1
Li and Rangaraju
Effect of Sand Content on the Properties of Self-Consolidating High 1
Performance Cementitious Mortar 2
3
Zhengqi Lia
4
Graduate Student 5
Glenn Department of Civil Engineering 6
Clemson University 7
Clemson, SC 29634 8
E-mail: [email protected] 9
Tel: (864)633-9882; 10
11
Prasada Rao Rangarajub*
12
Associate Professor 13
Glenn Department of Civil Engineering 14
Clemson University 15
Clemson, SC 29634 16
E-mail: [email protected] 17
Tel: (864)-656-1241 18
19
20
21
22
23
24
Corresponding Author: Prasada Rao Rangaraju, e-mail: [email protected] 25
26
Initial Manuscript Submission date: 8/1/2014 27
Revised Manuscript Submission date: 10/31/2014 28
Word count: 5087 + 9 Tables/Figures x 250 words (each) = 7337 words 29
30
31
2
Li and Rangaraju
ABSTRACT 32
The workability and compressive strength of a high performance cementitious mortar (HPCM) produced using a 33
natural siliceous sand were studied as a function of sand content (expressed as sand-to-cementitious materials ratio – 34
s/cm), silica fume (SFU) content and high-range water reducing admixture (HRWRA) dosage. The purpose of this 35
study is to maximize the sand content without negatively affecting workability, mechanical and durability properties, 36
while achieving these characteristics at a low cost. An index (Flow Reduction Factor – 𝑅𝑠/𝑐𝑚) was introduced to 37
reveal the sensitivity of the workability of HPCMs to the changes in the sand content. The test results indicated 38
that the workability of HPCM became less sensitive to sand content when the SFU content increased. Statistical 39
analysis was used to study the effect of increasing the sand content on the compressive strength of HPCMs. Rapid 40
chloride ion penetration (RCP) and drying shrinkage tests were conducted to investigate the effect of sand content 41
on the durability of HPCM without SFU. The compressive strength of self-consolidating HPCM was not 42
significantly impacted by sand content up to a certain maximum level, depending on the HRWRA and SFU dosage. 43
In this study, based on a combined consideration of both workability and compressive strength the maximum sand 44
content that can be used to produce a self-consolidating HPCM without SFU was 1.6 (s/cm ratio), and the maximum 45
sand content for producing a self-consolidating HPCM with SFU content at 10% and 20% was 1.6 and 2.0, 46
respectively. Also, a HRWRA dosage of 1% by weight of cementitious materials was found to be optimal to 47
maximize the sand content in the HPCM. Increasing the sand content was helpful in improving the durability of 48
HPCM, as chloride ion permeability and drying shrinkage decreased. 49
50
Keyword: Self-consolidating HPCM; Maximum sand content; Workability; Compressive strength; RCP; Drying 51
shrinkage 52
3
Li and Rangaraju
INTRODUCTION 53
54
Self-consolidating high performance cementitious mortar (HPCM) has been increasingly adopted as a pour-in-grout 55
for construction of shear keys in precast bridges. With good workability, self-consolidating HPCM is able to flow 56
into restricted spaces and consolidate well under its self-weight without segregation. It is preferable to use HPCM in 57
the application where narrow formwork and dense reinforcement are inevitable. 58
Self-consolidating HPCM commonly consists of cement, sand (fine aggregate), supplementary 59
cementitious material (SCM), and high range water reducing admixture (HRWRA). In the context of present 60
investigation, HPCM is characterized by low water-cementitious materials ratio (w/cm from 0.2 to 0.35), high 61
content of HRWRA and SCM, which are considered essential for achieving superior workability, compressive 62
strength and durability (1-3). 63
Low w/c and high content of HRWRA produce HPCM with a sticky consistency even at high workability, 64
which is different from normal cementitious mixtures (1; 4; 5). Such a sticky paste reduces the chance of 65
segregation (5-7). Low w/c also decreases the risk of segregation by lowering the difference in density between sand 66
and paste (8). Silica fume (SFU) is one of the widely used SCMs in HPCM formulations. Its super fine particles and 67
pozzolanic reactivity improve the compressive strength and durability of HPCM significantly (1-3). SFU is able to 68
reduce bleeding and increase the cohesiveness of mortar mixtures (4). Many studies also showed that HPCM with 69
SFU has improved fluidity (4; 9; 10), despite that SFU has large specific surface area. For example, a study on the 70
rheology of cementitious paste found that for mixtures in which less than 10% of cement was replaced by equal 71
volume of SFU the viscosity of paste decreased as the silica fume content increased when polyacrylate based 72
HRWRA was used(10). This was explained by the packing of SF particles between cement grains which displaced 73
water and by a ball-bearing effect of silica spheres (10). Sand is another component of mortar. The particle angularity, 74
shape and gradation of sand influence the workability and compressive strength of formulated mortar (1; 11). A 75
comprehensive study on the effect of sand content on the properties of normal strength mortar showed that 76
increasing sand content decreased the workability of mortar, and the increasing sand content might increase or 77
decrease the compressive strength which depended on the use of HRWRA (12). 78
It should be noted that, in many of the previous studies related to HPCM, the investigations have focused 79
on studying the influence of w/cm, SCM dosage and HRWRA dosage on various properties of HPCM. However, 80
there is limited information on the influence of sand content on the fresh and hardened state properties of 81
self-consolidating HPCM. Considering the economic benefit of increasing the sand content in the production of 82
self-consolidating HPCM, it is important to have a detailed knowledge on this topic. 83
The study was carried out in two stages. In the first stage, the workability and compressive strength of 84
HPCMs were studied as a function of sand content, SFU content, and HRWRA dosage. In this study, the sand 85
content of a mixture was quantified as sand-to-cementitious materials ratio (s/cm). An index – Flow Reduction 86
Factor, 𝑅𝑠/𝑐𝑚 was introduced to reveal the sensitivity of the workability of HPCMs to the changes in s/cm. 87
Statistical analysis was conducted to study the effect of increasing s/cm on the compressive strength of HPCMs. A 88
combined consideration of both workability and compressive strength of HPCM was applied to determine the 89
maximum s/cm for the self-consolidating HPCM both with and without SFU. In the second stage of the study, rapid 90
chloride ion penetration (RCP) and drying shrinkage tests were conducted to investigate the effect of s/cm on the 91
durability of HPCM without SFU. 92
93
4
Li and Rangaraju
EXPERIMENTAL PROGRAM 94
95
Materials 96
Type III portland cement meeting ASTM C150 specification was used for HPCM formulation. The principal oxide 97
composition of cement was as follows: CaO - 64.4%, SiO2 - 20.4%, Al2O3 - 6%, Fe2O3 - 3.5%, Na2Oeq - 0.49% and 98
SO3 - 3.5%. The specific surface area of cement was 540m2/kg. 99
In this study, the SFU was a white-colored silica fume with a low loss on ignition value of 0.22% and SiO2 content 100
of 92%. It was used as an SCM in addition to cement, not as a cement replacement material. The specific surface 101
area of SFU determined by BET method was 20000m2/kg. The sand used in this study was round natural siliceous 102
sand meeting the gradation specification in ASTM C33 for fine aggregates. The gradation of fine aggregate is shown 103
in Table 1. The specific gravity, water absorption, and fineness modulus of the sand were 2.62, 0.3%, and 2.65, 104
respectively. A polycarboxylic ether based HRWRA in a powder form was used to make workable HPCM. 105
106
Table 1 Gradation of fine aggregate 107
Sieve Percent Passing
9.5-mm 100.0
4.75-mm 99.8
2.36-mm 97.1
1.18-mm 82.0
600-µm 41.9
300-µm 14.0
150-µm 0.5
75-µm 0.1
108
Mixture proportions 109
Thirty seven different HPCMs were produced in this investigation to carry out experiments in order to study the 110
influence of sand content on the fresh and hardened state properties of HPCM at various SFU and HRWRA contents. 111
SFU was proportioned at three levels, 0%, 10%, and 20% by weight of cement. The HRWRA was dosed at four 112
levels - 0.5%, 0.75%, 1%, and 1.5% by weight of cementitious material. Sand content, expressed as s/cm ratio by 113
weight, of the mixtures was studied at 0, 0.5, 1.25, 1.6, and 2. For the entire study, the w/cm by weight was fixed at 114
0.20. No coarse aggregate was used in this study. The identifications of HPCMs (HPCM ID) are listed in Table 2. 115
116
117
5
Li and Rangaraju
TABLE 2 Identifications of HPCMs 118
SFU HRWRA s/cm (level)
Content (%) level Dosage (%) level 0(1st) 0.5(2
nd) 1.25(3
rd) 1.6(4
th) 2(5
th)
0 C
0.5 1st C1-1 C1-2 C1-3 - -
0.75 2nd
C2-1 C2-2 C2-3 C2-4 -
1 3rd
C3-1 C3-2 C3-3 C3-4 C3-5
1.5 4th
C4-1 C4-2 C4-3 C4-4 C4-5
10 L 0.75 2
nd L2-1 L2-2 L2-3 L2-4 L2-5-
1 3rd
L3-1 L3-2 L3-3 L3-4 L3-5
20 H 0.75 2
nd H2-1 H2-2 H2-3 H2-4 H2-5-
1 3rd
H3-1 H3-2 H3-3 H3-4 H3-5
Note: For HPCM ID, the letter in the front indicates the SFU content (C:0%, L:10%, and H:20%). The following two numbers, i-j, 119
indicate dosage level of HRWRA and s/cm, respectively. For example, L2-3 indicates HPCM with 10% SFU, the second level of 120
HRWRA dosage which is 0.75%, and the third level of s/cm which is 1.25; - Data unavailable. The dashed line in the table 121
represents the distinction between mixtures that were flowable (to the left) and non-flowable (to the right). 122
123
The detailed mixing proportions of selected HPCMs are shown in Table 3. 124
125
TABLE 3 Mixing proportions for 1 m3 of selected HPCMs 126
HPCM ID Constituent (kg)
HPCM ID Constituent (kg)
Cement SFU FA Water HRWRA Cement SFU FA Water HRWRA
C1-1 1933 0 0 387 9.7 L2-3 904 90 1244 203 7.5
C1-2 1413 0 707 285 7.1 L2-4 799 80 1406 180 6.6
C1-3 1007 0 1259 205 5.0 L2-5 705 70 1550 160 5.8
C2-1 1933 0 0 387 14.5 L3-1 1716 172 0 377 18.9
C2-2 1413 0 707 285 10.6 L3-2 1263 126 694 280 13.9
C2-3 1007 0 1259 205 7.6 L3-3 904 90 1244 203 9.9
C2-4 888 0 1421 182 6.7 L3-4 799 80 1406 180 8.8
C3-1 1933 0 0 387 19.3 L3-5 705 70 1550 160 7.7
C3-2 1413 0 707 285 14.1 H2-1 1542 308 0 370 13.9
C3-3 1007 0 1259 205 10.1 H2-2 1141 228 685 276 10.3
C3-4 888 0 1421 182 8.9 H2-3 821 164 1231 201 7.4
C3-5 783 0 1565 161 7.8 H2-4 725 145 1393 178 6.5
C4-1 1933 0 0 387 29.0 H2-5 641 128 1538 158 5.8
C4-2 1413 0 707 285 21.2 H3-1 1542 308 0 370 18.5
C4-3 1007 0 1259 205 15.1 H3-2 1141 228 685 276 13.7
C4-4 888 0 1421 182 13.3 H3-3 821 164 1231 201 9.8
C4-5 783 0 1565 161 11.7 H3-4 725 145 1393 178 8.7
L2-1 1716 172 0 377 14.2 H3-5 641 128 1538 158 7.7
L2-2 1263 126 694 280 10.4
127
6
Li and Rangaraju
Specimen preparation 128
Fresh HPCMs were prepared by using a UNIVEX M20 planetary mixer. At first, the cementitious materials, sand, 129
and HRWRA were dry mixed for 3 min at low speed (about 100 RPM), followed by the addition of mixing water. 130
The mixing continued at low speed for 4 or 5 min until the mixture became flowable. Finally, the flowable mixtures 131
were mixed for another 2 min at medium speed (about 300 RPM). The entire mixing process lasted for about 10 min. 132
Then, the flow test was conducted immediately. 133
Fresh mixture was poured into molds to prepare specimens for the test of hardened properties of HPCM. 134
Flowable HPCMs were allowed to consolidate in the molds under self-weight. However, for the other HPCMs 135
which were not able to flow, they were consolidated under external vibration for about 30 s. After casting, specimens 136
were kept in the moist room which was setup in accordance with ASTM C511. Specimens were de-molded 24 hr. 137
later. For the study of compressive strength and RCP, the specimens were stored in the moist room until right before 138
conducting the test. For the study of drying shrinkage, the specimens were stored following the procedures in ASTM 139
C596. 140
141
Test methods 142
143
Workability 144
The method to determine the flow of mortar in ASTM C1437 was slightly modified for self-consolidating HPCM. 145
The fresh HPCM was allowed to spread freely on a level plastic plate, instead of being dropped on a flow table for 146
25 times. When the mixture stopped spreading (about 5 min after the removal of the flow mold) the diameter of the 147
mixture was measured for calculating the flow described in ASTM C1437. 148
149
Compressive strength 150
Compressive strength of each HPCM was determined by testing three 50×50×50 mm cubes at the ages of 1 and 28 151
days. The compressive strength test was conducted in accordance with procedures in ASTM C109. 152
153
Rapid Chloride Ion Permeability 154
Two cylindrical specimens with diameter of 100 mm and height of 50 mm were prepared by sawing sections from a 155
cylinder with diameter of 100 mm and height of 200 mm. ASTM C1202 was followed for RCP test at the age of 28 156
days. 157
158
Drying shrinkage 159
Three specimens with dimensions of 25×25×285 mm were prepared for each of the studied HPCM. Length 160
comparator reading of each specimen stored in the environmental chamber was taken at selected ages, in accordance 161
with ASTM C596. Inside the environmental chamber, the temperature and the relative humidity was maintained at 162
23±2 oC and 50±4%, respectively, which was in accordance with ASTM C157. 163
164
TEST RESULTS AND DISCUSSIONS 165
166
Workability 167
168
7
Li and Rangaraju
Workability of HPCM without SFU 169
The flow of HPCMs without SFU is presented in Figure 1a. Each of the four curves in Figure 1a indicates the effect 170
of increasing sand content on the workability of HPCM at a constant HRWRA dosage. It can be observed that when 171
the HRWRA dosage was fixed the workability of HPCMs decreased as the sand content increased, which was the 172
expected behavior (12). It also can be observed that when the sand content was kept constant, increased HRWRA 173
dosage increased the workability of HPCMs. However, when the HRWRA dosage was higher than a certain level, 174
the workability of HPCMs did not show significant increase. For example, by comparing HPCMs with s/cm at 1.25 175
(HPCM C1-3, C2-3, C3-3, and C4-3), it can be observed that the flow of HPCM with HRWRA dosage at 0.75%, 1%, 176
and 1.5% was 125%, 263%, and 275% higher than that with HRWRA dosage at 0.5%, respectively. The rise in 177
HRWRA dosage from 1% to 1.5% only caused minimal increase in the workability of HPCM. A dosage of HRWRA 178
beyond which minimal increase in workability is observed is known as saturation dosage (13). In this study, the 179
saturation HRWRA dosage was determined to be 1%, and therefore a HRWRA dosage of 1.5% may be considered 180
as an overdose. 181
The results from flow tests indicated that the workability of HPCM without SFU is affected by the 182
combination of sand content and HRWRA dosage. The workability of HPCM can be increased through either 183
reducing the sand content at a fixed HRWRA dosage or by increasing HRWRA dosage at a fixed sand content. 184
However, the former approach is not economically preferable since manufacturers want more sand in HPCM to 185
reduce the cost. The latter approach also has its limitation, since excessive HRWRA dosage does not increase the 186
workability much further but causes other problems such as segregation and delayed setting (1; 5; 7). For 187
economical self-consolidating HPCM, a balance would probably be reached by finding out the maximum sand 188
content when HRWRA was dosed at the saturation dosage. 189
It should be noted that HPCMs with flow value ranging from 44% to 56% (HPCM C1-3, C2-4, C3-5, and 190
C4-5) had poor workability. They were not considered self-consolidating HPCMs, because external vibration was 191
required during casting the specimens for compressive strength test. Other HPCMs were assumed to be 192
self-consolidating HPCMs, because they exhibited flowable workability and seemed to be able to consolidate well 193
under self-weight. As Figure 1a shows, when the HRWRA was dosed at saturation dosage (1%), the maximum sand 194
content for flowable HPCM without SFU was s/cm=1.6. 195
196
Workability of HPCM with SFU 197
The workability of HPCMs with various SFU contents was studied at two HRWRA dosages, 0.75% and 1%. The 198
flow values are presented in Figure 1b and 1c, respectively. 199
Similar trends were observed for HPCM with SFU when compared with HPCM without SFU, in which the 200
increasing sand content reduced the workability of HPCM at both HRWRA dosages. When the HRWRA dosage was 201
0.75% (Figure 1b), the maximum sand content at which the HPCM without SFU remained flowable was s/cm=1.25, 202
and the maximum sand content at which the HPCM with SFU content at either 10% or 20% remained flowable was 203
s/cm=1.6. When the HRWRA dosage was 1% (Figure 1c), the maximum sand content at which the HPCM without 204
SFU remained flowable was s/cm=1.6, and the maximum sand content at which the HPCM with SFU content at 10% 205
and 20% remained flowable was s/cm=1.6 and s/cm=2, respectively. These HPCMs consolidated under self-weight 206
during casting and needed no external vibration. In mixtures with sand content exceeding the maximum s/cm ratios 207
(i.e. HPCM C2-4, L2-5, H2-5, C3-5, and L2-5), the workability was observed to be poor, indicated by flow values 208
ranging from 32% to 50%. For these HPCMs external vibration was applied during casting. 209
8
Li and Rangaraju
It should be mentioned that among all the flowable HPCMs, the HPCM H3-5 mixture has the lowest flow 210
value (i.e. 69%) that did not require any external vibration to consolidate. Therefore, based on these observations, 211
a flow value of 69% (about 70%) is considered as a minimum threshold value that distinguished non-flowable 212
HPCMs from flowable HPCMs. Figure 1 shows a threshold line marked at 69. HPCMs that were non-flowable were 213
subjected to external vibration during casting of the specimens for compressive strength test. 214
Both Figure 1b and 1c show that SFU seemed to be helpful in improving the workability of HPCM. The 215
effect of SFU in rendering the workability of HPCM less sensitive to the changes in sand content is discussed later. 216
(a)
(b) (c)
FIGURE 1 Flow of HPCMs: (a) HPCMs without SFU, (b) HPCMs with SFU (HRWRA dosage
at 0.75%), and (c) HPCMs with SFU (HRWRA dosage at 1%). The horizontal dashed line
delineates flowable versus non-flowable mixtures.
217
Sensitivity of workability to changes in sand content 218
An index (𝐹𝑙𝑜𝑤 𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟) 𝑅𝑠/𝑐𝑚 was introduced to understand the effect of SFU on the changes in the 219
workability of HPCM in response to the changes in the sand content. 𝑅𝑠/𝑐𝑚 was defined as the ratio of the 220
reduction of flow to the increase in s/cm, see equation (1). 221
𝑅𝑠/𝑐𝑚 =𝐹0−𝐹𝑠/𝑐𝑚
𝑠/𝑐𝑚−0 (1) 222
0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5
Flo
w (
%)
s/cm
HRWRA:0.5%
HRWRA:0.75%
HRWRA:1.0%
HRWRA:1.5%
0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5
Flo
w (
%)
s/cm
SFU:0%
SFU:10%
SFU:20%
0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5
Flo
w (
%)
s/cm
SFU:0%
SFU:10%
SFU:20%
9
Li and Rangaraju
Where 223
𝐹0 is the flow of HPCM with sand content at 0 224
𝐹𝑠/𝑐𝑚is the flow of HPCM with sand content at s/cm 225
𝑠/𝑐𝑚 is the sand-cementitious material ratio of HPCM 226
For example, 𝑅𝑠/𝑐𝑚 of HPCM L3-4 (SFU=10%; HRWRA dosage=1%; s/cm=1.6) was calculated as follow, 227
𝑅1.6 =275% − 131.3%
1.6 − 0= 89.8%
The value of 𝑅𝑠/𝑐𝑚 indicated how sensitive the workability of HPCM was to the changes in sand content. 228
The calculated 𝑅𝑠/𝑐𝑚 of HPCMs are shown in Figure 2a and 2b. 229
(a) (b)
FIGURE 2 Calculated 𝑹𝒔/𝒄𝒎 of HPCM: (a) HRWRA dosage at 0.75% and
(b) HRWRA dosage at 1%
230
It can be noticed from Figure 2a that when the HRWRA dosage was 0.75%, 𝑅𝑠/𝑐𝑚 decreased with the 231
increasing addition of SFU at all s/cm levels. For example, when the sand content was at s/cm=1.25, 𝑅𝑠/𝑐𝑚 of 232
HPCM with SFU content at 0%, 10%, and 20% was 115%, 80%, and 50%, respectively. This indicated that the 233
workability of HPCM became less sensitive to the increased sand content as the SFU content increased. When the 234
HRWRA dosage was 1.0% (see Figure 2b), 𝑅𝑠/𝑐𝑚 of HPCM with SFU content at 0% and 10% was pretty close. 235
However, HPCM with SFU content at 20% showed significant lower 𝑅𝑠/𝑐𝑚 at all s/cm levels. Probably the 236
increase in the HRWRA dosage diminished the difference in 𝑅𝑠/𝑐𝑚 of HPCM when SFU contents were low (0% 237
and 10%). 238
Thus far, all the HPCMs studied in this research can be classified into two groups - flowable HPCMs and 239
non-flowable HPCMs. The dashed line in Table 2 distinguishes these two groups. The HPCMs on the left side of the 240
dash line were flowable mixtures which were consolidated under self-weight during casting. HPCMs on the right 241
side of the dash line were non-flowable HPCMs which were consolidated under external vibration during casting. 242
243
Compressive strength 244
245
Compressive strength of HPCM without SFU 246
The effect of sand content on the 1-day and 28-day compressive strength of HPCM without SFU at various HRWRA 247
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5
Rs/
cm (
%)
s/cm
SFU:0%
SFU:10%
SFU:20%
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5
Rs/
cm (
%)
s/cm
SFU:0%
SFU:10%
SFU:20%
10
Li and Rangaraju
dosages is presented in Figures 3a and 3b. The HPCMs that consolidated under self-weight are indicated in the plots 248
using hollow symbols, and those that were subjected to external vibration are indicated using filled symbols. 249
As shown in Figures 3a and 3b, both the 1-day and 28-day compressive strength of HPCM seemed to 250
fluctuate around certain values as the sand content increased. No clear trends of compressive strength being affected 251
by sand content were observed. An analysis of variance is presented later to evaluate the influence of sand content 252
on the compressive strength of HPCM. 253
The increased HRWRA dosage appeared to have negative effect on the compressive strength of HPCMs, 254
especially at the age of 1 day. The 1-day compressive strength of HPCMs with s/cm=0.5 revealed that mixtures with 255
HRWRA dosages of 0.75%, 1%, and 1.5% had lower strength compared to mixture with 0.5% HRWRA dosage by 256
16%, 29%, and 40%, respectively. Although no calorimetric or setting time studies were conducted on these 257
mixtures in the present study, it is suspected that higher dosage levels of HRWRA may cause set-retardation 258
resulting in lower compressive strengths at early ages (1; 14). 259
A similar comparison of HPCMs with s/cm=0.5 at the age of 28 days revealed that the compressive 260
strength of HPCM with HRWRA dosages of 0.75% and 1% were 6% higher and 0.4% lower, respectively, compared 261
to mixture with HRWRA dosage of 0.5%. The effect of HRWRA dosage up to 1% on the compressive strength was 262
not significant at the age of 28 days. However, the compressive strength of HPCM with HRWRA dosage of 1.5% 263
was 23% lower than that of HPCM with HRWRA dosage of 0.5%. Similar findings were reported in another 264
research study, where the optimal HRWRA dosage was observed to be at 1% by weight of cement, and beyond 265
which compressive strength was negatively affected (12). The improved compressive strength with an increase in 266
HRWRA dosage up to 1% was explained by better dispersion of cement, while the reduced compressive strength 267
beyond 1% dosage of HRWRA was explained by segregation (12). However, in the present study no segregation 268
was observed in the HPCMs even with HRWRA dosage of 1.5%, and therefore it is unlikely for segregation to be 269
the reason for the observed reduction in the 28-day compressive strength. Considering that some HRWRA typically 270
tend to entrain air at high dosage levels, even in the absence of air-entraining agents, it is suspected that at HRWRA 271
dosage levels of 1.5%, increase in the air content of HPCM may have resulted in lowering of the 28-day 272
compressive strength compared to HPCMs with lower HRWRA dosage (1; 15-17). 273
Considering that the HRWRA dosage of 1% was determined as the saturation dosage from a workability 274
perspective and the HRWRA dosage of 1.5% was determined as an overdose in early part of this study, it is 275
reasonable to assume that from a compressive strength perspective the HRWRA dosage of 1% was also the 276
saturation dosage, and HRWRA dosage higher than 1% (i.e. 1.5%) was an overdose which had a lasting negative 277
effect on the compressive strength of HPCMs. 278
279
Compressive strength of HPCM with SFU 280
The effect of sand content on the 1-day and 28-day compressive strength of HPCM with various SFU contents was 281
studied under two HRWRA dosages. The HPCMs with HRWRA dosage at 0.75% are shown in Figure 3c and 3d. 282
The HPCMs with HRWRA dosage at 1% are shown in Figure 3e and 3f. Similarly to what was shown in Figures 3 283
(a) and (b), the HPCMs consolidated under self-weight are plotted as hollow symbols. The HPCMs consolidated 284
under external vibration are plotted as filled symbols. 285
286
11
Li and Rangaraju
(a) (b)
(c) (d)
(e) (f)
FIGURE 3 Compressive strength of HPCM: (a) HPCM without SFU at 1-day, (b) HPCM without
SFU at 28-day, (c) HPCM with SFU at 1-day (HRWRA dosage at 0.75%), (d) HPCM with SFU at
28-day (HRWRA dosage at 0.75%), (e) HPCM with SFU at 1-day (HRWRA dosage at 1%), and
(f) HPCM with SFU at 28-day (HRWRA dosage at 1%).
287
0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5
1-d
ay
co
mp
ress
ive s
tren
gth
(M
Pa
)
s/cm
HRWRA:0.5%
HRWRA:0.75%
HRWRA:1.0%
HRWRA:1.5%
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5
28
-da
y c
om
press
ive s
tren
gth
(M
Pa
)
s/cm
HRWRA:0.5%
HRWRA:0.75%
HRWRA:1.0%
HRWRA:1.5%
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5
1-d
ay
co
mp
ress
ive s
tren
gth
(M
Pa
)
s/cm
SFU:0%
SFU:10%
SFU:20%
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5
28
-da
y c
om
press
ive s
tren
gth
(M
Pa
)
s/cm
SFU:0%
SFU:10%
SFU:20%
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5
1-d
ay
co
mp
ress
ive s
tren
gth
(M
Pa
)
s/cm
SFU:0%
SFU:10%
SFU:20%
0
20
40
60
80
100
120
140
160
0 0.5 1 1.5 2 2.5
28
-da
y c
om
press
ive s
tren
gth
(M
Pa
)
s/cm
SFU:0%
SFU:10%
SFU:20%
12
Li and Rangaraju
From the Figures 3c, 3d, 3e, and 3f, it is difficult to tell the relation between compressive strength and sand content. 288
An analysis of variance is presented later to evaluate the influence of sand content on the compressive strength of 289
HPCM. However, it can be observed that increased SFU content at either 10% or 20% seemed to reduce the 290
compressive strength of the HPCMs at the age of 1 day. Reminding the w/cm was kept constant for HPCM with 291
SFU, it is reasonable to assume that the higher actual w/c probably attribute to the reduced 1-day compressive 292
strength of HPCM with higher SFU content. But, at the age of 28 days, the compressive strength of HPCM with 293
SFU was pretty close to that of HPCM without SFU. This increase could be because of the pozzolanic effect of SFU 294
which was more prominent at later ages (1). 295
296
Statistical analysis of compressive strength being affected by sand content 297
The purpose of the statistical analysis was to find out whether the change in sand content would cause statistically 298
significant difference in either 1-day or 28-day compressive strength of self-consolidating HPCMs. Analysis of 299
variance (F-test) on the compressive strength of HPCMs was only conducted on HPCMs consolidated under 300
self-weight. For each F-test at the age of either 1 day or 28 days, only HPCMs with same SFU content and same 301
HRWRA dosage were included. As shown in Table 4, HPCMs are sorted into eight groups, and HPCMs in each 302
group have same SFU content and same HRWRA dosage. Total sixteen F-tests were conducted on eight groups of 303
HPCMs (two F-tests for each group at 1 day and 28 days, respectively). 304
Before starting the analysis of variance the following assumptions were made: 305
a. The compressive strength of each HPCM had a normal distribution. 306
b. Under the same SFU content and the same HRWRA dosage, the variances of compressive strength 307
of HPCMs with various sand contents were equal. 308
c. The compressive strength of HPCMs with various sand contents was independent from each other. 309
The problem of the hypothesis testing was stated as, 310
𝐻0: µ0 = µ0.5 = ⋯ = µ𝑠/𝑐𝑚
𝐻𝑎 : At least one of the mean compressive strength of HPCM is different from the rest
Where µ𝑠/𝑐𝑚 is the mean compressive strength of HPCM with sand content at s/cm. 311
The possibility of Type I error was set at α=0.05. If the p-value of F-test was larger than α, we did not have 312
enough evidence to reject 𝐻0, which inferred that the sand content did not have statistically significant effect on the 313
compressive strength of HPCM. However, if the p-value of F test was equal or less than α, we had enough 314
evidence to reject 𝐻0, which inferred that the sand content had statistically significant effect on the compressive 315
strength of HPCM. The results of analysis of variance are presented in Table 4. 316
It can be observed that the calculated p-values of HPCMs without SFU were larger than α when HRWRA 317
dosage varied from 0.5% to 1%, which indicated that sand content did not have significant effect on both the 1-day 318
and 28-day compressive strength of HPCM with HRWRA dosage ranging from 0.5% to 1%. When the HRWRA 319
dosage was 1.5%, the decision was to reject H0 for 1-day compressive strength (p-value=0.041<α), but failed to 320
reject H0 for 28-day compressive strength (p-value=0.058>α). This inferred that when the HRWRA dosage was 321
1.5%, the changes in sand content resulted in changes in the 1-day compressive strength of HPCM, but it did not 322
have significant influence on the 28-day compressive strength. However, it was necessary to notice that these 323
decisions for HPCM with HRWRA dosage at 1.5% were not statistically strong, because the p-values were very 324
close to α which was set at 0.05 in this study. If lower α was set, say 0.04, the decision would be fail to reject H0 for 325
both 1-day and 28-day compressive strength. So far, a conclusion is drawn that, with HRWRA dosage at 1%, the 326
13
Li and Rangaraju
maximum sand content was able to go up to s/cm=1.6 without having statistically strong influence on either the 327
1-day or 28-day compressive strength of HPCM without SFU. 328
329
TABLE 4 Analysis of variance of compressive strength 330
SFU (%) Dosage of
HRWRA (%) HPCMs included
1-day 28-day
p-value
Decision a
p-value
Decision a
0
0.5 C1-1,C1-2 0.716 N
0.432 N
0.75 C2-1,C2-2,C2-3 0.449 N 0.354 N
1 C3-1,C3-2,C3-3,C3-4 0.191 N 0.197 N
1.5 C4-1,C4-2,C4-3,C4-4 0.041 Rej. 0.058 N
10 0.75 L2-1,L2-2,L2-3,L2-4 0.019 Rej. 0.052 N
1 L3-1,L3-2,L3-3,L3-4 0.302 N 0.789 N
20 0.75 H2-1,H2-2,H2-3,H2-4 0.091 N 0.002 Rej.
1 H3-1,H3-2,H3-3,H3-4,H3-5 0.599 N 0.713 N
Note: a N-did not reject H0 or Rej.-rejected H0 331
332
For HPCMs with SFU content at 10%, rejections to H0 only occurred for 1-day compressive strength when 333
the HRWRA dosage was 0.75%. When HRWRA dosage was 1%, we failed to reject H0 for both 1-day and 28-day 334
compressive strength. This indicated that when HRWRA dosage was at 0.75%, the change in s/cm from 0 to 1.6 335
resulted in noticeable changes in the 1-day compressive strength of HPCMs. However, when HRWRA dosage was at 336
1%, s/cm went up to 1.6 failed to cause significant changes in either 1-day or 28-day compressive strength of 337
HPCMs. 338
Similarly, for HPCMs with SFU content at 20%, rejections to H0 only occurred for 28-day compressive 339
strength when the HRWRA dosage was 0.75%. The decision was strong since p-value is remarkably smaller than α 340
(0.002< α). A test of Fisher’s least significant difference procedure (LSD) identified that HPCM with s/cm=1.6 had 341
the most significantly different 28-day compressive strength from the rest HPCMs. Considering the results presented 342
in Figure 3b, it was noticed that sand content at s/cm=1.6 resulted in remarkable compressive strength loss at the age 343
of 28 days. However, when HRWRA dosage was 1%, we failed to reject H0 for both 1-day and 28-day compressive 344
strength, which indicated that sand contents up to s/cm=2 did not have statistically significant influence on either the 345
1-day or 28-day compressive strength of HPCM. 346
347
Discussion of maximum sand content of self-consolidating HPCM 348
From the point of lowering economic cost, it is generally preferable to increase the sand content of HPCM. However, 349
increasing sand content would reduce the workability and cause compressive strength loss. The maximum sand 350
content at which the HPCM still maintained the ability of self-consolidating and the compressive strength of HPCM 351
was not significantly lowered is important in the design of self-consolidating HPCM. Based on a combined 352
consideration of both workability and compressive strength of HPCM in this study, it is reasonable to believe that 353
for self-consolidating HPCM with SFU contents at 0%, 10%, and 20%, the maximum sand content could go up to 354
1.6, 1.6, and 2, respectively. It should be reminded that such maximum sand contents are affected by many factors, 355
such as gradation and texture of sand. Different maximum sand contents of self-consolidating HPCM likely exist 356
when different type of sand was used. 357
14
Li and Rangaraju
358
Rapid Chloride Ion permeability 359
360
The RCP of HPCM without SFU was studied on HPCM C3-1, C3-2, C3-3, C3-4, and C3-5. The experimental 361
results are presented in Figure 4, which depicts the RCP values at different s/cm ratios and a prediction equation. 362
FIGURE 4 Influence of s/cm on RCP of HPCM without SFU
363
It can be observed that the amount of charge passed decreased as the s/cm increased, which indicated that 364
the chloride permeability of HPCM decreased as more siliceous sand was added into the mixture. Considering the 365
sand was less permeable than cement paste, the reduced chloride permeability of HPCM was likely because of the 366
reduced volume of cement paste through which the charge passed. However, when the sand content went up to 367
s/cm=2, the reduction in charge passed was not significant. For HPCM with sand content at s/cm=2 the charge 368
passed was only 3% lower than HPCM with sand content at s/cm=1.6. The lack of significant decrease in chloride 369
ion permeability beyond s/cm ratio of 1.6 can be attributed to two conflicting effects – the reduction in the cement 370
paste volume (which should reduce the permeability) and the percolation effect in cement paste due to interfacial 371
transition zone (ITZ) (which should increase the increase the permeability). 372
With increasing sand content, the volume of cement paste in the HPCM is proportionately reduced and 373
therefore the permeability of the HPCM should decrease. However, with increasing sand content, the volume of 374
paste that is in the ITZ is relatively more compared to the paste that is considered as bulk paste. These conflicting 375
effects neutralize any effect on the chloride permeability of HPCMs in which s/cm ratio is between 1.6 and 2.0. 376
This was attributed to the increased volume of interfacial transition zone (ITZ) as sand content increased (1; 18). As 377
it is widely known, ITZ which surrounds sand particles has higher porosity than the cement paste (1; 18). If sand 378
content goes up to certain point when adjacent ITZs start to percolate, the permeability of the whole structure of 379
concrete increases significantly (1; 18). The RCP of HPCM affected by increasing sand content is assumed to be a 380
function of reduced paste content and increased ITZ in the present study. 381
The following three-parameter regression equation based on five data points was used to describe the 382
charge passed during RCP test for HPCMs without SFU ( also see Figure 4), 383
𝑦 =a
𝑒b𝑥 + c (2) 384
Where 385
y is dependent variable 386
𝑘 =3400
𝑒3𝑟+ 800
R2=0.999
15
Li and Rangaraju
x is independent variable 387
a, b, and c are constants to be determined by the test results 388
In this study, the following equation was proposed, 389
𝑘 =3400
𝑒3𝑟 + 800 (R2=0.999) (3) 390
Where 391
k is charge passed 392
r is s/cm 393
The plot of Equation (3) is shown in Figure 4. 394
395
Drying shrinkage 396
397
The drying shrinkage of HPCM without SFU was studied on HPCM C3-1, C3-2, C3-3, C3-4, and C3-5. The drying 398
shrinkage developments of HPCM without SFU are shown in Figure 5a. 399
(a)
(b)
FIGURE 5 Drying shrinkage of HPCM without SFU: (a) Drying shrinkage development and
(b) Influence of s/cm on the maximum drying shrinkage.
400
-0.25
-0.2
-0.15
-0.1
-0.05
0
0 15 30 45 60 75
Dry
ing
sh
rin
ka
ge (
%)
Period of Exposure (days)
s/cm:0 s/cm:0.5
s/cm:1.25 s/cm:1.6
s/cm:2.0
𝐷 = −0.14
𝑒1.7𝑟− 0.04
R2=0.997
16
Li and Rangaraju
It was obvious that HPCM with high sand content presented lower drying shrinkage than HPCM with low 401
sand at all testing ages, and the curves of drying shrinkage development of HPCMs became almost flat after 56 days 402
of exposure. The drying shrinkage of 56 days of exposure was assumed to be the maximum drying shrinkage of 403
studied HPCM, which is shown as dot in Figure 5b. A simple calculation revealed that the maximum drying 404
shrinkage of HPCM with sand content at s/cm=0.5, 1.25, 1.6, and 2 was 44%, 65%, 72%, and 75% lower than that 405
of HPCM without sand, respectively. The reduction in drying shrinkage as sand content increased was likely because 406
of the reduced volume of cement paste, which is the main component resulting in shrinkage under drying (1). 407
The relationship between the 56-day shrinkage as a function of s/cm can be described by equation (4) 408
which is a three-parameter regression equation based on five data points (also see Figure 5b). 409
𝐷 = −0.14
𝑒1.7𝑟 − 0.04 (R2=0.997) (4) 410
Where 411
D is the maximum drying shrinkage 412
r is s/cm 413
414
CONCLUSIONS 415
416
The workability, compressive strength and durability of self-consolidating HPCM with and without containing SFU 417
were experimentally studied. Based on the experimental results, the following conclusions are drawn: 418
For HPCM without SFU, the workability was influenced by the combination of HRWRA dosage and sand 419
content. Increasing HRWRA dosage or decreasing sand content improved the workability of HPCM, however 420
HRWRA exceeding saturation dosage did not increase the workability further. Based on the material and mixture 421
proportions used in this study, the saturation dosage of HRWRA was established at 1% by weight of the cement. 422
The workability of HPCM became less sensitive to the changes in the sand content when the SFU content 423
increased, which was revealed by the index 𝑅𝑠/𝑐𝑚. 424
The compressive strength of self-consolidating HPCM was not significantly influenced by the sand 425
content up to a maximum sand content, depending on the dosage of SFU and HRWRA. In this study, with HRWRA 426
at saturation dosage (1%), the maximum sand content for self-consolidating HPCM without SFU was able to go up 427
to s/cm=1.6, and the maximum sand content for self-consolidating HPCM with SFU content at 10% and 20% was 428
able to go up to s/cm=1.6 and s/cm=2, respectively. 429
For self-consolidating HPCM without SFU, increased sand content was helpful in improving the 430
durability of HPCM. Lower chloride permeability and less drying shrinkage were observed as the sand content 431
increased. 432
Based on materials and proportions used in this study, it is recommended that to produce a workable HPCM 433
with good compressive strength a sand-to-cementitious materials ratio between 1.6 and 2.0 should be used, 434
depending on the dosage of SFU and HRWRA. It should be noted that round siliceous natural sand is highly 435
recommended for this purpose. Using sand of different angularity or particle size distribution than that was used in 436
this study may result in slightly different maximum s/cm. 437
438
REFERENCES 439
[1] Mindess, S., J. F. Young, and D. Darwin. Concrete. Prentice Hall, Upper Saddle River, NJ, 2003. 440
17
Li and Rangaraju
[2] Graybeal, B. A. Material property characterization of ultra-high performance concrete. Report 441
FHWA-HRT-06-103, FHWA, U.S. Department of Transportation, 2006. 442
[3] Durekovic, A. Cement Pastes of Low Water to Solid Ratio - an Investigation of the Porosity Characteristics 443
under the Influence of a Superplasticizer and Silica Fume. Cement and Concrete Research, Vol. 25, No. 2, 1995, 444
pp. 365-375. 445
[4] Nehdi, M., S. Mindess, and P. C. Aitcin. Rheology of high-performance concrete: Effect of ultrafine particles. 446
Cement and Concrete Research, Vol. 28, No. 5, 1998, pp. 687-697. 447
[5] Libre, N. A., R. Khoshnazar, and M. Shekarchi. Relationship between fluidity and stability of self-consolidating 448
mortar incorporating chemical and mineral admixtures. Construction and Building Materials, Vol. 24, No. 7, 449
2010, pp. 1262-1271. 450
[6] Schwartzentruber, L. D., R. Le Roy, and J. Cordin. Rheological behaviour of fresh cement pastes formulated 451
from a Self Compacting Concrete (SCC). Cement and Concrete Research, Vol. 36, No. 7, 2006, pp. 1203-1213. 452
[7] Khayat, K. H. Workability, testing, and performance of self-consolidating concrete. Aci Materials Journal, Vol. 453
96, No. 3, 1999, pp. 346-353. 454
[8] Saak, A. W., H. M. Jennings, and S. P. Shah. New methodology for designing self-compacting concrete. Aci 455
Materials Journal, Vol. 98, No. 6, 2001, pp. 429-439. 456
[9] Zhang, X., and J. H. Han. The effect of ultra-fine admixture on the rheological property of cement paste. Cement 457
and Concrete Research, Vol. 30, No. 5, 2000, pp. 827-830. 458
[10] Vikan, H., and H. Justnes. Rheology of cementitious paste with silica fume or limestone. Cement and Concrete 459
Research, Vol. 37, No. 11, 2007, pp. 1512-1517. 460
[11] Cortes, D. D., H. K. Kim, A. M. Palomino, and J. C. Santamarina. Rheological and mechanical properties of 461
mortars prepared with natural and manufactured sands. Cement and Concrete Research, Vol. 38, No. 10, 2008, 462
pp. 1142-1147. 463
[12] Han, V., S. Ros, and H. Shima. Effects of Sand Content, Superplasticizer Dosage, and Mixing Time on 464
Compressive Strength of Mortar. Aci Materials Journal, Vol. 110, No. 1, 2013, pp. 23-31. 465
[13] Punkki, J., J. Golaszewski, and O. E. Gjorv. Workability loss of high-strength concrete. Aci Materials Journal, 466
Vol. 93, No. 5, 1996, pp. 427-431. 467
[14] Pinto, R., and K. Hover. Effect of Silica Fume and Superplasticizer Addition on Setting Behavior of 468
High-Strength Mixtures. Transportation Research Record: Journal of the Transportation Research Board, Vol. 469
1574, No. -1, 1997, pp. 56-62. 470
[15] Lazniewska-Piekarczyk, B. The methodology for assessing the impact of new generation superplasticizers on 471
air content in self-compacting concrete. Construction and Building Materials, Vol. 53, 2014, pp. 488-502. 472
[16] Papayianni, I., G. Tsohos, N. Oikonomou, and P. Mavria. Influence of superplasticizer type and mix design 473
parameters on the performance of them in concrete mixtures. Cement & Concrete Composites, Vol. 27, No. 2, 474
2005, pp. 217-222. 475
[17] Lazniewska-Piekarczyk, B., and J. Szwabowski. The Influence of the Type of Anti-Foaming Admixture and 476
Superplasticizer on the Properties of Self-Compacting Mortar and Concrete. Journal of Civil Engineering and 477
Management, Vol. 18, No. 3, 2012, pp. 408-415. 478
[18] Winslow, D. N., M. D. Cohen, D. P. Bentz, K. A. Snyder, and E. J. Garboczi. Percolation and Pore Structure in 479
Mortars and Concrete. Cement and Concrete Research, Vol. 24, No. 1, 1994, pp. 25-37. 480
481
