Supplementary Material

I. Mix designs

The mix designs of the main mixes of the subgroups A1, A2, A3, B1, and B2 are presented here. The designations used are as follows C = Cement; FA = fly ash; S = silica fume; M = metakaolin; W = water; NW1 = sand, 0 – 4.75 mm; NW2 = coarse gravel, 4 – 8 mm; LWF1 = lightweight fine, 0 – 0.3 mm; LWF2 = lightweight fine, 0.25 – 0.5 mm; LWF3 = lightweight fine, 0.5 – 1 mm; LWF4 = lightweight fine, 1 – 2 mm; LWF5 = lightweight fine, 2 – 4 mm; LWC1 = lightweight coarse, 4 – 8 mm; LWC2 = lightweight coarse, 8 – 16 mm; sp/b is the superplasticizer/binder ratio (ratio of liquid weight of the superplasticizer to the weight of the binder); w/b is the water-to-binder ratio; volume of LWA refers to the overall volume of coarse and fine lightweight aggregates in the mix with respect to the overall concrete volume. For mixes with fibers, P1 = PVA fibers with aspect ratio 340; S1 = steel fibers with aspect ratio 40; S2 = steel fibers with aspect ratio 60; S3 = steel fibers with aspect ratio 50; S4 = corrugated steel fibers; S5 = hooked steel fibers.

More details about the properties of the materials used are presented in the main text.

Table 1S. Mixes of subgroup A1

Mix / A1_1 / A1_2 / A1_3 / A1_4 / A1_5 / A1_6 / A1_7 / A1_8
C (kg/m3) / 537 / 538 / 535 / 535 / 503 / 502 / 503 / 505
FA (kg/m3) / 55 / 55 / 55 / 55 / 52 / 52 / 52 / 52
W (kg/m3) / 212 / 207 / 207 / 205 / 235 / 237 / 239 / 240
NW1 (kg/m3) / 638 / 382 / 271 / 143 / 667 / 415 / 293 / 162
LWF2 (kg/m3) / 6 / 15 / 19 / 23 / 5 / 14 / 17 / 22
LWF3 (kg/m3) / 6 / 15 / 19 / 25 / 5 / 14 / 17 / 24
LWF4 (kg/m3) / 6 / 15 / 19 / 25 / 5 / 14 / 17 / 24
LWF5 (kg/m3) / 26 / 27 / 32 / 33 / 24 / 25 / 31 / 31
LWC1 (kg/m3) / 35 / 49 / 52 / 54 / 32 / 46 / 49 / 51
LWC2 (kg/m3) / 116 / 127 / 126 / 130 / 107 / 119 / 119 / 123
sp/b (%) / 1.2 / 1.2 / 1.1 / 1.1 / 1.2 / 1.2 / 1.2 / 1.2
w/b / 0.3 / 0.39
Volume of LWA (%) / 32 / 38 / 44 / 51 / 32 / 38 / 44 / 51
Density, 28 days (kg/m3) / 1591 / 1455 / 1416 / 1197 / 1583 / 1427 / 1310 / 1164
Strength, 28 days (MPa) / 22.8 / 21.0 / 17.8 / 16.2 / 19.2 / 17.6 / 15 / 12.3

In these mixes, the effect of w/b is checked at two values 0.3 and 0.39. Mixes with various volumes of lightweight aggregates are checked. These are initial mixes and present low strength values.

Table 2S. Mixes of subgroup A2

Mix / A2_1 / A2_2 / A2_3 / A2_4 / A2_5
C (kg/m3) / 537 / 538 / 535 / 535 / 535
FA (kg/m3) / 55 / 55 / 55 / 55 / 55
W (kg/m3) / 212 / 207 / 207 / 205 / 205
NW1 (kg/m3) / 638 / 382 / 271 / 223 / 143
LWF2 (kg/m3) / 6 / 15 / 19 / 22 / 23
LWF3 (kg/m3) / 6 / 15 / 19 / 22 / 25
LWF4 (kg/m3) / 6 / 15 / 19 / 22 / 25
LWF5 (kg/m3) / 26 / 27 / 32 / 32 / 33
LWC1 (kg/m3) / 35 / 49 / 52 / 52 / 54
LWC2 (kg/m3) / 116 / 127 / 126 / 128 / 130
sp/b (%) / 1.2 / 1.2 / 1.1 / 1.1 / 1.1
w/b / 0.3
Volume of LWA (%) / 32 / 38 / 44 / 47 / 51
Density, 7 days (kg/m3) / 1604 / 1502 / 1410 / 1310 / 1182
Strength, 7 days (MPa) / 22.7 / 18.1 / 17.7 / 15.9 / 14.9
Density, 28 days (kg/m3) / 1591 / 1455 / 1416 / 1321 / 1197
Strength, 28 days (MPa) / 22.8 / 21.0 / 17.8 / 17.8 / 16.2

In these mixes, the effect of the lightweight aggregate volume fraction and age are checked at w/b value of 0.3. These are initial mixes and present low strength values.

Table 3S. Mixes of subgroup A3

Mix / A3_1 / A3_2 / A3_3 / A3_4
C (kg/m3) / 541 / 541 / 536 / 538
FA (kg/m3) / 55 / 55 / 55 / 55
W (kg/m3) / 242 / 230 / 216 / 207
NW1 (kg/m3) / 593 / 575 / 536 / 382
LWF2 (kg/m3) / 82 / 50 / 21 / 15
LWF3 (kg/m3) / 82 / 42 / 21 / 15
LWF4 (kg/m3) / -- / 33 / 21 / 15
LWF5 (kg/m3) / -- / 33 / 21 / 27
LWC1 (kg/m3) / -- / -- / 114 / 49
LWC2 (kg/m3) / -- / -- / -- / 127
sp/b (%) / 1.0 / 1.0 / 1.0 / 1.2
w/b / 0.3
Volume of LWA (%) / 38
Maximum LWA size (mm) / 1 / 4 / 8 / 16
Density, 28 days (kg/m3) / 1528 / 1529 / 1450 / 1455
Strength, 28 days (MPa) / 30.1 / 23.5 / 25.1 / 21

In these mixes, the effect of the maximum lightweight aggregate size is checked. All mixes have the same w/b and the same lightweight aggregate volume. We find that the strength increases as maximum lightweight aggregate size decreases.

Table 4S. Mixes of subgroup B1

Mix / B1_1 / B1_2 / B1_3 / B1_4 / B1_5
C (kg/m3) / 570 / 570 / 507 / 501 / 432
FA (kg/m3) / -- / 59 / -- / 63 / 61
S (kg/m3) / 59 / -- / -- / 63 / 61
L (kg/m3) / -- / -- / -- / -- / 61
M (kg/m3) / -- / -- / 59 / -- / --
W (kg/m3) / 225 / 225 / 225 / 225 / 227
NW1 (kg/m3) / 112 / 112 / 112 / 105 / 110
NW2 (kg/m3) / 217 / 217 / 217 / 212 / 213
LWF1 (kg/m3) / 72 / 72 / 72 / 72 / 71
LWF2 (kg/m3) / 82 / 82 / 82 / 82 / 81
LWF3 (kg/m3) / 99 / 99 / 99 / 99 / 97
sp/b (%) / 2 / 1.4 / 1.8 / 2 / 2
w/b / 0.3
Volume of LWA (%) / 44
Density, 28 days (kg/m3) / 1349 / 1410 / 1337 / 1336 / 1372
Strength, 28 days (MPa) / 25.3 / 30.1 / 27.9 / 24.6 / 28.9

These mixes are designed using data from mix series A1 – A3. The maximum lightweight aggregate size is 1 mm (although there are coarse normal weight aggregates up to 8 mm) and the w/b value is 0.3. In these mixes, the effect of the binder composition is studied. The binder composition does not have a large effect on the strengths with respect to the density, and the best values obtained are 30 MPa at 1410 kg/3 and 29 MPa at 1372 kg/m3.

Table 5S. Mixes of subgroup B2

Mix / B2_1 / B2_2 / B2_3 / B2_4 / B2_5 / B2_6
C (kg/m3) / 432 / 432 / 432 / 432 / 432 / 432
FA (kg/m3) / 61 / 61 / 61 / 61 / 61 / 61
S (kg/m3) / 61 / 61 / 61 / 61 / 61 / 61
L (kg/m3) / 61 / 61 / 61 / 61 / 61 / 61
W (kg/m3) / 227 / 227 / 227 / 227 / 227 / 227
NW1 (kg/m3) / 110 / 110 / 110 / 110 / 110 / 110
NW2 (kg/m3) / 213 / 213 / 213 / 213 / 213 / 213
LWF1 (kg/m3) / 71 / 71 / 71 / 71 / 71 / 71
LWF2 (kg/m3) / 81 / 81 / 81 / 81 / 81 / 81
LWF3 (kg/m3) / 97 / 97 / 97 / 97 / 97 / 97
Fibers (%) / 0.5 % P1 / 0.5 % S5 / 1 % S4 / 1 % S5 / 1 % S1 + 1 % P1 / 1 % S2 + 1 % S3
sp/b (%) / 2 / 1.3 / 1.5 / 1.5 / 2 / 0.8
w/b / 0.3
Volume of LWA (%) / 44
Density, 28 days (kg/m3) / 1396 / 1469 / 1417 / 1520 / 1375 / 1419
Strength, 28 days (MPa) / 30.1 / 31.4 / 28.7 / 36.1 / 28.5 / 27.3

Using a mix of B1 with large amounts of additions (do not help significantly with strength but generally reduce shrinkage and improve workability), mixes in this series are tested with various amounts of different kinds of fibers. Although generally the strengths with respect to density do not increase due to the fibers, in some cases, high values of strength are obtained, for example, 36 MPa at 1520 kg/3.

II. Binder composition

Pastes were mixed in a 5 l paste mixer (Hobart Corp.) and isothermal calorimetry was performed on selected paste samples using an ICal 4000 (Calmetrix, Inc). The mixing procedure for the pastes was the same as that for the concretes (detailed in Section 2.2 of the main text). Several binder compositions were monitored for heat release, and Figure 1S shows some selected isothermal calorimetry results of pastes carried out for 200 hours. For all the pastes, the w/b was fixed at 0.30. When only cement paste is used, the heat release is about 335 Joules per gram of cement. When 10 % of the cement is replaced by silica fume, the heat release per gram of binder at 200 hours was almost the same as the samples without the replacement (335 J/g). Experiments at 30 % replacement rate using 10 % each of fly ash, silica fume, and limestone even showed an increase in the heat release per gram of binder (350 J/g). Other combinations with up to a 30 % replacement also showed similar results. Although it is acknowledged that the heat released is not a direct indicator of compressive strength (since other parameters such as porosity, etc, might change), these results suggest that decent compressive strengths can be obtained with a high replacement level of cement. This is advantageous in lightweight concretes as it results in a reduction in the rather high cement content (which makes the mix more environmentally friendly, reduces shrinkage, and improves workability).

Figure 1S: Isothermal calorimetry on pastes showing heat released per gram of binder as a function of time. C indicates a paste with cement as binder; the supplementary cementitious materials (FA, S, L, indicating fly ash, silica fume, and limestone) are used at a 10 % replacement each.

III. Density and air content

Both decreasing the w/b ratio and adding fibers increased the compressive strength of several mixes. However, these changes also increased the density, and the effective strength/density ratio did not improve much in most cases. When cement was replaced by supplementary cementitious materials, strength and density both decreased slightly, and the effective strength/density ratio did not change significantly. For optimized mixes (Section 3.1.6), the strength increased almost linearly with the density.

The density of the lightweight concrete mixes is also affected to a moderate extent by the air content. Fibers (Miao et al. 2003), superplasticizer (Felekoğlu et al. 2007), lightweight aggregates (Kim et al. 2012), and their combinations (Sadrmomtazi et al. 2012; Wang et al. 2013) are all known to increase the entrapped air content in concrete. The large air content (5 – 8 %) in several mixes is likely to have significantly reduced their strengths, perhaps by up to 20 % or more (Muethel 1995; Ansari et al. 2002). Such reductions in lightweight concrete strength due to their large air content have been reported earlier in literature (Sadrmomtazi et al. 2012; Wang et al. 2013). While other factors impact the compressive strength, their effect is possibly overshadowed by the larger influence of the associated variations in air content.

Some studies have shown an increase in compressive strength by pre-wetting the aggregates before mixing (Lo et al. 2004), which may in part be due to a reduction in air content. However our tests with pre-wetted aggregate using the whole mixing water did not show much improvement in the strength. It is possible that using higher dosages of de-foamers or certain shrinkage reducing admixtures (Wang et al. 2012; Wang et al. 2013) may help in reducing the air content and increasing strengths, but such tests were not performed in this study.