This paper aims to achieve a specific type of cemented sand-gravel mixtures with low permeability to implement in the impervious zone of hardfill dams. To this end, various mixtures are prepared by blending two native soils of sand and gravel with different amounts of kaolinite or bentonite additives in presence of various cement content. The compaction properties, uniaxial compressive strength, permeability and scanning electron microscope (SEM) images of mixtures are measured. According to the results, the cemented mixture containing 10% of kaolinite additive regardless of native soil type exhibits the maximum strength. However, the bentonite disturbs the cement hydration in the mixture, and the strength of mixtures especially with high cement content decreases with increasing the bentonite content. The permeability of mixtures is related to the amount of cement and fine additive in the mixture. The permeability of both cemented sand and gravel mixtures decreases with increasing the bentonite additive. However, the kaolinite additive has a limited influence on the permeability of cemented gravel mixtures. The lowest permeability is achieved in the mixture involving the higher amount of bentonite (with a weight ratio of 30%) in presence of adequate cement.

This paper aims to find a proper admixture of the cemented sand-gravel (CSG) material for constructing a hardfill embankment located in cold weather. To this end, the compaction, strength, permeability of the cemented sand-gravel mixtures with cement contents of 5, 7.5, 10, and 12.5% are experimentally studied. Besides, the freeze–thaw durability of native grains of the soil and stabilizing soil is examined. According to the test results, even though the compaction specifications of all mixtures do not considerably depend on the cement content, however the cement content in the mixture significantly influences the compressive strength, stiffness, and permeability of mixtures. The soil aggregates inherently have high water absorption and are thus severely fractured after 50 cycles of freeze–thaw. After stabilizing the soil grains with cement, the freeze–thaw durability of the cemented soil mixture is considerably improved, and the weight loss of all mixtures becomes less than 5% after 12 cycles of freeze–thaw. However, the freeze–thaw cycles reduce the mixture strength up to 40% in comparison with the intact mixture. The analysis of scanning electron microscope images implies that four factors including disintegration of the calcium-silicate-hydration complex, imposing new porosity, releasing interlayered water, and establishing the secondary ettringite are the main reasons for strength reduction of the cemented sand-gravel mixtures after encountering the freeze–thaw cycles which have not been observed in the previous researches.

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The hardfill embankments are composed of cemented sand-gravel (CSG) mixtures. In some cases, however, sand and gravel used in the mixture contain fine-grained fraction. This paper aimed to study the mechanical behavior and microstructure of CSG mixtures in which the base soil contains fine-grained particles with different plasticity specifications. Various contents of kaolinite and bentonite were added to a sand-cement mixture with different cement contents and uniaxial strength and deformation modulus in the mixtures were measured at two curing ages. According to the results, in low cement mixtures, the mixture containing 10% of the additive exhibited the maximum strength and deformation modulus, regardless of the additive type. In a family of bentonite-containing mixtures with higher cement, the strength of mixtures decreased with increasing the bentonite content. However, the mixture with higher cement and 10% of kaolinite presented the best performance from in terms of strength and stiffness. Analyzing the mineralogy and SEM images of mixtures showed that the structure of base soil attained the best packing and a strong matrix was devolved inside the mixture with 10% of fine additive. Furthermore, the kaolinite particles in the mixture containing 10% kaolinite contributed to the hydration process of cement.

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