Experimental Tests on Fiber-Reinforced Alkali-Activated Concrete Beams Under Flexure: Some Considerations on the Behavior at Ultimate and Serviceability Conditions.

Linda Monfardini,Fausto Minelli,Luca Facconi

doi:10.3390/ma12203356

Abstract

Alkali-activated concrete (AAC) is an alternative concrete typology whose innovative feature, compared to ordinary concrete, is represented by the use of fly ash as a total replacement of Portland cement. Fly ash combined with an alkaline solution and cured at high temperature reacts to form a geopolymeric binder. The growing interest in using AACs for structural applications comes from the need of reducing the global demand of Portland cement, whose production is responsible for about 9% of global anthropogenic CO2 emissions. Some research studies carried out in the last few years have proved the ability of AAC to replace ordinary Portland cement concrete in different structural applications including the construction of beams and panels. On the contrary, few experimental results concerning the structural effectiveness of fiber-reinforced AAC are currently available. The present paper presents the results of an experimental program carried out to investigate the flexural behavior of full-scale AAC beams reinforced with conventional steel rebars, in combination with fibers uniformly spread within the concrete matrix. The experimental study included two beams containing 25 kg/m3 (0.3% in volume) of high-strength steel fibers and two beams reinforced with 3 kg/m3 (0.3% in volume) of synthetic fibers. A reference beam not containing fibers was also tested. The discussion of the experimental results focuses on some aspects significant for the structural behavior at ultimate limit states (ULS) and serviceability limit states (SLS). The discussion includes considerations on the flexural capacity and ductility of the test specimens. About the behavior at the SLS, the influence of fiber addition on the tension stiffening mechanism is discussed, together with the evolution of post-cracking stiffness and of the mean crack spacing. The latter is compared with the analytical predictions provided by different formulations developed over the past 40 years and adopted by European standards.

Highlights

Alkali-activated concrete (AAC) has been studied over the past years as a “green” alternative to ordinary Portland cement (OPC), whose production is energy intensive and responsible for about8–9% of CO2 emissions worldwide [1]
The latter were first investigated by Hardjito et al (2004) [4], Sumajouw et al (2005) [5], and Sumajouw & Rangan (2006) [6], who performed a series of flexural tests on reinforced AAC beams and conventional reinforced concrete (RC) beams with different reinforcement ratios (0.64–2.69%)
Experimental results on full-scale beams made of AAC under flexure were presented and discussed in this paper, focusing on the structural response and fiber influence on the global and local behavior

Summary

Introduction

Alkali-activated concrete (AAC) has been studied over the past years as a “green” alternative to ordinary Portland cement (OPC), whose production is energy intensive and responsible for about8–9% of CO2 emissions worldwide [1]. Alkali-activated binders can be generated from different types of aluminosilicate precursors, with differing availability, reactivity, cost, and value worldwide [2]. Most literature regarding fly ash alkali-activated concrete focuses mainly on the study of the material properties, whereas limited attention has been paid to the structural behavior of AAC structures. The latter were first investigated by Hardjito et al (2004) [4], Sumajouw et al (2005) [5], and Sumajouw & Rangan (2006) [6], who performed a series of flexural tests on reinforced AAC beams and conventional reinforced concrete (RC) beams with different reinforcement ratios (0.64–2.69%)

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Conclusion