Volkan Okur

A Study on the Rheological Properties of Recycled Rubber-Modified Asphalt Mixtures

Using waste rubber in asphalt mixes has become a common practice in road construction. This paper presents the results of a study on the rheological characteristics of rubber-modified asphalt (RMA) concrete under static and dynamic loading conditions. A number of static and dynamic creep tests were conducted on RMA mix specimens with different rubber sizes and contents, and a series of resonant column tests were conducted to evaluate the shear modulus and damping values. To simulate the stress-strain response of traffic-induced loading, the measurements were taken for different confining pressures and strain levels. The results of the study indicated that rubber modification increases stiffness and damping ratio, making it a very attractive material for use in road construction. However the grain size of the rubber is very important. Although RMA may cost up to 100% more than regular asphalt, the advantages it brings, such as an increased service life of the road and proper waste utilization contributing to a more sustainable infrastructure, may justify the added cost.

Evaluation of Cyclic Behavior of Fine-Grained Soils Using the Energy Method

While seismic waves propagate through soil deposits, a part of their energy dissipates which results in a decrease in the amplitude of the applied shear stresses. To better understand the mechanisms leading to the dissipation of applied energy in fine-grained soils, undisturbed specimens having different geotechnical characteristics obtained from a site investigation after 1999 Kocaeli earthquake, were tested in a series of cyclic triaxial tests. Analysis of cyclic test data suggests that portions of fine-grained soil deposits, i.e., silts and clays could have developed high excess pore pressures and significant shear strains during cyclic loadings which contribute to stability problems. The effects of various factors such as confining stress, dynamic stress amplitude, and pore-water pressure accumulation on the cyclic softening of fine-grained soils were investigated and evaluated using the energy criterion.

Optimisation of Marshall Design criteria with central composite design in asphalt concrete

ABSTRACT In this study, optimum bitumen content (OBC), an important parameter on Marshall Design is described with a mathematical model by using statistical design method. The effects of independent variables such as number of blows, temperature, additive rate and bitumen content are analysed. The simultaneous optimisation of the dependent variables such as practical specific gravity, voids, voids of filled with asphalt cement, Marshall stability, flow and Marshall coefficient is determined with the central composite design. The optimum conditions are detected with 70 blows, temperature of 160°C, additive amount of 10% and OBC of 4.484%. The desirability function is applied to determine local optimisation points. Following the model application, practical specific gravity is estimated to be 2.418 g/cm3 with voids of 4%, voids of filled asphalt of 71.74%, Marshall stability of 1138.4 kgf under optimum conditions. While it is necessary to pour 126 samples to achieve a result with these variables in Marshall Design under normal conditions, the results are achieved just by pouring 30 samples thanks to the models established.

Dynamic Behavior of Soft Subgrade Soils Treated with Boron Waste

A series of laboratory tests using resonant column and dynamic torsional shear tests were conducted on kaolinite and montmorillonite clays treated with boron waste. The effect of the boron waste on the dynamic characteristics of two clays was studied considering the effects of the plasticity index. Pulverized boron waste was mixed with the clay soils in different proportions. It has been seen that treatment with boron waste improved the dynamic properties of the two clays. However, increasing the amount of boron waste does not affect the dynamic characteristics of the samples in the same proportions. Increasing the amount of boron waste in the mixture increased the initial shear modulus of the montmorillonite clay up to 300% compared to untreated samples, whereas the reaction of the kaolinite clay with boron waste treatment was moderate. Degradation curves of treated and untreated soils in regard to shear strain are presented. In general treatment, success is dependent on the amount of boron waste and the clay type. The continuous increase with the amount of boron waste in the shear modulus and damping ratio is apparent on both clays.

Performance of Steel Slag and Fly Ash Added Soil as Subbase Materials

The steel industry, which is an indicator of the developed countries with its production, also brings the problem of waste together. This waste product, that differs depending on the production process and is called slag, is generally referred as solid waste. Many researchers to use for different purposes are examining this type of wastes, which are difficult to store and dispose. It is also investigated about the usability as a filling material in civil engineering. The possibility of using such materials as an alternative to soil stabilization solutions, especially in the areas close to the industries producing these wastes, in the filling of such structures as the roads, railways, airport runways comprise of the basis of the surveys. In this study, the impact of steel slag and fly ash, another waste product released because of combusting lignite coal with low energy at the power plants, on the bearing ratio after blending with kaolin grade clay at different rates was observed. Keeping the 5% clay rate stable in weight, steel slag and fly ash with varying rates were added to prepare the test samples, which were cured for 0, 7, 28 and 56 days under stable conditions and subjected to California Bearing Ratio tests. The results showed that when steel slag and fly ash are used with clay, there were significant increases in their bearing ratios compared to the reference clay sample. While the wet California Bearing Ratio (CBR) was around 15% for the normal clay sample, when it is blended only with steel slag the wet CBR increased up to 70%, and when blended with fly ash the wet CBR went up to 130%. The used materials had very weak and weak binding properties when used alone while their binding properties increased by gaining pozzolanic property within the mix.

Energy approach to unsaturated cyclic strength of sand

The mechanical response to cyclic loading of saturated cohesionless soils is usually investigated by means of effective stress method considering pore water pressure changes that lead to reduced strength and stiffness. On the other hand, the behavior of partially saturated sands is different from the behavior of saturated sand deposits. The development of negative pore water pressures in particular makes it difficult to estimate the behavior of partially saturated sands. The response of partially saturated sands, however, can be examined in a physically understandable manner by investigating their energy characteristics independently of pore pressure behavior. To establish a general framework for understanding the behavior of partially saturated sand, a total of 52 resonant column and dynamic torsional shear tests were conducted under undrained conditions. The effects of factors such as the amplitude of shear strain, relative density, saturation ratio and confining pressure on the dynamic characteristics of the sand and on energy dissipation were studied. The use of the energy concept in the evaluation of partially saturated soils is shown to be a promising method for the evaluation of the cyclic behavior of partially saturated sands.

The Variation of Pore Pressure Related with Failure in Fine-Grained Soils Under Uniform Cyclic Loadings

This paper discusses pore- water pressure and failure in fine-grained soils and the influences of some factors under cyclic loading. A systematic study was conducted on pore-water pressure development during cyclic failure of low - to - medium plasticity clays. A series of cyclic triaxial and cyclic torsional tests were performed on undisturbed samples taken below the water table from various sites in Turkey. Consolidation tests were conducted to estimate preconsolidation pressures for each specimen. Tests were conducted under isotropic conditions in both test systems. The loadings were stopped at a prescribed strain level of ±2.5-3% assumed as failure. Pore-pressure accumulation during the tests was observed and pore-pressure values at the time of failure were analyzed with respect to different soil parameters. In addition to the other factors such as cyclic shear stress and cyclic strain amplitude, pore pressure-accumulation varies significantly with the mineralogy of the soil sample.