Indian Journal of Engineering & Materials Sciences Vol. 17, August 2010, pp. 289-294 Microstructure of 2 and 28-day cured Portland limestone cement pastes Gözde İnan Sezer a *, Oğuzhan Çopuroğlu b & Kambiz Ramyar a a Civil Engineering Department, Faculty of Engineering, Ege University, 35100 İzmir, Turkey b Materials Science Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628CN, Delft, The Netherlands Received 18 November 2008; accepted 10 June 2010 In this study, microstructures of limestone cement pastes cured for 2 and 28 days are investigated. For this purpose, limestone and clinker are separately ground in a ball-mill until obtained a given constant 32 μm sieve residue. The gypsum is kept constant as 5% by weight of cement. Cement pastes with 0.5 water/binder ratios and 0, 6, 35% limestone/clinker ratios are prepared. After 2 and 28 days standard curing, ESEM investigations are carried out on these specimens. It is found that hydration products are accumulated around limestone particles. In 2 days, compared to the control specimen, pore percentages of cements containing 6% limestone are decreased whereas pore percentages of cement pastes containing 35% limestone are increased. The difference between porosities of the control paste and limestone cement paste is decreased at 28 days. Keywords: Limestone, clinker, hardened cement paste microstructure Pore structure is a very important microstructural feature in porous solid because it affects physical, mechanical and durability properties of the material. Limestone addition influences the pore structure of hardened cement pastes 1,2 . Limestone changes capillary porosity of cementitious materials due to several physical effects. These effects are dilution effect, filler effect and heterogeneous nucleation. Limestone addition decreases cement content and increases effective water/cement ratio. The filler effect of limestone modifies initial porosity of the mix and generally resulted to decrease in water requirement with constant workability. Besides, limestone particles act as nucleation sites and increasing the early hydration of cement 3 . Limestone creates a nuclei effect for precipitation of hydration products and provides free dispersion of cement particles. As a result, accelerates the rate of cement hydration 4-6 . Limestone Portland cement (LPC) is a blended cement bearing up to 35% limestone (calcite) according to the European Standard EN 197-1 7 . It has a great potential in engineering applications and contemporarily used for special conditions. For instance, LPC is used vastly in the self-compacting high performance concrete because of its filler effect and prevent excessive heat development due to hydration 8 . Furthermore, the usage of LPC known to have noteworthy technical, economical and environmental advantages such as increasing early strength and workability as well as reducing water requirement, decreasing production cost of concrete and reducing the CO 2 emission in the cement production 4,9,10 . It is expected that the world wide production and the usage of limestone cement will be increased. Thus, there is need to further research on the effect of limestone on cement and concrete properties. Four types of portland limestone cements can be produced according to the European Standard EN 197-1. These types are classified as type II/A-L, II/A- LL, II/B-L and II/BLL. Types II/A-L, II/A-LL and types II/B-L, II/BLL contain 6-20% and 21-35% limestone, respectively. L and LL type cements can contain maximum 0.2% and 0.5% total organic carbon, respectively. This limitation is due to the fact that excessive amount of organic carbon decreases frost resistance of concrete 7,11 . In this study, ESEM investigations were carried out for the assessment of microstructure of Portland limestone cements after 2 and 28 days curing. There are several investigations related with the effect of clinker or limestone type on physical, chemical and mechanical properties of Portland limestone ____________ *Corresponding author (E-mail: [email protected])
Microstructure of 2 and 28-day cured Portland limestone cement pastes
Apr 27, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
