Preparation Of Konjac Glucomannan-Based Cement Admixtures And Their Effects On Properties Of Portland Cement

The goals of carbon peaking and carbon neutrality forced the cement industry to turn to the road of green,energy-saving and sustainable development,which has become the inevitable way of cement industry.In addition,various cement application scenarios and construction environment put forward more stringent and diversified requirements for the performance of concrete construction and environmental adaptability.As the fifth common component of cement,cement admixtures have been widely concerned for its small dosage,effective improvement of physical and chemical properties of cement-based materials,and low cost.However,the existing cement admixtures are mostly inorganic or synthetic polymers,which are liable to cause environmental pollution.In this paper,Konjac Glucomannan（KGM）,a typical natural macromolecule was selected,and a series of additives such as KGM hydrogel,KGM gel microspheres and konjac glucomannan biochar（KGMB）were prepared by ultrasonic dispersion,alkali cross-linking,electrospray and hydrothermal methods,respectively.The effects of KGM-based admixtures on the performance of setting time,anti-washout and plant growth of the cement-based materials were systematically discussed.This paper intends to explore the potential of natural polymer materials as additives for cement-based materials.The influence of KGM on the hydration of common Portland cement（OPC）was investigated by the setting time and hydration heat of OPC,infrared spectroscopy and X-ray diffraction pattern,etc.The addition of KGM could significantly prolong the setting time of OPC without late strength damage.The retarding effect is related to its molecular weight,dosage and the type of cement.Additionally,the deacetylation of KGM occurs in the strong alkali environment provided by the hydration reaction of cement,forming a gel network and adsorbing in situ on the surface of cement clinker particles,which effectively restrains the migration of water molecules and the dissolution of cement clinker.Then,the active hydroxyl groups rich in KGM forms a cross-linking network with the Ca²⁺released from the hydration of cement,which further inhibits the nucleation and growth of the hydration products of cement.Three kinds of KGM-based anti-washout admixtures（AWAs）were prepared by ultrasonic dispersion,alkali cross-linking and electrospray,respectively.And the mechanism of AWAs on the washout resistance of OPC was studied by simulation washout experiment and rheology,etc.The washout loss of cement paste with KGM solution is the smallest（0.3%）,which is better than that with KGM hydrogel（8.6%）and gel microspheres（17.4%）.Furthermore,the addition of solution-type and hydrogel-type KGM-AWAs enhances the cohesion of cement paste by increasing the viscosity and calcium ion chelation.KGMB loaded with nutrient elements（N,P,K）was prepared by hydrothermal reaction.The effects of KGMB on mechanical properties,alkalinity,porosity and growth performance of plant concrete were studied.The addition of KGMB effectively reduces the alkalinity of the pore solution of the planting concrete without strength damage.KGMB reduces the porosity of plant concrete due to its effectiveness in improving the fluidity of plant concrete.Moreover,the addition of KGMB provided essential nutrients for the growth of ryegrass,and the higher the KGMB content（0-0.3 wt%）,the better the plant growth characteristics（plant height,root length,etc.）of ryegrass.