摘要
硅灰可以显著提高水泥混凝土力学强度和耐久性,但其对天然水硬性石灰(NHL)早期物理力学性能和水化硬化进程的作用机理尚不明确。通过工作性、变形行为和力学强度研究了掺加硅灰的NHL物理力学性能发展过程,采用热重法、X射线衍射、扫描电子显微镜和压汞测试探究了硅灰对NHL水化过程物相组成和微结构演变的影响。结果表明:硅灰能够显著加速NHL的早期水化进程,缩短凝结周期,大幅度提高砂浆的抗压和抗折强度,并抑制其早龄期(<5 d)变形行为,但会对流动性有明显负面效应。硅灰除了作为成核位点促进C_(2)S水化外,也会与NHL中的Ca(OH)_(2)发生火山灰反应生成C-S-H,而与C_(2)S水化生成的Ca(OH)_(2)发生二次水化会进一步提升C-S-H生成量,此外掺加硅灰会间接影响NS体系的整体碳化程度。硅灰的颗粒填充效应以及C-S-H和CaCO_(3)的生成有效细化了孔隙结构,使平均孔径降低1个数量级(由285.42 nm降至20.70 nm),总孔隙率明显降低,在以上多重效应作用下,NHL的力学性能得以显著提高。
Introduction Natural hydraulic lime(NHL),as an inorganic cementitious material with both hydraulic and air-hardening properties,mainly consists of dicalcium silicate,calcium hydroxide and calcium carbonate.It has moderate strength,good breathability and low soluble salt content,and its inherent cementitious properties are significantly superior to traditional lime in the restoration of cultural relics and ancient buildings.However,there are still considerable challenges in the large-scale application of NHL in the restoration of ancient buildings,and the performance requirements for NHL in different restoration projects of ancient buildings may also vary.Due to the typical phase composition of NHL,the pozzolanic effect of silica fume can significantly affect the hydration process in NHL.However,the mechanism of silica fume action around typical performance development is not clear,which is obviously insufficient to explain the relationship between the physical and mechanical properties of NHL under the action of silica fume and the phase composition and microstructure evolution,as well as the macro and micro development influence mechanism.In this work,the physical–mechanical properties of NHL under the action of silica fume and its phase composition and microstructure were studied,and the corresponding relationship between phase composition,pore structure and performance was explored.Methods The experiment utilized NHL(NHL2 level),whose main mineral composition was dicalcium silicate(β-C_(2)S),calcium hydroxide(Ca(OH)_(2))and calcium carbonate(CaCO_(3)).Silica fume(SF)was used,which was composed of micro-nano amorphous silica spherical particles.The designed water-binder ratio was 0.55,and the binder-sand ratio was 1:3.The dosage of polycarboxylate superplasticizer was 0.4%(in mass,the same below).SF was used to replace 0%,5%,10%and 15%of the NHL mass respectively to prepare paste and mortar specimens.The specimens were covered with isolation film to prevent excessive evaporation of free water and were cured in a standard curing chamber for 72 h before demolding.After that,the specimens were cured under conditions of(20±2)℃and RH of 65%±5%for 7,14 and 28 days.The setting time,fluidity,compressive and flexural strength,drying shrinkage and mass change were tested in accordance with relevant standards.The phase composition was analyzed by XRD(Ultima IV,Rigaku)and thermogravimetry(STA 449 F3,NETZSCH).The microstructure and pore structure were analyzed by SEM(JSM-6700F)and MIP(Autopore 500)respectively.Before testing,the samples need to be treated with isopropanol to interrupt hydration,and then dried to a constant mass in a vacuum drying oven at 40℃.Results and discussion SF has a significant promoting effect on the setting of NHL paste,the initial and final setting times of NS15 paste were shortened by 0.96 h and 0.60 h respectively,while the fluidity of its slurry and mortar decreased by 48.3%and 68.1%respectively.The mechanical strength of NS mortar with SF was significantly increased compared to NHL mortar.The compressive strength of NS5,NS10 and NS15 mortar at 28 days reached 4.62,8.51 MPa and 10.92 MPa respectively.The drying shrinkage rate and mass loss rate of NS mortar with SF gradually increased,and the shrinkage amount exceeded that of NHL mortar after 7 days.At 28 days,the drying shrinkage reached about 1400μm·m^(–1),which was significantly greater than that of NHL mortar.The pozzolanic reaction caused free water to transform into chemical bound water,and the evaporation of free water in pores increased the number of pores available for the transmission of external CO_(2) into the interior,promoting the occurrence of carbonation in the system and resulting in an increase in mass.SF has a high specific surface area and may act as a nucleation site to promote the hydration of C_(2)S and the formation of C-S-H gel and Ca(OH)_(2) in NS.The pozzolanic reaction caused by SF in NS promotes the generation of a large amount of C-S-H gel while consuming Ca(OH)_(2).SF will further react with the Ca(OH)_(2) generated by hydration through“secondary hydration(pozzolanic reaction)”to form C-S-H gel.In addition,SF has a significant promoting effect on the carbonation of NS system.These effects significantly influence the pore structure composition in the hardened NS slurry.SF can refine the pore size and increase the pore density,thereby promoting a significant increase in mechanical strength.Conclusions SF can significantly shorten the setting period of NHL paste,but it will cause a significant decrease in its fluidity.The compressive strength of NS mortar with SF addition is significantly increased,and the 28-day compressive strength of NS15 mortar reaches 10.92 MPa,which is 3.97 times higher than that of NHL mortar.SF shows a change pattern of first inhibiting and then promoting the drying shrinkage of NHL mortar.The hydration of C_(2)S to form C-S-H gel and Ca(OH)_(2) is the basic hydration process in NHL.The combined effects of SF acting as a nucleation site to promote the hydration of C_(2)S,the pozzolanic reaction between SF and Ca(OH)_(2) in NHL,and the secondary hydration of SF and Ca(OH)_(2) formed by the C_(2)S hydration,and result in a significant increase in the C-S-H and a significant decrease in the content of Ca(OH)_(2) in NS system.The content of CaCO^(3) generated by carbonation in NS with SF addition increases significantly.Pore structure of NHL is mainly composed of capillary pores and macro pores,with a total porosity of 51.31%at 28 days.The proportion of gel pores and transition pores in NS significantly increases,and with the increase of SF dosage,the most probable pore diameter shifts towards smaller pores,and the average pore diameter also decreases significantly.The filling effect of SF and the generation of more C-S-H and CaCO_(3) due to the hydration and carbonation of NHL can significantly refine the pore size and densify the pore structure.
作者
张大江
董文博
王栋民
黄文
章文明
王剑锋
王亚丽
路易
崔素萍
ZHANG Dajiang;DONG Wenbo;WANG Dongmin;HUANG Wen;ZHANG Wenming;WANG Jianfeng;WANG Yali;LU Yi;CUI Suping(Collage of Materials Science and Engineering,Beijing University of Technology,Beijing 100124,China;State Key Laboratory of Materials Low-Carbon Recycling,Beijing University of Technology,Beijing 100124,China;School of Chemical and Environmental Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China;China Building Materials Academy Co.,Ltd.,Beijing 100024,China;Lingyuan Fuyuan Mining Industry Co.,Ltd.,Lingyuan 122500,Liaoning,China;Shanxi Academy of Ancient Building and Painted Sculpture&Fresco Preservation,Taiyuan 030012,China)
出处
《硅酸盐学报》
北大核心
2026年第1期258-270,共13页
Journal of The Chinese Ceramic Society
基金
国家自然科学基金(52572020,52202016,U24A2047)。
关键词
天然水硬性石灰
硅灰
火山灰反应
力学性能
孔隙结构
natural hydraulic lime
silica fume
pozzolanic reaction
mechanical properties
pore structure
