Positive Influence of Liquid Sodium Silicate on the Setting Time, Polymerization, and Strength Development Mechanism of MSWI Bottom Ash Alkali-Activated Mortars.

Lei Jin,Zhishan Xu,Guodong Huang,Xingyu Zhang,Yongsheng Ji,Yongyu Li

doi:10.3390/ma14081927

Abstract

Setting time and mechanical properties are key metrics needed to assess the properties of municipal solid waste incineration (MSWI) bottom ash alkali-activated samples. This study investigated the solidification law, polymerization, and strength development mechanism in response to NaOH and liquid sodium silicate addition. Scanning electron microscopy and X-ray diffraction were used to identify the formation rules of polymerization products and the mechanism of the underlying polymerization reaction under different excitation conditions. The results identify a strongly alkaline environment as the key factor for the dissolution of active substances as well as for the formation of polymerization products. The self-condensation reaction of liquid sodium silicate in the supersaturated state (caused by the loss of free water) is the major reason for the rapid coagulation of alkali-activated samples. The combination of both NaOH and liquid sodium silicate achieves the optimal effect, because they play a compatible coupling role.

Highlights

To alleviate problems associated with the disposal of harmful municipal solid waste (MSW), power generation via incineration has become an important means to dispose of MSW
The strengths of sample A-1 were still only 0.8 MPa (28 days) and 1.2 MPa (60 days), respectively, which does not represent a significant increase. This suggests that bottom ash (BA) and Ground granulated blast furnace slag (GGBFS) have very low binding ability and cannot effectively establish strength without strong alkali excitation (Table 2, pH = 10.12)
Several particles (BA and GGBFS) assembled and were embedded in the gels, suggesting that these particles have begun to participate in polymerization and have become part of the gels (as shown in (B) of Figure 3(a-1))

Summary

Introduction

To alleviate problems associated with the disposal of harmful MSW, power generation via incineration has become an important means to dispose of MSW. This uses the heat energy of burning MSW to generate electricity, and realizes the required reduction of the MSW volume. The products of MSW incineration can mainly be divided into two categories: (1) fly ash and (2) bottom ash (BA) [2,3]. BA accounts for ~80% of the total incineration products and is mainly composed of different types of large particles (45 mm), including molten slag blocks, glass, rocks, and small metal fragments [4]. The yield of BA is enormous, and relevant data indicate that China’s annual output of BA has reached 5 billion tons in

Methods

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Discussion

Conclusion