Self Compacting Concrete using Recycled Aggregate in Fresh and Hardened State

Construction and Demolition waste management issues have attracted researchers around the world. The boom in construction sector and large-scale mechanization in concrete production has led to setting up of several ready-mixed-concrete (RMC) plants. The present study aimed at producing fine and coarse aggregates from the hardened concrete waste available at the RMC plant on the outskirts of Bangalore. The material characterization for both fine and coarse aggregates was carried out as per IS: 2386 (Part IV) – 1963. The test results have shown that the properties of recycled aggregates satisfy the codal provisions specified for natural aggregates. The M-20 self compacting concrete mix with 0%, 25%, 50%, 75% and 100% replacement of fine and coarse aggregates were done separately in two batches. Third batch mixes consists of both fine and coarse aggregates replacement of 0%, 25%, 50%, 75% and 100%. Further the fresh and hardened properties of M-20 self compacting concrete mix has been carried out systematically. It was observed that 50% replacements in all the three batches of M-20 concrete mix have exhibited satisfactory flow and compressive strength values. Keywords— Recycled aggregates, RMC hardened concrete waste, river sand, self compacting concrete, partial-to-full replacement, workability, strength.


INTRODUCTION
Concrete is the most widely used material in the world and due to the advancement in the technology the RMC (Ready Mixed Concrete) usage is increasing. Nowadays no civil engineering projects will be undertaken without RMC, thus influencing the construction sector in a big way. It also decreases site supervising, labour cost and project time, thereby resulting in savings, proper quality control and economy in the use of raw materials. At the same time it has been observed that huge volumes of RMC waste is being piled up in RMC yards as shown in Fig. 1. RMC plants around the world are increasing day by day to accommodate to the increasing demands of the construction. But at the same time the wastage at every RMC plant is on the rise. Also the number of dumping sites is depleting. Due to this reason, these waste aggregates are used as recycled aggregates to attain sustainability. The transformation of this waste into RA (Recycled Aggregates) is an important step in the development of a more sustainable environment. Using RA in concrete is an alternative to dumping it and also helps in the sustainability of natural aggregates reserves. Recycling of concrete is very much necessary from the view point of environmental preservation and effective utilization of resources. The utilization of recycled aggregate in the concrete production is limited at present and large portion of concrete waste gets piled up at disposal sites. Using these RMC wastes in concrete is a challenging issue for engineers and many research works are still going on. Concrete is the most widely consumed construction material in the world. Placing of the conventional concrete requires skilled operatives using slow, heavy, noisy, expensive, energyconsuming and often dangerous mechanical vibration to ensure adequate compaction to obtain the full strength and durability of the hardened concrete. It was against this background that SCC (Self Compacting Concrete), which eliminates the need for compaction, was developed in Japan in late 1980s. The concept of SCC was proposed in 1986 by Professor Hajime Okamura, but the prototype was first developed in 1988 in Japan, by Professor Ozawa at the University of Tokyo. SCC is an innovative concrete, as the name itself signifies concrete that flow or pass and compact under its own weight without any vibration or compaction. When a huge amount of heavy reinforcement is to be placed in a reinforced concrete member, it is difficult to ensure that the formwork gets entirely filled with concrete, i.e., fully compacted without voids or honeycombs. This can be solved by SCC, which flows like honey that can pass around obstructions and fill all the nooks and corner without the risk of segregation or honey combs, giving a very smooth surface finish. Selfcompacting concrete is a fluid mixture, which is proper for placing it in difficult conditions and also in packed reinforcements, without any vibration. The SCC must:

A Study on the Properties of
 Contain a fluidity that allows selfcompaction without external vibration  Maintain homogeneous in a structure during and after the placing process and  Flow easily throughout reinforcement The use of SCC is gradually becoming more popular in Canada and USA. Some of the departments of transportation are currently accepting SCC in mix design in some of their projects. On the other hand, since SCC is a relatively new concrete, its durability & mechanical properties are not completely understood. European countries recognized the significance and potentials of SCC developed in Japan. During 1989, they founded European federations of natural trade association representing producers and applicators specialists building products (EFNARC). The utilization of self compacting concrete started growing rapidly. Most of the information particularly mix design guidelines for SCC is taken from EFNARC for this project. The main objective of this project is to develop, evaluate and compare the fresh and mechanical properties of new types of SCC mixtures incorporating RA.

II. OBJECTIVES
The main objective of present work is:- To determine the properties of RFA (Recycled Fine Aggregates) and RCA (Recycled Coarse Aggregates) obtained from RMC plant waste.  To propose a mix design of M-20 SCC using particular pro-portions of RA.  To determine the workability of self compacting concrete using chemical admixtures and recycled coarse and fine aggregates.  To determine the compressive strength, tensile strength and flexural strength of SCC using RCA and RFA.

III. METHODOLGY
The study has been divided into two parts:- In the first part, the material characterization of the recycled aggregates as per Indian standards was conducted.  In the second part, the suitability of RFA and RCA in M-20 self compacting concrete mix was investigated.  Table 1 and Table 2   Both the test results have shown that the properties of recycled aggregates satisfy the codal provisions specified for natural aggregates except that the water absorption of recycled aggregate (RA) was higher than the values for natural aggregates (NA).
The mix with OPC and fly ash are considered. Three batches of M-20 mix were prepared:- Batch-1 mixes has OPC and natural coarse aggregates (NCA) as determined in the mix design.
Only the fine aggregates were substituted with the recycled fine aggregates in proportions of 25%, 50%, 75% and 100% replacement for natural fine aggregates.  Batch-2, OPC and natural fine aggregates are taken as per mix design. However the coarse aggregates were substituted with RCA in the range of 25%, 50%, 75% and 100% replacement to natural coarse aggregates.  Batch-3 comprised of OPC, recycled fine aggregates and recycled coarse aggregates in varying proportions of 25%-25%, 50%-50%, 75%-25% and 100%-100% replacement for natural fine and coarse aggregate.
The mix design for M-20 of self compacting concrete using the unprocessed crushed aggregates was done as per "The European specification and guidelines for self compacting concrete". As per mix design, the cement, water and the aggregates required for 1m 3 of concrete is as shown in Table 3:     It can be observed that the slump flow decreases from 740mm (0% replacement) to 500mm slump for 100% replacement.

A. Tests on Fresh Property
From the above graph results, it is concluded that Batch-2 mix showed the good results than Batch-1 & Batch-3. Same pattern of results are observed in B-1 & B-2 whereas substantial decrease in values of flow are seen in batch-3 for higher replacements. This is mainly due to the reduction of the free water content in SCC mix due to the high water absorption of recycled aggregate. Also, the greater surface roughness and angularity of recycled aggregate enhance the friction between cement paste & coarse aggregates. These 2 effects are more prevailing for high percentages of recycled aggregate. Due to this, the SCC mixes with 75% and 100% recycled aggregate became more viscous and showed a lower slump flow values. This is attributed to decrease in the free water content in the Self Compacting Concrete mix due to the high absorption of water by recycled aggregates.   Fig. 8 i.e with increase in the % of replacement of NFA by RFA the strength decreases from 27.56MPa to 15.99Mpa.   From the above chart results, it is concluded that Batch-1 blend showed better results than Batch-2 & Batch-3. Same pattern of results are observed in B-1 & B-2 whereas substantial decrease in values of strength are seen in batch-3 for higher replacements. The compressive strength of all the mixes developed at early stages is lower than that of the normal concrete mix.

V. CONCLUSION
The following are the conclusions which are drawn from the experimental results: 1. From the current study it is observed that the properties of RCA and RFA are equivalent to that of NCA and NFA with the exception of water absorption value & a low density values. 2. Compressive strength are close to that of normal concrete in both Batch-1 and batch-2 mix. 100% replacement in both batches showed least strength i.e decreased by 30.4% (batch-1) and 45.64% (batch-2) 3. In Batch-3 mix, concrete mix with 100% and 100% replacement of RFA and RCA has showed the least strength i.e decreased by 55.3%. While considering flow and strength values, 50% replacement can be taken as the optimum mix. 4. The density of hardened concrete slightly decreased as the rate of replacement by recycled aggregate increased, since the RCA presented a lower density compared to NCA surface. 5. Considering flow and strength values, 50% replacement can be considered as the optimum mix in all the three batches.