PURWANTO, PURWANTO (2021) Self Compacting Geopolymer Concrete (SCGC) Haunch Sebagai Perkuatan Balok Lentur di Zona Dekat Muka Kolom. Doctoral thesis, UNDIP.

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Abstract

Many reinforced concrete structures are found that need strengthening due to mistakes in
detail engineering design, overloading, and incorrect quality of construction. Reality is most of
existing structures still use a planning philosophy based on the old earthquake load codes. So that
before a strong earthquake occurs, the beam needs strengthening with haunch beam. The haunch
beam increases the moment and shear capacity and relocates plastic hinge away from the column
face. Strengthening method with haunch beams at the front of the column face increases stiffness,
strength and durability of the structure so that debonding symptoms in the beam column joint can
be avoided. Ductility of the haunch beam is better than ductility of the prismatic beam, this is
because the reinforcement ratio () of the haunch beam is relatively smaller than prismatic beam.
Geopolymer concrete is an alternative concrete that does not use cement as a binder and
instead uses fly ash which is rich in silica and alumina which can react with alkaline activator
liquid (Na2SiO3 and NaOH) to produce binders. On the other hand, use of fly ash has a positive
impact because this material is a waste of coal combustion. Geopolymer concrete has a higher
bond, compressive and tensile strength than conventional concrete. For strengthening of beam in
front of the column it is necessary to use self-compacting geopolymer concrete (SCGC), because
strengthening of beam in front of the column has a difficulty level of implementation and limited
space due to there are of existing slabs and beams. Combining the concept of strengthening beam
in front of column using haunch beams with the use of SCGC has two benefits. This dissertation
research puts forward innovation in the form of technical solutions for handling strengthening
beam in front of the column with haunch beams made of self-compacting geopolymer concrete
(SCGC). Analytical approach is carried out through full-scale experimental tests in the laboratory
and finite element modeling, to explain micro aspects as a complementary test. The data used for
analysis in the form of primary data obtained from the results of measurements and recordings in
the experiments carried out, as well as observations of the finite element model. This research
begins with the test of the materials that make up the test object in the form of a tensile test for
steel. For conventional concrete and geopolymer concrete will be tested for compressive strength,
split tensile strength test and flexural tensile strength test of concrete. The data is used to input the
numerical model. Manufacture of prismatic concrete beams and haunch beams with a quality of
f'c=31 MPa. Dimensions of the test beam with a beam length of 3800 mm, beam cross section with
a width of 170 mm and a height of 340 mm and the reinforcement configuration with under
reinforced rules. The haunch beam has a fixed variable, namely the length dimension of the haunch
beam: L=2×H and the unfixed variable is the height of the haunch beam (h).
The results of bending beam test due to monotonic load on the prismatic and haunch beam
are expressed in the load–displacement, moment-curvature and observation of crack patterns.
Based on experimental test results and analysis of eight (8) specimens consist of two (2) prismatic
beams (BC), two (2) geopolymer haunch beams (BG0.5), two (2) geopolymer haunch beams
(BG1.0) and two (2) conventional haunch beams (BK1.0) can be concluded: (a). Obtained SCGC
composition of haunch beams: 42.0% coarse aggregate; fine aggregate 28.0% ; fly ash (FA) 19.5%
; alkaline activator (AA) 10.5% ; superplasticizer 2.0% of FA ; extra water 11.70% from binder
(FA+AA); extra cement 5.63% of binder (FA+AA). AA consists of NaOH 12 M and Na2SiO3 Be
52 with a ratio of NaOH: Na2SiO3 = 1.0: 2.5. (b). The difference in load capacity, displacement
ductility and curvature ductility between BG1.0 geopolymer haunch beam and the BK1.0
conventional haunch beam is quite significant. This is because geopolymer concrete has a fairly
large shrinkage value (667 ) so that it causes initial crack material to occur in geopolymer
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concrete (BG). (c). Compared to prismatic beams, the magnitude of the increase in load capacity
of BK1.0 beams by 73.27% and BG1.0. of 71.97% and BG0.5 by 54.70%. (d). Compare to
prismatic beams (BC), the magnitude of the increase in displacement ductility (d) beam BK1.0.
is 43.40% and beam BG1.0. is 25.10% and beam BG0.5. is 3.91%. This is because at BG0.5 with
a haunch beam height that is not optimal so that the increase is relatively small. (e). When
compared to prismatic beams (BC), the magnitude of the increase in curvature ductility () beam
BK1.0. is 46.89% and beam BG1.0, by 32.03% and for beams BG0.5, an increase of 7.23%. (f).
Plastic hinges in prismatic beams BC and haunch beams BG0.5 occur in face of column, while
beams BK1.0 and BG1.0. the occurred plastic hinge at the end of the haunch beam (2×H from face
of column). (g). Plastic hinge occurs at the end of haunch with minimum haunch angle () is 19.07o
or haunch height (h) is at least 0.7×height of prismatic beam (0.7×H). (h). Crack pattern of haunch
beam and prismatic beam due to monotonic load shows a prismatic beam crack pattern starting
from the crack propagation at face of column and haunch beam at the end of haunch. (i). The model
as a tool and comparison that provides predictions of load behavior, deflection, and crack
propagation patterns are relatively the same as the experimental test results. This shows that the
model can be used to predict the failure behavior of reinforced concrete beams. The model can
also simulate haunch height of 0.7×H with conclusion that it is proven that haunch height is 0.7×H,
so there has been move the plastic hinge from face of column to the end of haunch beam.
Keywords: strengthening, haunch beam, SCGC, displacement and curvature ductility, plastic
hinge.

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