Dr. Lakshmy Parameswaran, Chief Scientist (Retd), BES Division
Prof. Manoranjan Parida, Director, CSIR-Central Road Research Institute, New Delhi
Effects of Creep on Concrete
It can be said that ever since the publication of the document of World Commission on Environment and Development , the focus of the world has diverted towards sustainability. Gro Harlem Bruntland  defined sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”
Although sustainability issues concern all fields of science and technology, the omnipresent construction activities attract attention of all, and the sustainability issues related to the same are debated and discussed more often. It is well known that concrete is primarily made up of Portland cement, coarse and fine aggregates, and steel reinforcement. The production process of the major components of concrete are considered unsustainable. This paper is therefore aimed at deliberating the sustainability issues related to cement concrete and some of the results from research carried out at CSIR-. Central Road Research Institute (CSIR-CRRI) in this regard.
The projected growth of global market for cement from US $ 326.81 billion in 2021 to US $ 340.61 billion in 2022, and to US $481.73 billion by 2029, at a Compound Annual Growth Rate (CAGR) of 5.1% , clearly indicates that the construction activity is poised to grow at a rapid pace.
Different estimates of CO2 emissions have been reported for the manufacture of cement. International Energy Agency  estimated that one ton of cement produces about 0.5-0.6 ton of CO2. Another report estimated the same to be 0.6-0.7 ton of CO2. On an average, the cement industry contributes to about 7-8% of the total CO2 emission in the world. Reducing cement consumption in concrete is one among many sustainable options available to engineers in order to reduce the CO2 emissions.
Replacing ordinary Portland cement (OPC) with supplementary cementitious materials (SCM’s) in concrete is recognized as a viable option to reduce CO2 emissions. IS 456:2000  recommends the use of SCM’s such as fly ash, silica fume, ground granulated blast furnace slag, metakaolin, and rice husk ash, as part replacement of OPC in concrete. The Portland cements containing blends of OPC and one or more of the above SCM’s such as Portland pozzolana cement , Portland slag cement  and composite cement  are also being manufactured. Composite cement is coved in IS 16415.
The proportion of widely available SCM i.e., fly ash, is recommended up to a maximum of 35% in the PPC, although in reality fly ash content in PPC generally varies between 22-27%. Concrete made with fly ash replacements of more than 40% is often called High Volume Fly Ash Concrete (HVFAC). However, it may be noted that as the fly ash (in as available form) content in concrete increases, the performance of concrete at early ages decreases. The HVFAC fails to achieve high early age strength, resulting in longer periods of retention of formwork, loading etc. In this connection an attempt was made in CSIR-Central Road Research Institute (CSIR-CRRI) to develop High Early Strength-High Volume Fly Ash Concrete (HES-HVFAC) [8,9]. It was demonstrated that a HVFAC with fly ash content up to 70% can be prepared exhibiting a 28 day compressive strength as good as that of a 100% OPC concrete, by adding nanosilica up to 3% by weight of cement. This indicates that higher proportions of un-processed fly ash can used to obtain concrete exhibiting satisfactory mechanical and durability performance. Figure 1 shows variation of compressive strength of HVFAC made with and without nanosilica and fly ash content varying from 50 to 80%, Figure 2 shows the results of Rapid Chloride Permeability Test (RCPT).
Natural aggregate imparts to concrete its dimensional and volumetric stability. Aggregates are generally more durable and stable of the materials incorporated into concrete mixtures, and thus provide durability. Aggregates occupy about 3/4th of the volume of concrete. The global aggregates market size was valued at US $ 463.3 billion in 2019, and the CAGR is expected be 3.3% during 2020 -2027. Crushed stone led the global market and accounted for a revenue share of 58.1% in 2019. The demand for aggregates in India also has increased exponentially from 1000 MT in 2000 to 6000 MT in 2020 , and the same for crushed stones increased from 400 to 2050 MT during 2000- 2020. Apart from concrete, the coarse aggregate required as road base material is poised to increase, in view of the Indian government’s commitment to build large lengths of roads on daily basis. Aggregates are produced through large scale exploitation of natural resources. But, if the same continues the way it is, it will soon result in environmental and ecological imbalance, and requires alternatives to natural aggregates to maintain sustainability. Some of the alternatives to the natural aggregates are Recycled Aggregates from C&D Waste, Blast Furnace Slag, Fly ash aggregates, Foundry sand, Lead Slag, Plastic waste, Rubber waste, and Geo-polymer Aggregates.
A research study carried out in CSIR-CRRI showed that Recycled Concrete Aggregate (RCA) (generated from crushing of laboratory tested concrete specimen) can be used as partial replacement of natural aggregate for the production of structural concrete [11,12]. The IS mix design method IS 10262-2005 was modified to develop the mix proportions and produce a structural concrete with RCA exhibiting satisfactory performance. Figure 3 shows the compressive strength of concrete made with RCA at 50%, 75% and 100% (all with added fly ash) along with that of concrete made with 100 % natural aggregate (with and without fly ash). The e RCA used had a relatively lower adhered mortar (average of all sizes was 20%). The concrete produced exhibited satisfactory durability also (Figure 4).
A further study was carried out [13,14] to investigate properties of self-compacting concrete (SCC) made with RCA. Coarse RCA (CRCA) for this study was collected from a C&D Waste treatment plant in Delhi. The CRCA was used without any further processing. The average adhered mortar content on 10-20 mm size aggregate was determined as 29%, and that on 10-4.75 mm size aggregate as 50%. The IS-383 recommends a proportion of 20% of RCA in conventional RCC mixes. The aggregate proportions for this investigation were obtained by following aggregate packing density method to obtain an optimum RCA proportion in the total coarse aggregate (Fig.5). Two grades of concrete, i.e., 40 MPa and 60 MPa were prepared. A total of four mixes per each grade of concrete were prepared (SCC with 100% Natural aggregates, and 20%, 45% CRCA in total coarse aggregate, and 100% CRCA). SCC mixes with aggregate proportions different from the optimum aggregate proportions were also made for comparative study purposes. The SCC-CRCA mixes made with optimum aggregate proportions exhibited satisfactory flow, mechanical and durability properties. Figures 6 and 7 show the slump flow and compressive strength of the SCC-CRCA mixes, respectively. It was concluded that CRCA can be used up to 45% as a replacement of natural aggregates for preparing SCC. This proportion is higher than that recommended in IS-383 for conventional RCC.
Plastic is widely known to provide corrosion protection. The Indian Roads Concrete (IRC) has recently approved a document on use of Fibre Reinforced Plastic (FRP) bars as reinforcement in RCC . An Indian Standard on GFRP bars is also under preparation.
The sustainability issues related to materials in concrete construction are discussed in this paper, and some results of research carried out in CSIR-Central Road Research Institute in this regard are presented. Emission of carbon dioxide during the manufacture of cement, destruction of natural resources during extraction of natural aggregates, destruction of concrete structures due to corrosion are indicated. Salient properties of High Early Strength-High Volume Fly Ash Concrete, structural grade concrete made with recycled concrete aggregate, structural grade self-compacting concrete made with recycled concrete aggregates-proportioned by aggregate packing density, are presented. The study on performance evaluation of protective coatings/special steel bars undergoing at CSIR-CRRI is also mentioned.
- Gro Harlem Bruntland , World Commission on Environment and Development (WCED)Our common future. Oxford: Oxford University Press, p. 43. 1987.
- IS 456-2000., Indian standard – Plain and Reinforced Concrete – Code of Practice – (Reaffirmed 2021), Bureau of Indian Standards, New Delhi.
- IS 1489-2015., Indian Standard Portland Pozzolana Cement – Pt. 1-Fly ash based (Reaffirmed 2020), Bureau of Indian Standards, New Delhi
- IS 455-2015., Indian Standard Portland Slag Cement (Reaffirmed 2020), Bureau of Indian Standards, New Delhi
- IS 16415-2015., Indian Standard Composite Cement-Specification (Reaffirmed 2020), Bureau of Indian Standards, New Delhi
- Lincy Varghese, “Characterization of High Volume Siliceous Fly Ash Concrete containing Colloidal Nanosilica”, Ph.D Thesis, AcSIR-CRRI, 2019
- Lincy Varghese, Kanta Rao, V.V.L., and Lakshmy, P., “Properties of concrete with high volumes of unprocessed coarser fly ash and nanosilica”, Engineering Sustainability-Proceedings of the Institute of Civil Engineers , Vol. 175, No. 2, April, 2022, pp. 96-110.
- Venkataram Reddy, B.V., Hemanth Kumar H, Ullas, S.N. and Gourav, K., “Non-organic solid wastes – potential resource for construction materials”, Current Science, Vol 111, No. 12, p. 1968-1976, December 2016.
- Surya Maruthupandian, “Experimental investigation on structural properties of recycled aggregate concrete”, M.Tech. Thesis, AcSIR-CRRI, 2013
- Surya, M., Kanta Rao, V.V.L., and Lakshmy, P. “Mechanical, Durability and Time Dependant Properties of Recycled Aggregate Concrete with Fly Ash”, Materials Journal- ACI, Vol 112, No. 5, P . 653-667, 2015, American Concrete Institute, USA
- Dinesh Kumar Sharma, “A Study on Flow, Mechanical and Durability Properties of Self Compacting Concrete Containing Coarse Recycled Concrete Aggregate”, Ph.D. Thesis, AcSIR-CRRI, 2022
- Dinesh Kumar Sharma, Kanta Rao, V.V.L. and Lakshmy, P. “Flow, Mechanical and Durability Properties of 40 MPa Self Compacting Concrete Containing Coarse Recycled Concrete Aggregate”, International Conference on Ecstasy in Concrete (ACECON), Organised by Indian Concrete Institute, 24-25, September 2022, New Delhi.
- IS 13620-1993, “Indian Standard on Fusion Bonded Epoxy Coated Reinforcing bars-Specification”, (Reaffirmed 2020), Bureau of Indian Standards, New Delhi.
- IS 12594-1988 “Indian Standard on Hot-dip galvanized structural steel bars for concrete reinforcement- specification”, (Reaffirmed 2001), Bureau of Indian Standards, New Delhi.
- IS 16651-2017, Indian Standard high strength, deformed stainless steel bars and wires for concrete reinforcement-Specification, (Reaffirmed 2022), Bureau of Indian Standards, New Delhi.
- IRC 137-2022, “Guidelines on use of Fibre-Reinforced Polymer bars in Road Projects (Part1:Glass Fibre Reinforced Polymer Bars)”, Indian Roads Congress, New Delhi.