Role of Self-Compacting Concrete (SCC) in sustainable development

Concrete is the premier material that performs the major integral role in shaping the environment, providing the essential infrastructure for industries, transportation, accommodations, and energy production. The concrete industry tries to minimize the adverse impacts on the environment by reconciling the advantages and disadvantages of sustainable concepts during production, mixing, casting, and curing by facing challenges with innovative measures. It contributes to the current climate changes and concerns about the consumption of energy efficiently. According to the Energy Performance of Building Directive (JI, T., 2006), “the residential and tertiary sector, the major part of which is buildings, accounts for more than 40% of final energy consumption in the community and is expanding, a trend which is bounded to increase its energy consumption and hence also its carbon dioxide emissions”. Now the concern for the selection of construction material is dominated by ecological considerations and the growing sustainability ethics along with efficient use of the resource, health and safety, and improved productivity with fewer wastages. 

Sustainability in SCC production

SCC was proposed and developed by Prof.H.Okamura of University of Tokyo, Japan around 1988 as a solution for the problem of the low quality of structures resulting due to the lack of proper compaction of concrete. The SCC is a material that flows and gets compacted under the influence of self-weight only, without vibration and additional process emerged. Due to specific composition, a high fluidity of SCC allows for complete filling formwork and achieving full compaction, even in the presence of congested reinforcement. The density and homogeneity of hardened concrete are high and it gives the same engineering properties and durability as traditionally vibrated concrete (TVC) [1]. According to the high demand associated with sustainable development, a new type of SCC was developed with reduced cement content and diminished carbon footprint value since earlier SCC was not attractive with its high content of cement. As per Wallevik, this aspect of SCC is classified in Table 1 [2].

Self-compaction is defined by deformability, followability, and cohesiveness. SCC needs high viscosity and high deformability and these aspects are directly connected with the fluidity. When fluidity is increased by the high-range water reducer, it affects the stability which can be solved by providing constant water/cement ratio and sand content. However, the cohesiveness of SCC is reduced by the excessive dosage of high-range water reducer [3]. This can result in a higher degree of segregation and heterogeneity than normal concrete of similar water/cement ratio and lower fluidity. As a solution, a viscosity agent can be added to increase the water phase viscosity. On the other hand, the viscosity of fresh SCC can be increased by accumulating the solid fraction of the paste phase of concrete. Cement content can be increased to roll up the number of fines [4]. But, the excess amount of cement will greatly increase the cost of materials and the evolution of heat which can result in higher shrinkage. Thereupon, the use of materials of low reactivity finely ground materials will be the preferable method to provide necessary workability.  Hence, the main factor in the mix design of SCC is the increase in the power content to improve the separation of aggregate particles. Using cement as entire powder content is not sustainable in an economic and environmental manner. Recycled urban and industrial wastes such as fly ash are used as a replacement for cement. These replacements assure the production of sustainable SCC into the range of normal and high compressive strength class of SCC. When a substantial amount of cement is replaced with supplementary cementitious materials in concrete mixes, the environmental impact of concrete can be significantly reduced [5].

zAccording to Jacob and Hunkeler (2001), as the difference between standard concrete and SCC can be clearly stated that SCC requires higher binder and admixture content. The properties of different compositions of concretes were studied at the age of 28 days as presented in Table 2 [6].

The values shown in table 2, explain the difference in durability. The enhancement of the durability of concrete is the premier advantage achieved from the invention of SCC. The variation in water/powder ratio gives an idea regarding the mechanical resistance. The chloride diffusion coefficients deal with the use of ultra-fine material (the addition of minerals) which can cause environmental impacts as presented in table 3 [6].

Collectively both table 2 and table 3 shows the improvement in compressive strength. In terms of environmental impacts, it can be mitigated with the addition of industrial wastes such as fly ash, blast furnace slag, and silica dust as cement replacement and that can be classified according to the fine content as shown in the table 1. When cement is reduced, the fresh concrete will segregate. This can be solved with the introduction of special aggregate grading characterized by high fine content without colloidal particles. The low cement SCC leads to low consumption of material cost, less shrinkage, and reduced risk for crack formation due to the reduced paste volume in concrete.

Sustainability in Construction

The production of SCC is an energy conservation process, as the electricity consumption for vibration is eliminated. The SCC mixture incorporates industrial wastes such as fly ash, silica fume, and quarry dust and ensures sustainable production. It increases the lifespan of construction molds and reduces the necessity of skilled workers. SCC can be used for all types of structures due to the fact that it can be pumped at long distances without its segregation (Atkins, H.N., 2003). When vibration is omitted from casting operations the workers experience less strenuous work with significantly less noise and vibration exposure (Okamura, H., 2003). Nearly 0.11 kg of CO₂/m³ emits while using a flexible stick – type vibrator [7]. Similarly, the vibrator creates a 75-80 dB noise level [8]. These vibration and noise eliminations from construction ensure following the sustainability concept and occupational health and safety practices.  The environment gets rid of harmful continuous high-frequency noises and mechanical vibrations. Due to the elimination of external vibration, the probability of damages is abated with the increase of durability comparing to normal vibrated concrete. SCC is placed without the need for compaction using vibrating pokers and it provides solutions for the health-related issues-particularly “white finger” caused by mechanized vibration methods. From the contractor’s point of view, concrete placement is much faster with fewer laborers leads to cost reduction. The remedial cost is mitigated hence the structures are finalized with good finishing surfaces. It means, no plaster or other external layers are needed especially in architectural concrete elements: In these elements, concrete is permanently exposed to view. According to the BEES program developed by NIST, during the production and application of a 1 m² of cement plasterwork, approximately 0.57 kg of CO₂ emission is taken place [8]. As an architectural concrete element, the larger surface exposure increases the carbonation process. Thus, CO₂ uptake will be faster and in a wide range.

Conclusion

Regardless of chemical additives, SCC shows better mechanical properties and durability than TVC. The introduction of industrial waste cementitious materials leads the concrete industry towards sustainable development. Moreover, the use of SCC for infrastructure construction, through its contribution to reducing the manpower and energy requirements, bestows the achievement of the economic sustainability of concrete construction by overcoming the most expensive constituents.

Kavinthan Jeyasingam

Department of Civil Engineering

University of Sri Jayewardenepura

References

[1]   Ali Papzan, Taksiah.A.Majid, M.A.M.Johari, "A Review of Self-Compacting Concrete on Sustainable Development," Australian Journal of Basic and Applied Sciences.

[2]   Wallevik O., Mueller F., Hjartarson B., Kubens S., "The green alternative of Self Compacting Concrete, ECO-SCC," in 35th Conference on OUR WORLD IN CONCRETE & STRUCTURES, Singapore, 2010.

[3]   Oliveira, Luiz Antonio Pereira de, "The sustainable self-compacting concrete technology," Coimbra, 2009.

[4]   P, Billberg, "Fine Mortar Rhelogy in Mix Design of SCC," Proc fitst int Rilem symp on self compacting concrete, pp. 47 - 58, 1999.

[5]   R. S. Ravindrarajah, "High-strength self-compacting concrete for sustainable construction," 2010.

[6]   Jacobs F, Hunkeler F, "Ecological Performance of Self Compacting Concrete," in 2nd International Symposium on Self Compacting Concrete, Tokyo, 2011.

[7]   R. o. M. o. t. environment, Environment and health performance review, Poland: PUBLIC HEALTH ADMINISTRATION, 2009.

[8]   WITKOWSKI, Hubert, "Sustainability of Self-Compacting Concrete," p. 6, 2014.

[9]   Adnan Mujkanović, Marina Jovanović, Dženana Bečirhodžić, Amna Karić, "Self-Compacting Concrete - A sustainable Construction Material," in The 5th International Conference on Environmental and Material Flow Management, 2015.

[10] Heirman G, Vandewalle L, "The influence of fillers on the properties of self-compacting concrete in fresh and hardened state," Proc third int Rilem symp on self compacting concrete, 2003.

[11] B. P, "Fine Mortar Rheology in Mix Design of SCC," Proc first int Rilem symp on Self Compacting Concrete, pp. 47-58, 1999.