flexural response with higher ductility [11] . Beam specimens
To study the behaviour of members strengthened using HSC jacketed with micro concrete of strength 50 MPa exhibited
jacket, six beam-column specimens were prepared with high- higher load carrying capacity with rough interface, similar to the
strength self-compacting concrete (HSSCC) in the jacket portion case with smooth interface in the presence of dowel connectors
and tested. Their behaviour was then compared with six similar and bonding agent [12] .
specimens with normal-strength self-compacting concrete
(NSSCC) in jacket portion. In each set, the specimens had three
different percentages of longitudinal tension reinforcement 2.3 Tests on HSC Jacketed Members
in jacket. The details of the mix proportions, preparation of The inner core of a column specimen jacketed with HSC of
specimens, test procedure and test results are presented in this 82 MPa was found to provide full strength, in the presence
paper.
of proper confinement [13] . The flexure performance, bearing
capacity and ductility of an original column were found to
2. LITERATURE REVIEW get enhanced on jacketing with ultra-high performance fibre-
reinforced concrete of strength 130 MPa [14] . With the application
Selected studies related to experimental investigation on of steel-fibered HSC as a repair material over NSC beams, the
strengthening of columns and beams using concrete jacket and
the utilization of HSC as a jacket material are summarized here. importance of fibre dosage on the achievement of required
ductility, was demonstrated [15] .
2.1 Tests on Concrete Jacketed Columns
3. GAP AREAS AND RESEARCH
In shear-dominated short column specimens, the repair jacket SIGNIFICANCE
was found to be as strong and stiff as a strengthening jacket, in
the presence of normal-strength shotcrete of 35 MPa, additional In most cases of the reviewed literature on strengthening of
closely spaced ties and cross-ties . Column specimens repaired columns and beams, the concrete used in jacket was found to
[1]
and strengthened with normal-strength concrete (NSC) jacket be of normal-strength. Not many studies were reported on the
of 33 MPa reached 90% and 100% of capacity, respectively, utilization of HSC as a jacket material. In a few studies where
of the corresponding reference specimens, under flexural HSC was used in the jacket, the objectives were focussed
failure mode . Similar load versus deformation behaviour towards the enhancement of flexural strength. Studies were not
[2]
was exhibited by column specimens having light transverse reported on the performance of members strengthened with
reinforcement with repair and strengthening using NSC jacket HSC under shear. Even if the original members before jacketing
of 43 MPa . The shrinkage-compensating mortar jacket of 57 were shear-critical, they were transformed to flexure-critical
[3]
MPa was found to be incapable in transmitting shear leading to (failure governed by flexure) after jacketing. That is, the mode
the sudden drop of shear capacity of column specimens beyond of failure was deliberately changed. However, short members
ultimate . can still remain shear-critical after jacketing, and hence the shear
[4]
strength needs to be investigated.
Column specimens jacketed with 55 MPa strength concrete
showed improved deformation and energy dissipation Most of the studies involving HSC consisted of fibres in the
capacities irrespective of the presence or provided length of concrete. In the narrow space available around an existing
[5]
lap splice at the plastic hinge zone . Improved strength and member for jacket, there are possibilities of poor dispersion

6 The IndIan ConCreTe Journal | MaY 2020