Evaluation of Degradation in Stabilized Soils for Rural Roads: A Methodological Approach under Tropical Climate Conditions

Abstract

This study proposes a new experimental methodology, called DCP (Degradation by Capillarity and Precipitation), to evaluate the durability of clayey soils stabilized with cement and lime in tropical environments. The method combines rainfall (artificial) and capillary suction, simulating environmental conditions more representative than traditional tests. Specimens with 6% and 10% binder stabilizer content were tested under four conditions: wetting-drying cycles, capillary rise, artificial rainfall, and the combined DCP condition. Indirect tensile strength tests were performed to assess mechanical response. Results show that the DCP methodology leads to different deterioration patterns and lower strength values, without direct correlation to mass or volume loss. This indicates that volumetric stability alone is insufficient to assess performance and that tropical environmental conditions significantly influence behavior. The DCP methodology complements traditional evaluations and improves predictions of long-term performance based on the geomechanical behavior of stabilized soils in road infrastructure and geotechnical applications.

Keywords:
capillary rise; wetting and drying; precipitation; indirect traction

INTRODUCTION

Soil stabilization is a widely used technique in geotechnical and pavement engineering to improve the mechanical strength and durability of materials exposed to adverse climatic conditions ^{1), (2}. One of the most common approaches to enhance the properties of low-plasticity silty clay soils is the addition of cement and lime ^3)-(5. These stabilizers contain calcium, which increases the soil’s bearing capacity, reduces water absorption, and limits its tendency to deform ¹.

Since 1915, cement has been widely applied to improve the performance of soil in pavement structures and rural roads by enhancing their mechanical and physical properties. This technique is particularly useful in soils that require increased strength and adaptability. Additionally, cement stabilization helps reduce deformation problems typically observed in natural soils, thereby improving long-term durability and minimizing road maintenance needs ^{6), (7}. Durability is an important aspect, since this characteristic defines whether the stabilized soil has sufficient strength to withstand the destructive forces to which it will be exposed throughout its life cycle, especially in adverse environmental conditions ⁸.

In tropical regions, exposure to wetting and drying cycles, together with the action of capillary water and precipitation, can accelerate the degradation of stabilized soils, reducing their effectiveness and useful life ^{6), (9}. Degradation because of wetting and drying cycles (HyS) occurs because, in the wet state (H), the soil increases its volume and swells (expands) until it becomes saturated. Subsequently, during drying (S), the soil undergoes significant shrinkage. These cycles generate tensile stress that, over time, can overcome soil cohesion, causing cracks to form. As HyS cycles increase, the material can reach a point of plastic deformation, directly affecting its durability and structural performance ^{6), (10)-(12}. The action of capillary water is a problem in stabilized soils, as it causes a decrease in the strength and stiffness needed to support the structure of a pavement. Capillary rise depends on the type of soil, and in regions with adverse climates, this phenomenon is uncertain due to the high percentage of water absorption ⁹. Therefore, to stabilize these soils, it is essential to determine an optimum percentage of stabilizing material to reduce premature deterioration caused by capillary rise, thus ensuring greater durability of the stabilized soil ⁹.

Premature degradation of stabilized soils represents a challenge for the construction of resilient infrastructure in areas with high climate variability. Although stabilization with materials such as cement and lime is a common technique, in some cases, the natural properties of the soil can contribute to its accelerated deterioration, especially when exposed to severe environmental changes ^{3), (7}, and compaction of a stabilized soil can also influence its mechanical behavior ¹³. If stabilization is not performed properly and the area presents high climatic variability, frequent repairs may be required in short periods of time. This problem not only affects the durability of the soil, but also implies a high economic cost due to the recurrent need for maintenance and rehabilitation ^14)-(15.

Traditional methods of evaluating stabilized soils rely on standard tests that, while effective, do not always accurately reflect actual long-term exposure conditions. The method commonly used to simulate the conditions of long-term stabilized soils is the wetting and drying (HyS) test, regulated by ASTM D 559. This method consists of 48 h cycles, of which samples are subjected to 5 hours of wetting and 42 h of oven drying. Generally, 12 cycles are used to evaluate the long-term durability of stabilized soil ^{9), (11), (16)-(21), (22)-(32}. In some cases, the parameters of the cycles can be adjusted according to the specific conditions of the study area, although always taking as reference the traditional HyS test ^{11), (33)-(34}.

Standardized tests, such as the wetting and drying test (HyS), evaluate parameters such as mechanical strength, volume, and mass, but they do not consider the combined effects of humidity, temperature, and precipitation. Generally, climatic cycles characteristic of the study area are analyzed to estimate the behavior of stabilized soils throughout their service life. However, these tests are usually limited to the HyS procedure ¹¹. In tropical countries, wetting and drying cycles have an even greater impact on soil degradation. Unlike regions with defined seasons (winter, summer, spring, and autumn), tropical areas such as Colombia experience irregular and highly variable climatic patterns over time, which intensifies the deterioration of stabilized soils ^{9), (14}.

Recent studies have emphasized the importance of eco-friendly stabilization strategies and erosion control techniques in rural and forest road settings. For instance, Yüksel et al. (2025) ³⁵ demonstrated the effectiveness of wood residues and hydroseeding in reducing runoff and sediment yield on forest road cut slopes using an ANN-based evaluation, while Ramos-Scharrón et al. (2022) ³⁶ highlighted the critical role of slope reduction and erosion control blankets in mitigating erosion in actively cultivated tropical terrains. Currently, no standardized tests simultaneously consider the combined effects of precipitation and capillary rise on soil degradation, particularly under tropical climate conditions. Existing methods tend to isolate environmental variables or fail to reproduce the dynamic interactions present in real field conditions. Addressing this gap, the present study introduces a new approach designed to evaluate these interacting mechanisms in a more integrated and realistic manner.

This research provides three relevant contributions to the literature on stabilized soils. It proposes an experimental methodology, referred to as the Degradation by capillary and precipitation (DCP), which adapts the traditional wetting and drying procedure to reflect local climatic variability. The protocol simulates soil degradation under tropical conditions by integrating the effects of both precipitation and capillary rise in a single controlled framework. Additionally, it incorporates the evaluation of indirect tensile strength (ITS) after each exposure cycle, allowing for the characterization of mechanical behavior deterioration over time. Finally, the results demonstrate that the combined effects of this new methodological approach produce a greater reduction in mechanical strength, a critical factor in decision-making for the durability assessment of stabilized soils in rural infrastructure projects.

The manuscript is structured as follows: Section 2 details the materials used and the experimental methodology, including the Degradation Cycle Protocol (DCP). Section 3 presents and discusses the results related to indirect tensile strength, mass loss, and volume reduction throughout the degradation cycles. Finally, Section 4 contains the conclusions and recommendations for field application and future research.

MATERIALS AND METHODS

The soil used in the development of this experimental program is a material with low plasticity and moderate susceptibility to moisture degradation. This type of clayey-loamy material, coming from a quarry located in Colombia, in the city of Bogotá (Figure 1: Site of soil collection for the study), was selected with the purpose of generating a stabilization process with cement and lime, by performing the following characterization tests: liquid and plastic limit, granulometry by sieving and hydrometer, and specific gravity.

Figure 1:
Site of soil collection for the study

Once the corresponding soil characterization tests were applied, the particle size distribution and characteristics of the study soil were observed (Figure 2: Grain size distribution of the material.), classifying it as a low plasticity silty clay, with a liquid limit (LL) of 17%, a plasticity index (PI) of 6%, and a specific gravity of 2.63. The granulometric curve shows a poor particle size distribution, with a coefficient of curvature (CC) of 3.32. Its slope is a bit steep and abrupt, characteristic of a poorly graded soil, where certain particle sizes predominate. In addition, discontinuities are observed in some ranges and similarities in the percentages of material retained in different sieves, such as, for example, sieves N° 60, 80, and 100. The results obtained for the characterization of this material were obtained from the methodology established in ASTM D 4318-17, ASTM D 422-63, and ASTM D 854-23.

Figure 2:
Grain size distribution of the material.

A Scanning Electron Microscopy (SEM) analysis conducted on the silty-clay soil sample (Figure 3: SEM Analysis of the studied soil.), identified the presence of various minerals, such as quartz, an irregularly shaped mineral with a smooth to rough surface and no visible fractures (2-50 µm, scattered distribution); feldspar, exhibiting angular to subangular shapes with internal microfractures (5-100 µm, occurring individually or in larger fragments); iron oxides, irregular and amorphous, with rough and opaque surfaces (1-20 µm, often coating other particles) and clay minerals such as kaolinite and illite, in sheets or flakes smaller than 2 µm, forming dense aggregates or covering other particles.

Figure 3:
SEM Analysis of the studied soil.

The Portland cement used as a stabilizer in this experimental program was of general use (Type I, CEMEX brand), manufactured under ISO 9001 certified quality management systems. Similarly to the soil material, a SEM analysis of the cement was performed, evidencing a microstructure (Figure 4: SEM Analysis of the cement portland.) composed of alite (C3S-Tricalcium Silicate), its shape is angular or elongated crystals, well-defined edges, with rough texture, and its size is between 5 - 30 µm. Belite (C3S-Tricalcium silicate), its shape is irregular with a smoother texture than Alite, its size is in the range of 2-20 µm. Tricalcium aluminate (C3AI) and tetracalcium ferrite aluminate (C4 AF), their shape is irregular and amorphous with a smooth texture, its size is larger than 5 µm. Gypsum (CaSO₄ 2H₂O) has lamellar plates with a smooth surface and fractures, and its size varies from 5-50 µm.

Figure 4:
SEM Analysis of the Portland cement.

On the other hand, Calidra brand hydrated lime, used in this same experimental program, was obtained from the Caltek Río Claro Plant, Autopista Medellín-Bogotá kilometer 154, Puerto Triunfo, Colombia. This type of material complies with the technical specifications established in ASTM C-25 and ASTM C-110. Some of its physicochemical properties are: molecular weight of 74.10 g/mol, odorless, non-flammable, non-combustible, specific gravity of 3.3 g/cm³, pH equal to 12 at 25°C, and a bulk density of 0.6 g/ml, which depends on the granulometry.

Figure 5 shows the SEM microscopy of lime at a magnification of 1.00 KX, where several mineral particles with specific characteristics can be identified. Calcium oxide (CaO or quicklime) appears as irregular, angular, and fractured particles, typically with a rough texture and visible fissures. Its particle size ranges between 5 and 50 µm. Calcium hydroxide [Ca(OH)₂] is usually found in the form of scaly plates or sheet-like structures that tend to cluster together. These particles have a smooth to slightly rough texture and often appear as aggregates, with sizes ranging from 2 to 20 µm. Finally, calcium carbonate (CaCO₃) displays an irregular morphology, occasionally forming spherical or cubic structures, and its particle size varies from 5 to 30 µm. Silicates (SiO₂), their shape is angular with a glassy appearance, their texture is heterogeneous with fractures, and their size varies between 5-40 µm.

Figure 5:
SEM Analysis of the studied lime.

The compaction test was conducted to determine the maximum dry density and optimum moisture content of the soil stabilized with lime and cement at proportions of SC6%, SC10%, SL6%, and SL10%. This test followed the procedure described in ASTM D698-12. It allows evaluating the influence of compaction on the behavior of stabilized soils, using a 24.5 N hammer dropped from a height of 305 mm, achieving an approximate compaction energy of 600 kN·m/m³. The material was compacted in three layers within a mold measuring 101.6 mm in diameter and 116.4 mm in height. Based on the results obtained, the specimens used for the degradation tests were prepared. These were molded using a separate form with dimensions of 101.6 mm in diameter and 65 mm in height, designed to be tested under diametral compression to determine their indirect tensile strength (ITS) after completing the degradation cycles. Each cycle corresponds to one exposure period under simulated climatic degradation conditions.

Cylindrical specimens were prepared to compare their mechanical strength after 0, 6, and 12 degradation cycles under each test condition. For cycle 0, a total of four specimens were prepared, two with cement (SC6% and SC10%) and two with lime (SL6% and SL10%). For cycles 6 and 12, eight specimens were made for each cycle, with four for each stabilizer type. These included both brushed (B) and unbrushed (UB) conditions: SL6% B, SL6% UB, SL10% B, SL10% UB, SC6% B, SC6% UB, SC10% B, and SC10% UB. The brushed specimens were gently abraded with a steel-bristle brush (grata) at the end of each cycle to simulate surface wear and evaluate mass loss over time. UB indicates specimens that were not brushed during any degradation cycle.

A total of 72 specimens were prepared. Of these, 64 were cured in a humidity chamber for 7 days before testing. The remaining specimens were cured for 7 and 28 days to evaluate strength development using indirect tensile strength (ITS) testing. The specimens measured 4 inches in diameter and 2½ inches in height. The compaction process was based on ASTM D698-12 energy levels, using a Marshall-type hammer in accordance with ASTM D6926-20.

This test was carried out using the ASTM D 559 methodology, with the objective of determining the loss, mass change, and volume change (expansion and contraction) caused by the wetting and drying cycles. During the test, specimens were immersed in water for 5 h and then oven-dried at 70 °C for 42 h. Each cycle lasted 48 h which roughly simulates about six months of environmental exposure under real conditions. At the end of each HyS cycle, the brushed specimens (SL6% B, SL10% B, SC6% B, SC10% B) were abraded using a steel-bristle brush (grata) to replicate the effects of rain and surface wear typically experienced throughout their service life. Mass loss and volume change were used to evaluate degradation. Finally, graphs of mass and volume loss were prepared for specimens subjected to 6 and 12 cycles.

This test was performed following the methodology established in AS 1141.53 (1996) to assess mass loss and volume change (expansion and contraction) caused by capillary rise. During the test, specimens were immersed to one-third of their height for 48 hours and then oven-dried at 70 °C for 24 h. Each cycle had a total duration of 72 h

At the end of each capillary rise cycle, the brushed specimens (SL6% B, SL10% B, SC6% B, SC10% B) were gently abraded with a steel-bristle brush (grata) to simulate progressive surface wear. Degradation was evaluated by tracking changes in mass and volume. To clearly illustrate these results, graphs were prepared showing the loss trends for specimens exposed to 6 and 12 cycles.

This test was conducted based on the New Zealand standard NZS 4898:1998, aiming to evaluate the erodibility (degradation) of stabilized soil under simulated rainfall conditions. Rainfall was applied from a predefined height over 60 min.. To better reflect tropical rainfall patterns, precipitation data from Yopal (Casanare, Colombia) were reviewed. Using this information, the maximum hourly rainfall was identified, and the corresponding water volume was calculated according to the surface area of each specimen. This volume was then applied consistently during the 60 min. simulation.

Following exposure, specimens were left to dry at room temperature for 3 h, then oven-dried at 70 °C for 42 h. Each cycle had a total duration of 48 h, including time for measurement and brushing. At the end of each cycle, brushed specimens (SL6% B, SL10% B, SC6% B, SC10% B) were abraded using a steel-bristle brush (grata) to simulate erosion and wear caused by rainfall over the material’s service life. Degradation was assessed through mass and volume loss. To visualize these results, graphs were prepared for specimens subjected to 6 and 12 precipitation cycles.

This study proposes an experimental methodology, which is referred to as DCP (Degradation by Capillarity and Precipitation), to evaluate the combined effect of capillary rise and precipitation on stabilized soils (Figure 6: Design and Execution of the Capillary and Precipitation (DCP).). The test consists of placing the base of the specimen on a porous stone partially submerged in water, with a sheet of filter paper between the stone and the specimen to ensure uniform moisture distribution. Simultaneously, simulated rainfall is applied to the top of the specimen for 60 minutes. The simulated rainfall consisted of applying 1.2 liters of water over each specimen from a height of 40 cm. This volume was defined based on historical precipitation data from Yopal (Casanare, Colombia), located in the Orinoquía region, which is characterized by intense tropical monsoon conditions. According to meteorological records from the Instituto de Hidrología, Meteorología y Estudios Ambientales (IDEAM), hourly rainfall intensities in this area can exceed 100 mm/h during the peak rainy season (April-October). The applied volume corresponds to approximately 120 mm of rainfall over the exposed surface of the specimen, simulating an intense yet realistic tropical storm. The drop height of 40 cm was selected to reproduce moderate raindrop impact energy, enough to cause surface erosion and promote infiltration, while maintaining specimen integrity and ensuring repeatability under laboratory conditions.

Figure 6:
Design and Execution of the Capillary and Precipitation (DCP).

After the rainfall stage, specimens were allowed to dry at room temperature for 3 h, during which capillary rise remained active, followed by oven drying at 70 °C for 42 h. Each cycle lasted 48 hours, including the time needed for measurements and brushing. At the end of each cycle, brushed specimens (SL6% B, SL10% B, SC6% B, SC10% B) were abraded using a steel-bristle brush (grata) to simulate cumulative environmental erosion and rainfall-induced surface wear. Degradation was evaluated based on mass and volume loss, and the results were used to develop comparative graphs for specimens subjected to 6 and 12 DCP cycles.

The mechanical strength test was performed after the degradation cycles using the indirect tensile strength test, following the methodology established in ASTM C496/C496M-17. This test allowed the comparison of the values obtained as a function of the modified geometry of the specimens and also enabled the analysis of the performance of the different stabilizers, considering both the reduction in strength after exposure to degradation conditions and the strength gain in specimens cured for 7 and 28 days that were not subjected to degradation. Figure 6 shows the setup used to apply diametral compression to determine the indirect tensile strength (ITS) (Figure 7: Tensile failure mode of the specimens.).

Figure 7:
Tensile failure mode of the specimens.

The following figure presents a simplified schematic of the experimental procedure used to evaluate the durability of soils stabilized with different cementitious agents. Four degradation methods were employed: Hydration and Drying (HyS), Capillary Rise (AC), Simulated Rainfall (Pr), and a combined test referred to as DCP (Precipitation + Capillarity). All methods consisted of cycles involving controlled moisture exposure, oven drying, and surface brushing, simulating aggressive environmental conditions that accelerate degradation processes in tropical humid climates.

Figure 8:
Schematic Diagram of Durability Testing Protocols for Stabilized Soils.

Each protocol was applied to specimens compacted according to the Standard Proctor test and prepared with stabilized soils using 6% and 10% cementitious content (lime or Portland cement). The cycles included immersion, drying at 70 °C, and resting at room temperature. Indirect tensile failure of the briquettes was the final criterion to assess the degradation resistance of each stabilization strategy. This schematic provides a clear visualization of the differences between the testing protocols and their increasing severity as environmental factors are combined. In particular, the DCP method stands out by integrating multiple simultaneous stressors, offering a more demanding and realistic assessment of durability under tropical rainfall and moisture conditions.

RESULTS AND DISCUSSION

For the mixture with SC6%, an optimum moisture content of 13.5% and a maximum dry density of 1.89 g/cm³ was obtained. In the case of SC10%, the optimum moisture content was 13%, and the maximum dry density reached 1.87 g/cm³. On the other hand, for stabilization with lime, the SL6% mixture presented an optimum moisture content of 13.6% and a maximum dry density of 1.84 g/cm³, while for the SL10% mixture, the values obtained were 16.1% optimum moisture content and 1.78 g/cm³ maximum dry density (Figure 9: Compaction curve results for the materials used.).

Figure 9:
Compaction curve results for the materials used.

These observations align with established behavior in silty and clayey soils: the addition of cementitious or lime binders tends to increase optimum moisture content and decrease maximum dry density. For instance, Gruchot et al. (2025) ³⁷ and Mora et al. (2022, 2024) ^{38), (39} reported that higher binder contents lead to greater water demand and decreased compactability, primarily due to flocculation and the generation of fine particles, as also noted by Pandey et al. (2025) ⁴⁰. Similarly, Roohbakhshan (2013) ⁴¹ observed that cement-treated soils tend to exhibit a reduced densification capacity as the binder content increases. Furthermore, the values fall well within the ranges reported for stabilized tropical clay soils, with optimum moisture contents between 12-16% and maximum dry densities between 1.70-1.90 g/cm³ (dependent on soil mineralogy, binder type, and content).

The eight specimens prepared to evaluate the mechanical resistance to indirect tensile strength (ITS) at 7 and 28 days of curing were tested. The behavior observed with an increase in the curing time showed a notable rise in ITS values (Figure 10: Indirect tensile strength evolution at 7 and 28 days.), excluding the influence of degradation tests. For cement-stabilized specimens (SC6% and SC10%), the increase in strength between 7 and 28 days was 54% compared to their 7 day values. The SL6% specimen doubled its ITS at 28 days compared to 7 days, while the SL10% specimens exhibited an 80% increase in strength relative to their initial 7-day values.

Figure 10:
Indirect tensile strength evolution at 7 and 28 days.

This strength gain is primarily attributed to hydration reactions in the cement-stabilized mixtures, where the formation of calcium silicate hydrates (C-S-H) and calcium hydroxide (CH) progressively enhances particle bonding and matrix integrity ⁴². In lime-stabilized soils, the increase is driven by cation exchange and flocculation in early stages, followed by pozzolanic reactions between CH and the aluminosilicate phases in clay, which result in additional cementitious products ^{43), (44}. These reactions are particularly effective in tropical clays due to their high content of reactive minerals.

Moreover, the curing period plays a critical role in the development of microstructural changes. During the initial 7 days, rapid hydration leads to early strength gain, while continued curing up to 28 days allows for the formation of larger and more stable binding phases. These fill voids, increase compaction density, and significantly enhance mechanical resistance ^{45), (46}. The observed ITS trends are in agreement with findings from other studies on cement- and lime-stabilized tropical clays, which report progressive strength improvements within the first 28 days of curing ^{47), (48}.

The durability and degradation of 16 specimens were evaluated, of which eight were subjected to the conventional wetting and drying test for 12 cycles, and the remaining eight for six cycles. At the end of each testing sequence, indirect tensile strength (ITS) was measured to compare mechanical performance at different degradation stages.

Mass loss was analyzed in the specimens that were brushed at the end of each cycle. A greater mass loss was observed in the SL6% and SL10% specimens, with the most significant reduction occurring after the first cycle. This was because, upon exiting the oven, the specimen did not have moisture (Figure 11b), whereas before the first cycle, it still retained the initial humidity from manufacture and curing in the humidity chamber (Figure 12).

Figure 11:
Wet-Dry process: (a) Moistening (b) Oven drying (c) Lime soil, Cycle 6 (d) Cement soil, Cycle 6

Figure 12:
Mass loss due to wetting and drying: (a) Mass loss, (b) Percentage of mass change.

During the wetting phase of each cycle, progressive wear was visible on the upper edges of all specimens. Additionally, upon immersion, air trapped inside the material escaped as bubbles during the first few minutes, until full saturation was reached (Figure 11a). As the cycles progressed, holes began to form in the SC6% and SC10% specimens, becoming more pronounced after the sixth cycle (Figure 11d). The SL6% specimens exhibited hole formation until the fourth cycle, after which flaking began to occur, increasing porosity, a key factor affecting performance under wetting and drying conditions (49). In the case of SL10%, detachment of material was observed in the upper part after the sixth cycle (Figure 11c).

Figure 12: Mass loss due to wetting and drying: (a) Mass loss, (b) Percentage of mass change.b shows that the SC10% specimen had the lowest mass loss, with a reduction of 11.41% relative to its initial weight after 12 wetting and drying cycles. This performance is attributed to the higher stabilizer content, which effectively reduced material loss during testing. In contrast, the SL6% specimen recorded the highest mass loss, reaching 20.25%. In the case of the lime-treated specimens, increasing the stabilizer content from 6% to 10% resulted in a 3.38% decrease in mass loss, as observed in the SL10% specimen.

To determine volume loss, measurements were taken after each wetting and drying cycle using specimens that were not brushed. Noticeable volume changes were observed in the SC6%, SL6%, and SL10% specimens; however, these variations were not considered significant compared to their initial volumes (Figure 13. Volume loss due to wetting and drying: (a) Volume loss (b) Percentage of volume Change.b). The SC10% specimen presented the lowest volume loss, with a reduction of 1.83%, while the SL6% specimen recorded the highest, at 5.05%.

Figure 13:
Volume loss due to wetting and drying: (a) Volume loss (b) Percentage of volume Change.

Figure 14:
Indirect tensile strength under wetting and Drying: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change.

In the indirect tensile strength test, it was generally observed that the mechanical performance of the HyS specimens improved as the number of cycles increased, except for the SL6% B specimen (brushed), followed by the SC6% UB specimen at 0.74 MPa. Despite its significant volume loss, the SC6% UB mixture exhibited good mechanical behavior. Likewise, the SL10% specimens-both brushed and unbrushed-also showed favorable performance.

These experimental findings confirm that degradation patterns observed under wetting-drying cycles-particularly mass loss, surface flaking, and internal void formation-are strongly influenced by the type of binder and its interaction with the soil matrix. This aligns with literature on alternative binders, where strength and durability are known to depend on both pozzolanic activity and curing regime. Materials such as lime, fly ash, palm oil fuel ash (POFA), and waste paper ash (WPA) exhibit enhanced resistance when sustained hydration fosters the development of C-S-H and C-A-H gels, while cyclic moisture fluctuations can lead to microstructural deterioration ^50)-(52. Particularly, WPA has been reported to show moderate resilience under these conditions, although flaking and edge loss-similar to the SL6% behavior observed here-remain a challenge under prolonged cycling ⁵². Therefore, the balance between curing duration and environmental exposure plays a critical role in designing effective and sustainable stabilized soil systems.

During this test, wear on each specimen was analyzed through capillary water rise, which covered approximately one-third of the specimen’s height. Over the 48 h of wetting, visible moisture infiltration due to capillarity was observed (Figure 15a). Material wear became evident after the fourth cycle, particularly at the edges of the SC6% and SC10% specimens, both brushed and unbrushed, which began to show signs of deterioration (Figure 15b). In contrast, the SL6% and SL10% specimens showed only slight detachment around the perimeter (Figure 15c). At the end of the 12 cycles, changes were more noticeable in the unbrushed specimens, especially in the lime-stabilized ones, in the areas directly exposed to water during the wetting phase of each cycle. The specimen with the greatest mass loss was SL6%, with a 17.8% reduction, while SC10% showed the least mass loss, as illustrated in Figure 16.

Figure 15:
Capillary rise process: (a) Immersion (b) Cement-soil, cycle 6 (c) Lime-soil, cycle 6.

Figure 16:
Mass loss due to capillary rise: (a) Mass loss, (b) Percentage of mass change.

Figure 17:
Volume loss due to capillary rise: (a) Volume loss, (b) Percentage of volume change.

To evaluate volume loss, graphs were prepared showing volume variation as a function of the number of cycles. The SL6% specimen showed the highest reduction, with a 5.83% loss relative to its initial volume, followed closely by SC6%, which exhibited a similar loss of 4.78%. These results are consistent with established theory, which indicates that lower stabilizer content leads to faster degradation over time compared to soils treated with higher percentages of stabilizer.

The specimens subjected to the capillary rise test that exhibited the highest mechanical strength at the end of all cycles were SC10% UB and SC10% B, with values of 1.30 MPa and 1.08 MPa, respectively. The SC6% B specimen, evaluated after 6 cycles, showed greater strength than the other brushed specimens at the same stage, indicating a noticeable improvement. Although the increase in strength between cycles 6 and 12 was minimal, it still outperformed both SL6% and SL10% specimens (Figure 18: Indirect tensile strength under capillary rise: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change.). Overall, the lime-stabilized specimens (SL) showed more pronounced changes in strength over time, highlighting their greater sensitivity to degradation caused by capillary rise (Figure 18: Indirect tensile strength under capillary rise: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change.).

Figure 18:
Indirect tensile strength under capillary rise: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change.

These findings are consistent with the literature highlighting the influence of capillary action on soil stability. According to Hu et al. (2024) ⁵³, cement-stabilized soils experience microstructural changes during wetting-drying cycles, often showing an initial decline in strength followed by stabilization, due to hydration and pozzolanic reactions. Lime stabilization, while effective at modifying physicochemical properties and reducing plasticity ^{54), (55} typically generates less dense binding gels, making it more vulnerable to moisture-driven degradation. This is supported by capillary ascent studies such as those following AS 1141.53, which emphasize the importance of monitoring volumetric and mass losses as indicators of long-term durability. The increase in porosity observed in lime-treated specimens likely contributes to their greater susceptibility to degradation under capillary conditions.

This test was similar in duration to the wetting and drying cycles. All specimens subjected to simulated rainfall completed the full number of cycles. Visible wear was observed in the SC6% and SL6% specimens, where the continuous impact of raindrops caused surface deterioration and eventually lifted the exposed face (Figure 19a). In the SC10% and SL10% specimens, small holes developed on the impacted surface; however, no significant wear was detected on the lower part of the specimens (Figure 19b). Figure 20 shows that the specimen with the greatest mass loss was SL6% B, with a 16.5% reduction, while the SC10% B specimen exhibited the lowest loss, with a percentage of 11.8%.

Figure 19:
Simulated precipitation process: (a) Cement-stabilized specimen cycle 6, (b) Lime-stabilized specimen cycle 6.

Figure 20:
Mass loss due to simulated precipitation: (a) Mass loss, (b) Percentage of mass change.

The unbrushed specimens with the highest volume loss were SL6% and SC6%, with values of 5.83% and 4.77%, respectively (Figure 21: Volume loss due to simulated precipitation: (a) Volume loss, (b) Percentage of volume change.). The results obtained from the indirect tensile strength test showed that all specimens experienced an increase in mechanical strength throughout the cycles. However, as shown in Figure 22: Indirect tensile strength under simulated precipitation: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change., the SL6% UB specimen exhibited the lowest strength, which is consistent with its higher volume loss observed.

Figure 21:
Volume loss due to simulated precipitation: (a) Volume loss, (b) Percentage of volume change.

Figure 22:
Indirect tensile strength under simulated precipitation: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change.

An increase in stabilizer content resulted in some volume loss; however, this did not negatively impact the mechanical strength of the specimens. Although lime-stabilized specimens with 6% content showed the lowest strength, the SL10% specimen performed better, like the favorable performance observed in the unbrushed SC specimens. When examining the brushed specimens, Figure 22: Indirect tensile strength under simulated precipitation: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change. clearly shows that SC6% B and SC10% B achieved higher strength values, while SL6% B and SL10% B performed poorly. This behavior is likely related to the degradation patterns that occurred during the test.

The observed surface degradation patterns are consistent with previous studies where simulated rainfall accelerated aggregate disintegration and erosion ^{56), (57}. In particular, Dai et al. demonstrated how rainfall intensity and soil composition influence surface erosion in karst environments. Furthermore, Bertol et al. (2010) ⁵⁸ highlighted the role of microtopography in sediment transport under rainfall impact, reinforcing the relevance of surface texture and binder interaction. Interestingly, although the rainfall cycles resulted in surface erosion and quantifiable mass loss, an unexpected trend of increased compressive strength was recorded in some specimens post-cycling. This counterintuitive behavior-previously noted in studies involving biochar stabilization ⁵⁹-may be attributed to secondary pozzolanic reactions promoted by continued wetting, as well as densification from cyclic saturation and drying. However, this phenomenon warrants deeper microstructural investigation.

In this test, the durability of the specimens was evaluated under combined degradation processes: wetting and drying, capillary rise, and simulated precipitation (Figure 23: DCP process: (a) Simulation model (b) Porous stones saturated with filter paper (c) Cement-soil cycle 6.a and Figure 23: DCP process: (a) Simulation model (b) Porous stones saturated with filter paper (c) Cement-soil cycle 6.b). This approach exposed the specimens to simultaneous environmental conditions, allowing the observation of progressive durability loss over the cycles. The degradation patterns varied according to the type of stabilizer used, cement (Figure 23: DCP process: (a) Simulation model (b) Porous stones saturated with filter paper (c) Cement-soil cycle 6.c), and lime (Figure 23: DCP process: (a) Simulation model (b) Porous stones saturated with filter paper (c) Cement-soil cycle 6.d).

Figure 23:
DCP process: (a) Simulation model (b) Porous stones saturated with filter paper (c) Cement-soil cycle 6.

Figure 24:
Mass loss due to DCP: (a) Mass loss, (b) Percentage of mass change.

The results obtained from this new methodology aligned with expectations, as the specimens experienced a greater degree of degradation over the same period compared to when the wetting-drying, capillary rise, and simulated precipitation tests were performed individually. Regarding mass loss, the brushed specimens (SC6% B, SC10% B, SL6% B, and SL10% B) showed similar behavior, with losses ranging between 8.67% and 16.08% (Volume loss analysis of the unbrushed specimens (SC6% UB, SC10% UB, SL6% UB, and SL10% UB) revealed the following reductions after 12 DCP cycles: 5.3% for SC10%, 4.58% for SC6%, 3.76% for SL6%, and 2.27% for SL10% (Figure 25: Volume loss due to DCP: (a) Volume loss, (b) Percentage of volume change.). Regarding mechanical performance, the SC10% B specimen recorded the highest indirect tensile strength, likely due to its higher stabilizer content. In contrast, its unbrushed counterpart showed visible surface wear on the face exposed to dripping, which led to cracking and eventual material loss, factors that directly impacted its strength. A similar trend was observed in the SC6% B specimen, although its overall strength was lower, which can be attributed to the lower percentage of stabilizer used. These results suggest that cement-stabilized specimens perform better under adverse environmental conditions when the stabilizer content is 10%. Conversely, in both B and UB specimens with 6% stabilizer, tensile strength peaked at cycle 6 but decreased by cycle 12 (Figure 26: Indirect tensile strength under DCP: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change).).

Figure 25:
Volume loss due to DCP: (a) Volume loss, (b) Percentage of volume change.

Figure 26:
Indirect tensile strength under DCP: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change

Volume loss analysis of the unbrushed specimens (SC6% UB, SC10% UB, SL6% UB, and SL10% UB) revealed the following reductions after 12 DCP cycles: 5.3% for SC10%, 4.58% for SC6%, 3.76% for SL6%, and 2.27% for SL10% (Figure 25: Volume loss due to DCP: (a) Volume loss, (b) Percentage of volume change.). Regarding mechanical performance, the SC10% B specimen recorded the highest indirect tensile strength, likely due to its higher stabilizer content. In contrast, its unbrushed counterpart showed visible surface wear on the face exposed to dripping, which led to cracking and eventual material loss, factors that directly impacted its strength. A similar trend was observed in the SC6% B specimen, although its overall strength was lower, which can be attributed to the lower percentage of stabilizer used. These results suggest that cement-stabilized specimens perform better under adverse environmental conditions when the stabilizer content is 10%. Conversely, in both B and UB specimens with 6% stabilizer, tensile strength peaked at cycle 6 but decreased by cycle 12 (Figure 26: Indirect tensile strength under DCP: (a) Indirect tensile strength, (b) Percentage of indirect tensile strength change).

When comparing the ITS results from the DCP method to those from individual tests, a notable reduction in strength was observed, particularly in cement-stabilized specimens. For these, the ITS values obtained with the DCP method were approximately 19 - 24% lower than those from the wetting-drying (HyS) test, and up to 44% lower compared to the capillary rise (AC) test. In lime-stabilized specimens, the differences were less evident in the HyS test, but highly significant in the AC and precipitation (Pr) tests, with strength reductions reaching 65 - 75%. These findings indicate that the combined action of capillary rise and precipitation in the DCP test produces more severe degradation conditions, especially in soil stabilized with lime, and reveals deterioration mechanisms that isolated tests may fail to detect.

Overall, the results show (Figure 27: Comparative Increase in Indirect Tensile Strength (ITS) under Different Curing and Treatment Conditions.) that treatments with 10% binder content (both soil-cement and soil-lime) produce higher increases in indirect tensile strength (ITS) compared to 6%, confirming the effectiveness of higher cementitious content. Soil-lime (SL) stands out due to its higher ITS values, reaching up to 613.92% (Pr, 10% UB), suggesting greater chemical reactivity. In most cases, unbrushed (UB) specimens performed better, while brushing (B) slightly reduced ITS values, possibly due to the removal of reaction products or exposure of less consolidated surfaces.

Figure 27:
Comparative Increase in Indirect Tensile Strength (ITS) under Different Curing and Treatment Conditions.

On the other hand, the DCP test yielded the lowest ITS gains and the highest mass losses, indicating greater material vulnerability under repeated or aggressive conditions. For instance, SC 6% B showed only a 61.61% ITS increase and a mass loss of 13.56%. This highlights DCP’s usefulness in detecting less effective treatments, as it correlates with higher degradation and lower mechanical performance. Comparatively, soil-lime performs better under stress, particularly without surface brushing, making it a more efficient alternative in demanding environments.

CONCLUSIONS

The increase in indirect tensile strength observed during the durability cycles can be explained by two key mechanisms. First, cement hydration during wetting phases continuously generates calcium silicate hydrates (C-S-H), strengthening the soil structure. Second, drying cycles create controlled shrinkage, compacting the soil and reducing void spaces, which enhances particle-to-particle bonding. This densification promotes the formation of cementitious compounds, such as silicates, that bind soil particles together, improving cohesion. In lime-stabilized soils, a similar improvement occurs through secondary pozzolanic reactions between lime and clay minerals. In lime-stabilized soils, strength gains result from slower but ongoing pozzolanic reactions between lime and the clay fraction, forming C-A-H and C-S-H gels that improve binding over time.

The capillary rise test revealed that although both stabilizers enhance durability, lime-stabilized specimens exhibited greater sensitivity to water migration. This is likely due to their more porous structure and slower reaction kinetics, which result in less dense gel formation. In contrast, cement-stabilized specimens showed better resistance to degradation by capillarity, confirming findings from recent literature (e.g., Hu et al., 2024; Bessaim et al., 2018). These results highlight the importance of considering microstructural differences in evaluating long-term performance.

When comparing different degradation tests, it was clear that traditional methods, such as wetting-drying, capillary rise, or precipitation, evaluate each environmental factor separately, potentially underestimating the real deterioration. The newly applied DCP (Degradation by Capillarity and Precipitation) test, which integrates rainfall and capillary effects, imposed more aggressive conditions that effectively distinguished between stabilizers. This methodology offered a more comprehensive understanding of how stabilized soils respond to simultaneous environmental stressors, thereby providing a realistic evaluation framework for tropical settings.

The DCP methodology made it possible to observe degradation patterns that did not appear in individual tests. By combining precipitation and capillary rise in a single procedure, the test revealed more severe deterioration, especially in lime-stabilized specimens, where tensile strength values were up to 75% lower compared to those from the capillary rise test. In cement-stabilized specimens, the difference reached up to 44% when compared to individual precipitation or capillary tests. These results show that the interaction of multiple environmental factors can have a much stronger impact on soil performance and highlight the usefulness of the DCP test as a tool for evaluating durability in tropical regions with high rainfall and moisture.

The DCP method proved to be the most sensitive in detecting structural and quality variations, consistently showing the lowest ITS values and the highest mass loss among all test conditions. This reinforces its role as a powerful tool for identifying weaknesses in stabilized soil mixtures, particularly under realistic environmental stressors. Surface brushing slightly reduced tensile strength, evidencing how superficial treatments can influence internal cohesion and the exposure of less consolidated layers. Among the stabilizers tested, the soil-lime treatment emerged as the most effective in enhancing strength, although it showed greater variability in performance. Given the significant mass loss observed under DCP conditions, further long-term durability studies are recommended, especially in tropical environments where simultaneous exposure to moisture and mechanical action is common.

Despite the robustness of the proposed methodology, some limitations must be acknowledged. The degradation scenarios were simulated under laboratory conditions, which may not fully capture field heterogeneities. Furthermore, the approach was applied to a specific tropical soil and binder, limiting its extrapolation. Future research should validate the method in field conditions and extend it to other soils and stabilization agents.

ACKNOWLEDGMENTS

The authors would like to acknowledge the support provided by Universidad de La Salle (Colombia) through the research project “Implementation of Technological Tools for Improving Quality Control in the Construction Sector” (Code ICIV212-19) and the support of the Civil Engineering Program at the same institution. This work was partially funded by the Vice-Rectorate for Research and Transfer at Universidad de La Salle. The authors also thank the technical team from the Civil Engineering Laboratory for their assistance during the experimental tests, the research group INDETES, and the ASOMBRO student research group for their valuable support during the characterization phase.

DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Edited by

• (AE: Daniel Zanetti de Florio)

Publication Dates

• Publication in this collection
  17 July 2026
• Date of issue
  2026

History

• Received
  24 Mar 2025
• Reviewed
  26 Aug 2025
• Accepted
  21 Apr 2026