Utilization of MSWI fly ash as partial cement or sand substitute with focus on cementing efficiency and health risk assessment

Highlights

• Washed MSWI fly ash was used as partial cement or sand substitute.

• Sand replacing is beneficial for strength, while cement replacement reduces strength.

• Cementing efficiency factor and mortar pore structure explain the strength results.

• Health risk assessment was conducted for MSWI fly ash blended cement mortar.

• CR and HI contributed by different exposures and heavy metals were analyzed.

Abstract

The strength of cement substituted mortar decreases with the increase in fly ash amount, whereas the strength increases when the fly ash is blended as sand substitute. A mortar with highest strength (compressive strength= 30.2 Mpa; flexural strength= 7.0 Mpa) was obtained when the sand replacement ratio was 0.75%. The k value (cementing efficiency) of fly ash varied between 0.36 and 0.15 for the fly ash fraction in binder between 5% and 25%. The k values of fly ash used for sand replacement were all significantly above that used for cement substitution. The macropores assigned to the gaps between particles decreased when the fly ash was used as sand replacement, providing an explanation for the strength enhancement. The waste-extraction procedure (toxicity-sulphuric acid and nitric acid method (HJ/T 299-2007)) was used to evaluate metal leaching, indicating the reuse possibility of fly ash blended mortar. For the mortar with the mass ratio of fly ash to binder of 0.5%, the carcinogenic risks (CR) and non-carcinogenic hazard quotient (HQ) in sensitive scenario for blended mortar utilization were 9.66 × 10^-7 and 0.06, respectively; these results were both lower than the threshold values, showing an acceptable health risk. The CR (9.89 × 10^-5) and HQ (3.89) of the non-sensitive scenario for fly ash treatment exceeded the acceptable threshold values, indicating health risks to onsite workers. The main contributor to the carcinogenic and non-carcinogenic risk is Cr and Cd, respectively. The CR and HQ from inhalation was the main route of heavy metal exposure.

Graphical abstract

Keywords

MSWI fly ash / Cementing efficiency / Health risk assessment of heavy metal / Sand replacement / Cement replacement

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Acknowledgments

The authors gratefully acknowledge the support from the National Natural Science Foundation of China (Grant No. NSFC21107062) and the Key Laboratory for Solid Waste Management and Environment Safety (Tsinghua University) Foundation (Grant No. SWMES 2015-10).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-019-1184-6 and is accessible for authorized users.

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