عنوان مقاله [English]
Soil cement is a mixture of Portland cement, soil and water, in which hydration of cement and compaction causes the materials' constituents to bond together, making a dense and durable composition with low permeability and abrasion resistant. According to the definition of ACI 116R, soil-cement is a mixture of soil and a certain amount of cement and water which has been compacted to a high density. A more comprehensive definition has been provided in ACI 230 IR, which defines the soil-cement as a hard material with specific engineering properties produced by mixing, compaction and curing of soil, aggregate, Portland cement, additives and water. All types of soils can be used in soil-cement construction, except the organic and plastic soils and reactive sands. The most efficient soils for soil cement are those containing 5 to 35\% of fines passing sieve 200. However, the soils containing more than 2\% of organic materials are strictly unacceptable. Soil-cement application in dams and pavements construction has grown rapidly in recent years. These mixtures are similar to concrete, the main difference being the type and size of aggregate particles used. Soil-cement is principally made of round natural fines, while concrete is made of aggregates. Because most of the recent researches are focused on the addition of nano-$SiO_2$ on concrete, in this paper, we decided to use nano-$SiO_2$ particles in soil-cement and observe the out coming effects. Since there are no particles passing sieve 200 in concrete and this restriction does not apply to soil-cements, some tests were carried out on thenano-$SiO_2$ + soil-cement matrix because of the meaningful difference between concrete and soil-cement. The test procedure consists of moisture-dry density, unconfined compressive test, and hydraulic conductivity. In these tests, silica fume (with specific surface area of $21 m^2/g$) and, nano-$SiO_2$ (with specific surface areas of 200 and $380 m^2/g$) were added to soil-cement. The results show that adding certain amounts of nano-$SiO_2$ particles to soil-cement matrix can improve compressive strength and reduce impermeability and speed hydration reactions in the matrix in the presence of nano-$SiO_2$ particles.