Experimental study on macro–micro-structural properties and strength prediction model of wastewater concrete

Abstract

This study is intended to investigate the mechanical, durability, and drying shrinkage properties of concrete mixtures incorporating wastewater from ready-mixed concrete plants. The microstructural attributes were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) imaging, energy dispersive spectrometry (EDS), and mercury intrusion porosimetry (MIP). Meanwhile, rough set theory (RST) was used to analyze the influence of mean pore radius, porosity, fractal dimensions, and pore size distribution (PSD) on the compressive strength of wastewater concrete. The results showed that the seven-day cube compressive strengths for C20, C40, and C60 concrete specimens increased when wastewater was utilized, with the highest rise in the strength properties being observed as 16.84% for C40 mixture. Nevertheless, the 28-day cube compressive strengths of C20, C40, and C60 concretes were reduced by 4.85%, 9.33%, and 18.63%, respectively. The durability results showed that wastewater mixing reduced the frost resistance of C40 and C60 concrete, but improved for C20 concrete. The microstructural investigation revealed that mixing concrete with wastewater densifies the early-age concrete microstructure and refines the pore size. Nevertheless, the compactness of concrete microstructure at the later stage was reduced, and the pores in concrete were enlarged due to the poor cohesiveness of wastewater particles. The porosity and PSD have the greatest influence on the compressive strength of wastewater concrete. A strength and pore structure model of wastewater concrete was also developed and validated by considering PSD and porosity as bivariate parameters.

Highlights

• The addition of wastewater can improve the early compressive strength of concrete.

• The addition of wastewater reduces the carbonization resistance of concrete.

• A high-precision model of wastewater concrete strength was established.

KEYWORDS:

• Wastewater concrete
• compressive strength
• microstructure
• pore size distribution
• prediction model

Acknowledgements

This project was sponsored by the National Natural Science Foundation of China (Grant No. 52179132). Supported by Open Research Fund Program of State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi’an University of Technology (Grant No. 2021KFKT-10). The Henan Natural Science Fund for Distinguished Young Scholars (Grant No. 232300421016). The Program for Innovative Research Team (in Science and Technology) in University of Henan Province of China (Grant No. 24IRT ST HN010). The Cultivation Project of Innovative Technology Team for Hydraulic Engineering of NCWU (Grant No. 2023SZ100100084). Henan Province Science and Technology Research Project (Grant No. 232102320184). Joint Fund of Henan Province Science and Technology R&D Program (Grant No. 225200810056).

Ethics statement

Not applicable.

Consent form

Not applicable.

Author contributions

Yao XH: methodology, investigation, writing-review and editing, formal analysis, and funding acquisition. Xi JY: methodology, formal analysis, experiment, data curation, and writing-original draft preparation. Guan JF: conceptualization, visualization, methodology, supervision, project administration, writing-review and editing, and funding acquisition. Wen LF: visualization, methodology, supervision, and project administration. Liu L: investigation and writing-review. Shangguan LJ: project administration, supervision, and funding acquisition. Xu ZW: experiment and data curation.

Disclosure statement

The authors declare no conflicts of interest to this work.

Additional information

Funding

This project was sponsored by the National Natural Science Foundation of China (Grant No. 52179132). Supported by Open Research Fund Program of State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi’an University of Technology (Grant No. 2021KFKT-10). The Henan Natural Science Fund for Distinguished Young Scholars (Grant No. 232300421016). The Program for Innovative Research Team (in Science and Technology) in University of Henan Province of China (Grant No. 24IRT ST HN010). The Cultivation Project of Innovative Technology Team for Hydraulic Engineering of NCWU (Grant No. 2023SZ100100084). Henan Province Science and Technology Research Project (Grant No. 232102320184). Joint Fund of Henan Province Science and Technology R&D Program (Grant No. 225200810056).