Influence of Waste Fly Ash on the Rheological Properties of Fresh Cement Paste and the Following Electrical Performances and Mechanical Strengths of Hardened Specimens

Lili Cui,Hui Wang

doi:10.3390/coatings11121558

Abstract

Waste fly ash (WFA) is a kind of solid waste without reasonable disposition. The WFA with active substance can promote the cement hydration, therefore, WFA may enhance the mechanical strengths of cement-based materials. In this paper, the rheological properties (slump flow and plastic viscosity) of fresh cement paste with WFA ranging from 0% to 25% by mass ratio of cement were studied. The alternating current (AC) electrical resistance and direct current (DC) resistance time curves were determined. The AC impedance spectroscopy curves of the specimens cured for 1 day and 28 days were obtained. Finally, the mechanical strengths of hardened cement paste cured for 1 day, 3 days, 7 days, and 28 days were tested. The results showed that the slump flow was decreased and the plastic viscosity was increased by the addition of WFA and the increasing curing time. The AC electrical resistance increased in the form of the quadratic function with the cuing age. Meanwhile, the addition of WFA demonstrated an enhancing effect on the electrical conduction of cement paste. The variation rate of DC electrical resistance during the testing time increased with the increasing dosages of WFA and the curing age. The mechanical strengths increased with the addition of curing time and the content of WFA. The increasing rate of mechanical strengths increased with the addition of WFA (0~15%) and decreased with curing time. However, when the dosage of WFA increased from 15% to 25%, the increasing rate decreased.

Highlights

In recent years, environmentally friendly society has been the theme of the times
The waste fly ash contains electrically conductive elements, the alternating current (AC) impedance spectrum and time history curve of direct current (DC) electrical resistance may be effective to reflect the processes of cement hydration and mechanical strengths [17]
This was attributed to that the particle diameters of rice husk ash and waste fly ash were smaller than cement particles, resulting in increasing the surface area of cementitious m leading eventually to adsorbing the free water of fresh cement paste and decreas slump flow

Summary

Introduction

Environmentally friendly society has been the theme of the times. With the acceleration of urbanization, a large amount of domestic garbage is piled up in the city. When waste fly ash is considered to be used in the cement-based materials, the influence of waste fly ash on the rheological properties of fresh cement paste should be studied systematically. The waste fly ash contains electrically conductive elements, the AC impedance spectrum and time history curve of DC (direct current) electrical resistance may be effective to reflect the processes of cement hydration and mechanical strengths [17]. Several researches about the mechanical strengths and microscopic properties of cement-based materials with waste fly ash were reported [18,19]. The following AC electrical resistance, the DC electrical resistance time curves, and the mechanical strengths of hardened specimens were tested to reflect the influence of waste fly ash on the hydration process of cement.

Specimen Preparation and Measurement Methods

Results and Discussion

Conclusions