Binary Mixes of Self-Compacting Concrete with Municipal Solid Waste Incinerator Bottom Ash

Joel R Simões,Rui V Silva,Pedro R Da Silva

doi:10.3390/app11146396

Abstract

With the objective of establishing a viable alternative to the use of cement, the main objective of this study is to verify the possibility of using municipal solid waste incinerator bottom ash (MIBA) as a partial cement replacement, thereby reducing the environmental impact associated with the use of concrete as a building material. To this end, self-compacting concrete (SCC) binary mixes of cement and MIBA were evaluated in their fresh and hardened state (i.e., self-compactability, mechanical and durability related performance). Four SCC mixes were produced to cover a wide range of replacement levels of cement with MIBA, namely: 20%, 30%, 40% and 50%. A fifth SCC mix, without MIBA, was produced with 30% fly ash to carry out a comparative analysis with composites with well-established performance. The results showed that the use of bottom ash from municipal solid waste incinerators caused an overall decline in the performance of self-compacting concrete. Apart from the smaller number of reactive phases in the bottom ash when compared with fly ash, which led to a slower rate of strength development, the decline was also caused by the increased porosity from the oxidation of aluminium particles. Nevertheless, the results showed promising indicators regarding the durability of mixes with 20% MIBA, with values very similar to those of reference concrete.

Highlights

The concentration of CO2 in the atmosphere has been increasing progressively, with reported values of increase from 324 ppm in 1969 to 415 ppm in 2020 alone [1]
Two mineral additions were used as cement replacement: fly ash (FA), used to produce the reference concrete (RC), according to EN 450-1 [16] and bottom ash resulting from the municipal solid waste incinerator (MIBA) for the remaining mixtures
The results of the modified Chapelle test, by titration with 0.1M hydrochloric acid, determined the content of unconsumed Ca(OH)2, which were meant to react with the reactive aluminosilicate phases present in the FA and municipal solid waste incinerator bottom ash (MIBA), during 16 h at 90 ± 5 ◦ C

Summary

Introduction

The concentration of CO2 in the atmosphere has been increasing progressively, with reported values of increase from 324 ppm in 1969 to 415 ppm in 2020 alone [1]. To avoid climate change in the second half of the 21st century, CO2 emissions must be reduced by 90% by 2030 [2]. The World’s annual concrete production is approximately 1 × 1010 tonnes. This results in large amounts of CO2 emissions mainly due to the production of Portland cement. Of the total CO2 emissions of concrete manufacture [3]. The production of one tonne of Portland cement emits about 0.94 tons of CO2 and the cement industry is responsible for about 8% of all CO2 emissions from all economic sectors [4].

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Conclusion