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Article

Evaluating the Performance and Efficiency of Sandwich-Insulated Concrete Block Products in the Saudi Market

by
Hani Alanazi
1,2,*,
Abdullah Alzlfawi
1 and
Mohammed Albuaymi
1
1
Department of Civil and Environmental Engineering, College of Engineering, Majmaah University, Al-Majmaah 11952, Saudi Arabia
2
Engineering and Applied Science Research Center, Majmaah University, Al-Majmaah 11952, Saudi Arabia
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(22), 4172; https://doi.org/10.3390/buildings15224172
Submission received: 22 September 2025 / Revised: 12 November 2025 / Accepted: 17 November 2025 / Published: 19 November 2025
(This article belongs to the Special Issue Advances in Green Building and Environmental Comfort)
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Abstract

The sandwich-insulated concrete block is one of the innovative building units developed to enhance thermal insulation in buildings. However, there are still some drawbacks that hinder the optimum utilization of these types of insulating blocks. Therefore, this study aims to conduct a systematic and comparative assessment of the performance of the sandwich-insulated concrete block available in the local market. To accurately assess the efficiency of the insulated concrete blocks, several samples from various sources available in the local market were collected and examined. Visual inspection, dimensional tolerance, compressive strength, physical properties, thermal performance, and environmental resistance tests have been conducted in accordance with local and international standards. The obtained experimental results revealed that the mixture proportion of the concrete shell plays a crucial role in the properties and performance of the whole insulated concrete block. Blocks with volcanic aggregates exhibited lower compressive strength, ranging between 3.19 and 5.26 MPa, but better thermal conductivity with an average of 0.25 W/m·K. In comparison, normal aggregate blocks showed higher compressive strength up to 8.12 MPa but slightly reduced thermal insulation around 0.44 W/m·K. Water absorption varied widely from 5% to 16%, and chloride contents in volcanic aggregates exceeded the permissible 1% limit. Broken edges and cracks were mainly observed in low-strength blocks, emphasizing the importance of proper curing and material selection. Durability assessments revealed that accelerated weathering experiments demonstrated the susceptibility of expanded and extruded polystyrene to UV-induced degradation. Nevertheless, all tested polystyrene samples showed high resistance to fungal attack, with varying antibacterial activity.

1. Introduction

With the increasing urbanization and development in Saudi Arabia, energy demand is rising significantly to achieve thermal comfort in buildings. On the other hand, the severe climatic conditions in Saudi Arabia throughout the year-round seasons have led to intensive energy consumption to achieve thermal comfort in various residential, commercial, and governmental buildings. To address these challenges, new strategies are being implemented to enhance sustainability in our built environment and reduce energy consumption in the construction sector. Improving thermal insulation can guarantee fewer thermal losses between indoors and outdoors. Increasing energy efficiency in buildings has many benefits, such as reducing environmental damage and pollution, managing resources more efficiently, and providing economic advantages. Sandwich-insulated concrete blocks are increasingly used in construction because they offer good thermal performance in buildings, making them ideal choices for energy-efficient building envelopes. Sandwich-insulated concrete blocks typically include a polystyrene core layer that serves as an insulator and an outer shell of concrete or other aggregate materials.
Lightweight sandwich-insulated concrete blocks are being widely applied in the building sector worldwide due to their excellent thermal insulation capacity. It is available in different densities, sizes, and thicknesses [1]. The thermal and structural performance of concrete masonry hollow blocks was investigated using a finite element model [2]. It was found that aspect ratio, cavity width, hollow ratio, thermal bridges, and number of cavities are the main factors influencing the thermal efficiency of hollow block walls [2]. The shape, size, and distribution of voids in concrete blocks affect overall thermal efficiency significantly. The staggered holes were found to elongate the heat flow path through the wall and reduce heat transfer compared to solid block or aligned holes [3]. It was reported that a 30% reduction in thermal resistance of two webs of concrete blocks can be obtained compared to three webs [4]. It was reported that expanded polystyrene (EPS) has a compressive strength below 0.21 MPa, and no bonding was observed between concrete and EPS. Consequently, the strength of the block decreases with the increase in the volume content of EPS [5]. A new manufacturing method for the block was developed using lightweight concrete with dimensions of 20 × 40 × 20 cm3 [6]. It is concluded that the developed block has a smoother surface, and therefore, less plaster needs to be applied to the surface. A recent study aimed to optimize the thermal performance of lightweight building blocks, including those with lightweight concrete as outer layers [7]. A numerical model has been developed to calculate the actual thermal transmittances of the building wall. It was found that the type and density of lightweight concrete and the volume of the EPS inside the block are significant factors affecting thermal and mechanical performance.
Reducing energy consumption in the building sector will significantly contribute to the overall strategy of mitigating climate change and promoting energy conservation [8]. Thermal insulation of walls is essential because it decreases heat transfer and reduces the energy consumption rate. Therefore, Saudi specifications made a strategic decision and new building regulations; a U-value of 0.61 W/m2·K is recommended for the external walls of buildings. External walls with polystyrene panels can lead to a reduction in energy waste by three times [9]. A study was conducted to investigate the field performance of two test rooms: one with hollow-core concrete block walls (reference) and the other with concrete walls containing EPS Panels inside [10]. The results indicated that internal temperature is reduced by 3 °C and heat flux is decreased by 58% in the case of EPS blocks compared to the reference. Moreover, thermal transmittance is decreased significantly in the case of EPS panels, and energy consumption is reduced by about 29% during the summer months. Improving the thermal insulation of walls is a promising strategy to decrease energy consumption in operating buildings [11].
It was reported that approximately one-third of energy loss occurs due to inadequate wall insulation [12]. The performance of different lightweight materials used in the manufacturing of non-load-bearing hollow blocks was compared, including expanded polystyrene (EPS), low-density polyethylene (LDPE), volcanic scoria (VS), and vermiculite (VL). The results indicated that the strength was reduced by approximately 37–51%, while thermal conductivity was decreased by approximately 17–26%. The obtained density of the block is in the range of 1680–2000 kg/m3 [13]. Recently, there has been explosive growth in the utilization of expanded polystyrene in the construction industry [14]. EPS has several advantages over other lightweight materials: rigid foam with low thermal conductivity, appropriate load-bearing capacity at low weight, low water and air permeability, long life with low maintenance, and fast and economical construction [14]. The density of polystyrene has a significant influence on the thermal performance of insulated concrete blocks; low-density polystyrene provides better performance [15]. The addition of EPS as aggregate has negative influences on fire resistance, compressive strength, and volumetric expansion. Therefore, in the construction industry, it is mandatory to use flame-retardant agents, and bonding agents such as water-emulsified epoxies are required [16]. It was reported that the thermal conductivity of a hollow block can be decreased by 30% when expanded polystyrene is used to fill the cavities in the block [17]. A comparative study proved that polystyrene is more effective than vermiculite in reducing the thermal conductivity of the block [18].
Hollow blocks exhibit excellent thermal insulation, reducing heat transfer due to the high air volume inside building units. The effect of the geometry of the building block on the thermal performance of the building was studied [19]. A non-load-bearing lightweight concrete sandwich panel was developed, and it was found that a polystyrene with a thickness of 20–170 mm could lead to 22–79% energy savings [20]. EPS is a lightweight, rigid plastic material with excellent thermal insulation properties, low water absorption, and minimal thermal conductivity [21]. The advantages of insulated concrete blocks include low cost, better thermal insulation, and lightweight [21]. The wind fluctuations and temperature differences from season to season have a significant influence on the thermal performance of the insulated concrete block [22]. However, the combination of lightweight concrete and EPS is considered an effective solution to minimize the thermal transmittance of the block [6,23]. On the other hand, the durability and fire resistance of EPS can hinder the utilization of insulated-sandwich blocks, and there is no standard method for evaluating the fire resistance of a single concrete block. It was recommended to use a protection layer for external and internal insulation panels to improve their durability [11]. Water absorption is the key factor causing deterioration of thermal insulation efficiency [24]. EPS hollow blocks are suitable as non-load-bearing units due to their durability and strength [25]. However, EPS is highly flammable and can react violently, producing toxic black smoke during combustion [26]. Some researchers used flame retardants and coatings to improve the thermal stability and fire resistance of EPS composites [14,26,27,28], though added protection can increase weight and cost [29]. A bio-based coating for EPS particles was examined [27], and a green and highly effective flame-retardant coating for EPS foam was developed [30].
Although various types of blocks have been extensively studied worldwide, there are few studies on sandwich-insulated concrete blocks. Previous studies have generally focused on either thermal or mechanical performance, without considering durability factors such as chloride penetration, UV degradation, and water absorption. This study addresses that gap by evaluating locally manufactured blocks and illustrating the mechanical performance, thermal efficiency, and durability. This paper evaluates the quality, safety, and efficiency of sandwich-insulated concrete block products in the local market. An experimental program was planned and conducted to determine the physical and mechanical properties, as well as the durability performance, of the insulated concrete block. The properties of insulating concrete blocks were studied from different aspects, including materials, dimensions, density, strength, thermal conductivity, stability with time, and resistance to environmental conditions. Additionally, the influence of different types of polystyrene on the thermal properties and mechanical performance of sandwich-insulated concrete blocks was assessed. Also, the impact of biological attack and weathering conditions on the performance of insulating concrete blocks was investigated.

2. Experimental Procedures

Various samples of sandwich-insulated concrete blocks with different properties were sourced from the seven major manufacturers in the local market, Saudi Arabia. All sandwich-insulated concrete blocks with volcanic aggregates that were market-available were collected, and blocks with normal aggregates were collected from widely available sources in the local market. These samples were identified with specific names, as presented in Table 1. Figure 1 presents the photographs of sandwich-insulated concrete blocks with varying hole configurations and insulation arrangements. They are made from various materials, and all blocks have the exact dimensions of 40 × 20 × 20 cm. The shells of these blocks are made of concrete with different aggregates, including volcanic aggregates and normal (crushed limestone) aggregates. In addition, high-capacity thermal insulating materials such as EPS and extruded polystyrene (XPS) with a thickness of 7.5 cm have been employed as core materials. The shells of 5 samples (from 1 to 5) were made from volcanic rock. Group A and B blocks include two different blocks that were collected from two manufacturers. The differences between these blocks are the types of polystyrene and their densities, as shown in the table. The shells of the other four blocks (6–9) are made of traditional concrete with normal aggregates (crushed limestone aggregates). Several tests have been conducted to evaluate the physical and mechanical properties of insulated concrete blocks. The experiments include visual inspection, physico-mechanical tests, thermal performance, and resistance to environmental conditions and weathering. The following are details of the performed tests. Each experimental test was performed on at least three specimens per block type, and the mean values are presented.

2.1. Visual Inspection

The visual inspection was performed in accordance with ASTM C62 [31]. Surface characteristics such as cracks, chips, separation between polystyrene and shells, and efflorescence were checked.

2.2. Dry Density

The dry density was determined in accordance with EN 772-13 [32]. Blocks were dried in a lab oven at 75 °C for 24 h until constant weight. The dry weight was measured using a precision balance (capacity 30,000 g, accuracy ± 0.1 g). The gross volume (Vg) was measured after deducting voids.

2.3. Compressive Strength

The compressive strength test was carried out following ASTM C140 [33] using an automated CONTROLS compression machine (capacity 2000 kN). To ensure uniform pressure, block surfaces were capped with SikaEmaco S 488 mortar (11 mm thickness, w/m ratio 0.16) and cured for 7 days. Steel plates (20 mm) were placed on the top and bottom surfaces before testing. The load was applied at 0.3 kN/s until failure.

2.4. Thermal Performance

The thermal performance of sandwich-insulated concrete blocks was evaluated by measuring the thermal conductivity (K-value) of the used materials using a heat flow meter (HFM-100 HT) in accordance with ASTM C518 [34]. This technique determines the equivalent thermal conductivity of materials under steady-state conditions. Before testing, the blocks were completely dried to remove any moisture from the tested materials, as the high sensitivity of thermal properties to moisture made this necessary. The surfaces of hot and cold plates were covered with a smooth towel to minimize heat loss between the sample surfaces and the plates due to the high roughness of the surface of some samples.

2.5. Water Absorption

Water absorption of the sandwich-insulated concrete blocks was determined according to ASTM C140 [33]. The block specimens were first submerged in a water tank for 24 h at a room temperature of 23 ± 2 °C. After 24 h of submerging in the water tank, the specimens were removed and left for 1 min ± 5 s on a wire mesh to drain the excessive water. Then, the visible water was removed with a damp absorbent cloth. After that, the block specimens were weighed, and this weight is recorded as saturated weight. Subsequently, all blocks were dried in a lab oven at 75 °C for 24 h and recorded as dried weight. Then, the water absorption was calculated.

2.6. Chloride and Sulfate Contents

The concentration of chlorides and sulfates in concrete has been identified as one of the most critical parameters for the durability of concrete structures. The chloride and sulfate content tests were conducted on two volcanic-aggregate blocks (A and B) and two normal-aggregate blocks (E and G). A and B blocks were selected for testing because they are the most widely used volcanic-aggregate blocks in the local market. The presence of chloride and sulfate content can have detrimental effects on the concrete microstructure due to their reaction with cement hydration products. BS 1881-124 [35] describes test methods for the analysis of hardened concrete. It includes the measurement of the chloride and sulfate content in hardened concrete samples. Before grinding, the concrete samples were dried at 105 ± 5 °C until a constant mass was achieved, and then cooled to room temperature in a humidity-free environment. In this study, four different types of outer shells with different aggregates used in sandwich-insulated concrete blocks were tested. Shell samples of approximately 2 kg from different materials were crushed, ground into fine dust, and sieved using a 125-μm sieve. About 5 ± 0.005 g of the passing materials from each sample were taken and tested according to the BS 1881-124 [35] procedure for the chloride and sulfate content test. The chloride and sulfate contents as a percentage of cement content to the nearest 0.01% were calculated.

2.7. Polystyrene Degradation Tests

Sandwich-insulated concrete blocks are increasingly used in modern buildings because they offer good thermal performance, making them ideal choices for energy-efficient building envelopes. They are composed mainly of a concrete outer shell made with normal or volcanic aggregates and a polystyrene internal core, either EPS or XPS, which is prone to deterioration when exposed to direct environmental conditions. To ensure the performance of polystyrene and its compliance with governing regulations, several tests should be carried out. In this research study, the durability and long-term performance of two different types of EPS (density of 16 and 20 kg/m3) and one type of XPS (density 35 kg/m3) used in the local market were evaluated by measuring their resistance to weathering, chemical resistance, and resistance to fungi and bacteria growth. The following section presents a description of the testing procedure used to evaluate the resistance of polystyrene to degradation.

2.7.1. Accelerated Weathering Test

Ultraviolet and high-energy radiation cause fast degradation of polystyrene. Accelerated weathering tests predict whether materials are durable enough to meet service life demands, since natural weathering can take years. These tests simulate environmental conditions in the laboratory with controlled parameters such as temperature, humidity, and UV. Parameters must be chosen carefully to avoid destroying samples or producing unrealistic aging. In this study, accelerated weathering was performed according to ASTM G154 [36], exposing specimens to repetitive UV light cycles in humid conditions to reproduce the effects of sunlight and moisture. Three polystyrene samples were tested: EPS (20 kg/m3), EPS (16 kg/m3), and XPS (35 kg/m3). Samples were cut to 20 × 15 × 5 cm, fixed in corrosion-resistant cells, and tested for 1000 h.

2.7.2. Antibacterial Test

Infection caused by bacteria and other microorganisms leads to serious illness and many deaths each year. For building, it is imperative to ensure that materials are safe and do not cause diseases. Bacterial biofilm can grow on the EPS surface and come into contact with humans. One method to minimize this problem is by hindering their growth on material surfaces. ASTM E2149-20 [37] evaluates the antimicrobial activity of treated specimens under dynamic contact, determining activity by comparing the tested samples with controls. Constant agitation ensures good contact between bacteria and the treated substance. In this study, three insulating materials: two EPS and one XPS were examined following ASTM E2149-20 [37]. Polystyrene samples were prepared and tested as specified. The percentage reduction in organisms was calculated by comparing treated samples with inoculum-only flasks after a specified contact time, using the formula for the reduction in the number of certified bacteria strains recovered from the triplicate plates (control and test strain).

3. Results and Discussion

3.1. Appearance and Visual Inspection

The shape and appearance of the block units have been examined by visual inspection. It is a common technique used in engineering applications to assess the condition, integrity, and performance of materials and structures. Samples were collected from different suppliers and visually inspected, as seen in Figure 2. First of all, it is clear that the insulation layer in all collected blocks is extended through the whole cross-section; it has the same length as the block, which complies with SASO 2875 [38]. On the other hand, it is noticeable that depending on the type of shell concrete and the used aggregates, some types of sandwich-insulated concrete blocks suffer defects, particularly broken edges. Moreover, due to the weaken structural performance, irregular cracks appear in the middle of some samples during manufacturing and handling, as seen in Figure 2. Another reason for these cracks is the drying shrinkage or improper curing. Additionally, the group of samples with cracks suffers separation between the internal thermal insulating polystyrene layer and the outside shell concrete. The average compressive strength of this group is about 3.42 MPa, which is below the limits. Achieving the required strength of the governing standard can ensure a proper shape without cracking or separating the different layers. On the other hand, most of the samples with broken edges are observed in the sandwich-insulated blocks with volcanic aggregate. The reason for that is the decreased fractural strength and elastic modulus of volcanic aggregates compared to normal aggregate, which leads to decreased compressive strength of volcanic concrete. These defects in the insulated concrete blocks negatively affect both structural performance and thermal insulation. Moreover, one of the primary purposes of the external concrete shell is to protect the internal insulating layer from degradation due to weathering conditions. However, with such defects and cracks, harmful substances and weathering conditions can easily access the weak insulation layers inside and accelerate their deterioration. Additionally, these defects decrease the structural integrity of the block and compromise the thermal insulation, as they expose the polystyrene core, increasing vulnerability to moisture and thermal bridging.

3.2. Dry Density

The microstructural Dry density is an essential property for sandwich-insulated concrete blocks since it indicates thermal performance as well as helps reduce the dead load of the building. The sample used for testing should be dry to prevent the effect of moisture content on the results. The drying process of the used insulated concrete blocks should take into account the possibility of polystyrene melting. Therefore, in this study, the temperature used for drying was 75 °C. According to ASTM C 126 [39], concrete blocks with densities below 1680 kg/m3 are considered lightweight blocks. Figure 3 presents the dry density of 9 sandwich-insulated concrete blocks. A considerable variation in block density can be observed. The densities of groups A and C range between 600 and 700 kg/m3. Group B blocks have a 15% higher density than groups A and C, although the shells of these blocks were made with volcanic aggregates. This means that different volcanic aggregates were used from other sources. The block’s density depends mainly on the density of the used shell concrete and the volumetric ratio between the insulated polystyrene material and the outer concrete layer. When volcanic aggregates with a density smaller than conventional aggregate are used, the dry density of the block is gradually decreased. Similarly, when lightweight concrete is used in the outer shell concrete layer, the density is strongly reduced depending on the density of the used concrete. On the other hand, the holes in the concrete layer play an essential role in reducing the density. Still, attention should be paid to the minimum thickness of the individual concrete layer to ensure structural performance.

3.3. Mechanical Performance

For most construction materials, compressive strength is considered a robust indicator for evaluating the structural performance of the material. Though the insulated concrete block is used as a non-structural element, it should have a proper compressive strength to prevent damage and cracking during transportation and handling, and also to assure good quality of the units with uniform and plane surfaces. The strength of any material depends mainly on the volumetric ratio between solid structure content and the pores, and the properties of the used material. Figure 4 presents the average compressive strength of 9 sandwich-insulated concrete blocks. The compressive strength hugely varies due to the material properties, manufacturing quality, and curing process. Blocks whose shells were made with volcanic aggregates present lower compressive strength than those made with normal aggregates. According to ASTM C 129 [40], the minimum average compressive strength of three units is 4.14 MPa. Based on this, block type A group did not meet the requirement. Also, another volcanic sandwich-insulated block group (C5) did not meet the requirement. Group B blocks made with volcanic aggregates have compressive strength above 4.14 MPa. As a result, three out of five blocks that have shells made with volcanic aggregate fall below the standard requirement. The results are in line with [13]. However, one group (E7) of blocks made with normal aggregate has a compressive strength of 3.42 MPa, making this block unacceptable. This group of normal aggregate blocks developed cracks during handling and transportation as shown in Figure 2. Although the compressive strength tests were conducted on apparently defect-free specimens from this group, the average strength remained below the acceptable limit. This indicates that low strength in this group is linked to manufacturing or curing deficiencies. The highest measured compressive strength is 8.12 MPa, and the lowest measured compressive strength is 3.19 MPa. However, no separation between shells and polystyrene was observed in the failure pattern during the compressive strength of all sandwich-insulated concrete blocks.
Generally, the group of blocks with high density exhibited higher compressive strength, which can be attributed to the use of normal-weight aggregate in the shell concrete. The average compressive strength of each of these blocks is higher than the standard limit and equals 6.2 MPa. In contrast, when volcanic aggregate is used for manufacturing the outer concrete shell, the compressive strength of the block significantly decreases, and in some cases, it is below the standard limit. This can be attributed to the low crushing strength and elastic modulus of volcanic aggregate in comparison to the normal-weight aggregate. Figure 5 presents the relationship between the density of the blocks and their compressive strength, which is strong, with denser blocks generally achieving higher strength values. The positive correlation between density and compressive strength observed in this study aligns with previous research on lightweight concretes incorporating EPS and pumice aggregates [5,6]. One exception in the present study was group E7, which exhibited lower strength despite having a moderate density. This can be attributed to deficiencies in manufacturing or curing. While density can be a key indicator of block strength, the quality of production has a huge impact on the block strength. The compressive strength of the insulated concrete block depends mainly on the strength of the concrete layer because the strength of polystyrene is very low compared to traditional concrete. The internal insulating polystyrene layer does not contribute to the strength of the whole block. The strength of the shell concrete depends on the mixture composition, type of aggregate, water/cement ratio, and curing conditions. Therefore, the shell concrete should achieve a specific compressive strength and satisfy particular restrictions to ensure an acceptable compressive strength for the whole block. Additionally, the cross-section of the used insulating materials should not exceed a certain percentage of the total cross-section of the block in order to guarantee proper structural capacity.

3.4. Thermal Performance

The primary advantage of sandwich-insulated concrete blocks over other types of building materials is their superior thermal insulation capacity, which reduces thermal losses through building walls and decreases energy consumption to achieve thermal comfort in buildings. Thermal transmittance values (U-values) are considered the actual evaluation criteria for the thermal performance of different building walls. It is a property that depends on the wall thickness and the thermal conductivity of the materials used. Worldwide, each country has different limitations depending on its climate and energy consumption plans. For Saudi Arabia, the required thermal conductivity (K-value) of the single block unit should be below 0.5 W/m·K according to SASO 2875. To achieve these values, the building units used should exhibit low thermal conductivity to decrease the wall thickness. For traditional building bricks and masonry, the thickness of building walls is increased to achieve the required thermal performance requirements, which has several disadvantages from architectural and structural aspects. Sandwich-insulated concrete blocks present an ideal solution to achieve the necessary thermal transmittance. In this study, thermal conductivity was measured for different types of outer shell concrete, as well as for various polystyrenes. The measured values were then employed to calculate the U-value for different blocks. As can be seen in Table 2, the thermal transmittance values of the concrete blocks depend on the density of the material used, which reflects the proportion of the solid materials to the voids inside the material. Thermal insulation capacity depends on the void content in the material and is inversely proportional to the dry density [18]. When normal aggregate is used to manufacture the outer concrete shell, the density increases, and the thermal conductivity (K-value) ranges from 0.42 to 0.46 W/m·K for all insulated concrete shells prepared with traditional concrete. However, when volcanic aggregate is used to make the outer concrete shell, the thermal conductivity ranges from 0.23 to 0.28 W/m·K, thereby enhancing the thermal insulation of sandwich-insulated concrete blocks. Volcanic aggregate blocks achieved superior thermal insulation but frequently failed to meet compressive strength requirements, whereas normal aggregate blocks exceeded strength requirements but provided lower thermal insulation efficiency. This aligns with the results in [13], which reported similar trends. The properties of the polystyrene used for the internal insulating layer also significantly influence the thermal performance of the building unit. When XPS is used, thermal insulation efficiency improves. Different types of polystyrene have been examined, with densities ranging from 16 to 35 kg/m3. The type of polystyrene (extruded or expanded) and its density have a significant influence on thermal conductivity, as illustrated in Table 2. The calculated thermal transmittance (U-value) of the examined insulated concrete blocks ranges from 0.39 to 0.45 W/m2·K, depending on several factors. Figure 6 presents the correlation block density and insulation efficiency. There is a moderate correlation between increasing density and a gradual rise in U value. The thermal properties of the sandwich-insulated blocks were influenced by both the insulation core and the concrete shell. The volcanic blocks with XPS achieved the best thermal transmittance, with an average of 0.394 W/m2·K, followed by those with EPS, which had an average of 0.415 W/m2·K. In contrast, normal blocks with EPS exhibited the worst thermal performance with an average thermal transmittance of 0.4475 W/m2·K. These findings are consistent with previous research on multilayer insulated blocks [1,2]. All the tested samples have similar dimensions and layer thickness. It is clear that the type of shell concrete has a significant impact on thermal insulation efficiency. Most of the tested units meet the required U-value requirements per SBC 602 [41]. All blocks are acceptable from a thermal performance perspective. Optimization of sandwich-insulated concrete block design is necessary to achieve both excellent thermal insulation capacity, particularly the required U-value, and proper structural performance. More attention should be paid to the mixture proportioning of the shell concrete layer in order to develop a high-performance, lightweight mixture with both low density and appropriate mechanical properties.

3.5. Cost-Effectiveness Analysis

Three cases were considered to convert the cooling degree hours to degree hours: low = 75,168 °C·h/y, moderate = 136,512 °C·h/y, and high = 181,176 °C·h/y [42]. The additional annual savings (SAR/m2·yr) were estimated based on the difference in U-values (ΔU, in W/m2·K) between the improved and reference blocks as shown in Table 3, multiplied by the assumed annual degree-hours (K·h/y) and converted to energy (kWh) and monetary value using the local tariff (0.18 SAR/kWh). This approach is consistent with the standard transmission heat loss model (Φ = U × A × ΔT) and retrofit payback methodology used in building energy efficiency studies [43].
The results for the cost analysis are presented in Table 4. Although volcanic blocks with XPS achieve the lowest thermal transmittance (U = 0.394 W/m2·K), they are 70% more expensive than volcanic blocks with EPS and 153% more costly than normal blocks with EPS. Unit pricing for volcanic blocks with XPS is around 8.50 SAR/unit, volcanic blocks with EPS around 5.00 SAR/unit, and normal blocks with EPS around 3.35 SAR/unit. To assess economic viability, a simple payback analysis was conducted. The Results, summarized in Table 4, show that the payback for upgrading from normal EPS to volcanic EPS is highly climate-dependent, with payback periods of 46.9 years (low daily degree hours (DDH)), 25.8 years (moderate), and 19.5 years (high DDH). In contrast, upgrading to volcanic-XPS yields paybacks of 88.9, 49.0, and 36.9 years, respectively, all of which exceed typical envelope service lives (30–40 years). Most critically, the incremental benefit of substituting EPS with XPS within the same volcanic-shell system (ΔU = 0.021 W/m2·K) yields only 0.28–0.69 SAR/m2·yr in savings, while incurring an additional 43.75 SAR/m2, resulting in payback periods of 63.9 to 154.1 years, which is economically unjustifiable under current energy pricing. Therefore, despite superior thermal performance, volcanic–XPS does not offer a compelling cost–benefit case; volcanic-EPS represents the most rational compromise, yielding approximately 5% better U-value than normal-EPS at a modest cost premium, with viable payback (<20 years) in high-cooling-demand regions.

3.6. Absorption Results

Due to the critical influence of moisture content on thermal performance and resistance to the environmental conditions of the insulated concrete block, the water absorption resistance of the collected concrete blocks has been measured according to ASTM C 140 [33]. Figure 7 presents the water absorption percentages for various sandwich-insulated concrete blocks labeled A1 through G9. The water absorption values vary significantly across the blocks, from around 5% to over 15%. This variation indicates different levels of porosity or composition among the block types. The blocks with the highest water absorption percentages are C5 (around 16%), and the shells of this block type are made with volcanic aggregates. Abnormal water absorption was observed for block type E7, even though the shells are made from normal aggregates. Volcanic blocks have a double water absorption percentage compared to regular blocks. Blocks such as D6, F8, and G9 have some of the lowest water absorption percentages, ranging between 5% to 7%. These blocks may be better suited for applications where moisture resistance is essential, as they are less likely to absorb water, which can potentially contribute to durability and resistance to water-related deterioration. The findings of this test confirm the critical role of the aggregate origin and characteristics for manufacturing the outer concrete shell.

3.7. Durability of Outer Shell (Concrete) and Internal Insulating Layer (Polystyrene)

The concentration of chlorides and sulfates in concrete has been identified as one of the most critical parameters for concrete durability and service life prediction. The presence of chloride and sulfate can have detrimental impacts on concrete stability and performance. BS EN 206 [44] and BS 8110-1 [45] report the permissible limits for chlorides and sulfate content in non-reinforced concrete to be below 1% and 4% of cement mass, respectively. In this research study, standard test methods complying with BS 1881-124 [35] were followed to measure the actual chlorides and sulfate content in concrete. The obtained results, as shown in Table 5, revealed that all collected samples show acceptable sulfate content performance, while the values of concrete prepared with volcanic aggregates exceed the standard limits for chloride content. Some types of volcanic aggregates may contain high concentrations of leachable chemicals, depending on the origin and mineralogy of the material, which can negatively affect concrete. Therefore, preliminary tests of the raw material used should be performed to select the appropriate aggregate used for insulated concrete blocks based on the governing standards.
When exposed to direct environmental conditions or harmful substances, the internal insulating polystyrene layer is prone to degradation with time. In this research study, various tests have been conducted to ensure the high performance of the used polystyrene and its compliance with governing regulations, including resistance to weathering conditions and resistance to fungi and bacteria growth. Since it is planned to utilize the insulated concrete block for the long term during building operation, running the tests for such a long period is impossible. The accelerated weathering test, which complies with ASTM G154 [36], has been applied to shorten the testing period and to predict the degradation risk of different polystyrene materials. The test was carried out on three types of insulating materials: white expanded polystyrene with a density of 16 kg/m3, blue expanded polystyrene with a density of 20.6 kg/m3, and extruded polystyrene with a density of 34.1 kg/m3. Samples were exposed to UV light for 1000 h. From visual observation during the exposure period, changes in color and shape appeared on the surface of all samples after 600 h. Different polystyrene samples begin to shrink, exhibiting apparent deformation in their shape. Table 6 illustrates the influence of exposure to accelerated weathering for 1000 h on the density, thermal conductivity, and color and shape of the tested samples. In addition to color and shape changes, the dimensions of the tested samples shrink, leading to an increase in density and consequently increasing the thermal conductivity to a certain extent. It is evident that expanded and extruded polystyrene materials are sensitive to UV light, which negatively affects their properties and performance, and can lead to the formation of thermal bridges within the building walls. The findings of this test clarify the crucial role of the outer concrete layer in protecting the insulating polystyrene from direct weathering conditions.
In some environments, buildings can be exposed to harmful chemical substances from rain or the surrounding atmosphere, which may lead to the degradation of the building materials and increase maintenance and repair costs. Moreover, some materials represent an ideal environment for the growth of bacteria and fungi, which may cause serious illness in people. Therefore, it is imperative to examine the proper resistance of insulated concrete blocks, particularly the internal insulating polystyrene, to chemical and biological attacks. In this research study, an antibacterial activity test according to ASTM E2149-20 [37] has been carried out on three different types of polystyrene materials used as internal insulating layers in insulated concrete blocks. The experimental results obtained are presented in Table 7. The results showed that the XPS has the lowest antibacterial activity. In contrast, EPS with a density of 16 kg/m3 has the highest activity, as shown in Table 7. The voids content and material density have significant influences on the antibacterial resistance. The test was conducted for antifungal activity in accordance with ASTM G21 [46]. The experimental results showed that all tested polystyrene samples exhibited high resistance to fungal growth after 4 weeks of incubation, as observed under a stereomicroscope, and could be rated as ‘No Growth’ according to ASTM G21 [46].

4. Conclusions

This study experimentally investigated the physical and mechanical properties and the durability performance of the sandwich-insulated concrete block. The result analysis led to the following conclusions:
  • The properties of aggregate and shell composition significantly influence the performance of sandwich-insulated concrete blocks. As the volcanic aggregates used to enhance the thermal insulation, they compromised the mechanical performance and durability by increasing the absorption and chloride content.
  • Sandwich-insulated concrete blocks made with normal aggregates slightly reduce the thermal efficiency, while they exhibit superior mechanical strength, decreased absorption, and compliance with durability standards.
  • The selection of internal core insulating material is critical. The XPS has better performance than EPS in terms of thermal performance, but showed the lowest antibacterial resistance. In contrast, EPS exhibited higher antibacterial activity but was more vulnerable to UV-induced degradation. Therefore, the outer concrete shell is essential for protecting the insulation layer from environmental exposure and ensuring its long-term functionality.
  • To achieve the optimal performance and required standards of sandwich-insulated concrete blocks, the shell composition needs to be carefully designed and produced to make the sandwich-insulated concrete block a sustainable solution.

Limitations and Future Work

This research study has some limitations. It is limited to one block size (40 × 20 × 20 cm), which is the most commonly used, but other sizes will need to be investigated. Also, only nine block types from seven major suppliers were analyzed, which may not fully capture the variability of the Saudi market. Fire resistance was not evaluated, and it is critical for sandwich-insulated concrete blocks. Also, the chloride content test was conducted on only two specimens of volcanic aggregates; testing additional sources would strengthen representativeness. Future research should focus on fire resistance, cost-effectiveness analysis, and long-term durability assessments.

Author Contributions

Conceptualization, H.A. and A.A.; methodology, H.A. and A.A.; software, H.A. and A.A.; validation, H.A., A.A. and M.A.; formal analysis, H.A. and M.A.; investigation, H.A., A.A. and M.A.; resources, H.A. and M.A.; data curation, H.A. and A.A.; writing—original draft preparation, H.A.; writing—review and editing, A.A. and M.A.; visualization, H.A., A.A. and M.A.; supervision, H.A.; project administration, H.A. and M.A.; funding acquisition, H.A., A.A. and M.A. All authors have read and agreed to the published version of the manuscript.

Funding

The authors wish to acknowledge the support of the Saudi Standards (SASO) for funding this project through the project number (240701019927). The authors extend the appreciation to the Deanship of Postgraduate Studies and Scientific Research at Majmaah University for funding this research work through the project number (ER-2025-2144). The authors would like to acknowledge the support of the Engineering Research and Applied Sciences Center at Majmaah University.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

The researchers would like to thank the Saudi Standards, Metrology and Quality Organization (SASO) for funding (Project No. 240701019927). The authors extend their appreciation to the Deanship of Postgraduate Studies and Scientific Research at Majmaah University for funding this research work through the project number (ER-2025-2144). The authors gratefully acknowledge the use of facilities and instrumentation in the Engineering & Applied Science Research Center, Majmaah University.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Photographs of sandwich-insulated concrete blocks studied in this research.
Figure 1. Photographs of sandwich-insulated concrete blocks studied in this research.
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Figure 2. Defects of insulated concrete blocks: left: broken edge; middle: cracks due to weakness; and right: separation of polystyrene from concrete.
Figure 2. Defects of insulated concrete blocks: left: broken edge; middle: cracks due to weakness; and right: separation of polystyrene from concrete.
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Figure 3. Dry density of sandwich-insulated concrete blocks.
Figure 3. Dry density of sandwich-insulated concrete blocks.
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Figure 4. Compressive strength results of sandwich-insulated concrete blocks.
Figure 4. Compressive strength results of sandwich-insulated concrete blocks.
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Figure 5. Correlation between compressive strength and density of sandwich-insulated concrete blocks.
Figure 5. Correlation between compressive strength and density of sandwich-insulated concrete blocks.
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Figure 6. Correlation between density and insulation efficiency.
Figure 6. Correlation between density and insulation efficiency.
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Figure 7. Results of the water absorption of sandwich-insulated concrete blocks.
Figure 7. Results of the water absorption of sandwich-insulated concrete blocks.
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Table 1. Details of properties of sandwich-insulated concrete blocks.
Table 1. Details of properties of sandwich-insulated concrete blocks.
Block Dimensions Polystyrene Properties
GroupNoLength (cm)Width (cm)Depth (cm)Shell
Aggregate		TypeThickness (cm)Density (kg/m3)
A1402020VolcanicXPS7.535
2402020VolcanicEPS7.516
B3402020VolcanicXPS7.535
4402020VolcanicEPS7.520
C5402020VolcanicEPS7.516
E6402020NormalEPS7.516
F7402020NormalEPS7.516
G8402020NormalEPS7.516
H9402020NormalEPS7.516
Table 2. Thermal properties of the shell layer and polystyrene.
Table 2. Thermal properties of the shell layer and polystyrene.
GroupNoShell
Aggregate		Block Density (kg/m3)Measured
K-Value W/m·K		Polystyrene PropertiesCalculated U Value
W/(m2·K)
TypeThickness (cm)Density (kg/m3)Measured
K-Value W/m·K
A1Volcanic703.80.2335XPS7.5350.03870.398
2Volcanic733.60.2718EPS7.5160.04460.422
B3Volcanic818.90.2726XPS7.5350.03870.391
4Volcanic824.30.2725EPS7.5200.04240.406
C5Volcanic638.90.2548EPS7.5160.04420.419
E6Normal1086.00.4336EPS7.5160.04380.444
E7Normal916.20.4262EPS7.5160.04530.451
F8Normal1127.20.4515EPS7.5160.04420.447
G9Normal1132.40.468EPS7.5160.04350.448
Table 3. Variations in U-values and Cost for each block.
Table 3. Variations in U-values and Cost for each block.
ScenarioΔU (W/m2·K)Cost Variation (SAR)Additional Cost Per m2
Normal-EPS block vs. Volcanic-EPS block0.0325−1.65−20.62
Normal-EPS block vs. Volcanic-XPS block0.0535−5.15−64.37
Volcanic-EPS block vs. Volcanic-XPS Block0.021−3.5−43.75
Table 4. Cost analysis results.
Table 4. Cost analysis results.
ExposureScenario
/Case		ΔU (W/m2·K)Cost
Variation (SAR)		Additional Cost Per m2 (SAR/m2)Energy Saved (kWh/m2·y)Money Saved (SAR/m2·y)Simple
Payback (Years)
Low
Degree-hours = 75,168 °C·h/y		Normal EPS block vs. Volcanic EPS0.0325 −1.65−20.622.4430.44046.863
Normal EPS block vs. Volcanic XPS block0.0535−5.15−64.374.0210.72488.91
Volcanic EPS vs. Volcanic XPS Blocks0.021−3.5 −43.751.5790.284154.05
Moderate
Degree-hours =
136,512 °C·h/y		Normal EPS block vs. Volcanic EPS0.0325 −1.65−20.624.4370.79925.81
Normal EPS block vs. Volcanic XPS block0.0535−5.15−64.377.3031.31548.95
Volcanic EPS vs. Volcanic XPS Blocks0.021−3.5 −43.752.8670.51684.79
High
Degree-hours =
181,176 °C·h/y		Normal EPS block vs. Volcanic EPS0.0325 −1.65−20.625.8881.0619.45
Normal EPS block vs. Volcanic XPS block0.0535−5.15−64.379.6931.74536.89
Volcanic EPS vs. Volcanic XPS Blocks0.021−3.5 −43.753.8050.68563.87
Table 5. Experimental results of the chlorides and sulfates contents of outer shells.
Table 5. Experimental results of the chlorides and sulfates contents of outer shells.
Shell MaterialChloridesSulfatesEvaluationRemarks
Volcanic (group A)1.6-Not acceptedAccording to BS EN 206-1, Chlorides < 1% of cement mass
Volcanic (group B)1.5-Not accepted
Normal (group E)0.09-Accepted
Normal (group G)0.07-Accepted
Volcanic (group A)-2.1AcceptedAccording to BS 8110-1
Sulfates < 4%
Of cement mass
Volcanic (group B)-2.1Accepted
Normal (group D)-0.66Accepted
Normal (group G)-0.42Accepted
Table 6. Influence of accelerated weathering for 1000 h on expanded and extruded polystyrene properties.
Table 6. Influence of accelerated weathering for 1000 h on expanded and extruded polystyrene properties.
MaterialDensity (kg/m3)Thermal
Conductivity (W/m·K)		Color and Shape Changes
EPS whiteBefore160.0446Buildings 15 04172 i001Buildings 15 04172 i002
After18.10.0512Buildings 15 04172 i003
EPS blueBefore20.60.0418Buildings 15 04172 i004Buildings 15 04172 i005
After21.20.0436Buildings 15 04172 i006
XPSBefore34.10.0385Buildings 15 04172 i007Buildings 15 04172 i008
After37.30.0394Buildings 15 04172 i009
Table 7. Average number of bacterial growths.
Table 7. Average number of bacterial growths.
Sample NameContact TimeNo. of Tested PlatesEscherichia Coli (cgu/mL)Escherichia Coli ATCC 25922Antibacterial Activity
Control sampleAfter 1 h115 × 10215 × 102
213.9 × 102
316.1 × 102
EPS-blue 20After 1 h112 × 10212 × 10220%
212.2 × 102
311.8 × 102
EPS—white 16After 1 h19 × 1029 × 10240%
29.2 × 102
38.8 × 102
XPS-35After 1 hr113 × 10213 × 10213%
213.3 × 102
312.7 × 102
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Alanazi, H.; Alzlfawi, A.; Albuaymi, M. Evaluating the Performance and Efficiency of Sandwich-Insulated Concrete Block Products in the Saudi Market. Buildings 2025, 15, 4172. https://doi.org/10.3390/buildings15224172

AMA Style

Alanazi H, Alzlfawi A, Albuaymi M. Evaluating the Performance and Efficiency of Sandwich-Insulated Concrete Block Products in the Saudi Market. Buildings. 2025; 15(22):4172. https://doi.org/10.3390/buildings15224172

Chicago/Turabian Style

Alanazi, Hani, Abdullah Alzlfawi, and Mohammed Albuaymi. 2025. "Evaluating the Performance and Efficiency of Sandwich-Insulated Concrete Block Products in the Saudi Market" Buildings 15, no. 22: 4172. https://doi.org/10.3390/buildings15224172

APA Style

Alanazi, H., Alzlfawi, A., & Albuaymi, M. (2025). Evaluating the Performance and Efficiency of Sandwich-Insulated Concrete Block Products in the Saudi Market. Buildings, 15(22), 4172. https://doi.org/10.3390/buildings15224172

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