A geopolymeric composite of non-calcined rice husks made of metakaolin/sol–gel silica

Abstract

In this work, the development of a composite material with geopolymer and a high content of rice husks without heat treatment was investigated to create and characterize a low-cost composite made with agro-industrial wastes. The ratio used was about 12/88 wt./% of sol–gel and metakaolin related to rice husks. This kind of composite geopolymer was designed as both a construction material for load or aesthetic finishing. X-ray diffraction studies reveal that the composite has an amorphous phase and a crystalline one, which is typical of geopolymeric materials. The scanning electron microscopy showed that the geopolymeric matrix completely wrapped the rice husks. The composite material has a compressive strength close to some mortars with a value of about 110 kg/cm2 (10.8 MPa). Laser scanning confocal microscopy reveals that there is a difference of emission in the visible spectrum between the inner and outer sides of the rice husks, which corroborates that they have a different chemical composition. Differential scanning calorimetry analysis confirmed that the composite material has combined characteristics of its raw materials. X-ray diffraction studies show that metakaolin with sol–gel solutions had temperature-dependent interactions besides that, after the dehydroxylation, the composite material is mostly amorphous. The material of high content of rice husk bound by geopolymer could be applicable in various areas of the construction industry and finishing.

Geopolymeric Composite Materials Made of Sol-Gel Silica and Agroindustrial Wastes of Rice, Barley, and Coffee Husks with Wood-Like Finishing

“…All materials and reagents were used without any further pretreatment or purification procedure. The alkaline chemical solution of silica (sol-gel solution) was prepared by adding the colloidal silica and sodium silicate to an alkaline solution composed of deionized water and sodium hydroxide [21,32,[43][44][45].…”

“…Rice husks are another agricultural residue produced in large quantities, which has the same basic constituents as wood, but in different proportions. The availability of rice husks, which is related to global rice production, can be estimated using a husk-to-paddy ratio (HPR) of about 0.2 [18][19][20][21]. Global production was about 756.74 Mton rice in 2020 [20], which corresponds to 151.…”

“…Geopolymers contain thermally activated natural materials (e.g., kaolinite clay) or industrial by-products (e.g., fly ash or slag). In addition, they have properties such as high compressive strength, low shrinkage, slow or fast setting, fire resistance, and low thermal conductivity [21,[30][31][32][33][34].…”

Geopolymers and Functionalization Strategies for the Development of Sustainable Materials in Construction Industry and Cultural Heritage Applications: A Review

“…The sol–gel technique is widely employed in developing hybrid geopolymeric based materials [ 5 , 76 , 77 , 78 , 79 ]. Moreover, as it is well known, this process is one of the primary approaches for manufacturing ceramic materials and glasses at low temperatures [ 80 ].…”

“…The results showed a homogeneous Al-rich geopolymeric matrix for the molds with less water content. Moreover, a composite based on geopolymers synthesized through the sol–gel technique was designed by Magdaleno-Lòpez et al The rice husk was added in the matrix, obtaining good results in terms of mechanical resistance and making it a material applied in the construction and restoration field [ 76 ]. An example of a sol–gel solution to be added to the geopolymer matrix contemplates the use of organosilane reagents.…”