Effect of Fly Ash on the Mechanical Properties and Microstructure of Cement-Stabilized Materials with 100% Recycled Mixed Aggregates

Tao Meng,Dawang Dai,Hongming Yu,Xiufen Yang

doi:10.3390/min11090992

Abstract

The use of recycled mixed aggregates (RMA) in cement-stabilized materials (CSM) is an effective way to dispose of and reuse demolition waste. However, this approach faces various challenges; for example, the drying shrinkage of CSM with 100% RMA is very high, which is unfavorable for use in road engineering. In order to use a simple method to reduce the drying shrinkage of the CSM with 100% RMA and give it reliable strength, the effect of fly ash on the mechanical properties, drying shrinkage, and abrasion resistance of CSM with 100% RMA was investigated in this study, and the mechanism was examined by X-ray Diffraction (XRD), Mercury Intrusion Porosimetry (MIP), and Scanning Electron Microscopy (SEM). The results revealed that the addition of fly ash would decrease the drying shrinkage of CSM with 100% RMA. Moreover, when the amount of fly ash was less than 20%, the later strength increased remarkably despite the slight decrease in the early unconfined compressive strength, indirect tensile strength, compressive and splitting elastic modulus, and abrasion resistance of CSM with 100% RMA. The microstructure analysis results indicated that fly ash increased the decline range of diffraction intensity of C2S and C3S at a later age and also helped to optimize the pore structure. Research results of this article can be used to optimize the mechanical properties of CSM with 100% RMA and guide its application in road base.

Highlights

Using construction and demolition waste instead of natural sand to make recycled mixed aggregates (RMA), which can be used as cement-stabilized materials (CSM) in road base, can alleviate the shortage of natural sand, reduce construction costs, and effectively solve the difficulties of construction demolition waste recycling [4]
The results indicated that the relationship between the unconfined compressive strength of CSM and the amount of cement changes depending on the aggregate type
The results showed that the slump loss behavior could be improved when the replacement of fly ash is about 35~50% in recycled aggregate concretes

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As the process of urbanization continues to accelerate, many old buildings have been demolished or repaired and a huge amount of construction and demolition waste has been produced [1]. Most construction and demolition waste is either temporarily stacked, landfilled, or processed into low-value building materials, such as recycled bricks, and the resource utilization is less than 10% [2,3]. Using construction and demolition waste instead of natural sand to make recycled mixed aggregates (RMA), which can be used as cement-stabilized materials (CSM) in road base, can alleviate the shortage of natural sand, reduce construction costs, and effectively solve the difficulties of construction demolition waste recycling [4]

Methods

Results

Conclusion