Physicomechanical Properties of Mortar with Diluted EPS as the Binding Material

Amariles-López, Cristhian C.; Aristizábal-Torres, Daniel; Alzate-Buitrago, Alejandro; Osorio-Gómez, Cristian C.; Mancilla-Rico, Edwin

doi:10.1061/JMCEE7.MTENG-18010

Open access

Technical Papers

Sep 27, 2024

Physicomechanical Properties of Mortar with Diluted EPS as the Binding Material

Authors: Cristhian C. Amariles-López https://orcid.org/0000-0002-9858-2795 [email protected], Daniel Aristizábal-Torres https://orcid.org/0000-0002-6552-2585 [email protected], Alejandro Alzate-Buitrago https://orcid.org/0000-0002-2504-0653 [email protected], Cristian C. Osorio-Gómez https://orcid.org/0000-0003-4141-1052 [email protected], and Edwin Mancilla-Rico, Ph.D. https://orcid.org/0000-0002-5133-0283 [email protected]Author Affiliations

Publication: Journal of Materials in Civil Engineering

Volume 36, Issue 12

https://doi.org/10.1061/JMCEE7.MTENG-18010

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Abstract

Expanded polystyrene (EPS) is a widely used material in multiple industries, especially in the construction and packaging of appliances and equipment, owing to its properties of lightweight, sound insulation, thermal insulation, and strength. However, in the final stage of the EPS life cycle, multiple environmental issues arise related to the management of this material’s waste due to the large volume occupied and greenhouse gas emissions. This issue has generated growing interest among researchers worldwide, seeking sustainable alternatives to mitigate these negative impacts. In this study, an alternative for utilizing EPS waste was explored, using it in a diluted form with gasoline to manufacture mortar, where EPS acts as a binder. The properties of the material were evaluated, including compressive strength (CS), density (D), and ultrasonic pulse velocity (UPV), using nonparametric statistical tests and multiple linear regression. Variables such as the weight ratio of EPS, the curing method and temperature, and the pressing load were considered in manufacturing 175 cylindrical samples. The results revealed notable strengths of up to 25 MPa, and correlations were established with nondestructive test data, such as UPV. This research opens new perspectives in the search for sustainable solutions for using EPS waste.

Practical Applications

Optimizing the proportion of diluted EPS using gasoline as a solvent and implementing thermal curing resulted in the material’s outstanding performance. The most imperative results were achieved with a 9% EPS content, followed by 24 h of air drying and an additional 24 h at 110°C. It is relevant to highlight that applying a pressing load of 35 kN led to an additional improvement in compressive strength. The research presents an environmentally friendly curing method characterized by its energy efficiency compared to conventional materials, such as clay blocks. In addition, up to 46% of the solvent evaporates during manufacturing, offering opportunities for solvent recovery techniques. The development of materials, such as dilute EPS mortars, is positioned as a promising and sustainable alternative in construction, with the potential to generate significant savings and environmental benefits. In the construction field, these innovations could find applications in manufacturing masonry blocks, both structural and nonstructural, paving stones, pavements, and filling in structural expansion joints for buildings, among other architectural and structural elements. These applications illustrate the broad spectrum of possibilities of these advanced mortars in the construction landscape.

Introduction

The construction industry represents one of the main generators of economic value at the global level (Tafesse et al. 2022). Nevertheless, its negative environmental impact is significant due to the large amount of construction and demolition waste (CDW) it generates (Del Río Merino et al. 2010). For this reason, it is convenient for the sector to adopt new sustainable and environmentally friendly materials and production models (Vidales 2019). In order to reduce the amount of waste that accumulates in increasingly saturated landfills, it is sought to promote the reuse and recycling of those materials that can be used to generate new materials or products (Villoria et al. 2018). The growing concern for the environmental impact has driven the implementation of different studies to address this problem, as well as the use of CDW in the production of structural concrete as an alternative to reduce

{CO}_{2}

pollution (Behera et al. 2014; Kisku et al. 2017) and the reuse of CDW through dismantling techniques of construction materials at the end of their useful life (Zabalza Bribián et al. 2011), through quality management that includes the characterization of processes and an evaluation of quality costs (Formoso et al. 2002).

In addition, there has been a growing interest in using agricultural and industrial waste as raw materials to develop material components that can replace traditional construction materials (Madurwar et al. 2013; Pappu et al. 2007). In particular, the masonry industry has implemented these types of materials in its mixtures to improve their functionality or replace polluting materials that make it up. The development of masonry blocks using palm kernel shells as raw material has been explored concerning the implementation of organic waste. These blocks meet the compression strength requirements established by Malaysia’s technical regulations, reaching strengths of up to 23 MPa and contributing to the reduction of

{CO}_{2}

emissions by 20% per tonne (Muntohar and Rahman 2014). Similarly, the fiber of aloe vera (Juárez et al. 2010) and jute fibers (Castañeda et al. 2020) have been used in concrete blocks that present a greater crack control with compressive strength (CS) of 16.3 MPa and 8.1 MPa, respectively, in addition to reducing the apparent density of the samples compared to traditional concrete blocks.

Industrial waste has also been considered for the manufacture of prefabricated elements through various research studies. Turgut (2008) investigated prefabricated block-type elements made of limestone residue and glass powder for their production, allowing for an improvement in compressive and flexural strength of up to 21% (24.9 MPa) and 77% (3.94 MPa), respectively, concerning British technical regulations. Similarly, Holmes et al. (2016) have investigated the use of incinerator bottom ash as a substitute for fine aggregate in the manufacture of prefabricated elements, with which it has been shown that these elements maintain good CS and meet the absorption criterion (12%) according to the ASTM C-90 standard for structural masonry. Likewise, Mahoutian et al. (2018) produced cement masonry blocks using steel slag as a binder and carbon dioxide as a curing activator, demonstrating that these blocks exhibit mechanical and durability properties equal to or even better than commercial blocks, helping to reduce 1.5 million tonnes of

{CO}_{2}

per year if all the steel slag produced in the United States and Canada were used in this product.

Similarly, Dahmen et al. (2018) developed blocks made from stabilized soil, reducing

{CO}_{2}

emissions by 46% compared to concrete elements and presenting similar CS. Conversely, Sangrutsamee et al. (2012) use recycled paper that meets the required standard for nonload-bearing masonry (ASTM C129), with a compressive strength of 3.23 MPa, in addition to reducing thermal conductivity as they become a thermal insulator, improving energy performance (Nagy 2019). Alternatively, supplementary natural materials such as limestone, class C fly ash, silica fume, and water are presented and used to create a new mixture for the production of masonry blocks that reach compressive strengths of up to 26 MPa, without including portland cement, reducing

{CO}_{2}

emissions (Turgut 2012).

From another perspective, plastic waste on a global scale has become an important environmental problem due to high mass production and the generation of waste that it becomes. Consequently, approximately 12% of waste is burned, 79% is deposited in landfills and oceans, and only 9% is recycled (Noor and Rehman 2022). Consequently, large volumes of waste are generated that must be managed properly to minimize the negative impact on the environment. Within plastic waste is expanded polystyrene (EPS), a foamed material that is produced from polystyrene beads (Chaukura et al. 2016), characterized as a nonbiodegradable (Bicer 2021) and large-volume material that generates a high impact on the environment (Rodriguez 2019). Recycling these products is expensive as a consequence of the large volume of waste storage, making transportation (Milling et al. 2020; Moghaddam and Alkhansari 2021) and disposal (Kan and Demirboǧa 2009) difficult. As a result, most EPS waste is incinerated or landfilled, causing significant emissions of gases to the atmosphere and generating large amounts of leachate into the soil resulting from the decomposition of the materials (Munir et al. 2022).

Regarding EPS, the construction industry is making significant efforts to improve the management of this type of waste (Hidalgo-Crespo et al. 2022). Currently, EPS in the form of beads has been used as an aggregate in lightweight concrete, reaching CS of up to 12 MPa, and can be applied to nonstructural elements (Bouvard et al. 2007; El Gamal et al. 2023; Li et al. 2015; Liu and Chen 2014). Similarly, Meddage et al. (2022) implemented lightweight concretes based on EPS for the construction of roof slabs, reducing costs and carbon emissions and decreasing operating energy consumption by 8.3%, 20%, and 41%, respectively, in comparison to traditional reinforced concrete slabs.

Similarly, adding EPS as a substitute for cement in conventional mortars has been implemented, resulting in CS of 6 MPa and bond strengths of 3.96 MPa, doubling those of cement mortars (Milling et al. 2020). In related topics, Ferrándiz-Mas et al. (2016) presented lightweight mortars by adding EPS to the mixture in a proportion of up to 60%, developing maximum CS of 11.7 MPa. Flow values between 168 and

180 \pm 4 mm

were determined, and apparent densities were between 1,280 and

1,110 \pm 100 kg / m^{3}

, characteristics that make them suitable for masonry, plastering, and cladding works. Similarly, these mortars improve energy efficiency as thermal insulators (Gomes et al. 2018). Analogously, EPS has been used in pavement construction, mainly in the filling function, helping to reduce vibrations (Mohajerani et al. 2017), even as a stabilizer in embankments (AbdelSalam et al. 2019; Shelke and Murty 2011).

Despite the efforts to improve EPS waste management, the exponential increase in use and negative environmental impacts have made effective waste management imperative. In this context, there has been a growing interest in using diluted EPS as a construction material. This practice offers a sustainable and effective alternative to EPS waste management, promoting material reuse and contributing to construction sustainability. Therefore, Sariisik and Sariisik (2012) produced masonry blocks using EPS, pumice, and lightweight concrete, providing better thermal and acoustic insulation, and their CS meets the Turkish requirements for nonstructural masonry blocks with 2.99 MPa. Similarly, Vinod et al. (2022) have also explored the use of EPS as an aggregate in concrete blocks, although it is only used in nonstructural masonry because of low compressive strength but presents low density and shrinkage.

Nevertheless, this practice represents a good economic option and can offer greater strength than conventional nonstructural blocks. Consequently, various studies have been conducted on implementing alternative waste materials to address the environmental problems generated by construction on a global scale. Despite this, few studies, such as the one developed by Milling et al. (2020), have explored using EPS as the only binding material in mortar or concrete mixtures, obtaining compressive strength results of up to 10.96 MPa. This study aims to evaluate compressive strength from destructive tests correlated with nondestructive test parameters such as ultrasonic pulse velocity (UPV) and density of mortar mixtures made of sand and EPS binder, considering independent variables such as the optimal proportion of EPS diluted using gasoline as a solvent in the mortar mixture, in addition to the effect of oven and air curing and the application of pressing load for compaction of the material. Consequently, the reuse of waste materials is promoted, contributing to sustainability in construction. The implementation of independent variables resulted in a notable improvement in the mechanical and physical properties of the material.

Materials and Methods

This study evaluated the mechanical parameters of mortar mixtures made of sand and EPS diluted with gasoline as an aggregate. This work belongs to the sustainable construction materials research line and seeks to propose innovative and ecological alternatives to conventional materials. A structured and systematic methodology was followed, which included the classification of materials, the preparation of samples, nondestructive and destructive tests, and a statistical analysis of the results obtained. The methodological scheme used is presented in Fig. 1.

Fig. 1. Methodological diagram of the research.

Various research techniques and tools were used to collect, analyze, and organize information, including laboratory tests and statistical analysis of results. This experimental research provides valuable information about the properties and performance of this type of material, considering variables such as the optimal proportion of EPS diluted with gasoline, in addition to the effect of thermal curing and the application of pressing load for compaction of the material, offering a sustainable and ecological alternative to traditional construction materials.

Phase 1: Materials Quality Control

Concrete sand was selected as the fine aggregate for the preparation of the specimens in this project, crushed and recycled EPS was used as the binder, and gasoline was added as a solvent. The fine aggregate was subjected to four laboratory tests: particle size distribution (ASTM 2023a), organic impurities in fine aggregate (ASTM 2023d), relative density (specific gravity) of fine aggregate (ASTM 2022a), and sand equivalent value of fine aggregate (ASTM 2022b) to determine the viability of using the material in the production process. On the other hand, white EPS with spherical particle geometry with a diameter ranging from 1.21 mm to 3.93 mm was used. No initial quality tests were performed as it was considered a standard recycled clean material from packaging elements of appliances and equipment. Regular gasoline with 87 octanes was also used as a solvent. According to the technical sheet, it is a colorless or yellow liquid with a characteristic odor at room temperature. Its specific gravity at 20°C varies between 0.72 and 0.76, and its boiling point ranges from 25°C to 225°C. It has an extremely low melting point, reaching

- 70 ° C

. The relative density of the vapor is greater than three compared to air. The vapor pressure at 20°C is 55 kPa.

Phase 2: Specimen Preparation

Practical concepts were applied in the fabrication of the samples, such as the diameter–length ratio of the cylinders, based on the specification (ASTM 2015) standard practice for making and curing concrete test specimens in the laboratory. Molds based on the specifications (ASTM 2023b) standard specification for molds for forming concrete test cylinders vertically were utilized.

The process for manufacturing 175 cylindrical specimens, with typical dimensions of 50 mm in diameter and 100 mm in height, is described. These specimens were fundamental to investigate the impact of the independent variables, namely, EPS ratio (%), oven curing temperature (°C), compaction stress (MPa), and air curing days without oven (days). The distribution and mortar mixture design of these 175 specimens is detailed in Table 1.

Table 1. Distribution and mortar mixture design of specimens for the study of independent variables

Independent variable	Number of specimens	Mortar mixture design
Independent variable	Number of specimens	Fine aggregate (g)	EPS (Fine aggregate %)	Gasoline (mL)
EPS proportioning (%)	47	395	Variation 4%–15%	125
Curing oven temperature (°C)	50	395	9%	125
Compaction stress (MPa)	48	395	9%	125
Days of air curing without an oven (days)	30	395	9%	125
Total	175	—	—	—

Mechanical Mixing

The material mixing process was carried out in a standardized manner for all samples using mechanical means. A mixing procedure was defined based on tests, obtaining the best results by initially mixing the fine aggregate with half the volume of gasoline and then adding the EPS Fig. 2(a). Next, while the mixing equipment stirred the material, as shown in Fig. 2(b), the remaining volume of solvent was added as the EPS dissolved. The EPS dosage in the mixture was determined as a proportion of the weight of the fine aggregate, evaluating proportions from 4%, 6%, 8%, 9%, 10%, 11%, 12%, 13%, and 15%. Likewise, on average, the amount of solvent used for samples with dosages close to 9% of EPS was 125 mL.

Compaction

The compaction of the material was carried out using controlled mechanical means to determine the best pressing pressure for the material, as shown in Fig. 3. Metal molds with dimensions of 50 mm in diameter and 100 mm in height were used to shape the compacted specimens. According to the tests carried out for the pressure variable, the optimal pressing load was 35 kN, generating a compaction stress of 15.3 MPa in the specimens. This optimal load was used to manufacture the specimens to determine the effect of the other independent variables studied in this research.

Curing

Two material curing methodologies were evaluated; the first consisted of generating curing conditions at an average ambient temperature of 22°C so that the evolution of the material’s compressive strength (CS) was evaluated from the first day to the 90th day of curing. Alternatively, the second curing method consisted of the application of the first 24 h of curing in air, to later apply temperature through an oven to the samples for three days, as shown in Fig. 4, the temperature variations applied were 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, and 150°C. Additionally, during the three days of oven curing, the weight of each sample was recorded to determine the evaporation rate of the solvent used in the mixture of each sample.

Phase 3: Nondestructive Testing

The physical properties of all the manufactured specimens were evaluated using nondestructive tests such as UPV, as it provides information about the propagation speed of ultrasonic waves in the material, which is directly related to its mechanical properties. This process allows obtaining crucial data about the quality and strength of the mortar without causing physical damage to the sample. It also enables the detection of potential defects or anomalies in the mortar without compromising the sample’s integrity. This test is essential for assessing the homogeneity of the material and identifying possible internal issues. Additionally, it allows for the optimization of resources and provides additional detail for the samples.

The dimensions and mass of each sample were recorded to determine the density of the material, as shown in Fig. 5(a). Additionally, the UPV through concrete (ASTM 2022c) test was applied using the direct method on the cylindrical samples, as shown in Fig. 5(b).

Fig. 5. (a) Individual sample measurement; and (b) UPV test.

Phase 4: Destructive Testing

The mechanical properties of all the cylindrical specimens manufactured were evaluated using destructive testing. The CS test (ASTM 2023c) was applied to each sample, as shown in Fig. 6.

Phase 5: Statistical Analysis

The behavior of the physical and mechanical properties of the material was analyzed based on the results of destructive and nondestructive tests categorized into the dependent variables, such as CS, density (D), and UPV.

Initially, tests were carried out to select parametric or nonparametric statistical techniques, so the Kolmogorov–Smirnov (KS) test was performed to determine if the results follow a normal probability distribution (Gaussian) (Massey 1951). The null hypothesis H0 was established, which assumes that the data follow a normal distribution, and the analyses were carried out using the IBM SPSS Statistics software; the results are presented in Table 2. According to the asymptotic significance (Two-Tailed) − p-value associated with the KS statistic, which is less than the predefined significance level of 0.05 in all data groups, the null hypothesis is rejected, and it is concluded that the data do not follow the normal distribution.

Table 2. Kolmogorov–Smirnov Normality test

Sample group	Density ( $g / {cm}^{3}$ )	Compressive strength (MPa)	UPV ( $m / s$ )
EPS proportioning
N − EPS proportioning (%)	47	47	47
Asymptotic significance (Two-tailed) − p-value	0.009	$< 0.001$	$< 0.001$
Curing oven temperature	—	—	—
N − Curing oven temperature (°C)	50	50	50
Asymptotic significance (Two-tailed) − p-value	0.025	0.003	$< 0.001$
Compaction stress
N − Compaction stress (MPa)	48	48	48
Asymptotic significance (Two-tailed) − p-value	$< 0.001$	0.021	0.017
Days of air curing without oven
N − Days of air curing without oven (days)	30	30	30
Asymptotic significance (Two-tailed) − p-value	0.007	$< 0.001$	$< 0.001$

Note: N = number of samples tested.

Considering the results of the Kolmogorov–Smirnov normality test, the effect of independent variables such as EPS weight ratio, curing method, curing temperature, and pressing load were analyzed. The nonparametric Kruskal–Wallis statistical test was used since the data distribution did not follow a normal distribution (Ostertagová et al. 2014) to determine if there were significant differences between independent groups for each dependent variable studied.

Additionally, since the assumptions of equal variances and normality in the data were not met, post hoc analyses were performed using the Games–Howell test to compare the specific resulting data groups that involved the independent variables on the dependent variables and obtain details of the behavior and significant differences between them (Games and Howell 1976). In addition, a multiple linear regression model with the Enter method was calculated to predict the effect of measurements from nondestructive tests, such as UPV (

m / s

) and material density (

g / {cm}^{3}

), on the results of destructive tests, such as CS (MPa).

Results

The following section presents the results and analysis of the procedural methodological development of this study. Aspects related to material quality control, nondestructive testing, destructive testing, and statistical data analysis are addressed. This section provides a detailed overview of the findings derived from each process stage, contributing to a comprehensive understanding of the research.