Title:
Axial Load-Bearing Concrete Confined with Ultra-High- Performance Concrete Jackets and Basalt Fiber-Reinforced Polymer Grids
Author(s):
Yail J. Kim and Yordanos Dinku
Publication:
Structural Journal
Volume:
122
Issue:
1
Appears on pages(s):
19-34
Keywords:
fiber-reinforced polymer (FRP); rehabilitation; retrofit; strengthening; ultra-high-performance concrete (UHPC)
DOI:
10.14359/51743290
Date:
1/1/2025
Abstract:
This paper presents the behavior of unreinforced cylindrical
concrete elements confined with a hybrid system, consisting of
an ultra-high-performance concrete (UHPC) jacket and basalt
fiber-reinforced polymer (BFRP) grids. For exploring the feasibility
of the proposed strengthening scheme, a series of tests are
conducted to evaluate material properties and to obtain results
related to interfacial bond, load-bearing capacity, axial responses,
and failure modes. To understand the function of the individual
components, a total of 57 cylinders are loaded under augmented
confining conditions, including plain cores with ordinary concrete
(CONT), plain cores with UHPC jackets (Type A), and plain cores
with UHPC jackets plus BFRP grids (Type B). By preloading the
cores at up to 60% of the control capacity (60%fc′) before applying
the confinement system, the repercussions of inherent damage
that can take place in vertical members on site are simulated. The
compressive strength of UHPC rapidly develops within 7 days,
whereas its splitting strength noticeably ascends after 14 days.
The adhesion between the ordinary concrete and UHPC increases
over time. While the Type B specimens outperform their Type A
counterparts in terms of axial capacity by more than 18%, reliance
on the BFRP grids is reduced with the growth of UHPC’s strength
and adhesion because of the interaction between the hardened
UHPC and the core concrete. The adverse effects of the preloading
are noteworthy for both types, especially when exceeding a level
of 30%fc′. The BFRP grid-wrapping alleviates the occurrence of
a catastrophic collapse in the jacketed cylinders, resulting from
a combination of the axial distress and lateral expansion of the
core. Analytical models explain the load-carrying mechanism of
the strengthened concrete, including confinement pressure and
BFRP stress. Through parametric investigations, the significance
of the constituents is clarified, and design recommendations are
suggested.