The chapter delves into the use of foundry industry wastes, specifically ceramic mold shells and paraffin wax, in cement mortars. It begins by highlighting the global environmental challenges and the need for sustainable construction practices. The study focuses on the physical properties of mortars, such as water absorption by capillarity and immersion, and their relationship with the porosity of the materials. It also examines the mechanical properties, including flexural and compressive strengths, and how the incorporation of waste affects these properties. Additionally, the durability of the mortars is evaluated through freeze-thaw resistance tests, revealing a correlation between compressive strength and mass loss. The chapter concludes by emphasizing the potential of these waste materials in reducing the consumption of raw materials and energy, while maintaining adequate mechanical behavior and durability for construction industry applications.
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Abstract
Planet Earth is facing real challenges that require urgent and significant measures. It is necessary to give a new direction to the construction sector, making it essential to change the way that raw material is selected, giving preference to industrial by-products. The utilization of industrial wastes allows minimize the high consumption of natural raw materials, energy consumption and waste deposition in landfills. It is important to note that the use of waste in the construction industry is a great opportunity, however, the heterogeneity of these materials and sometimes their contamination can compromise the durability. The lost-wax process in foundry industry is currently an expanding area, so more and more manufacturing industries have serious problems related to their waste management. During its production process, wastes of ceramic mold shells and paraffinic wax are generated and until now any practical application is known. The main objective of this study was the correlation between the physical, mechanical behavior and durability of cement mortars with incorporation of paraffin wax and ceramic mold shells. The main results revealed a decrease in water absorption, flexural strength, and compressive strength of the mortars, along with a slight increase in degradation during freeze-thaw cycles. Additionally, a correlation was observed between the physical, mechanical performance, and durability of the mortars. This included factors such as water absorption through immersion and capillarity, as well as the relationship between compressive strength and the mass loss suffered during freeze-thaw tests.
1 Introduction
Our planet is facing serious environmental challenges due to the excessive consumption of natural raw materials and energy resources during their extraction and processing, as well in maintaining the energy needs associated with the different activity sectors. Earth's Overshoot Day is occurring earlier each year, currently falling around mid-year (August 2 in 2023), indicating that nowadays the humanity requires approximately 1.7 planets to sustain its needs.
The retreat of Overshoot Day is also linked to the consumption of natural resources, which has been exacerbated by the significant levels of urbanization we are currently experiencing. It is known that replacing traditional concrete by a concrete made from recycled aggregate could immediately delay Earth Overshoot Day by 2.4 days [1]. Therefore, the construction industry needs to invest in reusing industrial by-products from its own sector, like construction or demolition waste, as well as by-products from other industries, such as the foundry industry, to create new and sustainable construction materials.
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The foundry industry works with various types of metals, producing metal pieces for the automotive, domestic, military and agro-industrial industry all over the world. Consequently, its waste production is enormous. In 2020, approximately 105. 5 million metric tons of solid foundry waste were generated globally [2‐4]. Precision foundry industry also known as lost-wax foundry industry, produces two main types of waste: ceramic mold shells and paraffinic wax. Initially, paraffinic wax is used to create a replica of the metal piece to be molded. This replica is then coated with multiple layers of ceramic material to create the mold into which the liquid metal will be poured.
Next, the set will be placed in an oven to create a ceramic mold with increased resistance and to facilitate the removal of the paraffinic wax, which liquefies due to the temperature. This process results in the extraction of the first residue, the paraffin wax waste. Finally, the molten metal is poured into the ceramic mold cavity, where it cools down and solidifies, resulting in a flawless final piece. During the demolding of the metal pieces, it is necessary to break the molds, obtaining in this way the ceramic mold shells waste [5]. It is important to note that these wastes cannot be reincorporated in any stage of a new production process. Until now, very little is known about the use of these wastes in construction materials. Only few studies conducted by this research team have explored the behavior of these wastes in cement mixtures [6‐8].
However, it was necessary to establish a treatment process for the ceramic mold shells, to eliminate the alkali-aggregate reaction caused by the presence of sodium, potassium, calcium and magnesium in their chemical composition. The results of this work [7] revealed that washing process was a practical, simple, cheap and effective method for using this waste as a substitute for natural aggregate in mortars. Thus, the main objective of this work was the correlation between the physical, mechanical behavior and durability of cement mortars with incorporation of paraffin wax and ceramic mold shells.
2 Experimental Program
2.1 Materials
The materials used considered other research works carried out by this research team [6‐8]. It was selected a Portland cement CEM I 42.5 R, a natural sand, a ceramic mold shell waste, a paraffin wax waste and a superplasticizer. The raw materials densities are present in Table 1.
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The waste used as a substitute for natural aggregate underwent a treatment process, to enable its incorporation into cement mortars. In this way, the ceramic mold shells underwent a crushing and washing process, while the paraffin wax waste only underwent a crushing process. Table 2 presents the average particle size and water absorption capacity of the different aggregates used in this study.
Table 1.
Materials densities.
Materials
Density (kg/m3)
Cement
3184
Natural Sand
2569
Ceramic mold shells
2630
Paraffin wax
1013
Superplasticizer
1041
Table 2.
Particle average size and water absorption of the aggregates.
Materials
Water absorption (%)
Particle average size (mm)
Natural Sand
1.2
0.68
Ceramic mold shells
6.6
1.25
Paraffin wax
1.6
1.8
2.2 Compositions
Six different compositions were developed with different contents of ceramic mold shells and paraffin wax. The development of these mortars was carried out in a previous study [8], developed by this research team. Table 3 presents the mixture of aggregates used to produce the different mortars, along with their water/cement ratio. A cement dosage of 750 kg/m3 and a superplasticizer dosage of 7. 5 kg/m3 were used.
Table 3.
Mortars aggregates mix and water-cement ratio.
Composition
Aggregates mixture
Water/Cement
REF
100% natural sand
0.36
CMS100
100% ceramic mold shells waste
0.42
CMS80PW20
80% ceramic mold shells waste and 20% of paraffin wax waste
0.41
CMS60PW40
60% ceramic mold shells waste and 40% of paraffin wax waste
0.40
CMS40PW60
40% ceramic mold shells waste and 60% of paraffin wax waste
0.38
CMS20PW80
20% ceramic mold shells waste and 80% of paraffin wax waste
0.37
2.3 Test Procedures
The developed mortars were tested in order to evaluate their physical, mechanical and freeze-thaw behaviors. Thus, several tests were performed based in European and national standards.
The behavior in the fresh state was evaluated according to consistence determination tests, by flow table method, in accordance with the specification EN 1015–3 [9]. Having established an average spreading diameter of 200 ± 5mm to fix the water cement ratio (Table 3).
The behavior in the hardened state was evaluated according to tests of water absorption by capillarity based in the specification EN 1015–18 [10], water absorption by immersion in accordance with the Portuguese specification LNEC E 394 [11], flexural and compression strengths in accordance with the specification EN 1015–11 [12] and the evaluation of the freeze-thaw behavior according to the specification CEN/TS 12390–9 [13].
3 Results and Discussion
3.1 Physical Properties
The physical properties studied were water absorption by capillarity and immersion (Table 4).
Table 4.
Water absorption by immersion and water absorption by capillarity coefficient of the mortars.
Composition
Water absorption by immersion (%)
Water absorption by capillarity coefficient (kg/(m2.min0.5))
REF
14.49
0.0014
CMS100
20.88
0.002
CMS80PW20
13.24
0.0012
CMS60PW40
8.26
0.0008
CMS40PW60
5.84
0.0005
CMS20PW80
3.62
0.0003
The water absorption by immersion and the water absorption by capillarity coefficient show the same tendency (Fig. 1). Mortars with a lower water absorption capacity by immersion are also those with a lower water absorption coefficient by capillarity. In this way, it is possible to verify that there is a relationship between the macroporosity and microposity of mortars. Mortars produced from a mixture of 100% aggregate from ceramic mold shells exhibit a higher water absorption capacity compared to mortar with 100% natural aggregate and mortars with a combination of ceramic mold shells and paraffin wax. This behavior is influenced by the nature of the aggregate, leading to a higher water-cement ratio as shown in Table 3. Mortars containing a mixture of aggregates (ceramic mold shells and paraffin wax) exhibit a lower water absorption capacity. This is attributed to the hydrophobic nature of paraffin wax and lower water-cement ratio in the mortars.
Fig. 1.
Relationship between water absorption by immersion and water absorption by capillarity coefficient of mortars.
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3.2 Mechanical Properties
The mechanical properties studied were the flexural and compressive behavior (Table 5).
Table 5.
Flexural and compressive strength of the mortars.
Composition
Flexural strength (MPa)
Compressive strength (MPa)
REF
7.9
41.6
CMS100
7.3
34.7
CMS80PW20
5.5
21.2
CMS60PW40
4.6
16.7
CMS40PW60
3.9
13.4
CMS20PW80
3.9
11.9
Mortars produced with 100% of natural sand exhibit superior mechanical properties, showing increased flexural and compressive strengths. These properties are influenced by the shape and composition of the aggregate, as well as the lower water-cement ratio. Mortars developed with wastes, especially mortars incorporating aggregate made up entirely of ceramic mold shells, show a decrease in their mechanical performance, due to the higher water cement ratio and porosity (Table 4). Finally, mortars incorporating ceramic mold shells and paraffinic waxes show the greatest losses in mechanical performance, especially in mortars with a higher paraffinic wax content, even presented lower water cement ratios. This behavior is justified by the lower adhesion of the paraffin wax particles to the mortar matrix, as well as by the presence of a higher water-cement ratio.
It should be noted that the incorporation of ceramic mold shells and paraffin wax, although reducing the compressive strength of the developed mortars, does not prevent them from exhibiting mechanical behavior suitable for the construction industry. All developed mortars meet the maximum resistance class according to the European specification NP EN 998–1 [14], based on their compressive strength.
3.3 Durability
The durability of the mortars was evaluated based on their resistance to freeze-thaw cycles, as outlined in the European standard NP EN 998–1 [14]. The freeze-thaw resistance was directly connected with the mass loss of the specimens during the freeze and thaw cycles. Table 6 presents the mass loss values of the specimens due to degradation from 56 freeze-thaw cycles conducted on various mortars.
Table 6.
Mass loss suffered during mortar freeze-thaw tests.
Composition
Mass loss (MPa)
REF
0.43
CMS100
0.70
CMS80PW20
0.77
CMS60PW40
1.72
CMS40PW60
1.70
CMS20PW80
0.80
Mortars incorporating waste as a substitute for natural aggregate show greater degradation compared to mortar with 100% aggregate of natural origin. This situation is aggravated for mortars incorporating paraffin wax, which can be justified by their lower mechanical performance (flexural and compressive strengths). Figure 2 illustrates a correlation between mass loss in freeze-thaw tests and the compressive strength of the mortars, indicating that those with lower compressive strength experience more significant degradation. However, it is important to note that all developed mortars exhibit very high resistance to freeze-thaw action, without a total degradation or significant superficial degradation of the specimens.
Fig. 2.
Relationship between compressive strength and mass loss of mortars.
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4 Conclusions
This study made it possible to evaluate the possibility of successfully incorporating waste from the foundry industry (ceramic molds shells and paraffin wax) into mortars for buildings applications, as well establishing correlations between the performance of several of their properties.
Based on the physical properties of the mortars, it is possible to determine a close relationship between the macroporosity and microporosity of the mortars. Additionally, it can be observed that the presence of ceramic mold shells increases the water absorption capacity of the mortars. This increase is largely due to the greater absorption capacity of the recycled aggregate, as well as the higher water-cement ratio. However, the presence of paraffin wax resulted in a decrease in the porosity of the mortars, due to the hydrophobic nature of the paraffin wax, as well as the lower water-cement ratio of the mortars.
Regarding mechanical performance, it was found that the presence of paraffin wax weakens the mortars, due to the low adhesion of the paraffin wax particles to the cement paste.
Concerning the durability of mortars, particularly in freeze-thaw tests, a correlation was observed between the degradation of specimens and their compressive strength. Mortars with higher resistance resulted in less degradation of specimens and, therefore, less mass loss.
The reuse of these wastes remains an area with significant research needs. However, the mortars studied exhibit adequate mechanical behavior and durability suitable for the construction industry. This approach can also be viewed as a potential contribution to reducing the consumption of raw materials and energy associated with the extraction of natural resources.
Acknowledgements
This work was supported by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Centre for Territory, Environment and Construction (CTAC) under reference UIDB/04047/2020.
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