Recycled aggregate concrete

1. MODIFIED RECYCLED AGGREGATE
CONCRETE
- CHANDAN & KANAV
1

2. 2
TABLE OF CONTENT
 OBJECTIVE
 INTRODUCTION
 SUMMARY
 METHODOLOGY
 CONCLUSION
 REFERENCES

3. 3
OBJECTIVE
 some common objective for modified RAC include:
 Enhancing Quality
 Removing Contaminants
 Gradation Control
 Improving Strength and Durability
 These all modifications results in better performance, increased sustainability, and
broader utilization of recycled aggregates in the construction industry.

4. 4
INTRODUCTION
 Modification in recycled aggregate concrete (RAC) refers to the application of various techniques
or treatments to enhance the properties and performance of concrete made with recycled
aggregates.
 Modifications aim to overcome the challenges posed by recycled aggregates, such as higher
porosity, weaker interfacial transition zone, and variable quality.
 By improving the properties of recycled aggregate concrete, modifications enable its wider
application in construction while promoting sustainability and resource conservation.

5. 5
SUMMARY
 Various Researches have been focusing on various modifications to enhance the performance of
RAC such as :
 The use of supplementary cementitious materials (SCMs) as fly ash, slag, or silica fume. These materials
can improve the workability, strength, and durability of RAC by enhancing the cementitious properties and
reducing the porosity of the concrete matrix.
 The incorporation of chemical admixtures, such as superplasticizers and viscosity-modifying agents. These
admixtures can enhance the flowability and workability of RAC, allowing for better compaction and reduced
segregation.
 Fiber reinforcement can be added to RAC to enhance its toughness, crack resistance, and flexural strength.
Fibers such as steel, polypropylene, or glass can effectively distribute the stresses and inhibit crack
propagation within the concrete, leading to improved overall performance.

6. 6
 Optimizing the mix design and proportioning of RAC is crucial. The proper combination
of aggregates, cementitious materials, water-cement ratio, and other additives can
significantly influence the properties of RAC.
 These modifications aim to overcome the limitations of RAC, improve its mechanical
properties, enhance durability, and promote its widespread usage as a sustainable
construction material.

7. 7
METHODOLOGY
 REMOVAL OF ATTACHED MORTAR OF RCA
 The Acid is used to dissolve and breakdown the mortar ,allowing it to be
removed from the recycled aggregate and retains the form of RCA, without
damaging the internal structure.
 Acid interacts with concrete three major reactions are triggered.
 Firstly, the hydration products react with acid, forming dissolved ions, thus
losing the mortar adhered to the NA; this reaction is called Acidolysis.
 Secondly, depending on the type of acid insoluble salts form and precipitate,
causing expansion and cracking of concrete waste.
 Third reactions create complexes with calcium, aluminum, iron, and silicate
ions, which produce much higher concentrations of these ions in the solution
that would otherwise lead to dissolution.

8. 8
 MICROSCOPIC VIEW OF ACIDOLYSIS

9. 9
 PERFORMANCE EFFECT ON RAC USING NYLON FIBER.
 MATERIAL - Ordinary Portland cement , Crushed stone aggregate (CA) and recycled coarse aggregate
(RA), nylon fibers (NF) , polycarboxylate-based superplasticizer (SP) was used to improve the initially low
workability of the fresh concrete.
 compressive strength ratio (CSR) of concrete mixes at 7, 28 and 91 days was calculated resulting in a
reduction of micro-cracks. Approximately 11.5% increase in the compressive strength of concrete with 0.6
kg/m3 of NF content, compared to concrete without NF ,clearly observed that the CSR increased when the
NF contents increased.
METHODOLOGY

10. 10
 Split Tensile Strength:
 The strength results showed that there was a great increase in the split tensile
strength values with the addition of NF up to 1.2 kg/m3 in both the CAC and RAC
mixes at 7,28,91 days.

11. 11
CONCLUSION
 The main conclusions of the papers were :
 RCA has seen improvements in its physical and mechanical characteristics when
treated with solutions at low concentrations, e.g., improving water absorption, density,
and RCA surface.
 Concrete mixes that contain treated RCA showed better mechanical behavior than
those incorporating RCA without treatment. Thanks to the removal of the paste and
improvement of the ITZ between RCA and the new cement paste, higher tensile
strength, elasticity modulus, and tensile strength are achieved. In terms of durability,
treated RCA mixes had better values than untreated RCA ones.
 From the literature review carried out, it can be concluded that the use of acids as a
treatment for improving the physical and mechanical properties of RCAs can be an
optimal
solution, depending on the environment to which the concrete will be exposed. An
option

12. 12
CONCLUSION
 Due to the adhered mortar in RA, the compressive strength values of the RAC mixes were significantly
lower than those of the CAC mixes. However, we found that the addition of NF led to an increase in
compressive strength of both the CAC and RAC mixes. In particular, this trend was more remarkable in
the RAC mixes with a high content of NF. The compressive strength ratio results revealed that there
was a beneficial effect of NF on the increase in compressive strength.
 The Test results revealed that there was a significant increase in the split tensile strength, especially
with the addition of 1.2 kg/m3 NF, regardless of concrete types. In the case of the RAC3 mix, we
examined an increase of 80.6% in the split tensile strength over the RAC1 mix without NF
 Within the scope of this study, we can conclude that the addition of NF enhanced the permeability as
well as the mechanical properties, especially in concrete incorporating RA. The enhancement is
primarily attributed to the bridge effect of NF, which allowed for a higher development of strength
and concrete density.

13. 13
REFERENCES
1. Improvement of the Quality of Recycled Concrete Aggregate Subjected to Chemical Treatments:
A Review - Javier A. Forero 1,2 , Jorge de Brito 2 , Luís Evangelista 3,* and Cláudio Pereira .
Published: 8 April 2022
Link - https://doi.org/10.3390/ ma15082740.
2. Effect of Nylon Fiber Addition on the Performance of Recycled Aggregate Concrete: Seungtae
Lee
Department of Civil Engineering, Kunsan National University, Kunsan 54150, Korea.
Published: 22 February 2019
Link - https://doi.org/10.3390/app9040767