Linear shrinkage and the methylene blue spot test in the analysis of plasticity of granulometrically stabilized laterites

Abstract For a soil to be granulometrically stable, it must present low plasticity and a granulometric composition that conforms with the limits regulated by standards. This article presents a study of the clay fraction activity and plasticity of three laterites from the Triângulo Mineiro region, aiming to use them in a granulometrically stabilized base. The experimental phase contained the determination of liquidity limit, plastic limit, sand equivalent and silica sesquioxide ratio, in addition to a Methylene Blue spot test, linear shrinkage, MCT classification and X-ray diffraction. The results show that the sand equivalent alone is not able to evaluate the content of impurities of the clay fraction; it needs to be performed along with the Methylene Blue spot test. Linear shrinkage proved to be an important indicator of plasticity, capable of measuring small values of plasticity. Finally, the MCT classification precisely indicated the lateritic behavior of the samples.摘要 若土壤需具备颗粒级配稳定性，则应同时满足低塑性要求，且颗粒级配组成需符合标准规定的限值。本文针对巴西米纳斯吉拉斯州三角地带（Triângulo Mineiro）的3种红土开展黏粒组分活性与塑性特性研究，旨在将其应用于颗粒级配稳定基层。试验阶段依次开展了液限（Liquid Limit）、塑限（Plastic Limit）、砂当量（Sand Equivalent）、硅铝铁比的测定，同时实施了亚甲基蓝斑点试验（Methylene Blue Spot Test）、线缩率（Linear Shrinkage）、MCT分类（MCT Classification）及X射线衍射（X-ray Diffraction）测试。研究结果显示，单独采用砂当量无法准确评价黏粒组分的杂质含量，需与亚甲基蓝斑点试验联合开展方能实现有效评估。线缩率被证实为一项重要的塑性评价指标，可精准测量极低水平的塑性值。最终，MCT分类法精准判定了各试样的红土化性状。