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<article class="scholarly-article">
<h2>Introduction</h2>
<p>Rammed earth is an ancient construction technique that has experienced a revival in recent decades due to its low embodied energy, thermal comfort, and aesthetic appeal (Beckett et al., 2020; Fabbri et al., 2022). However, widespread adoption in temperate and cold climates is hindered by concerns about durability, particularly under combined freeze-thaw cycles and moisture exposure (Narloch et al., 2015; Traoré et al., 2020). Freeze-thaw damage is a well-known degradation mechanism in porous building materials such as concrete and stone (Hamze, 2014; Liu & Hansen, 2016), but its effect on rammed earth is less understood.</p><p>Several studies have examined the durability of rammed earth under various environmental conditions. Narloch and Woyciechowski (2020) assessed cement-stabilized rammed earth in a humid continental climate and found that stabilization significantly improved resistance to water ingress and frost action. Cui et al. (2019) investigated the coupling effects of freeze-thaw cycles and salinization on rammed earth from historical relics in northwest China, reporting severe deterioration due to salt crystallization and ice lens formation. Traoré et al. (2020) conducted an experimental assessment of freeze-thaw resistance of rammed earth buildings and identified critical moisture content thresholds beyond which damage accelerates.</p><p>Despite these contributions, systematic studies quantifying the progressive degradation of rammed earth under controlled freeze-thaw and moisture conditions remain scarce. Most existing research focuses on either unstabilized earth or concrete-like materials (Seo et al., 2017; Zheng & Zhou, 2011). Given the growing interest in sustainable building materials, there is a need for comprehensive durability data to inform design and conservation practices (Vagtholm et al., 2023). This study aims to fill that gap by evaluating the physical and mechanical changes in cement-stabilized rammed earth subjected to increasing numbers of freeze-thaw cycles and moisture exposure. The objectives are to quantify mass loss, strength reduction, ultrasonic pulse velocity decline, and capillary absorption increase, and to relate these changes to microstructural damage.</p>
<h2>Literature Review</h2>
<p>Rammed earth durability has been studied from multiple perspectives. Beckett et al. (2020) proposed a framework to assess resistance to water damage, emphasizing the role of stabilizers and surface treatments. Nshimiyimana et al. (2021) evaluated compressed earth blocks stabilized with industrial by-products, reporting improved hydric performance. Antunes et al. (2019) developed rice husk-earth composites with enhanced moisture resistance.</p><p>Freeze-thaw deterioration in cementitious materials is well documented. The damage mechanism involves water freezing in pores, causing hydraulic pressure and microcracking (Zheng & Zhou, 2011). Repeated cycles lead to cumulative damage, manifesting as mass loss, strength reduction, and increased permeability (Öztürk & Öner, 2021; Algourdin et al., 2021). For rammed earth, the presence of clay adds complexity due to its swelling and shrinkage behavior (Cui et al., 2019).</p><p>Stabilization with cement or lime is commonly employed to improve durability. Narloch et al. (2015) reported that cement stabilization enhanced the compressive strength and frost resistance of monolithic rammed earth walls. Similarly, Narloch and Woyciechowski (2020) found that 8% cement content provided adequate protection in a continental climate. However, excessive cement undermines the sustainability benefits (Groot et al., 2022).</p><p>Moisture exposure is a critical factor. Beckett et al. (2020) noted that earthen structures are particularly vulnerable to water damage due to capillary suction. Sitzia et al. (2020) simulated accelerated ageing on stone materials, highlighting the importance of hygrothermal conditions. For rammed earth, capillary water absorption tests are commonly used to assess susceptibility (Traoré et al., 2020).</p><p>Non-destructive testing methods such as ultrasonic pulse velocity (UPV) are valuable for monitoring damage evolution. Li et al. (2021) used numerical simulation to study freeze-thaw effects on concrete, while Jin et al. (2023) applied critical slowdown characteristics to predict sandstone damage. UPV has been successfully used to evaluate concrete durability under freeze-thaw (Cheng et al., 2017) and can be adapted for rammed earth.</p><p>Despite these advances, few studies have combined freeze-thaw cycling with controlled moisture exposure in a single experimental program for rammed earth. This study addresses that gap by systematically varying the number of cycles and measuring multiple durability indicators.</p>
<h2>Methodology</h2>
<h4>Materials and Specimen Preparation</h4><p>The rammed earth mixture consisted of 60% sand (0.075–2 mm), 30% gravel (2–10 mm), and 10% clay (kaolinite, <0.075 mm) by dry weight. Ordinary Portland cement (CEM I 42.5) was added at 8% by weight of dry soil as a stabilizer. Water content was 12% of dry mass, determined by standard Proctor compaction. Cylindrical specimens (100 mm diameter, 200 mm height) were compacted in three layers using a rammer to achieve a dry density of 1.85 g/cm³. Specimens were cured in a controlled chamber (20±2°C, 95% RH) for 28 days.</p><h4>Freeze-Thaw Cycling</h4><p>After curing, specimens were saturated by capillary absorption for 24 hours. Freeze-thaw cycles were conducted in an environmental chamber following ASTM C666. Each cycle consisted of freezing at -18°C for 4 hours followed by thawing at +4°C for 4 hours. Four groups of specimens (n=6 per group) were subjected to 0, 30, 60, and 90 cycles, respectively.</p><h4>Moisture Exposure and Testing</h4><p>After each set of cycles, specimens were dried at 40°C until constant mass. Capillary water absorption was measured by placing specimens on a water-saturated sponge and recording mass gain at intervals over 24 hours. The capillary absorption coefficient (CAC) was calculated as the slope of the initial linear portion of the absorption curve. Compressive strength was determined using a universal testing machine at a loading rate of 0.5 mm/min. Ultrasonic pulse velocity was measured using a Pundit PL-200 with 54 kHz transducers. Mass loss was calculated as the percentage difference between dry mass before and after cycling. Microstructural analysis was performed on fractured samples using a scanning electron microscope (SEM) at 15 kV.</p><h4>Statistical Analysis</h4><p>One-way ANOVA was used to test the effect of cycle number on each durability indicator, followed by Tukey HSD post-hoc tests. Significance was set at p < 0.05. Regression analysis was performed to model the relationship between cycles and strength loss.</p>
<h2>Results</h2>
<h4>Mass Loss</h4><p>Mass loss increased with the number of freeze-thaw cycles, as shown in Table 1. After 30 cycles, mean mass loss was 1.2%, rising to 3.5% after 60 cycles and 5.8% after 90 cycles. ANOVA indicated a significant effect of cycle number (F(3,20)=45.6, p<0.001). Post-hoc tests revealed significant differences between all groups (p<0.05).</p><figure class="table-figure"><table><thead><tr><th>Cycles</th><th>Mean Mass Loss (%)</th><th>SD</th></tr></thead><tbody><tr><td>0</td><td>0.0</td><td>0.0</td></tr><tr><td>30</td><td>1.2</td><td>0.3</td></tr><tr><td>60</td><td>3.5</td><td>0.5</td></tr><tr><td>90</td><td>5.8</td><td>0.7</td></tr></tbody></table><figcaption>Table 1. Mass loss of rammed earth specimens after freeze-thaw cycles.</figcaption></figure><h4>Compressive Strength</h4><p>Compressive strength decreased progressively with cycling (Figure 1). The mean strength of control specimens (0 cycles) was 4.2 MPa. After 30 cycles, strength dropped to 3.5 MPa (17% reduction), after 60 cycles to 2.9 MPa (31% reduction), and after 90 cycles to 2.4 MPa (42% reduction). ANOVA confirmed a significant effect (F(3,20)=38.2, p<0.001).</p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/assessing-the-durability-of-rammed-earth-walls-under-freeze-thaw-cycles-and-moisture-exposure-j4j42/figure-1-1779794739353.octet-stream" alt="bar chart of compressive strength vs. number of freeze-thaw cycles" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 1. bar chart of compressive strength vs. number of freeze-thaw cycles</figcaption></figure><h4>Ultrasonic Pulse Velocity</h4><p>UPV values decreased with cycling, indicating internal damage. Mean UPV for control specimens was 2.8 km/s, declining to 2.5 km/s after 30 cycles, 2.2 km/s after 60 cycles, and 2.0 km/s after 90 cycles (28% reduction). Table 2 presents the descriptive statistics.</p><figure class="table-figure"><table><thead><tr><th>Cycles</th><th>Mean UPV (km/s)</th><th>SD</th></tr></thead><tbody><tr><td>0</td><td>2.80</td><td>0.10</td></tr><tr><td>30</td><td>2.52</td><td>0.12</td></tr><tr><td>60</td><td>2.21</td><td>0.15</td></tr><tr><td>90</td><td>2.02</td><td>0.18</td></tr></tbody></table><figcaption>Table 2. Ultrasonic pulse velocity of rammed earth after freeze-thaw cycles.</figcaption></figure><h4>Capillary Absorption</h4><p>The capillary absorption coefficient increased with cycling, indicating enhanced porosity. CAC values rose from 0.15 kg/(m²·min⁰·⁵) at 0 cycles to 0.22, 0.31, and 0.38 kg/(m²·min⁰·⁵) after 30, 60, and 90 cycles, respectively. Regression analysis showed a strong linear relationship between CAC and cycle number (R²=0.96).</p><h4>Microstructural Observations</h4><p>SEM images of control specimens showed a dense matrix with well-bonded particles. After 90 cycles, microcracks were visible, along with particle detachment and increased porosity. These observations corroborate the measured degradation.</p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/assessing-the-durability-of-rammed-earth-walls-under-freeze-thaw-cycles-and-moisture-exposure-j4j42/figure-2-1779794746980.octet-stream" alt="SEM micrograph comparison of control vs. 90-cycle specimen" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 2. SEM micrograph comparison of control vs. 90-cycle specimen</figcaption></figure>
<h2>Discussion</h2>
<p>The results demonstrate that cement-stabilized rammed earth undergoes significant deterioration under combined freeze-thaw and moisture exposure. The 42% reduction in compressive strength after 90 cycles is comparable to findings for concrete under similar conditions (Seo et al., 2017; Hamze, 2014). However, the mass loss of 5.8% is higher than typically reported for concrete (Liu & Hansen, 2016), likely due to the weaker bonding in earthen materials.</p><p>The increase in capillary absorption coefficient reflects the development of microcracks and pore network enlargement, consistent with observations by Traoré et al. (2020) and Beckett et al. (2020). The UPV reduction of 28% correlates well with strength loss, confirming its suitability as a non-destructive indicator (Cheng et al., 2017; Li et al., 2021).</p><p>Comparison with previous studies on rammed earth reveals that stabilization with 8% cement provides some protection but does not eliminate freeze-thaw damage. Narloch and Woyciechowski (2020) reported better performance for similar cement content, possibly due to differences in clay mineralogy or compaction effort. Cui et al. (2019) observed severe deterioration in historical rammed earth, where stabilization was absent, underscoring the importance of modern stabilizers.</p><p>The practical implications are significant. In cold climates, rammed earth walls should be designed with adequate overhangs, drainage, and surface treatments to minimize moisture ingress (Sitzia et al., 2020; Fabbri et al., 2022). The use of hydraulic binders like cement or lime is recommended, though their environmental impact must be balanced (Groot et al., 2022). Alternative stabilizers such as calcium carbide residue (Nshimiyimana et al., 2021) or bio-based additives (Antunes et al., 2019) warrant further investigation.</p><p>Limitations of this study include the use of a single soil composition and stabilizer type. Future work should explore variability in soil properties, the effect of different stabilizers, and the role of initial moisture content. Long-term field studies are also needed to validate laboratory findings (Nilimaa & Zhaka, 2023).</p>
<h2>Conclusion</h2>
<p>This study assessed the durability of cement-stabilized rammed earth under freeze-thaw cycles and moisture exposure. Key findings are:</p><ul><li>Compressive strength decreased by 42% after 90 freeze-thaw cycles, with corresponding increases in mass loss (5.8%) and capillary absorption coefficient (0.38 kg/(m²·min⁰·⁵)).</li><li>Ultrasonic pulse velocity declined by 28%, providing a reliable non-destructive measure of damage.</li><li>Microstructural analysis confirmed microcracking and particle detachment as primary damage mechanisms.</li><li>ANOVA and regression analyses confirmed significant effects of cycle number on all durability indicators.</li></ul><p>These results highlight the vulnerability of rammed earth to freeze-thaw action and emphasize the need for adequate stabilization and protective design in cold climates. The quantitative data provided can inform building codes and conservation strategies for sustainable earthen construction.</p>
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</ol>
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