4. Utilization of by-products in UHPFRCC

Based on the earlier sections, there are several types of by-products or industrial wastes other than SF that can be used as an SCM or as an additive material in UHPFRCC products. Some of these wastes are metakaolin (MK), rejected fly ash, ground-granulated blast furnace slag, rice husk ash, recycled glass powder, palm oil fuel ash, and so on. The general chemical and physical properties of some of these SCMs and ordinary Portland cement (OPC) are summarized in Table 4. The influence of some of these SCMs on mechanical properties of UHPFRCC is described in the following subsections.

#### 4.1. Metakaolin

impermeability. Thus, significant improvement on the strength and durability of UHPFRCC matrix is observed; however, special SPs should be used to have adequate flowability [63].

SPs are chemical admixtures used for reducing water demand. They are also known as highrange water reducers (HRWR) [64]. Ultra-high-range polycarboxylic ether-based (PCE-based) SPs are commonly used to have adequate concrete UHPFRCC flowability. Thus, UHPFRCC behaves similar to self-compacting concrete. Therefore, UHPFRCC can be used for casting very

Alsadey [65] concluded that compressive strength decreases if the applied SP dosage is beyond the optimum dosage because segregation and bleeding phenomena will occur. This finding

The fine aggregate (sand) functions by confining the cement matrix to add strength [13, 66]. Yurdakul [39] and Shilstone and Shilstone [67] revealed that an insufficient amount of sand induces the segregation of mixture and increases mix flow. By contrast, increasing sand content causes stiff mixture because the sand has a high water requirement due to its high specific surface area. Moreover, workability decreased as the cement content decreased for a given W/C and aggregate content because of inadequate amount of paste that lubricates the

Quartz sand is usually used for UHPFRCC production. This sand type is not chemically active in the cement hydration reaction [13, 66]. As outlined earlier, UHPFRCC is characterized as a composite that has a large volume of steel fiber and lacks coarse aggregates that are larger than

The recommended mean aggregate size used in producing UHPFRCCs is less than 1 mm, and

Generally, decreasing the W/C will decrease the permeability, the porosity of the paste decreases and concrete becomes less permeable thus reducing the passage of water and aggressive compounds such as chlorides and sulfates, thus the durability and strength increased [39, 41, 70]. Increasing W/C will increase workability [70]. Strength is considered to be a function of W/C [38, 39, 41]. To increase strength, thus, the W/C should be reduced; it is more efficient to reduce the

Improving the relative density of concrete is the main goal in producing UHPFRCCs and not water content reduction. Several researchers optimized the water-binder ratio (W/B) for UHPFRCCs. Wen-yu et al. [71] reported an optimum W/B ration of 0.16 based from their experimental work. Table 3 summarizes the mean and range for the W/C ratios and W/B ratios used in UHPFRCCs. The used W/B ration in producing UHPFRCC was in the range of

0.10–0.25, while for W/C it was found to be in the range of 0.13–0.37.

slender elements [34, 36, 63].

aggregate [38, 39, 68, 69].

3.2.5. Sand

120 Cement Based Materials

4 mm [4].

3.2.6. Water

can affect concrete uniformity and cohesiveness.

the aggregate-cement ratio can be up to 1.4 [21].

water content than to use more cement [39].

Metakaolin (MK) is considered as a by-product material that is manufactured from kaolin clay. MK is a very fine-white clay mineral that has been traditionally used in porcelain production.


OPC, refers to ordinary Portland cement; GGBS, refers to ground-granulated blast-furnace slag; SF, refers to silica fume; FA, refers to fly ash; r-FA, refers to rejected fly ash; GP, refers to glass powder; RHA, refers to rice husk ash; MK, refers to metakaolin; POFA, refers to palm oil fuel ash.

Table 4. Chemical and physical properties of OPC and mineral admixtures (%) [12, 72–74].

MK is considered as highly pozzolanic materials, where major constituents of MK are SiO2 and Al2O3, as tabulated in Table 4 [75].

Table 4 shows that MK is characterized with the highest alumina content compared with other mineral admixtures and OPC, showing the capability to produce strengthening gel, that is, calcium aluminates hydrate (CAH) by reacting with the primary hydrate of cement. Moreover, MK has a considerable silica content which produce calcium silicate hydrate (CSH), by reacting with calcium hydroxide [72].

Nuruddin et al. [72] studied the effect of MK and the aspect ratio (l/d) of fibers on the mechanical properties of high-strength ductile concrete (HSDC) with constant slump (50 10) as shown in Figure 3.

Nuruddin et al. [72] concluded that as the MK content increases the mechanical properties improved as shown in Figure 3. Among all the mix, the highest strengths have been observed with 10% MK and 2% volume fraction.

MK develops a high pozzolanic activity, however, degrading workability. Moreover, MK is its high embodied CO2 generated for the production of one ton of MK, which is about 330 kg/ton compared with silica fume and fly ash 14 and 4 kg/ton, respectively. On the other hand, MK is characterized with a faster strength development along with a lower drying shrinkage compared with plain cement and silica fume [76].

### 4.2. Rejected fly ash

Kou and Xing [15] stated that more than 1 million tons of fly ash is produced annually in Hong Kong, as a by-product of electricity generation, where the finer fraction (f-FA) produced by passing the raw materials of ash via a classifying process is routinely used in the production of blended cements for construction. f-FA has a fineness requirement of not more than 12% by mass retained on the 45-μm test sieve. However, the remaining proportion is rejected due to its large particle size. In Hong Kong, this rejected fly ash (r-FA) has to be disposed of in large lagoons, creating an ever-increasing environmental hazard. Effect of r-FA and steam curing on mechanical properties of UHPFRC is shown in Figure 4. The chemical and physical properties of r-FA are tabulated in Table 4.

Kou and Xing [15] concluded that as the r-FA replacement level with silica sand increases, the mechanical strengths of UHPRCC tend to increase compared with the control mix. This increase in strength due to the replacement of fine aggregate with r-FA is attributed to (1) the improvement of packing density with r-FA and (2) the pozzolanic action of r-FA. However, the rate strength development decreases with the increase in r-FA content. This is due to the fact that r-FA reacts very slowly with calcium hydroxide liberated during the hydration of cement and does not contribute significantly to the densification of the concrete matrix at early ages. The highest replacement level is reached up to 50%.

Glass has been used in the concrete production as a crushed glass, as a raw siliceous material

Figure 3. Influence of MK and fibers on mechanical properties of HSDC: (I) Plain concrete and (II) MK concrete: (a)

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Jin et al. [77] stated that glass powder (GP) is considered as amorphous and characterized with a high silica content. A particle size of 45 μm or less is reported to be favorable for pozzolanic

in the production of Portland cement [78], and as a hydration-enhancing filler [78].

Compressive Strength, (b) Splitting Strength, and (c) Flexural Strength [72].

reaction [15, 79].

#### 4.3. Glass powder

Jin et al. [77] stated that the recycling process of glass is considered as a major problem in urban areas of developed countries.

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MK is considered as highly pozzolanic materials, where major constituents of MK are SiO2 and

Table 4 shows that MK is characterized with the highest alumina content compared with other mineral admixtures and OPC, showing the capability to produce strengthening gel, that is, calcium aluminates hydrate (CAH) by reacting with the primary hydrate of cement. Moreover, MK has a considerable silica content which produce calcium silicate hydrate (CSH), by

Nuruddin et al. [72] studied the effect of MK and the aspect ratio (l/d) of fibers on the mechanical properties of high-strength ductile concrete (HSDC) with constant slump

Nuruddin et al. [72] concluded that as the MK content increases the mechanical properties improved as shown in Figure 3. Among all the mix, the highest strengths have been observed

MK develops a high pozzolanic activity, however, degrading workability. Moreover, MK is its high embodied CO2 generated for the production of one ton of MK, which is about 330 kg/ton compared with silica fume and fly ash 14 and 4 kg/ton, respectively. On the other hand, MK is characterized with a faster strength development along with a lower drying shrinkage com-

Kou and Xing [15] stated that more than 1 million tons of fly ash is produced annually in Hong Kong, as a by-product of electricity generation, where the finer fraction (f-FA) produced by passing the raw materials of ash via a classifying process is routinely used in the production of blended cements for construction. f-FA has a fineness requirement of not more than 12% by mass retained on the 45-μm test sieve. However, the remaining proportion is rejected due to its large particle size. In Hong Kong, this rejected fly ash (r-FA) has to be disposed of in large lagoons, creating an ever-increasing environmental hazard. Effect of r-FA and steam curing on mechanical properties of UHPFRC is shown in Figure 4. The chemical and physical properties

Kou and Xing [15] concluded that as the r-FA replacement level with silica sand increases, the mechanical strengths of UHPRCC tend to increase compared with the control mix. This increase in strength due to the replacement of fine aggregate with r-FA is attributed to (1) the improvement of packing density with r-FA and (2) the pozzolanic action of r-FA. However, the rate strength development decreases with the increase in r-FA content. This is due to the fact that r-FA reacts very slowly with calcium hydroxide liberated during the hydration of cement and does not contribute significantly to the densification of the concrete matrix at early ages.

Jin et al. [77] stated that the recycling process of glass is considered as a major problem in

Al2O3, as tabulated in Table 4 [75].

122 Cement Based Materials

reacting with calcium hydroxide [72].

with 10% MK and 2% volume fraction.

pared with plain cement and silica fume [76].

(50 10) as shown in Figure 3.

4.2. Rejected fly ash

of r-FA are tabulated in Table 4.

urban areas of developed countries.

4.3. Glass powder

The highest replacement level is reached up to 50%.

Figure 3. Influence of MK and fibers on mechanical properties of HSDC: (I) Plain concrete and (II) MK concrete: (a) Compressive Strength, (b) Splitting Strength, and (c) Flexural Strength [72].

Glass has been used in the concrete production as a crushed glass, as a raw siliceous material in the production of Portland cement [78], and as a hydration-enhancing filler [78].

Jin et al. [77] stated that glass powder (GP) is considered as amorphous and characterized with a high silica content. A particle size of 45 μm or less is reported to be favorable for pozzolanic reaction [15, 79].

Several studies [80, 81] have showed that a cement replacement between 10 and 20% yields the highest strength, while fine aggregate replacement of up to 40% has little effect on compressive

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Kou and Xing [15] utilized the GP as supplementary cementitious materials in UHPFRC. The effect of GP and steam curing on mechanical properties of UHPFRC is shown in Figure 5. The results showed that the replacement of cement by glass powder decreased the early (before 7 days), but increased the later (after 28 days) strengths of UHPFRC, at all ages. The highest

Palm oil fuel ash (POFA) is a by-product of burning: empty fruit bunches, kernel shells, and

Palm oil industry is one of the major agro-industries in countries, such as Malaysia, Indonesia, and Thailand [84]. Most of the POFAs are disposed as waste in landfills, which may contribute to environmental problems in the future [85]. Therefore, a lot of research works have been

Many researchers have found that POFA has pozzolanic qualities and properties in concrete.

Awal and Hussin [84] showed that POFA can be utilized as supplementary cementitious materials, and POFA has a high potential in suppressing expansion associated with alkali-

POFA has been utilized in high-performance concrete (HPC) production, the highest compressive strength was found in the range of 60–86 MPa, which was obtained at POFA (with a median particle size of approximately 10 μm) replacement level of 20% at day 28 with

Megat Johari et al. [88] modified the treatment and grinding process of POFA by heat treatment to remove the excess carbon content and to decrease the POFA median particle size to approximately 2.06 μm as tabulated in Table 4. A highly efficient pozzolan was obtained through their treatment processes. The modified ultrafine POFA (UPOFA) was utilized for improving the properties of high-strength green concrete (HSGC). They concluded that the compressive strength could exceed 95 MPa with a replacement level of up to 60% OPC with

Recently, Aldahdooh et al. [10] reduced the binder content by replacing greater portions of the cement and silica fume in UHPFRCCs with UPOFA as supplementary cementitious materials while generally maintaining its mechanical properties as shown in Figure 6. The results showed that the ultimate flexural and uniaxial tensile strengths increased when the replacement levels of OPC by UPOFA increased and decreased when the replacement levels of densified silica fume (DSF) by UPOFA increased. Moreover, the optimal result was the production of a green UHPFRCCs (GUSMRC) with a low cement content of 360.25 kg/m3 and

fibers, which are used in generating electricity for the boiler of palm oil mills [82, 83].

conducted to find a suitable solution for proper POFA disposal.

In fact, POFA can be considered as a pozzolanic material [86–88].

strength.

replacement level reached up to 30%.

4.4. Palm oil fuel ash

silica reaction in concrete.

UPOFA.

550–560 kg/m<sup>3</sup> total binder [87, 89, 90].

Figure 4. Influence of r-FA and steam curing (S) on mechanical properties of UHPFRC: (a) Compressive strength and (II) Flexural strength [15].

Several studies [80, 81] have showed that a cement replacement between 10 and 20% yields the highest strength, while fine aggregate replacement of up to 40% has little effect on compressive strength.

Kou and Xing [15] utilized the GP as supplementary cementitious materials in UHPFRC. The effect of GP and steam curing on mechanical properties of UHPFRC is shown in Figure 5. The results showed that the replacement of cement by glass powder decreased the early (before 7 days), but increased the later (after 28 days) strengths of UHPFRC, at all ages. The highest replacement level reached up to 30%.

#### 4.4. Palm oil fuel ash

Figure 4. Influence of r-FA and steam curing (S) on mechanical properties of UHPFRC: (a) Compressive strength and (II)

Flexural strength [15].

124 Cement Based Materials

Palm oil fuel ash (POFA) is a by-product of burning: empty fruit bunches, kernel shells, and fibers, which are used in generating electricity for the boiler of palm oil mills [82, 83].

Palm oil industry is one of the major agro-industries in countries, such as Malaysia, Indonesia, and Thailand [84]. Most of the POFAs are disposed as waste in landfills, which may contribute to environmental problems in the future [85]. Therefore, a lot of research works have been conducted to find a suitable solution for proper POFA disposal.

Many researchers have found that POFA has pozzolanic qualities and properties in concrete. In fact, POFA can be considered as a pozzolanic material [86–88].

Awal and Hussin [84] showed that POFA can be utilized as supplementary cementitious materials, and POFA has a high potential in suppressing expansion associated with alkalisilica reaction in concrete.

POFA has been utilized in high-performance concrete (HPC) production, the highest compressive strength was found in the range of 60–86 MPa, which was obtained at POFA (with a median particle size of approximately 10 μm) replacement level of 20% at day 28 with 550–560 kg/m<sup>3</sup> total binder [87, 89, 90].

Megat Johari et al. [88] modified the treatment and grinding process of POFA by heat treatment to remove the excess carbon content and to decrease the POFA median particle size to approximately 2.06 μm as tabulated in Table 4. A highly efficient pozzolan was obtained through their treatment processes. The modified ultrafine POFA (UPOFA) was utilized for improving the properties of high-strength green concrete (HSGC). They concluded that the compressive strength could exceed 95 MPa with a replacement level of up to 60% OPC with UPOFA.

Recently, Aldahdooh et al. [10] reduced the binder content by replacing greater portions of the cement and silica fume in UHPFRCCs with UPOFA as supplementary cementitious materials while generally maintaining its mechanical properties as shown in Figure 6. The results showed that the ultimate flexural and uniaxial tensile strengths increased when the replacement levels of OPC by UPOFA increased and decreased when the replacement levels of densified silica fume (DSF) by UPOFA increased. Moreover, the optimal result was the production of a green UHPFRCCs (GUSMRC) with a low cement content of 360.25 kg/m3 and

Figure 5. Influence of GP and steam curing (S) on mechanical properties of UHPFRC: (a) compressive strength and (II) flexural strength [15].

with a ultra-high compressive strength of 158.28 MPa as given in Table 5. Furthermore, the use of UPOFA (particularly in high volume) can contribute to a healthier and more sustainable

Figure 6. Effect of UPOFA on the mechanical strength of UHPFRCCs at 7 and 28 days: (a) compressive strength, (b)

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environment, which increases green concrete products and may reduce concrete cost.

flexural strength, and (c) tensile strength [10, 17].

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Figure 6. Effect of UPOFA on the mechanical strength of UHPFRCCs at 7 and 28 days: (a) compressive strength, (b) flexural strength, and (c) tensile strength [10, 17].

with a ultra-high compressive strength of 158.28 MPa as given in Table 5. Furthermore, the use of UPOFA (particularly in high volume) can contribute to a healthier and more sustainable environment, which increases green concrete products and may reduce concrete cost.

Figure 5. Influence of GP and steam curing (S) on mechanical properties of UHPFRC: (a) compressive strength and (II)

flexural strength [15].

126 Cement Based Materials


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Table 5. Optimum GUSMRC mix constituents and properties [10, 17, 51].
