Keywords

1 Introduction

The rapid growth of high-performance concrete structures resulted in the development of innovative construction materials like Self-Compacting Concrete, which offers the best solutions viz., high workability, passing ability through confined and densely reinforced spaces, economical and noise-free construction for the development of concrete industry and opened up new areas for the use of this product all over the world. Economically and technically, the Self-Compacting Concrete offers very attractive benefits over Normally Vibrated Concrete (NVC), which can be further extended when combined with fibres, particularly steel fibres. Today, SCC is widely accepted material for the construction of bridge deck overlays, reinforced concrete bridges, prestressed bridge elements and railroad structures.

2 Self-Compacting Concrete (SCC)

In the past one decade, a significant number of researches related with various aspects of concrete technology and practice have been dedicated specifically to SCC and the available literature on SCC is further growing rapidly. The following section briefly discusses the characteristics of SCC in fresh and hardened state investigated in the recent past.

2.1 Properties of Fresh SCC

The SCC is much more preferred over NVC due to its fresh state properties, i.e. flowing characteristics and it is therefore more important to verify its fresh state properties. Alteration in the water-to-cement ratio and the amount of admixtures is the main properties in obtaining workable and stable SCC mixtures. Feys et al. (2008) and Khayat et al. (2010) studied the effect of water-to-cement ratio, superplasticizer (SP) and viscosity modifying agent (VMA) dosage levels on the workability and rheology of Self-Compacting Concrete. The optimum parameters for self-compatibility were determined through the tests of workability such as L-Box, V-funnel and slump flow. The constant dosage of superplasticizer was more effective in increasing the mix workability when applied at constant at lower water/cement ratios. The decrease in w/c ratio increases the extent of possible workability improvements of SCC. The optimal dosage of superplasticizer depends on the concrete mix proportions, which can be determined through experimental trials only. A range of 0.84–1.07 by volume is the suggested optimum water-to-cement ratio for producing SCC. The blocking may happen if the ratio is above and segregation of the mixture may happen for ratios outside this range. The use and type of VMA have affected the fresh properties of SCC significantly. The addition of VMA resulted in major enhancement in passing ability with the increase in slump flow without any negative impact on surface settlement, rheological properties and mechanical properties (Khayat et al. 2010).

Hwang et al. (2006) investigated about 70 SCC mixtures made with water-to-cementitious material ratios (w/cm) of 0.35 and 0.42 to evaluate the acceptability of various test methods for workability assessment and to propose stipulations for better structural performance of SCC. It was suggested to evaluate workability parameters of SCC to supervise the quality and design for place ability in constrained sections, encountered in various structures, through use of a combination of the slump flow and the L- box, J-Ring or V-funnel tests.

Sonebi et al. (2007) investigated the consequence of the water-to-cement ratio, superplasticizers (HRWRA) and the content of coarse aggregates, on filling ability and passing ability of Self-Compacting Concrete through statistical models. The established models provide a capable method to determine the effect of main variables on fresh characteristics of SCC and the models are applicable for a wide array of mix proportions. Kovler and Roussel (2011) reviewed the data related to workability, i.e. loss of slump, setting time and rheological characteristics of SCC, i.e. thixotropy, bleeding, segregation and problems related to formwork filling and pressure.

A number of investigations have been made to study the impact of different filler material viz., fly ash, limestone powder, metakaolin, chalk powder, etc. on the workability and stability of fresh SCC. The use of some other waste materials like spent foundry sand, ground-granulated blast-furnace slag (GGBFS), crump rubber, were also studied to investigate the SCC in its fresh state. It has been found that different filler materials, as well as waste materials investigated, could be efficiently used to develop SCC mixes with minute modification in dosage of superplasticizer. A summary of the some recent studies conducted in this regard is presented in Table 1.

Table 1 Summary of investigations made on properties of fresh SCC
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For the successful placement of SCC, a concrete mixture with tailor-made workability properties was required to ensure a good balance between deformability and stability and ensure a homogeneous distribution of the concrete constituents. To ensure adequate structural performance and durability, such a homogeneous distribution is of utmost importance. There was a huge challenge for researchers and technologists to deal with intricate task of manipulating several variables to enhance concrete performance and at the same time reduce the cost while using SCC. Initially, Okamura and Ozawa (1995) has proposed an effortless mix design method in which the fine and coarse aggregate amount was kept constant and the water/powder ratio and dosage of superplasticizer were adjusted to achieve the self-compactability, which was later on modified by Okamura and Ouchi (1999). Su et al. (2001) used the concept of packing factor (PF) to suggest a new method for proportioning of SCC mixes. The most important deliberation of the proposed method was to fill the voids between the loosely piled aggregates by the paste of binders. The aggregate packing factor (PF) determines the amount of aggregate and affects the strength, flowability and self-compactability and other desired SCC properties. The guidelines for proportioning of SCC mix proposed by EFNARC (2005) and ACI 237R 2007 are presented in Table 2.

Table 2 Proposed limits for constituents for SCC mixes
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Lately, Kheder and Al Jadiri (2010) developed a new method for proportioning SCC mixtures based on specified strength under compression, not just emphasizing on the fulfilment of fresh properties requirements unlike the previous methods of proportioning. It also considers the effect of fineness modulus of fine sand and maximum size of coarse aggregate in proportioning SCC mixtures. This method suggested the design of SCC for compressive strength from 15 to 75 MPa. Silva et al. (2011) also studied the technical practicality of two design methods for proportioning of SCC to obtain required characteristics with minimum number of experiments.

2.2 Properties of Hardened SCC

Initially, when SCC was adopted by the construction industry, the achievement of fresh properties was the major concern of the research and development work. It is, however, the properties of hardened concrete that are of principal interest to structural engineers and designers and contractors. A significant amount of research data has also been generated relating to properties of hardened SCC and a comprehensive review of the characteristics such as strength under compression and tension, fracture mechanism, modulus of elasticity, creep, shrinkage and other in situ and structural properties are presented in this section.

An investigation to compare the strength, elastic modulus, creep and shrinkage characteristics of SCC with NVC was conducted by Persson (2000). The study included specimens of eight different mix proportions with water-to-binder ratio (w/b) ranging from 0.24 and 0.80. The result shows that modulus of elasticity, creep and shrinkage of Self-Compacting Concrete at constant strength was similar to much extent with the corresponding properties of NVC.

Druta (2003) compared the values of strength under compression splitting tension for SCC and NVC. The coarse aggregate–cement paste bonding was also examined. All SCC mixtures exhibited higher strength compared to NVC under compression as well as split tension. The increase in strength under compression was approximately 60% while the strength under splitting tension of SCC was 30% higher than NVC. The reason for the increase observed in strengths was the enhancement in the bonding between aggregate and cement paste due to the use of mineral and chemical admixtures, which ultimately has increased the strength of concrete. The scanning electron microscope images taken from concrete samples have shown that the greater widths of the aggregate–cement paste interface micro-cracks for NVC than for SCC. Brouwers and Radix (2005) observed a higher splitting tensile strength for SCC compared to NVC of similar strength under compression.

The deformation behaviour of Self-Compacting Concrete under sustained loading was investigated by Wustholz and Reinhardt (2007). The different compressive strength grades of SCC were subject ted to sustained tensile load for up to 2.5 years. It was reported that the long-term tensile strength was found to be 69% of the short-term tensile strength and the stress-induced shrinkage tends to amplify on decreasing the compressive strength.

A widespread assessment of mechanical properties of SCC under hardened state was done by Domone (2007). The data have been analysed from more than 70 investigations and correlated to compare with the properties of NVC with similar strengths. The data so obtained depicted significant scatter, which may be due to a wide variety of materials and mixes used for SCC. It is evident that limestone powder makes a significant increase in strength, which was a common supplementary addition to SCC mixes. SCC showed similar or higher bond strength to reinforcing and prestressing steel as that for NVC. The in situ properties and the performance of the structural elements cast with SCC showed similar behaviour as that with NVC. A significant data has been obtained from this analysis which gives assurance in the general behaviour of Self-Compacting Concrete, and further investigations need to be designed to obtain confirmatory data for particular applications such as earthquake resistant structures and structures subjected to fatigue loads.

Hassan et al. (2008) studied the strength under shear and cracking behaviour of large-scale beams made with Self-Compacting Concrete and compared with NVC. The study revealed that ultimate strength under shear for NVC beams was somewhat higher than that of similar beams of SCC and the difference increases with the decrease in main steel reinforcement and increase of depth of beam.

The bond characteristics of Self-Compacting Concrete plays an important role when SCC is specifically to be used in structural elements with dense and congested reinforcement under difficult casting conditions without applying vibration. Esfahani et al. (2012); Desnerck et al. (2010) carried out extensive investigations to determine the bond strength and top-bar effect between deformed steel bars and different SCC mixes. SCC performed better than NVC depicted by less decrease in bond strength of SCC due to more stable and less inhomogeneous mix compared to NVC. The variation in bond strengths at different casting levels was also observed to be lesser in SCC than that of NVC. Due to its more consistent nature and superior filling ability, the Self-Compacting Concrete also showed a lesser top-bar effect compared to NVC. The behaviour of different structural elements of SCC under statically applied loads has been studied by several researchers and the results were compared with that of NVC. Table 3 summarized the results of such tests conducted on various structural elements made with Self-Compacting Concrete and NVC of similar strengths.

Table 3 Summary of tests on structural concrete elements
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The effect of addition of different types of mineral admixtures/filler materials on the characteristics of Self-Compacting Concrete in hardened state viz., compressive strength and tensile strength, fracture processes, rupture modulus, creep and shrinkage, etc. were investigated by a number of researchers under statically applied loads. The impact of specimen size, size and type of aggregate on properties of hardened Self-Compacting Concrete has also been studied by various researchers. Thus, Table 4 presents a brief summary of the investigations carried out to study the afore-mentioned characteristics of SCC in hardened state.

Table 4 Summary of investigations on properties of hardened SCC
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The durability properties of SCC mixes viz., chloride ion penetration, freeze and thaw resistance, alkali-aggregate reaction, carbonation sulphate attack, resistance to fire, etc. have also been a subject of investigation (Persson 2003). It has, in general, been observed that the sorptivity and oxygen permeability of SCC mixes had remarkably reduced than that of NVC of the same strength. Zhu and Bartos (2003) depicted that the type of filler used is one of the main factors affecting the chloride diffusivity of SCC. The Self-Compacting Concrete mixes with no additional cementitious material were found to have significantly better chloride diffusion than the reference mixtures and other Self-Compacting Concretes, in presence of a viscosity modifying agent. Reinhardt and Stegmaier (2006) tested normal and high-performance SCC, respectively, under fire. The study revealed that the risk of spalling was greater in normal SCC as well as high-performance Self-Compacting Concrete in comparison to NVC and high performance NVC. The initial and residual mechanical properties for SCC were similar. The properties viz., internal frost resistance and salt resistance were extensively explored by Persson (2003). The results indicated a significant improvement in the freeze and thaw resistance of SCC as compared to NVC whereas, frost scaling due to salt and internal fundamental frequency were more or less similar in SCC and in NVC.

Dinakar et al. (2008) studied the effect of adding high volume fly ash on the durability of Self-Compacting Concrete. The results indicated that the high volume fly ash SCCs depicted higher water absorption and permeable voids in comparison to normal NVCs of the similar strength under compression. The high-volume fly ash SCCs has shown a significant reduction in loss of weight and diffusion of chloride ion. Boel et al. (2008) concluded in a study that the gas permeability of SCC is almost five times less than the gas permeability of similar NVC.

Hwang and Khayat (2009) suggested that regardless of the water/cementitious material (w/cm) ratio, binder type or admixture combination, properly designed SCC can develop high resistance to freezing and thawing with frost durability factor greater than 80%. Guneyisi et al. (2011) have studied the permeability properties of SCCs made with different blends of Portland cement, fly ash, metakaolin and GGBFS. The type and amount of the cementitious material used significantly effects the permeability properties of SCCs. The metakaolin has been found to be the most efficient in reducing the permeability properties of Self-Compacting Concrete mixes.

The results derived from different investigations showed an overall improvement in the properties of SCC in hardened state over the NVC of similar grades. The improved homogeneity and density of concrete coming from vibration free production and better interface bond between aggregates and paste has contributed to the better performance of SCC over NVC.

3 Concluding Remarks

The review of the literature in the preceding sections presented in brief the characteristics of Self-Compacting Concrete made using recycled materials. It can be seen that numerous investigations have been carried out to assess the properties of fresh SCC as well as the properties of hardened SCC under static conditions of loading. Different types of cementitious materials have been incorporated in concrete to enhance the properties of SCC. The aim has been to review the workability and suitability of SCC concrete for use in different structures viz., in bridge decks and piers, highway and airfield pavements, offshore structures, rapid mass transport systems, dams, tunnel linings, high-rise structures, precast and prestressed elements.