【作者】 李伟；

【导师】 张鸿儒；

【作者基本信息】 福州大学 ， 土木工程（专业学位）， 2023， 硕士

【摘要】 矿渣是碱激发胶凝材料中常用的前驱体,但由于其消耗量巨大,未来可能出现供不应求的局面。硅藻土是一种硅质沉积岩,主要成分是无定形Si O₂,具有潜在活性且在我国储量丰富,有望成为部分替代矿渣的碱激发前驱体。课题拟采用不同硅藻土（原土DE、煅烧硅藻土CDE、废弃硅藻土SDE）部分取代矿渣制备新型碱激发矿渣-硅藻土胶凝材料,研究碱激发剂种类（氢氧化钠NH、氧化钙+碳酸钠CNC、水玻璃NS）、碱当量、硅藻土种类及掺量对碱激发矿渣-硅藻土砂浆工作性能和力学性能的影响,采用水化热、XRD、TG-DTG、MIP、SEM等微观测试技术表征其水化进程及微观结构,据此揭示上述因素对碱激发矿渣-硅藻土砂浆性能的影响机理,并利用熵值-层次分析法综合优选激发剂种类、碱当量及硅藻土掺量,最后对碱激发矿渣-硅藻土砂浆进行全生命周期评价。主要结论如下:1、同碱当量下,NS作激发剂时,碱激发矿渣-硅藻土凝结很快,且掺入硅藻土后强度降低;CNC作为激发剂,砂浆流动度差,掺入硅藻土后强度提升不明显;而NH作激发剂,掺硅藻土后砂浆流动度与纯矿渣对照组相当,凝结时间略有延长,强度提升显著,28 d抗折和抗压强度最高提升43.5%和85.2%。2、同激发剂下,碱当量从4%增至6%,碱激发矿渣-硅藻土砂浆流动度改善,凝结时间缩短,抗折强度呈无规律变化,但对抗压强度存在最优碱当量,NH组及CNC、NS组最优碱当量分别为4%和6%;同激发剂及碱当量下,砂浆流动度随硅藻土掺量增加变差,凝结时间缩短,抗折、抗压强度先升后降。3、微观测试表明,以NH为激发剂时,相较于另两种激发剂,碱激发矿渣-硅藻土体系反应更充分,生成更多的C-（A）-S-H和类水滑石,孔结构细化,总孔隙率最小;但随碱当量增加,水化产物减少,浆体总孔隙率更高且大孔占比增加;硅藻土掺量为20%时,水化产物生成量最多,总孔隙率及大孔占比最小。4、采用熵值-层次分析对碱激发矿渣-硅藻土砂浆的工作性能和力学性能进行综合评价,确定碱激发矿渣-硅藻土砂浆最优激发剂为NH,最优碱当量为4%,最优硅藻土掺量为20%;三种硅藻土对比,则CDE系列的综合性能最优。5、SDE掺入可有效降低碱激发矿渣-硅藻土砂浆的环境影响,而掺入DE、CDE仅有效降低AP、POCP两指标。同时考虑力学性能时,三种硅藻土的掺入均可有效降低碱激发矿渣砂浆的单位强度环境影响指标,且掺量20%时最显著。更多还原

【Abstract】 Slag is a commonly used precursor in alkali-activated cementitious materials,but its huge consumption may lead to supply shortages in the future.Diatomaceous earth,a type of siliceous sedimentary rock with abundant reserves in China and potential reactivity,is expected to become a promising substitute precursor in alkali-activated materials.In this study,different types of diatomaceous earth,including raw DE,calcined CDE,and waste SDE were partially used to replace slag to prepare a new type of alkali-activated slag-diatomaceous earth cementitious material.The effects of alkali activators(sodium hydroxide,calcium oxide plus sodium carbonate and water glass,i.e.,NH,CNC,and NS),the alkali content,the type and dosage of diatomaceous earth on the workability and mechanical properties of the alkali-activated slag-diatomaceous earth mortar were investigated.Microscopic testing techniques such as hydration heat,XRD,TG-DTG,MIP,and SEM were used to characterize the hydration process and microstructure,based on which the mechanism of how these factors influence the properties of the alkali-activated slag-diatomaceous earth mortar was investigated.The entropy value and hierarchical analysis method was used to comprehensively evaluate the performance of the alkali-activated slag-diatomaceous earth mortar so that the optimal alkali activator as well as the diatomaceous earth type and dosage can be determined.The life-cycle assessment of the alkali-activated slag-diatomaceous earth mortar was also conducted.The main conclusions are as follows:1.Given that the alkali content was constant,the alkali-activated slag-diatomaceous earth mortar set quickly when water glass(NS)was used as the activator,and the strength decreased with the incorporation of diatomaceous earth.Using calcium oxide and sodium carbonate(CNC)was as activator led to poor flowability and the strength improvement was not significant with the incorporation of diatomaceous earth compared to the control group.In contrast,using sodium hydroxide(NH)as activator can help gain comparable flowability of the alkali-activated slag-diatomaceous earth mortar to that of the control group,and the setting time was slightly prolonged.The strength improvement was significant in this case,with the 28-day flexural and compressive strength improved by up to 43.5%and 85.2%,respectively.2.Given that the type of activators was constant,the flowability of the alkali-activated slag-diatomaceous earth mortar was improved and the setting time was shortened when increasing the alkali content from 4%to 6%.The flexural strength showed irregular changes,but there was an optimal alkali content for compressive strength.The optimal alkali content for NH and CNC/NS groups were 4%and 6%,respectively.Given that the activators and alkali content were constant,the flowability of the mortar decreased and the setting time was shortened,when the diatomite content increases,the flexural and compressive strengths first increased and then decreased.3.Microscopic testing showed that the reaction degree was more complete given that NH was used as the activator.Compared with the other two activators,the NH activator helped generate more C-(A)-S-H and hydrotalcite-like phases,thereby refining the pore structure and achieving the smallest porosity.As the alkali content increased,less hydration products were produced,meanwhile the total porosity and the proportion of large pores increased.The optimal diatomaceous earth content was 20%at which the quantity of hydration products was maximized while the total porosity and the large pore proportion were minimized.4.The workability and mechanical properties of alkali-activated slag-diatomaceous earth mortar were comprehensively evaluated using entropy-weighted analytic hierarchy process(AHP)in this present work.The optimal activator for the alkali-activated slag-diatomaceous earth mortar was determined to be NH,while the optimal alkali content and diatomaceous earth dosage were 4%and 20%,respectively.Basically,the CDE series exhibited the best performance among the three types of diatomaceous earth.5.Life-cycle assessment(LCA)showed that the addition of SDE can effectively reduce the environmental impact of alkali-activated slag-diatomaceous earth mortar.The addition of DE and CDE can only effectively reduce the AP and POCP values.When the environmental impact was considered in conjunction with the mechanical properties,it was found that the addition of all the three types of diatomaceous earth can effectively reduce the environmental imprength of the alkali-activated slag mortar.Moreover,the reduction was most sign acts per unit significant when the dosage of the diatomaceous earth was 20%.更多还原