Lightweight gypsum mortar with construction waste to be used as coatings with improved superficial hardness

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International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste

21-23 June 2017, Delft University of Technology, Delft, The Netherlands

165

Lightweight gypsum mortar with construction waste to be used as coatings with improved superficial hardness

Mercedes del Río Merino1, Paola Villoria Sáez1, Jaime Santa Cruz Astorqui1, Antonio Rodríguez Sánchez1, César Porras Amores1

1

Technical University of Madrid, School of Building Engineering, TEMA Research Group. E-mail: mercedes.delrio@upm.es

Abstract

This work studies the physical and mechanical behavior of a light gypsum eco-mortar, made with aggregates from ceramic waste and extruded polystyrene (XPS) waste. The main objective to include waste into the gypsum compound is to reduce the amount of raw material used (gypsum) and thus reduce the environmental impact, improving the characteristics of a gypsum without additions to be applied as coatings that require hardness values higher than usual and even better behavior against water. For this, gypsum samples of dimensions 4x4x16 cm were made to which different percentages of the residues were added according to the weight of the plaster (1%, 2% and 3% of XPS and 25% and 50% of ceramics) and also reference samples (without additions). These specimens were tested in the laboratory and the following characteristics were determined: dry density, surface hardness, flexural strength, compressive strength, water absorption by capillarity and adhesion. After a comparative analysis, the following conclusions were drawn: it is possible to elaborate gypsum mortars with addition of XPS and ceramic residues and that these gypsums reduce the water absorption by capillarity and increase the surface hardness of the reference gypsum without additions.

Keywords: Gypsum mortar, Waste, Ceramic, Extruded polystyrene. Recycling. Introduction

The construction sector consumes 60% of raw materials extracted from the lithosphere and generates large amount of construction and demolition waste (CDW). Of these CDW the most generated are ceramic waste, which represent 54% of the total generated. The volume of ceramic waste is such that its use is already normalized as aggregate in cement mortars, but not in gypsum [1]. Other CDW that have been increasing over recent years are waste from insulation, given the bigger consumption of these products after the entry into force of the Building Regulation. In addition, it is estimated that only 30% of these wastes are recycled [2].

Trying to increase CDW recycling percentage, numerous research works have been found replacing traditional construction raw materials with other alternative materials with lower environmental impact. In the case of gypsum composites, several research works have been found suggesting the use of CDW as raw materials and thus, with criteria of circular economy, close the cycle of the waste generated in building construction. Among the works found, San Antonio et al. [2] analyzed the feasibility of adding extruded polystyrene (XPS) waste in a gypsum matrix, concluding that it is possible to use XPS waste to design lightweight gypsum compounds with improved thermal properties. However, other characteristics worsen: the mechanical resistance and surface hardness. Moreover, Santos Jimenez et al. [1] incorporated up to 50% of ceramic waste in a gypsum matrix improving the surface hardness and reducing the water absorption by capillarity. However, these compounds have higher densities and thus poorer thermal performance.

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Therefore, due to the good results obtained with these wastes in previous works, a synergistic effect could take place by incorporating them combined. Therefore, this research work shows the results of an experimental plan analyzing the viability of incorporating --in gypsum compounds-- mixed waste mixtures and specifically ceramic waste and XPS waste. These compounds can be used as light weight gypsums for continuous coatings with improved superficial hardness and water absorption.

Materials and method

Gypsums are classified according to UNE EN 13279-1. Gypsum mortars are designated as B2 and the characteristics to be met are the same to those required for normal gypsum plasters (B1) --the type of gypsum from which we start in this research (reference gypsum)-- and for lightweight gypsums (B4). High hardness gypsums are designated as B7 and they must meet the following specifications according to UNE EN 13279-1 and RP 35.04 (table 1).

Table 1. Main characteristics required by UNE EN 13279-1. [3, 4] Gypsum Code Density Flexural S. Comp. S Surface

hardness Adherence

Gypsum B1

--

≥1 MPa ≥2 MPa --

Breakage occurs in the support or in the gypsum mass; when it occurs in the interface layer of plaster – support Ad ≥ 0.1 N/mm2 Gypsum mortar B2

Lightweight G. B4 <1g/cm3

High hardness G. B7 -- ≥2 MPa ≥6 MPa ≥2.5 MPa ≥75 Shore C

The gypsum used corresponds to the Iberplast brand manufacturer Placo Saint Gobain, characterized as B1 according to UNE-EN 13279-1. The extruded polystyrene used corresponds to wastes of XPS plates of thermal insulation for roofs. Plates were scratched and sieved. The final product was a particle size between 6-4 mm referred to as XPS. The ceramic waste was obtained from rough brick fragments that were crushed in a crusher. The resulting product was sieved and characterized as "Coarse aggregate" (Ag): 70% aggregate retained on the sieve of 2 mm and 30% aggregate retained on the sieve of 1 mm.

To achieve this objective, an experimental plan was done considering the best results obtained in previous works [2] [1]. The compounds shown in table 1 were prepared using a water/gypsum ratio (w/g) of 0.8. Prismatic specimens of dimensions 40x40x160 mm were made according to standard UNE-EN 13279-2 and the following tests were carried out to determine the following characteristics: (1) Dry density; (2) Shore C hardness; (3) Flexural strength; (4) Compressive strength; (5) Water absorption by capillarity; (6)Adherence. Finally, an analysis was performed to compare the results obtained with the compounds with additions and those of reference. Finally, the relation between the mechanical resistance and the density of the compounds was also explored and compared with the formula defined by del Rio Merino (1999) for lightweight gypsums[5].

Results

Table 2 shows the average results obtained in the tests. The values that do not meet the standards for lightweight gypsums have been marked in bold.

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167 Table 2. Average results obtained in tests on the compounds.

Compound D F C SH A AC 1 Reference 1.14 2.91 5.09 61.87 0.40 a 81.7 2 Ag25% 1.13 3.02 5.15 68.20 0.53 a 60.0 3 Ag50% 1.22 3.00 5.00 75.30 H 0.61 a 55.0 4 XPS 1% L 0.91 2.85 4.95 71.17 - 75.0 5 XPS 2% L 0.84 2.21 3.06 57.33 - 71.0 6 XPS 3% L 0.82 1.99 2.76 50.10 - 68.0 7 XPSg1% + Ag25% 1.02 2.71 3.94 70.37 0.36 b 52.7 8 XPSg1% + Ag50% 1.05 2.65 4.19 71.83 0.44 b 50.3 9 XPSg2% + Ag25% L 0.92 2.04 2.66 54.83 0.36 b 60.7 10 XPSg2% + Ag50% L 1.00 2.41 3.30 79.43 H 0.38 b 46.3 11 XPSg3% + Ag25% 0.80 1.61 1.85 55.67 - 51.7 12 XPSg3% + Ag50% L 0.91 1.75 2.15 50.70 - 48.0

D: Density (g/cm³); F: Flexural Strength (MPa); C: Compressive Strength (MPa); SH: Surface Hardness (Shore C); A: Adherence (N/mm2_{); AC: Absorption capillarity (mm)}

L:

Complies with lightweight gypsum regulation

H_{: Complies with high hardness gypsum regulation (except for compression resistance)}

Figure 1 compares the relation between the density and mechanical resistance of the compounds with ceramic and XPS waste. Moreover, mechanical strength results increase when the density increases, following the equation set by Del Rio Merino (1999) for lightweight gypsums.

Figure 1. Relation between the mechanical strength and the density of the compounds - Comparison

with Del Rio Merino equation

However, results with XPS+Ag obtained slightly lower resistance than compounds with only XPS or than the expected resistance achieved with the equation. This can be due to the greater amount of aggregates incorporated to the gypsum matrix (both XPS and Ag) and the reduction of gypsum. Therefore, a more heterogeneous material is achieved --with greater pores—and thus the mechanical resistance of these compounds is reduced.

Conclusions

It is feasible to incorporate ceramic waste along with XPS waste in a gypsum matrix, obtaining plaster mortars that meet the requirements of current regulations for light weight gypsums (B4):

· All samples with ceramic waste and XPS waste present flexural strength > 1.0 MPa and surface hardness > 45 units Shore C.

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The addition of XPS and ceramic waste in a gypsum matrix does not improve mechanical strength values of the gypsum of reference.

In the case of gypsum mortars with ceramic recycled aggregates, the addition of XPS:

· Reduces the mechanical strength of the ceramic gypsum mortar without XPS and the gypsum of reference (with no additions).

· Improves adherence, getting breaks type b (within the mass of gypsum).

· Improves behavior in the water. Moreover, water absorption by capillarity is inversely proportional to the amount of added wastes, mainly ceramic.

Among the compounds studied, Ag50% +2%XPS compound can be considered as lightweight gypsum --due to its density— with higher surface hardness --as it exceeds the required values for high hardness gypsums--. However, the compound does not meet the requirements of the standard for high hardness gypsums in terms of compressive strength (6 MPa). Moreover, this compound obtained up to 43.27% decrease in water absorption by capillarity compared to the gypsum of reference.

Moreover, mechanical strength results increase when the density increases, following the equation set by Del Rio Merino (1999) for lightweight gypsums.

Finally, these mortars can be applied in continuous coatings for their good properties of surface hardness, adherence and behavior in water.

Acknowledgement

This research was supported by the Ministry of Economy and Competitiveness of the Spanish Government (Project reference number BIA2013-43061-R).

References

[1] R. S. Jiménez, et al., "Análisis de la viabilidad del yeso con adiciones de residuo cerámico para la aplicación en edificación," in Jornadas internacionales de

investigación en construcción: vivienda: pasado, presente y futuro: resúmenes y actas, 2013.

[2] A. San-Antonio-Gonzalez, et al., "Lightweight material made with gypsum and extruded polystyrene waste with enhanced thermal behaviour," Construction and

Building Materials, vol. 93, pp. 57-63, 2015.

[3] RP 35.04, Supplementary Regulation of high hardness Gypsum for construction,

2009.

[4] RP 35.03, Reglamento particular de la marca AENOR para yesos y escayolas de

construcción, sus prefabricados y productos afines. Yesos de construcción aligerados (B4) 2009.

[5] M. del Rio Merino, "Elaboración y aplicaciones constructivas de paneles prefabricados de escayola aligerada y reforzada con fibras de vidrio E y otros aditivos," Arquitectura, 1999.