Experimental Investigation of a New Design of Insulation Gypsum Plaster Blocks

Abstract

Green building materials are an alternative to ordinary materialsoffering multiple environmental benefits. This study consists of an experimental investigation of a new design of gypsum plaster blocks. First, a mix design of gypsum plaster and water mixture was prepared. The optimal mix composition was determined according to the mechanical and physical properties, such as the water absorption, the temperature of hydration, the density, and the compressive strength of different gypsum plaster and water mixtures made by varying the water dosage. The second part of this investigation aims to study a new design of green blocks prepared from the optimal water and gypsum plaster mixture. The new blocks are perforated to lighten them and to reduce their thermal conductivity in order to make them moreinsulate. Experimental tests were conducted on the block prototype, such as the measurement of dimensional tolerances, compressive strength, density, flatness, water absorption, residual moisture, surface hardness, and thermal conductivity. Experimental test results show that the new blocks have very low density, and their compressive strength is sufficient for wall construction. In addition, the manufacturing process of the new blocks is very easy and very fast. Finally, the obtained physical and mechanical properties of the new gypsum plaster blocks give it the opportunity to be used for interior walls for building constructions.

1. Introduction

The traditional fired clay bricks industry is a source of environmental pollution. This is due to the high gas emissions into the atmosphere generated during the process of firing in this industry [1]. In order to resolve this problem, little research has investigated reducing or controlling the gases evolved from the firing process of the clay bricks industry. In this case, Santos et al. [2] and Toledo et al. [3] studied the correlations between clay properties and the amount of gas emissions as a function of the temperature of firing. On the other hand, Gonzalez et al. [4] and Cusido et al. [5] show that the control of mineral contents of clay and the temperature during the firing process allows reducing gas emissions, especially fluorine, chlorine, and sulfur gases.

Nowadays, researchers investigated new materials for the development of sustainable green blocks. This aims first to decrease the traditional brick industry’s impacts on human health and on the environment, and second, to reduce the high energy consumption of the traditional brick industry.

Gypsum plaster is one of materials providing many solutions to conventional material problems. This is due to its interesting physical and mechanical properties, such as low thermal conductivity, low density, and high firing resistance [6]. Many studies have investigated the improvement of the thermal insulation of gypsum plaster blocks for interior walls [7,8,9,10,11,12]. Other studies have investigated the incorporation of other natural raw materials and chemical additives in gypsum plaster blocks to improve their physical properties, especially the thermal conductivity and the density [13,14,15,16,17]. In the other case, the results of the works of Zach et al. [18], Korjenic et al. [14], and Hroudová et al. [17] show that the capillary activity of gypsum plaster blocks has a significant effect on the residual moisture of buildings. In addition, Gencel et al. [19], Khalil et al. [20], and Benazzouk et al. [21] show that the mechanical and physical properties of gypsum plaster mixture are improved by adding some additives’ waste to the mixtures. As an example, Gencel et al. [19] demonstrate that the sound-proofing property and thermal property of gypsum plaster mixture were improved by adding pore-forming agents.

Finally, this study aims to explore the advantages of gypsum plaster mixture for developing a new design of gypsum plaster blocks perforated using circular alveolar. he holes perforated on blocks aim to lighten them and to reduce their thermal conductivity in order to make them more insulate.

Notice that if the mechanical and physical properties of the new blocks verify the requirements of the international standards, they will be a good alternative for the construction of buildings interior walls with high thermal insulation.

The first part of this study consists of studying both the physical and chemical properties of the used gypsum plaster. The second part aims to elaborate an optimal mix design of gypsum plaster and water mortar. The second parts consists of evaluating both the physical and mechanical properties of the optimal mixture. The third part aims to validate the possibility of use of perforated gypsum plaster as an ecological green block by experimental tests on the newly designed block prototypes.

2. Experimental Program

The objective of this work is the development of new perforated blocks using gypsum plaster and water mixture. The experimental study flow chart representing all conducted experiment tests is shown in Figure 1.

The main parts of this experimental study are the following:

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Evaluate the chemical, physical, and mineral properties of the gypsum plaster used in this study, such as:

• Chemical composition using an X-ray fluorescence spectrometry (XRF).
• Microstructure analysis by scanning electron microscope.
• Particle size analysis.
• Densities.
• Blaine specific surface (BSS).

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Mix design of gypsum plaster and water mixture in order to determine the optimal mixture composition.

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Study of the mechanical and the physical properties of gypsum and water mixture, such as:

• Density.
• Water absorption.
• Temperature of hydration.
• Compressive strength.

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Preparation of the block prototypes.

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Study of the mechanical and the physical properties of gypsum plaster block prototype:

• Dimensional tolerances.
• Density.
• Compressive strength.
• Flatness.
• Residual moisture.
• Water absorption.
• Surface hardness.
• Thermal conductivity.

3. Materials and Methods

3.1. Gypsum Plaster

3.1.1. Chemical Analysis

Gypsum plaster used in this work is a local product. The chemical analysis was performed by an X-ray fluorescence spectrometry (XRF). This test consists of evaluating the content in percent of Al₂O₃, CaO, F_e2O₃, K₂O, MgO, Na₂O, SiO_2, and SO₃. The chemical analysis result of gypsum plaster is presented in

Table 1. Gypsum plaster chemical composition.

Component	Al2O3	CaO	Fe2O3	K2O	MgO	Na2O	SO3	SiO2
Percentage	0.10	34.85	0.08	0.03	0.53	0.09	46.63	0.70

. Result shows that the tested gypsum plaster is too rich in calcium oxide (CaO ≈ 35%) and in sulfur dioxide (SO₃ ≈ 47%).

3.1.2. Microstructure Analysis by Scanning Electron Microscope

The morphological forms of the used gypsum plaster were studied using a scanning Electron Microscope (SEM). Results of SEM image, presented in Figure 2, show that almost all plaster grains have a spherical shape, which means that this gypsum plaster is highly semihydrated.

3.1.3. Particle Size Analysis

The distribution of gypsum plaster grain size was carried out using the sedimentation method according to NF P 94-057 [22] standard requirements.

Figure 3 shows the curve the distribution of the particle size of gypsum plaster. According to this curve, the fineness modulus is about 0.95, which means that the tested plaster is very fine.

Two other important factors, characterizing grains size distribution, are determined: the curvature coefficient (C_c) and the uniformity coefficient (C_u). C_c and C_u are expressed as follow [23]:

$${\mathrm{C}}_{\mathrm{c}}=\frac{{\mathrm{D}}_{30}·{\mathrm{D}}_{30}}{{\mathrm{D}}_{10}·{\mathrm{D}}_{60}}$$

(1)

$${\mathrm{C}}_{\mathrm{u}}=\frac{{\mathrm{D}}_{60}}{{\mathrm{D}}_{10}}$$

(2)

where D₁₀, D₃₀, and D₆₀ are the grain size at 10%, 30%, and 60% passing, respectively.

Test results indicate that C_u and C_c of the used gypsum plaster are, respectively, 5.6 and 1.6. Indeed, due to C_u > 2 and 1 < C_c < 3, it can be concluded that the gypsum plaster is effectively graded and graduated.

3.1.4. Physical Properties

Table 2. Physical properties of gypsum plaster.

Parameters	Particle Size (mm)	Absolute Density (g/cm3)	Bulk Density (g/cm3)	Blaine Specific Surface (BSS) (cm2/g)
Standard	NF P 94-056 [22]	NF EN 1097-7 [25]		NF EN 196-6 [24]
Test result	0/0.5	2.65	0.60	5705

presents the physical properties of gypsum plaster. Tests results demonstrate that gypsum plaster has a bulk density and an absolute density equal to 0.60 g/cm³ and 2.65 g/cm³, respectively. Results also show that the Blaine specific surface (BSS) of gypsum plaster, determined using the NF EN 196-6 [24] requirements, is about 5705 cm²/g. This result confirms that gypsum plaster used in this study is very fine.

3.2. Tests Setup on Gypsum Plaster and Water Mixture

3.2.1. Mix Design of the Mixture

The objective of this part is to evaluate the mix design of the gypsum plaster and water mixture. The appropriate water volume is that given a workability that makes the mixture molding without any vibration process easy. To perform this, different mixtures are prepared by varying the water/gypsum plaster ratio, and thereafter their flow times were measured by using an LCL mortar maniabilimeter (Figure 4).

The flow time measurements results are presented in

Table 3. Results of flow time measurements test.

Water/Gypsum plaster	0.54	0.58	0.59	0.60	0.61	0.62	0.63	0.64
Flow time (s)	5.23	4.53	3.41	2.38	1.99	1.75	1.55	1.49

and in Figure 4. The presented results show that the flow time decreases when increasing the water amount. In addition, results of Figure 5 show that until a water/gypsum plaster ratio of 0.60, the flow times of the mixtures remain constant, and thereafter the workability of these mixtures is the same. As a conclusion, the water amount is chosen as equal to 60% of the gypsum plaster amount.

3.2.2. Test Specimens Preparation

In this experimental study, cubic and cylindrical specimens are manufactured using a gypsum plaster and 60% water mixture. The dimensions and the number of each specimen shape per test are shown in

Table 4. Specimens shape and dimensions.

Test	Specimen Shape	Specimen Dimensions	Number of SpecimensbyTest
Density	Cubic	100 × 100 × 100 mm	3
Absorption degree	Cubic	100 × 100 × 100 mm	3
Hydration temperature	Cubic	100 × 100 × 100 mm	3
Compressive strength	Cylindrical	50 × 100 mm	12

.

The mixing process of gypsum plaster and water mixture are the following:

▪

Add the gypsum plaster amount to 60% water (Figure 6a).

▪

Mix in wet condition first for 30 s with slow speed and then for 1 min with high speed (Figure 6b).

▪

Prepare the molds (Figure 6c,d).

▪

Pour the mixture on the molds (Figure 6e).

▪

Dry the specimens for 10 min before demolding (Figure 6f,g).

▪

Demold the specimens (Figure 6h).

▪

Finally, keep specimens under a temperature degree of 23 °C and a relative humidity between 55 and 65% to the testing date.

3.2.3. Density

Density measurements consist, as presented in Figure 7, of weighting a cubic specimen as a function of time until its mass is stabilized.

3.2.4. Water Absorption Degree

This test consists of measuring the mass of water absorbed by a cubic specimen of gypsum plaster and water mixture as a function of time. Measurement process steps, presented in Figure 8, consist of weighting the sample both in its dry state and in its wet state.

3.2.5. Temperature of Hydration

Measurement of the hydration temperature of gypsum plaster and water mixture steps are as follows:

▪

Prepare an insulating cubic mold (Figure 9a).

▪

Pour the mixture on the molds (Figure 9b).

▪

Place a thermometer in a copper tube containing oil in the specimen center (Figure 9c).

▪

Measure hydration temperature with time.

▪

Measure the ambient temperature using another thermometer.

3.2.6. Compressive Strength

Compressive strength tests are carried out on cylindrical specimens of gypsum plaster mixture at the ages of 1, 3, 5, 7, 14, 21, and 28 days. Compressive tests were carried out using a UTM machine according to the requirements of EN 12390-4 [26] standard.

4. Properties of Gypsum Plaster and Water Mixture

4.1. Density

The density measurement results of gypsum plaster and water mixture are presented in

Table 5. Physical properties of gypsum plaster specimen.

Initial Density (g/cm3)	Final Density (g/cm3)	Water Loss (%)	Degree of Absorption (%)
1.711	1.278	25.30	24.3

. Results show that the initial density, measured just after removing the specimen, is about 1.711 g/cm^3, and the stabilized density, measured after specimen mass stabilization, is about 1.278 g/cm³. Indeed, the total water loss is about 25.30% of the initial weight.

Figure 10 presents the density of mixture and time relationship. Two conclusions are deduced from this result: first, the density of specimen decreases with time, and second, the weight of the specimen was stabilized after 16 days, which is the end of the hardening step.

Finally, a final density of 1.278 g/cm³ classifies the gypsum plaster blocks as high-density building materials [27].

4.2. Degree of Absorption

The results presented in Table 5 show that the maximum water absorption of gypsum plaster specimen is about 24.3%. The curve presented in Figure 11 shows the absorption degree and time relationship. It can be concluded that the absorption degree of the specimen increases with time, and the maximum absorption degree was reached after 25 h. Results also show that 50% of the maximum degree of absorption was reached during only the three first hours.

4.3. Temperature of Hydration

The curve of temperature of gypsum plaster and water specimen as a function of time is presented in Figure 12. The first remark observed from this curve is that the maximum temperature of the mixture is about 47 °C, reached during the first 25 min. The second remark is that the setting of mixture due to the hydration reaction is very quick. Indeed, setting begins only after 10 min and finishes after nearly 25 min. As a consequence, a quick block removing is possible.

4.4. Compressive Strength

The compressive strength results at the ages of 1, 3, 5, 7, 14, 21, and 28 days are presented in

Table 6. Compressive strength tests results.

Age [day]	1	3	5	7	14	21	28
Compressive strength [MPa]	6.7	6.7	6.7	6.5	8.5	11.1	11.2

. Results show that the maximum strength of gypsum plaster and water specimen, of about 11.2 MPa, was reached after 21 days. In addition, 50% of its maximum compression strength was reached only after one day.

Figure 13 shows the curve of the compressive strength as function of strain after weight stabilization. According to this curve, it can be concluded that the gypsum plaster specimen has a nonlinear elastic behavior.

5. Design of New Gypsum Plaster Blocks

5.1. New Blocks Description

A new design of blocks made using a water and gypsum plaster mixture was developed. As it is known, the manufacturing process of gypsum plaster blocks is low energy consumption compared with that of ordinary clay fired bricks [5]. In addition, fired bricks are an important source of atmospheric pollution [4].

According to the new design presented in Figure 14, the new blocks are 600 mm in length, 550 mm in height, and 100 mm in thickness. In addition, the new blocks are equipped with a circular alveolar system of 60 mm in diameter.

The circular alveolar gives to the gypsum plaster blocks both a high thermal insulation and phonic insulation and a high compressive strength. Moreover, gypsum plaster makes the new blocks good hygrometric regulators, which means that they regulate internal humidity by rejecting it outside the room or by absorbing it. Moreover, as known, gypsum plaster blocks have high fire resistance [28].

Finally, the new design of gypsum plaster blocks makes them an important alternative for the construction of interior walls of buildings.

5.2. Manufacturing of Gypsum Plaster Block Prototypes

As shown in Figure 14, the block prototypes have 100 mm × 550 mm × 600 mm dimensions.

The different steps for preparing the block prototypes are the following [29]:

▪

Prepare the steel mold (Figure 15a).

▪

Place the mixture on the mold (Figure 15b).

▪

Remove the blocks from the molds after 24 h (Figure 15c).

▪

Dry the blocks on air (Figure 15d).

Finally, the following experimental tests were carried out on the hardened blocks:

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Dimensional tolerances.

-

Density.

-

Surface hardness.

-

Residual moisture.

-

Thermal conductivity.

-

Compressive strength.

-

Flatness.

5.3. Properties of Gypsum Plaster Blocks

5.3.1. Dimensional Tolerances

After hardening, blocks will be expanded due to the hydration of gypsum plaster with water and, as consequence, block dimensions increase. he specifications of the standard NF EN 12859 [29] show that the maximum accepted tolerances in dimension change are ±5 mm for length, ±0.5 mm for thickness, and ±2 mm for height.

The results of

Table 7. Mechanical and physical properties of gypsum plaster blocks.

Property		Result
Dimensional tolerances (mm)	Length	600.2
	Height	550.7
	Thickness	100.3
Drying time (h)		48
Flatness (mm)		0.5
Density (Kg/m3)		856
Compressive strength (MPa)		5.6
Residual moisture (%)		5
Water absorption (%)		24.3
Surface hardness (shore C)		35
Thermal conductivity (W/mK)		0.45

show that after removing gypsum plaster blocks, their dimensions increased to 100.3 mm, 550.7 mm, and 600.2 mm for thickness, height, and length, respectively. As a conclusion, the increases in block dimensions are lower than the maximum recommended tolerances.

5.3.2. Flatness

The specifications of the standard NF EN 12859 [29] show that the maximum deviation of metal ruler placed along the diagonals of the block and the shims must not exceed 1 mm. A flatness test made on the block prototypes (Figure 16) showed that its flatness index is about 0.5 mm (Table 7). This flatness index is lower than the maximum recommended value of 1 mm.

5.3.3. Density

The results of Table 7 show that the density of the gypsum plaster block is about 856 kg/m³. As a consequence, gypsum plaster blocks can be considerate as average density blocks.

5.3.4. Compressive Strength

The results of Table 7 show that the average compressive strength of gypsum plaster blocks is about 5.6 MPa. This compressive strength value makes possible the use of these blocks as building materials for interior walls [27].

5.3.5. Residual Moisture

The residual moisture content of the blocks was determined by weighting the block after it was dried until the stabilization of weight at a temperature of 20 ± 5 °C in a ventilated room under relative humidity of 65 ± 5% [28]. Results demonstrate that the average moisture content of the gypsum plaster block prototype is about 5%. This obtained result is lower than the maximum recommended value of 6% [28].

5.3.6. Water Absorption

The measurement of the degree of water absorption of gypsum plaster blocks was performed in accordance with NF EN 772-21 requirements [30]. The results of Table 7 show the water absorption degree of gypsum plaster blocks is about 24.4%.

5.3.7. Surface Hardness

The hardness of blocks surface was measured, using a durometer, on dried blocks. Experimental results show that the hardness of the gypsum plaster blocks surface is about 35 (Table 7). Consequently, the class of the prepared gypsum plaster blocks is as low-density bricks.

5.3.8. Thermal Conductivity

The thermal conductivity of gypsum plaster bricks was carried out with the specifications of NF EN ISO 8990 standard [31] by using the “boxes method”. The process of this method is presented in Figure 17. Results of Table 7 show that gypsum plaster blocks have an average thermal conductivity of about 0.45 W/mK. As a main conclusion, the developed gypsum plaster blocks have a low thermal conductivity value, 0.35 W/mK ≤ λ ≤ 0.87 W/mK [31], for use as an insulation building material for the construction of interior walls.

5.4. Discussion

Experimental tests results on gypsum plaster block prototypes show that these blocks can be an alternative for insulation building materials for interior walls construction. This result makes the possibility to manufacture this new block due to these reasons:

-

They have a tolerated dimensions after drying.

-

They have a flat surface.

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They are considered lightweight blocks because of their very low density, about 865 kg/m³.

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They have a recommended compressive strength for wall construction.

-

They can be used only after one day because of their very quick setting.

Finally, a prototype of an interior wall was constructed using the new gypsum plaster blocks and a mortar of gypsum plaster and water, as shown in Figure 18.

The following conclusions were noted:

• The construction of the walls by the new blocks is very easy and very fast due to the flat surfaces and to the similarity in size of blocks.
• Compared with the ordinary brick blocks, the mortar consumption is considerably low.
• The possibility of faience attachment was observed.
• There are no cracks observed at joints between blocks.

6. Conclusions

This work presents the results of an experimental study on a new design of green gypsum plaster blocks with circular alveolar.

The main conclusions of the experimental results are the following:

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Gypsum plaster blocks have a tolerated dimensions after drying.

-

The flatness index shows that gypsum plaster blocks have a flat surface.

-

Gypsum plaster blocks can be considered as average density blocks because of their very low density.

-

Gypsum plaster blocks have a recommended compressive strength for wall construction.

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Gypsum plaster blocks have very quick setting.

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The construction of the walls by the new blocks is very easy and very fast due to the flat surfaces and to the similarity in size of blocks.

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Because these gypsum blocks are very sensitive to water, they are not intended for dry zones.