Study on the Utility of Recycled Coarse Aggregates in Concrete Introducing Bacteria

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Study on the Utility of Recycled Coarse Aggregates in Concrete Introducing Bacteria

Adul Hadi Jeelani, Er. Brahamjeet Singh, Dr. Sandeep Singla

Department of Civil Engineering, Rimt University

Opposite Floating Restaurant, Sirhind Side, Mandi Gobindgarh-147301, Punjab (INDIA)


:- The construction industry utilizes Portland cement which is known to be a substantial supporter of the CO2 emissions and ecological harm. Incorporation of industrial squanders like demolished old concrete, silica fumes (SF) and fly ash remains (FA) as valuable cementing materials (SCMs) could result in a significant decrease of the general CO2 impression of the last concrete item. Be that as it may, utilization of these beneficial materials in development industry particularly really taking shape of concrete is profoundly testing. Huge research endeavors are required to ponder the building properties of concrete joining such industrial squanders. Present research is a push to examine the properties of concrete joining industrial squanders, for example, demolished concrete.

Recycled coarse aggregate (RCA) concrete development method can be called as 'green concrete', as it limits the ecological danger of the concrete waste disposal. Indian standard prescribes target mean compressive strength of the ordinary concrete as far as water cement ratio (w/c). The conduct of RCA concrete, arranged from two examples of parent concrete having distinctive age gatherings, is researched, to propose the relationship of compressive strength with water cement ratios, in the present investigation. Number of reusing may impact the mechanical properties of RCA concrete. The impact of age and number of reusing on the properties, for example, capillary water absorption, drying shrinkage strain, air content, flexural strength and tensile splitting strength of the RCA concrete are analyzed. While the compressive strength diminishes with number of reusing step by step, the capillary water absorption increments unexpectedly, which prompts the end that further reusing may not be advisable.

Past examinations demonstrate that the properties of RCA concrete are sub-par in quality contrasted with NCA concrete. The enhancement of properties of RCA concrete with the expansion of two ureolytic-type bacteria, Bacillus subtilis and Bacillus sphaericus to upgrade the properties of RCA concrete. The test examinations are completed to assess the enhancement of the compressive strength, capillary water absorption and drying shrinkage of RCA concrete joining bacteria. The compressive strengths of RCA concrete are observed to be expanded by about 20% and 35% at the cell concentrations of 106 cells/ml for the two bacteria. The capillary water absorption just as drying shrinkage of RCA are diminished when bacteria is consolidated.


Most of the engineering constructions are not friendly to the environment. The construction industries use Portland cement which is a major contributor to the CO2 emissions

and environmental damage. The amount of construction in India has increased rapidly since the last twenty years. Thus, by using different kinds of supplementary cementing materials (SCMs), especially SF and FA as cement replacement could result in a significant reduction in the overall CO2 footprint of the final concrete product. Lesser the quantity of Portland cement used in concrete production, lesser will be the impact of the concrete/construction industry on our environment.

The utilization of demolished concrete, SF and FA in the construction industry is more holistic as it contributes to the ecological balance. However, the utilization of these waste materials in the construction industry especially in the making of concrete is highly challenging. Significant research efforts are needed in order to study the engineering properties of concrete made of these industrial wastes.

The demolished concrete can be utilized as recycled coarse aggregate (RCA) in order to make a new concrete (RCA concrete) by either partially or fully replacing the natural coarse aggregate (NCA). Many researchers have examined the physical and mechanical properties of RCA concrete and have concluded that the mechanical strength of RCA concrete is less as compared to that of conventional concrete with NCA. This is because of the highly porous nature of the RCA compared to NCA and the amount of replacement of NCA [Rahal 2007].


The major objective of the research work is the investigation of the properties of concrete made using these alternative materials (i.e RCA) and its possible improvement. The sub-objectives to achieve the major goal are as follows :

  1. To study the relationship of w/c ratio and compressive strength of RCA concrete.

  2. To study the improvement of engineering properties of RCA concrete using bacteria.


In order to achieve the above objectives following step by step methodology is adopted:

  1. Prepare RCA from demolished concrete, prepare test specimens and perform different tests to evaluate the effect of age and number of recycling on the properties of RCA concrete.

  2. Incorporate the bacteria on the RCA concrete to enhance the properties.


  1. Compressive Strength test

  2. Tensile Splitting Strength test

  3. Flexural Strength test

  4. Capillary Water Absorption test

  5. Drying Shrinkage test

  6. Air content test


The following specific conclusions are drawn from the research:

Conduct of RCA concrete

The compressive strength of concrete arranged from more seasoned (2 years, RC-2) aggregate is observed to be bring down in comparison to RC1 (1-year-old). The decrease of compressive strength was about 6%. The decrease in compressive strength was most likely higher measure of followed permeable mortar which diminishes the strength of aggregate altogether.

The strength of NCA concrete is higher than RCA concrete at lower w/c ratios. Nonetheless, an inversion of this pattern, for example RCA concrete shows higher compressive strength than NCA concrete after a specific limit w/c ratio. The present examination found that the RCA concrete requires a limit least amount of water contingent on the parent clung mortar to add to the strength. This base amount of water as far as w/c ratio for RC-1 and RC-2 was about 0.37 and 0.42 individually. So as to get higher compressive strength for RCA (than NCA), w/c ratio ought to be higher than the previously mentioned least breaking points.

The compressive strength of concrete after progressive (multiple times) reusing, N2-RC-1 is not as much as that of

RC-1 (once) and the decline in strength of N2-RC-1 is about 2% contrasted with that of RC-1. N2-RC-1 indicates higher compressive strength than NCA for w/c ratios higher than 0.42. The progressive reusing lessens the nature of the followed mortar and this might be explanation behind the decline in strength after further reusing.

Capillary water absorptions of RC-1 and RC-2 concrete are about 11% and 76% more contrasted with that of NCA. It is discovered that the capillary water absorption of N2- RC-1 is around multiple times bigger than both RC-1 and NCA concrete. This sudden increment of water absorption conduct of N2-RC-1 prompts reason that progressive reusing may yield low quality of aggregates that may not suit for concrete.

The drying shrinkage strain of RC-1 and RC-2 are about

1.9 and 2.6 occasions more than that of NCA concrete individually though that of progressive recycled concrete, N2-RC-1 is about 1.2 occasions more than RC-1, which demonstrates that progressive reusing builds the drying shrinkage strain of concrete.

Air contents of RC-2 and N2-RC-1 are observed to be higher than that of NCA and RC-1.

While the decline in splitting tensile strength of RC-2 concrete contrasted with RC-1 is in the scope of 14-28%, the equivalent in flexural strength is in the scope of 6% to 21%. The progressive reusing lessens the splitting tensile strength and flexural strength by 6% and 12% separately.

Enhancement of RCA concrete utilizing bacteria

Properties of RCA concrete, for example, compressive strength, capillary water absorption and drying shrinkage are enhanced by the expansion of B. subtilis bacteria.

The compressive strength of RCA concrete at 28 days is observed to be expanded by 20.93% for B. subtilis (B-3a) and 35.87% for B. sphaericus (B-3b) regarding RCA control blend at an ideal cell concentration of 106 cells/ml. Both bacillus bacteria assume crucial jobs for augmentation in compressive strength of RCA concrete because of the calcium carbonate precipitation in the pores.

Both bacteria decline the drying shrinkage strain and capillary water absorption of RCA concrete and accordingly upgrades the strength. This can be ascribed to denser RCA concrete shaped by bacterial movement.

Air content in bacterial RCA concretes are observed to be marginally more than control blend RCA concrete amid the underlying phase of blending. This can be decreased maybe by expanding the blending time to enable the additional air to leave the concrete blend. Summed up ends on this angle require further research.

Fig 1: Correlation between w/c ratio and compressive strength.

Table 1. Drying Shrinkage

Table 2. Air content of RC-1, RC-2, N2-RC1 and NCA samples

Table 3. Splitting tensile and flexural strength of RCA concrete

Table 4. Effect of bacteria on compressive strength (MPa) at 7 & 28 days


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