Recycling of water treatment sludge in concrete: The role of water-binder ratio from a nanoscale perspective

Zhi-Hai He; Xu-Dong Han; Jia-Xu Jin; Jiang-Shan Li; Wei Tang; Jin-Yan Shi

doi:10.1016/j.scitotenv.2023.162456

Recycling of water treatment sludge in concrete: The role of water-binder ratio from a nanoscale perspective

Sci Total Environ. 2023 May 15:873:162456. doi: 10.1016/j.scitotenv.2023.162456. Epub 2023 Feb 25.

Authors

Zhi-Hai He¹, Xu-Dong Han², Jia-Xu Jin³, Jiang-Shan Li⁴, Wei Tang⁵, Jin-Yan Shi⁶

Affiliations

¹ College of Civil Engineering, Shaoxing University, Shaoxing 312000, China; Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing 312000, China.
² College of Civil Engineering, Shaoxing University, Shaoxing 312000, China.
³ School of Civil Engineering, Liaoning Technical University, Fuxin, Liaoning 123000, China.
⁴ State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China.
⁵ Department of Architecture and Design Art, Shaoxing Vocational and Technical College, Shaoxing 312000, China.
⁶ School of Civil Engineering, Central South University, Changsha 410075, China. Electronic address: jinyan.shi@csu.edu.cn.

PMID: 36842600
DOI: 10.1016/j.scitotenv.2023.162456

Abstract

For eutrophic water bodies, potassium permanganate is an effective pre-oxidant to remove algae and its residue in water treatment sludge. Recycling water treatment sludge in concrete is an environmentally friendly and high-value utilization measure. However, little research has been done on the effect of manganese-rich drinking water sludge ash (DWSA) on concrete. The effect of water-binder ratio (w/b) on strength, shrinkage and microstructural characteristics of concrete containing DWSA was investigated, and the structural behavior was explained from a nanoscale perspective. The results show that recycling 10 % DWSA in concrete improved the strength and shrinkage resistance of the samples. Reducing the w/b effectively increased the strength of DWSA-modified concrete and reduced the shrinkage deformation. The paste with high w/b had higher contents of non-evaporated water and calcium hydroxide, as well as higher reaction degree of DWSA. Nanoscale characterization shows that reducing the w/b reduced the volume fraction of pore and unhydrated phases in the matrix and increased the proportion of high-density C-S-H. Meanwhile, reducing the w/b also reduced the interfacial transition zone width of DWSA-modified concrete. Recycling DWSA in concrete effectively reduced the total carbon footprint and cost of the mixture. The combined application of reducing the w/b and incorporating DWSA effectively improved the economic and environmental benefits of concrete material. For the concrete modified with 10 % DWSA (w/b = 0.3), its cost and carbon emissions are reduced by 14 %-21 % and 19 %-25 % compared with the reference sample, respectively. Overall, this study reveals the action mechanism of DWSA in cement system at different w/b from nanoscale perspective, and gives a new insight on determining the optimal w/b in full-scale application of DWSA concrete.

Keywords: Concrete; Drinking water sludge ash; Microstructure; Nanoscale; Water-binder ratio.