ZHU Tao¹，MA Yapeng^1a，MAO Mingjie^1a， YANG Qiuning^1a，ZHANG Dongsheng^1a，2

1a. School of Civil and Hydraulic Engineering，1b. Key Laboratory of the Internet of Water and Digital Water Governance of the Yellow River in Ningxia， Ningxia University， Yinchuan 750021， China；2. Department of Civil Engineering， KU Leuven， Campus Bruges， Bruges 8200， Belgium

Abstract

Objective In terms of sustainability in civil engineering， a large amount of construction waste is treated to replace cement in order to conserve natural resources and reduce carbon emissions. However， the mortar containing recycled micro-powder and slag powder often shows poor performance. Therefore， when a specific water-binder ratio is maintained， water-reducing agents are often used to improve the performance of slurries containing recycled micro-powder and slag. At present， rheology is considered to be the most effective method to characterize the workability of gellable materials. Hence， the influence of different types of water-reducing agents on the rheological properties of the slurry was studied， especially the relationship between the rheological properties and the thickness of the water film. This study aims to provide a reference for the working performance of slurries that cannot be accurately measured in practical engineering.

Methods In view of the above problems， this paper comprehensively studied the rheological properties of different types of water-reducing agents and RSCM. The water film thickness of RSCM with different dosages of three water-reducing agents was determined based on volumetric density. The relationship between the water film thickness and rheological parameters was studied， validating the applicability of the water film thickness model. Subsequently， a prediction model was established to accurately reflect the changes of rheological parameters caused by the original variables such as flocs. The specific test methods are described as follows： After the slurry was stirred， it was poured into the rheometer test vessel. After the test was completed， the rheological curve was obtained by analyzing the data. The classical Bingham model was applied to fit the descending section of the curve to obtain the desired rheological parameters. In order to determine the water film thickness of the slurry， the packing density of the solid particles must be measured first. In this paper， the wet packing density method was used to measure the particle packing density of the actual slurry.

Results and Discussion With the increase in the dosage of water-reducing agents， the thixotropic loop area， yield stress， and plastic viscosity of RSCM decreased， while the thickness of the water film layer increased. Among them， the melamine-based water-reducing agent had the most significant improvement effect on rheological properties. When the mass fraction of the melamine-based water-reducing agent was 0. 6%， the thixotropic loop area of RSCM was 2660 Pa/s， the yield stress reached 74. 7 Pa， the plastic viscosity reached 2. 79 Pa·s， and the thickness of the water film layer was 0. 67 μm. If the dosage continued to increase， the RSCM became very thin and could not be applied to practical engineering. In this study the thickness of the water film layer of RSCM was functionally related to the yield stress.