**4.6 Compressive strength results**

Strength is measured at different test ages (7, 28, and 90 days) to evaluate the strength development as affected by the inclusion of CWP as partial cement replacement. The strength development due to the inclusion of any cement

replacing material is mainly affected by the cement hydration and pozzolanic reaction the used material, and the effect on the concrete microstructure especially the densification of the microstructure with a particular focus on the aggregate-paste interfacial zone [77].

**Figure 20** shows the compressive strength development with age. The COV ranged from 0.4 to 3.0%. At the 7 days of age, it is noticed that the inclusion of CWP decreases the strength and the reduction is proportional to the CWP content. This could be a direct result of replacing cement by CWP which has no hydraulic reaction. At the 28 days of age, the mixture including 20% by weight CWP showed higher strength compared to the control mixture. Nevertheless, the mixture of 60% by weight CWP shows the least developed strength. Since CWP is characterized by the slow pozzolanic reaction, it is expected not to see much effect until late ages. At the 90 days of age, the improvement in strength is noticeable. At the 90 days of age, mixtures with 20 and 40% by weight CWP achieve the highest compressive strength compared to the control mixture. This implies that 20–40% by weight CWP is the optimum cement replacement to obtain high compressive strength.

**Figure 19.** *Segregation resistance results.*

**27**

**Figure 21.**

*Electrical resistivity of SCC.*

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

The increase in the strength can also be explained through the nucleation sites (i.e., nucleation of CH around the CWP particles). The CWP improves the packing of the concrete mixture due to its high SSA and its pozzolanic reaction, and the cement hydration acceleration similar to the effect of rice husk ash (RHA) observed in another investigation [76]. On the other hand, the use of 60% by weight CWP shows marginal improvement in strength; this can be due to the high amount of silica from the CWP, and the insufficient amount of calcium hydroxide (CH) from the cement hydration. Hence, some silica is left without chemical reaction. Similar behavior was observed by using RHA (i.e., characterized by high SSA and high

The electrical resistivity of concrete is affected by several factors such as porosity, pore size distribution, connectivity, concrete's moisture content, and ionic mobility in pore solution. Electrical resistivity assesses the concrete protection of reinforcing steel against corrosion. According to ACI 222R-01 [57], the corrosion

The resistivity values are presented in **Figure 21** at 28 and 90 days of age. The

COV ranged from 6.4 to 13.2%. The resistivity increases with age. The inclusion of CWP significantly increases the mixtures' resistivity. The significant increase in the resistivity due to the inclusion of CWP suggests that CWP tended to reduce the interconnected pore network contributing to the reduction of the concrete's conductivity. With age, CWP pozzolanic activity contributes to the refinement of concrete pores and microstructure, thus further reduces the ionic mobility and hence the concrete's conductivity. The improved resistivity indicated that the durability of the CWP concrete mixtures to protect reinforcing steel against the corrosive environment is much better than that of the control

The MIP test provides information about the pore system (i.e., pore volume and median pore diameter). The MIP results can help understand the development

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

silica content) as cement replacement [48].

protection level is improved as the resistivity value increases.

**4.7 Bulk electrical resistivity results**

mixture without CWP.

**4.8 Mercury intrusion porosimetry (MIP)**

**Figure 20.** *Compressive strength development with age.*

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

The increase in the strength can also be explained through the nucleation sites (i.e., nucleation of CH around the CWP particles). The CWP improves the packing of the concrete mixture due to its high SSA and its pozzolanic reaction, and the cement hydration acceleration similar to the effect of rice husk ash (RHA) observed in another investigation [76]. On the other hand, the use of 60% by weight CWP shows marginal improvement in strength; this can be due to the high amount of silica from the CWP, and the insufficient amount of calcium hydroxide (CH) from the cement hydration. Hence, some silica is left without chemical reaction. Similar behavior was observed by using RHA (i.e., characterized by high SSA and high silica content) as cement replacement [48].

### **4.7 Bulk electrical resistivity results**

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

interfacial zone [77].

replacing material is mainly affected by the cement hydration and pozzolanic reaction the used material, and the effect on the concrete microstructure especially the densification of the microstructure with a particular focus on the aggregate-paste

**Figure 20** shows the compressive strength development with age. The COV ranged from 0.4 to 3.0%. At the 7 days of age, it is noticed that the inclusion of CWP decreases the strength and the reduction is proportional to the CWP content. This could be a direct result of replacing cement by CWP which has no hydraulic reaction. At the 28 days of age, the mixture including 20% by weight CWP showed higher strength compared to the control mixture. Nevertheless, the mixture of 60% by weight CWP shows the least developed strength. Since CWP is characterized by the slow pozzolanic reaction, it is expected not to see much effect until late ages. At the 90 days of age, the improvement in strength is noticeable. At the 90 days of age, mixtures with 20 and 40% by weight CWP achieve the highest compressive strength compared to the control mixture. This implies that 20–40% by weight CWP is the optimum cement replacement to obtain high compressive strength.

**26**

**Figure 20.**

**Figure 19.**

*Segregation resistance results.*

*Compressive strength development with age.*

The electrical resistivity of concrete is affected by several factors such as porosity, pore size distribution, connectivity, concrete's moisture content, and ionic mobility in pore solution. Electrical resistivity assesses the concrete protection of reinforcing steel against corrosion. According to ACI 222R-01 [57], the corrosion protection level is improved as the resistivity value increases.

The resistivity values are presented in **Figure 21** at 28 and 90 days of age. The COV ranged from 6.4 to 13.2%. The resistivity increases with age. The inclusion of CWP significantly increases the mixtures' resistivity. The significant increase in the resistivity due to the inclusion of CWP suggests that CWP tended to reduce the interconnected pore network contributing to the reduction of the concrete's conductivity. With age, CWP pozzolanic activity contributes to the refinement of concrete pores and microstructure, thus further reduces the ionic mobility and hence the concrete's conductivity. The improved resistivity indicated that the durability of the CWP concrete mixtures to protect reinforcing steel against the corrosive environment is much better than that of the control mixture without CWP.

#### **4.8 Mercury intrusion porosimetry (MIP)**

The MIP test provides information about the pore system (i.e., pore volume and median pore diameter). The MIP results can help understand the development

**Figure 21.** *Electrical resistivity of SCC.*


#### **Table 8.**

*MIP results at 90 days of age (modified from [42]).*

of the concrete microstructure and can also explain the other obtained results. **Table 8** shows the MIP test results at 90 days of age. Test results show that high CWP content has a significant reduction of the pore volume and the pores' size. The reduction in the pore volume and the pores' size indicates densification of the microstructure. Also, the MIP results confirm the improvement observed in the resistivity results and compressive strength.

### **5. Zero-cement alkali activated concrete (AAC)**

Zero-cement alkali-activated concrete (AAC) emerged as an alternative to cement-based concrete [78–84]. Sometimes, AAC is referred to as inorganicpolymer or geopolymer concrete. In AAC, cement is completely replaced. AAC utilizes and silica and alumina rich materials to be alkali-activated to form a threedimensional CaO-free alumino-silicate binder. AAC offers a significant opportunity for the reuse of several industrial by-products and wastes such as fly ash, metakaolin, and blast-furnace slag. Geopolymerization technology is based on the reaction of alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH) and sodium silicate solution. The CWP is characterized by its high silica and alumina content which makes it a good candidate to be used in making ACC. The limited studies on suing CWP in AAC [38–40] concluded that the optimum curing temperature ranges from 60 to 80°C, the curing period ranges between 24 and 48 hours, and the molarity of the alkali solution is 12 M.

The use of CWP in the making AAC still needs further investigations to develop a better understanding of its performance. CWP is used to make AAC using different alkali solutions, mainly NaOH and KOH. Several parameters are investigated which include alkaline solutions with 12 M concentration (i.e., NaOH alone, KOH alone and combination), CWP to aggregate ratio (i.e., 1:1.5–1:2.0–1:2.5), admixture dosage (i.e., 1.5 and 4.0%), curing time (i.e., 60°C for 24 and 48 hours), the inclusion of slag in addition to CWP (i.e., slag content 10, 20 and 40%). Several tests are used to evaluate the performance of the mixtures which include flowability (i.e., ASTM C1437 [85]), cube compressive strength, permeable pores (i.e., ASTM C642 [54]), initial rate of water absorption (i.e., ASTM C1585 [86]), and electrical resistivity (i.e., ASTM C1760 [53]). The COV ranged from 0.3 to 2.8%.

The sodium hydroxide flakes and potassium hydroxide are dissolved in distilled water to make a solution with the desired concentration (i.e., 12 M) at least 1 day before its use. **Table 9** shows the alkali solutions used and the combination of NaOH and KOH solutions. The dry ingredients are first mixed for about 1 minute. The sodium hydroxide and potassium hydroxide solutions are added to the dry materials based on the order of mixing in **Table 9** and mixed for 3 minutes.

**29**

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

A 0 100 — B 100 0 —

*Mixtures' I.D., alkali solutions used and mixing regime of solutions.*

**I.D. Alkali solutions % Mixing regime of the solutions with the CWP**

C 20 80 NaOH solution is added first and mixed with solids for 1 minute, then KOH

D 40 60 NaOH and KOH solutions are mixed then added to solids and mixed for

E 60 40 KOH solution is added first and mixed with solids for 1 minute, then NaOH

is added and mixing continues for an additional 2 minutes

3 minutes

is added and mixing continues for an additional 2 minutes

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

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

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

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

**KOH NaOH**

**5.1 Effect of aggregate content**

**5.2 Effect of admixture content**

compressive.

**Table 9.**

compressive strength.

**5.3 Effect of curing time**

point of reducing the energy consumption.

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


#### **Table 9.**

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

**Mixture Porosity (%) Median pore diameter\***

R-C-0 24.989 8.1265 R-C-20 17.737 5.3136 R-C-40 15.604 3.9109 R-C-60 13.304 2.5002  **(μm)**

of the concrete microstructure and can also explain the other obtained results. **Table 8** shows the MIP test results at 90 days of age. Test results show that high CWP content has a significant reduction of the pore volume and the pores' size. The reduction in the pore volume and the pores' size indicates densification of the microstructure. Also, the MIP results confirm the improvement observed in the

Zero-cement alkali-activated concrete (AAC) emerged as an alternative to cement-based concrete [78–84]. Sometimes, AAC is referred to as inorganicpolymer or geopolymer concrete. In AAC, cement is completely replaced. AAC utilizes and silica and alumina rich materials to be alkali-activated to form a threedimensional CaO-free alumino-silicate binder. AAC offers a significant opportunity for the reuse of several industrial by-products and wastes such as fly ash, metakaolin, and blast-furnace slag. Geopolymerization technology is based on the reaction of alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH) and sodium silicate solution. The CWP is characterized by its high silica and alumina content which makes it a good candidate to be used in making ACC. The limited studies on suing CWP in AAC [38–40] concluded that the optimum curing temperature ranges from 60 to 80°C, the curing period ranges between 24 and

The use of CWP in the making AAC still needs further investigations to develop a better understanding of its performance. CWP is used to make AAC using different alkali solutions, mainly NaOH and KOH. Several parameters are investigated which include alkaline solutions with 12 M concentration (i.e., NaOH alone, KOH alone and combination), CWP to aggregate ratio (i.e., 1:1.5–1:2.0–1:2.5), admixture dosage (i.e., 1.5 and 4.0%), curing time (i.e., 60°C for 24 and 48 hours), the inclusion of slag in addition to CWP (i.e., slag content 10, 20 and 40%). Several tests are used to evaluate the performance of the mixtures which include flowability (i.e., ASTM C1437 [85]), cube compressive strength, permeable pores (i.e., ASTM C642 [54]), initial rate of water absorption (i.e., ASTM C1585 [86]), and electrical

The sodium hydroxide flakes and potassium hydroxide are dissolved in distilled water to make a solution with the desired concentration (i.e., 12 M) at least 1 day before its use. **Table 9** shows the alkali solutions used and the combination of NaOH and KOH solutions. The dry ingredients are first mixed for about 1 minute. The sodium hydroxide and potassium hydroxide solutions are added to the dry materials based on the order of mixing in **Table 9** and mixed for 3 minutes.

resistivity results and compressive strength.

*MIP results at 90 days of age (modified from [42]).*

*\**

**Table 8.**

*Based on the intruded volume.*

**5. Zero-cement alkali activated concrete (AAC)**

48 hours, and the molarity of the alkali solution is 12 M.

resistivity (i.e., ASTM C1760 [53]). The COV ranged from 0.3 to 2.8%.

**28**

*Mixtures' I.D., alkali solutions used and mixing regime of solutions.*
