Elsevier

Construction and Building Materials

Volume 192, 20 December 2018, Pages 70-84
Construction and Building Materials

Effect of slag, nano clay and metakaolin on mechanical performance of basalt fibre cementitious composites

https://doi.org/10.1016/j.conbuildmat.2018.10.090Get rights and content

Highlights

  • Heat-rain test is realised most effective test to find out durability problem of BRC.

  • Aim is to eliminate accumulation of hydration products on fibre surface in BRC, BFRC.

  • Positive effect of pozzolanic admixtures on strength-strain degradation is addressed.

  • Results after standard curing and aging tests reveal most effective additive is metakaolin.

  • High reactivity of Al2O3 and fineness largely prevent accumulations on fibre.

Abstract

In this study, the effects of pozzolanic admixtures (ground granulated blast furnace slag, nano-clay, metakaolin) are investigated in chopped basalt fibre cementitious composites (BRC). First, the variations in compressive strengths and flexural characteristics during 3, 7, 28, 56, 90 and 120-day curing periods are addressed. Afterwards, most importantly, the degradation in the flexural performance during aging tests (freeze-thaw test, heat-rain test) are focused. The main aim is considerably to save the pull-out behaviour of BRC, even when exposed to harsh atmospheric conditions. All the test results are compared with control specimens (100% cement). The results arising from the experiments including metakaolin are promising to enhance the durability performance of BRC. The implications in this experimental study are valid for basalt fibre reinforced concrete (BFRC) subjected to those atmospheric conditions as well.

Introduction

Basalt fibre (BF) was produced from igneous rock in Russia 1954, the industrial process was completed in 1985 at Ukraine fibre laboratory [1]. Besides the simplicity of the manufacturing process, BF has attracted attention with the characteristics of 20–30% higher tensile strength, modulus of elasticity, fire resistance [2], [3] than glass fibre (GF), and chemical stability [4], [5]. Its similarities in the mechanical characteristics promote the industrial utilization in marine [6], automotive [7] sectors etc. as an alternative to GF since 1990s.

More recently, BF usage in different civil engineering applications are in progress with increasing attention. Retrofitting the structural members through fibre reinforced polymer composites (BFRP) [8] or textile reinforced mortar (BTRM) [9] occupy a prominent position. Basalt fibre reinforced concrete (BFRC) [10], [11] and cement/cementitious composites (BRC) in façade panels [12], [13] as well as BF usage in geopolymer concrete (BFRGC) [14] and non-corrosive basalt reinforcements [3], [15], [16], [17], [18] by replacing with steel in structural members are another notable research areas as well. Most recently, a mini version of basalt rebars modified through epoxy resin coating was also developed [19].

BFRC experiments are carried out via chopped fibres generally from 12 mm to 25 mm in length. Ayub et al. [20] produced high-performance fibre reinforced concrete (HPFRC) through 25-mm BF (Vf = 0–3%) replacing 10% of cement with silica fume and metakaolin. They concluded metakaolin replacement is more effective to improve 28-day splitting tensile strength, also indicated high fibre volume of basalt fibres may cause voids in the mix process. Kizilkanat et al. [11] studied 28-day splitting tensile strengths by using 12 mm-BF and GF (Vf = 0 to 1%) with 10% fly ash addition. They reported the highest increases as 40% for 1% BF and 27% for 0.75% GF compared with plain concrete. Jiang et al. [10] carried out the flexural tests via 12 mm and 22 mm BF (Vf = 0–0.5%) up to 90 days. They draw attention to significantly improvement in toughness index and 0.3% BF ratio to be suitable. In their study, about 10% reduction in flexural strengths is observed from 28 days to 90 days.

Recently BF and GF reinforced cement/cementitious composites were investigated by Girgin and Tak [12] and then Girgin [13] for Vf = 2%. For BF and GF-specimens, Girgin and Tak [12] observed rather close compressive and flexural characteristics in control mix (100% cement) during early curing stages, however ongoing hydration in later curing stages leads BF-specimens to brittle fracture through gradually disappearing pull-out mechanism. That reality is pronounced especially during heat-rain aging test by starting from early cycles. According to the author’s knowledge, in the current literature, first time Girgin and Tak [12] and then Girgin [13] indicated to durability problem of BRC, or BFRC via the heat-rain test, and to further steps to overcome this problem. As for the results of freeze thaw tests, they can be regarded more acceptable.

In this study, it is focused to pursue the enhancement of the flexural performance in BF reinforced cementitious composites (BRC). In order to modify fibre-matris interface chemically and to optimize bond strength, ground granulated blast-furnace slag (GGBS), less familiar nano-clay (NC), and highly reactive metakaolin (MK) are incorporated into the mixtures. It should be mentioned that, in the last decades, NC emerges as another natural resource for chloride impermeability, enhancement in early-age and long-term mechanical characteristics [21], [22], [23], [24], [25], [26]. Compression tests, four-point bending tests and durability tests were executed, and fibre-matrix interface as well as filament surfaces were also observed under scanning electron microscope (SEM) to comprehend the failure mechanism more clearly. These techniques will direct the further investigations to design proper mixtures for BRC or BFRC as well.

Section snippets

Materials and mix proportions

In this study, four series together with control mix are under consideration. As the pozzolanic admixtures, ground granulated blast furnace slag or shortly slag (GGBS, S), nano-clay (NC) and metakaolin (MK) were replaced with CEM II/B-L 42.5R cement [27] in the ratios of 50%, 15%, 15%, respectively. Chemical compositions of all the binding materials are given in Table 1, the particle size-fractions are presented in Fig. 1, and the typical characteristics of chopped basalt fibres are denoted in

Compressive strength tests

For each one of four series, the average compressive strength of five cubes in each curing period are given in Fig. 4, standard deviations were determined in the range ± 0.8–2.2 MPa. For 2% fibre content, compression tests on control specimens (100% cement) were conducted during 28-day period. The compression tests of other three series (S, NC, MK) were executed up to 120 days.

For 50% slag (S) replacement, significant drop in 3,7-day early strengths is under consideration compared with control

Discussion

In this section, the pozzolanic reactions of four mixtures (Control, S, NC, MK) as well as the change in pull-out behaviour are evaluated via experimental results. Microstructural characteristics were examined through Zeiss EVO LS 10 type scanning electron microscope (SEM).

Conclusion

In this study, the variations in the flexural performance of basalt fibre cement/cementitious composite (BRC) were addressed especially for harsh atmospheric conditions. In four series, the effect of three mineral admixtures were investigated compared with pure cement-one. The following main results were attained from this study:

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    Any reduction, crack or delamination in section and surface of basalt filaments were not observed, BF presented high dimensional stability in all the tests of four

Conflict of Interest

There is no conflict in this manuscript.

Acknowledgement

The experiments in this study were carried out in Fibrobeton Inc. Material, employer and equipment support of those firm to these experimental researches are greatly appreciated. The author would like to thank to Kaolin Industrial Minerals Inc. providing metakaolin as well. I’m also thankful to MSc student Cihan Yolcu for his assistance to compiling of some data and to Dr.Ali Can Zaman for his attention in SEM micrographs.

There is no conflict in this manuscript.

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