The Dosage of Superplasticizer in Cemented Coal Waste Backfill Material Based on Response Surface Methodology

Qingdong Li,Xianjie Du,Guorui Feng,Tingye Qi,Huayun Li,Zehua Wang,Yuxia Guo

doi:10.1155/2019/5328523

Qingdong Li, Xianjie Du + Show 5 more

Open Access

https://doi.org/10.1155/2019/5328523

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Abstract

Cemented coal waste backfill material (CCWBM) is developed for backfilling the goaf in coal mines. As fresh CCWBM slurry is generally transported into underground openings through a pipeline, the fluidity of fresh slurry becomes one of the most important properties. Adding superplasticizer is considered to improve the flow performance of the slurry without alerting the mechanical performance of filling body. The dosage of superplasticizer (SP) is related to filling cost, thus response surface methodology (RSM) is adopted to study the influence of material composition on SP when target slump is 250 mm. The effects of fly ash content, fine gangue ratio, and mass concentration on SP are analyzed using the software of Design-Expert and central composite design (CCD), and models are established for SP. Results show that the SP model coincides greatly with the test results and can be applied to analyze and predict SP in CCWBM. Mass concentration, fly ash content, and fine gangue ratio influence SP from high to low. The interaction of fine gangue ratio and mass concentration between SP is the most significant. The fact that the improved aggregate space model can be applied to analyze the fluidity of CCWBM is proved too. The research results provide guidance for the design and preparation of CCWBM with favourable performance and low cost in practical production.

Highlights

In China, underground coal mines produce about 95% of total coal [1]
Fine gangue ratio, and mass concentration are the three key parameters which decide the mix composition of Cemented coal waste backfill material (CCWBM), this paper studies SP through analyzing the influences of these three factors
An improved aggregate space model is introduced to explain the variation of SP. e research results provide a reference for subsequent research and practical production of CCWBM

Summary

Introduction

In China, underground coal mines produce about 95% of total coal [1]. Underground coal mining contributes a large amount of coal, but it creates a tremendous amount of mined-out void and discharges a great deal of solid waste [2, 3]. Filling slurry is prepared in a filling plant and transported to underground openings, thereby necessitating the use of sufficient water to gain favourable fluidity [14] This could lead to a high water/cement ratio, which will lower the strength and durability of filling body [15, 16]. Considering this challenge, the additive of superplasticizer into CCWBM is considered to reduce mixing water to enhance mechanical properties. Design-Expert software is applied to discuss the influences of fly ash content, fine gangue ratio, and mass concentration on SP when target slump is 250 mm. An improved aggregate space model is introduced to explain the variation of SP. e research results provide a reference for subsequent research and practical production of CCWBM

Materials and Methods

Establishment of RSM Model

Analysis of Test Results