Microscopic investigation of modified hydration kinetics in tricalcium silicate paste and mortar strength caused by dica
- PDF / 397,382 Bytes
- 5 Pages / 585 x 783 pts Page_size
- 28 Downloads / 160 Views
Paul E. Stutzman Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8621
Richard A. Livingston Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115 (Received 19 July 2007; accepted 4 January 2008)
It was recently revealed that some processes of hydrating tricalcium silicate are altered by the addition of dicalcium silicate. Previous neutron scattering results revealed two critical tri/dicalcium silicate compositions. At one composition, changes in the early time hydration kinetics were observed that result in the formation of more products (reflected in increased 28 day strength), despite dicalcium silicate being essentially unreactive at early times. At the other composition, changes in the early-time hydration kinetics were observed that correspond to reduced strength. The current work uses scanning electron microscope analysis with backscattered electron imaging of 50 day hydrated tri- and dicalcium silicate mortars to reveal that at the former critical composition increased hydration of the tricalcium silicate phase occurs, and at the latter critical composition, the amount of dicalcium silicate reacted is decreased.
I. INTRODUCTION
Portland cement is predominantly a complex calcium silicate mixture that reacts with water to produce a calcium–silicate–hydrate (C–S–H) gel that serves as the binder in concrete. Tricalcium silicate and dicalcium silicate (C3S and C2S) constitute the two main phases of ordinary portland cement (Ca3SiO5 ⳱ C3S and Ca2SiO4 ⳱ C2S in cement chemist’s notation, where C ⳱ CaO and S ⳱ SiO2).1 The hydration reaction of C 3 S is Ca 3 SiO 5 + zH 2 O → Ca x Si(OH) y nH 2 O +(3 − x)Ca(OH)2, where CaxSi(OH)ynH2O is the C–S–H. Despite the similar hydration products of C3S and C2S, C3S is far more reactive than C2S with water, with about 70% of the C3S and 30% of the C2S typically reacted after 28 days.1 Consequently, C3S is the most important component contributing to early strength development in cement paste. The C3S:C2S ratio in portland cement can vary depending on the raw materials and the kiln firing conditions. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0121 J. Mater. Res., Vol. 23, No. 4, Apr 2008
Recent studies used quasi-elastic neutron scattering to quantify the amount of water consumed and inelastic neutron scattering to quantify the amount of Ca(OH)2 produced during the simultaneous hydration of C3S and C2S and found an important interaction where both the hydration kinetics and the strength development departed from the simple law of mixtures.2–4 A critical C3S and C2S mixture composition was identified at approximately 80% to 90% mass fraction of C3S that resulted in changes to the hydration kinetics up to 50 h, resulting in an increased 28 day strength of corresponding mortars of this mixture. It was hypothesized that the addition of C2S allowed more C3S to react through the provision of an incre
Data Loading...
