What are Durability Properties of Concrete with GGBFS?

The durability of concrete plays a vital role in determining the performance and longevity of structures. In this article, we examine the impact of Ground Granulated Blast Furnace Slag (GGBFS) on the durability properties of concrete. Durability is a crucial aspect that must be sufficiently addressed in any structure to ensure it meets the intended requirements over time. This requirement applies to all structures, regardless of the materials used in their construction. Therefore, when selecting materials for building construction, durability considerations should be taken into account. In this discussion, we explore how the replacement of concrete with GGBFS affects the durability properties of a structure.

What are Durability Properties of Concrete with GGBFS?

Following are the durability properties of Concrete with GGBFS:

1. Effects of GGBFS on Creep and Shrinkage Behavior of Concrete

Concrete deformation under sustained load over time is known as creep. Shrinkage, which can be categorized as drying, chemical, or autogenous, also plays a significant role. Drying shrinkage, primarily caused by water evaporation from the concrete structure’s voids, is the most prominent type. Creep and drying shrinkage are essential time-dependent factors that impact the properties of high-performance concrete (HPC). In this study, the variation of creep and shrinkage in an HPC specimen was examined for three different concrete types: Concrete A with no replacement, Concrete B with GGBS replacement, and Concrete C with silica fume plus GGBS replacement. The creep analysis was conducted at 180 days of age, while the shrinkage measurements were taken at 210 days of age.

The replaced samples in Figure-1 exhibit lower creep values compared to samples with ordinary Portland cement (OPC) alone. This can be attributed to the strength-gaining property of slag over time. As shown in Figure-2, the drying shrinkage values are also lower in the replaced samples compared to those containing only OPC. This can be explained by a primary factor, namely the absence of voids. Ground granulated blast furnace slag (GGBS) effectively contributes to densifying the concrete and eliminating voids. Consequently, water is trapped within these voids, reducing water vaporization and preventing the shrinking effect.

2. Improving Chloride Resistance in Concrete through GGBFS Addition

A study conducted by Dhir et al. (1996) found that adding ground granulated blast furnace slag (GGBS) to ordinary Portland cement (OPC) concrete improves its resistance to chloride. The researchers tested the chloride binding capacity of OPC concrete samples and those with GGBS replacements at percentages of 33.3, 50, and 60. The water cement ratio was kept constant at 0.55 throughout the tests. The results showed that the chloride binding capacity of concrete increased with higher GGBS content. In particular, replacements above 50% exhibited a fivefold increase in chloride binding capacity. Additionally, as the chloride exposure increased, the binding capacity also increased proportionally, indicating a positive correlation.

Measuring the strength and permeability of the concrete can also provide insights into its chloride resistance. In this regard, concrete containing GGBS demonstrated lower permeability compared to OPC concrete. This reduced permeability helps prevent the movement of chloride ions, thereby enhancing the concrete’s resistance to chloride attack.

3. Strengthening Sulphate Resistance in Concrete with GGBFS

Sulphate attack is a detrimental factor that leads to the deterioration of hardened concrete structures. The extent of sulphate attack depends on the duration of exposure to sulphate ions and the type of cement used. Clayey soils, commonly containing magnesium or calcium sulphates, can transmit sulphate ions and contribute to the spread of the attack. These salts have the potential to react with calcium hydroxide ions or calcium aluminate hydrate (C3A) present in the concrete.

The reaction produces calcium sulphoaluminate and gypsum, which occupy a larger volume than their original compounds. This expansion, combined with temperature fluctuations, causes disruption and damage to the concrete structure. Penetration of sulphate ions into the concrete is a prerequisite for these processes to occur. This is where Ground Granulated Blast Furnace Slag (GGBS) plays a role, as it significantly enhances the impermeability of concrete, thereby reducing the impact of sulphate attack. Figure 3 illustrates the relationship between the expansion rate of concrete and the percentage of cement replacement with GGBS: higher replacement amounts of GGBS result in lower expansion.

Special cement types such as sulphate resisting Portland cement (SPRC), despite having a low C3A content, demonstrate lesser performance compared to GGBS concrete. GGBS particles contribute to sulphate resistance through three distinct mechanisms. Firstly, GGBS contains no C3A, and as the amount of GGBS replacing cement increases, the overall C3A composition decreases accordingly. Secondly, GGBS participates in pozzolanic reactions, consuming a significant portion of calcium hydroxide (CaOH2). Consequently, there is less CaOH2 available for the formation of ettringite by C3A. Finally, GGBS enhances resistance against sulphate ion penetration by increasing the permeability of the concrete.

4. Strengthening Concrete Against Freeze-Thaw Damage: The Role of GGBFS

Temperature variations can significantly affect the properties of concrete, raising concerns about the durability of structures. Freezing and thawing, triggered by water entrapment in the concrete, play a key role in this process. Water behaves differently in cold and hot temperatures, leading to freezing and thawing phenomena. These temperature fluctuations cause the concrete to expand and contract, resulting in the formation of small cracks that can propagate and eventually lead to significant damage. To counteract this rapid deterioration, high-quality concrete mixes are crucial. Incorporating Ground Granulated Blast Furnace Slag (GGBS) in the concrete mixture contributes to its overall quality. GGBS particles aid in reducing porosity, which is a fundamental factor in water entrapment. Moreover, the inclusion of GGBS imparts distinct mineralogical characteristics to the concrete, further enhancing its durability.

5. Effects of GGBFS on Reinforcement Corrosion in Concrete Structures

Porosity and corrosion activity in concrete are closely related, as indicated by studies. When concrete is exposed to seawater, there is a risk of chloride ion penetration, which leads to reinforcement corrosion. Replacing ground granulated blast furnace slag (GGBS) with silica fume in a conventional concrete mix has been found to enhance corrosion resistance compared to ordinary Portland cement (OPC) concrete.

The corrosion rate of the surface area is lower when using 25%, 40%, and 55% replacement of cement with GGBS compared to using zero percentage replacement. This comparison was made for three different cover thicknesses: 1cm, 2cm, and 3cm. The study considered two types of cement, ASTM Type I and ASTM Type V.

FAQs about Durability Properties of Concrete with GGBFS

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