Dieses Kapitel untersucht die Nachhaltigkeit und Leistungsfähigkeit von Vinylester- und Polyester-Polymerbeton, wenn er künstlich induzierten klimatischen Umgebungen ausgesetzt ist. Es wurden sechs verschiedene Mischungsdesigns entwickelt, die recycelte Materialien wie Polypropylen-Kunststoff und Gummikrümel enthalten. Die Studie bewertet die Druckfestigkeit, den Massenverlust und den ästhetischen Wert dieser Mischformen nach hohen Temperaturen, niedrigen Temperaturen und hoher Feuchtigkeit. Insbesondere das Polyesterharz mit konventionellen Zuschlagstoffen wies die beste Gesamtleistung auf, während Vinylester mit Polypropylen-Kunststoff einen überlegenen ästhetischen Wert aufwiesen. Die Ergebnisse unterstreichen das Potenzial von Polymerbeton als nachhaltige Alternative zu herkömmlichem Beton, obwohl weitere Forschung empfohlen wird, um die Verwendung von Recyclingmaterialien zu optimieren.
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Abstract
The exposure of polymer concrete to artificially designed environmental conditions of high-and low-temperatures, and moisture levels allowed for the assessment of strength performance and aesthetic value. Strength performance indicated the maximum capability of the product to carry a load successfully, whereas the aesthetics assessed the appearance of the product, that can be measured using spectrophotometry. In this study, materials such as water and Portland cement typically used to form traditional concrete were replaced by two polymer resins namely - vinyl ester and polyester, thus making it polymer concrete. As such, compressive strengths of cube samples were tested, the change in cubes’ masses was measured using a balance - prior and post exposure to the artificially induced environments, the colour change tests (spectroscopy analysis) were performed using the spectrophotometer tests. Compressive strengths of over 75MPa were achieved, thereby justifying promising concrete strengths. Mass losses recorded were almost negligible, thereby showing toughness to conditions presented in the artificially induced environments. Minor colour changes were noticed- thereby showing a good resistance to harsh weather conditions on the surface properties. Therefore, the assessed products displayed desired characteristics for strength performance and aesthetic value, subsequently, creating a product that promotes sustainability.
1 Introduction
Polymer concrete can be defined as the composite material formulated from the use of polymeric resins to fully replace the cement binders in conventional cement concrete [1]. The normalised use of cement in conventional concrete has thus developed the need to investigate more sustainable methods of producing concrete without compromising the durability and strength properties of the composite material, when exposed to harsh climatic environments.
The use of polymeric resins such as vinyl ester and polyester to replace water and conventional Portland cement in concrete, coupled with the use of recycled materials as aggregates such as polypropylene plastic and rubber crumbs, can be a sustainable way to producing polymer concrete. It can be touted to be a “greener” product by reducing the overall carbon dioxide emissions [2], achieving higher strength properties, increasing hardening rates, and upholding the aesthetic value of the composite materials.
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Like conventional concrete, the impact that various environmental conditions have on polymer concrete is important to consider as these conditions will govern the sustainability, durability, strength performance and suitability of these composite materials.
Thus, to investigate the sustainability of the strength performance and aesthetic value of polymer concrete materials when exposed to artificially induced climatic environments, six different polymer concrete mix designs were formulated. These mix designs incorporated the use of vinyl ester and polyester polymer resins, which were mixed with three different aggregate systems, namely: recycled polypropylene plastic, recycled rubber crumbs from old tyres and a conventional crusher sand/crusher stone mix.
Polyester and vinyl ester resins are unsaturated polymer resins which are essential thermosetting matrix components for composite materials. Polyester and vinyl ester resins are available at a lower cost when compared to epoxy resins, however their matrix systems are used for improved strength properties and chemical resistance [3, 4], thus contributing to their economic sustainability. In this investigation, these six polymer concrete materials were exposed to artificially induced climatic environments.
2 Experimental Design
For this test, a total of one hundred and twenty cube specimens were produced. Twenty specimens were made for each mix design. From the twenty, ten underwent exposure of harsh climates for testing, whereas the other ten were used as control specimens.
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2.1 Mix Designs
The two different polymer resins were incorporated with three different sets of aggregate systems. For the mixes, 1.2% of the supplier-provided catalyst was mixed with the vinyl ester resin for the three mix designs utilising vinyl ester resin, while 2% of the supplier-provided catalyst was mixed with the polyester resin for the remaining three mix designs utilising polyester resin. Table 1 details the six mix designs used for the tests.
Table 1.
Mix design compositions and volume ratios.
Mix Design Composition
Abbreviation
Volume Ratio
Ratio Explanation
Vinyl ester resin with conventional aggregates and recycled rubber crumbs
RV
1: 4.2: 1.4: 1.4
Vinyl ester: Sand: Stone: Rubber
Vinyl ester resin with conventional aggregates and recycled polypropylene plastic
PV
1: 5: 1.7: 1.7
Vinyl ester: Sand: Stone: Plastic
Vinyl ester resin with conventional aggregates
CV
1: 5: 2.5
Vinyl ester: Sand: Stone
Polyester resin with conventional aggregates and recycled rubber
RP
1: 4.2: 1.4: 1.4
Polyester: Sand: Stone: Rubber
Polyester resin with conventional aggregates and recycled polypropylene plastic
PP
1: 5: 1.7: 1.7
Polyester: Sand: Stone: Plastic
Polyester resin with conventional aggregates
CP
1: 5: 2.5
Polyester: Sand: Stone
2.2 Casting of Cube Specimens
Casting of cube specimens was done with guidelines from the South African Bureau of Standards (SANS 5861, SANS 5863 and SANS 50196) [5‐7] and the American Society for Testing and Materials (ASTM C109) [8], whereby 50mm x 50mm x 50mm cube specimens were casted. The cube moulds were filled with the various mix designs and compacted. After 24 h, it was demoulded and stored at room temperature.
2.3 Exposure of Cube Specimens to Artificially Induced Climatic Environments.
Sixty cube specimens (experimental group) were exposed to artificially induced climatic environments, namely: high temperatures, negative temperatures, and high moisture levels. High temperatures up to 70 ℃, negative temperatures up to -13 ℃ and 100% moisture levels were used as parameters to expose the specimens to the induced climatic environments.
Exposure to high temperatures and high moisture levels. Sixty cube specimens were exposed to high temperatures of up to 70 ℃ at two-hour intervals. Thereafter, the specimens were submerged into water for a two-hour period, to replicate a harsh environment of rapid heating followed by high moisture. This cycle was replicated twenty-five times.
Exposure to low temperatures. The same sixty cube specimens were exposed to negative temperatures reaching as low as -13 ℃ in eight-hour intervals. After the eight-hour period, the specimens were left at room temperature for four hours to replicate a freeze-thaw action sequence. This cyclic exposure was replicated twenty-five times.
2.4 Compressive Strength Testing
Upon exposing the sixty cube specimens (experimental group) to the artificially induced climatic environments, the compressive strength of the experimental and control group was tested and recorded to ascertain the effect that the harsh conditions have on degree of degradation for strength performance. The testing of the compressive strengths was done with guidelines outlined by the South African Bureau of Standards (SANS 5863) [6].
2.5 Mass Loss
After exposing the sixty cube specimens (experimental group) to the artificially induced climatic environments, the mass of the specimens in both the experimental and control group were recorded to determine the effect that the harsh conditions have on durability and weathering resistance. Mass loss is an undesired property that compromises durability.
2.6 Aesthetic Value
The assessment of aesthetics was determined through the analysis and measurement of colour change by using spectrophotometry tests. These spectrophotometry tests were performed on all one hundred and twenty cube specimens and were done in line with the ASTM D2244 – 21 [9]. The way the different mix design constituents affect colour change was of significance to its visual aesthetic value.
3 Results and Discussion
The results of findings of the compressive strength test, mass loss test and aesthetics test are detailed and discussed in this section.
3.1 Compressive Strength
Compressive strength testing was conducted on all one hundred and twenty cube specimens, sixty of which were exposed to the artificially induced climatic environments and sixty of which acted as the control group. This was done to ascertain the effect that these harsh climatic environments have on the strength performance of the polymer concrete mix designs. The compressive strength performance is illustrated in Fig. 1.
Fig. 1.
Compressive strength results of the various polymer concrete mix designs before and after exposure to the various artificially induced climatic environments.
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Figure 1 shows the compressive strengths achieved for the various mix designs. A relationship can be observed between the aggregate systems utilised in each mix design, whereby the use of conventional aggregates exhibited the highest overall compressive strength, followed using recycled plastic and recycled rubber aggregates.
High compressive strengths of about 89 MPa were recorded by the polyester resin mix with conventional aggregates (CP) and the vinyl ester resin mix with conventional aggregates (CV). These compressive strengths are like that of M80 concrete that can be used for the construction of dam spillways, high-rise buildings, and bridges [10, 11]. Further, the use of polypropylene plastic for compressive strength tests results showed promising results. Vinyl ester resin with polypropylene plastic mix (PV) and polyester with polypropylene plastic mix (PP), achieved compressive strengths of just under 30 MPa. This is slightly short of achieving a M30 concrete, which is necessary for footings, slabs, patios, and strainer posts [10, 11, 13]. The mix designs utilising the recycled rubber crumbs achieved compressive strengths ranging from 7 MPa to 9 MPa, which is like the compressive strength of M7.5 and M10 concrete, which can be utilised as plain cement concrete (PCC) for the purposes of levelling course or bedding [10, 11].
In the case of recycled plastic materials incorporated into the aggregate system and like that of conventional concrete incorporated with plastic materials, a reduction of compressive strength was observed with an increased content of plastic aggregate. This is attributed to low strength properties of the plastic aggregates and poor bonding within the mix design composition [12, 13]. In the case of recycled rubber crumbs incorporated into the aggregate system and like that of conventional concrete incorporated with rubber crumbs, the lower compressive strengths observed is attributed to the low elastic modulus of rubber when compared to the conventional aggregates and poor adhesion within the mix design composition [14, 15].
3.2 Mass Loss
Fig. 2.
Mass loss of the various polymer concrete mix designs after exposure to artificially induced climatic environments.
Figure 2 shows that the mix design incorporating the polyester resin, coupled with the conventional aggregate system (CP) displayed the best durability as it showed no changes to its average mass. Vinyl ester with normal aggregate (CV), follows as the next ideal mix design due to a small loss in mass of 0.8g. Recycled polypropylene plastic within the aggregate system also showed promising results, indicating a good level of binding strength. Rubber crumbs in the aggregate system, particularly with the use of the polyester resin (RP), indicated the highest level of overall degradation and mass change, making it an inadequate choice.
The compressive strength results and mass losses observed are largely attributed to the content of recycled materials within the mix design. The increased content of recycled materials resulted in lower strength and durability which is attributed due to poor bonding and thus contributing to poor abrasion resistance and durability thereof. However, the incorporation of recycled plastic and rubber within the mix designs at varying contents are said to improve its overall impact resistance and energy absorption [12, 14, 15].
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3.3 Colour Change
The vinyl ester with conventional aggregates (CV) mix design was the next best result, that recorded a change in colour, ΔE* of 1.2. Therefore, the use of vinyl ester with plastic is recommended for esthetics of sight and environmental sustainability. The mix designs that contained polyester with either polypropylene plastic or normal aggregates yielded promising results, since the change in colour, ΔE* was less than 2. However, the use of recycled rubber was shown to yield higher changes of colour, thus making it a less visually aesthetic product, despite it being a more environmentally sustainable product. Figure 3 illustrates the degree of colour change observed.
Fig. 3.
Spectrophotometer test results
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4 Conclusion
In this study, the performance of the polymer resins of vinyl ester and polyester used with conventional aggregates, rubber crumbs and plastic were assessed for strength, mass loss and aesthetics, upon exposure of test samples to the artificially induced climatic conditions of high temperature, low temperature, and high moisture levels. For compressive strength performance and resistance to mass loss, polyester resin with a conventional aggregate system (CP) yielded the best results. This shows that polyester resin is promising, though its compatibility with recycled aggregate substitutes needs to be better incorporated, due to it having poor adhesive properties and a low elastic modulus. The aesthetic test revealed optimistic findings for both polymers in terms of colour change resistance. Vinyl ester with polypropylene plastic (PV) revealed the best aesthetic value, since the colour change was the least. A resistance to colour change indicates that it could withstand the harsh climate. Therefore, the ideal mix design from this study is polyester resin with a conventional aggregate system (CP). That is due to it having the best compressive strength, the least mass loss, and acceptable aesthetic value properties. It is, however, recommended that future research in this study be continued for the selected polyester resins with varying content of recycled materials, and/ or different recycled materials to replace conventional aggregates when utilised in polymer concrete, to achieve similar or better performance.
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