Mechanical Performance and Mechanism of Nano-silica Sol Reinforced Sodium Carbonate Activated Slag Mortar
LIU Huanghai1, JI Tao2, LIU Xinsuo3, HU Zhilong1, ZHENG Qiaofang1, ZHENG Xiaoyan1,*
1 College of Transportation and Civil Engineering, Fujian Agriculture and Forestry University, Fuzhou 350108, China 2 College of Civil Engineering, Fuzhou University, Fuzhou 350108, China 3 Zhejiang Commun Construct Grp Co., Ltd., Hangzhou 310052, China
Abstract: Sodium carbonate activated slag mortar (SCASM) has the advantages of low carbon emissions, high long-term strength and excellent durability, but its disadvantages such as long setting time and low early strength limit its practical application. Nano-silica sol (NSS) is a colloidal solution formed by the stable dispersion of nano-SiO2 particles in water, exhibiting high activity and dispersibility. In this work, the effect of various NSS contents on the workability and mechanical performance of SCASM was investigated, and its mechanism was explored by hydration heat, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope and energy dispersive spectrometer analysis (SEM-EDS). The results show that NSS can effectively improve the setting speed and mechanical properties of SCASM. NSS provides nucleation effect and nano-filling effect to effectively accelerate the hydration rate, increase the polymerization degree of SCASM, and densify the matrix microstructure. Under alkaline action, the Si-O bond of nano-SiO2 particles in NSS is further opened to form monomer [SiO4]4- in the early stage, providing more nucleation sites. This is prior to the reaction of CO32- with Ca2+ and Al3+ in the slag to form C-(A)-S-H gel, which plays an important role in the early strength. The gel formed has lower Al/Si ratio and denser structure. At the same time, the unreacted SiO2 particles could fill the pores and further optimize the pore structure. With the increasing of NSS content, the setting time, bleeding rate and fluidity of SCASM gradually decrease, while the mechanical properties and the ratio of flexural to compression firstly increase and then decrease. When the NSS content is 11%, the initial setting time and final setting time of the pastes can be shortened by 96.0% and 93.1%, respectively. When the NSS content is 5%, the mortar sample has the highest flexural strength, compared with mortar sample without NSS, its 7 d and 28 d flexural strength significantly increases by 75.4% and 24.7%, respectively. When the NSS content is 8%, the mortar sample has the highest compressive strength, and its 7 d and 28 d compressive strength significantly improve by 91.7% and 21.6%, respectively. However, when the NSS content is too high, the mechanical properties of SCASM will reduce due to the decreased dispersibility of NSS.
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2025, Vol. 39 
