This study presents geotechnical characteristics of a low-plasticity clay improved by xanthan gum biopolymer, which is an innocuous microbially induced polymer with high tensile strength. The samples were prepared by mixing clay at various proportions by weight of xanthan gum biopolymer (0, 0.5, 1.0, 1.5, 2.0, and 3.0%), and then tested at the end of different curing times (0, 7, 28, and 56 days). To demonstrate the influence of xanthan gum biopolymer on the clay, an intensive series of unconfined compressive strength, laboratory vane shear, fall cone, oedometer, permeability, swelling, and shrinkage tests were carried out on the samples. According to the testing results, strength of the clay samples increased with both the content of biopolymer and the curing time. The test results also indicated that permeability of the samples with xanthan gum biopolymer is lower, while the compression index and swelling percentage values are higher than the samples without treatment. Evidently, xanthan gum biopolymer application was identified as an environmentally friendly and sustainable alternative material for improving a clay.

The objective of this study was to evaluate the influences of both tyre buffings and lime in clay. California Bearing Ratio (CBR) and Unconfined Compression (UC) tests were conducted on the mixtures prepared with tyre buffings and lime. Tyre buffings and lime contents in the mixtures were 0%, 5%, 10%, and 15%, and 0%, 2%, 4%, and 6% by dry weight of the specimens, respectively. The response of the specimens was investigated with the inclusion of tyre buffings only, lime only, and tyre buffings and lime together. Test results revealed that addition of tyre buffings only reduces the CBR value of clay, while addition of lime only increases the CBR value of clay. Addition of a small amount of lime to the clay with tyre buffings increases the CBR values of the specimens, and thereby may cause a substantial decrease in design thickness of a highway pavement. Similar results were also obtained by the UC tests. Consequently, this research suggests to use both tyre buffings and lime as an alternative method to improve the performance of clay in an economically and environmentally beneficial way.

The aim of this study is to evaluate the use of waste ceramic tiles as a raw material in the design of road pavement subgrade. Instead of disposal in landfills, ceramic tiles can be used in highway engineering applications, thereby reducing their potential impact on environment and may result in a substantial decrease in design thickness of a pavement. California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), compaction, oedometer, and swelling tests were conducted on the mixtures prepared with waste ceramic tiles and a low-plasticity clay (CL)-type soil. Waste ceramic tile contents in the mixtures were 0%, 5%, 10%, 15%, 20%, and 30% by dry weight of the specimens. Test results revealed that addition of waste ceramic tile increases the CBR value of soil, while addition of it reduces the UCS value of soil. Besides, an increase in dry unit weight (γ_dry) and a decrease in corresponding water content (w) by an increase in the amount of waste ceramic tile were observed in the compaction tests. Further, the results of the tests show a decrease in the void ratio (e) with an increase in the amount of waste ceramic tiles. Consequently, this research suggests to use waste ceramic tiles as an alternative material to improve the performance of CL-type soil in an economically and environmentally beneficial way.

This paper presents the use of construction and demolition (C&D) materials with clay, and a comparative study on the C&D and natural aggregate (NA) utilisation for road pavement subgrade. California bearing ratio (CBR), unconfined compressive strength (UCS), and swelling tests were conducted to analyse the response of recycled concrete aggregate (RCA), dragged asphalt pieces (DAP), and natural gravel aggregate (NA) mixed with a low plasticity clay at various contents (0%, 10%, 20%, 30%, 40%, 50%, and 100%) by dry weight. The laboratory tests indicated that the use of clay in all the aggregates resulted in sharp increase in the UCS values. The CBR analysis showed an 80%, 75%, and 50% decrease in the performance of NA, RCA, and DAP with 50% clay, respectively. Further, the testing results also revealed a slight increase in the swelling percentage of the mixtures by clay additions. Consequently, this research has implications in the design of road pavement subgrades for the field performance of gravel-size-waste and/or NAs and clay mixtures.

Hydraulic conductivities of sands with different gradation and grain shape were estimated experimentally at a relative density (Dr) of about 40 % and a 22 ± 2 °C of constant temperature. Narli Sand (NS) with 0.67 of sphericity (S) and 0.72 of roundness (R), and Crushed Stone Sand (CSS) with 0.55 of S and 0.15 of R values were artificially graded into sixteen different grain-size fractions (4.75–2, 2–1.18, 1.18–0.6, 0.6–0.425, 0.425–0.3, 0.3–0.075, 4.75–0.075, 2–0.075, 1.18–0.075, 0.6–0.075, 0.425–0.075, 4.75–0.6, 2–0.6, 4.75-0.425, 2–0.425, 1.18–0.425 mm). Hydraulic conductivities of the NS estimated by use of constant head test ranged from 1.61 to 0.01 cm/s, whilst those of the CSS estimated by the same test ranged from 2.45 to 0.012 cm/s. It was observed that the hydraulic conductivity values of the NS are lower than those of the CSS samples, which is likely to be the result of differences in shape, particularly in R values. The results clearly demonstrated that the hydraulic conductivity can be significantly influenced by grading characteristics (d10, d20, d30, d50, d60, cu, cc, n, Io). Furthermore, comparisons between results obtained in the present study and hydraulic conductivity estimated with other formulas available in the literature were made. The comparisons indicated that the best estimation of hydraulic conductivity changes based on the gradation and shape properties of the sands tested.