4. Application of geopolymer composites

Several studies have been carried on to produce alkali-activated materials from RM. Due to its low reactivity and low SiO2/Al2O3 molar ratio (<2.0), it has been combined with other higher grade precursors such as metakaolin and fly ash to prepare alkali-activated materials using sodium hydroxide (NaOH) and sodium silicate as alkaline activators solutions. The authors obtained 10.8 MPa compressive strength after 28 days curing. The main application fields of GP are presented in Table 4. The potential use of red mud for synthesis of inorganic polymeric composites was studied to use it in the construction sector as artificial structural elements such as massive bricks [9]. RM was reacted with FA, sodium silicate via geopolymerization reaction to get red mud geopolymers which are a viable OPC material that can be used in roadway constructions. Giannopoulou et al. studied the geopolymerization of the red mud and the slag generated in the ferronickel production, in order to develop inorganic polymeric composites with advanced mechanical and physical properties. The inorganic polymeric materials produced by the geopolymerization of the red mud developed compressive strength up to 21 MPa and presented water absorption lower than 3%.

They stated that red mud may be viewed as alternatives in the industrial sectors of construction and building materials [39]. The compressive strength of the RM-RHA geopolymers seems to be enough competitive, which is also comparable to that of all types of OPC with strengths of 9–20.7 MPa. Thus GP can be used as a OPCitious binder to replace OPC in certain civil engineering applications, such as roadway construction, building materials. Moreover, GP-binder has the ability to immobilize toxic chemicals. Potential use of RM in GP synthesis is summarized in Table 4. It should be expected that the application of the RM-based geopolymers can bring both environmental and economic advantages [15]. Geopolymerization of the RM and byproducts can save not only the expenses for waste disposal, but also the costs for manufacturing OPC. Then recycling of abundant wastes can minimize


Table 4.

Applications of Geopolymeric materials based on the silica to alumina atomic ratio [9].

#### Survey of Bauxite Resources, Alumina Industry and the Prospects of the Production… DOI: http://dx.doi.org/10.5772/intechopen.82413

their potential damage to the environment. Lastly the elimination of OPC usage can reduce the CO2 emission caused by firing carbonates.

Silicate-based geopolymer binders have been utilized in applications such as pathways, pavers, mine backfill, railway sleepers, sewerage pipes, and earth retaining [40]. For red mud-based geopolymers to penetrate similar markets, in situ and ambient temperature curing are required. This has been achieved in laboratory trials while targeting a compressive strength above 20 MPa [37].

#### 4.1 Environment considerations on Geopolymers applications

Geopolymer production tackles two main issues of the present time. On one hand, with the increasing amount of waste generation from different processes, there has been a growing interest in the use of waste in producing sustainable building materials to achieve potential benefits. Cleaner production is a pressing issue of our time. Residues or byproducts resulting from different industrial processes requires proper management to ensure a sounder environment [14]. The use of recycled materials in new sustainable materials production is very attractive due to the low-cost related to the waste materials in addition to saving required space for landfill purposes and the development as well as improvement in the materials properties.

On the other, the global warming is one of the most pronounced terms in the present time. Thus reducing the greenhouse gas emissions, which is the main reason behind global warming, is the need of the present time and the future. Efforts are underway to develop environmentally sustainable construction materials, which make minimum utility of fast dwindling natural resources and help to reduce greenhouse gas emissions [41–43]. It is an established fact that the greenhouse gas emissions are reduced by 80% in GP concrete vis-a-vis the conventional OPC manufacturing, as it does not involve carbonate burns. In this connection, GP are showing great potential and several researchers have critically examined the various aspects of their viability as binder system. For manufacturing each tone of the OPC as the primary component of concrete about 1.5 tons of raw materials is needed. Furthermore; in this process about one tone of carbon dioxide will be released into the atmosphere. Geopolymers generate just 0.184 t of CO2 per ton of binder. Although the CO2 emissions generated during the production of Na2O are very high, still the production of alkali-activated binders is associated to a level of carbon dioxide emissions lower than the emissions generated in the production of OPC.

#### 5. Conclusion

bounded only weakly in the nanostructure of the geopolymer gel and are therefore

Several studies have been carried on to produce alkali-activated materials from RM. Due to its low reactivity and low SiO2/Al2O3 molar ratio (<2.0), it has been combined with other higher grade precursors such as metakaolin and fly ash to prepare alkali-activated materials using sodium hydroxide (NaOH) and sodium silicate as alkaline activators solutions. The authors obtained 10.8 MPa compressive strength after 28 days curing. The main application fields of GP are presented in Table 4. The potential use of red mud for synthesis of inorganic polymeric composites was studied to use it in the construction sector as artificial structural elements such as massive bricks [9]. RM was reacted with FA, sodium silicate via geopolymerization reaction to get red mud geopolymers which are a viable OPC material that can be used in roadway constructions. Giannopoulou et al. studied the geopolymerization of the red mud and the slag generated in the ferronickel production, in order to develop inorganic polymeric composites with advanced

mechanical and physical properties. The inorganic polymeric materials produced by the geopolymerization of the red mud developed compressive strength up to

They stated that red mud may be viewed as alternatives in the industrial sectors of construction and building materials [39]. The compressive strength of the RM-RHA geopolymers seems to be enough competitive, which is also comparable to that

> Ceramics Fire protection

Foundry equipment

Radioactive and toxic waste encapsulation

Heat resistant composite 200–1000°C Tooling for aeronautics titanium process

Tooling for aeronautics SPF aluminum

of all types of OPC with strengths of 9–20.7 MPa. Thus GP can be used as a OPCitious binder to replace OPC in certain civil engineering applications, such as roadway construction, building materials. Moreover, GP-binder has the ability to immobilize toxic chemicals. Potential use of RM in GP synthesis is summarized in Table 4. It should be expected that the application of the RM-based geopolymers can bring both environmental and economic advantages [15]. Geopolymerization of the RM and byproducts can save not only the expenses for waste disposal, but also the costs for manufacturing OPC. Then recycling of abundant wastes can minimize

almost completely leachable.

Geopolymers and Other Geosynthetics

4. Application of geopolymer composites

21 MPa and presented water absorption lower than 3%.

Si/Al Ratio Application 1 Bricks

Table 4.

92

2 Low CO2 cement and concrete

3 Fire protection fiber glass composite

>3 Sealants for industry 200–600°C

20–35 Fire resistant and heat resistant fiber composites

Applications of Geopolymeric materials based on the silica to alumina atomic ratio [9].

In the light of the above it appears clearly that extensive research has been carried out into the field of geopolymers for better understanding the chemical mechanism conducting to their formation and to develop the ability to design geopolymers with specific applications. In particular the variance of source material makes difficult a standard mix design. Nowadays the most investigations agree that source material, mixing ratio, alkali activator, curation time are key factors in the geopolymerization process. With regard to the immense bauxite resources of Guinea, the development of a subsequent alumina industry is expected and implies two questions: (i) a highly qualified manpower is required to manage the very complex issue of the alumina production and the management of the resulting waste; (ii) a worldwide integrated approach will be required to Takle the management of industrial wastes an environmental challenge and a technological opportunity to develop promising engineering application. The valorization of the red mud is at the same ns.

Geopolymers and Other Geosynthetics
