Tan Manh Do

Thermal Conductivity of Controlled Low Strength Material (CLSM) Made Entirely from By-Products

Various by-products generated from thermal power plants and chemical industries have considerably economic and environmental impacts in South Korea. This study focuses on evaluating thermal conductivity of controlled low strength material (CLSM) made entirely from by-products (e.g., coal ash, gypsum, red mud). In the experimental program, pond ash is used as a full replacement of natural sand whereas fly ash activated by a little lime, red mud, and gypsum is the main binder in the production of CLSM. Various laboratory tests including flowability, bleeding, initial setting time, and unconfined compressive strength were performed on the prepared CLSM mixtures to determine its general characteristics. Thermal conductivity is then measured subjected to saturated curing condition (SC) and room temperature curing condition (RTC). As a result, all general characteristics meet the specification of CLSM reported in ACI 229R by controlling the ratio of gypsum to red mud. In particular, the good flowability of higher than 20 cm is observed as the G/Rm ratio of smaller than 1.33. The bleeding values, ranging from 0.30% to 2.70%, fall into the bleeding requirement of CLSM of less than 5%. Moreover, the initial setting time and strength results are also in the acceptable specification of general CLSM in ACI 229R. Eventually, the thermal conductivity of the proposed CLSM was in the range of 0.84–0.87 (W/mK) and these values were considerably affected by the saturation states and curing conditions rather than binder proportion.

Soil Stabilization by Using Alkaline-Activated Ground Bottom Ash Coupled with Red Mud

This study evaluates the feasibility of incorporating bottom ash and red mud into a binder to stabilize soil. In this study, the bottom ash collected from Honam Thermal Power Plant in South Korea was ground to decrease particle size. It was then coupled with red mud to form a new binder based on the geopolymer synthesis theory. Sodium silicate solution (Na2SiO3) in terms of alkaline-activator was added into mixture to enhance the activity of binder. Weathered granite soil which is classified as SM in USCS is the target of stabilization. Unconfined compressive strength of stabilized soil and heavy metal content of leachate were examined. Experimental results showed that ground bottom ash coupled with red mud can be used to stabilize weathered granite soil at the ambient curing condition. The highest compressive strength of stabilized soil was 4.1 MPa. Red mud in certain limits has contributed to the increment of soil strength, however, the long-term strength decreased with the increase of red mud content. In addition, based on the results obtained with leaching test, it can be concluded that leachate from the stabilized soil is not harmful to the environment.

Thermal Conductivity of Controlled Low Strength Material (CLSM) Made with Excavated Soil and Coal Ash

This paper focused on the quantitative evaluation of thermal conductivity of CLSM made with excavated soil and coal ash for a possible use as thermal grout for borehole heat exchangers. In a preliminary study, control mixtures were produced with Portland cement or cementless binder, Class F fly ash, and ponded ash. Then, for other mixtures, excavated soil substituted for ponded ash in amounts of 10, 20, 30, and 40% by weight. A series of laboratory tests including bleeding, flowability, initial setting time, and unconfined compressive strength were carried out in accordance with applicable ASTM Standard. Afterward, thermal conductivity was measured by using thermal needle probe, conforming ASTM D 5334 to verify the feasibiliy as thermal grout for borehole heat exchangers. The test results presented herein showed that the engineering properties of CLSM with excavated soil, possibly up to 30%, satisfied the specifications of ACI 229R. Moreover, an increase of excavated soil amount in CLSM could lead an improvement in thermal conductivity.