It is reported that between 500˚C - 700˚C, the silica in RHA remains amorphous and very reactive in the presence of alkaline solutions. The nature of this silica depends on the burning temperature. Hence, it leads to serious environmental pollution issues derived from its disposal. Rice husk (RH) is an important residue derived from rice paddy that represents about 20% of its mass. Thus, sodium silicate can be obtained by reacting concentrated aqueous sodium hydroxide with siliceous products derived from agricultural by-products such as sugar cane bagasse and rice husk. In the same manner, agro-industrial by-products have been the subject of several investigations regarding the manufacture of sodium silicate. In this direction, Zivica developed alkaline activators based on silica fume. For geopolymers to be a viable alternative and industrially interesting, many technological issues must be overcome, especially research on low cost activators. This manufacturing process consumes large amount of energy and produces considerable air pollutants such as dust, nitrogen oxide and sulfur oxide. Sodium silicate, for example, is currently obtained industrially by melting sand with sodium carbonate at high temperature between 1300˚C - 1500˚C. The constituents of these alkaline solutions are manufactured products.
#BRICKS N BALLS 335 ACTIVATOR#
The conventionally used alkaline activator is a mixture of sodium (NaOH) or potassium (KOH) hydroxide with sodium (Na 2SiO 3) or potassium (K 2SiO 3) silicate. They can be volcanic ash and ceramic wastes. In recent years, for environmental concerns, by-products, containing alumina and silica were also increasingly used. The commonly used aluminosilicates are metakaolin and fly ash. The geopolymerization’s reaction is done at temperatures close to the ambient between an aluminosilicate material and an alkaline silicate solution. Geopolymers are used in their pure state, charged or reinforced and they are applied where traditional materials (metals, ceramics, organic polymers) do not yield satisfactory results especially in the industrial sector such as foundry, metallurgy, civil engineering, waste management and aviation industry. Geopolymers are assimilated to mineral polymers exhibiting good mechanical properties, good resistance to high temperature and to acid attack. The term “geopolymer” was first used in 1972 by Joseph Davidovits. Binders made from activated aluminosilicates by alkaline solution also called geopolymer represent an attractive alternative. That is why, for decades, researchers have been developing substitutes to Portland cement. However, the production of Portland cement which is one of its components leads to the emission of significant quantities of greenhouse gases. However, appropriate filtration process is needed for the RHA-NaOH gel to reduce its impurities as undissolved entities, which will consequently contribute to improve the flexural strength, the density and the microstructure of its products which were low compared to when commercial sodium silicate was used.Ĭoncrete is the most used material worldwide in construction because of its multiple technical advantages. The gel obtained by mixing RHA and NaOH can contribute to the reduction of the use of costly commercial sodium silicate in the production process of geopolymers. Results showed that RHA-NaOH alkaline activator has good potential in consolidating FCBW powder through geopolymerization process which gave products that had characteristics not far from that when the commercial sodium silicate was used. Biaxial four point flexural strength, bulk density, water absorption and scanning electron microscopy (SEM) tests were also done on products. Fourier Transformed Infrared Spectroscopy (FTIR) was done on the gel, commercial sodium silicate and products.
Chemical and mineralogical analyses were done on raw materials. Characteristics of the gel were compared to that of commercial sodium silicate which was also mixed with 8 M NaOH in the ratio 1:1 to produce geopolymers.
To contribute to the reduction of the use of costly industrial sodium silicate in activators for geopolymers, a gel obtained with RHA and concentrated sodium hydroxide was used in the present study to develop an alkaline activator with 8 M NaOH and to produce geopolymers with crushed fired clay bricks wastes (FCBW). High cost has been pointed among factors that limit the promotion of geopolymers.