Effect of thermomechanically beneficiated recycled concrete aggregates on the mechanical and durability characteristics of concrete Rohit Prajapati, Stefie J. Stephen, Ravindra Gettu, Surender Singh

This paper describes the potential of using thermomechanicallybeneficiated recycled aggregates to replace pristine (natural) aggregates in concrete. The recycled concrete aggregates (RCA) were produced by heating waste concrete chunks at 500ºC and scrubbing in a ball mill. Concretes were made by replacing pristine aggregates with the RCA at different proportions. The properties influencing the performance of concretes, such as compressive and tensile fracture characteristics that govern failure, and the durability characteristics associated with the transport mechanisms governing the service life are assessed. The electrical resistivity of concrete, oxygen permeability and chloride migration, which are parameters related to durability, are seen to be on par with, if not better than, those of the reference concrete. The mechanical response is also comparable, though the strength is slightly lower at higher replacement levels. One of the important outcomes of this study is the feasibility of the complete substitution of river sand by fine RCA without significant loss in performance. The concrete mixture having only coarse and fine beneficiated recycled aggregates was found to be suitable for structural grade applications.

Alkali silica reactivity of cements with manufactured sands obtained through recycling Nisheeth Agnihotri, Vaishali Sahu

Alkali silica reactivity (ASR) is considered as one of the greatest jeopardy to the durability of concrete structures. ASR poses a serious threat to many important concrete structures, specially those dealing with the hydraulic effect, as these conditions offer sufficient moisture, which accelerates the reaction and forms gel having swelling character inside the concrete pore structure. The sustainability of civil structures is directly associated with global environmental challenges. It is also imperative to kerb the carbon footprint involved in construction, extraction of natural resources and production of Portland cement. In recent times, the focus of construction industry has shifted towards more durable and sustainable structures. The present study provides a way forward to utilize recycled concrete aggregate (RCA) as partial to full replacement of quarried natural aggregate (NA). The present study encompasses eight different combinations of RCA and NA to determine the percentage expansion by the accelerated test method caused by ASR. The study also integrates the mitigation measures to be adopted to withstand the deleterious expansion instigated because of ASR.

Experimental investigation using non biodegradable PET as a partial replacement of sand in concrete Monika Dagliya, Rewa Bochare, Divyansh Nekia

Tremendous collection of single use plastic in the form of non-biodegradable solid waste is a major global issue. Plastic ending up in landfills poses a major threat to the environment. To reuse this plastic waste is a persisting challenge for one and all. This study explores the adaptability of using polyethylene terepthalate (PET) as a partial replacement of sand in concrete as well as cement mortar. A group of five concrete and cement mortar mixtures containing PET were prepared as a partial substitute for sand with substitution levels 0, 1, 3, 5, and 10 %. The cubes were tested for compressive strength. The experimental results showed that the compressive strength for a sand replacement ratio of 3 % (28.6 MPa) was comparable to that of the control mix (28.7 MPa). However, a slight dip in the strength was observed from 28.6 to 28.3 MPa when plastic replacement was increased from 3 to 5 %. There was no change found in the flexural strength of concrete for all ratios. The findings show that plastic waste may be disposed off in a calculative manner in specific ratios in concrete and therefore, can be effectively applied in industrial construction usage.

Flexure design of high strength concrete slender shear walls using the limit state design philosophy for reinforced concrete sections as per IRC: 112 (2020) Anasuya Mondal, Santanu Bhanja

IS:456 (2000) provides design methodology for structural concrete up to M60 grade, design parameters for higher grades of concrete are not prescribed by this code. IS: 13920 (2016) can be considered as an add-on standard to IS: 456 (2000) whereby design and detailing of structures subjected to earthquake forces are prescribed. IRC: 112 (2020) prescribes design provisions for high strength concrete from M65 to M90 along with those for normal concrete. The design provisions are in line with those prescribed in the international standards like Eurocode2. IS: 13920 (2016) provides some simplified closed form expressions to calculate the moment capacity of slender rectangular shear wall sections. As the shear walls are subjected to axial compression along with flexure, design should be performed by using P-M interaction charts. The P-M interaction charts for RC shear walls made of concrete up to M60 grade have been recently published in a companion paper. But tools for design of shear walls with concrete grades beyond M60 are not available. In the present paper an attempt has been made to enumerate design principles for high strength concrete and develop P-M interaction charts for high strength concrete shear walls (M65 to M90) using the fundamental principles of limit state philosophy as per IRC: 112 (2020). Total 24 numbers of P-M interaction charts have been proposed which are valid for all high strength concrete and HSD bars of grades Fe415 to Fe600 as permitted by the standard. IS: 456 (2000) has already been taken up for revision and the revised version is expected to be in line with the RC design provisions of IRC: 112 (2020). Hence, the design charts proposed in the present study are expected to cater to the design considerations of the revised version of IS: 456 (2000).

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