Effect of Calcium Carbonate Whisker and Fly Ash on Mechanical Properties of Cement Mortar under High Temperatures

Li Wang,Bendong Zhao,Hongliang Zhang,Yang Gao

doi:10.1155/2019/9430804

Li Wang, Bendong Zhao + Show 2 more

Open Access

https://doi.org/10.1155/2019/9430804

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Abstract

Calcium carbonate (CaCO3) whisker, as a new type of microfibrous material, has been extensively used in the reinforcement of cementitious materials. However, the combined effect of CaCO3 whisker and fly ash on mechanical properties of cementitious materials under high temperatures was still unknown. In this study, the coupling effect of CaCO3 whisker, and fly ash on mechanical properties of the cement was investigated. Two sets of cement mortars were fabricated, including CaCO3 whisker-based mortar which contained 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% CaCO3 whisker as cement substitution and CaCO3 whisker-based fly ash mortar which contained 30 wt.% fly ash in addition to 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% CaCO3 whisker as cement substitution. Mass loss, compressive strength, and flexural strength of these two sets of specimens before and after being subjected to high temperatures of 200°C, 400°C, 600°C, 800°C, and 1000°C were measured. Based on the results of the aforementioned tests, load-deflection test was performed on the specimen which exhibited the superior performance to further study its mechanical behavior after exposure to high temperatures. Moreover, microstructural analysis, such as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), was conducted to reveal the damage mechanism of high temperature and to illustrate the combined effect of CaCO3 whisker and fly ash on high-temperature resistance of the cement. Results showed that fly ash could improve the high-temperature performance of CaCO3 whisker-based mortar before 600°C and limit the loss of strength after 600°C.

Highlights

Fire is one of the fatal threats which seriously affect human life, property security, and economic development in the world
The physical and chemical deteriorations of cementitious materials due to moisture loss and decomposition of hydrated products at high temperatures may result in the generation of cracks and the loss to mechanical strengths of concrete, lead to the structural damage [1]
Previous investigations have indicated that the mass loss of the cementitious material after exposure to high temperatures is mainly due to the evaporation of physically bounded water (80–150°C), the dehydration of C-S-H, AFm, and AFt (≤350°C), the decomposition of calcium hydroxide (CH) (400–550°C), and the decarbonation of CaCO3 (≥600°C) [35]. e mass loss of CaCO3 whiskerbased specimens is presented in Figure 2, and it is discovered that the mass loss for all the specimens regardless of without or with fly ash exhibited an upward trend with the increase in maximum temperature

Summary

Research Article

Received 8 February 2019; Revised 9 April 2019; Accepted 18 April 2019; Published 7 May 2019. The combined effect of CaCO3 whisker and fly ash on mechanical properties of cementitious materials under high temperatures was still unknown. Based on the results of the aforementioned tests, load-deflection test was performed on the specimen which exhibited the superior performance to further study its mechanical behavior after exposure to high temperatures. Microstructural analysis, such as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), was conducted to reveal the damage mechanism of high temperature and to illustrate the combined effect of CaCO3 whisker and fly ash on high-temperature resistance of the cement. Results showed that fly ash could improve the high-temperature performance of CaCO3 whisker-based mortar before 600°C and limit the loss of strength after 600°C

Introduction

Mix proportions

Type of mortar