Can Portland cement be replaced by low-carbon alternative materials? A study on the thermal properties and carbon emissions of innovative cements

Environmentally sustainable repair materials with reduced carbon footprint have been in great demand by the construction industry worldwide. Gradual deterioration of concrete containing large quantities of Portland cement is inevitable, and requires repair or replacement. Numerous repair materials including cementitious mortars, polymer-modified cementitious mortars, resinous mortars, etc. have been utilized to rectify the problem. Cement-free geopolymer mortars prepared from waste materials with high content of silicate aluminum and alkaline activator solution are emerging as prominent sustainable repair materials. Geopolymer binders are preferred because they generate 70–80% less carbon dioxide with remarkably lesser greenhouse gas emissions than ordinary Portland cement. These new binders are highly sought-after due to their enhanced durability performance, sustainability, and environmental affability. This paper provides a comprehensive overview of state-of-the-art research on sustainable geopolymers for repairing deteriorated and damaged concrete structures as well as restoring their integrity. Present challenges and future prospects of various geopolymer mortars as repair materials are emphasized.

Geopolymer mortars as sustainable repair material: A comprehensive review

A comparative study on fly ash, geopolymer and faujasite block for Pb removal from aqueous solution

Effect of metakaolin replaced granulated blast furnace slag on fresh and early strength properties of geopolymer mortar

Porous geopolymers have emerged as one of the most promising inorganic porous materials over the last decade, due to their inexpensive and easy fabrication process, suitable properties, thermal and chemical stability, and extensive applications. To further improve or optimize the properties of porous geopolymers or to endow them with new functionalities, a significant effort has been devoted to the exploitation and application of porous geopolymer composite materials. This review article highlights the current state-of-the-art in the field of porous geopolymer composites manufacturing methods (direct foaming, embedding lightweight (porous) fillers, additive manufacturing, etc.), properties (mechanical properties, thermal properties, adsorption properties, and others), and applications. With the summary and analysis of previous research literature, this review aims to foster further investigations into developing innovative routes for the fabrication of porous geopolymer components with improved properties and to encourage the widespread technological application of these materials.

Porous geopolymer composites: A review

Influence of synthesis parameters on NaA zeolite crystals

The invention mainly discloses a method for preparing a NaA molecular sieve from a geopolymer. The method comprises the following steps: with metakaolin or chemically-synthesized aluminum silicate active powder as a solid raw material and sodium potassium silicate or sodium hydroxide solution as an exciting agent, adjusting the ratio of silicon to aluminum in a system by using boehmite; mixing the solid raw material with the alkali exciting agent according to the ratio of silicon to aluminum and the ratio of sodium to aluminum in the raw materials in the composition design of the NaA molecular sieve; stirring the solid raw material and the alkali exciting agent and injecting the mixture into a die; carrying out sealed curing the mixture in a thermostat at the temperature of 60-80 DEG C for 6-24 hours; feeding the cured geopolymer sample into a hydrothermal reactor; and carrying out hydrothermal crystallization on the cured geopolymer sample at the crystallization temperature of 70-110 DEG C for 4-10 hours to obtain the NaA molecular sieve. According to the method disclosed by the invention, due to the utilization of the characteristic that the geopolymer is easily formed, a NaA molecular sieve blocky material can be prepared in situ at one time. Compared with the preparation method for the NaA molecular sieve, the prepared method disclosed by the invention has the advantages of simplicity in operation, low cost and suitability for scale preparation.

Method for preparing NaA molecular sieve from geopolymer

The invention mainly relates to a method for preparing faujasite by using a geopolymer by hydrothermal crystallization. The method comprises the following steps: by using metakaolin as a solid raw material and sodium water glass as an activator, adjusting the silica-alumina ratio of the system by use level of metakaolin; designing the silica-alumina ratio and the sodium-alumina ratio in the raw material according to theoretical composition of faujasite; mixing and stirring the solid raw material with an alkali-activator and injecting into a mould; maintaining for 12-24 hours in a constant temperature box at 40-80 DEG C; placing the maintained geopolymer in a hydrothermal kettle; and performing hydrothermal crystallization for 8-12 hours at 70-120 DEG C to prepare the faujasite material. The faujasite material can be prepared in-situ at one time by characteristic of easy moulding of the geopolymer. Compared with conventional preparation of faujasite, the method provided by the invention is simple to operate, low in cost and suitable for large-scale preparation.

Method for preparing faujasite by using geopolymer by hydrothermal crystallization

Self-supporting faujasite zeolite(FAU) membranes were synthesized by an in-situ hydrothermal growth method from geopolymers, which were prepared with metakaolin and sodium silicate as raw materials. The crystal properties, microstructure and compressive strength of the membranes were analyzed by X-ray diffraction、scanning electron microscopy and universal pressure tester,respectively. The effects of feed composition and temperature on the permeation flux and separation factor of the FAU zeolite membrane were investigated via pervaporation(PV) experiment and mathematical model. The results show that the size of zeolite granular is small, and the membrane surface appears complete and continuous. The increase of the curing time can improve the compressive strength of geopolymers, and the increase of the hydrothermal time can enhance the phase composition of FAU zeolites. For the ethanol content of 70% at 50 ℃, thepermeation flux and separation factor of the FAU type zeolite membrane are 1.41 kg/(h·m2) and 16.8,respectively.

In-situ Synthesis of Faujasite Zeolite Membrane from Geopolymer and Its Pervaporation Properties

Synthesis of a self-supporting faujasite zeolite membrane using geopolymer gel for separation of alcohol/water mixture

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