Elsevier

Structures

Volume 28, December 2020, Pages 774-785
Structures

Prediction of the elastic modulus of concrete with spontaneous-combustion and rock coal gangue aggregates

https://doi.org/10.1016/j.istruc.2020.09.021Get rights and content

Abstract

Adopting crushed coal gangue as aggregates for new concrete production could be a sustainable alternative to natural aggregates and could reduce landfill space. For the structural applications of innovative concrete, the elastic modulus is a key parameter influencing its serviceability limit state. Prediction models are presented herein for the elastic modulus of concrete prepared with coarse coal gangue aggregates (CGAs), including spontaneous-combustion coal gangue aggregate (SCGAs) and rock coal gangue aggregate (RCGAs). Experimental data from our previous studies and other literature were first collected to quantify the effects of the replacement ratio of CGAs, as well as the density and compressive strength of CGA concrete on the elastic modulus of the resulting concrete. Based on our previous experimental data, empirical models were proposed and validated against 150 groups of tested data. The obtained results indicated that the replacement ratio of CGAs is the major factor, and there were up to 57% and 41% reductions in the elastic modulus of the resulting concrete prepared with 100% SCGAs and RCGAs, respectively; by considering the replacement ratio, compressive strength and density of concrete, the newly proposed models in this study estimated the elastic modulus of both SCGA and RCGA concrete accurately.

Introduction

Using crushed coal gangue from coal mining and washing as aggregates (known as coal gangue aggregates, CGAs) to manufacture new concrete materials can reduce the consumption of natural sources and reduce landfill space [1], [2]. CGAs are generally classified into two categories, i.e., rock coal gangue aggregates (RCGAs) and spontaneous-combustion coal gangue aggregates (SCGAs), in which SCGAs are formed by spontaneous combustion. In this case, the major difference between RCGAs and SCGAs is their aggregate stiffness, which is governed by their porosity [3]. The appearances of CGAs and natural aggregates (NAs) are shown in Fig. 1. Initially, CGAs were used in non-structured members, e.g., hollow blocks [4]; currently, they are primarily used as a mineral admixture and a grouting material. Based on the systematic study by the authors in this study, a new material concrete was developed that satisfied the requirements of engineering structures [5], [6], [7], [8], [9], [10], [11] through controlling the aggregate gradation [12], controlling the pre-soaking time of coarse aggregates [13], controlling the activation temperature of CGAs [14], and limiting the CGA content [15].

Elastic modulus is a fundamental parameter for controlling the serviceability limit state of concrete structures. Generally, it exhibits a power function relationship with the compressive strength and the density of NA concrete [16], [17], [18], [19], [20], [21]. CGAs are a new type of aggregate that exhibit mechanical properties different from those of NAs [1], [4], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], which results in a difference in the compressive strength and density of concrete [3], [12], [14], [32], [33], hence affecting the elastic modulus of CGA concrete. Although experimental studies have been conducted, no prediction models are available for CGA concrete hitherto; furthermore, considering that the basic properties of SCGAs and RCGAs differ [3], [34], [35], [36], [37], the prediction model of CGA concrete should be proposed according to the aggregate type, i.e. SCGA or RCGA.

Hence, this study aims to propose empirical models to predict the elastic modulus of CGA concrete, including RCGA concrete and SCGA concrete. As such, test databases containing SCGA and RCGA concrete separately were first prepared; subsequently, an analysis was performed to evaluate the effect of CGA replacement ratio on the elastic modulus. The correlation between compressive strength and elastic modulus and that between the density of CGA concrete and elastic modulus were validated by statistical analysis. Finally, CGA replacement ratio, compressive strength and density of CGA concrete were regarded as major factors to predict the elastic modulus based on 30 groups of previous experimental data by the authors, and the newly proposed models were validated through a comparison between calculated and experimental values from literature.

Section snippets

Database of elastic modulus

The purpose of this study is to propose prediction models for the elastic moduli of spontaneous-combustion coal gangue aggregate (SCGA) and rock coal gangue aggregate (RCGA) concrete. Based on experimental studies, previous results by the authors and those from other researchers were adopted in the test database to quantify the influential factors. Table 1 lists the test parameters and test results of coal gangue aggregate (CGA) concrete, and these parameters can be categorised into four

Proposed empirical model

The elastic modulus of concrete is known to be affected by the cement paste, nature of aggregates, interfacial transition zones (ITZs), and strength of concrete [44]. Different types and proportions of aggregates result in dissimilar mechanical properties of coal gangue aggregate (CGA) concrete. An accurate assessment of elastic modulus must consider unavoidable uncertainties to reflect the influencing factors comprehensively.

The relationship between compressive strength and elastic modulus for

Conclusions

Empirical models to predict the elastic modulus of spontaneous-combustion and rock coal gangue coarse aggregate concrete in structural applications were proposed herein. The parameters considered included the coal gangue aggregate (CGA) type, replacement ratio from 0 to 1, compressive strength between 20 and 50 MPa, and density of concrete between 2000 and 2500 kg·m−3. A database containing thirteen parameters from 11 reports and the authors’ previous study was established for the CGA concrete.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was funded by the National Natural Science Foundation of China, China (51808351, 51808352), Liaoning Revitalization Talents Program, China (XLYC1902027), Doctoral Scientific Research Foundation, China (2019-BS-193, 2019-BS-197), Science and Technology Project of MHRUD, China (2019-K-054), Liaoning Province Key R&D Project (2018230008) and by the Liaoning Basic Scientific Plan (LJZ 2017021).

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