3. UHPFRCCs

UHPFRCC is an advanced reinforced cementitious material and is one of the high-strength ductile concrete (HSDC) [1, 21]. In this review, the product is generally called UHPFRCC according to [22]. In the case of mechanical performance, UHPFRCC is characterized with a super-compressive strength, tensile strength, bending tensile strength, elastic modulus, energy absorption capacity, and elastic post-cracking bending strength. In terms of durability, UHPFRCC shows an extremely dense microstructure (negligible water adsorption, water and gas permeability, and porosity) and an extremely low diffusion coefficient [1–3, 23–25]. Meanwhile, in the case of sustainability, this type of concrete still needs to be evaluated with regard to their high binder content (especially the cement content) relative to the regularly used mixtures [25].

#### 3.1. Principles of UHPFRCC composition

The principles applied in UHPFRCC matrix development can be detailed based on previous studies:

	- Filler between the cement particles,
	- Lubricant,

On the other hand, an increase in the cement content implies an increase in the overall demand for cement [8, 9], which could be translated into a greater cement production, which correspondingly increases the emission of certain greenhouse gases (CO2, etc.), in addition to increasing the concrete cost as well as the electrical energy consumption [9]. Therefore, UHPFRCC products can be considered as uneconomical construction materials and pose a

Aldahdooh et al. [10] stated that there are several methods that can be employed to reduce the binder content (cement and silica fume) in UHPFRCCs. For example, (i) optimizing the mix design of concrete using mathematical or statistical methods, such as response surface methodology, and so on [11, 12], (ii) utilizing industrial solid wastes and by-products as a supplementary cementitious materials (SCMs) in producing green UHPFRCCs, such as crushed quartz (CQ) [13], fly ash (FA) [14–16], palm oil fuel ash (POFA) [10, 17], recycled glass powder (RGP) [15], activated metakaolin (AM), and ground granulated blast-furnace slag (GBFS) [15, 18, 19].

Nowadays, the utilization of solid wastes is the challenge for engineers to use friendly SCMs produced at a reasonable cost with a low environmental impact. The addition of cost-saving materials by the replacement of a considerable amount of cement reduces CO2 emission during the manufacturer of Portland cement. Moreover, SCMs can improve the majority of

Based on the above, this review focused on the second method that is particularly dependent on the utilization of wastes and by-products in developing green UHPFRCCs, including their

This review focused on the utilization of industrial wastes and by-products in UHPFRCCs. This could lead to the greater utilization of SCMs in concrete. Subsequently, it could be useful in protecting the environment by minimizing the volume of waste disposed on the wasteland and minimizing the emission of greenhouse gases. Furthermore, it contributes to cost-saving,

UHPFRCC is an advanced reinforced cementitious material and is one of the high-strength ductile concrete (HSDC) [1, 21]. In this review, the product is generally called UHPFRCC according to [22]. In the case of mechanical performance, UHPFRCC is characterized with a super-compressive strength, tensile strength, bending tensile strength, elastic modulus, energy absorption capacity, and elastic post-cracking bending strength. In terms of durability, UHPFRCC shows an extremely dense microstructure (negligible water adsorption, water and gas permeability, and porosity) and an extremely low diffusion coefficient [1–3, 23–25].

threat to the environment.

114 Cement Based Materials

fresh and hardened properties of concrete [12, 20].

influence on the mechanical properties of UHPFRCCs.

which contributes to the sustainability of the concrete industry.

2. Significance of review

3. UHPFRCCs


Figure 1. Ultrafine powder acting as "filler" between the cement particles [1].

#### 3.2. Constituent materials and mix proportions of UHPFRCCs

In general, UHPFRCC is characterized as a composite that has a large content of cement and silica fume, a large volume of steel fiber, a high dosage of superplasticizer (SP), a low water/ binder ratio, and the absence of coarse aggregates that are larger than 4 mm [4]. Table 1 shows a summary of the ranges of UHPFRCC compositions and the average material properties. One example of UHPFRCCs is known under the trade name, CARDIFRC [22, 29, 30].

appropriate cement content should be used [39]. On the other hand, for a given W/C, decreas-

Utilization of By‐Product Materials in Ultra High‐Performance Fiber Reinforced Cementitious Composites

http://dx.doi.org/10.5772/intechopen.74376

Yurdakul [39] stated that workability is a function of W/C and cement content; increasing W/C or cement content improves workability. The workability is affected by paste volume, because the paste lubricates the aggregates [39, 41]. For a given water content, decreasing the cement content increases the stiffness of concrete having poor workability [39, 43]. Although workability is increased by an increasing cement content, it causes higher internal temperatures in the concrete during the finishing and curing processes [39]. In addition, the workability increases as the cement content (paste content) increases for a given W/C ratio and aggregate

content because there is more paste to lubricate the aggregates in the mixtures [38, 39].

Aldahdooh [12] stated that no special standard is published for UHPFRCC mix design. Therefore, an ideal strategy is needed for improving the mechanical properties of UHPFRCC relative to the binder contents. This finding can be realized by optimizing the mix design of concrete

In the case of using the mathematical or statistical methods, the mix design of UHPFRCC is still based on trial mix; therefore, no standard has been adopted yet and no rigorous mathematical approach is available. De Larrard and Sedran [44] already optimized the ultra-high performance concrete (UHPC) mix proportion using density-packing model (solid suspension model). The optimal mix was characterized with a cement content up to 1080 kg/m3 and silica

be optimized using the group method of data handling and genetic programming [45]. They concluded that the optimum cement amount must be approximately from 1400 to 1600 kg/m3

and the amount of silica fume might be 20 or 25% cement content. Yu, et al. [46] recently used the modified Andreasen & Andersen particle-packing model to achieve a densely compacted cementitious matrix. They concluded that by applying this modified model, producing dense UHPFRCCs using a relatively low binder content is possible as outlined in Table 2. They also stated that a large amount of unhydrated cement in the matrix has been observed, which can be further replaced by fillers to improve workability and cost efficiency of UHPFRCCs.

Recently, an advanced optimization method called as a response surface methodology (RSM) has been used for optimizing the binder contents by Aldahdooh et al. [11]. They concluded that although the results indicate that the prediction by RSM was satisfactory in adjusting the amount of binders in the production of UHPFRCCs materials, these values still need to be reduced further, meaning that another method could be used to reduce the cement and silica fume contents through partial replacement of cement by external ultrafine (or by-product) materials, such as crushed quartz [13], fly ash [14–16], recycled glass powder [15], and ground

granulated blast-furnace slag [15, 18, 19], palm oil fuel ash [51], as outlined in Table 2.

Silica fume is considered as one of the main components in producing UHPFRCCs [1, 13]. Silica fume is an extremely fine non-crystalline silica produced by electric arc furnaces as a byproduct of smelting process in the metallic silicon or ferrosilicon alloy production as outlined

. Furthermore, the mix proportion of reactive powder concrete can

,

117

ing cement content reportedly decreases permeability [38, 39, 41].

using mathematical or statistical methods or by utilizing SCMs.

fume was up to 334 kg/m3

3.2.2. Silica fume

More details about the function of each ingredient in the UHPFRCC mix are presented in the following subsection.

#### 3.2.1. Cement

Normally, ordinary Portland cement (OPC) can be used to produce UHPFRCCs [13, 35, 36]. UHPFRCC is characterized with a high cement content, which can be as high as 1000 kg/m<sup>3</sup> (Table 1). Vernet [37] stated that in the matrix of UHPFRCCs, not all of the cement contents become hydrated because of a low water content.

For a given W/C, the strength of concrete is largely dependent on cement content. Increasing the cement content does not improve the strength, after the required content is reached [38, 39]. A high cement content both increases air permeability and chloride penetration and may cause shrinkage-related-cracking problems [40–42], which will shorten the longevity of concrete, thus decreasing its performance (durability and strength). To prevent these problems,


Table 1. The range of UHPFRCC compositions and average mechanical properties.

appropriate cement content should be used [39]. On the other hand, for a given W/C, decreasing cement content reportedly decreases permeability [38, 39, 41].

Yurdakul [39] stated that workability is a function of W/C and cement content; increasing W/C or cement content improves workability. The workability is affected by paste volume, because the paste lubricates the aggregates [39, 41]. For a given water content, decreasing the cement content increases the stiffness of concrete having poor workability [39, 43]. Although workability is increased by an increasing cement content, it causes higher internal temperatures in the concrete during the finishing and curing processes [39]. In addition, the workability increases as the cement content (paste content) increases for a given W/C ratio and aggregate content because there is more paste to lubricate the aggregates in the mixtures [38, 39].

Aldahdooh [12] stated that no special standard is published for UHPFRCC mix design. Therefore, an ideal strategy is needed for improving the mechanical properties of UHPFRCC relative to the binder contents. This finding can be realized by optimizing the mix design of concrete using mathematical or statistical methods or by utilizing SCMs.

In the case of using the mathematical or statistical methods, the mix design of UHPFRCC is still based on trial mix; therefore, no standard has been adopted yet and no rigorous mathematical approach is available. De Larrard and Sedran [44] already optimized the ultra-high performance concrete (UHPC) mix proportion using density-packing model (solid suspension model). The optimal mix was characterized with a cement content up to 1080 kg/m3 and silica fume was up to 334 kg/m3 . Furthermore, the mix proportion of reactive powder concrete can be optimized using the group method of data handling and genetic programming [45]. They concluded that the optimum cement amount must be approximately from 1400 to 1600 kg/m3 , and the amount of silica fume might be 20 or 25% cement content. Yu, et al. [46] recently used the modified Andreasen & Andersen particle-packing model to achieve a densely compacted cementitious matrix. They concluded that by applying this modified model, producing dense UHPFRCCs using a relatively low binder content is possible as outlined in Table 2. They also stated that a large amount of unhydrated cement in the matrix has been observed, which can be further replaced by fillers to improve workability and cost efficiency of UHPFRCCs.

Recently, an advanced optimization method called as a response surface methodology (RSM) has been used for optimizing the binder contents by Aldahdooh et al. [11]. They concluded that although the results indicate that the prediction by RSM was satisfactory in adjusting the amount of binders in the production of UHPFRCCs materials, these values still need to be reduced further, meaning that another method could be used to reduce the cement and silica fume contents through partial replacement of cement by external ultrafine (or by-product) materials, such as crushed quartz [13], fly ash [14–16], recycled glass powder [15], and ground granulated blast-furnace slag [15, 18, 19], palm oil fuel ash [51], as outlined in Table 2.

#### 3.2.2. Silica fume

3.2. Constituent materials and mix proportions of UHPFRCCs

become hydrated because of a low water content.

following subsection.

3.2.1. Cement

116 Cement Based Materials

In general, UHPFRCC is characterized as a composite that has a large content of cement and silica fume, a large volume of steel fiber, a high dosage of superplasticizer (SP), a low water/ binder ratio, and the absence of coarse aggregates that are larger than 4 mm [4]. Table 1 shows a summary of the ranges of UHPFRCC compositions and the average material properties. One

More details about the function of each ingredient in the UHPFRCC mix are presented in the

Normally, ordinary Portland cement (OPC) can be used to produce UHPFRCCs [13, 35, 36]. UHPFRCC is characterized with a high cement content, which can be as high as 1000 kg/m<sup>3</sup> (Table 1). Vernet [37] stated that in the matrix of UHPFRCCs, not all of the cement contents

For a given W/C, the strength of concrete is largely dependent on cement content. Increasing the cement content does not improve the strength, after the required content is reached [38, 39]. A high cement content both increases air permeability and chloride penetration and may cause shrinkage-related-cracking problems [40–42], which will shorten the longevity of concrete, thus decreasing its performance (durability and strength). To prevent these problems,

> Coarse aggregate (0–200) [1, 31] 0 Fine aggregate (1000–2000) [1, 31] 940–1173 Silica fume (200–300) [1, 31] 178–214 Water (110–200) [1, 31] 149–188 Superplasticizer (9–71) [32] 28–55 Reinforcement/fibers (>150) [1, 31] 468 Water/cement ratio (<0.24) [1, 31] 0.20–0.22 Water/binder ratio (<0.22) [1, 31] 0.16–0.18 Superplasticizer/cement ratio (0.018–0.051) [32] 0.033–0.074 Silica fume/cement ratio (>0.25) [1, 31] 0.24–0.25

Tensile strength (MPa) (>7) [33] 12–13.5 Modulus of elasticity (GPa) (50–70) [1, 31] >48 Splitting tensile strength (MPa) (>18) [34] 24–25 Flexural strength (MPa) (>25) [1, 3] >30

Matrix composition Portland cement (700–1000) [1, 31] 744–855

Properties Compressive strength (MPa) (>150) [1, 31] >185

Table 1. The range of UHPFRCC compositions and average mechanical properties.

UHPFRCCs (kg/m<sup>3</sup>

) CARDIFRC [2, 22, 29, 30]

example of UHPFRCCs is known under the trade name, CARDIFRC [22, 29, 30].

Silica fume is considered as one of the main components in producing UHPFRCCs [1, 13]. Silica fume is an extremely fine non-crystalline silica produced by electric arc furnaces as a byproduct of smelting process in the metallic silicon or ferrosilicon alloy production as outlined


The utilization of silica fume in microfiber-reinforced concrete can improve the degree of fiber dispersion, matrix interface, and interfacial zone [57], which results from the fineness of silica fume particles when compared with cement [55, 57, 58]. Furthermore, the bonding between steel fibers and matrix of steel fiber-reinforced concrete is significantly improved by utilizing silica fume. In addition, silica fume can enhance the properties of the materials used as filler

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119

The theoretical amount of silica fume required for the reaction with cement product is 18% cement content [59]. The silica fume content must be practically increased from 25 to 30% cement content to obtain the densest mixture and to achieve the greatest compressive strength [1, 31, 59]. Chan and Chu [60] concluded that the highest interfacial bond strength and pullout energy between the steel fiber and concrete matrix can be obtained at a silica fume dosage of as high as 30%. The interfacial-toughening effect in the bond strength decreases when the silica

UHPFRCCs without reinforcement with fibers may exhibit high strength but are extremely brittle. The additional function of fibers in UHPFRCCs is enhancing ductility in tension and

UHPFRCC mix is generally characterized with a steel fiber content that is more than 2.5% of its volume as outlined in Tables 1 and 2. The dimensions range from 0.1 to 0.25 mm in diameter and from 6 to 20 mm in length with a tensile strength of more than 2000 MPa [21, 34]. For example, a large amount (up to 6% by volume) of brass-coated short straight steel fibers (6 and 13 mm) with 0.16 mm diameter has been used in CARDIFRC materials [22, 29]. The short fiber was used to enhance flexural and tensile strength, whereas the long fiber was used to increase toughness. Generally, the long steel fiber enhances the roughness of matrix by enhancing the tensile strength and strain capacity at the breakage stage at the same time, while the short steel fiber improves the tensile strength of matrix more than strain capacity at the breakage stage

Vande Voort et al. [13] stated that fiber size and aggregate size in any concrete mix are considered as the main factors that influence mix workability. Hence, in the absence of coarse aggregates, fiber size is considered as the primary factor influencing concrete flow (e.g., UHPFRCCs). Moreover, UHPFRCC workability tends to decrease with an increasing fiber

The steel fiber-reinforced concrete with a high workability has a high probability of experiencing steel fiber segregation, which automatically reflects mechanical properties and concrete

W/C ratios used in producing UHPFRCCs are generally less than 0.20, which lead to a notable reduction in the porosity of UHPFRCC matrix; this reduction in porosity increases

[55, 58].

[22, 29].

content [13, 61].

performance [62].

3.2.4. Superplasticizer

fume content increases to 40%.

improving its tensile capacity [1, 13, 26].

3.2.3. Fiber reinforcement

SCM refers to supplementary cementitious materials; C refers to cement content; GGBS refers to ground granulated blastfurnace slag; SFrefers to silica fume; L.S. refers to limestone; W/B refers to water-binder ratio; St.F. refers to steel fiber; Comp. 28 d refers to compressive strength at day 28.

Table 2. Examples on the binder content and compressive strength of optimized UHPFRCCs.

in Table 2. Silica fume is a highly reactive pozzolanic material. This substance has sphericalshaped particle and is characterized with an average particle size between 0.1 and 0.2 μm. Moreover, the SiO2 content ranges from 58 to 98% [53]. Silica fume is observed to be much finer and have a higher SiO2 content compared with the other by-products. For a given water content, addition of silica fume more than the limited value will degrade the workability of the mix, which results from the larger surface area of silica fume [54, 55].

The main functions of silica fume in UHPFRCCs are (i) acting as a filler between cement particles, (ii) for a given water-binder ratio (W/B), improving mixture lubrication caused by particle shape (sphericity), and (iii) producing hydration products by pozzolanic activity [3, 13, 35] as presented in Figure 2.

Figure 2. An example of steel fiber types used in UHPFRC [56].

The utilization of silica fume in microfiber-reinforced concrete can improve the degree of fiber dispersion, matrix interface, and interfacial zone [57], which results from the fineness of silica fume particles when compared with cement [55, 57, 58]. Furthermore, the bonding between steel fibers and matrix of steel fiber-reinforced concrete is significantly improved by utilizing silica fume. In addition, silica fume can enhance the properties of the materials used as filler [55, 58].

The theoretical amount of silica fume required for the reaction with cement product is 18% cement content [59]. The silica fume content must be practically increased from 25 to 30% cement content to obtain the densest mixture and to achieve the greatest compressive strength [1, 31, 59]. Chan and Chu [60] concluded that the highest interfacial bond strength and pullout energy between the steel fiber and concrete matrix can be obtained at a silica fume dosage of as high as 30%. The interfacial-toughening effect in the bond strength decreases when the silica fume content increases to 40%.

#### 3.2.3. Fiber reinforcement

in Table 2. Silica fume is a highly reactive pozzolanic material. This substance has sphericalshaped particle and is characterized with an average particle size between 0.1 and 0.2 μm. Moreover, the SiO2 content ranges from 58 to 98% [53]. Silica fume is observed to be much finer and have a higher SiO2 content compared with the other by-products. For a given water content, addition of silica fume more than the limited value will degrade the workability of

SCM refers to supplementary cementitious materials; C refers to cement content; GGBS refers to ground granulated blastfurnace slag; SFrefers to silica fume; L.S. refers to limestone; W/B refers to water-binder ratio; St.F. refers to steel fiber;

C GGBS SF L.S. POFA [47] Without SCMs 950 0 238 0 0 0.2 2 190 [2, 22, 29, 30] 855 0 214 0 0 0.18 6 207 [2, 22, 29, 30] 744 0 178 0 0 0.16 6 185 [48] 860 0 215 0 0 0.2 2 198 [46] 875 0 44 0 0 0.19 2.5 156 [25] 1011 0 58 0 0 0.15 2 160 [49] 960 0 240 0 0 0.16 2.5 155 [50] 1050 0 275 0 0 0.14 6 160 [5] With SCMs 657 418 119 0 0 0.15 2 150 [46] 612 0 44 263 0 0.19 2.5 142 [46] 700 0 44 175 0 0.19 2.5 149 [51, 52] 360 0 214 0 290 0.19 6 158

) W/B St.F. (Vol. %) Comp. 28 d (MPa)

The main functions of silica fume in UHPFRCCs are (i) acting as a filler between cement particles, (ii) for a given water-binder ratio (W/B), improving mixture lubrication caused by particle shape (sphericity), and (iii) producing hydration products by pozzolanic activity [3, 13, 35] as presented

the mix, which results from the larger surface area of silica fume [54, 55].

Table 2. Examples on the binder content and compressive strength of optimized UHPFRCCs.

in Figure 2.

References Binder (kg/m<sup>3</sup>

118 Cement Based Materials

Comp. 28 d refers to compressive strength at day 28.

Figure 2. An example of steel fiber types used in UHPFRC [56].

UHPFRCCs without reinforcement with fibers may exhibit high strength but are extremely brittle. The additional function of fibers in UHPFRCCs is enhancing ductility in tension and improving its tensile capacity [1, 13, 26].

UHPFRCC mix is generally characterized with a steel fiber content that is more than 2.5% of its volume as outlined in Tables 1 and 2. The dimensions range from 0.1 to 0.25 mm in diameter and from 6 to 20 mm in length with a tensile strength of more than 2000 MPa [21, 34]. For example, a large amount (up to 6% by volume) of brass-coated short straight steel fibers (6 and 13 mm) with 0.16 mm diameter has been used in CARDIFRC materials [22, 29]. The short fiber was used to enhance flexural and tensile strength, whereas the long fiber was used to increase toughness. Generally, the long steel fiber enhances the roughness of matrix by enhancing the tensile strength and strain capacity at the breakage stage at the same time, while the short steel fiber improves the tensile strength of matrix more than strain capacity at the breakage stage [22, 29].

Vande Voort et al. [13] stated that fiber size and aggregate size in any concrete mix are considered as the main factors that influence mix workability. Hence, in the absence of coarse aggregates, fiber size is considered as the primary factor influencing concrete flow (e.g., UHPFRCCs). Moreover, UHPFRCC workability tends to decrease with an increasing fiber content [13, 61].

The steel fiber-reinforced concrete with a high workability has a high probability of experiencing steel fiber segregation, which automatically reflects mechanical properties and concrete performance [62].

#### 3.2.4. Superplasticizer

W/C ratios used in producing UHPFRCCs are generally less than 0.20, which lead to a notable reduction in the porosity of UHPFRCC matrix; this reduction in porosity increases 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 slender elements [34, 36, 63].

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 can affect concrete uniformity and cohesiveness.

4. Utilization of by-products in UHPFRCC

is described in the following subsections.

4.1. Metakaolin

Specific surface (m2

metakaolin; POFA, refers to palm oil fuel ash.

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

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Properties Low Mean High W/B 0.10 0.17 0.25 W/C 0.13 0.22 0.37

Table 3. Classification of W/B and W/C ratios for UHPFRCCs summarized by Vande Voort et al. [13].

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.

SiO2 20.44 35–60 47.23 34.4 91.4 53.87 71.4 88.32 65.01 Al2O3 2.84 10–30 24.54 9.0 0.09 38.57 1.4 0.46 5.72 Fe2O3 4.64 4–20 8.42 2.58 0.04 1.4 0.2 0.67 4.41 CaO 67.73 1–35 8.28 44.8 0.93 0.04 10.6 0.67 8.19 MgO 1.43 1.98 1.62 4.43 0.78 0.96 2.5 0.44 4.58 SO3 2.20 0.35 0. 39 2.26 0.01 — 0.1 — 0.33 Na2O 0.02 0.48 — 0.62 0.39 0.04 12.7 0.12 0.07 K2O 0.26 0.4 — 0.5 2.41 2.68 0.5 2.91 6.48 MnO 0.16 — —— 0.05 0.01 — — 0.11 TiO2 0.17 — 0.99 — 0.0 0.95 — — 0.25 Specific gravity 3.05 2.2–2.8 2.19 2.79 2.6–3.8 2.5 2.48 2.11 2.55 Particle size (μm) 10–40 ≤45 >45 — 0.1 0.5–20 <45 11.5–31.3 2.06

OPC FA r-FA GGBS SF MK GP RHA UPOFA

/g) 1.75 5–9 0.119 0.4–0.599 16.455 12.174 0.756 30.4–27.4 1.77

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

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

### 3.2.5. Sand

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 aggregate [38, 39, 68, 69].

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 4 mm [4].

The recommended mean aggregate size used in producing UHPFRCCs is less than 1 mm, and the aggregate-cement ratio can be up to 1.4 [21].

#### 3.2.6. Water

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 water content than to use more cement [39].

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.

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Table 3. Classification of W/B and W/C ratios for UHPFRCCs summarized by Vande Voort et al. [13].
