Properties of steel fiber reinforced fly ash concrete

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Abstract

This paper reports on a comprehensive study on the properties of concrete containing fly ash and steel fibers. Properties studied include unit weight and workability of fresh concrete, and compressive strength, flexural tensile strength, splitting tensile strength, elasticity modulus, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.25%, 0.5%, 1.0% and 1.5% in volume basis. The laboratory results showed that steel fiber addition, either into Portland cement concrete or fly ash concrete, improve the tensile strength properties, drying shrinkage and freeze–thaw resistance. However, it reduced workability and increase sorptivity coefficient. Although fly ash replacement reduce strength properties, it improves workability, reduces drying shrinkage and increases freeze–thaw resistance of steel fiber reinforced concrete. The performed experiments show that the behaviour of fly ash concrete is similar to that of Portland cement concrete when fly ash is added.

Introduction

The use of fly ash in concrete is found to affect strength characteristics adversely. One of the ways to compensate for the early-age strength loss associated with the usage of fly ash is by incorporating fibers, which have been proved very efficient in enhancing the strength characteristics of concrete [1]. The addition of fibers to concrete considerably improves its structural characteristics such as static flexural strength, impact strength, tensile strength, ductility and flexural toughness [2]. For long term, strength and toughness and high stress resistance, steel fiber reinforced concrete (SFRC) is increasingly being used in structures such as flooring, housing, precast, tunnelling, heavy duty pavement and mining. Generally, aspect ratios of steel fibers used in concrete mix are varied between 50 and 100. The most suitable volume fraction values for concrete mixes are between 0.5% and 2.5% by volume of concrete [3]. In general, the character and performance of fiber reinforced concrete changes with varying concrete formulation as well as the fiber material type, fiber geometry, fiber distribution, fiber orientation and fiber concentration [4].

Although, there were numerous studies carried out on the influence of fiber addition in concrete mixture on mechanical and durability properties of concrete limited research work has been carried out concerning the influence of fiber addition in concrete with pozzolans.

Topcu and Canbaz [5] studied the effect of steel and polypropylene fibers on the mechanical properties of concrete containing fly ash. According to the results of the study, addition of fibers provide better performance for the concrete, while fly ash in the mixture may adjust the workability and strength-loss caused by fibers, and improve strength gain.

Qian and Stroeven [6] investigated the optimization of fiber size, fiber content, and fly ash content in hybrid polypropylene-steel fiber concrete with low fiber content based on general mechanical properties. The results show that a certain content of fine particles such as those found in fly ash is necessary to evenly disperse fibers.

Gutierrez et al. [7] studied the effects of the pozzolans on the performance of fiber reinforced mortars. They reported that in general, pozzolanic materials, especially silica fume and metakaolin, improve the mechanical performance and the durability of fiber-reinforced materials. The fly ash addition had a low performance, which was attributed to its low degree of pozzolanicity.

Eren and Celik [8] investigated the effect of silica fume and steel fibers on some properties of high-strength concrete. The results show that increase in the amount of silica fume and fibers decrease workability. They reported that while silica fume has an effect on compressive strength, volume percentage of steel fibers has little effect.

Ahmed et al. [9] studied the flexural responses of hybrid steel-polyethylene fiber reinforced cement composites containing high volume fly ash. They reported that 50% replacement of cement by fly ash is found to be the optimum fly ash content in hybrid fiber composites.

An area that has not been extensively examined previously is the effect of steel fiber additions on the mechanical and durability properties of fly ash concrete. Researchers have studied fly ash concrete and fiber reinforced concrete separately; however, considering reinforcing fibers with fly ash in concrete is an area that needs more study. The purpose of this research is to study the effects of steel fibers on the unit weight, workability, compressive strength, flexural tensile strength, splitting tensile strengths, modulus of elasticity, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of fly ash concrete.

Section snippets

Cement

The cement used was Portland cement CEM I 42.5 R with a specific gravity of 3.16. Initial and final setting times of the cement were 140 min and 205 min, respectively. Its Blaine specific surface area was 3250 cm2/g and its chemical composition is given in Table 1.

Fly ash

Fly ash used was obtained from Yumurtalik Sugozu power station located in southern Turkey. According to ASTM C 618 [10] standard it was classified as class F fly ash. Specific gravity and Blaine specific surface area were 2.31 and 2900 cm2

Unit weight and workability

Unit weight, V-B time and slump value workability measurement were carried out on fresh fiber reinforced fly ash concrete. The results of unit weight, V-B time and slump values are presented in Table 4. The results indicate that the unit weight of concrete increased uniformly with the increase in fiber content and decreased with the increase of fly ash content. Generally, the unit weights of steel fiber reinforced concretes were higher than that of concrete without fibers for each group.

Table 4

Conclusions

From this laboratory work the following conclusions were made.

The unit weight of concrete increased uniformly with the increase in fiber content and decreased with the increase of fly ash content. The inclusion of steel fiber reduced workability with increasing fiber content. However, incorporation of fly ash as cement replacement in fresh steel fiber reinforced concrete increases workability when compared to control concrete made without fly ash. The comparisons made between V-B time and slump

Acknowledgement

The authors would like thank to Cukurova University Scientific Research Projects Directorate (Project No. MMF 2004 D17) for the financial support.

References (23)

  • TS EN 12350-2

    Testing fresh concrete – part 2: slump test

    (2002)
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