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Article

The Application and Effects of Aerogel in Ultra-Lightweight Mineralised Foams

by
Tongyu Xu
*,
Harald Garrecht
,
Chao Jiang
and
Chuanyuan Lu
Institute of Construction Materials, University of Stuttgart, Pfaffenwaldring 4, 70569 Stuttgart, Germany
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(15), 2671; https://doi.org/10.3390/buildings15152671
Submission received: 5 June 2025 / Revised: 22 July 2025 / Accepted: 25 July 2025 / Published: 28 July 2025
(This article belongs to the Section Building Materials, and Repair & Renovation)
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Abstract

This study aims to explore the potential of aerogel to optimise the thermal conductivity of mineralised foam materials. Experiments were conducted with (i) addition methods of aerogel, (ii) proportion of aerogels in cement slurry, and (iii) water/cement ratio as influencing parameters for mineralised foam. Additionally, mixed Ordinary Portland Cement (OPC)/Calcium Sulphoaluminate Cement (CSA) slurries were used to test whether a synergy could be achieved. In this study, the defoaming effect of the aerogel and its mitigation to a certain extent by pre-mixing the aerogel with cement slurry were confirmed. The thermal conductivity of the mineralised foams was reduced from 0.049 to 0.036 W/(m·K) when the aerogel was up to 10 wt.% of the cement. In the specimens prepared from the mixed OPC/CSA slurry, a homogeneous circular pore structure was observed under the microscope along with a reduction in the thermal conductivity. The use of aerogels and CSA cements can effectively reduce the thermal conductivity of ultra-low-density mineralised foams to levels comparable with certain plastic foams that dominate the building insulation market.

1. Introduction

In recent decades, concerns over global climate change and the energy crisis have grown steadily. The 2023 report by the International Energy Agency (IEA) highlighted that the building sector has been one of the largest consumers of energy. About 45% of this energy was used for space and water heating, contributing to nearly 80% of direct carbon emissions [1]. This energy has primarily been consumed to maintain indoor temperatures and ensure comfortable living environments, making it difficult to reduce directly. Therefore, the importance of using thermal insulation materials to minimise heat exchange between the interior and exterior of buildings and enhance energy efficiency has become increasingly prominent [2,3,4].
There are a wide variety of insulation materials available on the market, each designed to meet different needs under various conditions. Among these, foamed concrete stands out as a material that combines a certain level of strength and thermal insulation properties [5,6]. The key factor determining the performance of foamed concrete is its density. As density decreases, thermal insulation performance typically improves [7]. When the density of foamed concrete drops below 400 kg/m3 or even lower, it is called mineralised foam (hardened state) or mineral foam (in fresh state). However, materials within this density range have been investigated in a limited manner.
Currently, plastic foams occupy the largest market share of building insulation materials because of their excellent thermal insulation performance (thermal conductivity is roughly in the range of 0.02–0.05 W/(m·K) [8,9,10,11]). In comparison, mineralised foams exhibit higher thermal conductivity, but have other unique advantages. For example, the inherent recyclability as a mineral material and the potential to use recycled materials as raw materials [12,13,14,15,16]. The material’s fluidity and workability enhance its suitability for on-site construction [17,18,19], and its resistance to high temperatures and fire is crucial for industrial and building applications [20,21]. With these advantages, if mineralised foam could achieve thermal conductivity comparable to that of plastic foam while maintaining a certain level of strength, it would undoubtedly possess a unique competitive edge as an insulation material.
The objective of this study is to optimise the properties of mineralised foams with dry densities close to 100 kg/m3, in particular the thermal conductivity, to expand their application prospects. To this end, aerogel particles with aggregate-like shape were observed to have the necessary potential [22,23,24]. An improvement in the thermal insulation properties of concrete or cementitious materials by addition of aerogel particles has been reported [25]. The addition of aerogel particles can improve the overall hydrophobicity of the material, increase the softening coefficient of the material, and enhance the durability of the material in wet conditions [26,27]. As the density of the foam concrete material decreases, the solid matter content of the system decreases and the stability of the foam becomes more sensitive to external influences. A very limited number of studies have addressed these effects of aerogels in mineralised foams in the ultra-low-density range. This study attempts to address these issues by finding a suitable preparation method and confirming the effect of aerogel addition in a more sensitive system.
Several studies have indicated that the pore structure of foam concrete significantly influences its properties [28,29]. CSA cements are noted for their ability to accelerate the hardening process, which reduces the time window for internal bubbles to collapse, resulting in a denser pore structure and improved performance of foam concrete [30,31,32,33,34].
These two approaches, (i) adding components having special advantageous properties into the material system and (ii) altering the properties of the material system in its fresh state to achieve an improvement in its post-hardening performance, are the two guiding routes in the performance improvement for foam concretes. Both these approaches are considered within the scope of this paper, namely, (i) adding aerogels to mineralised foams in the very-low-density range and (ii) adding CSA to material systems in the fresh state. It is noted here that addition of aerogels is the primary approach in this study. CSA cement was used to evaluate whether a synergistic improvement in material properties can be achieved through dual modification.

2. Materials and Methods

2.1. Design of Experiments

The experimental work can be visualised in the following 3 phases:
(1)
In the first phase, the study focused on the addition method of aerogel particles in mineralised foams. By adding aerogel particles in different steps of the mineral foam preparation, the properties of mineralised foams were investigated and the workflow for mineral foam preparation was confirmed.
(2)
In the second phase, the water/cement ratio (w/c ratio) of the cement slurry was varied, the number of aerogel particles added was adjusted, and the aerogel particles were pre-ground to obtain powdered aerogels, and then the properties of the obtained mineralised foam specimens were tested.
(3)
In the third phase, cement slurry with the addition of aerogel was prepared by partially replacing OPC with CSA cement, and then mineralised foam specimens were produced and tested.

2.2. Materials

2.2.1. Cement

To ensure a clearer assessment regarding the variables investigated in this study, it was required to minimise the effects caused by components other than clinkers. Hence, the binder material OPC CEM I 42.5 N from Heidelberg Materials AG, Heidelberg, Germany was used in this study.

2.2.2. Foaming Agent

The synthetic surfactant SCHAUMBILDNER 97 from Ha-Be Betonchemie GmbH, Hameln, Germany was used as a foaming agent. The concentration was set at 4.0 wt.%.

2.2.3. Calcium Sulphoaluminate Cement

The CSA cement chosen to partially replace the OPC in the experiments was Newchem ACC-C65 from Newchen GmbH, Traiskirchen, Austria.

2.2.4. Aerogel Particle

In this study, the P200 aerogel particles from Cabot Aerogel GmbH, Frankfurt, Germany were used. According to the data sheet provided by the company, their particle sizes range from 0.1 to 1.2 mm and the particle density ranges from 120 to 180 kg/m3. For the calculation of the theoretical density of mineral foams in this study, the aerogels were treated as closed solid particles and an average density of 150 kg/m3 was taken as the standard.

2.3. Specimen Preparation Process

The framework underlying the preparation of the mineral foams used in this study is shown in Figure 1. A total of three mixing steps were involved: (i) mixing the required materials in a dry state, (ii) mixing with water to obtain a slurry, and (iii) mixing the slurry with the foam to obtain the mineral foam. The workflow is described in detail as follows.
(i)
Firstly, the required substances (depending on the experimental phase) were added to the F80 forced action mixer manufactured by Baron A/S and stirred at 60 rpm/min for about 3 min to ensure that the substances were homogeneously mixed. Note that in the first experimental phase, when testing the aerogel addition method, the aerogel particles were either pre-mixed or added separately during the mixing step between slurry and foam.
(ii)
The dry mixture was added to water and stirred for 2 min at a speed of 1800 rpm in the CIM 30 E colloidal mixer manufactured by GERTEC Maschinen-und Anlagenbau GmbH, Sulzberg, Germany to obtain a homogeneous slurry. At the same time, foam was produced using a foaming machine SBM 8 manufactured by the same company. In order to achieve the target dry density, the foam density was selected to be around 45 ± 5 kg/m3, which could be controlled by adjusting the parameters of the water and air flow rates of the foaming machine.
(iii)
Finally, the prepared slurry and foam were placed in the F80 forced action mixer again and stirred for 4 min at a speed of 60 rpm to produce the mineral foam.
After completing the mixing process, the mineral foams were poured into moulds and six cubic specimens with sides of 10 cm and three with sides of 15 cm were produced per group for subsequent testing. The surface of the material was covered with plastic film and left for 48 h before demoulding. After demoulding, the specimens were cured in a storage room at a controlled temperature of 20 ± 2.5 °C and relative humidity of 70 ± 5%.

2.4. Variables and Tests

To evaluate the performance of mineralised foams and understand the influencing parameters, rheological properties of the slurry, change in density with time, compressive strength, and thermal conductivity of the specimens were the parameters evaluated in the experiments.
During the mineral foam preparation, once the slurry was evenly mixed, a 30 mL sample was taken to test its rheological properties using the RHEOTEST®RN 4.1 rotational rheometer according to DIN EN 13302 [35]. In this process, a cylindrical container holding the slurry was placed in a temperature control device to maintain a constant temperature of 20 °C throughout the test. The conical rotor used for the tests gradually increased its speed from 0 to 300 rpm over a 3-min period. The results were fitted using the Bingham model to determine the viscosity and yield stress of the slurry [36,37], with a minimum R2 of 0.876 in all experimental groups.
The compressive strength of the specimens was tested in accordance with DIN EN 12390-3 [38]. The combined testing machine manufactured by TESTING Bluhm&Feuerherdt GmbH, Berlin, Germany with a maximum pressure of 20 kN was used. Considering the expected low strength of the specimens, the loading rate was set at 10 N/s [39]. Three cubic specimens with a side length of 10 cm were tested at 7 and 28 days, respectively, and the results were expressed as mean values.
After the specimens had cured for 28 days, three cubic specimens with side length of 15 cm were placed in an oven and dried at 105 °C for three days. The dried specimens were then cut, polished, wrapped in plastic film, and placed at room temperature (23 ± 2 °C). Once the specimens naturally cooled to room temperature, their thermal conductivity was tested using the THB 100 device manufactured by Linseis Messgeraete GmbH, Selb, Germany which operates based on the transient hot wire method [40,41]. The sensor of the device was randomly placed inside the cut specimen and completely covered by the two halves. At least 8 tests were conducted on each specimen. The results were given as an average value.
A VHX-5000 electron microscope manufactured by KEYENCE DEUTSCHLAND GmbH, Frankfurt, Germany was used to observe the pore structure. With reference to the microscope method described in DIN EN 480-11 [42], several observation points were randomly selected on the surface of each specimen. At each point, a rectangular area of approximately 7 × 5 mm2 was captured under the microscope, and the pore radius within this area was measured. A minimum of 300 pores were measured for a set of specimens to obtain a distribution of pore radius.

3. Results and Discussion

3.1. Effect of Addition Method

3.1.1. Effect of Aerogel Particles on Foam

Research carried out by [43] concluded that silica aerogel has a destructive effect on foam structure. A similar conclusion was confirmed in the first phase of this study. Four sets of controlled experiments were designed for this purpose. In each experiment, 1400 g foam with a density of about 45 ± 5 kg/m3 was added to the F80 forced action mixer. In Group 1, no additive was added. In Group 2, 200 g original aerogel particles P200 were added. In group 3, 200 g aerogel particles P200 were ground to a white powder form in a small mixer manufactured by Rotor Lips AG. This aerogel powder was added as substance. In Group 4, 200 g defoaming agent was added to the foam. For each experiment, the foam and additives were mixed in the F80 forced action mixer at 60 rpm for 4 min following step (iii) described in Section 2.3. Before and after mixing, the level heights of the mixture were measured at randomly selected positions at least 4 times. The average heights are given in Table 1. The difference between the average heights before and after mixing was used to indicate the destructive effect of the additives.
Using the first group as blank control group, the results of the second and third groups showed a large deviation. In the second group, the height of the mixture was reduced by 0.38 cm, while in the third group, the height of the mixture was reduced by 11.13 cm. The result of the third group was in agreement with the findings of Li et al. [43] that aerogels with smaller particle diameters and larger contact areas are more destructive to foams, whereas the results in the second group point to the conclusion that the foam was not disrupted by mixing with the aerogel particles.
In the study by Wang et al. [44], it was pointed out that defoamers need to be dispersed in small droplets and extended to the surface of the gas/liquid phases in order to work effectively. In [45], it was noted that fine, highly hydrophobic particles, when penetrated into bubbles, lead to the destabilisation of the bubble structure. Perhaps this explains why there was no significant height difference in the second group when larger aerogel particles were added.

3.1.2. Effect of the Addition Method of Aerogel Particles on Mineralised Foam

In the first experimental phase, aerogel was added at different mixing steps (as described in Section 2.3) of the mineral foam preparation, and their effects were tested. The material compositions and in which mixing step the aerogel was added are shown in Table 2 for each group.
In addition to the groups shown in Table 2, attempts to prepare mineral foams by adding aerogel to a cement paste with w/c ratio of 0.4 in mixing step (i) were unsuccessful. The reason was that at a w/c ratio of 0.4, the product obtained from mixing step (i) resembled loose clay particles rather than a homogeneous, flowable slurry. Therefore, it could not be used in subsequent mixing. This problem can be mitigated by using a suitable superplasticizer or by increasing the w/c ratio, but in order to ensure consistency in the material composition, no further changes using superplasticizer were made in this test. Based on the mixing difficulty that occurred with low w/c ratio, the material composition of 1-06-F80 was used. The w/c ratio was increased to 0.6, and aerogel was added in the mixing step (i). To test the influence of adding aerogel in mixing step (iii), a cement paste with a w/c ratio of 0.4 was still used and mixed in two different mixers, a turboprop F80 forced mixer that horizontally drove and mixed the materials and a single-shaft forced mixer CEM 60 S ELBA from AMMANN Group, Langenthal, Switzerland that mixed the materials by repeatedly driving them up and letting them fall freely. All obtained specimens were tested for compressive strength and thermal conductivity, as described in Section 2.4. The test results, as well as the density of the mineral foams, are shown in Table 3.
First, the design densities of the specimens were calculated according to Formula (1), and the densities of the specimens in the three groups were compared. In this case, the design density of 3-04-F80 and 3-04-ELBA was the same because of the same material composition of these two groups, while in 1-06-F80, the w/c ratio of the cement slurry was increased from 0.4 to 0.6, which corresponds to a slight decrease in the design density of the specimens.
ρ d e s i g n = m c e m e n t + m w a t e r + m a e r o g e l + m f o a m m c e m e n t ρ c e m e n t + m w a t e r ρ w a t e r + m a e r o g e l ρ a e r o g e l + m f o a m ρ f o a m
The actual fresh densities of the specimens in the three groups behaved differently. In group 1-06-F80, the fresh density of the specimens was close to their design density, while in both groups 3-04-F80 and 3-04-ELBA, their fresh densities were much higher than their design density. In the previous study [46], it was confirmed that using high-viscosity (low w/c ratio) cement paste causes external air to enter the mineral foam material during the mixing process, leading to a decrease in fresh density and irregularly shaped cavities inside the specimen after hardening. However, though cement paste with lower w/c ratio was used in both groups, the fresh density of the mineral foams was much higher than their design density. This indicated, on the one hand, that the aerogels may have been partially crushed when mixed with the highly viscous cement paste, as described in the study by [47], and, on the other hand, it pointed to the volume reduction of the mineral foams due to the aerogels.
Corresponding to the changes in the density of the specimens were their changes in compressive strength and thermal conductivity. Comparing Group 3-04-F80 and Group 3-04-ELBA, both groups had the same material composition, and the aerogel was added at the same mixing step (iii). However, the mineralised foam behaved differently due to the type of mixer used. In terms of compressive strength, the average value of W-04-ELBA specimens was 10.4 times higher than that of W-04-F80. The thermal conductivity value was about 1.6 times higher. Among all groups, 1-06-F80 specimens showed the lowest compressive strength and thermal conductivity.
The cross-sections of the specimens in the three groups are shown in Figure 2. In particular, the specimen from 3-04-ELBA exhibited dense structure compared to normal foam concrete materials, and showed similar properties to the aerogel concrete discussed in the [24,48,49,50]. According to the summaries in the studies by [51,52], depending on the material composition and production method, the compressive strength of aerogel concrete ranges from less than 5 MPa to 40 MPa, corresponding to a fluctuating thermal conductivity in the range of 0.1–1.0 W/(m·K). The mixing difficulties due to the large amount of solid materials, as mentioned in some of these studies, might be solved by using the foam as a cushion. Then, after sufficient mixing, the foam structure was disrupted by the defoaming effect of the aerogel, resulting in aerogel concrete with a dense structure. This may serve as a future research interest, but was not in line with the original design intent of this study. As for the specimen from 3-04-F80 prepared with the F80 action mixer, although a porous structure can be seen on its surface, the difference between the design density and the fresh density certainly showed that the volume of the materials had been reduced during the mixing process, which suggested that the foam had been disrupted.
Adding aerogel to the mixing phase of foam and cement slurry may lead to direct contact between the exposed aerogel particles and the foam during the mixing process. As discussed in [44,45], when the smaller-sized hydrophobic particles are integrated into the film that forms the bubbles, it triggers the collapse of the film by building bridges between the gas phases of the surrounding bubbles, then ultimately leads to a rapid volume decrease in the material, an increase in its density, and other changes in relevant properties. In contrast, in the preparation process corresponding to Group 1-06-F80, by pre-mixing the aerogel with the cement slurry, a cement layer was added to the surface of the aerogel. This cement coating layer may have resulted in the following effects during the mixing process. The first was to reduce the direct contact between the aerogel and the foam in order to prevent the collapse of the bubble film due to hydrophobic particles. In [53,54,55], it was stated that hydrophilic particles (cement particles) of higher concentration tend to increase the plateau boundary of the foam and its stability to a higher extent by decelerating decay mechanisms. In addition, the surface of the aerogel particles was covered with cement slurry and partially wetted. In studies on pickering foams, attempts to partially hydrophobicize the surface of hydrophilic particles are often carried out to adjust the contact angle between the particles and the foam, which can help the particles to adsorb more efficiently at the air/liquid interface or to be integrated into the foam film, forming a network structure and preventing the thinning of the liquid film and the coalescing due to drainage [53,56,57]. By partially wetting the surface of the hydrophobic particles, it may be possible to achieve a similar effect and adjust the contact angle between the aerogel and the foam.
Although further analysis is required to confirm the main contributing factors, the small difference between the designed and fresh densities of the specimens in the 1-06-F80 group, and the corresponding lowest thermal conductivity properties, as compared to the data recorded in Table 3, may serve to demonstrate that this method of production is more favourable for the limited density range in this study, as well as for the properties required for the corresponding application. Consequently, the use of this pre-mixing method of the aerogel with the cement slurry was confirmed in further experiments, and a higher w/c ratio was chosen.

3.2. Effect of Pre-Ground/Unground Aerogel Particle Content on Mineralised Foams at Different Water/Cement Ratios

In the second experimental phase, factors related to the material composition were examined. The factors included the added amount of aerogel, the w/c ratio of the cement slurry, and whether the aerogel was pre-ground or not. This followed the procedure used in experimental group 3, as described in Section 3.1.1. The aerogel that was not pre-ground was referred to as particles, while the pre-ground aerogel was referred to as powder.
The test results of the rheological properties are shown in Figure 3. It was confirmed that as the aerogel content increased, both the viscosity and yield stress of the slurry increased. At the same aerogel content, slurries with lower w/c ratio showed higher viscosity and higher yield stress. For experimental groups with the same w/c ratio, the viscosity was similar at lower aerogel contents, regardless of whether aerogel particles or powder were used. In groups with a w/c ratio of 0.6, a noticeable difference in viscosity appeared when the aerogel content exceeded 7.5 wt%. The group using aerogel powder exhibited higher viscosity. A similar difference appeared earlier in groups with a w/c ratio of 0.7, starting when the aerogel content exceeded 5 wt%.
As for yield stress, in groups with a w/c ratio of 0.6, the slurries containing aerogel powder showed slightly higher yield stress than those containing aerogel particles at the same aerogel content. This result was in line with the findings of Han et al. [58], who reported that the viscosity and yield stress of mortar with a w/c ratio of 0.45 increased as the average size of solid particles decreased. However, for groups with w/c ratio of 0.7, the slurries containing aerogel particles showed higher yield stress than those containing aerogel powder at the same aerogel content.
The measured results of dry density, compressive strength, and thermal conductivity are shown in Figure 4. As shown in Figure 4a, the dry density of the mineralised foam did not show a clear trend with increasing aerogel content. Instead, it fluctuated slightly between 120 and 140 kg/m3. Previous studies often noted that incorporating aerogel led to a decrease in the density of the material system. However, this conclusion usually applies to higher density ranges. For example, Gao et al. [48] studied the incorporation of aerogels into concrete systems with specimen densities ranging from around 750 to 2250 kg/m3. Wu et al. [59] studied the incorporation of aerogel in foam concrete systems where the minimum specimen densities were also above 200 kg/m3.
Several factors may have contributed to the changes in density. These included the reduction in overall material density due to the low density of aerogel used, an increase in slurry viscosity that trapped more air during mixing [46], and possible structural damage to the foam caused by the aerogel, which may have increased the density. However, in the density range studied here, the effects of density reduction caused by the low density of the aerogel were less pronounced than they were in the higher-density systems.
Combined with the difference between the design density and the fresh density of the specimens under different mixing modes, as shown in Table 3, it can be further demonstrated that using aerogels in cementitious materials does not always lead to a decrease in the material’s density, as noted in the studies of [48,59]. Especially in low-density material systems, the effects of changes in foam structure and slurry viscosity caused by aerogel were more pronounced. The final density appeared to result from a combination of these factors.
Nevertheless, the dry density of all specimens remained within the target range defined at the beginning of this study. In addition, other factors, such as the w/c ratio and the form of aerogel (powder or particles), did not have a significant effect on dry density.
As for compressive strength, as shown in Figure 4b, both aerogel content and the w/c ratio had clear effects. In groups with a w/c ratio of 0.6, the compressive strength decreased with increasing aerogel content. When using aerogel particles, this decrease became noticeable when the aerogel content exceeded 5 wt%. However, when using aerogel powder, the compressive strength began to decline significantly at a lower aerogel content of 2.5 wt%. In groups with a w/c ratio of 0.7, the use of aerogel led to a reduction in compressive strength, but increasing the aerogel content did not result in further noticeable changes. And in these groups, the form of the aerogel had little impact. Both curves were almost identical, regardless of whether aerogel powder or particles were used.
As shown in Figure 4c, the change in thermal conductivity of the mineralised foam followed a trend similar to that of compressive strength. In the groups with the w/c ratio of 0.6, the thermal conductivity decreased with increasing aerogel content, and in the groups with the w/c ratio of 0.7, although the thermal conductivity also showed a general decrease with the addition of aerogel, no clear trend was observed from the curves.
It should be noted that if experimental groups with the same w/c ratio but different aerogel forms (particle or powder) were compared in pairs, the trends of the curves for compressive strength and thermal conductivity were similar. As a high-energy mixer was used in the experiments, and the proportion of aerogel particles that may have been crushed in the process, as well as the variation of this proportion with the w/c ratio of the cement slurry, were not measurable, it was possible that the aerogel forms within the cement converged after mixing and led to an approximate trend in the curves. Therefore, more detailed studies are still required.

3.3. Aerogel-Containing Mineralised Foams Prepared Using OPC/CSA Mixed Cement Bases

In the third experimental phase, OPC/CSA mixed cement was prepared by partially replacing OPC with CSA cement. The w/c ratio was set at 0.7. The aerogel powder was premixed into the cement slurry and then used to prepare mineralised foam specimens. In the study of [33], it was stated that the compressive strength, thermal conductivity, and pore structure of ultra-lightweight foam concrete materials with densities between 200 and 500 kg/m3 were optimised by using CSA cement. The main purpose of this experimental phase was to confirm whether similar or synergistic effects can be achieved in aerogel-containing mineralised foam. The amount of CSA cement was set at 7.5 wt.% of the total cement mass. This proportion was determined in preliminary tests as the optimal dosage that avoids flash setting, while also significantly improving the compressive strength of mineralised foam not containing aerogel (The results for the preliminary tests can be seen in the Supplementary Materials, Figures S1 and S2).
The rheological properties are shown in Figure 5. For viscosity, the two curves representing the use of OPC and OPC/CSA cements remained similar as the aerogel content increased, whereas, in terms of the yield stress, there was a significant difference. In particular, the yield stress of the slurry prepared with OPC/CSA cement was always higher than that prepared with OPC cement at all aerogel contents. This may be partly due to the higher reactivity of the mixture caused by the CSA cement. During the early stages of hydration, the formation of interlocked needle-like ettringite crystals may lead to an increase in the yield stress of the slurry. However, as the slurry is stirred again in the rheometer, the interlocked ettringite structures are broken down, resulting in no significant effect on the viscosity.
The dry density, compressive strength, and thermal conductivity of the tested mineralised foam specimens are shown in Figure 6. Regarding the dry density, two phenomena were observed. First, for the same aerogel contents, the specimens prepared with OPC/CSA mixed cement always showed slightly lower dry density than those made with pure OPC. Second, while the specimens made with OPC showed slight fluctuations in dry density as aerogel content increased, the specimens prepared with OPC/CSA mixed cement exhibited a more consistent decreasing trend, as increasing the amount of low-density aerogel in the material system should theoretically have reduced the overall density, and this had been confirmed in other studies on aerogel-integrated concretes and foam concretes with a higher density range [48,49]. However, within the lower density range focused on in this study, the trend of dry density variation with increasing aerogel content showed greater fluctuation. Referring to Figure 4a, it could be inferred that when the aerogel content was low, external factors and variations in foam structure had a more significant effect on the specimen’s density than the mix composition itself. As these variables mainly affected the mixing phase, it was possible that the addition of CSA cement also helped stabilize the material system during mixing.
As shown in Figure 6b, for specimens with low aerogel content, using OPC/CSA cement effectively improved compressive strength. However, when the aerogel content exceeded 5 wt.%, the compressive strength of the specimens became lower than that made with pure OPC. Here, the expected increase in compressive strength through the use of OPC/CSA cement was not observed. As for the thermal conductivity, a clear decreasing trend was observed with increasing aerogel content in Figure 6c. In this case, CSA cement showed the expected effect, i.e., under the same conditions, specimens made with OPC/CSA cement consistently demonstrated lower thermal conductivity than those made with pure OPC.
To examine the effects of using aerogel and OPC/CSA cement on the pore structure of the material, measurements were conducted on the cross-sections under the microscope. The corresponding results are shown in Figure 7.
Figure 7a shows the frequency of pores in a given radius range based on the total number of pores measured. The number on the x-axis represents the upper limit of the given radius range. For example, 100 on the x-axis corresponds to a radius range between 50 and 100 µm. Figure 7b presents the corresponding cumulative frequency. From Figure 7a, it can be seen that the specimens prepared with OPC and aerogel showed a clearly concentrated pore distribution, with most pores falling within the 100–150 µm range. In contrast, specimens made with OPC/CSA cement exhibited a more uniform pore distribution, mainly between 100 and 300 µm. Figure 7b further shows that, as the aerogel content increased, the cumulative frequency curves shifted to the right for specimens with the same cement base. This indicated an overall increase in pore size with higher aerogel content. Notably, the curves for OPC/CSA-based specimens shifted less, suggesting that the use of CSA cement helped to suppress the increase in pore size caused by higher aerogel content.
However, in the density range given in this study, it was difficult to characterize the actual pore structure solely based on the pore radius distribution shown in Figure 7. Another key aspect lay in the shape of the pores, where irregularly shaped pores/cavities could not be effectively included in the statistical analysis during measurement. As shown in Figure 8 and Figure 9, microscope images of specimens containing 5 wt% aerogel, prepared using OPC and OPC/CSA cement, respectively, are presented as examples.
In both cases, the aerogel appeared to be well embedded within the hardened cement matrix, with no visible cracks observed at the interface between these two materials. However, the pores in the OPC-based specimen (Figure 8) clearly showed irregular shapes, with noticeable interconnections and uneven cavities between multiple pores. In contrast, the specimen prepared with OPC/CSA cement (Figure 9) exhibited a more ideal pore structure, resembling the spherical form typically expected in foam materials. The pores within the hardened cement matrix tended to be more uniform, intact, and approximately circular in shape, indicating better preservation of the foam structure.

4. Conclusions

This study thoroughly investigated the effects of incorporating aerogel into mineralised foam materials using different mixing methods. It also examined how the resulting specimens, prepared through the optimised mixing process developed in this research, were influenced by various factors, including w/c ratio, type of cement binder used, aerogel content, and the form of the aerogel. Based on the experimental results, the following conclusions could be drawn:
(1)
In the extremely-low-density range, aerogels had a slightly different effect on mineralised foams than they did on dense material systems. Depending on the mixing method used, aerogels could seriously affect the stability of the foam during the mixing phase, leading instead to an increase in the density of the material and a change in the corresponding properties.
(2)
By mixing the aerogel with the cement slurry in advance, it was possible to limit the defoaming effect of the aerogel to a certain extent and to achieve the production of mineralised foams containing aerogel within an ultra-low-density range.
(3)
In this study, the high-energy mixer likely caused the differently shaped aerogels to become uniform during mixing with cement slurry. Although this method ensured a homogeneous mixture of aerogel and cement slurry, it also prevented the evaluation of the effect of aerogel shape on the mineralised foam performance.
(4)
By adding aerogel to the mineralised foam, the thermal conductivity of the material was effectively reduced to achieve better thermal insulation without significantly changing its dry density. At w/c ratio of 0.6 for the slurry used, the thermal conductivity of the material reached its lowest point as the aerogel content rose to 10 wt% of the cement, with an average measurement of 0.036 W/(m·K), which was in a comparable range to plastic foams reported in the literature.
(5)
By partially replacing the Ordinary Portland Cement with a suitable CSA cement, the pore structure of the mineralised foam was improved. The formation of irregular cavities, cracks, and connections between pores was suppressed, allowing most pores to retain a near-ideal circular (spherical) shape. In addition, the distribution of pore radius became more uniform, and the overall increase in pore size caused by high aerogel content was inhibited. The observations also indicated that the pore radius distribution alone was not sufficient to represent the pore structure of mineralised foams within this density range. It was recommended that future work include the influence of irregularly shaped pores and cavities in the structural analysis, as they also had a significant impact on the material’s overall performance.
(6)
The combined use of CSA cement and aerogel for optimising the performance of mineralised foam was feasible to a certain extent. In terms of thermal conductivity, the combination showed a clear synergistic reduction effect, with specimens prepared using OPC/CSA cement generally showing lower thermal conductivity at the same aerogel content. However, for compressive strength, the synergistic enhancement effect only appeared at low aerogel content (smaller than 5 wt.%). As the aerogel proportion increased, the use of CSA cement continued to improve the pore structure by preventing irregular cavities and connected pores, but the compressive strength of the material was weakened. It was recommended that future studies consider the relationship between the aerogel particle size and the thickness of the pore walls.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/buildings15152671/s1, Figure S1: CSA-thermal condutivity.png; Figure S2: CSA-28d compressive strength.

Author Contributions

Conceptualization, T.X.; methodology, T.X.; investigation, T.X.; data curation, T.X., C.J., and C.L.; writing—original draft preparation, T.X.; writing—review and editing, T.X.; supervision, H.G.; funding acquisition, H.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Carl Zeiss Stiftung (Perspectives project ChitinFluid, grant number P2019-02-004) and the APC was funded by Open access funding provided by The University of Stuttgart.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors declare that the data supporting the findings of this study are available within the paper. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.

Acknowledgments

It is gratefully acknowledged for materials samples provided by NEWCHEM GmbH and the advice provided by Vinay Mahadik.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
OPCOrdinary Portland Cement
CSACalcium sulphoaluminate

References

  1. Agency, I.E. World Energy Outlook 2023—Analysis; Technical Report; International Energy Agency: Paris, France, 2023. [Google Scholar]
  2. Paraschiv, S.; Paraschiv, L.S.; Serban, A. Increasing the Energy Efficiency of a Building by Thermal Insulation to Reduce the Thermal Load of the Micro-Combined Cooling, Heating and Power System. Energy Rep. 2021, 7, 286–298. [Google Scholar] [CrossRef]
  3. Bentoumi, L.; Touba, B.; Bessaïh, R.; Bouttout, A. Impact of Thermal Insulation on Energy Consumption in Buildings. J. Therm. Eng. 2024, 10, 924–935. [Google Scholar] [CrossRef]
  4. Kosny, J.; Yarbrough, D. Thermal Efficiency of Insulation in Building Structures—The Impact of Thermal Bridging. In Thermal Insulation and Radiation Control Technologies for Buildings; Springer Nature: Cham, Switzerland, 2022; pp. 443–486. [Google Scholar] [CrossRef]
  5. Othuman Mydin, M.A.; Wang, Y.C. Structural Performance of Lightweight Steel-Foamed Concrete–Steel Composite Walling System under Compression. Thin-Walled Struct. 2011, 49, 66–76. [Google Scholar] [CrossRef]
  6. de Souza, T.B.; Medeiros, M.H.F.; Araújo, F.W.C.; de Melo Neto, A.A. The Influence of Expanded Polystyrene Granules on the Properties of Foam Concrete. Mater. Struct. 2023, 56, 19. [Google Scholar] [CrossRef]
  7. Amran, Y.H.M.; Farzadnia, N.; Abang Ali, A.A. Properties and Applications of Foamed Concrete; a Review. Constr. Build. Mater. 2015, 101, 990–1005. [Google Scholar] [CrossRef]
  8. Zhu, Y.; Zhu, J.; Yu, Z.; Ye, Y.; Sun, X.; Zhang, Y.; Zhu, P.; Jiang, F. Air Drying Scalable Production of Hydrophobic, Mechanically Stable, and Thermally Insulating Lignocellulosic Foam. Chem. Eng. J. 2022, 450, 138300. [Google Scholar] [CrossRef]
  9. Zhao, J.R.; Zheng, R.; Tang, J.; Sun, H.J.; Wang, J. A Mini-Review on Building Insulation Materials from Perspective of Plastic Pollution: Current Issues and Natural Fibres as a Possible Solution. J. Hazard. Mater. 2022, 438, 129449. [Google Scholar] [CrossRef] [PubMed]
  10. Cai, S.; Deng, X.; Beiyuan, J.; Chen, X.; Liu, D.; Lv, D.; Duan, C.; Lin, L.; Cha, R.; Xie, W.; et al. Review of Synthetic Polymer-Based Thermal Insulation Materials in Construction and Building. J. Build. Eng. 2024, 97, 110846. [Google Scholar] [CrossRef]
  11. Michalak, J. External Thermal Insulation Composite Systems (ETICS) from Industry and Academia Perspective. Sustainability 2021, 13, 13705. [Google Scholar] [CrossRef]
  12. Gencel, O.; Nodehi, M.; Hekimoğlu, G.; Ustaoğlu, A.; Sarı, A.; Kaplan, G.; Bayraktar, O.Y.; Sutcu, M.; Ozbakkaloglu, T. Foam Concrete Produced with Recycled Concrete Powder and Phase Change Materials. Sustainability 2022, 14, 7458. [Google Scholar] [CrossRef]
  13. Şimşek, O.; Ünal, M.T.; Gökçe, H.S. Performance of Foam Concrete Developed from Construction and Demolition Waste. Mater. Today Sustain. 2024, 27, 100822. [Google Scholar] [CrossRef]
  14. Xiao, J.; Zhang, H.; Zou, S.; Duan, Z.; Ma, Y. Developing Recycled Foamed Concrete for Engineered Material Arresting System. J. Build. Eng. 2022, 53, 104555. [Google Scholar] [CrossRef]
  15. Lalrinmawii, E.; Sahu, S.; Sarkar, P.; Davis, R. Feasible Use of Recycled Foam Concrete in Cement Mortar. IOP Conf. Ser. Mater. Sci. Eng. 2020, 936, 012011. [Google Scholar] [CrossRef]
  16. Klemczak, B.; Gołaszewski, J.; Cygan, G.; Gołaszewska, M.; Jonkers, H.; Zhilyaev, D.; Koenders, E.A.B. Utilization of Waste Foam Concrete with MPCM as a Substitution Material for Cement in Mortars. J. Build. Eng. 2024, 90, 109284. [Google Scholar] [CrossRef]
  17. Decký, M.; Drusa, M.; Zgútová, K.; Blaško, M.; Hájek, M.; Scherfel, W. Foam Concrete as New Material in Road Constructions. Procedia Eng. 2016, 161, 428–433. [Google Scholar] [CrossRef]
  18. Serpilli, M.; Clementi, F.; Lenci, S. An Experimental and Numerical Study on the In-Plane Axial and Shear Behavior of Sprayed in-Situ Concrete Sandwich Panels. Eng. Struct. 2021, 232, 111814. [Google Scholar] [CrossRef]
  19. Liu, Y.; Zhao, Z.; Amin, M.N.; Ahmed, B.; Khan, K.; Arifeen, S.U.; Althoey, F. Foam Concrete for Lightweight Construction Applications: A Comprehensive Review of the Research Development and Material Characteristics. Rev. Adv. Mater. Sci. 2024, 63. [Google Scholar] [CrossRef]
  20. Sulik, P.; Kukfisz, B.; Dowbysz, A.; Oszczak-Nowińska, A. Fire Resistance of Foamed Concrete for Discontinuous Partition Filling. Materials 2024, 17, 1315. [Google Scholar] [CrossRef]
  21. Awoyera, P.; Onoja, E.; Adesina, A. Fire Resistance and Thermal Insulation Properties of Foamed Concrete Incorporating Pulverized Ceramics and Mineral Admixtures. Asian J. Civ. Eng. 2020, 21, 147–156. [Google Scholar] [CrossRef]
  22. Schiavoni, S.; D´Alessandro, F.; Bianchi, F.; Asdrubali, F. Insulation Materials for the Building Sector: A Review and Comparative Analysis. Renew. Sustain. Energy Rev. 2016, 62, 988–1011. [Google Scholar] [CrossRef]
  23. Neugebauer, A.; Chen, K.; Tang, A.; Allgeier, A.; Glicksman, L.R.; Gibson, L.J. Thermal Conductivity and Characterization of Compacted, Granular Silica Aerogel. Energy Build. 2014, 79, 47–57. [Google Scholar] [CrossRef]
  24. Fickler, S.; Milow, B.; Ratke, L.; Schnellenbach-Held, M.; Welsch, T. Development of High Performance Aerogel Concrete. Energy Procedia 2015, 78, 406–411. [Google Scholar] [CrossRef]
  25. Li, P.; Wu, H.; Liu, Y.; Yang, J.; Fang, Z.; Lin, B. Preparation and Optimization of Ultra-Light and Thermal Insulative Aerogel Foam Concrete. Constr. Build. Mater. 2019, 205, 529–542. [Google Scholar] [CrossRef]
  26. Lu, L.; Wang, H.; Yun, S.; Hu, J.; Wang, M. A State-of-the-Art Review of Novel Aerogel Insulation Materials for Building Exterior Walls. Energy Sources Part A Recover. Util. Environ. Eff. 2024, 46, 16231–16252. [Google Scholar] [CrossRef]
  27. Li, Z.; Yao, S.; Wang, G.; Deng, X.; Zhou, F.; Wu, X.; Liu, Q. Enhancing Water Resistance in Foam Cement through MTES-Based Aerogel Impregnation. Gels 2024, 10, 118. [Google Scholar] [CrossRef] [PubMed]
  28. Wei, S.; Yiqiang, C.; Yunsheng, Z.; Jones, M.R. Characterization and Simulation of Microstructure and Thermal Properties of Foamed Concrete. Constr. Build. Mater. 2013, 47, 1278–1291. [Google Scholar] [CrossRef]
  29. Mydin, M. Influence of Density, Porosity and Void Size on Thermal Conductivity of Green Lightweight Foamed Concrete. J. Adv. Res. Fluid Mech. Therm. Sci. 2022, 92, 25–35. [Google Scholar] [CrossRef]
  30. Ge, Z.; Yuan, H.; Sun, R.; Zhang, H.; Wang, W.; Qi, H. Use of Green Calcium Sulphoaluminate Cement to Prepare Foamed Concrete for Road Embankment: A Feasibility Study. Constr. Build. Mater. 2020, 237, 117791. [Google Scholar] [CrossRef]
  31. García-Maté, M.; De la Torre, A.G.; León-Reina, L.; Losilla, E.R.; Aranda, M.A.G.; Santacruz, I. Effect of Calcium Sulfate Source on the Hydration of Calcium Sulfoaluminate Eco-Cement. Cem. Concr. Compos. 2015, 55, 53–61. [Google Scholar] [CrossRef]
  32. Li, T.; Huang, F.; Li, L.; Zhu, J.; Jiang, X.; Huang, Y. Preparation and Properties of Sulphoaluminate Cement-Based Foamed Concrete with High Performance. Constr. Build. Mater. 2020, 263, 120945. [Google Scholar] [CrossRef]
  33. Gołaszewski, J.; Klemczak, B.; Smolana, A.; Gołaszewska, M.; Cygan, G.; Mankel, C.; Peralta, I.; Röser, F.; Koenders, E.A.B. Effect of Foaming Agent, Binder and Density on the Compressive Strength and Thermal Conductivity of Ultra-Light Foam Concrete. Buildings 2022, 12, 1176. [Google Scholar] [CrossRef]
  34. Ndiaye, K.; Samson, G.; Ginestet, S.; Rouviere, Y.; Cyr, M. Foamed Calcium Sulfoaluminate Cement with Controlled Porous Network for Daily or Seasonal Heat Storage in Ettringite. J. Build. Eng. 2024, 98, 111284. [Google Scholar] [CrossRef]
  35. DIN EN 13302:2018-08; Bitumen Und Bitumenhaltige Bindemittel– Bestimmung der Dynamischen Viskosität von Bitumenhaltigem Bindemittel Mit Einem Viskosimeter Mit Rotierender Spindel. German Institute for Standardization: Berlin, Germany, 2018. [CrossRef]
  36. Yousuf, N.; Olayiwola, O.; Guo, B.; Liu, N. A Comprehensive Review on the Loss of Wellbore Integrity Due to Cement Failure and Available Remedial Methods. J. Pet. Sci. Eng. 2021, 207, 109123. [Google Scholar] [CrossRef]
  37. Zhang, C.; Wang, M.; Liu, R.; Li, X.; Liu, Y.; Jiang, P.; Yan, J.; Zhu, Z.; Chen, M. Rheological Properties of Cement-Based Slurry and Evaluation of Rheological Model: Influence of Particle Size and Shape. Constr. Build. Mater. 2023, 406, 133498. [Google Scholar] [CrossRef]
  38. DIN EN 12390-3:2019-10; Prüfung von Festbeton—Teil_3: Druckfestigkeit von Probekörpern. German Institute for Standardization: Berlin, Germany, 2018. [CrossRef]
  39. Falliano, D.; Parmigiani, S.; Suarez-Riera, D.; Ferro, G.A.; Restuccia, L. Stability, Flexural Behavior and Compressive Strength of Ultra-Lightweight Fiber-Reinforced Foamed Concrete with Dry Density Lower than 100 Kg/M3. J. Build. Eng. 2022, 51, 104329. [Google Scholar] [CrossRef]
  40. Gökçe, H.S.; Hatungimana, D.; Ramyar, K. Effect of Fly Ash and Silica Fume on Hardened Properties of Foam Concrete. Constr. Build. Mater. 2019, 194, 1–11. [Google Scholar] [CrossRef]
  41. Wei, J.; Wang, T.; Zhong, Y.; Zhang, Y.; Leung, C.K.Y. Performance Evaluation of Foamed Concrete with Lightweight Aggregate: Strength, Shrinkage, and Thermal Conductivity. Materials 2024, 17, 3869. [Google Scholar] [CrossRef] [PubMed]
  42. DIN EN 480-11:2005-12; Zusatzmittel Für Beton, Mörtel Und Einpressmörtel—Prüfverfahren—Teil_11: Bestimmung von Luftporenkennwerten in Festbeton. German Institute for Standardization: Berlin, Germany, 2018. [CrossRef]
  43. Li, Z.; Wang, G.; Deng, X.; Liu, Q.; Shulga, Y.M.; Chen, Z.; Wu, X. Preparation and Characterization of Silica Aerogel Foam Concrete: Effects of Particle Size and Content. J. Build. Eng. 2024, 82, 108243. [Google Scholar] [CrossRef]
  44. Wang, G.; Pelton, R.; Hrymak, A.; Shawafaty, N.; Heng, Y.M. On the Role of Hydrophobic Particles and Surfactants in Defoaming. Langmuir 1999, 15, 2202–2208. [Google Scholar] [CrossRef]
  45. Pott, J.U. Entwicklungsstrategien Für zementgebundene Schäume. Ph.D. Thesis, Leibniz Universität Hannover, Hannover, Germany, 2006. [Google Scholar]
  46. Xu, T.; Garrecht, H. Effects of Mixing Techniques and Material Compositions on the Compressive Strength and Thermal Conductivity of Ultra-Lightweight Foam Concrete. Materials 2024, 17, 2640. [Google Scholar] [CrossRef]
  47. Strzałkowski, J.; Garbalińska, H. The Dynamic Thermal Properties of Aerogel-Incorporated Concretes. Constr. Build. Mater. 2022, 340, 127706. [Google Scholar] [CrossRef]
  48. Gao, T.; Jelle, B.P.; Gustavsen, A.; Jacobsen, S. Aerogel-Incorporated Concrete: An Experimental Study. Constr. Build. Mater. 2014, 52, 130–136. [Google Scholar] [CrossRef]
  49. Hub, A.; Zimmermann, G.; Knippers, J. Leichtbeton mit Aerogelen als Konstruktionswerkstoff. Beton Stahlbetonbau 2013, 108, 654–661. [Google Scholar] [CrossRef]
  50. Ślosarczyk, A.; Vashchuk, A.; Klapiszewski, Ł. Research Development in Silica Aerogel Incorporated Cementitious Composites—A Review. Polymers 2022, 14, 1456. [Google Scholar] [CrossRef] [PubMed]
  51. Welsch, T.; Vievers, Y.; Schnellenbach-Held, M.; Bialuschewski, D.; Milow, B. Comparison of Different Aerogel Granules for Use as Aggregate in Concrete. Gels 2023, 9, 406. [Google Scholar] [CrossRef]
  52. Fickler, S.; Heidrich, T.; Welsch, T.; Schnellenbach-Held, M. Hochleistungsaerogelbeton – Optimierung, Tragverhalten, Festigkeit. Beton Stahlbetonbau 2022, 117, 498–509. [Google Scholar] [CrossRef]
  53. Amani, P.; Miller, R.; Javadi, A.; Firouzi, M. Pickering Foams and Parameters Influencing Their Characteristics. Adv. Colloid Interface Sci. 2022, 301, 102606. [Google Scholar] [CrossRef]
  54. Moradpour, N.; Yang, J.; Tsai, P.A. Liquid Foam: Fundamentals, Rheology, and Applications of Foam Displacement in Porous Structures. Curr. Opin. Colloid Interface Sci. 2024, 74, 101845. [Google Scholar] [CrossRef]
  55. Hu, N.; Li, Y.; Wu, Z.; Lu, K.; Huang, D.; Liu, W. Foams Stabilization by Silica Nanoparticle with Cationic and Anionic Surfactants in Column Flotation: Effects of Particle Size. J. Taiwan Inst. Chem. Eng. 2018, 88, 62–69. [Google Scholar] [CrossRef]
  56. Krzan, M.; Jarek, E.; Petkova, H.; Santini, E.; Szyk-Warszynska, L.; Ravera, F.; Liggieri, L.; Mileva, E.; Warszynski, P. Hydrophobisation of Silica Nanoparticles Using Lauroyl Ethyl Arginate and Chitosan Mixtures to Induce the Foaming Process. Polymers 2022, 14, 4076. [Google Scholar] [CrossRef]
  57. Choi, M.; Choi, W.K.; Jung, C.H.; Kim, S.B. The Surface Modification and Characterization of SiO2 Nanoparticles for Higher Foam Stability. Sci. Rep. 2020, 10, 19399. [Google Scholar] [CrossRef] [PubMed]
  58. Han, D.; Kim, J.H.; Lee, J.H.; Kang, S.T. Critical Grain Size of Fine Aggregates in the View of the Rheology of Mortar. Int. J. Concr. Struct. Mater. 2017, 11, 627–635. [Google Scholar] [CrossRef]
  59. Wu, H.; Zhang, H.; Zhang, G.; Liu, J.; Liu, Z.; Du, F. Study on Preparation and Performance of Advanced Aerogel Foamed Concrete with Ultra-Light Aerogel. Constr. Build. Mater. 2023, 366, 130166. [Google Scholar] [CrossRef]
Buildings 15 02671 g001
Figure 1. Mineral foam preparation process.
Figure 1. Mineral foam preparation process.
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Figure 2. Cross-sections of specimens in each group, from left to right: 3-04-ELBA, 3-04-F80, 1-06-F80.
Figure 2. Cross-sections of specimens in each group, from left to right: 3-04-ELBA, 3-04-F80, 1-06-F80.
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Figure 3. Rheological properties of aerogel-added cement slurry. (left) Viscosity; (right) yield stress.
Figure 3. Rheological properties of aerogel-added cement slurry. (left) Viscosity; (right) yield stress.
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Figure 4. Properties of mineralised foam with aerogel addition.
Figure 4. Properties of mineralised foam with aerogel addition.
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Figure 5. Rheological properties of cement slurry containing aerogel with CSA cement and without CSA cement. (left) Viscosity; (right) Yield stress.
Figure 5. Rheological properties of cement slurry containing aerogel with CSA cement and without CSA cement. (left) Viscosity; (right) Yield stress.
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Figure 6. Properties of mineralised foam with different cement bases and aerogel addition.
Figure 6. Properties of mineralised foam with different cement bases and aerogel addition.
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Figure 7. Pore distribution.
Figure 7. Pore distribution.
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Figure 8. Microscope image of specimen containing 5 wt% aerogel, prepared using OPC cement.
Figure 8. Microscope image of specimen containing 5 wt% aerogel, prepared using OPC cement.
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Figure 9. Microscope image of specimen containing 5 wt% aerogel, prepared using OPC/CSA cement.
Figure 9. Microscope image of specimen containing 5 wt% aerogel, prepared using OPC/CSA cement.
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Table 1. The defoaming effect of aerogel represented by change in foam height.
Table 1. The defoaming effect of aerogel represented by change in foam height.
GroupInitial Height (cm)Final Height (cm)Height Difference (cm)
112.2511.880.38
212.0011.630.38
313.502.3811.13
413.130.6311.50
Table 2. Material composition for testing the effect of the addition method of aerogel on mineralised foam.
Table 2. Material composition for testing the effect of the addition method of aerogel on mineralised foam.
GroupMaterial Content (kg/m3)Aerogel Addition
Cement Water Aerogel Foam
3-04-F80113.1445.255.6639.60Addition in step (iii)
3-04-ELBA113.1445.255.6639.60Addition in step (iii)
1-06-F8098.9057.534.7939.56Addition in step (i)
Table 3. Properties of specimens obtained from various mineral foam preparation processes.
Table 3. Properties of specimens obtained from various mineral foam preparation processes.
GroupDesign DensityFresh DensityCompressive Strength (28d)Thermal Conductivity
kg/m3 kg/m3 N/mm2 W/(m·K)
3-04-F80203.64310.480.200.055
3-04-ELBA203.64669.032.070.090
1-06-F80197.79176.370.040.044
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Xu, T.; Garrecht, H.; Jiang, C.; Lu, C. The Application and Effects of Aerogel in Ultra-Lightweight Mineralised Foams. Buildings 2025, 15, 2671. https://doi.org/10.3390/buildings15152671

AMA Style

Xu T, Garrecht H, Jiang C, Lu C. The Application and Effects of Aerogel in Ultra-Lightweight Mineralised Foams. Buildings. 2025; 15(15):2671. https://doi.org/10.3390/buildings15152671

Chicago/Turabian Style

Xu, Tongyu, Harald Garrecht, Chao Jiang, and Chuanyuan Lu. 2025. "The Application and Effects of Aerogel in Ultra-Lightweight Mineralised Foams" Buildings 15, no. 15: 2671. https://doi.org/10.3390/buildings15152671

APA Style

Xu, T., Garrecht, H., Jiang, C., & Lu, C. (2025). The Application and Effects of Aerogel in Ultra-Lightweight Mineralised Foams. Buildings, 15(15), 2671. https://doi.org/10.3390/buildings15152671

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