Comparison between expansion and microstructural changes of mortars under sulfate attack

Author(s): C. Yu, K. Scrivener, W. Sun
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 595-603
Total Pages: 8
Language: English

Sulfate attack is an environmental issue for concrete structure exposed to aggressive environment contains sulfate ions. The interaction of cementitious materials with sulfate solutions leads to a reaction front within the porous material. The consequences are expansion and/or softening. Laboratory tests usually focus on expansion, while in the field, softening and spalling of material may be more important. The aim of the study presented here is to study the effects of specimen size and solution concentration during laboratory sulfate exposure. A long-term sulfate resistance test close to real conditions was conducted. Mortar prisms were made from Portland cement (PC) and ground granulated blast furnace slag (GGBS) in different sizes with w/c of 0.55. The original surface of mortar prisms was removed prior to exposure to sulfate solutions (3, 10 and 30g/L of Na₂SO₄), in order to accelerate the ingress of sulfate ions. The linear expansion was measured every 2 weeks accompanied by renewal of the solution. Quantitative SEM-mapping and EDS was applied to compare to the macroscopic expansion. It reveals that the reaction between incoming sulfate ions and solid phase buffers the increase of [SO₄²⁻] in pore solution. When all freely transformable Al₂O₃ has reacted, the [SO₄²⁻] in pore solution will increase, fine monosulfate crystal within C-S-H can then react to ettringite, which gives the origin of expansion. As sulfate continues penetrating, the affected area increases with time, so does the expansion. For slag addition samples, more solid phase can uptake sulfate, buffer the increase of [SO₄²⁻] in pore solution, leading to a delay of expansion. But once the pore solution starts to be oversaturated, because more AFt phases have been formed, significant expansion occurs.

Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00