Phosphogypsum (PG) is a by-product of the phosphoric acid fertilizer industries that has possible applications in paving when stabilized with cement or lime. This study’s aim is to compare the mechanical performance of the hemi-hydrate (HH) and dihydrate (DH) mixes with tropical soil, lime, and cement. The results of physical, mechanical, and mineralogical tests are presented, which demonstrate that the use of HH in cement and lime mixes reduces the swelling of this material compared to the use of DH; in addition, HH provides better mechanical behavior. These findings indicate that DH has limited application in pavement construction, but when converted into HH and mixed with tropical soil or chemical stabilizers, its alternative uses are possible, and more content (approximately 90%) of this material can be used.

The aim of this paper is to evaluate the relationship between pore-size distribution and compressibility of a lateritic soil. Soil fabric was analysed under different conditions of preparation: compacted, reconstituted and intact, by means of mercury intrusion porosimetry tests on loading to different stress levels. The results show that all samples present bimodal pore distribution. However, the conditions of preparation and loading affected macropores more intensely, with subtle effects on micropores. This behaviour was attributed to the presence of aggregations with cementation. The compression curve of macro and micropores were determined and it was observed that the compression curve of macropores is very similar to the compression curve of the samples. In addition, it was observed that the fabric parameter regarding the uniformity of macro and micropores changed during loading. The new fabric parameter proposed captures the change in pore uniformity with loading. This parameter appears to be related to the soil compressibility, indicating that the most compressible samples also show greater changes in the uniformity of macropores.

Soil compaction is one of the most common techniques used to engineer the soil. It is especially appealing to developing countries for its cost-effective and sustainable attributes for improving the soil's geotechnical characteristics. The compaction process along with the complexity of residual soils, abundant in the tropics zone, can have an impact on the performance of geotechnical structures built with these soils. Therefore, it is important to understand the influence that certain compaction conditions have on the structure of these materials. To investigate that, mercury intrusion porosimetry tests were performed on compacted samples of a tropical residual soil from Brazil under different conditions of water content and compactive effort. Results show that the compacted soil under all studied conditions presents a bimodal pore-size distribution (PSD). It appears that the low availability of water within the macro-pores, hence suction, could have played a decisive role in maintaining the bimodal framework of the PSD. In this respect, this study contributes to a better understanding of the tropical residual soils’ structure when subjected to different compaction conditions, thus providing means to improve field applications.

Modelling clay behaviour is a challenging task because many of the microscopic features are still unknown including interparticle forces and particle association, which may explain the different behaviours of clay when subjected to hydro-mechanical loading. This paper presents an experimental study to investigate the micromechanical interactions of clay particles. Kaolinite samples were compacted to high vertical stresses and granulometry laser tests were carried out to investigate particle agglomeration. Samples were compacted in a dry state, with 10% water content and 10% dispersant solution content. The results show that loading generated agglomeration. When comparing specimens compacted using different pore fluids, the agglomeration process is more pronounced at high values of dielectric permittivity (water). This study concludes that the association of particles forming agglomerates is due to van der Waals forces. This was mainly inferred from the observation that agglomeration occurred even when compacted samples were prepared with dispersant solution. This also indicates that association of particles occurs in face-to-face mode due to the high stress applied. A similar response of samples compacted with water and sodium hexametaphosphate solution and the environmental scanning electron microscope images of compacted samples also show this type of arrangement. The comprehension of interparticle forces and particle associations can improve discrete modelling of fine-grained materials.