Effects of very high CaO fly ashes on properties of concrete and limitations of free lime and SO3 contents in concrete

Name: Sharaniya Visvalingam

keyword: Fly ash

; CaO content

; Free lime

; SO3 content

; Autoclave expansion

; Sodium sulfate expansion

Abstract: Fly ash is a well-known pozzolan and is commonly used as a supplementary cementitious material in concrete. This study mainly focuses on the fly ash from Mae Moh power plant which produces around 80%-85% of total fly ash production in Thailand. In recent years, Mae Moh power plant has occasionally produced fly ashes which are identified as the unusable fly ash because of the high CaO, high free lime and high SO3 contents. The chemical compositions of Mae Moh fly ash were analyzed based on the collected data from the power plant. It indicates that even though the fly ash has CaO and SiO2 contents beyond the limit, which is specified in TIS 2135, the reactivity of the fly ash passes the standard requirement. As a result, it is necessary to determine the maximum CaO content of fly ash that may be used as pozzolan, as well as to modify the SiO2 content requirement. High free lime and SO3 contents in fly ash cause long-term volume expansion in concrete. Furthermore, there is no limit for free lime in standards other than EN 450, and previous research found that free lime in fly ash can be up to 4%. However, the limit of free lime is expected to fluctuate with SO3 level and fly ash replacement as well. The aim of this study is to determine the effects and limit of free lime by autoclave expansion, which indicates the influence of free lime, and sodium sulfate expansion, which reveals the effects of both free lime and SO3 contents. Autoclave expansion results revealed that, despite the fact that high CaO fly ash tended to have high free lime content, the limit of free lime based on autoclave expansion was still greater than 10%, for instance, free lime can be 14% and 22% for 60% and 40% high CaO fly ash replacements, respectively. It was observed that fly ash with high free lime and SO3 contents showed deleterious sulfate expansions. The limit of free lime based on sulfate expansion in fly ash was obtained for fly ashes with different CaO contents (low CaO and high CaO fly ashes), SO3 contents and for different fly ash replacements as well as water to binder ratios by considering sodium sulfate expansions which are equivalent to OPC type I cement expansion for general application. The free lime limit decreases with increasing SO3 contents and w/b ratios. In contrast, free lime limit increases with increasing fly ash replacements. These findings indicated that the free lime limit is not a fixed value, but it is related to SO3 contents, water-to-binder ratios, and fly ash replacements. It should be noted that limit of free lime should be obtained by considering the more severe condition between autoclave expansion and sulfate expansion

Thammasat University. Thammasat University Library

Address: BANGKOK

Email: preserv@tu.ac.th

Name: Somnuk Tangtermsirikul

Role: advisor

Name: Warangkana Saengsoy

Role: co-advisor

Created: 2020

Modified: 2024-07-03

Issued: 2024-07-03

วิทยานิพนธ์/Thesis

application/pdf

DOI: 10.14457/TU.the.2020.1468

eng

DegreeName: Master of Science

Level: Master's Degree

Descipline: Engineering and Technology

Grantor: Thammasat University

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