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Assessment of strength properties of cemented paste backfill by ultrasonic pulsevelocity test
Tekin Yılmaz, Bayram Ercikdi, Kadir Karaman, Gökhan Külekçi
PII: S0041-624X(14)00043-2DOI: http://dx.doi.org/10.1016/j.ultras.2014.02.012Reference: ULTRAS 4771
To appear in: Ultrasonics
Received Date: 19 November 2013Revised Date: 11 February 2014Accepted Date: 12 February 2014
Please cite this article as: T. Yılmaz, B. Ercikdi, K. Karaman, G. Külekçi, Assessment of strength properties ofcemented paste backfill by ultrasonic pulse velocity test, Ultrasonics (2014), doi: http://dx.doi.org/10.1016/j.ultras.2014.02.012
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1
Assessment of strength properties of cemented paste backfill by ultrasonic 1
pulse velocity test 2
Tekin Yılmaza, Bayram Ercikdia*, Kadir Karamana, Gökhan Külekçib 3
aDepartment of Mining Eng., Karadeniz Technical University, 61080 Trabzon, Turkey 4
bDepartment of Mining Eng., Gümüşhane University, Gümüşhane, Turkey 5
*Phone: +90-462-3773171; Fax: +90-462-3257405 6
E-mail address: bercikdi@ktu.edu.tr
2
Abstract: 7
Ultrasonic pulse velocity (UPV) test is one of the most popular non-destructive techniques 8
used in the assessment of the mechanical properties of concrete or rock materials. In this 9
study, the effects of binder type/dosage, water to cement ratio (w/c) and fines content (<20 10
µm) of the tailings on ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) 11
samples were investigated and correlated with the corresponding unconfined compressive 12
strength (UCS) data. A total of 96 CPB samples prepared at different mixture properties were 13
subjected to the UPV and UCS tests at 7, 14, 28 and 56–days of curing periods. UPV and 14
UCS of CPB samples of ordinary Portland cement (CEM I 42.5 R) and sulphate resistant 15
cement (SRC 32.5) initially increased rapidly, but, slowed down after 14 days. However, 16
UPV and UCS of CPB samples of the blast furnace slag cement (CEM III/A 42.5 N) steadily 17
increased between 7-56 days. Increasing binder dosage or reducing w/c ratio and fines content 18
(<20 µm) increased the UCS and UPV of CPB samples. UPV was found to be particularly 19
sensitive to fines content. UCS data were correlated with the corresponding UPV data. A 20
linear relation appeared to exist between the UCS and UPV of CPB samples. These findings 21
have demonstrated that the UPV test can be reliably used for the estimation of the strength of 22
CPB samples. 23
Keywords: Ultrasonic pulse velocity, unconfined compressive strength, cemented paste 24 backfill, mixture properties 25
3
1. Introduction 26
Ultrasonic pulse velocity (UPV) test, a non-destructive and easy method to apply in both field 27
and laboratory conditions, is increasingly being used to determine the geotechnical properties 28
of rock or concrete materials in mining, civil and geotechnical engineering. It employs the 29
principle of measuring the travel velocity of ultrasonic pulses through a material medium. 30
Knowing the UPV, changes of the geotechnical properties can be evaluated using known 31
relationships between velocities and mechanical properties [1]. There are many studies on the 32
use of ultrasonic pulse velocity (UPV) test. Karpuz and Paşamehmetoğlu [2] utilized UPV test 33
to determine the weathering degree of Ankara andesites. Kahraman et al. [3] reported that the 34
quality classification and estimation of slab production efficiency of the building stones can 35
easily be made by ultrasonic UPV test. Others attempted to assess grouting and 36
blasting/fragmentation efficiencies in a rock mass [4,5] and thermal conductivity of any rock 37
[6] by laboratory UPV test. In addition, UPV test was used for predicting the stress 38
distribution around the mine tunnel and estimating the thickness of damaged zones caused by 39
the tunnel excavation [7]. Many researchers have found that there is a good relationship 40
between UPV and unconfined compressive strength of rock or concrete materials [8-12]. 41
Cemented paste backfill (CPB) is primarily composed of mill tailings (75–85% solids by 42
weight), a hydraulic binder (usually 3–9% by weight) and mixing water [13-15]. The 43
unconfined compressive strength (UCS) of CPB at a given time is one of the most important 44
parameter since the CPB structure must remain stable during the extraction of adjacent stopes 45
to ensure the safety of the mine workers and to avoid ore dilution. Although UPV test as a 46
low-cost, less time consuming and practical method is known to be extensively exploited for 47
estimating the UCS of rock and concrete [8-12,16], there are no detailed studies on the 48
utilization of UPV test for predicting the mechanical performance of CPB. In this regard, the 49
UPV test method can be beneficial for the rapid estimation of the UCS of CPB instead of 50
4
conventional compressive strength test. Chou et al. [1] determined the geotechnical properties 51
such as Young, shear and bulk modulus of rockfill by measuring P and S waves over a curing 52
period of 120 days. The P–and S–waves velocity changes in CPB having 3 to 5 wt.% binder 53
content at early curing ages were monitored by Diezd’Aux [17]. He suggested that the 54
evaluation of ultrasonic properties should be performed after several days of curing due to the 55
inaccurate results obtained in the short term. Galaa et al. [18] also measured the P– and S–56
waves in CPB samples to understand the development of strength and stiffness of CPB over a 57
curing period of 7 days. However, they did not correlate UCS data with UPV. 58
In the present study, ultrasonic pulse velocity (UPV) was evaluated as a non-destructive, low-59
cost and practical method for the estimation of CPB strength. The effects of binder type, 60
binder dosage, water to cement ratio (w/c) and fines content (<20 µm) of the tailings on the 61
strength and, particularly, ultrasonic properties of CPB produced from the mill tailings was 62
investigated over 7-56 days of curing periods. The UCSs of CPB samples were correlated 63
with the UPV results in an attempt to use the UPV measurement to predict the strength of 64
CPB. Potential benefits of UPV test in CPB were discussed. 65
2. Materials and methods 66
2.1. Tailings and binders 67
In this study, a tailings sample was obtained from the tailings dam of a copper flotation plant 68
(Kastamonu Küre, Turkey). The tailings sample was collected from the point that is 40 m far 69
away from the tailings discharge point by hydraulic excavator (Fig. 1a). Annually, 70
approximately 0.55 Mt of sulphide tailings were produced as a result of milling operations 71
and disposed into the tailings dam. The tailings sample was deslimed by hydrocyclone at the 72
plant in order to investigate the effect of fines content (<20 µm) on the strength and ultrasonic 73
5
properties of CPB. Table 1 shows the physical, chemical and mineralogical properties of the 74
as-received and deslimed tailings. Compared with the as-received tailings, the deslimed 75
tailings were determined to contain less fines (e.g. 35% c.f. 58.4% finer than 20 µm) and 76
higher pyrite content (43.5% c.f. 52.2%) presumably due to the removal of silicate minerals in 77
slimes fraction as suggested by the decrease in SiO2+Al2O3 contents of tailings (Table 1). The 78
coefficient of uniformity (Cu) was determined to be 11.0 and 6.54 for the as-received and 79
deslimed tailings, respectively. X-ray diffraction (XRD) analysis indicated that the major 80
mineral phase was identified to be pyrite. Although both the as-received and deslimed tailings 81
contain quartz and chlorite, other silicates such as muscovite and albite were identified only in 82
the as-received tailings (Table 1). 83
In this study, blast furnace slag cement (CEM III/A 42.5 N) was used as the main binder in 84
the tests where the effect of binder dosage, w/c ratio and fines content (<20 µm) of the tailings 85
on the strength and ultrasonic properties of CPB were evaluated. Ordinary Portland cement 86
(CEM I 42.5 R) and sulphate resistant cement (SRC 32.5) were also used to study the effect of 87
binder type on the UCS and ultrasonic pulse velocity (UPV) of CPB. The physical, chemical 88
and mineralogical characterisations of the cements were summarized in Table 1. SRC was 89
characterized by its low C3A content (Table 1), which is an important phase that controls the 90
long term performance of CPB against acid and sulphate attack [19,20]. However, only the 91
short term (up to the 56 days) performances of binders were evaluated in this study. It is 92
relevant to note that CEM III/A 42.5 N contains granulated blast furnace slag (35%) as 93
additive to improve its binding performance and to reduce the binder costs. 94
6
2.2. Preparation of CPB samples 95
A total of 96 CPB samples in triplicate were prepared by mixing and homogenizing the 96
tailings samples (as-received and deslimed), binder and tap water in a Univex Stand model 97
blender equipped with a double spiral (Fig. 1b). The paste was then placed in the slump cone 98
in one-third length increments, each being tamped 25 times with a small rod. The CPB 99
samples were prepared at a slump consistency of 16.51-21.59 cm, which were verified using 100
the 30.48 cm high concrete cone test according to ASTM C 143 [21]. The solids contents of 101
paste mixtures were set to 73.58-80.17 wt.% The effect of w/c ratio, binder type and fines 102
content was examined at a fixed binder dosage of 7 wt.% while binder dosage was tested at 5, 103
6 and 7 wt.% (Table 2). 104
The CPB mixtures after being thoroughly mixed were poured into the plastic cylinders with a 105
diameter x height of 10x20 cm. Bottom of these cylinders were perforated (seven holes with 2 106
mm diameter) to allow the drainage of excess water. The cylinders were sealed in plastic bags 107
and allowed to cure in a curing room maintained at 20 ±1°C. 108
2.3. UPV and UCS tests 109
CPB samples were subjected to the ultrasonic pulse velocity (UPV) tests according to ASTM 110
C 597 [22] at 7, 14, 28 and 56 day curing periods. The UPV was measured on CPB samples 111
by a Portable Ultrasonic Nondestructive Digital Indicating Tester (PUNDIT) that measures 112
the time of propagation of ultrasound pulses with a precision of 0.1 µs and its transducers 113
were 42 mm in diameter with 54 kHz (Fig. 1c). Length of the measuring base was determined 114
within an accuracy of 0.1 mm. End surfaces of the CPB samples were polished to provide a 115
good coupling between the transducer face and the sample surface to maximize accuracy of 116
the transit time measurement. A thin film of vaseline was applied to the surface of the 117
7
transducers (transmitter and receiver) in order to ensure full contact and to eliminate the air 118
pocket between transducers and the test medium. The direct transmission technique, as the 119
most satisfactory and reliable method, was used in the test in which the transmitter and 120
receiver were positioned on the opposite end surfaces of the specimens tested. Repeated 121
readings at a particular location were taken and a minimum value of transit time was taken as 122
the experimental result [16]. After the measurements, the velocity of P–wave, UPV, was 123
calculated from the measured travel time and the distance between the transmitter and 124
receiver as below: 125
UPV (x,t) = x/t (Eq.1) 126
Where UPV (x,t) is the velocity of P–wave in CPB, x is the distance between the transmitter 127
and receiver and t is the travel time. 128
After UPV tests, the UCS tests [23] were performed on the same CPB samples using a 129
computer–controlled mechanical press (ELE Digital Tritest) (Fig. 1d), which had a load 130
capacity of 50 kN and a displacement speed of 0.5 mm per minute. All the experiments were 131
carried out in triplicate and the mean UPV and UCS values were presented in the results. 132
3. Results and discussion 133
3.1. Effect of binder type and dosage 134
Fig. 2 illustrates the strength and UPV of CPB samples prepared from as-received tailings 135
using CEM I 42.5 R, CEM III/A 42.5 N and SRC 32.5 at a constant binder dosage of 7 wt.%. 136
The UPV and UCSs of all the CPB samples increased over the curing time of 56 days 137
irrespective of the binder type and dosage (Figs 2a,b). CPB samples of CEM I 42.5 R 138
8
produced consistently higher UCS than those of CEM III/A 42.5 N and SRC 32.5 at all curing 139
times. CPB samples of CEM III/A 42.5 N yielded relatively low UCSs at early ages, but, with 140
the elapse of curing time, a steady increase was observed. The low early UCSs for CEM III/A 141
42.5 N could be attributed to the low heat of hydration of blast furnace slag [9]. Furthermore, 142
increasing curing time led to a reduction in the gap between the UCSs of CEM I 42.5 and 143
CEM III/A 42.5 N (Fig. 2a), which could be interrelated with the pozzolanic activity of blast 144
furnace slag [24]. In CPB practice, a 28-day UCS of 0.7-2.0 MPa is often required by mine 145
operators to be threshold for the self–supporting stopes and the mined stopes adjacent to ore 146
extraction [25]. In this regard, the CPB samples prepared from these binders at 7 wt.% dosage 147
failed to achieve a 28–day strength of 0.7 MPa, when the tailings sample was used as 148
received. 149
It is well known that as the curing time increases, CPB gains stiffness with the hydration of 150
cement phase, leading to the formation of solid products (i.e. C-S-H) that fill the pore space 151
and creates bonds between the particles of mine tailings. Self–weight consolidation and 152
evaporation of water from the CPB samples can also contribute to the development of solid 153
stiffness [18,26]. In this regard, the UPV increased as the samples cured irrespective of the 154
CPB mixture. However, the UPV of CPB samples of different binders increased by 8.3-19.4% 155
compared with 31.5-120% increase in UCSs between 7 and 56 days. These findings agree 156
well with Gesoğlu [27] who observed similar behavior for the UCS and UPV values of 157
concrete samples between 7 and 28 days. It can be inferred that compressive strength tends to 158
increase faster than UPV due to the increased stiffness and density of materials. A substantial 159
increase in the UPV of the CPB samples of CEM I 42.5 and SRC 32.5 were observed to occur 160
between 7 and 14 days. This indicates that more hydration products become connected to each 161
other at early curing periods due to the inherent chemical characteristics of CEM I 42.5 R and 162
9
SRC 32.5. Thereafter, a trend of slight increase in the UPV was observed. The UPV profiles 163
for these binders were similar in character to the corresponding UCS profiles. However, a 164
different trend of UPV was observed for CEM III/A 42.5 N in that the UPV increased linearly 165
between 7-56 days. This could be attributed to the continuing development of strength in 166
these samples i.e. the formation of hydration products is still in progress, probably linked with 167
inherently slow pozzolanic reactions. These observations are well consistent with the findings 168
of Ye et al. [28] who stated that an increase in UPV is limited after the fully connected solid 169
frame occurred in cement-based materials. It is relevant to note that UPV values in CPB 170
samples varied between 1328 and 1616 m/s at the 28–day curing period (Figs. 2-6). Various 171
researchers [9,11,29-31] measured higher (>3640 m/s) UPV values in concrete samples cured 172
for 28 days. Concrete samples have higher cement contents (≥300 kg/m3) and lower w/c ratios 173
(usually ranges between 0.3–0.6) than CPB. Additionally, the type and volume of the more 174
rigid aggregates result in high UPV of concrete samples. Therefore, the comparatively low 175
UPV values in CPB samples could be ascribed to the high void ratio due to the lower cement 176
content (82–136 kg/m3) and higher w/c ratios (3.81–6.82) (Table 2). Furthermore, CPB does 177
not contain rigid aggregate. Trtnik et al. [16] reported that binder type does not significantly 178
affect the P-wave velocity of concrete samples. In this regard, the variation of UPV and UCS 179
values in CPB samples of different binders at the same curing periods was determined to vary 180
in the range of 1–9% and 5.8-77.7%, respectively (Fig. 2). Accordingly, binder type appeared 181
to have a significant effect on the strength development of CPB while its effect on UPV is 182
insignificant. 183
As expected, the UCS and UPV values of CPB samples increased with increasing the binder 184
dosage irrespective of the curing periods (Figs. 3a,b). The CPB samples prepared at 7 wt.% 185
binder dosage had slightly greater UPV values than those of 5 wt.% binder dosage, in spite of 186
10
a marked difference observed in the compressive strength. Similar results were also found in 187
previous studies [17,31]. Mahure et al. [31] reported that an increase in the binder dosage 188
from 257 kg/m3 to 425 kg/m3 have resulted in 15% and 76% increase in the UPV and UCS of 189
concrete samples, respectively, at 28 days of curing period. Similarly, Diezd’Aux [17] 190
observed that the CPB samples prepared at 5 wt.% binder content generated approximately 191
5% higher UPV values than those prepared at 3 wt.% binder content over the same curing 192
period. The beneficial effect of increasing binder dosage on UPV and UCS can be ascribed to 193
the increase in quantity of hydration products (CH and C–S–H) with the resultant reduction in 194
void ratio and porosity [13]. Notwithstanding this, the binder dosage should be increased 195
beyond 7wt.% to achieve the required 28 day UCS of ≥0.7 MPa for CPB samples of the as-196
received tailings when the CEM III/A 42.5 N is used as the binder. 197
3.2. Effect of w/c ratio and fines content 198
It has been reported that water to cement ratio (w/c) significantly affects the strength and P-199
wave velocity (UPV) of cementitious materials [16,28,30]. Galaa et al. [18] reported that the 200
lower the w/c ratio the higher is the cementing bonds leading to a rapid strength development 201
of CPB. Lafhaj et al. [30] also demonstrated that the porosity of mortar samples increased 202
with increasing w/c ratio with the resultant reduction in the UPV values. In agreement with 203
these studies, CPB mixtures with a lower w/c ratio had higher UPV and UCS values (Figs. 204
4a,b). This could be ascribed to the higher solid volume fraction and lower porosity and void 205
ratios of the mixtures with lower w/c ratios [24,28]. The CPB samples prepared at 4.62 w/c 206
ratio were observed to develop consistently 1.06–1.10 and 1.18–1.26 times higher UPV and 207
UCSs than those at 5.13 w/c ratio, respectively. These findings suggest that the UPV is less 208
sensitive to w/c ratio changes. It is pertinent to note that those CPB samples prepared from the 209
11
as-received tailings failed to produce a 28-day UCS of ≥0.7 MPa even at the lowest w/c ratio 210
of 4.62 tested. 211
Fig. 5 indicates that decreasing the fines content (<20 µm) resulted in an increase in the UPV 212
and UCS of CPB samples at all curing periods. Like compressive strength, there was a 213
systematic increase in the UPV values of CPB samples with increasing curing time being 214
more distinct particularly at 28 and 56 days. Additionally, the CPB samples of the deslimed 215
tailings produced higher UPV and UCS values (by 1.07-1.2 and 1.22-1.28 fold, respectively) 216
than those of reference tailings at the same curing periods (Figs 5a,b). In contrast to the binder 217
type, dosage and w/c ratio, the UPV appears to be more sensitive to fines content (<20 µm). 218
The quantity of pores in a CPB sample has been reported to increase with increasing fines 219
content (<20 µm) of the tailings [32,33]. Singh and Kripamoy [34] and Karaman et al. [35] 220
have also indicated that UPV decreases with increasing silicate minerals (i.e. mica, clay, 221
quartz), which is presumably due to the water retention potential of these minerals [25]. 222
Furthermore, Ercikdi et al. [36] demonstrated that CPB samples produced from coarse tailings 223
release more water (by drainage) than those of medium or fine tailings. The loss of water by 224
drainage leads to the settling of the paste backfill (increasing of the packing density) and the 225
consequent reduction of total porosity and void ratio of the backfill material [32]. In this 226
regard, the comparatively high UPV and UCSs in CPB samples of the deslimed tailings can 227
be attributed to their lower water retention capacity (i.e. lower water–to–cement ratio) mainly 228
due to its lower silicate (SiO2+Al2O3) content (26.6% c.f. 32.5% for the as-received tailings) 229
and fines content (35.0% c.f. 58.4% for the as-received tailings) (Table 1). 230
Wichtmann and Triantafyllidis [37] investigated the effect of grain size distribution curve on 231
UPV of quartz sand and found that UPV decreases with increasing the coefficient of 232
12
uniformity (Cu) due to the improvement in the gradation of sand. Similarly, Trtnik et al. [16] 233
observed that UPV increased with increasing the aggregate content. The high UPV and UCS 234
values in CPB samples of the deslimed tailings can be also linked with their higher solids 235
content (80.17%), lower w/c ratio (3.81) and lower coefficient of uniformity (Cu=6.54) of the 236
deslimed tailings (Table 1 and 2). Consistent with these findings, the highest UPV (1821 m/s) 237
was obtained from the deslimed CPB samples over a curing period of 56 days. Moreover, 238
only the CPB samples of the deslimed tailings produced the desired 28-day UCS of ≥0.7 MPa. 239
3.3. Relationship between UCS and UPV 240
There are a number of empirical equations developed between UPV and UCS for concrete in 241
the literature [9,16,31]. In the current study, the relationship between UPV and UCS of the 242
CPB samples was sougth after by using simple regression analysis. Linear (y= ax+b), 243
logarithmic (y= a+ Inx), exponential (y= aex) and power (y= ax
b) curve fitting 244
approximations were undertaken. Fig.6 represents the relationship between UPV and UCS for 245
all CPB samples (96 specimens) regardless of the composition of the material. As shown in 246
Fig. 6, the UPV increased with increasing UCS irrespective of the mixture properties (i.e. 247
binder type, w/c ratio).The plots of UPV versus UCS in Figs. 7-10 show that there is a linear 248
relationship between the UCS and UPV for all CPB samples. A relatively high correlation 249
coefficient of 0.86 was found (Eq. 2) when all the UCS and UPV results obtained from CPB 250
samples (96 specimens). Compared with all CPB specimens, lower correlation coefficient of 251
0.83 was found (Eq. 3) when all the mean UCS and UPV results obtained from CPB samples 252
of different binders were taken into account (Fig. 7a). However, a higher correlation 253
coefficients for a particular set of data e.g. data collected from the same binder type (Fig. 7b), 254
binder dosage (Fig. 8b), w/c ratios (Fig. 9b) and fines content (<20 µm) (Fig. 10b) were 255
obtained. Taking into account all the average UCS and UPV results obtained from CPB 256
13
samples for different binder types (Eq. 3) (Fig. 7a), dosages (Eq. 4) (Fig. 8a), w/c ratios (Eq. 257
5) (Fig. 9a) and fines content (Eq. 6) (Fig. 10a), the following general equations were 258
determined, respectively: 259
UCS = 0.0011UPV - 1.0397 (r=0.86) (Eq.2) 260
UCS = 0.0015UPV - 1.5151 (r=0.83) (Eq.3) 261
UCS = 0.0013UPV - 1.3212 (r=0.90) (Eq.4) 262
UCS = 0.0014UPV - 1.3917 (r=0.94) (Eq.5) 263
UCS = 0.0009UPV - 0.7190 (r=0.92) (Eq.6) 264
Although the high correlation coefficients (r value) were found for the obtained equations, 265
they do not necessarily indicate the goodness-of-fit of these equations. Thus, t- and F tests 266
were conducted in order to check the validity of these equations. The t-test compares the 267
computed values with tabulated values using null hypothesis. According to the t-test, when 268
computed t value is greater than tabulated t-value, the null hypothesis is rejected and obtained 269
correlation coefficient (r-value) is acceptable. The significance of the regressions was 270
determined by analysis of variance (F-test). In these tests, a 95 per cent level (p<0.05) of 271
confidence was chosen. As seen in Table 3, the computed t and F values are greater than the 272
tabulated t and F values, indicating the significance of r values and the validity of the derived 273
equations. In this regard, these empirical equations (Eqs. 2-6) can provide an estimate of the 274
UCS of CPB samples using UPV data. 275
Conclusions 276
In this study, the effect of binder type/dosage, water to cement ratio and fines content (<20 277
µm) of the tailings on the mechanical and ultrasonic properties of CPB samples produced 278
14
from mill tailings was evaluated. CPB samples prepared at different mixture properties were 279
subjected to UPV and UCS tests at 7, 14, 28 and 56 days of curing periods. A change in 280
mixture properties was observed to produce a significant effect on the UCS development of 281
CPB samples, whilst, its effect on UPV was relatively low. CPB samples of CEM I 42.5 and 282
SRC 32.5 demonstrated similar UCS and UPV behavior at a given curing time while those of 283
CEM III A 42.5 N exhibited a different trend apparently due to the inherent hydration 284
characteristics of this binder. Strength and ultrasonic properties of CPB samples increased 285
with increasing the binder dosage (5 to 7 wt.%) or reducing the w/c ratio (5.13 to 4.62) and 286
fines content (58.4% to 35.0% finer than 20 µm). The strength development and ultrasonic 287
properties of CPB samples were found to be highly sensitive to the fines content (<20 µm) of 288
the tailings. Only the CPB samples of the deslimed tailings prepared at 7 wt.% binder dosage 289
were able to achieve the 28–day UCS of ≥0.7 MPa. A linear correlation between the UCS and 290
corresponding UPV values was obtained at a particular mixture property (i.e. binder dosage, 291
w/c ratio). Furthermore, the relationship between the UPV and corresponding UCS values 292
was acceptable according to the statistical analysis by t- and F-tests. These findings suggest 293
that the UPV test as a low-cost, less time consuming and practical method can be reliably 294
used to predict the UCS of CPB samples. 295
Acknowledgement 296
The authors would like to express their sincere thanks and appreciation to the EtiBakır A.S., 297
for the material and financial support and, to Prof. Dr. Hacı Deveci and Associate Prof. Dr. 298
Gülten Yaylalı Abanuz for improving paper quality. 299
15
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394
395
396
19
397
398
399
400
LIST OF FIGURES 401
Figure 1. Preparation and testing of CPB samples: tailings collection (a); mixing (b); UPV 402
tests (c) and UCS tests (d). 403
Figure 2. Effect of binder type on the strength (a) and ultrasonic (b) properties of CPB 404
samples prepared from the as-received tailings at a fixed binder dosage. 405
Figure 3. Effect of binder dosage on the strength (a) and ultrasonic (b) properties of CPB 406
samples prepared from the as-received tailings. 407
Figure 4. Effect of w/c ratio on the strength (a) and ultrasonic (b) properties of CPB samples 408
prepared from the as-received tailings. 409
Figure 5. Effect of fines content (<20 µm) on the strength (a) and ultrasonic (b) properties of 410
CPB samples prepared from the deslimed tailings. 411
Figure 6. Relationship between UCS and UPV for all CPB samples (96 specimens) 412
Figure 7. Relationship between UCS and UPV for CPB samples produced from all (a) and 413
each (b) binders at 7 wt.% binder dosage. 414
Figure 8. Relationship between UCS and UPV for CPB samples produced from all (a) and 415
each (b) binder dosages. 416
Figure 9. Relationship between UCS and UPV for CPB samples produced from all (a) and 417
each (b) w/c ratios. 418
Figure 10. Relationship between UCS and UPV for CPB samples produced from all (a) and 419
each (b) fines content (<20 µm). 420
20
Fig. 1 421
(a) (b)
(c) (d)
21
Fig. 2 422
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 14 28 42 56
Com
pres
sive
str
engt
h (M
Pa)
Curing time (days)
CEM I 42.5 R CEM III/A 42.5 N SRC 32.5
1200
1300
1400
1500
1600
0 14 28 42 56
P-
wav
e ve
loci
ty (
m/s
)
Curing time (days)
CEM I 42.5 R CEM III/A 42.5 N SRC 32.5
(a)
(b)
22
Fig. 3 423
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 14 28 42 56
Com
pres
sive
str
engt
h (M
Pa)
Curing time (days)
5 wt. % 6 wt. % 7 wt. %
1100
1200
1300
1400
1500
1600
0 14 28 42 56
P-
wav
e ve
loci
ty (
m/s
)
Curing time (days)
5 wt. % 6 wt. % 7 wt. %
(a)
(b)
23
Fig. 4 424
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 14 28 42 56
Com
pres
sive
str
engt
h (M
Pa)
Curing time (days)
w/c: 4.62 w/c: 4.87 w/c: 5.13
1100
1200
1300
1400
1500
1600
1700
0 14 28 42 56
P-
wav
e ve
loci
ty (
m/s
)
Curing time (days)
w/c: 4.62 w/c: 4.87 w/c: 5.13
(a)
(b)
24
Fig. 5 425
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 14 28 42 56
Com
ress
ive
stre
ngth
(MP
a)
Curing time (days)
As-received Deslimed
1100
1200
1300
1400
1500
1600
1700
1800
1900
0 14 28 42 56
P-
wav
e ve
loci
ty (
m/s
)
Curing time (days)
As-received Deslimed
(a)
(b)
25
Fig. 6 426
UCS = 0.0011UPV - 1.0397r= 0.86
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1100 1200 1300 1400 1500 1600 1700 1800 1900
UC
S (
MP
a)
UPV (m/s)
26
Fig. 7 427
UCS = 0.0015UPV - 1.5151r= 0.83
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1200 1300 1400 1500 1600
UC
S (
MP
a)
UPV (m/s)
CEM I 42.5 R
UCS = 0.0013UPV - 1.1473r = 0.98
CEM III/A 42.5 N
UCS = 0.0013UPV - 1.3370r= 0.94
SRC 32.5
UCS = 0.0011UPV - 1.0318r = 0.99
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1200 1300 1400 1500 1600
UC
S (
MP
a)
UPV (m/s)
(a)
(b)
27
Fig. 8 428
UCS = 0.0013UPV - 1.3212r= 0.90
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1100 1200 1300 1400 1500 1600
UC
S (
MP
a)
UPV (m/s)
5 wt.%
UCS = 0.0009UPV - 0.817r= 0.97
6 wt.%
UCS = 0.001UPV - 0.9699r= 0.93
7 wt.%
UCS = 0.0013UPV - 1.337r= 0.94
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1150 1250 1350 1450 1550 1650
UC
S (
MP
a)
UPV (m/s)
(a)
(b)
28
Fig. 9 429
UCS = 0.0014UPV - 1.3917r= 0.94
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1150 1250 1350 1450 1550 1650
UC
S (
MP
a)
UPV (m/s)
(a)
(b)
w/c=4.87
UCS = 0.0013UPV - 1.337r= 0.94
w/c= 4.62
UCS = 0.0015UPV - 1.5676r= 0.96
w/c= 5.13
UCS = 0.0016UPV - 1.6286r= 0.94
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1150 1250 1350 1450 1550 1650
UC
S (
MP
a)
UPV (m/s)
(b)
29
Fig. 10 430
431
UCS= 0.0009UPV- 0.7190r= 0.92
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1150 1350 1550 1750 1950
UC
S (
MP
a)
UPV (m/s)
As-received
UCS = 0.0013UPV - 1.3386r= 0.94
Deslimed
UCS = 0.0008UPV - 0.6827r= 0.93
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1150 1350 1550 1750 1950
UC
S (
MP
a)
UPV (m/s)
(a)
(b)
30
LIST OF TABLES 432
Table 1. Chemical, physical and mineralogical properties of tailings and binders. 433
Table 2. A summary of the experimental conditions used in the preparation of CPB samples. 434
Table 3. Results of t and F tests for the linear models obtained for the relationships between 435
the UCS and UPV 436
31
Table 1. 437
D30= Particle size at 30% passing 438
Characteristics
Tailings
As-received
(%)
Deslimed Tailings
(%)
CEM I 42.5 R (%)
CEM III/A 42.5 R (%)
SRC 32.5 (%)
Chemical composition
SiO2 25.80 21.21 20.57 27.58 20.88 Al2O3 6.68 5.42 4.81 7.04 3.84 Fe2O3 39.83 45.43 3.67 2.37 4.52 MgO 2.14 2.21 1.35 3.91 1.49 SO3 - - 2.97 2.91 2.84 CaO 2.79 1.64 65.27 52.75 64.56 Na2O 0.35 0.24 0.41 0.25 0.31 K2O 0.42 0.31 0.85 1.06 0.67 TiO2 0.43 0.38 0.45 0.40 0.33 P2O5 0.03 0.03 0.13 0.03 0.10 MnO 0.06 0.05 0.11 1.00 0.12 Cr2O3 0.02 0.017 0.075 0.015 0.177 Free CaO - - 1.19 - 0.43 Loss–on–ignition (LOI) 20.6 21.9 2.1 2.8 2.8 Total 99.15 98.84 99.90 99.21 99.87
Sulphide content (S-2) (%) 23.18 27.82 - - -
Pyrite content (FeS2) (%) 43.47 52.16 - - -
Physical properties Specific gravity (g/cm3) 3.66 3.81 3.14 3.08 3.27 Specific surface area (cm2/g) 4630 1810 4335 4260 3170 Coefficient of curvature (Cc=(D30)2/(D10 ×D60)
0.99 1.17 - - -
Coefficient of uniformity (Cu=(D60/D10)
11.00 6.54 - - -
Fines content (<20 µm) ( %) 58.40 35.00 - - - Mineralogical properties
Pyrite Quartz
Chlorite Calcite
Muscovite Albite
Pyrite Quartz
Chlorite Calcite
Ankerite
C3S: 58.44 C2S: 14.95 C3A: 6.54
C4AF: 11.16
- C3S: 61.96 - C2S: 13.18 - C3A: 2.54 - C4AF:13.74
32
Table 2. 439
Tailings
type
Solids content,
(SC)1, wt%
Binder dosage
(BD)2, wt%
Water to cement ratio
(w/c)3
Slump
(cm)
Binder dosage
74.58 5 6 7
6.82 19.05 As-received 5.68
4.87
Water to cement ratio 75.58
7 4.62 16.51
As-received 74.58 4.87 19.05 73.58 5.13 21.59
Binder type
As-received 74.58 7 4.87 19.05
Fines content (<20 µm) Deslimed 80.17 7 3.81 19.05
1
)(
)(100:
waterbinderdrytailingsdry
binderdrytailingsdry
MMM
MMxSC
++
+
−−
−−
; 2
)
)(100:
tailingsdrybinderdry
binderdry
MM
MxBD
−−
−
+
; 3
binderdry
water
M
Mcw
−
:/ ; (M: Weight) 440
33
Table 3. 441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
Parameter Correlation
coefficient (r) tcomputed ttabulated Fcomputed Ftabulated Equation number
Total (96 specimens) 0.86 108.649 ±1.664 11778.478 1.592 (2)
Binder type 0.83 4.586 ±1.80 21.029 2.82 (3)
Binder dosage 0.90 6.502 ±1.80 42.278 2.82 (4)
w/c ratio 0.94 8.814 ±1.80 77.684 2.82 (5)
Fines content (<20µm) 0.92 5.697 ±1.90 32.453 3.79 (6)
34
460
461
462
463
464
465
HIGHLIGHTS 466
►Desliming significantly affects the UPV and UCS properties of CPB. ►Binder type plays 467 an important role for UCS and UPV of CPB ►The UPV of CPB increases with increasing 468 binder dosage and reducing w/c ratio. ►There is a linear relation between UCS and UPV of 469 CPB. ►The UCS of CPB can be estimated by ultrasonic UPV test. 470
471 472
Recommended