Compressive strength and sulfate resistance properties of concretes containing Class F and Class C fly ashes

doi:10.1016/j.conbuildmat.2012.02.023

Construction and Building Materials

Volume 34, September 2012, Pages 531-536

https://doi.org/10.1016/j.conbuildmat.2012.02.023 Get rights and content

Abstract

This paper presents the results of an experimental investigation carried out to evaluate compressive strength and sulfate resistance properties of concrete mixtures in which Turkish Class C and Class F fly ashes were partially replaced with cement. A total of 39 mixtures with different mix designs were prepared. Compressive strength tests were carried out and the mixtures with similar compressive strength values were used for sulfate resistance tests. The degree of sulfate attack was evaluated using expansion and weight loss tests. Compression test results indicate that the concrete mixture with Class C fly ash showed higher compressive strength than that with Class F fly ash. Moreover, regardless the fly ash type, the addition of fly ash significantly increased the resistance to sulfate attack.

Highlights

► I examine compressive strength and sulfate resistance properties of concrete. ► Turkish Class C and Class F fly ashes were partially replaced with cement. ► The degree of sulfate attack was evaluated using expansion and weight loss tests. ► Class C fly ash showed higher compressive strength than that with Class F fly ash. ► The addition of fly ash significantly increased the resistance to sulfate attack.

Introduction

The usage of industrial byproducts in concrete, both in regard to environmental pollution and the positive effect on a country’s economy are beyond dispute [1]. These waste products are often incorporated into the concrete to improve workability, mechanical and durability properties of concrete. These additives include fly ash, silica fume, ground granulated blast furnace slag and other calcined natural pozzolanic materials such as metakaolin [2], [3], [4], [5], [6], [7]. The use of these waste products in concrete is increasing because they result in lower cost of construction and improve some physical, mechanical and durability properties of concrete in aggressive environments. It has been well established that fly ash (FA), despite its slow rate of reaction, induces significantly improved workability and higher long-term age strength by converting the calcium hydroxide into calcium silicate hydrate (C–S–H). Fly ash is also quite effective in producing concrete with low permeability [8]. This definitely enhances chemical resistance by reducing the potential for ionic ingress, migration, and concentration. This is done by subsequently controlling expansion and crack associated with sulfate attack, alkali–silica reaction, and corrosion [9], [10], [11]. Furthermore, the use of FA is beneficial in resisting the sulfate attacks into concrete. This is because of the microstructural densification imparted by the pozzolanic reaction or secondary hydration of these materials [12]. The main role of FA in concrete consists of three aspects, often called morphologic effect, pozzolanic effect, and micro aggregate effect. The morphologic effect states that there are many micro beads in FA working as “lubricating balls” when incorporated in fresh concrete; hence it benefits the fluidity. The micro aggregate effect of FA states the micro beads in FA can disperse well in concrete and combine firmly with gel produced in cement hydration, and thus promote concrete density. The pozzolanic effect is the main benefit of FA, which states that the unfixed AI₂O₃ and SiO₂ in FA can be activated by Ca(OH)₂ product of cement hydration and produce more hydrated gel. Since the gel produced from pozzolanic action can fill in the capillary in concrete, it effectively increases to concrete strength [13].

There were numerous studies carried out on the influence of FA in concrete mixture on mechanical and durability properties of concrete, limited research work has been carried out concerning the effectiveness of Turkish Class C and Class F fly ashes in concrete and comparing their sulfate resistance properties which the mixtures containing Class C and Class F fly ashes had similar compressive strength values to control mixtures for each series.

The objective of the present study is to investigate the resistance against sulfate attack, in particular, magnesium sulfate attack, of the concrete specimens containing Class C and Class F fly ashes which the mixtures with similar compressive strength values. The degree of sulfate attack was evaluated by measuring the expansion of concrete prisms, weight change of concrete prisms which the specimens have been subjected to 15% magnesium sulfate solutions for one year.

Section snippets

Materials

In this study, different concrete mixture designs were prepared using CEM I 42.5 Portland cement and Class C and Class F fly ashes binding materials. The chemical compositions and properties of the concrete mixtures are shown in Table 1. Both Class C and Class F fly ashes were obtained from power plants in Turkey. Specific gravity of the cement used is 3.12 g/cm³. Initial and final setting times of the cement were 210 and 265 min, respectively. A crushed limestone aggregate with a maximum size of

Compressive strength

Table 4 presents the variation of compressive strength with age for various fly ash percentages of all 39 mixtures at 28 d and at 90 d, respectively. The results show that the use of Class C fly ash improves the workability of concretes and reduces the water requirement of the concretes when compared to Class F fly ash and control concretes. At 28 d, the compressive strength of Class C fly ash additive concretes including different amounts of fly ash can be seen to be generally higher than that of

Conclusions

Laboratory tests were performed to determine the deterioration induced by the magnesium sulfate on the control and Turkish C and F classes fly ashes concretes and the following conclusion are reached:

•
The use of Class C type fly ash instead of Class F type fly ash with the same cement dosage and fly ash percentage generally increased compressive strength. The test results showed that elastic modulus of fly ash additive concretes were generally similar to the control concretes. So, the fly ash

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Compressive strength and sulfate resistance properties of concretes containing Class F and Class C fly ashes

Abstract

Highlights

Introduction

Section snippets

Materials

Compressive strength

Conclusions

Constr Build Mater

Constr Build Mater

Constr Build Mater

Constr Build Mater

Cem Concr Compos

Constr Build Mater

Constr Build Mater

Constr Build Mater

Cem Concr Res

Cem Concr Res

Cem Concr Compos

Cem Concr Res

Cem Concr Res

Cem Concr Res

Cem Concr Res