**3. Technical requirements of lightweight aggregate**

Lightweight aggregate (LWA) includes artificial, natural, industrial waste slag, cinder, and spontaneous combustible coal gangue LWA [2]. LWA is called superlightweight coarse aggregate (SLWCA) when *ρ*<sup>b</sup> does not exceed 500 kg/m<sup>3</sup> . The tube crushing strengths (TCS) of the different grades of high-strength lightweight coarse aggregates (HSLWCAs) are provided in **Table 3**. The softening coefficient should be equal to or higher than 0.8 and 0.7 for artificial and industrial waste slag LWCA and natural LWCA, respectively. The fineness modulus (*M*x, LA) of LWFA should be between 2.3 and 4.0.

According to the current LWA production technology and its use in actual engineering, the particle size distribution of LWA is shown in **Table 4**.


*Notes: The bulk density grade is a size range, not an exact number. For example, ρ<sup>b</sup> = 600 kg/m<sup>3</sup> means 500 < ρ<sup>b</sup> 600 kg/m<sup>3</sup> and so on.*

#### **Table 3.**

*Tube crushing strength and strength grade of LWAC for artificial HSLWCA stipulated in [2].*


#### **Table 4.**

*Particle size distribution for LWFA and LWCA.*

## **4. Lightweight aggregate concrete**

All-lightweight aggregate concrete (ALWAC), also known as all-lightweight concrete (ALWC), is made from LWFA, LWCA, cement, water, and other admixtures. Although ALWC has many excellent properties, such as high specific strength (ratio of cubic compressive strength to dry apparent density, *SS*, kNm/kg), high anti-deformability, excellent fire resistance, and so on, there are a number of negative aspects, such as low elastic modulus, the fact that LWCA rises more easily when pumping and vibrating LWAC, high costs, and so on. In order to satisfy the quality of both normal-weight concrete (NWC) and ALWC, new types of LWACs are formed by replacing parts of LWA with normal-weight aggregate (NWA) and vice versa. The naming rules are as follows.

The term 'ALWAC' was first mentioned in 1972 based on the available literature in the EI and SCI databases [7]. If, on the basis of ALWAC, only a part of LWFA is replaced with normal-weight sand in the same volume ratio *S*<sup>S</sup> (%, 0 < *S*<sup>S</sup> ≤ 100%), the LWAC is called sand lightweight concrete (SLWC) [7]. Similarly, if only a part of LWCA is replaced (0 < *S*<sup>G</sup> ≤ 100%) with normal-weight gravel, the concrete is called gravel lightweight concrete (GLWC). When both lightweight fine and coarse aggregates are replaced at the same time, the concrete is named hybrid aggregate lightweight concrete (HALWC). On the other hand, if on the basis of NWC, only a part of normal-weight coarse aggregate is replaced with expanded ceramsite (0 < *S*<sup>C</sup> < 100%), the concrete is named hybrid aggregate concrete with less ceramsite (HACC). The other corresponding SCCs, fibre-reinforced concrete (FRC) and reinforced concrete (RC), obey the rules too.

Compared to ALWC and NWC, the abovementioned concrete can be uniformly named semi-lightweight concrete (semi-LWC), where the term 'semi' means the LWA is less than half, just half, or more than half in volume. But according to [8], the concrete is called LWAC when the dry apparent density of concrete (*ρ*d, kg/m<sup>3</sup> ) is less than or equal to 1950 kg/m3 . Otherwise, it should be called specified density concrete (SDC) when 1950 < *ρ*<sup>d</sup> ≤ 2300 kg/m<sup>3</sup> . The grade of dry apparent density is ranked from 600 to 1900 kg/m<sup>3</sup> , the gradation is 100 kg/m<sup>3</sup> , and the density range is 50 kg/m<sup>3</sup> . For instance, *ρ*<sup>d</sup> is 600 kg/m<sup>3</sup> and the range is 560–650 kg/m<sup>3</sup> .

In this study, the LWFA and LWCA are shale pottery (SP) and shale ceramsite (SC), while the NWFA and NWCA are MS or natural sand (NS, also known as river sand) and crushed stone (CS), respectively. Both LWCA and NWCA are crushed aggregates. The technical parameters of LWA and normal-weight aggregate (NWA) are listed in **Tables 5** and **6**, respectively.

The porosity of SC and SP is 51.3 and 23.9%, and the void ratio is 41.7 and 47.0% according to tests following GB/T17431.2-2010 [9], respectively. So the SC must be pre-wetted 24 hours (h) before production of concrete in order to prevent reabsorption of mixing water, because the water absorption rate (%, *ω*a) is stable after 24 h, as shown in **Table 6**.

Generally, the strength of NWC increases with curing time; however, the strength of ALWC decreases when the diameter of LWCA is larger than 20 mm. Because of that, the maximum diameter of LWCA should be 15 mm or smaller. On the other hand, the SC has a softening effect, the softening coefficient (*Ψ*s*)* stipulated in GB/T17431.1–2010 [2] is not less than 0.8, and increasing the maximum diameter leads to a decrease in *Ψ*s. The test result is shown in **Table 7**, which can explain the difference in the strength forming mechanism between ALWC and NWC. Besides the abovementioned, when the maximum diameter of LWCA is larger, the damage area (area of LWCA versus mortar in a cross-section) is larger, so the strength of ALWC is lower; for example, the cubic compressive strength of ALWC is 32 MPa in 28 days, while the mortar strength after removing all LWCA in

fresh concrete is 45 MPa.

SC >16 mm

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

SP 4.75 mm

Gravel >16 mm

MS 4.75 mm

NS 4.75 mm

**Table 5.**

**Table 6.**

**85**

(%)

(%)

(%)

(%)

(%)

*Notes: The fineness module values of MS and NS are 3.06 and 2.98, respectively.*

*Water absorption rate (ωa) of SC after different numbers of hours (h).*

GB/T17431.1–2010 ≤ 5 ≤ 10 20–60 85–100 Experimental values 0.1 1.6 34.2 99.7

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

≥4.75 mm 3.54 3.58 3.59 3.57

16.0 mm (%)

Tube crushing strength (TCS) (MPa)

> 2.36 mm (%)

16.0 mm (%)

GB/T 14685–2011 0 0–10 30–60 85–100 95–100 Experimental values 0 8.4 48.6 92.3 98.7

> 2.36 mm (%)

> 2.36 mm (%)

≥9.50 mm 3.63 3.67 3.68 3.66 3.62 2.0–3.0

GB/T17431.1–2010 ≤10 ≤35 20–60 30–80 65–90 75–100 Experimental values 2.5 11.6 39.8 58.9 69.1 99.8

GB/T 14684–2011 0–10 0–25 10 50 41–70 70–92 80–94 Experimental values 7.8 24.6 47.2 66.9 89 93.7

GB/T 14684–2011 0 10 0–25 10–50 41–70 70–92 90–100 Experimental values 6.5 21.4 37.9 63.9 89.9 97.9

*Technical parameters of LWA and NWA stipulated in the Chinese national standard and test values.*

**Diameter range (mm) 0.5 h 1 h 2 h 4 h 6 h 8 h 12 h 24 h 32 h 48 h 72 h** 5–8 7.5 8.6 8.8 8.9 9.3 9.5 9.8 10.4 10.5 10.6 10.6 8–15 6.6 7.3 7.5 7.6 7.7 8.0 8.1 8.7 8.8 8.9 8.9

9.50 mm (%)

1.18 mm (%)

9.50 mm (%)

1.18 mm (%)

1.18 mm (%)

4.75 mm (%)

0.6 mm (%)

4.75 mm (%)

0.6 mm (%)

0.6 mm (%)

Mean Over

mean

0.3 mm (%)

2.36 mm (%)

0.3 mm (%)

0.3 mm (%)

GB/ T17431.1–2010

≤0.15 mm (%)

≤0.15 mm (%)

≤0.15 mm (%)

The ALWC is more sensitive to mix design than NWC mainly because of the higher porosity, lower bulk density, and lower tube crushing strength (TCS). Although the interface between crushed angular LWA and mortar is very good, the TCS is significantly lower compared to the mortar, and the LWCA floats more easily. The internal structure of ALWC becomes non-uniform, and thus the strength of ALWC depends on the strength of the mortar.

Many experiments have shown that the strength of ALWC mainly depends on the mass of the maximum diameter of LWCA, the mass of cementitious material (cement, fly ash (FA), silica fume, and other admixtures with gelling capacity), the water-to-binder weight ratio (*W*/*B*), and the fine aggregate to overall aggregate weight ratio (%, *S*p) (42–47% in general).


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

#### **Table 5.**

)

**4. Lightweight aggregate concrete**

*Sandy Materials in Civil Engineering - Usage and Management*

versa. The naming rules are as follows.

reinforced concrete (RC), obey the rules too.

concrete (SDC) when 1950 < *ρ*<sup>d</sup> ≤ 2300 kg/m<sup>3</sup>

are listed in **Tables 5** and **6**, respectively.

weight ratio (%, *S*p) (42–47% in general).

is less than or equal to 1950 kg/m3

ranked from 600 to 1900 kg/m<sup>3</sup>

after 24 h, as shown in **Table 6**.

is 50 kg/m<sup>3</sup>

**84**

All-lightweight aggregate concrete (ALWAC), also known as all-lightweight concrete (ALWC), is made from LWFA, LWCA, cement, water, and other admixtures. Although ALWC has many excellent properties, such as high specific strength (ratio of cubic compressive strength to dry apparent density, *SS*, kNm/kg), high anti-deformability, excellent fire resistance, and so on, there are a number of negative aspects, such as low elastic modulus, the fact that LWCA rises more easily when pumping and vibrating LWAC, high costs, and so on. In order to satisfy the quality of both normal-weight concrete (NWC) and ALWC, new types of LWACs are formed by replacing parts of LWA with normal-weight aggregate (NWA) and vice

The term 'ALWAC' was first mentioned in 1972 based on the available literature in the EI and SCI databases [7]. If, on the basis of ALWAC, only a part of LWFA is replaced with normal-weight sand in the same volume ratio *S*<sup>S</sup> (%, 0 < *S*<sup>S</sup> ≤ 100%), the LWAC is called sand lightweight concrete (SLWC) [7]. Similarly, if only a part of LWCA is replaced (0 < *S*<sup>G</sup> ≤ 100%) with normal-weight gravel, the concrete is called gravel lightweight concrete (GLWC). When both lightweight fine and coarse aggregates are replaced at the same time, the concrete is named hybrid aggregate lightweight concrete (HALWC). On the other hand, if on the basis of NWC, only a part of normal-weight coarse aggregate is replaced with expanded ceramsite (0 < *S*<sup>C</sup> < 100%), the concrete is named hybrid aggregate concrete with less ceramsite (HACC). The other corresponding SCCs, fibre-reinforced concrete (FRC) and

Compared to ALWC and NWC, the abovementioned concrete can be uniformly named semi-lightweight concrete (semi-LWC), where the term 'semi' means the LWA is less than half, just half, or more than half in volume. But according to [8], the concrete is called LWAC when the dry apparent density of concrete (*ρ*d, kg/m<sup>3</sup>

, the gradation is 100 kg/m<sup>3</sup>

. For instance, *ρ*<sup>d</sup> is 600 kg/m<sup>3</sup> and the range is 560–650 kg/m<sup>3</sup>

In this study, the LWFA and LWCA are shale pottery (SP) and shale ceramsite (SC), while the NWFA and NWCA are MS or natural sand (NS, also known as river sand) and crushed stone (CS), respectively. Both LWCA and NWCA are crushed aggregates. The technical parameters of LWA and normal-weight aggregate (NWA)

The porosity of SC and SP is 51.3 and 23.9%, and the void ratio is 41.7 and 47.0% according to tests following GB/T17431.2-2010 [9], respectively. So the SC must be

The ALWC is more sensitive to mix design than NWC mainly because of the higher porosity, lower bulk density, and lower tube crushing strength (TCS). Although the interface between crushed angular LWA and mortar is very good, the TCS is significantly lower compared to the mortar, and the LWCA floats more easily. The internal structure of ALWC becomes non-uniform, and thus the

Many experiments have shown that the strength of ALWC mainly depends on the mass of the maximum diameter of LWCA, the mass of cementitious material (cement, fly ash (FA), silica fume, and other admixtures with gelling capacity), the water-to-binder weight ratio (*W*/*B*), and the fine aggregate to overall aggregate

pre-wetted 24 hours (h) before production of concrete in order to prevent reabsorption of mixing water, because the water absorption rate (%, *ω*a) is stable

strength of ALWC depends on the strength of the mortar.

. Otherwise, it should be called specified density

. The grade of dry apparent density is

, and the density range

.

*Technical parameters of LWA and NWA stipulated in the Chinese national standard and test values.*


#### **Table 6.**

*Water absorption rate (ωa) of SC after different numbers of hours (h).*

Generally, the strength of NWC increases with curing time; however, the strength of ALWC decreases when the diameter of LWCA is larger than 20 mm. Because of that, the maximum diameter of LWCA should be 15 mm or smaller. On the other hand, the SC has a softening effect, the softening coefficient (*Ψ*s*)* stipulated in GB/T17431.1–2010 [2] is not less than 0.8, and increasing the maximum diameter leads to a decrease in *Ψ*s. The test result is shown in **Table 7**, which can explain the difference in the strength forming mechanism between ALWC and NWC. Besides the abovementioned, when the maximum diameter of LWCA is larger, the damage area (area of LWCA versus mortar in a cross-section) is larger, so the strength of ALWC is lower; for example, the cubic compressive strength of ALWC is 32 MPa in 28 days, while the mortar strength after removing all LWCA in fresh concrete is 45 MPa.


**Table 7.**

*Softening coefficient (Ψs) of SC after soaking in water for different numbers of days (d).*


*Notes: (1) mC, mFA, mSC, mCS, mSP, mMS, and mW stand for cement (C), fly ash (FA), shale ceramsite (SC), crushed stone (CS), shale pottery (SP), manufactured sand (MS), and water (W), respectively; (2) fcu, fc, and fts stand for the cubic compressive strength, axial compressive strength (prism specimen, height width ratio is 2 or 3), and splitting tensile strength (cubic specimen) at 28 days, respectively; (3) Ec is Young's elastic modulus; (4) ρ<sup>d</sup> stands for dry apparent density; (5) HACC is the specified density concrete (SDC) judged by ρd.*

*\*HACC is the specified density concrete (SDC), the symbol of concrete strength grade can be expressed by "SC", which can be different from the symbol "C" of normal-weight concrete (NWC), and "LC" of lightweight aggregate concrete (LWAC).*

According to GB50496-2009 [6], the adiabatic temperature rise of LWACs is

Time (h) 31.0 34.0 36.0 27.5 Maximum temperature (°C) 66.4 63.9 62.4 65.5 Calculated temperature (°C) 66.1 69.7 59.5 53.5

*Test and calculated values of adiabatic temperature rise for LWACs.*

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

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

*Relationships between adiabatic temperature rise and time.*

reaction proceeds, the Thermos glass liners burst at a certain time, as shown in **Table 9**. However, the length of time is shortest for HALWC. The reason may be the uniform distribution of normal-weight fine and coarse aggregates, which can improve the heat conduction rate and provide a better temperature distribution. On the contrary, the time period of the temperature rise is shorter for SC and SP compared to SLWC and GLWC, because of the higher porosity of LWA, which provides a better insulation performance. The difference between SLWC and GLWC may be that the distribution of NWFAs is more uniform than that of coarse

aggregate, such as the sand particles touched in dot form can speed up heat

Autogenous shrinkage of concrete mainly happens after the initial setting time, but chemical shrinkage, which includes three complete stages, also has a significant influence. According to the mechanism of concrete shrinkage, chemical shrinkage happens because the absolute volume of hydration products is smaller than that of water and binding material during the early stage. Autogenous shrinkage happens during the skeleton structure forming in a later stage, so the unhydrated cement particles react further. In fresh concrete, the volume can also cause shrinkage because of the setting of parts of particles. Drying shrinkage is caused by water loss. In short, the cracks in concrete are mainly caused by plastic shrinkage in the early

In **Figure 2**, the curves are smoothed after the peak values because of higher fluctuation (shown by dashed lines). The higher porosity and rougher surfaces of

conduction.

**Table 9.**

**Figure 1.**

stage.

**87**

Because the gas pressure in the Thermos bottle becomes higher as the hydration

**ALWC SLWC GLWC HALWC**

shown in **Table 9** (tested with a 3.7-litre Thermos bottle) and **Figure 1**.

#### **Table 8.**

*Reference mixes (1 m<sup>3</sup> ) and test results of LWACs and SDC for LC30.*

All of the following concretes are designed by pumping concrete; that is, the slump is 160–220 mm, mainly taking LC30, for example. The reference mixes and test results are shown in **Table 8**.

In **Table 8**, the cementitious material is PO42.5 Portland cement and Grade II fly ash. The water reducing rate of high performance water reducing agent is not less than 20% and added 1.6–2.0 wt% (by mass of cementitious material).

Because of the difference of LWA and NWA, the strength, elastic modulus, and dry apparent density are increased when LWFA or LWCA is replaced separately by normal-weight aggregates, but it is more complex when replaced at the same time.

Also, the ratio (*ζ*) of axial compressive strength to cubic compressive strength for LWAC is usually close to 1.0, which is larger than the value of 0.66–0.67 required by JGJ51-2002 [6] and also larger than the value of 0.76 given for NWC. This phenomenon is precisely because the LWA with lower TCS will be crushed before the cement mortar and will show larger deformation, which is equivalent to antifriction and thus with self-lubricated capability.

#### **4.1 Autogenous shrinkage properties of LWACs**

Because the hydration reaction of cement is an exothermic process, the amount of heat released leads to a temperature difference both inside and outside the concrete, and the temperature stress induces the appearance of cracks.


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

#### **Table 9.**

*Test and calculated values of adiabatic temperature rise for LWACs.*

**Figure 1.**

All of the following concretes are designed by pumping concrete; that is, the slump is 160–220 mm, mainly taking LC30, for example. The reference mixes and

*\*HACC is the specified density concrete (SDC), the symbol of concrete strength grade can be expressed by "SC", which can be different from the symbol "C" of normal-weight concrete (NWC), and "LC" of lightweight aggregate concrete*

**Diameter range (mm) 7 d 14 d 28 d 60 d 90 d 120 d 180 d**

5–8 0.86 0.81 0.77 0.72 0.66 0.58 0.55 8–15 0.92 0.90 0.86 0.81 0.75 0.72 0.70

5–8 0.88 0.85 0.83 0.81 0.79 0.78 0.77 8–15 0.96 0.94 0.92 0.90 0.89 0.88 0.87

*Softening coefficient (Ψs) of SC after soaking in water for different numbers of days (d).*

*m***SP (kg)** *m***MS (kg)**

ALWC 481 157 444 — 408 — 171 29.3 28.6 2.32 14.56 1594 SLWC 444 — 367 70 30.5 29.7 2.47 16.54 1612 GLWC 311 339 408 — 32.2 32.0 3.01 17.26 1796 HALWC 333 283 367 70 31.8 31.3 2.81 16.86 1785 HACC\* 300 128 45 957 — 624 235 37.3 24.6 3.90 36.47 2280 *Notes: (1) mC, mFA, mSC, mCS, mSP, mMS, and mW stand for cement (C), fly ash (FA), shale ceramsite (SC), crushed stone (CS), shale pottery (SP), manufactured sand (MS), and water (W), respectively; (2) fcu, fc, and fts stand for the cubic compressive strength, axial compressive strength (prism specimen, height width ratio is 2 or 3), and splitting tensile strength (cubic specimen) at 28 days, respectively; (3) Ec is Young's elastic modulus; (4) ρ<sup>d</sup> stands for dry*

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

*f***cu (MPa)**

*f***c (MPa)**

*f***ts (MPa)**

*E***c (GPa)**

*ρ***d (kg/m3 )**

than 20% and added 1.6–2.0 wt% (by mass of cementitious material).

*) and test results of LWACs and SDC for LC30.*

antifriction and thus with self-lubricated capability.

**4.1 Autogenous shrinkage properties of LWACs**

for LWAC is usually close to 1.0, which is larger than the value of 0.66–0.67 required by JGJ51-2002 [6] and also larger than the value of 0.76 given for NWC. This phenomenon is precisely because the LWA with lower TCS will be crushed before the cement mortar and will show larger deformation, which is equivalent to

In **Table 8**, the cementitious material is PO42.5 Portland cement and Grade II fly ash. The water reducing rate of high performance water reducing agent is not less

Because of the difference of LWA and NWA, the strength, elastic modulus, and dry apparent density are increased when LWFA or LWCA is replaced separately by normal-weight aggregates, but it is more complex when replaced at the same time. Also, the ratio (*ζ*) of axial compressive strength to cubic compressive strength

Because the hydration reaction of cement is an exothermic process, the amount

of heat released leads to a temperature difference both inside and outside the concrete, and the temperature stress induces the appearance of cracks.

test results are shown in **Table 8**.

*Ψ*s1 (saturated surface dry condition)

*Ψ*s2 (oven dry condition)

*m***<sup>C</sup> (kg)** *m***FA (kg)**

*m***SC (kg)**

*m***CS (kg)**

*Sandy Materials in Civil Engineering - Usage and Management*

*apparent density; (5) HACC is the specified density concrete (SDC) judged by ρd.*

**Table 7.**

**Type of concrete**

*(LWAC).*

**Table 8.**

**86**

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

*Relationships between adiabatic temperature rise and time.*

According to GB50496-2009 [6], the adiabatic temperature rise of LWACs is shown in **Table 9** (tested with a 3.7-litre Thermos bottle) and **Figure 1**.

Because the gas pressure in the Thermos bottle becomes higher as the hydration reaction proceeds, the Thermos glass liners burst at a certain time, as shown in **Table 9**. However, the length of time is shortest for HALWC. The reason may be the uniform distribution of normal-weight fine and coarse aggregates, which can improve the heat conduction rate and provide a better temperature distribution. On the contrary, the time period of the temperature rise is shorter for SC and SP compared to SLWC and GLWC, because of the higher porosity of LWA, which provides a better insulation performance. The difference between SLWC and GLWC may be that the distribution of NWFAs is more uniform than that of coarse aggregate, such as the sand particles touched in dot form can speed up heat conduction.

Autogenous shrinkage of concrete mainly happens after the initial setting time, but chemical shrinkage, which includes three complete stages, also has a significant influence. According to the mechanism of concrete shrinkage, chemical shrinkage happens because the absolute volume of hydration products is smaller than that of water and binding material during the early stage. Autogenous shrinkage happens during the skeleton structure forming in a later stage, so the unhydrated cement particles react further. In fresh concrete, the volume can also cause shrinkage because of the setting of parts of particles. Drying shrinkage is caused by water loss. In short, the cracks in concrete are mainly caused by plastic shrinkage in the early stage.

In **Figure 2**, the curves are smoothed after the peak values because of higher fluctuation (shown by dashed lines). The higher porosity and rougher surfaces of

**Figure 2.** *Test curves of autogenous shrinkage strain with time.*

SC and SP also result in larger specific surface areas (total area of material per unit mass, m2 /g), which can absorb more cement particles and thus improve hydration conduction, so the autogenous shrinkage of ALWC is greater in a shorter time period and then becomes stable. Among SLWC, GLWC, and HALWC, the autogenous shrinkage is mainly determined by the amounts of LWA. Because the specific surface area of aggregates is different, the internal distribution of aggregates is uniform, and parts of cement particles are subsident, which can determine the internal temperature stress field, so the resistance capability of plastic deformation is different.

#### **4.2 Durability properties of LWACs**

The effects of different mineral admixtures on the durability of LWACs were studied. **Table 10** shows the effects of substituting 75 wt% mineral powder (denoted as MP75; the activity index is 96% in 28 days) for fly ash and 50 wt% limestone powder (denoted as LP50), respectively. And both mineral powder and limestone powder are mixed in a ratio of 1:1, and total substitution for fly ash (marked MP75 + LP50) is based on **Table 8** (with a slight difference). The test method is according to GB50082–2009 [10].

**Table 11** shows that the concrete strength and elastic modulus increase under curing in water on different days. However, the HALWC falls slightly, and the elastic modulus is almost constant. Similarly, for any type of LWAC, all of the *ζ*

*chloride ion penetration of concrete at 28 d; (3) Δm<sup>21</sup> and fcu<sup>21</sup> stand for the mass loss and cubic compressive strength of concrete after 21 dry-wet cycles under sulphate attack, respectively; (4) the test is stopped when the ratio of*

The test results show the LWACs are without a softening effect, so they can be

Although the mass loss in different types of concretes shows no obvious difference after high-temperature treatment, the effect of the addition of NWAs alone on the strength and elastic modulus is higher and changes regularly; that is, added NWCA alone larger than added NWFA alone, but smaller when added at same time

In general, the residual values of elastic modulus are larger than those of strength, which means the anti-deformation capacity of concrete decreases with

used in hydraulic structure engineering and underground engineering.

The appearance characteristics and strength of LWACs are shown in **Tables 12** and **13** under different temperatures (*T*, °C), respectively. When the temperature is below 200°C, the surface of concrete shows no change, and the strength increases, but when the temperature is above 300°C, changes in both colour and crack shape can be observed. The maximum width of cracks (*w*max, mm)

**4.4 Properties of LWACs after elevated temperature treatment**

*28 d stands for the carbonation depth of concrete at 28 d; (2) Q <sup>e</sup>*

*Kf = fcu21/fcu28 d* � *100% is larger than 75% according to GB50082–2009 [10].*

*Test results of durability for different LWACs and SDC with LC30.*

increases with increases in temperature and the strength decreases.

values are also close to 1.0 on different days.

**Type** *h***<sup>c</sup>**

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

*Notes: (1) hc*

**Table 10.**

**28 d (mm)** *Q***<sup>e</sup>**

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

ALWC 12.6 1235 31.3 30.1 31.2 96.5 ALWC-MP75 10.8 1126 28.6 32.6 33.4 97.6 ALWC-LP50 11.8 1226 46.8 28.2 32.6 86.5 ALWC-MP50 + LP50 — — 33.7 29.8 34.7 85.9 SLWC 11.2 1126 32.6 36.6 38.6 94.8 SLWC-MP75 9.3 1042 31.6 38.1 40.6 93.8 SLWC-LP50 10.4 1092 43.1 34.3 39.4 87.1 SLWC-MP50 + LP50 — —— — 40.1 — GLWC 10.2 1326 35.5 41.2 44.5 92.6 GLWC-MP75 8.3 1265 34.2 43.7 45.4 96.3 GLWC-LP50 9.5 1301 44.5 38.6 46.5 83.0 GLWC-MP50 + LP50 — —— — 46.1 — HALWC 12.9 1410 34.7 36.9 39.7 92.9 HALWC-MP75 10.6 1339 33.5 38.3 40.8 93.9 HALWC-LP50 11.2 1389 46.3 35.2 40.5 86.9 HALWC-MP50 + LP50 — —— — 40.8 — HACC 9.0 1007 — 36.4 38.3 95.0

**28 d (C) Δ***m***<sup>21</sup> (g)** *f***cu21 (MPa)** *f***cu28 d (MPa)** *K***<sup>f</sup> (%)**

*28 d stands for electric flux after 6 h under*

than added NWCA only.

**89**

Mineral powder can enhance both the strength and durability of concrete. Although the added limestone powder only reduces the strength of concrete, the requirements can be met, and the cost can be reduced. Because fly ash has become a scarce resource in China, mineral and limestone powder can be an effective alternative in the ready-mixed concrete industry.

Generally, the effects of normal-weight aggregates and mineral admixtures on carbonation and electric flux are not obvious, but according to GB50082-2009 [10], when the electric flux is between 1000 and 2000 C, the grade of chloride iron penetration is low, so the concretes can meet the requirements of the code.

#### **4.3 Softening properties of LWACs**

Since SC has a softening effect according to **Table 7**, is there also an SC concrete softening effect? The test results (**Table 11**) show that the LWACs almost have no softening effects. A possible reason is that the LWAs are strengthened because of their absorption of cement particles and hydration; on the other hand, the main contribution to the strength comes from the cement mortar, which does not show softening.


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

*Notes: (1) hc 28 d stands for the carbonation depth of concrete at 28 d; (2) Q <sup>e</sup> 28 d stands for electric flux after 6 h under chloride ion penetration of concrete at 28 d; (3) Δm<sup>21</sup> and fcu<sup>21</sup> stand for the mass loss and cubic compressive strength of concrete after 21 dry-wet cycles under sulphate attack, respectively; (4) the test is stopped when the ratio of Kf = fcu21/fcu28 d* � *100% is larger than 75% according to GB50082–2009 [10].*

#### **Table 10.**

SC and SP also result in larger specific surface areas (total area of material per unit

The effects of different mineral admixtures on the durability of LWACs were

Mineral powder can enhance both the strength and durability of concrete. Although the added limestone powder only reduces the strength of concrete, the requirements can be met, and the cost can be reduced. Because fly ash has become a scarce resource in China, mineral and limestone powder can be an effective alter-

Generally, the effects of normal-weight aggregates and mineral admixtures on carbonation and electric flux are not obvious, but according to GB50082-2009 [10], when the electric flux is between 1000 and 2000 C, the grade of chloride iron penetration is low, so the concretes can meet the requirements of the code.

Since SC has a softening effect according to **Table 7**, is there also an SC concrete softening effect? The test results (**Table 11**) show that the LWACs almost have no softening effects. A possible reason is that the LWAs are strengthened because of their absorption of cement particles and hydration; on the other hand, the main contribution to the strength comes from the cement mortar, which does not show softening.

stress field, so the resistance capability of plastic deformation is different.

studied. **Table 10** shows the effects of substituting 75 wt% mineral powder (denoted as MP75; the activity index is 96% in 28 days) for fly ash and 50 wt% limestone powder (denoted as LP50), respectively. And both mineral powder and limestone powder are mixed in a ratio of 1:1, and total substitution for fly ash (marked MP75 + LP50) is based on **Table 8** (with a slight difference). The test

**4.2 Durability properties of LWACs**

*Test curves of autogenous shrinkage strain with time.*

*Sandy Materials in Civil Engineering - Usage and Management*

method is according to GB50082–2009 [10].

native in the ready-mixed concrete industry.

**4.3 Softening properties of LWACs**

**88**

/g), which can absorb more cement particles and thus improve hydration conduction, so the autogenous shrinkage of ALWC is greater in a shorter time period and then becomes stable. Among SLWC, GLWC, and HALWC, the autogenous shrinkage is mainly determined by the amounts of LWA. Because the specific surface area of aggregates is different, the internal distribution of aggregates is uniform, and parts of cement particles are subsident, which can determine the internal temperature

mass, m2

**Figure 2.**

*Test results of durability for different LWACs and SDC with LC30.*

**Table 11** shows that the concrete strength and elastic modulus increase under curing in water on different days. However, the HALWC falls slightly, and the elastic modulus is almost constant. Similarly, for any type of LWAC, all of the *ζ* values are also close to 1.0 on different days.

The test results show the LWACs are without a softening effect, so they can be used in hydraulic structure engineering and underground engineering.

#### **4.4 Properties of LWACs after elevated temperature treatment**

The appearance characteristics and strength of LWACs are shown in **Tables 12** and **13** under different temperatures (*T*, °C), respectively. When the temperature is below 200°C, the surface of concrete shows no change, and the strength increases, but when the temperature is above 300°C, changes in both colour and crack shape can be observed. The maximum width of cracks (*w*max, mm) increases with increases in temperature and the strength decreases.

Although the mass loss in different types of concretes shows no obvious difference after high-temperature treatment, the effect of the addition of NWAs alone on the strength and elastic modulus is higher and changes regularly; that is, added NWCA alone larger than added NWFA alone, but smaller when added at same time than added NWCA only.

In general, the residual values of elastic modulus are larger than those of strength, which means the anti-deformation capacity of concrete decreases with


