Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk

This work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92\u20130.75 MPa and 1.88\u20131.70 g/cm 3 , respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars

Microstructural and mechanical properties of (Ca, Na)-poly(sialate-siloxo) from metakaolin as aluminosilicate and calcium silicate from precipitated silica and calcined chicken eggshell

The aim of this work is to investigate the influence of the amorphous calcium silicate on the microstructural, physical and mechanical properties of (Ca, Na)-poly(sialate-siloxo) networks. The calcium silicate with molar ratio CaO/SiO 2 equal to 1.0 was prepared from the precipitated silica and calcined chicken eggshell. The X-ray patterns and infrared spectra of the synthesized calcium silicate indicate that it mainly constitutes of the amorphous calcium silicate hydrate. The X-ray patterns of geopolymer cements indicate that the prepared amorphous calcium silicate hydrate does not include in the network. The compressive strengths of the geopolymer mortars decrease from 28.92 to 12.03 MPa with increasing the replacement level of metakaolin (from 0 to 25% by mass). Whereas, the values of the apparent densities increase with increasing the replacement level of metakaolin. It seems that the amorphous calcium silicate hydrate in the structure of calcium silicate affects negatively the mechanical properties of the (Ca, Na)-poly(sialate-siloxo) network. The heterogeneous structure of geopolymer mortars containing 25% of calcium silicate could be related to the higher calcium content and the amorphous structure of calcium silicate hydrate. It was typically found that in the absence of significant levels of dissolved calcium, the precursors such as silicate and aluminate condense to form (Ca, Na)-poly(sialate-siloxo) networks. This implies the homogenous structure and the higher values of the compressive strengths of geopolymer mortars containing 0, 5, 10 and 15% of calcium silicate. Whereas those from the replacement level of metakaolin by 20 or 25% of calcium silicate contain significant levels of dissolved calcium and amorphous calcium silicate hydrate in their structure which hinder the formation of the precursors and therefore impede the formation of the (Ca, Na)-poly(sialate-siloxo) networks

Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk

This work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92\u20130.75 MPa and 1.88\u20131.70 g/cm 3 , respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars