Alessandra Mendes 1 Dr Frank Collins 1 Professor Jay G Sanjayan 2 1 Civil Engineering Department Monash University 2 Swinburne University of Technology Contraction Compressive Strength Results ID: 361272
Download Presentation The PPT/PDF document "Fire Resistance of Concrete" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Fire Resistance of ConcreteAlessandra Mendes1, Dr Frank Collins1, Professor Jay G Sanjayan21 Civil Engineering Department, Monash University, 2 Swinburne University of Technology
Contraction
Compressive Strength Results
Compressive strength results for OPC and OPC/slag pastes after exposure to elevated temperatures, as in a fire event. OPC pastes presented total strength loss above 400ºC (red dotted-curve). OPC/slag blends (35%, 50% and 65% replacement by weight) with slag presented compressive strength in the range of 15 MPa at temperatures as high as 800ºC. After 1 year, OPC paste reduced to powder (photo top right) while OPC/slag blends presented no visual or strength changes.
Scanning electron microscope (SEM) enables characterization of the cement paste and concrete microstructure. The first photo on the left relates to a polished specimen of OPC concrete exposed to 800ºC. Magnification of 200x enables visualization of microcraks and dehydrated materials (light grey) formed as a result of the elevated temperatures. Energy–dispersive X-ray (EDX) system colour mapping and phase analysis provide qualitative and semi-quantitative information regarding the chemical elements and phases present in the concrete before/after exposure to elevated temperatures. Examples of the different chemical elements found in OPC concrete after 800ºC are shown (Ca, Al, Si, Mg, Fe).
Concrete is made by combining cement , water, fine aggregates (sand) and coarse aggregates. The most common cement used is ordinary Portland cement (OPC). When OPC is mixed with water the general reaction occurs:
OPC + H2O → C-S-H + CaOH2
CaOH
2 → CaO + H2O This reaction occurs above 400ºC and leads to the contraction and cracking of the OPC paste
CaO + H
2O → CaOH2 After cooling and in the presence of air moisture, this reaction takes place causing the OPC paste to expand and complete disintegrate
Expansion
OPC paste 1 year after exposure to 800ºC
Slag is a by-product of the steel and iron industry and has cementitious properties. When OPC is partially replaced with slag the following reaction takes place:
Slag + CaOH
2
→ C-S-H
The partial replacement with slag consumes CaOH
2 reducing or even eliminating the negative effects observed for OPC pastes.
Slag Replacement
Photo: OPC paste disintegrated after 800ºC. All OPC/slag pastes presented no visible cracks.
Scanning Electron Microscope (SEM)
OPC concrete after 800ºC
Calcium - Ca
Aluminum - Al
Silicon - Si
Magnesium - Mg
Iron - Fe
Cement Chemistry at Elevated Temperatures, as in a Fire Event