Properties and microstructure of reactive powder concrete having a high content of phosphorous slag powder and silica fume

https://doi.org/10.1016/j.conbuildmat.2015.10.046Get rights and content

Highlights

  • Phosphorous slag powder was utilized to produce reactive powder concrete (RPC).

  • Mechanical strength, freeze–thaw and sulfate resistance of RPCs are investigated.

  • The content of phosphorous slag could be as high as 35% (by the weight of binder).

  • RPCs prepared herein have excellent mechanical and durability properties.

  • The diameter of the most probable pore in RPC samples is less than 10 nm.

Abstract

Reactive powder concrete (RPC) specimens whose content of phosphorous slag powder (PS) and silica fume was about 50% (by the weight of binder) were produced after they had been cured in 95 °C steam for a given duration. The test results of strength (compressive and flexural), freeze–thaw and sulfate resistance verified the excellent mechanical and durability properties of RPC containing a high content of PS. The investigation of selected RPC compositions by Thermogravimetric Analysis, Mercury Intrusion Porosimetry and Scanning Electronic Microscope made it possible to better understand their mechanical and durability properties depending on their microstructure. Thermogravimetric Analysis and Scanning Electronic Microscope demonstrated the sequential hydration effect of cementitious composites during heat treatment. Mercury porosimetry results showed that RPC had very low porosity and the diameter of the most probable pore was less than 10 nm. These microstructural characteristics would enable RPC to have excellent mechanical and durability properties.

Introduction

Reactive powder concrete (RPC) is developed through microstructural enhancement techniques and is characterized by super-high strength, extreme durability and superior toughness [1], [2]. The mechanical properties that can be achieved include the compressive strength of the range between 200 MPa and 800 MPa, the flexural strength of the range between 30 MPa and 60 MPa, fracture energy of the range between 1200 J/m2 and 40,000 J/m2, Young’s modulus of the range between 50 GPa and 60 GPa, and ultimate tensile strain at the order of 1% [1], [2], [3]. RPC with superior performance has been applied extensively in civil, petroleum, nuclear power, municipal, marine and military facilities, as well as in other projects [4], [5]. However, cement dosage of conventional RPC is generally high and silica fume (SF) content is often over 25% (by the weight of cement), which not only increases the production costs, but also has negative effects on the hydration heat and may cause shrinkage problems. Replacing cement with mineral admixtures and decreasing SF content seemed to be a feasible solution to these problems [6], [7], [8], [9], [10], [11], [12].

Electric furnace phosphorus slag which is different from granulated blast furnace slag (GBFS) is a kind of industrial waste and mainly contains SiO2, CaO and Al2O3. Its total content of SiO2 and CaO is more than 85% (by weight) and the SiO2/CaO ratio ranges from 0.8 to 1.4. Ground granulated electric furnace phosphorous slag has a glassy microstructure which is similar to that of granulated blast furnace slag and the weight percentage of the glassy structure could be as high as 90% [13], [14]. Therefore, ground granulated electric furnace phosphorous slag may be used as reactive composition of RPC.

Previous findings demonstrated that reactive powder concrete containing high volume binary blends (SF + PS) had no significant mechanical performance loss and incorporation of phosphorous slag powder (PS) in RPC was feasible [15]. This paper aims to achieve the following objectives:

  • to obtain RPCs with strength grade of C200 by utilizing phosphorous slag powder;

  • to examine the freeze–thaw and sulfate resistance of RPCs containing high content of phosphorous slag powder; and

  • to reveal the relationship between the performance and microstructure of RPCs containing phosphorous slag powder through Thermogravimetry, Mercury porosimetry and Scanning Electronic Microscope.

Section snippets

Materials

The RPCs considered here was prepared by the following ingredients. Cement: ordinary Portland cement P.O 52.5, which complies with Chinese Standard GB 175-2007, from Huaxin (Yidu, Hubei Province, China) Cement Co. Ltd. Phosphorous slag (PS): granulated electric furnace phosphorous slag produced by Yichang Yatai Chemical Co., Ltd. (Hubei Province, China). Silica fume (SF): undensified silica fume with average size of 0.1 μm–0.2 μm provided by China Construction Ready Mixed Concrete Co. Ltd.

Strength

RPC specimens containing a high content of PS and SF were obtained according to Table 2. The compressive and flexural strength results of these specimens are summarized in Table 3.

From Table 3, it is noted that the flexural and compressive strength of these RPCs are about 21 MPa and 150 MPa respectively. The addition of 1% (by volume) steel fiber gave 187 MPa or more compressive strength of RPC. The result implied that the hydration activity of phosphorous slag powder (PS) was intensified. On one

Conclusions

  • (a)

    Reactive powder concrete specimens containing high content of phosphorous slag powder and silica fume were produced after they had been cured in 95 °C steam for a given duration in this study. The compressive and flexural strength of specimens, whose content of PS was 35% (by weight of the binder) and volume percentage of steel fiber was 1%, were 187 MPa and 29.7 MPa respectively. The results of freeze–thaw and sulfate resistance verified the excellent durability properties of RPCs.

  • (b)

    The

Acknowledgments

This research work was financially supported by the Open Fund of State Key Laboratory of Silicate Materials for Architecture in Wuhan University of Technology (Grant No. SYSJJ2014-05), the Science and Technology Supporting Project of Hubei Province (Grant No. 2014BCB035) and the Construction Science and Technology Project of the Department of Housing and Urban-Rural Development of Hubei Province.

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