Determination of permissible content of free lime in cement-fly ash mixtures and development of relationship between properties of coal and resulting fly ash | |
| Author | Nawez, Adnan |
| Call Number | AIT Diss. no.ST-16-01 |
| Subject(s) | Precast concrete construction Concrete--Curing Cement Building materials |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Structural Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ST-16-01 |
| Abstract | This study is conducted to investigate the effect and limitation of free lime content in fly ash. A detailed experimental program is carried out in order to evaluate the extent to which free lime content in fly ash can be tolerated, particularly for fly ashes with different sulfur trioxide contents. Some basic and durability properties of fly ash mixtures with varied free lime contents are considered. Four distinct types of fly ashes are obtained from two different sources, and free lime is added to obtain overall free lime contents of 5%, 7% and 10% for each type of fly ash. Water requirement, initial and final setting times, compressive strength, autoclave expansion, alkali aggregate reaction (AAR), and sulfate resistance tests of fly ash mixtures, containing various free lime contents, with two fly ash replacement percentages (20% and 40%), are conducted. Experimental results revealed that an increase in the free lime content caused an increase in water requirement. Higher free lime content also lead to faster setting times, improved compressive strength, and higher autoclave expansion. Mixtures with 20% fly ash replacement and free lime content up to 10% as well as mixtures with 40% fly ash replacement and free lime content up to 7.72% experienced autoclave expansion within the specified limit of ASTM C618. Similar trends of expansion are observed in the cases of alkali-aggregate reaction and sulfate resistance tests where fly ash mixtures with high free lime led to higher expansion. In alkali-aggregate reaction testing, the mixtures with 20% fly ash replacement and free lime content up to 7.95%, as well as mixtures with 40% fly ash replacement and free lime content up to 10%, expanded less than the cement-only mixtures. The effect of added free lime are more severe in the sulfate resistance test, as fly ash mixtures tend to expand more than cement-only mixtures, especially in the case of fly ashes with very high SO3 content (>5%). Test results revealed that it is possible to utilize 20% of tested fly ash in a mixture as binder, with SO3 content < 5% and free lime content up to 10% and 4.23%, for 20% and 40% fly ash replacements, respectively. In the case of high SO3 content in fly ash, i.e., 8.53% and 9.44% in this study, the limit of free lime content of fly ash is reduced to 5.31% and 3.73%, for 20% and 40% fly ash replacements, respectively to satisfy the durability requirements. Additionally, fly ashes with different free lime contents are blended together and the resulting fly ashes are utilized in cement-fly ash mixtures and tested for the above mentioned properties to determine the effect of mixing high and low free lime fly ashes on the properties of cement-fly ash mixtures. The performances of blended fly ash mixtures fell in between the performances of mixtures of high and low free lime fly ashes. Moreover, in order to forecast the properties of fly ash produced by the coal combustion in a thermal power generating plant, properties of coal and resulting fly ash are statistically analyzed and related together. The relationships developed between different coal and fly ash properties can be helpful in the management and production of fly ashes with desired properties. |
| Year | 2016 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ST-16-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Pennung Warnitchai ;Somnuk Tangtermsirikul; |
| Examination Committee(s) | Thanakorn PheeraphanWarangkana SaengsoyParnthep JulnipitawongPunchet Thammarak ;Sugiyama, Takafumi ; |
| Scholarship Donor(s) | Higher Education Commission (HEC) Pakistan; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2016 |