**2. Use of sustainable binder materials**

passing ability, SCC possesses superior capability to deform and flow, fills up constricted spaces and far-reaching corners, passes through small clearance between objects including reinforcing bars, and achieves proper consolidation without compaction applied [3]. These allow proper placement of concrete even at locations of congested reinforcement and sophisticated formwork shape. At the same time, the concreting operations would be much quieter without the noise generated from concrete compaction, and part of the labour input for concreting can be saved [4]. The production of SCC was mainly enabled by the advent of superplasticising admixtures. With the adoption of appropriate dosage of superplasticiser and water to binder ratio, the workability of concrete can be dramatically improved while the strength can be maintained at the desired level or even increased. The favourable properties of SCC have enabled its widespread adoption in many parts of the world [5]. In recent years, guidelines and specifications of SCC have been developed in Japan [6], Europe [7], USA [8],

114 Sustainable Buildings - Interaction Between a Holistic Conceptual Act and Materials Properties

Nevertheless, there are two major issues associated with the SCC mixes commonly used in practice. The first issue is that the cement content is usually at the high side, and the adverse effects of high cement content are twofold. Since the production of cement involves calcination at high temperature which is an energy-intensive process [10], the high cement content imparts high embodied energy (EE) and carbon footprint to the SCC mixes [11]. Besides, since the hydration of cement is an exothermic chemical reaction, the high cement content would generate a large amount of heat during concrete hardening and increase the temperature [12]. When the temperature drops to the ambient subsequently and if the thermal contraction is constrained, early thermal cracking would result and that would impair structural integrity

The second issue is that the strength of concrete is usually limited in practical applications to around grade 60, which is considered as medium strength in nowadays achievable norm [14]. It is well known that the strength of concrete can be increased by decreasing the water to cementitious materials (W/CM) ratio. In the past, the practical limit of W/CM below which the concrete would be insufficiently workable was rather high. That was due to the limited efficiency of the then plasticisers or superplasticisers (SP) available. With the advancement of superplasticising technology over the past decades, lower W/CM ratio could be achieved while the concrete could remain highly workable, and this can be translated to high-strength performance. However, though different high-strength SCC mixes had been developed in laboratories [15, 16], the same range of strength has not yet been commonplace in practice. One of the main reasons of limited strength is that the W/CM ratio has not been minimised by effective utilisation of SP. As will be illustrated later in this chapter, with the increasing usage of cementitious materials with high fineness, instead of the conventional way of dosing the superplasticiser (SP) based on the mass content of cementitious materials, the SP can be more effectively utilised with its dosage being

To address the above two issues, the authors have conducted research on improving the sustainable performance and mechanical strength of SCC, as reported in this chapter. With respect to the first issue, the cement consumption is reduced with the incorporation of sustainable binder materials including fly ash (FA), shale ash (SA) and microsilica (MS). With respect to the second issue, the compressive strength of SCC was improved by lowering the W/CM

set based on the specific surface area of cementitious materials.

China [9] and many parts of the world.

and necessitate repair [13].

Supplementary cementitious or binder materials have been increasingly used in recent years to yield various beneficial effects on the performance of concrete [17]. For such materials which are naturally occurring or are industrial by-products, their embodied energy and carbon emission are usually much lower than those of silicate cement. The use of these materials as part of the binder to reduce cement consumption can promote the sustainability of concrete, and for this reason they are referred to as sustainable binder materials herein. The different physical properties and chemical reactivity of sustainable binder materials would affect the performance of SCC in different manners. From chemistry viewpoint, common supplementary binder materials can be broadly classified into three types. The first type is silica dominated (mainly single composition of SiO<sup>2</sup> ), as exemplified by MS, recycled glass powder, perlite and quartz powder [18]. The second type is alumino-silicate dominated (mainly binary composition of Al<sup>2</sup> O3 -SiO<sup>2</sup> ), as exemplified by activated clays and metakaolin [19]. The third type is calcium-alumino-silicate dominated (mainly ternary composition of CaO-Al<sup>2</sup> O3 -SiO<sup>2</sup> ), as exemplified by FA and slags such as ground granulated blast-furnace slag (GGBS) [20]. While the chemical composition of supplementary binder materials determines their pozzolanic reactivity in reacting with calcium hydroxide formed during cement hydration to produce extra cementitious products, the physical characteristics, mainly the granulometry, strongly influence the rate of pozzolanic reaction and various performance attributes of the concrete.

In this study, FA, SA and MS were employed and their effects on SCC are discussed in the following. FA is produced mainly from power stations during the burning of pulverised coal. The ash particles are predominantly spherical in shape and their fineness resembles that of cement. Depending on the source and classification, the silica content of FA would be in the range of 50–70%. Due to its rounded shape, the workability of SCC would not be adversely affected by adding FA. The strength development of concrete with FA is slower than cement concrete, and longer curing period is necessary. The benefits of FA in concrete production are rather established [21, 22]. Particularly, it is very effective in reducing the heat generation of mass concrete during curing to prevent the early thermal cracking problem.

SA is produced by the combustion process of oil shale that contains fossil energy. It is yielded from the solid residue (known as spent shale) resulted from the burning of oil shale [23]. The disposal of SA has been an environmental problem faced by countries that produce shale oil [24]. Though SA may be ground to similar size as cement grains and utilised in the manufacturing of bricks [25], its use in the production of SCC has been much less explored [26]. Due to the minerology of shale, SA contains relatively high content of calcium oxide, usually in the range of 10–40%. The pozzolanicity of SA is similar to that of GGBS, and it has a silica content of 30–40%. In terms of chemical composition, SA can be classified as calcium-alumino-silicate dominated, with a subtle content of aluminium oxide. The addition of SA in concrete had been reported to increase the concrete strength, reduce the permeability and improve frost resistance [27]. However, the alkali content in SA is generally at the high side, and the content of SA in concrete should be limited to prevent expansive alkali-silicate reaction [28].

ratio to be reduced by up to 40% without adversely affecting the workability of concrete. The molecular structure of PCE is characterised by an active-monomer (such as polymethacrylate acid, or abbreviated as PMAA) formed main chain, attached with numerous graft copolymers (such as polyethylene glycol, or abbreviated as PEG) formed long side chains. Such long side

PCE improve the workability of concrete mixes by dual effects, namely the dispersion effect and steric hindrance or steric repulsion effect. This is in contrast to SMF and SNF which improve the workability of concrete mixes only by dispersion effect. The dispersion effect is explained as follows. There are four main types of minerals in ordinary Portland cement,

negatively charged, while aluminate and ferrite are positively charged. Because of the opposite electrostatic potentials, the cement grains tend to coagulate together, making it less readily to thoroughly mix with water to form a uniform paste [37]. With the addition of SP, the SP molecules are adsorbed onto the surfaces of cement grains, and they impart negative charges to all the cement grains. The electrostatic repulsion derived from the negative charges disperses the cement grains apart. For PCE, it is the main chain of PCE molecule that is adsorbed and imparts negative charges to cement grains, whereas the side chains act as physical barriers to separate the cement grains further apart [38]. Such steric hindrance further promotes

In determining the SP dosage to concrete, attention should be paid to the quantities of SP demand for given levels of workability, the saturation SP dosage beyond which further addition of SP would yield no return, and the maximum SP dosage beyond which further addition of SP would cause segregation. Conventionally, the SP demand, saturation dosage and maximum dosage are expressed in percentage by mass of cementitious materials. However, as SP is a surfactant adsorbed onto the surface of cementitious materials, its effectiveness should be dependent on the amount of SP per surface area of cementitious materials [41]. Therefore, the SP demand, saturation dosage and maximum dosage should be controlled by the fineness and the content of each cementitious material. This forms the basis to rationalise

A total of 12 concrete mixes were produced for testing. The materials employed were as follows. The cement used was an ordinary Portland cement that complied with the requirements in European Standard EN 197. It has a solid density of 3.1 and a specific surface of 350 m<sup>2</sup>

The fly ash (FA) used was produced from coal-fired power station and the properties complied with the requirements in European Standard EN 450. The shale ash (SA) used was produced from shale oil fuelled power plant and the properties have been investigated in this research. To show the morphology of SA particles, **Figure 1** depicts the scanning electron

A) and ferrite (C<sup>4</sup>

Development of Sustainable High-Strength Self-Consolidating Concrete Utilising Fly Ash, Shale…

AF) [36]. Belite and alite are

http://dx.doi.org/10.5772/intechopen.75508

117

/kg.

S), aluminate (C<sup>3</sup>

chains are absent in SMF and SNF molecules.

S), alite (C<sup>3</sup>

dispersion and prolongs workability retention [39, 40].

namely belite (C<sup>2</sup>

the usage of SP.

**4. Method**

**4.1. Materials employed**

MS (also called condensed silica fume) is a by-product of the smelting process used to produce silicon metal and ferrosilicon alloys. MS is characterised by the high content of reactive silica of over 85% and the extremely fine particle size in the order of 0.2 μ. The high fineness of MS allows it to fill the voids between larger cement particles and increases packing density. The displaced water becomes excess water to lubricate the solid particles. From mix design perspective, the water demand for packing is greatly reduced and a lower W/CM can be used for achieving higher strength. The high fineness and large specific surface area risk of MS also mitigate the plastic settlement and segregation problems. The use of MS in concrete production is rather established, and it is among the common constituent materials for making high-strength concrete [29, 30]. The use of MS as well as the combined use of MS and FA in producing SCC had been investigated and confirmed to be effective by the authors [31, 32].
