The Effect of Cement Removal in Measuring the Texture of Iran Soils

In soil laboratories of Iran to determine the initial soil particle size distribution (PSD) curve, different methods and strategies and pretreatments are used to remove soil cement materials, which in many cases make it difficult to compare the results and also evaluate their accuracy. The current research was performed to achieve an economical, simple and accurate protocol to mesure the soil PSD analysis. First, 112 soil samples from the top and sub soils were collected from 16 provinces. Then 91 soil samples were selected based on hydrometer method and they were analyzed mechanically with and without removal of different cement agents; such as Organic matter, lime, iron and aluminum oxides and combined removal of organic matter and iron oxide. Results showed that the removal of cement agent increases the clay fraction and reduces the silt and sand fractions. The removal of cement agents should be conducted where i) organic matter content is more than %4 or ii) iron oxides is more than %2 or iii) the amount of  organic matter + iron oxides is more than %5. In average, the removal of organic matter and iron oxide increases clay fraction 7%. Since the carbonates are often exist as the primary particles in the Iranian soils, the removal of carbonates is not suggested from the soils with more than %10 carbonates. Finally it is concluded that the cement agent in some soils may cause incorrect determination of soil texture class.