Properties of Fresh and Hardened Concrete Containing Supplementary Cementitious Materials

Since the discovery of the latent hydraulic reactivity of ground granulated blast-furnace slag (ggbfs) by Emil Langen at the end of the 19th century, this material has been used successfully as cement and concrete addition. This chapter includes all relevant information about this valuable material—from production and processing to the effect, which ggbfs additions have on the concrete performance. In this context, light is shed on decisive performance parameters of ggbfs. Of special interest nowadays is certainly also the information given about trace element contents in ggbfs and their leachability. Here and throughout the entire chapter, the latest insights from research and development work are included. Last but not least, the chapter contains very practical information when it comes to the use of ggbfs in concrete, including insights on rheological effects, concrete color and “greening”, and adequate curing. Moreover, an overview about relevant norms and standards on ggbfs as concrete addition is given.

Fly ash is an industrial by-product deriving from electricity generating plants. It is the by-product of burning coal or lignite. Fly ash is one of the first artificial admixtures used for the production of concrete since the first decades of the 20th century. Its chemical and mineralogical composition mainly depends on the relevant properties of the raw material used as well as on the type of furnace and the way it is collected. Fly ash may have beneficial effects on both the fresh and hardened properties of concrete mixtures. This chapter provides an extensive report on the use of fly ash in concrete. Reference is made to the regulatory framework governing the application of fly ash, mainly in Europe and America, to factors affecting the quality of the product and to the effects of different fly ashes on fresh and hardened characteristics of concrete.

Silica fume concretes have been used since the mid-1970s, in many areas of the world. Such uses have included high strength, high chemical resistance—especially high chloride and sulfate resistance—abrasion and erosion resistance. With the increased focus on sustainability, silica fume—being a by-product—is used to great effect in reducing the Portland cement content of a mix, and allowing the use of higher cement replacement levels of other SCMs such as blastfurnace slag and fly ash. This can reduce both the energy used and the carbon footprint. The higher performance of the silica fume concrete, in terms of strength, can allow for reductions in structural element size, thus reducing the concrete volume needed, saving natural resources. The increased durability can provide greatly extended lifetimes compared to normal Portland concretes, thus also reducing the need for repairs and replacement. Numerous examples are available from the past 40 years of use, and reference should be made to the relevant manufacturers and associations web-sites, for more information.

Limestone has been successfully used as a constituent of cement and concrete for decades. Fine limestone is commonly included in Portland cement by intergrinding, resulting in an optimal particle size distribution of the modified cement. In other applications, limestone powder is added separately from cement, for producing more stable and robust mixes, especially self-compacting concrete. This chapter examines the performance of limestone modified Portland cement and concrete. The review comprises the effects on cement hydration in relation with the fineness of the limestone, on the fresh properties of mortar and concrete (including its role in self-compacting concrete), and on the strength development in the hardened state. Complementarily, comments regarding sulphate attack and environmental benefits of the use of limestone modified cement are included. Limestone is an effective constituent of cement and concrete, and comparative analyses should always be made to mixes produced to the same strength. In this way, it has to be regarded as a supplementary cementitious material when included by intergrinding with cement clinker, or as a filler when added separately to concrete.

Metakaolin (MK) is known to be a highly pozzolanic material that can be used in concrete. MK is usually produced by heating kaolin-containing clays, within the temperature range of about 600–900 ℃. This chapter summarizes the utilization of metakaolin in relevant worldwide standards, mainly in Europe and North America. The health, safety and environmental sustainability concerns on using metakaolin as a supplementary cementitious material are also addressed in this chapter. It is reported that MK incorporation has benefits on both early-age and long-term properties. On the other hand, this chapter also reports that the results of heat of hydration and rate of reaction in metakaolin-blended concrete are controversial and need further investigation. Overall, the optimum level of cement replacement by MK is around 10–20%, which provides concrete the maximum strength. Metakaolin appears to have an excellent potential as a supplementary cementitious material in structures made of high-performance concrete, because it controls deleterious expansion due to alkali-silica reaction in concrete (depending on the nature of the aggregate), and reduces the ingress of chloride by improving the microstructure and chloride binding behavior.

This chapter is dedicated to several kinds of natural pozzolans that occur around the globe and describes their specific characteristics, origin and use in concrete. Moreover, the advantages and disadvantages of their use in concrete mixes are highlighted in terms of concrete properties. In particular, the referenced properties in this chapter are that of fresh and hardened concrete, its microstructure and chemical durability. The chapter is summarized by mentioning the specifications concerning natural pozzolans according to the relative standards. Overall, the benefits of using natural pozzolans in cement and concrete are evident in terms of higher later age compressive strength, increased concrete durability, lower heat of hydration, reduced bleeding and others.

The use of supplementary cementitious materials (SCM) has become a major trend in concrete technology with effective utilization of industrial by-products (IBP) such as fly ash, ground granulated blast furnace slag and silica fume. Many types of industrial by-products (IBP) such as fly ash, silica fume, rice husk ash and waste glass are becoming the predominant source of mineral components with pozzolanic properties required to improve the performance of portland cement based materials. The availability of decent quality SCM has almost reached its limits and cannot offset the need for higher volumes of concrete required by developing markets. The use of alternative supplementary cementitious materials, including off-spec products and less-investigated by-products can be a viable alternative. However, there are many obstacles and limitations which hinder the utilization of such products. These are related to the lack of long-term results related to strength and durability, the potential variability in terms of composition and the presence of undesirable substances including heavy metals. These limitations dictate the need for higher production control and product consistency. This report presents the state of the art experience with utilization of modern technologies and potential SCM such as steel slag, pulverized bottom ash, sugarcane bagasse ash, waste glass and low-grade silica fume. Certainly, the current economic conditions make recycling feasible for only a limited number of by-products. Waste materials can be used only when they can be collected, processed, and reused at a cost the same or less than natural raw materials. To increase the rates of recycling, cement and concrete manufacturers need a uniform supply of quality waste; this would require better sorting and also the development of waste identification technology. On the other hand, it is also evident that innovative technologies capable of tolerating multiple contaminants are needed to boost the recycling of industrial by-products and waste beyond the current limits.

This chapter reviews the performance of rice husk ash (RHA) as partial cement replace in ordinary Portland cement concrete. After pyroprocessing with controlled combustion, highly pozzolanic RHA can be produced. Due to the high specific surface area and pozzolanic properties, RHA shows very good performance as a supplementary cementitious material in concrete. For early age properties, concrete made of RHA needs more water and high dosages of superplasticizer compared to ordinary Portland cement concrete. The RHA concrete has slightly longer setting times than ordinary Portland cement concrete. When the replacement level of ordinary Portland cement by RHA is about 20% by weight of the total binder material, the compressive strength, tensile strength and flexural strength of concrete made of RHA are enhanced. Due to the special porous structures, RHA shows excellent capacity to keep high relative humidity in the concrete, thus RHA significantly mitigates the autogenous shrinkage of concrete, especially high performance or ultra-high performance concrete made with RHA as addition. From water permeability and chloride diffusivity tests the coefficient of water absorption of RHA concrete is lower and the chloride diffusion coefficient is reduced.

Ternary binders have become used more frequently for several reasons. In some cases, such as combining a rapidly reactive SCM such as silica fume with a more slowly reactive SCM such as fly ash or slag, the use of ternary binders can provide benefits for both early-age and later-age properties and durability of concrete. In other cases, high-alkali pozzolans have been combined with slag to both accelerate the slag hydration and bind the alkalis from the pozzolan. As well, two SCMs may be combined to improve economy of the concrete mixture. This chapter describes properties of various ternary binders.