Thaís Radünz Kleinert

This paper proposes a sustainability-oriented approach to evaluate the incorporation of lime-stabilized soils into pavement systems as a strategy to reduce the environmental impacts associated with conventional unbound granular structures. Pavement sections were designed for three tropical subgrades (Argisol, Latosol, and Luvisol), considering five traffic levels ranging from low to high. Soil–lime layers containing 3% and 5% calcitic hydrated lime were compared with conventional unbound granular sections. Pavement design was performed through a mechanistic–empirical approach. Environmental impacts were quantified using life-cycle assessment from a cradle-to-construction perspective, including midpoint and endpoint indicators, and assessed together alongside relative construction costs. Pavement sections incorporating soil–lime layers reduced environmental impacts and relative costs for low and intermediate traffic levels, particularly for Argisol and Latosol subgrades. Reductions in global warming potential reached approximately 48%, while endpoint damage reductions exceeded 60% in some scenarios. However, the environmental benefits became progressively less pronounced as traffic levels increased. For the Luvisol subgrade, the lower suitability for lime stabilization required an additional graded crushed stone layer, reducing the environmental advantages of the stabilized systems. Soil–lime stabilization can represent an environmentally advantageous and economically competitive alternative for pavement design in tropical regions, particularly under low-to-moderate traffic conditions, although benefits may also be achieved at high traffic levels depending on subgrade characteristics.

The mechanical behavior of lime-stabilized layers is essential for mechanistic–empirical pavement design, particularly in tropical regions where soil behavior differs from that of temperate residual soils. This study investigated three tropical soils (Argisol, Luvisol, and Latosol) stabilized with two hydrated lime sources (calcitic and dolomitic) at contents of 3% and 5%, compacted at standard or modified effort. Unconfined compressive strength (UCS) was measured at 7, 28, and 90 days, while flexural tensile strength (FTS) was obtained at 28 days, from which the flexural static modulus (FSM) and strain at break (ε_b) were derived. The results showed a strong soil-dependent response to lime treatment, with Argisol and Latosol behaving as lime-stabilized materials, whereas Luvisol exhibited more moderate improvements typical of soil modification. Compactive effort, lime type, and lime content significantly influenced UCS, FTS, and FSM, with compactive effort being the dominant and operationally achievable factor. Higher compactive effort, calcitic lime, and a 5% lime content consistently resulted in improved mechanical behavior, while curing time strongly influenced compressive strength due to progressive pozzolanic reaction. In contrast, strain at break was not significantly affected by the studied controllable factors and converged toward approximately 200 microstrain for soil–lime mixtures with UCS > 1 MPa, indicating a less brittle behavior relative to cement-stabilized materials and providing a representative input for preliminary design. Finally, significant correlations were established between UCS and FTS and between UCS and FSM, enabling the estimation of flexural parameters directly from compressive strength and supporting design simplifications when flexural testing is unavailable.

The tensile behavior of cold recycled cement-treated mixtures (CRCTMs), typically produced through full-depth reclamation (FDR), is critical for pavement design. Since no universal design method exists, different tests are applied, leading to varying results. In this context, this study aimed (a) to statistically analyze the flexural tensile strength (FTS) and indirect tensile strength (ITS) of CRCTMs incorporating reclaimed asphalt pavement (RAP) and lateritic soil (LS); (b) to evaluate how using FTS or ITS influences the design of CRCTM layers. FTS and ITS tests were conducted with different cement (1–7%) and RAP (7–93%) contents at multiple curing times (3–28 days), and results were used for statistical and mechanistic analyses. Results showed that cement and RAP contents significantly increased FTS and ITS. RAP exhibited the strongest influence on ITS. This indicates that CRCTMs with similar materials benefit from higher RAP contents. Mechanistic analysis revealed that lower RAP contents require thicker pavement structures, suggesting that increasing RAP can reduce costs and environmental impacts. FTS was about 65% higher than ITS, but using ITS in design led to structures 1.7–3.3 times thicker for the same service life. These findings highlight the need for proper CRCTM characterization, with flexural tests recommended for more reliable and cost-effective pavement design.

Lime stabilization is a sustainable technique due to its use of local materials, increased durability, reduced maintenance, and improved resistance to water action. This paper examines the impact of lime stabilization on the mechanical, microscopic, and mineralogical properties of a tropical soil. Two types of lime, calcitic and dolomitic, were tested at 3% and 5% by weight. Compressive, indirect tensile and flexural test results and statistical analysis revealed that calcitic lime mixtures had higher strength and stiffness, whereas dolomitic lime mixtures exhibited greater deformability with higher tensile strain at break. Scanning electron microscopy indicated that the soil’s porous matrix closed within 7 days for both lime types due to flocculation, with increased matrix interlocking over time. The calcitic lime mixture developed a more closed matrix compared to the dolomitic lime, which showed weaker cementing. X-ray diffraction analysis indicated higher consumption of clay minerals and a notable reduction in calcium hydroxide peaks in the lime-treated soils. The study concludes that calcitic lime provides better pavement performance for stabilizing the soil, enhancing its engineering properties while also being sustainable by reducing the need for raw material extraction and improving resilience to climate-related issues such as floods.

As with other chemically stabilized materials, cold recycled cement-treated mixtures inherently shrink. Shrinkage cracks might accelerate the rate of pavement deterioration. The research reported here aimed at studying variables that may affect the shrinkage of recycled mixtures. An experimental plan was set to evaluate the effects of cement and reclaimed asphalt pavement (RAP) contents and curing time on the shrinkage of such mixtures with different recycled base course materials (namely cement-treated base [CTB], soil-cement [SC], and lateritic soil [LS]). Previously studied recycled mixtures with graded crushed stone (GCS) base course material were also considered in the analysis. From test results and statistical analysis, it was concluded that the finer the recycled mixture (with SC and LS base course materials), the higher the shrinkage potential. Conversely, coarser mixtures (with CTB and GCS as base materials) tend to shrink less. Accordingly, increasing RAP contents might help to reduce the shrinkage of finer mixtures because of coarser RAP gradation. Shrinkage increases with time and shows higher increasing rates at the early stages. Statistics showed that a stronger curing time effect occurs by the third week, and because of that, it is important to avoid moisture loss at the early stages. For the levels considered (1–7 %), cement content did not greatly impact the shrinkage, although it was statistically significant in most cases. Statistical analysis confirmed this, contradicting the practice of often adopting low cement contents to reduce shrinkage hazards.

This paper evaluates the flexural static and cyclic behaviour of cement-treated mixtures of reclaimed asphalt pavement (RAP) and lateritic soil (LS). Flexural strength and resilient modulus increased with RAP percentage. Strain at break increased with higher RAP and lower cement amounts, increasing mixtures flexibility. Higher cement contents led to stronger and stiffer mixtures. Strain-based fatigue relationships were obtained. Mechanistic analyses showed that the fatigue life of cement-treated recycled base layers of RAP and LS increases with RAP percentage and with the thicknesses of asphalt wearing course and recycled base layer. The effect of cement content depends on the thickness of the layers.

Nesse estudo foi verificada a aplicação da metodologia de projeto de experimentos na dosagem de misturas de reciclagem de pavimentos com adição de cimento. Adotou-se um método de dosagem que avalia propriedades mecânicas, volumétricas e de erodibilidade, e foram desenvolvidas todas as etapas que contemplam um projeto de experimentos. O planejamento possibilitou definir as variáveis que exercem maior influência nos resultados, de modo a estabelecer uma matriz experimental abrangente e reduzida. Na análise dos resultados foi possível quantificar o efeito dos fatores controláveis estudados (teor de cimento e porcentagem de fresado) em cada variável de resposta. A partir da otimização multivariada, obteve-se o ajuste ótimo dos fatores controláveis considerando todas as variáveis de resposta simultaneamente. A ferramenta adotada nesse trabalho se mostrou bastante eficiente, podendo ser amplamente empregada na otimização de processos, como é o caso da dosagem de misturas recicladas.