*Review* **Review on the Application of Supplementary Cementitious Materials in Self-Compacting Concrete**

**Lang Pang <sup>1</sup> , Zhenguo Liu <sup>2</sup> , Dengquan Wang 3,\* and Mingzhe An <sup>1</sup>**


**Abstract:** For the sustainable development of construction materials, supplementary cementitious materials (SCMs) are commonly added to self-compacting concrete (SCC). This paper reviewed the application techniques and hydration mechanisms of SCMs in SCC. The impacts of SCMs on the microstructure and performance of SCC were also discussed. SCMs are used as a powder material to produce SCC by replacing 10% to 50% of cement. Hydration mechanisms include the pozzolanic reaction, alkaline activation, and adsorption effect. Moreover, the filling effect and dilution effect of some SCMs can refine the pore structure and decrease the temperature rise of concrete, respectively. Specifically, the spherical particles of fly ash can improve the fluidity of SCC, and the aluminumcontaining mineral phase can enhance the resistance to chloride ion penetration. Silica fume will increase the water demand of the paste and promote its strength development (a replacement of 10% results in a 20% increase at 28 days). Ground-granulated blast furnace slag may reduce the early strength of SCC. The adsorption of Ca2+ by CaCO<sup>3</sup> in limestone powder can accelerate the hydration of cement and promote its strength development. *Crystals* **2022**, *12*, x FOR PEER REVIEW 2 of 15 in SCC, which can promote the sustainable development of SCC technology and improve the comprehensive utilization of solid wastes. The application techniques and hydration mechanisms of SCMs in SCC were reviewed in this work, and the impacts of fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GBFS), and limestone powder (LP) on the microstructure and performance of SCC were also summarized. **2. Mixture Design of SCC** 

> **Keywords:** self-compacting concrete; supplementary cementitious materials; hydration mechanisms; microstructure; fresh properties The fresh paste of SCC should have high fluidity as well as resistance to segregation and bleeding during pouring, especially when the paste flows through the limited space of reinforcing bars. It should be noted that the higher the proportion of coarse aggregate

in concrete, the smaller the relative distance between particles, which increases the frequency of collision and friction. As a result, the internal stress caused by coarse aggregate

### **1. Introduction** consumes a large amount of energy for flowing, which reduces the fresh properties of the

Self-compacting concrete (SCC) is a type of high-performance concrete that can be poured into structural formwork by gravity and compacted without vibration. Okamura et al. [1] pioneered the application of SCC in Japan in 1988. The outstanding features are that SCC eliminates the mechanical vibration process and lowers labor costs as compared to normal vibrating concrete (NVC), and SCC has a high powder material content in the mixture to increase fresh properties (Figure 1). However, using cement solely as a powder material leads to high production cost for SCC, which restricts its wide use. In addition, the high cement content in SCC poses increasing environmental risks as cement production is a high-resource-consuming and waste-discharging process, and its annual production has reached 3000 million tons worldwide [2]. paste and even causes blockage. To avoid this, Okamura et al. [1] initially modified the mix proportion by reducing aggregate content, increasing powder content, and adding superplasticizer. To generate self-compacting concrete, this work first sets the amount of aggregate and next changes the water-to-binder ratio and superplasticizer dosages. Figure 1 depicts the proportion of each component. In China, the mixture proportion design of SCC is often done by the absolute volume technique (Chinese standard: CECS203, 2006). In this technique, the cement paste that meets the performance requirements is prepared first, and the fine and coarse aggregates are added sequentially to produce the appropriate mortar and concrete. In addition, Wu et al. [5] and Nie et al. [6] have proposed a mix design method based on the rheological characteristics of paste.

It can be found that SCC contains a larger proportion of powder material than NVC.

The most common SCMs used in SCC are fly ash, silica fume, ground granulated blast furnace slag, and limestone powder. In addition, some other SCMs with fewer use cases are also used in SCC, such as copper slag [11], zeolite powder [12], etc. From the results of existing studies, the percentages of SiO2, Al2O3, and CaO in FA, SF, GBFS, LP, and cement were compared and shown in Figure 2. FA has the highest Al2O3 content; GBFS mainly contains SiO2 and CaO; the chemical composition of SF and LP is relatively simple, containing only SiO2 and CaCO3, respectively. It is worth noting that the chemical composition of the same kind of SCM varies greatly due to the considerable variances in

demonstrates that more SCMs can be added to SCC. The application of SCMs reduces the production costs of SCC while improving concrete performance. For example, adding FA can improve the fresh properties of SCC [8], and adding SF can enhance its strength properties [9]. Moreover, the viscosity modifying admixture should be added to stabilize the rheology and setting time when segregation occurs due to the addition of high-content or


**Figure 1.** Comparison of component proportions between SCC and NVC [1]. **Figure 1.** Comparison of component proportions between SCC and NVC [1].

**Citation:** Pang, L.; Liu, Z.; Wang, D.; An, M. Review on the Application of Supplementary Cementitious Materials in Self-Compacting Concrete. *Crystals* **2022**, *12*, 180. https://doi.org/10.3390/ cryst12020180

Academic Editors: Yifeng Ling, Chuanqing Fu, Peng Zhang, Peter Taylor and Helmut Cölfen

Received: 1 December 2021 Accepted: 24 January 2022 Published: 26 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

composite SCMs [10].

**3. Material Characteristics**  *3.1. Characteristics of SCMs* 

The addition of supplementary cementitious materials (SCMs) as a partial substitute for cement can significantly lower the production cost of SCC as well as relieve the shortages of cement raw materials and solid waste pollution [3]. SCMs can adjust the fresh properties and improve the durability properties [4]. Specifically, SCMs can effectively enhance the microstructure of SCC. Furthermore, SCMs will have superposition effects when two or more of them are used together. Although SCMs have been widely employed in SCC, there is still a lack of a summary in its mix proportions. Moreover, the functions of SCMs in SCC remain unclear, and the systematic analysis of macroscopic properties does not exist yet. Therefore, it is necessary to outline the influences of SCMs in SCC, which can promote the sustainable development of SCC technology and improve the comprehensive utilization of solid wastes. The application techniques and hydration mechanisms of SCMs in SCC were reviewed in this work, and the impacts of fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GBFS), and limestone powder (LP) on the microstructure and performance of SCC were also summarized.

### **2. Mixture Design of SCC**

The fresh paste of SCC should have high fluidity as well as resistance to segregation and bleeding during pouring, especially when the paste flows through the limited space of reinforcing bars. It should be noted that the higher the proportion of coarse aggregate in concrete, the smaller the relative distance between particles, which increases the frequency of collision and friction. As a result, the internal stress caused by coarse aggregate consumes a large amount of energy for flowing, which reduces the fresh properties of the paste and even causes blockage. To avoid this, Okamura et al. [1] initially modified the mix proportion by reducing aggregate content, increasing powder content, and adding superplasticizer. To generate self-compacting concrete, this work first sets the amount of aggregate and next changes the water-to-binder ratio and superplasticizer dosages. Figure 1 depicts the proportion of each component. In China, the mixture proportion design of SCC is often done by the absolute volume technique (Chinese standard: CECS203, 2006). In this technique, the cement paste that meets the performance requirements is prepared first, and the fine and coarse aggregates are added sequentially to produce the appropriate mortar and concrete. In addition, Wu et al. [5] and Nie et al. [6] have proposed a mix design method based on the rheological characteristics of paste.

It can be found that SCC contains a larger proportion of powder material than NVC. Domone [7] summarized a lot of instances from previous research and discovered that roughly 95% of self-compacting concrete had powder masses of more than 400 kg/m<sup>3</sup> . This demonstrates that more SCMs can be added to SCC. The application of SCMs reduces the production costs of SCC while improving concrete performance. For example, adding FA can improve the fresh properties of SCC [8], and adding SF can enhance its strength properties [9]. Moreover, the viscosity modifying admixture should be added to stabilize the rheology and setting time when segregation occurs due to the addition of high-content or composite SCMs [10].

### **3. Material Characteristics**
