Pavel Krivenko

Alkali-Activated Cements and Concretes

Introduction 1. Alkaline Activators 2. Cementing Components 3. Hydration and Microstructure of Alkali-Activated Slag Cement 4. Properties of Alkali-Activated Slag Cement Pastes and Mortars (Under Both Atmospheric Pressure and Autoclave Conditions) 5. Properties of Alkali-Activated Slag Cement Concrete 6. Durability of Alkali-Activated Slag Cement and Concrete 7. Mix Design of Alkali-Activated Slag Cement Concrete 8. Alkali-Activated Portland Cement Based Blended Cement 9. Alkali-Activated Lime-Pozzolan Cement 10. Other Alkali-Activated Cementitious Systems 11. Applications of Alkali-Activated Cement And Concrete 12. Standards and Specifications

Characterization of Aged Slag Concretes

Slag concretes, activated by carbonates or carbonate/hydroxide mixtures and cast between 1964 and 1982, are examined. These concretes have served for prolonged periods under conditions in which portland cements would have deteriorated rapidly, and yet have remained sound and actually increased in strength over their service life. By a combination of microscopic and nuclear magnetic resonance (NMR) analysis, this durability is attributed to the combination of a highly polymerized, relatively low-Ca, amorphous C-S-H outer product, with an inner product that undergoes continuing hydration via a cyclic process involving carbonate anions. The relatively consistent Ca/Si ratio across all phases is believed to contribute to durability, as is the low Al content of the C-S-H phases formed in systems using hydroxide activators. The low permeability of the concretes also appears to have contributed to their durability.

Demonstration Projects and Applications in Building and Civil Infrastructure

In the context of a Report such as this, it is of immense value to be able to provide tangible examples of structures and applications in which alkali-activated concretes have been utilised throughout the past decades. A detailed outline of the utilisation of AAM concretes in the former Soviet Union and in China is given in Chap. 12 of the book by Shi, Krivenko and Roy [1], and this chapter will briefly describe some of the applications mentioned in that (more extensive) document, along with applications elsewhere in the world where AAMs have been utilised on a significant scale in the construction of buildings and other civil infrastructure components. An overview of developments and applications in the former USSR has also been presented by Brodko [2] and by Krivenko [3]. Each project reported in this chapter involves at least pilot-scale, and in some cases full commercial-scale, production of alkali-activated concretes utilising largely standard concrete mixing and placement equipment and labour, indicating that these materials are both accessible and useful on this length scale, given sufficient expertise in mix design based on locally available precursors. In the former USSR in particular, slags obtained from local iron production facilities were used in each of the different locations in which the concretes were produced, and activators were sourced in large part from locally available alkaline industrial waste streams.

Durability and Testing – Degradation via Mass Transport

In most applications of reinforced concrete, the predominant modes of structural failure of the material are actually related more to degradation of the embedded steel reinforcing rather than of the binder itself. Thus, a key role played by any structural concrete is the provision of sufficient cover depth, and alkalinity, to hold the steel in a passive state for an extended period of time. The loss of passivation usually takes place due to the ingress of aggressive species such as chloride, and/or the loss of alkalinity by processes such as carbonation. This means that the mass transport properties of the hardened binder material are essential in determining the durability of concrete, and thus the analysis and testing of the transport-related properties of alkali-activated materials will be the focus of this chapter. Sections dedicated to steel corrosion chemistry within alkali-activated binders, and to efflorescence (which is a phenomenon observed in the case of excessive alkali mobility), are also incorporated into the discussion due to their close connections to transport properties.

Historical Aspects and Overview

Cement and concrete are critical to the world economic system; the construction sector as a whole contributed US

Other Potential Applications for Alkali-Activated Materials

3.3 trillion to the global economy in 2008 [1]. The fraction of this figure which is directly attributable to materials costs varies markedly from country to country – particularly between developing and developed countries. Worldwide production of cement in 2008 was around 2.9 billion tonnes [2], making it one of the highest-volume commodities produced worldwide. Concrete is thus the second-most used commodity in the world, behind only water [3]. It is noted that there are certainly applications for cement-like binders beyond concrete production, including tiling grouts, adhesives, sealants, waste immobilisation matrices, ceramics, and other related areas; these will be discussed in more detail in Chaps. 12 and 13, while the main focus of this chapter will be large-scale concrete production.

The role of solid-phase basicity on heat evolution during hardening of cements

The focus of this chapter is the discussion of a variety of niche applications (other than as a large-scale civil infrastructure material) in which alkali-activated binders and concretes have shown potential for commercial-scale development. The majority of these applications have not yet seen large-scale AAM utilisation, except as noted in the various sections of the chapter. However, there have been at least pilot-scale or demonstration projects in each of the areas listed, and each provides scope for future development and potentially profitable advances in science and technology. In addition to the applications specifically discussed in this chapter, there are also commercial and academic developments in alkali-activation for specific applications including a commercial product which is being marketed as a domestic tiling grout showing some self-cleaning properties [1], as well as alkali-activated metakaolin binders as a vehicle for controlled-release drug delivery [2, 3]. Although undoubtedly promising and of commercial interest, these are rather specialised applications, and so the focus of this chapter is instead on broader categories of research and development rather than in providing detailed analysis of specific products. The areas to be discussed will include lightweight materials, well cements, fire-resistant materials, and fibre-reinforced composites.

Decorative Multi-Component Alkali Activated Cements for Restoration and Finishing Works

This paper deals with effect of solid phase basicity on heat evolution of different cementitious materials varying in basicity between 3.16 and 1.34. A differential microcalorimeter was used for thermokinetic analysis, and the heat evolution was examined with regard to non-isothermal conditions. The experimental results allowed us to conclude that, the lower the basicity of cement, the slower the rate and the less the completeness of heat evolution processes.

New Thermal Insulating Material Based on Geocement

The paper is devoted to development and research of decorative multi-component alkali activated cements with enhanced quality characteristics. The use of finely dispersed mineral additives and alkali metal salts allows to obtain multi-component cements with the lower content of OPC clinker. In chemical composition these decorative multi-component cements are similar to Roman cement. The developed multi-component cements have comparable or better performance properties compared to Roman cement and allow for to use them successfully in making plasters, mortars, etc. for restoration, finishing works and decoration of facades.

Status and Prospects of Research and Application of Alkali-Activated Materials

A new thermal insulating material was developed on the basis of a geocement, formulated as Na2OAl2O36SiO220H2O. Ground limestone and aluminosilicate pellets were used as fillers for its production (composition: geocement 64.29 wt. [%]; fillers 35.71 wt. [%]). This material, which is applied having a thickness of 3.0-4.5 mm, swells when it is exposed to an external heat flow of 1273 K average temperature. Swelling is due to the matrix phases and filler dehydration, which include heulandite, ussingite, sodium zeolite and other phases. As a result, a finely porous glassy aluminosilicate frame of jadeite-albite composition is formed, which is characterized by low thermal conductivity (0.09-0.175 Wm-1K-1). The developed material can be used to protect and to insulate wooden, metal and concrete surfaces from an one-sided heat source. The paper is dedicated to the great scientist of the XXI century in the field of alkali-activated cements and materials based on them, Pavlo Kryvenko, in honor of his 75th birthday anniversary.