SME Annual Meeting
Feb. 24 - 27, 2018, Denver, CO
Preprint 19-122
EXPERIMENTAL STUDY ON EARLY-STRENGTH OF CEMENTED PASTE BACKFILL
A. Bascetin, Istanbul Univ.-Cerrahpasa, Istanbul, Turkey
S. Tuylu, Istanbul Univ.-Cerrahpasa, Istanbul, Turkey
H. Eker, Gumuşhane Univ., Gumuşhane, Turkey
D. Adiguzel, Istanbul Univ.-Cerrahpasa, Istanbul, Turkey
Y. Baktarhan, Istanbul Univ.-Cerrahpasa, Istanbul, Turkey
ABSTRACT
Blast furnace slag (BFS) was used as a substitute for cement.
BFS was obtained from the iron and steel plant in Karabük. In addition,
tap water was used in the mixtures.
The purpose of this study is improving the strength of the
cemented paste backfill. Also the effect of blast furnace slag (BFS)
was investigated on short - term mechanical properties of CPB. In this
study, CPB samples were prepared by 9% portland cement and also
25%, 50% and 75% of the cement were replaced with BFS. The paste
materials prepared according to the value of 180 mm slump were cast
into cylinder molds. The uniaxial compressive strength (UCS) and
Ultrasonic P-Wave Velocities tests were performed. The maximum
values of UCS 0.80, 1.70 and 3.03 MPa respectively at 3, 7 and 14
curing period were obtained from 25 wt% BFS added samples. 25%wt.
BFS showed a strength of 1.79 times in the 7 days cure period and 2
times in the 14 day cure period according to the reference cemented
samples. On the contrary, substitution of 50 and 75 wt.% BFS were
reduced strength of CPB samples. Ultrasonic pulse velocity of
cemented paste backfill showed similar trend with UCS. But,
substitution of 25, 50 and 75 wt.% BFS were below the values of
reference samples. The maximum values of UCS are 25% additive
BFS. This situation directly affects the cost of CPB due to reduces the
cement ratio.
Preparation of paste backfill mixture
Reference samples were prepared by mixing copper tailing and
tap water with cement (CEM I 42.5 R) 9 % wt. Then, paste backfill
mixtures were formed containing BFS substitution at rates of 25%,
50% and 75% for % 9 cement used.
A homogeneous mixture of the CPB was achieved by stirring for 7
minutes by means of the mixer. These mixtures were prepared
according to the 18 cm slump (7.09 inch) and 80% solids ratio. Paste
backfill mixtures were poured into cylindrical specimen molds with 5
cm diameter and 10 cm height drainage (4 holes at the bottom). The
samples were kept in the curing cabinet at a rate of at least 80%
humidity and at 25 °C (3, 7 and 14 days).
Method
Ultrasonic pulse velocity (UPV) tests were carried out at the end
of the determined curing time (3, 7, 14 days). The time of passing P
waves sent from the surface of the cylindrical sample into the paste
sample by the ultrasonic tester is measured and the wave velocity is
calculated. Ultrasonic pulse velocity (Pundit) Experiments; In
accordance with ASTM C 597 standard, it has been realized with
proceq-tico brand test device with 0.1 -µs precision signal time and 54
kHz signal frequency with the help of transducers (geophones)
(Figure 1).
INTRODUCTION
Cemented paste backfill (CPB) contains 70-85% solids by total
mass that is a mixture of process tailings, water (fresh and/or mine
process), and 3-9 % wt. a hydraulic binder (often ordinary Portland
cement) (Kesimal et al., 2003; Fall et al., 2005, Ercıkdı et al., 2013;
Yılmaz et al., 2017; Yılmaz and Guresci, 2017, Bascetin et al, 2018a;
Bascetin et al, 2018b; Bascetin et al, 2018c).
Cement cost is very important in the CPB. The biggest financial
expense of the paste backfill plant is the cement cost. Therefore,
pozzolans (Silica fume, Zeolite, Fly ash, Blast furnace slag etc.) are
used to reduce the cost of cement.
There are several studies in the literature about the use of BFS in
CPB. Ercikdı et. al (2009); industrial waste products (waste glass, fly
ash, granulated blast furnace slag and silica fume) are investigated
using partial substitution and a pozzolanic additive in containing sulfurrich a cementitious paste backfill (CPB). Also; alkali-activated neutral
and acidic blast furnace slags (AASs) with aqueous sodium silicate
(LSS) and sodium hydroxide (SH) were tested as alternative binders to
OPC for CPB of high-sulphide mill tailings (Ferdi et. al, 2012).
The purpose of this study is improving the strength of the
cemented paste backfill. Also the effect of blast furnace slag (BFS)
was investigated on short - term mechanical properties of CPB. In this
study, CPB samples were prepared by 9% portland cement and also
25%, 50% and 75% of the cement were replaced with BFS.
MATERIALS AND METHOD
Tailings were taken from the copper mine in the Turkey. The
vacuum disc in the paste backfill plant is filled into the barrel from the
filter outlet. they were brought to the Mining Engineering Laboratory in
Istanbul. CEM I 42.5 from Çatalça cement plant was used as binder.
Figure 1. Device of Ultrasonic Pulse Velocity.
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SME Annual Meeting
Feb. 24 - 27, 2018, Denver, CO
BFS containing samples (50% and 75%) were not increased the
strength to reference specimens.
The roughness of the upper and lower surfaces of the samples
was corrected prior to the experiment. In addition, the length is
measured with an electronic caliper gage with a precision of 0.1 mm.
Length values obtained from the caliper gage are entered to the device
in length. To ensure a smooth connection between the transducers
and the upper and lower surfaces of the sample, gel was coated on
both surfaces and UPV values were obtained for each sample. 3
samples were tested for each curing time and the values obtained in
the results were averaged.
Figure 3. UPV of 9% cemented and blast furnace slag substituted
samples.
Figure 4. UCS of 9% cemented and blast furnace slag substituted
samples.
In the 14 days cure period, the paste backfill limit value of ≥ 0.7
MPa was exceeded in the mixture ratio of 25% and 50%. Also, the
highest UCS strength in 14 days is 3.03 MPa (25% BFS). As a roof
support, no mixing ratio exceeds the desired limit value ≥ 4 MPa.
Furthermore, all mixing ratios of ≥ 0.15 MPa, which are the limit of
liquefaction risk, are provided.
Figure 2. The Press Used in the Uniaxial Compressive Strength Test.
Cemented Paste Backfill (CPB); The uniaxial compressive
strength test was performed on cylindrical samples prepared in 50 ×
100 mm dimensions in accordance with ASTM C 39 standard.
Samples which reached the determined cure times were calculated
separately for the 3, 7 and 14 days cure periods by breaking the
automatic controlled press at a constant loading speed of 1 mm / min
with a loading capacity of 50 kN (Figure 2). The length/diameter ratio of
the cylindrical CPB samples is at least 2 cm and the upper and lower
surfaces of the samples are corrected before the test. For each cure
period, 3 samples were tested in the experiment and the mean values
were obtained as a result.
CONCLUSION
In this study, CPB samples were prepared by 9% portland cement
and also 25%, 50% and 75% of the cement were replaced with BFS.
25%wt. BFS showed a strength of 1.79 times in the 7 days cure period
and 2 times in the 14 day cure period according to the reference
cemented samples. On the contrary, substitution of 50 and 75 wt.%
BFS were reduced strength of CPB samples. Ultrasonic pulse velocity
of cemented paste backfill showed similar trend with UCS. But,
substitution of 25, 50 and 75 wt.% BFS were below the values of
reference samples. The maximum values of UCS are 25% additive
BFS. This situation directly affects the cost of CPB due to reduces the
cement ratio.
RESULTS
In Figure 3; Samples of %25 BFS compared to reference samples
received higher UPV values. In addition, UPV values show a similar
tendency with uniaxial compressive strength results (9% cement and
BFS substituted samples). UPV values; depending on the curing time,
it varies from 493 to 1700 µ / s. A decline in values is observed with 14.
days cure time (for %25 BFS). Also; in other examples, the UPV value
was increased depending on the cure time. UPV value of 1 MPa
<UCS< 4 MPa are 1440-1700 µ / s.
The further researches; UCS and UPV values at different cement
rates and at different cure rates should be examined.
ACKNOWLEDGEMENT
This study was funded by Istanbul University with the project
number FDK-2018-24707.
REFERENCES
In Figure 4; addition of BFS in paste backfill mixture containing
9% cement increased compressive strength. 25% BFS containing
samples increased the strength to reference specimens. But, another
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2
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Copyright © 2019 by SME
SME Annual Meeting
Feb. 24 - 27, 2018, Denver, CO
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