**Table 11.**

*Test results of LWACs with LC30 under water curing on different days.*


The compressive strength and elastic modulus of the specimens cured at 5°C meet the basic requirements (up to 90%) both with and without anti-freezing agent, but at 10°C, they can satisfy the requirements when added anti-freezing agent. Although the strength and elastic modulus of other groups fail the basic requirements, the hydration reaction does not stop but only diminishes. Compared with NWC, the strength of the specimen is higher, which shows that it helps promote the hydration reaction because of the heat preservation and inner curing effect of LWA. On the other hand, the strength of GLWC is slightly higher than that of ALWC under the same conditions. The reason is the same as the one mentioned above, namely, that the elastic modulus of gravel is larger than that of ceramsite.

**Type 200°C 300°C 400°C 500°C 600 °C** *η<sup>T</sup>*

SLWC 32.05 28.98 25.01 21.35 17.22 56.4 GLWC 33.23 32.25 25.86 23.05 18.34 57.0 HALWC 32.65 31.82 25.14 22.21 17.90 56.8

SLWC 26.76 25.31 21.82 18.90 15.12 50.9 GLWC 29.77 26.96 23.19 19.14 15.95 50.9 HALWC 28.51 26.92 22.65 18.51 14.82 48.1

SLWC 2.22 1.93 1.59 1.36 1.14 46.2 GLWC 2.73 2.40 1.96 1.69 1.47 48.8 HALWC 2.53 2.25 1.80 1.55 1.35 48.0

SLWC 15.68 13.75 10.98 8.88 6.13 37.1 GLWC 16.89 16.46 14.53 11.19 8.76 50.8 HALWC 16.11 15.32 13.65 10.11 8.12 48.2

SLWC 1.3 4.6 5.6 6.7 7.2 GLWC 0.9 4.2 4.7 5.5 6.8 HALWC 0.8 4.2 4.9 5.8 6.9 *f*cu (MPa) ALWC 30.54 25.70 22.02 19.79 16.48 55.9

*f*<sup>c</sup> (MPa) ALWC 26.88 23.43 20.04 17.50 14.68 52.0

*f*ts (MPa) ALWC 2.06 1.79 1.46 1.25 1.07 46.1

*E*<sup>c</sup> (GPa) ALWC 12.61 10.13 8.19 6.62 5.03 34.5

*Notes: Δm stands for the ratio of mass after high-temperature treatment to that under room temperature. η<sup>T</sup>*

Δ*m* (%) ALWC 1.1 4.5 5.4 6.4 7.0

*The Influence of Hybrid Aggregates on Different Types of Concrete*

*DOI: http://dx.doi.org/10.5772/intechopen.88254*

*<sup>c</sup>* **(%)**

*<sup>c</sup> stands for*

Also, fibre can enhance the strength and elastic modulus of specimens cured at negative temperature, and the laws are also the same; that is, the performance of

The uniaxial stress-strain curve of LWACs is similar to that of NWC, as shown in **Figure 3**, but the total strain of LWACs is significantly larger than that of NWC.

To summarise, the LWACs can meet the requirements of freezing process

concrete is better with elastic modulus of fibre increasing.

*the ratio of strength or elastic modulus at 600°C to that at room temperature.*

*Test results of LWACs for LC30 after elevated temperature treatment.*

**4.6 Uniaxial stress-strain curves of LWACs**

construction.

**91**

**Table 13.**

#### **Table 12.**

*Appearance characteristics of LWACs after high-temperature treatment.*

rises in temperature. On the other hand, the residual strengths of LWCAs after high-temperature treatment are very close to or even higher than that of NWC, which indicates that LWACs can be used for fire-resistant design. For example, the residual strength of axial compression is 95% at 200°C, 80–90% at 300°C, 70–75% at 400°C, 60–65% at 500°C, and around 50% at 600°C. The residual splitting tensile strength is around 90%, 75–80%, 60–65%, 5055%, and around 45% at 200, 300, 400, 500, and 600°C, respectively.

### **4.5 Properties of LWACs cured at negative temperature**

During the construction process used by the artificial freezing method, the ambient temperature in the working place is from 8 to 12°C in China. Concrete properties after curing at negative temperature are shown in **Tables 14** and **15**, where the specimen is wrapped with a layer of quilt after being poured and then put into a low-temperature test chamber.


*The Influence of Hybrid Aggregates on Different Types of Concrete DOI: http://dx.doi.org/10.5772/intechopen.88254*

*Notes: Δm stands for the ratio of mass after high-temperature treatment to that under room temperature. η<sup>T</sup> <sup>c</sup> stands for the ratio of strength or elastic modulus at 600°C to that at room temperature.*

#### **Table 13.**

rises in temperature. On the other hand, the residual strengths of LWCAs after high-temperature treatment are very close to or even higher than that of NWC, which indicates that LWACs can be used for fire-resistant design. For example, the residual strength of axial compression is 95% at 200°C, 80–90% at 300°C, 70–75% at 400°C, 60–65% at 500°C, and around 50% at 600°C. The residual splitting tensile strength is around 90%, 75–80%, 60–65%, 5055%, and around 45% at 200, 300,

*T* **(°C) Colour Visible phenomenon** *w***max (mm)**

300 Light grey Fewer hairline cracks 0.06 0.04 0.05 0.04 400 Off-white More hairline cracks 0.16 0.12 0.14 0.12 500 Hazel Honeycomb cracks 0.20 0.20 0.20 0.18 600 Brownness Honeycomb cracks with surface wrapping 0.30 0.26 0.28 0.24

**Type 28 d 60 d 90 d 120 d 180 d** *ψ***<sup>c</sup> (%)**

SLWC 31.48 32.43 31.87 31.44 31.20 100.9 GLWC 34.43 35.18 35.09 34.92 34.81 102.8 HALWC 33.56 34.22 33.96 33.68 33.47 102.5

SLWC 30.87 31.56 30.78 30.49 30.15 100.6 GLWC 33.59 34.14 33.96 33.75 33.62 102.7 HALWC 31.35 32.84 32.61 32.39 32.18 102.9

SLWC 3.04 3.11 3.03 2.95 2.90 104.3 GLWC 3.15 3.23 3.20 3.18 3.15 104.3 HALWC 3.07 3.19 3.14 3.11 3.09 105.1

SLWC 21.62 22.24 22.85 23.41 23.98 115.3 GLWC 21.92 22.80 23.35 23.96 24.71 116.4 HALWC 21.58 22.45 23.09 23.62 24.35 116.3

*f*cu (MPa) ALWC 30.98 31.54 31.05 30.15 29.78 101.3

*f*<sup>c</sup> (MPa) ALWC 29.45 30.27 29.81 28.95 28.07 99.9

*f*ts (MPa) ALWC 2.96 3.03 2.95 2.86 2.79 104.5

*E*<sup>c</sup> (GPa) ALWC 21.23 21.74 22.35 23.24 23.79 115.2

**ALWC SLWC GLWC HALWC**

During the construction process used by the artificial freezing method, the ambient temperature in the working place is from 8 to 12°C in China. Concrete properties after curing at negative temperature are shown in **Tables 14** and **15**, where the specimen is wrapped with a layer of quilt after being poured and then put

400, 500, and 600°C, respectively.

*Notes: ψ<sup>c</sup> stands for the softening coefficient of concrete.*

**Table 12.**

**90**

**Table 11.**

into a low-temperature test chamber.

**4.5 Properties of LWACs cured at negative temperature**

*Appearance characteristics of LWACs after high-temperature treatment.*

*Test results of LWACs with LC30 under water curing on different days.*

*Sandy Materials in Civil Engineering - Usage and Management*

*Test results of LWACs for LC30 after elevated temperature treatment.*

The compressive strength and elastic modulus of the specimens cured at 5°C meet the basic requirements (up to 90%) both with and without anti-freezing agent, but at 10°C, they can satisfy the requirements when added anti-freezing agent.

Although the strength and elastic modulus of other groups fail the basic requirements, the hydration reaction does not stop but only diminishes. Compared with NWC, the strength of the specimen is higher, which shows that it helps promote the hydration reaction because of the heat preservation and inner curing effect of LWA. On the other hand, the strength of GLWC is slightly higher than that of ALWC under the same conditions. The reason is the same as the one mentioned above, namely, that the elastic modulus of gravel is larger than that of ceramsite.

Also, fibre can enhance the strength and elastic modulus of specimens cured at negative temperature, and the laws are also the same; that is, the performance of concrete is better with elastic modulus of fibre increasing.

To summarise, the LWACs can meet the requirements of freezing process construction.

#### **4.6 Uniaxial stress-strain curves of LWACs**

The uniaxial stress-strain curve of LWACs is similar to that of NWC, as shown in **Figure 3**, but the total strain of LWACs is significantly larger than that of NWC.


*Notes: (1) wA stands for the ratio of anti-freezing agent to cement (by mass); (2) η<sup>T</sup> <sup>c</sup> stands for the ratio of strength at 28 days and curing at negative temperature to that at room temperature; (3) the mixes are slightly different from Table 8.*

#### **Table 14.**

*Compressive strength of LWACs cured at negative temperature with anti-freezing agent for LC30.*


#### **Table 15.**

*Test results of LWACs cured at negative temperature without anti-freezing agent for LC30.*

The symbols of stress and strain obey the following rules: the plus sign '+' denotes tension; the minus sign '–' denotes compression.

Generally, the stress-strain curve can be expressed by Eqs. (3) and (4) [11]. Ascending curve:

$$y = a\mathbf{x} + (\mathbf{3} \cdot \mathbf{2}a)\mathbf{x}^2 + (a \cdot \mathbf{2})\mathbf{x}^3 \quad \mathbf{x} \le \mathbf{1} \tag{3}$$

Descending curve:

$$y = \frac{\varkappa}{\beta \left(\varkappa - 1\right)^2 + \varkappa} \quad \varkappa \ge 1 \tag{4}$$

Eqs. (3) and (4) can be fitted for all kinds of concretes, whether or not the curve is complete. In particular, direct measurement of the descending curve is not usu-

*α R***<sup>2</sup>** *β R***<sup>2</sup>**

Although **Figure 4** does not contain descending curves, the law of different LWACs is the same; that is, the ultimate stress decreases, and the ultimate strain increases with the temperature increase, which shows that the plastic deformation gets larger because the strength of the cement mortar matrix decreases. On the other hand, under the same temperature, the effects of a small quantity of NWA on the ultimate strain are not significant; only the effect on the ultimate stress is remarkable. At the same time, ALWC is similar to SLWC, and GLWC is similar to

**Strength grade Ascending curve Descending curve**

LC 30 0.3777 0.9332 4.7704 0.9921 LC 35 0.4398 0.9855 9.0217 0.9975

Under multiaxial compressive stresses, the ultimate compressive strength of concrete will increase significantly, and therefore the failure modes change. For example, ALWC undergoes the phenomenon of squeeze flow, and a plastic plateau

**Tables 17** and **18** show the bi- and triaxial ultimate compressive strengths tested by a large real triaxial test system, respectively. To reduce the friction, a two-layer polythene film with lithium base oil smeared between the layers is used, which can guarantee that the strength under single stress action (*σ*0) is close to the axial compressive strength (*f*c). In the test, *σ*<sup>0</sup> is slightly smaller than *f*c, and the loading type is proportional loading. The samples were tested after 120 days of curing. The formulas for calculating bi- and triaxial ultimate strength are shown as

appears in the stress-strain curve under the two larger lateral stresses.

ally easy (**Figure 4**).

**4.7 Multiaxial strength of LWACs**

*Test curves of stress-strain under uniaxial compression for ALWC.*

*The Influence of Hybrid Aggregates on Different Types of Concrete*

*DOI: http://dx.doi.org/10.5772/intechopen.88254*

*Fitting coefficients and relative coefficients in Eqs. (3) and (4).*

Eqs. (5) and (6) [12], respectively:

HALWC.

**93**

**Figure 3.**

**Table 16.**

where *<sup>x</sup>* <sup>¼</sup> *<sup>ε</sup> <sup>ε</sup>*<sup>0</sup> and *<sup>y</sup>* <sup>¼</sup> *<sup>σ</sup> σ*0 . *α* and *β* are fitting coefficients shown in **Table 16**. *ε*<sup>0</sup> and *σ*<sup>0</sup> stand for peak strain and peak stress under uniaxial compression, respectively.

*The Influence of Hybrid Aggregates on Different Types of Concrete DOI: http://dx.doi.org/10.5772/intechopen.88254*

#### **Figure 3.**

*Test curves of stress-strain under uniaxial compression for ALWC.*


#### **Table 16.**

*Fitting coefficients and relative coefficients in Eqs. (3) and (4).*

Eqs. (3) and (4) can be fitted for all kinds of concretes, whether or not the curve is complete. In particular, direct measurement of the descending curve is not usually easy (**Figure 4**).

Although **Figure 4** does not contain descending curves, the law of different LWACs is the same; that is, the ultimate stress decreases, and the ultimate strain increases with the temperature increase, which shows that the plastic deformation gets larger because the strength of the cement mortar matrix decreases. On the other hand, under the same temperature, the effects of a small quantity of NWA on the ultimate strain are not significant; only the effect on the ultimate stress is remarkable. At the same time, ALWC is similar to SLWC, and GLWC is similar to HALWC.

#### **4.7 Multiaxial strength of LWACs**

Under multiaxial compressive stresses, the ultimate compressive strength of concrete will increase significantly, and therefore the failure modes change. For example, ALWC undergoes the phenomenon of squeeze flow, and a plastic plateau appears in the stress-strain curve under the two larger lateral stresses. **Tables 17** and **18** show the bi- and triaxial ultimate compressive strengths tested by a large real triaxial test system, respectively. To reduce the friction, a two-layer polythene film with lithium base oil smeared between the layers is used, which can guarantee that the strength under single stress action (*σ*0) is close to the axial compressive strength (*f*c). In the test, *σ*<sup>0</sup> is slightly smaller than *f*c, and the loading type is proportional loading. The samples were tested after 120 days of curing.

The formulas for calculating bi- and triaxial ultimate strength are shown as Eqs. (5) and (6) [12], respectively:

The symbols of stress and strain obey the following rules: the plus sign '+' denotes

Generally, the stress-strain curve can be expressed by Eqs. (3) and (4) [11].

*<sup>β</sup>*ð Þ *<sup>x</sup>* � <sup>1</sup> <sup>2</sup> <sup>þ</sup> *<sup>x</sup>*

*ε*<sup>0</sup> and *σ*<sup>0</sup> stand for peak strain and peak stress under uniaxial compression,

*<sup>y</sup>* <sup>¼</sup> *<sup>x</sup>*

*Test results of LWACs cured at negative temperature without anti-freezing agent for LC30.*

*<sup>y</sup>* <sup>¼</sup> *<sup>α</sup><sup>x</sup>* <sup>þ</sup> ð Þ <sup>3</sup>‐2*<sup>α</sup> <sup>x</sup>*<sup>2</sup> <sup>þ</sup> ð Þ *<sup>α</sup>*‐<sup>2</sup> *<sup>x</sup>*<sup>3</sup> *<sup>x</sup>*≤<sup>1</sup> (3)

. *α* and *β* are fitting coefficients shown in **Table 16**.

*x*≥1 (4)

*<sup>c</sup>* **(%) GLWC,** *f***cu (MPa)** *η<sup>T</sup>*

*<sup>c</sup>* **(%) GLWC,** *f***<sup>c</sup> (MPa)** *η<sup>T</sup>*

**1 d 2 d 3 d 7 d 14 d 28 d 3 d 7 d 14 d 28 d**

2 6.2 12.5 17.9 27.3 — 32.1 98.7 ———— —

2 5.8 12.1 16.1 24.4 — 29.7 91.3 ———— —

3 5.3 11.8 15.4 18.9 — 27.5 84.6 ———— —

–5 0 4.9 11.3 16.5 20.5 24.7 29.3 90.1 16.9 21.1 26.0 31.3 90.9

�10 0 4.1 10.8 13.8 17.5 21.4 25.0 76.9 14.4 18.9 23.3 27.2 79.0

�15 0 37 8.5 10.3 13.3 15.8 18.6 57.2 11.4 14.3 17.5 20.7 60.1

*28 days and curing at negative temperature to that at room temperature; (3) the mixes are slightly different from*

**3 d 7d 14 d 28 d 3 d 7d 14 d 28 d** �5 14.46 18.41 22.36 24.63 83.0 15.81 20.34 24.64 26.45 85.0 �10 12.65 16.16 19.63 21.34 71.9 14.86 17.87 21.98 23.34 75.0 �15 10.88 13.18 15.54 16.62 56.0 11.94 14.49 17.21 18.15 58.3 *f*ts (MPa) *f*ts (MPa) –5 1.87 2.49 3.03 3.42 91.9 2.03 2.54 3.13 3.49 92.3 –10 1.69 2.15 2.71 2.99 80.4 1.83 2.30 2.75 3.06 81.0 –15 1.50 1.88 2.21 2.46 66.1 1.69 1.97 2.32 2.55 67.5 *E*<sup>c</sup> (GPa) *E*<sup>c</sup> (GPa) –5 9.43 13.22 16.49 18.77 92.0 10.02 14.23 17.56 19.36 94.0 –10 8.81 12.58 15.03 16.52 81.0 8.97 12.01 14.98 17.10 83.0 –15 8.26 11.57 13.61 14.28 70.0 8.44 11.15 13.22 15.04 73.0

*Compressive strength of LWACs cured at negative temperature with anti-freezing agent for LC30.*

*<sup>c</sup>* **(%)**

*<sup>c</sup>* **(%)**

*<sup>c</sup> stands for the ratio of strength at*

tension; the minus sign '–' denotes compression.

*T* **(°C)** *w***<sup>A</sup> (%) ALWC,** *f***cu (MPa)** *η<sup>T</sup>*

*Sandy Materials in Civil Engineering - Usage and Management*

*Notes: (1) wA stands for the ratio of anti-freezing agent to cement (by mass); (2) η<sup>T</sup>*

*T* **(°C) ALWC,** *f***<sup>c</sup> (MPa)** *η<sup>T</sup>*

*<sup>ε</sup>*<sup>0</sup> and *<sup>y</sup>* <sup>¼</sup> *<sup>σ</sup>*

*σ*0

Ascending curve:

*Table 8.*

**Table 14.**

**Table 15.**

Descending curve:

where *<sup>x</sup>* <sup>¼</sup> *<sup>ε</sup>*

respectively.

**92**

*Sandy Materials in Civil Engineering - Usage and Management*

$$
\sigma\_3 = \frac{1 + o\_2}{1 + o\_2^{\cdot 1}} \sigma\_2, o\_2 = \frac{\sigma\_3}{\sigma\_2} \tag{5}
$$

increasing lateral stress; the law is the same as for NWC, but the ratio of *σ*<sup>30</sup> to *f*<sup>c</sup> is larger than that of NWC. Also, the stress-strain curves show that the deformation resistance capacity of LWACs is stronger than that of NWC, so the LWACs cannot be crushed easily and thus have higher strength under the action of multiaxial

*σ***3:***–σ***2:***–σ***<sup>1</sup>** *–σ***<sup>1</sup> (MPa)** *–σ***<sup>2</sup> (MPa)** *–σ***<sup>30</sup> (MPa) Eq. (6) (MPa)** *E***<sup>r</sup> (%)** *σ***<sup>30</sup> /***f***<sup>c</sup>**

*The Influence of Hybrid Aggregates on Different Types of Concrete*

*DOI: http://dx.doi.org/10.5772/intechopen.88254*

1:0.1:0.1 5.11 4.98 49.77 �51.1 2.6 1.56 1:0.25:0.25 19.58 19.10 75.85 �78.32 3.2 2.37 1:0.5:0.5 50.61 49.21 97.94 �101.22 3.3 3.06 1:1:0.1 6.48 60.81 60.51 �64 5.7 1.89 1:1:0.25 22.56 87.03 86.48 �90.24 4.3 2.70 1:1:0.5 55.61 107.37 106.78 �111.22 4.1 3.34 1:0.25:0.1 7.56 36.62 58.62 �60.60 3.3 1.83 1:0.5:0.1 19.04 30.98 72.85 �75.80 4.1 2.28 1:0.5:0.25 6.06 14.77 73.64 �76.16 3.4 2.30

**120 d**

The ultimate strength and elastic modulus of LWACs under traditional triaxial

All of the strength and elastic modulus values increase with increasing confining pressure. Under the same temperature and confining pressure, the effect on NWA is highest when using the lowest amount of hybrid aggregate, such as gravel, NS, and LWS. However, when the temperature is above 300°C, the strength of HALWC is smaller than those of SLWC and GLWC. At the same time, below 300 °C, the strength increases, except for HALWC, whose strength increases at temperatures below 200°C. The relationship between ultimate compressive strength and confining pressure can be expressed by Mohr-Coulomb theory as shown in Eq. (7).

ALWC *–σ*<sup>30</sup> (MPa) 20 29.30 32.92 35.25 39.29 43.23

SLWC *–σ*<sup>30</sup> (MPa) 20 31.06 34.23 37.97 39.49 44.50

GLWC *–σ*<sup>30</sup> (MPa) 20 37.44 44.89 49.84 55.19 59.23

*T* **(°C)** �**2 MPa** �**4 MPa** �**6 MPa** �**8 MPa** �**10 MPa**

200 31.04 37.45 42.98 48.10 51.86 300 26.96 31.57 37.55 40.89 44.76 400 22.15 27.30 32.77 38.14 40.83 500 25.90 27.04 30.58 32.57 36.26

200 36.36 40.56 43.54 45.90 50.27 300 40.76 42.41 49.27 51.07 53.70 400 30.80 33.48 39.63 43.33 48.22 500 30.66 32.73 37.52 42.04 43.74

200 40.59 47.56 51.44 57.85 62.10 300 41.08 47.51 54.31 60.44 63.99 400 34.74 40.07 45.90 46.66 54.76 500 30.91 35.71 38.59 45.81 49.18

stress.

**95**

**Table 18.**

stresses are shown in **Table 19**.

*Triaxial compressive strength under proportional loading.*

$$\sigma\_3 = \frac{\sqrt{\sigma\_1 \sigma\_2 (1 + a\_1 + a\_3) \left(1 + a\_2 + a\_3^{-1}\right)}}{1 + a\_1^{-1} + a\_2^{-1}} \text{ or}\_1 = \frac{\sigma\_3}{\sigma\_1}, \alpha\_3 = \frac{\sigma\_2}{\sigma\_1} \tag{6}$$

The smaller relative error indicates that the test data are reliable and the formulas are correct. On the other hand, the multiaxial ultimate strength increases with

**Figure 4.**

*Test curves of stress-strain under uniaxial compression for LWACs after elevated temperature treatment. (a) ALWC, (b) SLWC, (c) GLWC, and (d) HALWC.*


#### **Table 17.**

*Biaxial compressive strength under proportional loading.*



## **Table 18.**

*<sup>σ</sup>*<sup>3</sup> <sup>¼</sup> <sup>1</sup> <sup>þ</sup> *<sup>ω</sup>*<sup>2</sup> <sup>1</sup> <sup>þ</sup> *<sup>ω</sup>*‐<sup>1</sup> 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi *σ*1*σ*2ð Þ 1 þ *ω*<sup>1</sup> þ *ω*<sup>3</sup> 1 þ *ω*<sup>2</sup> þ *ω*‐<sup>1</sup>

> <sup>1</sup> þ *ω*‐<sup>1</sup> 2

*Test curves of stress-strain under uniaxial compression for LWACs after elevated temperature treatment.*

*σ***3:***σ***<sup>2</sup>** *–σ***<sup>30</sup> (MPa) Eq. (5) (MPa)** *E***<sup>r</sup> (%)** *σ***<sup>30</sup>** */ f***<sup>c</sup>**

1:0.25 40.94 �42.62 4.10 1.28 1:0.5 39.92 �41.75 4.58 1.24 1:0.75 39.88 �41.96 5.22 1.25 1:1 41.88 �44.28 5.73 1.31 *Notes: (1) σ<sup>30</sup> stands for peak stress, namely, ultimate compressive strength. Er stands for relative error.*

*(a) ALWC, (b) SLWC, (c) GLWC, and (d) HALWC.*

*Biaxial compressive strength under proportional loading.*

The smaller relative error indicates that the test data are reliable and the formulas are correct. On the other hand, the multiaxial ultimate strength increases with

q � �

1 þ *ω*‐<sup>1</sup>

*Sandy Materials in Civil Engineering - Usage and Management*

*σ*<sup>3</sup> ¼

**Figure 4.**

**Table 17.**

**94**

*<sup>σ</sup>*2*,ω*<sup>2</sup> <sup>¼</sup> *<sup>σ</sup>*<sup>3</sup>

*σ*2

*<sup>ω</sup>*<sup>1</sup> <sup>¼</sup> *<sup>σ</sup>*<sup>3</sup> *σ*1

*,ω*<sup>3</sup> <sup>¼</sup> *<sup>σ</sup>*<sup>2</sup> *σ*1

3

(5)

(6)

**120 d**

*Triaxial compressive strength under proportional loading.*

increasing lateral stress; the law is the same as for NWC, but the ratio of *σ*<sup>30</sup> to *f*<sup>c</sup> is larger than that of NWC. Also, the stress-strain curves show that the deformation resistance capacity of LWACs is stronger than that of NWC, so the LWACs cannot be crushed easily and thus have higher strength under the action of multiaxial stress.

The ultimate strength and elastic modulus of LWACs under traditional triaxial stresses are shown in **Table 19**.

All of the strength and elastic modulus values increase with increasing confining pressure. Under the same temperature and confining pressure, the effect on NWA is highest when using the lowest amount of hybrid aggregate, such as gravel, NS, and LWS. However, when the temperature is above 300°C, the strength of HALWC is smaller than those of SLWC and GLWC. At the same time, below 300 °C, the strength increases, except for HALWC, whose strength increases at temperatures below 200°C. The relationship between ultimate compressive strength and confining pressure can be expressed by Mohr-Coulomb theory as shown in Eq. (7).



cause the foamed concrete to crack. According to the properties, the bulk density of LWA is smaller than that of water, and thus the foamed concrete consists of LWA foamed by physical foaming, which can be called all-lightweight foamed concrete (ALWFC). It does not crack and also makes a higher-strength-grade concrete (up to LFC 30; LFC is the code name of strength grade of mortar). Because of these properties, it can be widely used in non-structure and structure concrete and pumped but not vibrated. The LWAs are SC and SP in foamed concrete in this

*) and test results of all-lightweight foamed concrete.*

Although there are countless air pores in ALWFC, most of these pores are discontinuous, so ALWFC has better durability. According to the test results, the carbonation depth generally does not exceed 5 mm in 56 days, and the resistance performance with regard to chloride ion permeability, that is, the electric flux after 6 hours, is smaller than 1000 C. On the other hand, the ALWFC also has better fire

Taking a reinforced ALWC beam, for example, the parameters of the tested

For the shear beam, because there is no warning before the occurrence of diagonal cracks, the diagonal cracks occur in the shear span section when the load is 20% of the ultimate load and then rapidly expand to the length of 100–150 mm. The initial width of the diagonal crack is generally 0.05 mm in the reinforced NWC beam compared to 0.03 mm in this study. At the same time, the maximum width of cracks and the deflection under service loads are 0.29 mm and 10.05 mm, respec-

The theoretical and test values of ultimate strength for normal and diagonal sections are shown in **Table 25**. All the test values slightly exceed the theoretical values. Compared to a reinforced NWC beam with the same stiffness, the width and height of the cross-section need to be increased by 18%, respectively. On the other

According to [16, 17], during the beam flexural test, the maximum crack width should not exceed 0.3 mm under service loads, and the deflection should not exceed *l*0/200 = 10.5 mm. The test values are 0.27 and 5.21 mm for the crack width and deflection, respectively, so ALWC can meet the code requirements. On the other hand, the crack load is about 28% of the ultimate load, and the service load is about

resistance, sound insulation, and sound absorption capabilities.

The test results according to GB50152-2012 [15] are as follows.

72%; these values are basically the same as those for the RC beam.

beams are shown in **Tables 21**–**25** and **Figures 5** and **6**.

study, and the mixes are shown in **Table 20**.

**Type** *m***<sup>C</sup>**

**Table 20.**

*Reference mixes (1 m<sup>3</sup>*

**(kg)**

*Notes: mF stands for the mass of foam agent.*

*m***FA (kg)**

*DOI: http://dx.doi.org/10.5772/intechopen.88254*

*m***SP (kg)**

*The Influence of Hybrid Aggregates on Different Types of Concrete*

*m***SC (kg)**

*m***<sup>W</sup> (kg)**

LFC 5 230 130 430 110 112 407 5.2 973 0.12 LFC 10 260 145 520 130 126 370 12.1 1185 0.26 LFC 20 360 198 543 136 173 280 24.5 1410 0.35 LFC 30 360 235 630 220 184 208 33.1 1723 0.42

*m***<sup>F</sup> (g)**

*f***cu28d (MPa)**

*ρ***d (kg/m<sup>3</sup> )**

*λ* **(w/(m.k))**

**6. Properties of reinforced ALWC**

tively, thus meeting the code requirements.

**97**

#### **Table 19.**

*Test results of LWACs under traditional triaxial compression after elevated temperature treatment for LC30.*

$$\frac{\sigma\_{30}}{f\_{\text{c}}} = 1 + C \left(\frac{\sigma\_1}{f\_{\text{c}}}\right)^{\epsilon} \sigma\_1 = \sigma\_2 \tag{7}$$

where *C* and *c* are the fitting coefficients for each temperature group and concrete group, respectively.

The absolute values of relative error are all smaller than 5%.

### **5. Properties of lightweight sand foamed concrete**

In China, traditional foamed concrete generally consists of cement, NS, water, foam agent, and so on [13, 14]. Because the densities of cement and NS are significantly higher than the density of water, these particles sink easily and therefore


*The Influence of Hybrid Aggregates on Different Types of Concrete DOI: http://dx.doi.org/10.5772/intechopen.88254*

#### **Table 20.**

*Reference mixes (1 m<sup>3</sup> ) and test results of all-lightweight foamed concrete.*

cause the foamed concrete to crack. According to the properties, the bulk density of LWA is smaller than that of water, and thus the foamed concrete consists of LWA foamed by physical foaming, which can be called all-lightweight foamed concrete (ALWFC). It does not crack and also makes a higher-strength-grade concrete (up to LFC 30; LFC is the code name of strength grade of mortar). Because of these properties, it can be widely used in non-structure and structure concrete and pumped but not vibrated. The LWAs are SC and SP in foamed concrete in this study, and the mixes are shown in **Table 20**.

Although there are countless air pores in ALWFC, most of these pores are discontinuous, so ALWFC has better durability. According to the test results, the carbonation depth generally does not exceed 5 mm in 56 days, and the resistance performance with regard to chloride ion permeability, that is, the electric flux after 6 hours, is smaller than 1000 C. On the other hand, the ALWFC also has better fire resistance, sound insulation, and sound absorption capabilities.
