Microstructure and Properties of Steel-Reinforced Concrete Systems Hydrated at 20C and 38C

• Main Author: Duraman, Pg Saiful Baharin Pg
• Published: University of Leeds 2007
• Subjects: 624.1834
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485783

The microstructure and engineering properties of steel-reinforced ordinary Portland cement (OPC) concrete hydrated at standard 20°C and elevat~d 38°C temperatures were investigated. Conduction calorimetry and microanalysis supported the main tests. Neat OPC, and blended OPC with 50% and 70% ground granulated blastfumace slag (GGBS) were' used for all tests. The principal microstructural investigation was quantification of hydration products from both rebar-concrete and aggregate-hcp interfaces using- Image Analysis of Backscattered Electron (BSE) Images. Engineering tests showed that elevated temperature mixes had lower workability and late age strength, and higher early strength and heat evolution compared to standard temperature mixes. Blended OPC mixes had higher workability and lower heat evolution but generally did not exceed their neat OPC mix counterparts In compressive strengths. Quantitative microstructural results showed that OPC mixes had higher calcium hydroxide (CH) and porosity, and lower anhydrous at the interfaces compared to the bulk. The GGBS mixes showed higher porosity, and lower anhydrous and GGBS at - - the. interfaces compared to the bulk, whilst CH levels were low throughout. The interface slope trends of.GGBS showed better packing and hence a narrower interfacial transition zone (ITZ) for the GGBS mixes compared to the OPC mixes. Elevated temperature GGBS mixes showed poorer quality rebar-concrete interfaces suggesting the importance of curing. Microanalytical results showed statistically different Inner Product (IP) C-S-H ratios between the. OPC and GGBS mixes, and generally between the mixes at different temperatures. Predominantly non-statistically significant differences were observed between the different distances from the rebar-concrete interface for the same mixes. The study suggested benefits of GGBS at elevated temperatures, provided sufficient curing is applied. Microstructural tests showed that it was pos~ible to analyse sectioned polished real reinforced concrete specimens. Image Analysis showed that it was possible although difficult to analyse elevated temperature and GGBS mixes.