The chapter delves into the application of recycled cement concrete as an aggregate in polymer composites, focusing on the feasibility and benefits of this eco-friendly approach. It begins by discussing the global challenges of waste management and resource depletion in the construction industry, emphasizing the need for sustainable practices. The study then introduces the concept of using recycled aggregate in polymer concrete, which offers advantages such as high strength, corrosion resistance, and rapid hardening. The experimental design and methods used to prepare and test polymer concrete samples with varying levels of recycled aggregate replacement are detailed. The results show that recycled aggregate does not negatively impact the technological or strength characteristics of the composites, with some samples even exhibiting enhanced compressive strength. The chapter concludes by highlighting the potential of recycled aggregate in polymer concretes for reducing the carbon footprint and promoting a closed-cycle economy, while also suggesting areas for further research.
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Abstract
Over the years, the development of sustainable and ecofriendly concrete has been found in the reuse of construction and demolition materials. One such waste is recycled aggregate from cement concrete structure demolition process. This paper analyzes the effect of substitution of natural stone aggregate with recycled aggregate in polymer composites. An experimental plan for the mixtures was prepared. Technological characteristics (setting course, consistency) and strength characteristics (flexural strength and compressive strength) were analyzed. The obtained results were statistically analyzed. A generalized utility function has been established. Based on it, the maximum dosage of recycled aggregate was determined without significant deterioration of technological and strength characteristics. The average compressive strength results obtained were in the range of 88.5 to 96.5 MPa. The highest compressive strength value (96.5 MPa) was obtained for the samples with the composition with the highest proportion of recycled aggregate.
1 Introduction
Increasing climate challenges and a limited supply of new natural resources for construction projects have shifted research toward sustainability. The concept of circular economy is one of the effective ways to achieve a long-term sustainable construction sector [1‐4]. At the same time huge amount of construction and demolition wastes are produced every year. In Poland, these wastes are usually sent to landfills [5]. The disposal of these wastes is a severe social and environmental problem. The recycling of these wastes as aggregate to produce building composites can reduce the problem of waste and help the preservation of natural aggregate resources. Many researchers found that recycled aggregate offers a good alternative aggregate for making concrete in terms of both environment friendly and economically, also taking into account the LCA analysis [6‐8].
It should also be taken into account that polymer concrete is widely use in building industry composite with its low carbon footprint compared to the cement concrete. Polymer concrete wide application results from its performing properties like high strength, excellent corrosion resistance, frost resistance, good abrasion behavior, rapid hardening and easy preparation [9‐12]. There is usually no reactivity between the surrounding polymer matrix and aggregate particles [13]. Therefore, the replacement of natural aggregates in the production of polymer concrete is a very effective method of waste material waste disposal which preserves natural resources. There are many studies on the effective use of waste dusty materials [14, 15] and plastic waste [16, 17], as an ingredient in polymer concrete.
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Due to the carbonation that occurs [18, 19], the use of recycled cementitious aggregate for the production of cement concrete is limited, as it could contribute to the corrosion of reinforcing steel. With polymer concrete, this problem does not occur. The use of concrete CDW aggregate to produce polymer concrete could be economically as well as environmentally beneficial. In the study presented in this paper, an attempt was made to replace part of the coarse aggregate with recycled aggregate, mainly containing crushed cement concrete.
2 Materials and Methods
The purpose of the conducted research was to determine the impact of partial substitution of the coarse aggregate by the recycled aggregate. Polymer concrete samples were prepared according to the experimental design. The prepared samples were subjected to the following tests: consistency, compressive and flexural strength and density.
2.1 Materials
The polymer used to prepare all composites presented in the study was synthetic vinyl-ester resin of low viscosity (350 ± 50 mPa·s at 25 ℃) and high flexural strength and tensile strength (declared by the producer as respectively 110 MPa and 75 MPa). Therefore, concretes made from this resin should retain the high mechanical strength in long-term exploitation, even when exposed to aggressive environment.
As virgin coarse aggregates, two size fractions were used, one with aggregate size 2–4 mm (2–4N) and the other with 4–8 mm (4–8N) with a fineness modulus of 5.56 and 5.63 respectively. Both of which are from natural gravel. Furthermore, recycled coarse aggregates obtained from the demolition of concrete structures were used, so they mainly consisted of aggregates with adhered mortar. The size fraction was 4–8 mm (4–8R) with a fineness modulus of 6.95. Lastly, the fine aggregate was just a natural sand with a maximum aggregate size of 2 mm (0–2N) and a fineness modulus of 4.70.
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As the microfiller the limestone powder (LP) was used. Table 1 summarizes the basic properties of the aggregates used. Figure 1 exhibits the composition of the recycled coarse aggregates according to EN 933-11. The recycled aggregate consisted mainly of crushed cement concrete (Rc = 88.5%).
On the basis of these results, they can be classified as recycled coarse aggregates from concrete demolition waste and named as RCA (recycled concrete aggregate).
Five different concrete compositions were adopted for the study, differing in the level of replacement of natural aggregate (4-8N) with recycled aggregate (4-8R) from 0% to 100%. A constant resin/microfiller ratio of 1.0 was assumed. A constant resin content of 300 kg was determined. The recycled aggregate was washed on a 0.125 mm sieve and then dried in a drying oven at 100 ℃ for 48 h. The mass compositions of the composites per cubic meter are summarized in Table 2.
Table 1.
Basic properties of the aggregate. LP- limestone powder, 0-2N natural sand, 2-4N, 4-8N natural gravel, 4-8R recycled aggregate.
Property
LP
0-2N
2-4N
4-8N
4-8R
Density (EN 1097–6), g/cm3
2.71
2.54
2.64
2.67
2.53
Density in owen-dry conditions (EN 1097–6), g/cm3
-
2.13
2.46
2.60
2.25
Water absorption (EN 1097–6), %
-
7.5
2.8
1.2
4.8
Los Angeles Abrasion (EN 1097–2), %
-
-
27.0
25.0
75.0
Fines percentage (EN 933–1), %
100
1.0
0.1
0.1
0.9
Fig. 1.
Composition of recycled coarse aggregate according to EN 933–1 (percentage by weight)
Table 2.
Composites composition
In weight
R00
R10
R20
R30
R40
Synthetic vinyl-ester resin, kg
300
300
300
300
300
Limestone powder, kg
300
300
300
300
300
Natural sand (0-2N), kg
600
600
600
600
600
Gravel (2-4N), kg
300
300
300
300
300
Gravel (4-8N), kg
600
450
300
150
0
Recycled aggregate (4-8R), kg
0
150
300
450
600
RA in total aggregate, %
0
10
20
30
40
Gravel replacement, %
0
25
50
75
100
×
2.2 Methods
The consistency of the mixture was assessed according to the procedure for measuring the plasticity of construction mortars (according to PN-EN 1015-3 standard), just after mixing the ingredients. A truncated cone (with dimensions: bottom diameter 100 mm, top diameter 70 mm, height 60 mm) was formed on the flow table. The fresh composite thus formed was subjected to 15 generative shakes by lifting and dropping the measuring table to a height of 10 mm at a rate of 1 per second). The diameter of resulting flow as then measured. To test the flexural strength of the composite, 3 rectangular specimens measuring 40 mm by 40 mm by 160 mm were made for each composition. The specimens were tested according to EN 196-1 standard. The three-point loading method was used. To test the compressive strength of the composite 6 specimens were made for each composition. The specimens were tested according to EN 196-1 standard. The compressive area was 1600 mm2.
3 Results
Consistency testing showed that for every composition an equal composite spread of (180 ± 5) mm was obtained each time. Therefore, the use of recycled aggregate did not affect the basic technological characteristic of the mixtures. The average flexural strength results obtained were in the range of 20.5 to 21.5 MPa. The differences between the average values for different compositions are within the limits of the standard deviations of the results (Fig. 2).
Fig. 2.
Composition of recycled coarse aggregate according to EN 933-1 (percentage by weight)
×
The average compressive strength results obtained were in the range of 88.5 to 96.5 MPa. The differences between the average values for different compositions are within the limits of the standard deviations of the results. The highest compressive strength value (96.5 MPa) was obtained for the samples with the composition with the highest proportion of recycled aggregate. Such results were obtained despite the fact that the resistance of the recycled aggregate itself was lower than that of the natural aggregate. (Fig. 3). This was probably due to the fact that the resin binder penetrated the hardened cement slurry, increasing its strength and strengthening the resin-aggregate transition zone. This assumption was also confirmed by the nature of the failure of the specimens in the flexural and compressive test.
Fig. 3.
Composition of recycled coarse aggregate according to EN 933-1 (percentage by weight)
×
4 Conclusions
Studies conducted indicate that recycled aggregate from demolition of concrete structures has great potential as an aggregate in polymer concrete. The presence of hardened cement slurry does not adversely affect the basic technological and strength characteristics of the composites. Further research is required on the microstructure. It is also necessary to conduct chemical resistance analyses. The use of recycled aggregate in polymer concretes can contribute to reducing the carbon footprint of composites and developing a closed-cycle economy.
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