Influence of high-volume water treatment plant sludge powder on strength and microstructure of concrete
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摘要: 以煅烧后的自来水厂污泥粉 (CWTS) 取代部分水泥制备大掺量污泥粉混凝土，研究了大掺量 CWTS对于混凝土强度、孔结构和纳米力学性能的影响。结果表明：尽管大掺量CWTS不利于混凝土的28天抗压强度发展，但是20wt%和40wt%的CWTS能够增强混凝土的90天抗压强度；由于CWTS的火山灰活性和填充作用，掺有20wt%~40wt%CWTS的混凝土90天孔结构被明显细化，大于1 µm的孔隙含量明显减少；同时，从纳米尺度特征中观察到掺加20wt%CWTS能够明显降低基体中孔隙相和未水化相含量，并提高C—S—H相的体积分数，特别是高密度C—S—H相；此外，掺加20wt%的CWTS能够使界面过渡区(ITZ)宽度相对降低20%，并且掺加40wt%CWTS的实验组与对照组 (0wt%CWTS) 具有相似的ITZ宽度。由此可见，使用大掺量 (20wt%~40wt%) CWTS取代水泥制备混凝土，不仅具备较好的经济和环境效应，也有益于其90天力学性能和微结构的改善。Abstract: The calcined water treatment plant sludge powder (CWTS) was used to replace part of the cement to prepare high-volume sludge concrete, and the effect of the high-volume CWTS on the mechanical properties and microstructure of concrete was studied. The results show that although the high-volume CWTS is detrimental to the development of the 28-days compressive strength of concrete, 20wt% and 40wt% of the CWTS can significantly improve the 90-days compressive strength of concrete. The CWTS has pozzolanic reactivity and filling effect, which makes the 90-days pore structure of concrete mixed with 20wt%‒40wt%CWTS significantly refined, and the harmful pore volume (>1 µm) is significantly reduced. Meanwhile, it is observed from the nanoscale characteristics that adding 20wt%CWTS can significantly reduce the content of pore phase and unhydrated phase in the matrix, and increase the volume fraction of C—S—H phase, especially the high-density C—S—H phase. In addition, the addition of 20wt%CWTS can reduce the width of the interface transition zone (ITZ) by 20%, the addition of 40wt%CWTS and the control group (0wt%CWTS) have similar ITZ width. Therefore, using a large amount (20wt%‒40wt%) of CWTS to replace cement to prepare concrete not only has better economic and environmental benefits, but also benefits the improvement of its 90-days mechanical properties and microstructure.
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图 2 纳米压痕混凝土试样的制备流程
Figure 2. Flow chart of nanoidentation concrete specimen preparation
R—Roughness
图 4 CWTS掺量对于混凝土孔结构的影响：(a) 累计孔隙率；(b) 不同尺寸孔隙的比例
Figure 4. Effect of CWTS on pore structure of concrete: (a) Cumulative porosity; (b) Proportion of different sizes of pores
图 5 不同CWTS掺量试件中水泥基体的90天弹性模量
Figure 5. 90-Days elastic modulus of cement matrix of sample with different CWTS content
图 6 CWTS对水泥基体弹性模量频率分布的影响
Figure 6. Effect of CWTS on frequency distribution of elastic modulus of cement matrix
MP—Micro-pores; LD—Low density; HD—High density; CH—Calcium hydroxide; UC—Unhydrated clinker
图 7 CWTS对水泥基体各相体积分数的影响
Figure 7. Effect of CWTS on volume fractions of constituent phases of cement matrix
图 8 不同CWTS掺量的试件界面过渡区 (ITZ) 的弹性模量分布云图
Figure 8. Contour map of elastic modulus distribution in interfacial transition zone (ITZ) of sample with different CWTS content
图 9 不同CWTS 掺量的试件界面过渡区宽度分布
Figure 9. Widths of interface transition zone of sample with different CWTS content
表 1 水泥和煅烧自来水厂污泥粉 (CWTS)的化学组成 (wt%)
Table 1. Chemical compositions of cement and calcined water treatment plant sludge powder (CWTS) (wt%)
CaO SiO2 Al2O3 Fe2O3 MgO SO3 Na2O MnO K2O P2O5 Cement 57.39 18.06 4.60 8.31 2.53 3.01 0.10 — 0.75 — CWTS 1.15 33.09 44.51 3.11 0.46 0.28 — 5.25 1.45 0.77 
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表 2 混凝土配合比
Table 2. Mix proportions of concrete
Sample number Mass fraction
of CWTS/wt%Mix proportion/(kg·m−3) Cement CWTS Sand Coarse aggregate Water Super plasticizer C-0%CWTS 0 540 0 715 1040 162 9.8 C-20%CWTS 20 432 108 715 1040 162 10.7 C-40%CWTS 40 324 216 715 1040 162 13.4 C-60%CWTS 60 216 324 715 1040 162 15.2
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