Study On The Mechanism Of Ba²⁺ Stabilize /Control AFt Formation In The High Sulfur Cementitious Materials

Phosphogypsum is an industrial by-product of phosphorus chemical enterprises,and its output and accumulative storage are very large.Due to high treatment cost and low comprehensive utilization rate,phosphogypsum is also considered as one of the most difficult solid wastes to be utilized.The accumulation of phosphogypsum not only occupies a large amount of land resources,but also causes serious pollution and damage to the surrounding environment.The application of phosphogypsum in the preparation of cementitious materials is an effective method for the treatment of phosphogypsum.At present,phosphogypsum cementitious materials are mainly used to prepare non-reinforced products such as floor tiles,slope protection stones,grass planting bricks and kerb stones,which cannot be used as structural materials and load-bearing materials.This article will be the same phosphogypsum dry sieving,direct preparation of phosphorus gypsum and cement composite high sulfur gelled material ore and phosphorus gypsum-cement-quick lime sulfur compound high cementing materials,adding suitable amount of barium chloride,by measuring the setting time of high sulphur cement materials,mechanical properties,pore structure,carbonation resistance and volume stability performance to study the Ba²⁺of high sulfur the influence law of gelled material structure and performance;The mechanism of Ba²⁺stabilizing AFt formation in high-sulfur cementing materials was studied by means of pore solution pH value,Ca²⁺concentration,XRD and SEM.Through systematic experimental analysis and research,the following conclusions are obtained in this paper:1.In the phosphogypsum cement composite high-sulfur cementitious material,when the phosphogypsum content is 5wt%,10wt%,15wt%and 20wt%respectively,adding appropriate amount of barium chloride can effectively improve its structure and performance,providing a basis for further research on the role of barium chloride in the phosphogypsum cement–slag powder-quicklime composite high-sulfur cementitious material.2.As the content of barium chloride,sodium silicate and barium chloride-sodium silicate increases,the setting time and compressive strength of phosphogypsum-cement-slag powder-quicklime composite high-sulfur cementitious materials are shortened and their compressive strength first increases and then decreases.When the barium chloride content was 18wt%,the initial setting time was shortened to 270min.The 28d compressive strength reached 32.8MPa,60.0%higher than the sample.When barium chloride and sodium silicate were mixed with 16wt%,the initial setting time was shortened to 180min.The 28d compressive strength reached 38.1MPa,85.8%higher than that of the sample.The setting time and mechanical properties of high sulfur gelling materials were improved by barium chloride and sodium silicate.3.In the phosphogypsum-cement-slagl powder-quicklime composite high-sulfur cementitious material system,with the increase of the content of barium chloride,sodium silicate and barium chloride-sodium silicate,the total porosity,average pore diameter and linear expansion rate of the product decrease.When the barium chloride content was 18wt%,the total porosity of the sample decreased by 36.9%and the linear expansion rate decreased by 35.6%on 28d.When barium chloride and sodium silicate were mixed with 16wt%,the total porosity of the sample decreased by 48.1%,and the 28d linear expansion rate decreased by 68.9%.In other words,appropriate amount of barium chloride and sodium silicate can effectively improve the porosity,pore size,pore diameter distribution and volume stability of high sulfur cementitious materials.4.The incorporation of barium chloride increased the concentration of Ba²⁺in the composite high-sulfur cementing material solution,reacted with SO₄^2-in the system to form BaSO₄ precipitation,and partially SO₄^2-in the curing system,inhibited the formation of delayed ettringite in the late hydration period,and improved the structure and performance of the product.The incorporation of barium chloridium-sodium silicate composite admixtures not only effectively promoted the formation of AFt in the early stage of hydration but also inhibited the formation of delayed ettringite in the late stage of hydration,stably controlled the formation period of AFt in the high-sulfur cementitious material system,and improved the structure and performance of high-sulfur cementitious material.