**5.1 Effect of aggregate content**

The effect of aggregate content was evaluated by the flowability and 7 days compressive strength. Mixtures are cured at 60°C for 24 hours. **Figure 22** shows the flowability and 7 days compressive strength as affected by the CWP to aggregate ratio. It is noticed that the flowability decreases as the aggregate content increases. This is similar to the behavior cement concrete as the CWP content acts as a lubricant between aggregate particles. Oppositely the 7 days compressive strength improved by the increase of the aggregate content. The mixing regime of the solution affects the flowability and strength. The mixing regime (A) shows the best flowability performance while the other mixing regimes show similar flowability values. The mixing regimes (D) and (E) produce the highest compressive.

#### **5.2 Effect of admixture content**

Superplasticizer (i.e., polycarboxylic ether based) is added with a dosage of 1.5 and 4.0% of the CWP weight. The AAC mixture with CWP to the aggregate ratio (1:2.5) and 24 hours curing at 60°C is used to examine the effect of admixture dosage. Flowability and the 7 days compressive strength results are presented in **Table 10**. The use of 1.5% by weight superplasticizer, shows variable improvement in the flowability and marginal improvement in the strength. By increasing the admixture dosage to 4.0%, the flowability and strength are improved. For both admixture dosages, the mixing regimes (D) and (E) show the best flowability improvement and highest compressive strength.

### **5.3 Effect of curing time**

The AAC mixture with CWP to aggregate ratio (1:2.5) and 4% admixture is used to examine the effect of curing time (i.e., 24 and 48 hours) at 60°C. **Figure 23** shows the effect of curing time on the 7 days compressive strength. The compressive strength increases as the curing time increases. A similar trend is reported for metakaolin-based AAC [87]. Although increasing the curing time improves the compressive strength, the application of shorter curing time is considered from the point of reducing the energy consumption.

#### **Figure 22.**

*Flowability and 7 days compressive strength as affected by CWP to aggregate ratio.*


#### **Table 10.**

*Effect of admixture on flowability and 7 days compressive strength.*

### **5.4 Effect of slag content and curing regime**

Several studies investigated the use of slag in making AAC [88–92]. Slag proved to be a suitable material in making AAC. Slag is characterized by having some

**31**

**Figure 23.**

*time at 60°C.*

**Figure 24.**

*Flowability of AAC including CWP and slag.*

*The Use of Ceramic Waste Powder (CWP) in Making Eco-Friendly Concretes*

hydraulic reaction due to the existence of calcium oxide (CaO) beside the existence of silica and alumina for the alkali activation. Therefore, slag is used to replace part of the CWP. This will help improve the flowability of the AAC mixture and improve the strength development without the need to increase curing time. The AAC mixture with CWP to aggregate ration 1:2.5 and 4% admixture is used to assess the effect of including slag as a binder material in addition to the CWP. The slag replaced the CWP with 10, 20 and 40% by weight. The AAC mixtures including slag are subjected to three curing regimes; air curing, 24 hours at 60°C followed by air curing, and 24 hours at 60°C followed by water curing for 6 days. **Figure 24** shows the flowability of AAC mixtures including slag and CWP. The inclusion of slag improves the mixtures' flowability. The improvement is proportional to the slag

*Seven days compressive strength for the AAC mixture with CWP to aggregate ratio 1:2.5 as affected by curing* 

The effect of including slag with CWP on the 7 days strength is displayed in **Figure 25**. The air cured mixtures showed the lowest strength development. It is observed that the (oven + air) and (oven + water) results are comparable for both the 20 and 40% slag replacements. The strength values are found to increase with

the increase in slag % replacing the CWP, with the highest at 40% slag.

content with the highest improvement at 40% slag.

*DOI: http://dx.doi.org/10.5772/intechopen.81842*

*The Use of Ceramic Waste Powder (CWP) in Making Eco-Friendly Concretes DOI: http://dx.doi.org/10.5772/intechopen.81842*

#### **Figure 23.**

*Ceramic Materials - Synthesis, Characterization, Applications and Recycling*

**30**

*\**

**Table 10.**

**Figure 22.**

**5.4 Effect of slag content and curing regime**

*Effect of admixture on flowability and 7 days compressive strength.*

*Superplasticizer admixture dosage by weight of the CWP.*

*Flowability and 7 days compressive strength as affected by CWP to aggregate ratio.*

Several studies investigated the use of slag in making AAC [88–92]. Slag proved

to be a suitable material in making AAC. Slag is characterized by having some

**Mixing regime Flowability (mm) 7 Days compressive strength (MPa)**

A 95 107 12 14 B 95 107 10 12 C 99 110 11 13 D 110 116 13 15 E 112 117 14 16

**1.5%\* 4.0%\* 1.5%\* 4.0%\***

*Seven days compressive strength for the AAC mixture with CWP to aggregate ratio 1:2.5 as affected by curing time at 60°C.*

#### **Figure 24.** *Flowability of AAC including CWP and slag.*

hydraulic reaction due to the existence of calcium oxide (CaO) beside the existence of silica and alumina for the alkali activation. Therefore, slag is used to replace part of the CWP. This will help improve the flowability of the AAC mixture and improve the strength development without the need to increase curing time. The AAC mixture with CWP to aggregate ration 1:2.5 and 4% admixture is used to assess the effect of including slag as a binder material in addition to the CWP. The slag replaced the CWP with 10, 20 and 40% by weight. The AAC mixtures including slag are subjected to three curing regimes; air curing, 24 hours at 60°C followed by air curing, and 24 hours at 60°C followed by water curing for 6 days. **Figure 24** shows the flowability of AAC mixtures including slag and CWP. The inclusion of slag improves the mixtures' flowability. The improvement is proportional to the slag content with the highest improvement at 40% slag.

The effect of including slag with CWP on the 7 days strength is displayed in **Figure 25**. The air cured mixtures showed the lowest strength development. It is observed that the (oven + air) and (oven + water) results are comparable for both the 20 and 40% slag replacements. The strength values are found to increase with the increase in slag % replacing the CWP, with the highest at 40% slag.

#### **Figure 25.**

*Seven days compressive strength of AAC including CWP and slag.*

The inclusion of slag is beneficial in producing AAC using CWP with a level of replacement of 40%. Based on the flowability and the 7 days compressive strength, the following are the optimum mixture's parameter to make AAC using CWP:

i.the CWP to the aggregate ratio is 2.5,

ii.the alkali solutions mixing regime (D) (i.e., NaOH 60% and KOH 40% mixed) produces suitable flowability and strength;

**33**

cement replacement.

*The Use of Ceramic Waste Powder (CWP) in Making Eco-Friendly Concretes*

iii.the use of 4% of superplasticizer to improve flowability;

v.the use of 40% by weight slag to replace CWP.

*Seven and twenty-eight days results for optimum AAC mixture.*

similar to Portland cement concrete.

ingredient in making eco-friendly concretes.

used to optimize all required characteristics.

**6. Conclusions**

**Table 11.**

iv.the application of 24 hours at 60°C followed by air curing; and

The performance of an AAC mixture following the above parameters is assessed. **Table 11** summarizes the obtained results. Results show that CWP in combination with 40% slag can produce AAC with strength suitable for different structural applications. The electrical resistivity and initial rate of absorption indicate that the produced AAC is characterized by high durability. The change in the test results values with age indicates that most of the reactions are finished at 7 days of age. Hence there is no need for waiting to evaluate the performance at 28 days of age

Compressive strength (MPa) 39.3 40.7 Permeable pores % 8.89 8.32 Electrical bulk resistivity (kΩ.cm) 17.9 18.2 Initial rate of absorption (mm/min1/2) sorptivity 0.15 0.12

**Test age (days) 7 28**

The CWP contains high silica and alumina content (i.e., >80%). Also, it is characterized by having some amorphous content which shows pozzolanic activity especially at late ages. Therefore, CWP has strong potentials to be used as an

Using CWP as an ingredient in making CVC is viable. High-performance concrete can be produced by including CWP as partial cement replacement. CWP improves the workability retention of the CVC mixtures. The inclusion of CWP will reduce the early-age strength and slowed the strength development. Significant improvement of CVC durability can be achieved by including high content of CWP. The CVC performance varies according to the CWP content. CWP can be used in the range of 10–20% to improve workability retention and late strength development. A CWP content ranging from 30 to 40% is needed to improve durability. If the performance of mixture requires the combination of workability retention, strength and durability, a CWP content ranging from 20 to 30% can be

CWP can be used as a partial cement replacement to produce SCC that meets international requirements. All fresh concrete properties, except for slump flow, are significantly improved by the incorporation of CWP. The improvement is proportional to the CWP content. Similar to CVC, the inclusion of CWP affected the strength development and enhanced the durability. SCC with improved fresh performance and optimized strength can be produced using 40% CWP as partial

The use of CWP in making AAC showed promising potentials. The production of AAC using CWP should consider the aggregate content of the mixture, the

*DOI: http://dx.doi.org/10.5772/intechopen.81842*


#### *The Use of Ceramic Waste Powder (CWP) in Making Eco-Friendly Concretes DOI: http://dx.doi.org/10.5772/intechopen.81842*

**Table 11.**

*Ceramic Materials - Synthesis, Characterization, Applications and Recycling*

The inclusion of slag is beneficial in producing AAC using CWP with a level of replacement of 40%. Based on the flowability and the 7 days compressive strength, the following are the optimum mixture's parameter to make AAC using CWP:

ii.the alkali solutions mixing regime (D) (i.e., NaOH 60% and KOH 40% mixed)

i.the CWP to the aggregate ratio is 2.5,

*Seven days compressive strength of AAC including CWP and slag.*

produces suitable flowability and strength;

**32**

**Figure 25.**

*Seven and twenty-eight days results for optimum AAC mixture.*

iii.the use of 4% of superplasticizer to improve flowability;

iv.the application of 24 hours at 60°C followed by air curing; and

v.the use of 40% by weight slag to replace CWP.

The performance of an AAC mixture following the above parameters is assessed. **Table 11** summarizes the obtained results. Results show that CWP in combination with 40% slag can produce AAC with strength suitable for different structural applications. The electrical resistivity and initial rate of absorption indicate that the produced AAC is characterized by high durability. The change in the test results values with age indicates that most of the reactions are finished at 7 days of age. Hence there is no need for waiting to evaluate the performance at 28 days of age similar to Portland cement concrete.
