Mechanical properties and mechanism of magnesium oxychloride cement composites modified by biomass silicon
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摘要: 为了提高氯氧镁水泥的力学及耐水性能，同时解决废弃农作物青稞秸秆的资源处置问题，采用一定条件下煅烧及研磨处理制备而成的青稞秸秆灰(HBSA)，改善氯氧镁水泥的力学及耐水性能。首先，对不同HBSA掺入方式及掺量的氯氧镁水泥砂浆(MOCM)的力学性能进行试验，分别测试了MOCM的抗折强度、抗压强度、折压比及软化系数的变化规律。其次，对MOCM的孔隙结构和微观结构进行测试分析，进一步阐释了掺入HBSA对MOCM力学性能影响的作用机制。研究结果表明：HBSA外掺时，MOCM可以获得较高的力学性能及耐水性能。当HBSA掺量为5wt%时，MOCM的抗折强度和抗压强度最高；当HBSA掺量为10wt%时，MOCM在饱水状态下的抗压强度损失最小，耐水性能最优。当HBSA外掺且掺量为10wt%时，MOCM的孔隙结构中有害孔和多害孔的比例显著降低，无害孔和少害孔的比例显著增加。MOCM中的水化产物Mg(OH)2能够与HBSA中的活性SiO2发生二次水化反应，生成大量的水化硅酸镁(M-S-H)凝胶，有效地填充了MOCM内部的有害孔隙，阻碍了水分的传输与侵蚀，提高了MOCM的耐水性能。Abstract: In order to improve the mechanical properties and water resistance of magnesium oxychloride cement and solve the problem of resource disposal of abandoned crop highland barley straw, highland barley straw ash (HBSA) prepared by calcination and grinding under certain conditions was used to improve the mechanical properties and water resistance of magnesium oxychloride cement. First of all, the mechanical properties of magnesium oxychloride cement mortar (MOCM) with different HBSA mixing methods and amounts were tested, and the changing laws of the flexural strength, compressive strength, flexural compression ratio and softening coefficient of MOCM were tested respectively. Secondly, the pore structure and microstructure of MOCM were tested and analyzed to further explain the mechanism of the influence of HBSA on the mechanical properties of MOCM. The results show that MOCM can obtain higher mechanical properties and water resistance when HBSA is added with the external mixing method. When the content of HBSA is 5wt%, MOCM has the highest flexural strength and compressive strength; When the content of HBSA is 10wt%, the compressive strength loss of MOCM in saturated state is the smallest, and the water resistance is the best. When HBSA is added with the external mixing method and the content is 10wt%, the proportion of harmful pores and more harmful pores in the pore structure of MOCM is significantly reduced, and the proportion of harmless pores and less harmful pores is significantly increased. The hydration product Mg(OH)2 in MOCM can react with the active SiO2 in HBSA to generate a large number of hydrated magnesium silicate (M-S-H) gel, which effectively fills the harmful pores in MOCM, hinders the transmission and erosion of water, and improves the water resistance of MOCM.
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图 2 不同HBSA掺量的MOCM的抗折强度
Figure 2. Flexural strength of MOCM with different HBSA contents
图 3 不同HBSA掺量的MOCM的抗压强度
Figure 3. Compressive strength of MOCM with different HBSA contents
图 4 不同HBSA掺量的MOCM的折压比ff/fc
Figure 4. Ratio of flexural strength and compressive strength (ff/fc) of MOCM with different HBSA contents
图 5 不同HBSA掺量的MOCM的软化系数
Figure 5. Softening coefficient of MOCM with different HBSA contents
R2—Fit coefficient
图 6 不同HBSA掺量的MOCM的横向弛豫时间T2图谱(a)与孔径分布(b)
Figure 6. Transverse relaxation time T2 spectra (a) and pore diameter distribution (b) of MOCM with different HBSA contents
图 7 不同HBSA掺量的MOCM的SEM图像
Figure 7. SEM images of MOCM with different HBSA contents
M-S-H—Hydrated magnesium silicate
图 8 不同HBSA掺量的MOCM的热重曲线
Figure 8. Thermogravimetric curves of MOCM with different HBSA contents
图 10 生物质硅改性氯氧镁水泥复合材料的作用机制
Figure 10. Mechanism of magnesium oxychloride cement composites modified by biomass silicon
表 1 青稞秸秆灰(HBSA)的化学组成
Table 1. Chemical compositions of highland barley strawash (HBSA)
SiO2/wt% CaO/wt% SO3/wt% MgO/wt% Al2O3/wt% Fe2O3/wt% K2O/wt% Na2O/wt% P2O5/wt% Others/wt% 61.75 10.63 1.75 2.04 5.92 3.83 5.31 2.60 5.72 0.44 
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表 2 氯氧镁水泥砂浆(MOCM)的配合比设计
Table 2. Mix propertion design of magnesium oxychloride cement mortar (MOCM)
kg/m3 MgCl2 Sand Superplasticizer Water resistant agent HBSA Internal mixing (IM) External mixing (EM) MgO H2O MgO H2O 221.7 937.5 16.0 6.9 0 583.4 203.4 583.4 203.4 29.2 554.2 211.7 58.3 525.1 220.0 87.5 495.9 228.4 116.7 466.7 236.7 175.0 408.4 253.2
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表 3 不同HBSA掺量的MOCM中各类孔隙占比及孔隙率
Table 3. Proportion of various pores and porosity in MOCM with different HBSA contents
Mixing method HBSA content <0.02 μm 0.02-0.05 μm 0.05-0.20 μm >0.20 μm Porosity/% Without mixing 0wt% 0.03 2.39 6.08 0.64 9.14 Internal mixing 10wt% 0.85 3.88 6.99 0.96 12.68 External mixing 10wt% 1.45 3.88 4.75 0.24 10.32
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