|Nishant Yadav||Department of Civil Engineering, SSIPMT, Raipur, India
|Shirish V. Deo||Department of Civil Engineering, National Institute of Technology, Raipur, Chhattisgarh, India|
|G.D. Ramtekkar||. Department of Civil Engineering, National Institute of Technology, Raipur, Chhattisgarh, India|
Full fledged use of construction & demolition (C&D) waste in the construction industry is inevitable. Concrete technologists across the world are engaged to scale its properties and potential uses since last 65 years. The general consensus for the mechanical property is to some extent is acceptable however the workability and durability properties are still under a scanner and needs to be improved. The present paper reports the optimistic results of series of experimental work carried out using high range replacement of normal aggregates (NA) with recycled aggregates (RA) (50-80%) from C&D waste for producing sustainable and durable concrete (water cement ratio 0.4) using C&D waste. Multiple strategies were used in research to enhance workability and durability properties of concrete produced by using C&D waste. Firstly the RA was used as an internal curing (IC) agent to enhance the micro structure and Interfacial Transition Zone (ITZ) of concrete. Secondly by apparently lowering the water cement ratio by using additional low-lime fly ash similar to class F of ASTM C 618 mainly to improve workability, packing of concrete, later age strength and durability. The results show that water diffusion in concrete with RA being used as an IC agent was delayed leading to decrease in shrinkage and micro cracks development; also increase the hydration, compressive strength and improvement of durability indexes such carbonation depth and electrical resistivity is seen. The Scanning Electron Microscope (SEM) result illustrated the considerable improvement in the microstructure. By adopting these strategies which are economical & sustainable, mixtures show additional benefits that should permit their broader application.
Concrete; Construction & Demolition (C&D) waste; Interfacial Transition Zone (ITZ); Internal Curing (IC); Shrinkage
Today land is a scarce commodity in the urban cities and to accommodate more population Floor Area Ratio is increased causing the demolition of existing structures for reconstruction. Good engineering practice advocates for recycling and reuse of materials. The reuse of Construction & Demolition (C&D) waste has potential to save a huge amount of natural resources, reduce CO2 footprint, reduce environmental impact, reduction of large space required for dumping sites, create space in urban areas, and also the creation of jobs and business opportunities (Yadav et al., 2017). The C&D wastes mainly consist of concrete, brick, ceramic and mortar which together constitute around 80%, but are in a complex mixed form and requires processing before being put to use. Un-engineered disposal and illegal dumping of these C&D waste is a threat and is causing environmental degradation. Huge heaps of C&D waste causes rise in flood levels of the rivers, scouring of the banks, depletion of resources, leaching out of hazardous material in the water causing an impact on aquatic life. Buried wastes cause the formation of an impervious layer which does not allow the growth of vegetation and prevents infiltration of rainwater. The other environmental impact includes deforestation, illegal mining of river beds for aggregates, air and water pollution, consumption of fossil fuels for transportation, topsoil loss etc. (Yadav et al., 2017).
The general wisdom on the use of recycled aggregates for making concrete affects the workability, strength, and durability of concrete. To sum up the experimental investigations on concrete produced by using C&D waste aggregate, 0-100% replacement of natural aggregates has already been done and reported. To scale the potential use of C&D waste it is unreasonable to generalize all the results thus here the replacement is categorized into a low replacement (up to 50%) and high replacement (more than 50%). In low replacement, comparable compressive strength is achieved. At higher replacement percentage of natural aggregates with C&D waste aggregate, the compressive strength of concrete is reduced (Brito & Saikia, 2013). The reason attributed to this is poor Interfacial Transition Zone (ITZ), (Medina et al., 2015). Concrete made with C&D waste aggregates have poor workability and durability performance as compared to natural aggregates concrete (Bravo et al., 2015). For 100% coarse recycled concrete aggregate (RCA) in concrete, Silva et al. (2015) reported an increase in shrinkage by up to 80%. This high shrinkage characteristic causes micro cracks within the concrete matrix and leads to poor ITZ and durability issues in aggressive environments.
As per ACI-308, “Internal curing refers to the process by which the hydration of cement occurs because of the availability of additional internal water that is not part of the mixing water” (Bentz & Weiss, 2011). Internal curing (IC) supplies the extra curing water throughout the concrete mix thus maintaining the relative humidity and avoiding self-desiccation and reducing autogenous shrinkage. IC also works well with supplementary cementitious materials (SCM) like fly ash, especially at higher dosage levels, due to increased water demand for SCM reaction in later age. IC can address various age-old complex issues of concrete like shrinkage, prominent ITZ, a considerable fraction of un-hydrated cement due to lack of proper curing, and durability issues arising from micro cracks due to various combinations of factors (Bentz & Weiss, 2011). IC is an additional curing which supplements conventional curing. The effectiveness of an IC agent depends on the quantity of water IC agent can absorb and release in concrete. Brito and Saikia (2013) reported that recycled aggregates adheres mortar around 16-17%, the water absorption capacity of recycled aggregate is also higher compared to natural aggregate. Recycled aggregates marginally qualifies as an IC agent and is not an effective IC agent because the pore size of the mortar or paste coating on its surface is smaller or of similar size as that of the mix around it. For proper functioning of IC mechanism pore size of the IC agent acting as a water reservoir should be larger than that of the mix around it. This is essential for the capillary pull of absorbed water from IC agent to the desiccating mix around (Bentz & Weiss, 2011).
1.1. Research Objective
The primary objective of the research is to reuse the C&D waste for producing concrete which is viable from laboratory research scale as well as for field practical implementation. To produce sustainable concrete using C&D waste as an IC agent and hence to carry out a parametric study on the five essentials of modern concrete – Workability, Strength, Durability, Micro Structure, and Sustainability. The study also aims to address the contemporary issues of the modern concrete mentioned in conclusion and to propose simple and sustainable remedial measures to overcome limitations of using C&D waste in concrete.
The constraints of using C&D waste as coarse aggregate for making concrete: workability and durability issues have been successfully dealt with by using multiple strategies. Higher DoH should result in higher shrinkage, but in the present study, using multiple strategies the shrinkage in the mix has been restricted successfully in spite of the increase in DoH. Adjusting proportions of coarse aggregate fractions using maximum density method and minimizing voids by using additional fly ash is highly recommended for better strength and durability of concrete. Internal curing should be applied for field applications especially in sub tropical regions it is the grey area of study and scope for future work are as follows: (1) The benefits of using combinations of different size fractions of coarse aggregates, recycled aggregates and fly ash are clearly seen in results of strength and durability. However the evidence that which size fraction of fly ash precisely contributed to which property of concrete in the present study could not be mapped. This calls for a further specific study in some advanced research laboratory; (2) Smaller fractions of coarse aggregate (4.75 mm - 10 mm) can be used which might give some interesting results, as smaller recycled aggregates as an IC agent will have better distribution across the mix. Three replacements (50%, 65% and 80%) using recycled aggregates are tried in the present study however it is expected that even better results exist between 50% and 65% replacements. Further, it is suggested to carry out a similar test using micro step increment of fly ash dose between 5.26% and 11.11%.
Bentz, D.P., Weiss, W.J., 2011. Internal Curing: A 2010 State-of-the-Art Review, National Institute of Standards and Technology, NISTIR 7765, U.S. Dept of Commerce
Bentz, D.P., Lura, P., Roberts, J.W., 2005. Mixture Proportioning for Internal Curing. Concrete International, Volume 27(2), pp. 35–40
Bentz, D.P., Snyder, K.A., 1999. Protected Paste Volume in Concrete: Extension to Internal Curing using Saturated Lightweight Fine Aggregate. Cement and Concrete Research, Volume 29(11) , pp. 1863–1867
Bravo, M., Brito, J., Pontes, J., Evangelista, L., 2015. Durability Performance of Concrete with Recycled Aggregates from Construction and Demolition Waste Plants. Construction and Building Materials, Volume 77, pp. 357–369
Brito, J., Saikia, N., 2013. Recycled Concrete in Aggregate. Springer-Verlag London
Herrera-Durán, A., Mendoza-Rangel, J.M., De-Los-Santos, E.U., Vázquez, F., Valdez, P., Bentz, D.P., 2015. Accelerated and Natural Carbonation of Concretes with Internal Curing and Shrinkage/ Viscosity Modifiers. Materials and Structures, Volume 48(4), pp. 1207–1214
Lam, L., Wong, Y.L., Poon, C.S., 2000. Degree of Hydration and Gel/Space Ratio of High-volume Fly Ash/Cement Systems. Cement and Concrete Research, Volume 30(5), pp. 747–756
Medina, C., Zhu, W., Howind, T., Frías, M., Sánchez de Rojas, M.I., 2015. Effect of the Constituents (Asphalt, Clay Materials, Floating Particles and Fines) of Construction and Demolition Waste on the Properties of Recycled Concretes. Construction and Building Materials, Volume 79, pp. 22–33
Mehta, P.K., Monteiro, P.J.M., 2009. Concrete – Microstructure, Properties and Materials. Third Edition, Tata McGraw Hill
Neville, A.M., 2009. Properties of Concrete. Fourth Impression, Pearson Education
Ramachandran, V., Beaudoin, J.J., 2001. Handbook of Analytical Techniques in Concrete. William Andrew Publishing/Noyes Publications
Silva, R.V., De Brito, J., Dhir, R.K., 2015. Prediction of the Shrinkage Behaviour of Recycled Aggregate Concrete: A Review. Construction and Building Materials Volume 77, pp. 327–339
Yadav, N., Deo, S.V., Ramtekkar, G.D., 2017. Mechanism and Benefits of Internal Curing of Concrete using Light Weight Aggregates and its Future Prospects in Indian Construction Industry. International Journal of Civil Engineering & Technology, Volume 8(5), pp. 323–334
Yadav, N., Deo, S.V., Ramtekkar, G.D., 2018. For Parametric Study of Sustainable Concrete Produced using Marginal Material as an Internal Curing Agent for Partial Replacement of Natural Sand in Subtropical Climate of Central India. International Journal of Advance Research and Development. Volume 3(1),pp. 109–119