Influence of limestone on the hydration of Portland cements
Introduction
Portland–limestone cements are the most widely used cements in Europe. Two classes exist in EN 197-1 designated as CEM II/A-L and CEM II/B-L in which the maximum contents of limestone are 20 and 35% respectively. Besides these special classes, limestone is widely used in all other European common cement types as 0–5% minor additional constituents. The use of up to 5% ground limestone in Portland cement is also permitted by the Canadian cement standard since the early 1980s (CSA 1998 - CAN/CSA-A5) and in more than 25 other countries.
From the point of view of the hardened concrete, up to 5% limestone per mass of cement seems to have little effect on the short and long term macroscopic performance. Regarding mechanical properties, several studies have shown that the compressive strength is more or less the same, or slightly increased, this effect is usually attributed to the fine particle size distribution of the limestone, enhancing the hydration of the clinker by the filler effect, rather than its influence on the chemistry or the packing. The same trend is observed with the flexural strength and the drying shrinkage. As for durability issues, the behaviour of the material with respect to all major aggressive species (sulfates, chlorides, carbonation) and main pathologies (freezing-thawing, ASR, corrosion…) is the same as for limestone free concrete. Neither are the diffusion processes significantly modified: measured oxygen permeability and water sorption are more or less unchanged. Negative effects on the properties discussed above start to be observed when the amount of limestone per mass of cement exceeds 10-15%, such that the drop in the reactive clinker component results in significant physical modifications of the material. A good review on all these aspects can be found in Hawkins et al. [1].
At the low addition level of < 5%, some modification of the heat of hydration at early ages may be observed depending on the fineness of the limestone, and the long term heat flow is a bit lower than without limestone due to the smaller fraction of hydrating clinker.
The chemistry associated with the hydration process seems to be the area where the effects of limestone are observed, even at such low levels. Early in the 1990s, several studies showed that limestone seems to favour crystallization of monocarbonate rather than monosulfate [2], [3], [4], with the consequence of increasing the amount of ettringite [2]. The high affinity between calcium aluminate and carbonate phases to form monocarbonate had previously been reported by Feldman et al. [5] and Bensted [6]. Some studies therefore looked at the possible substitution of calcium sulfate with limestone. It has been shown that depending on the fineness of the ground clinker and the level of sulfate in the system, calcium sulfate can be replaced up to 25% by calcium carbonate without any modification of the properties of the system [6], [7], [8].
In this paper the hydration of two cements was investigated, an OPC containing < 0.3% CO2 intermixed with 0 and 4% of limestone (equivalent to 1.7% CO2). Thermodynamic modelling has been used to predict the composition of the liquid and solid phase in a hydrating Portland cement in the absence and presence of limestone in the cement.
Section snippets
Materials and methods
All experiments were carried out using the same Portland cement with and without limestone. Laboratory ground clinker was homogenized with gypsum (Fluka purum p.a.; previously ground in isopropanol to a mean particle size of 4μm). A part of the cement was blended with 4% of ground natural limestone (mean particle size: 4μm): PC4, while the other part was used without limestone addition (PC). The chemical compositions of the materials as given in Table 1 were determined by X-ray fluorescence
Modelling approach
When cement is brought into contact with water, rapidly soluble solids such as gypsum dissolve and come close to equilibrium with the pore solution. The clinker phases hydrate at various rates, continuously releasing Ca, Si, Al, Fe and hydroxide into the solution, which then precipitate as C–S–H, ettringite and other hydrate phases. The dissolution rates of the clinker phases may be considered to determine the amount of Ca, Al, Fe, Si, and hydroxide released into solution and thus to control
Heat evolution
Isothermal conduction calorimetry (Fig. 5) indicates the onset of the acceleration period at approx. 3h in both PC and PC4. The maximal heat evolution was observed for PC4 after 10h and for PC after 11h, indicating a slight acceleration of the cement hydration in the presence of finely ground calcite. This is due to the additional surface provided for the nucleation and growth of hydration products [23], [24]. Accordingly, the cumulative heat after 72h expressed per g clinker, is higher for the
Modelling and experimental results
Thermodynamic modelling of hydrated limestone blended cement PC4 predicts the presence of C–S–H, portlandite, traces of hydrotalcite, calcite, ettringite and monocarbonate (Fig. 3). In agreement with the calculations, experimentally C–S–H, portlandite, calcite, monocarbonate and ettringite could be identified by XRD and TGA in the hydrated samples.
The amounts of portlandite deduced by XRD and TGA agree well with the calculated quantities (Fig. 11). As previously noticed by comparing NMR and XRD
Conclusions
Blending of Portland cement with limestone was found to not only accelerate the initial hydration reaction but also to influence the hydrate assemblage of the hydrating cement pastes. Both thermodynamic calculations and experimental observations indicate that in presence of limestone monocarbonate instead of monosulfate is stable at room temperatures.
hermodynamic modelling shows that the stabilisation of monocarbonate indirectly also stabilises ettringite. This is calculated to lead to a
Acknowledgements
The authors would like to thank Holcim Group Support for the supply of clinker and limestone samples. Thanks are extended to G. Möschner (Empa) and H. Mönch (EAWAG) for support during the experiments and for the analysis of the solutions, to J. Kaufmann for the MIP and to D. Rentsch (Empa) for NMR measurements.
References (56)
- et al.
Thermodynamic modelling of the hydration of Portland cement
Cem. Concr. Res.
(2006) - et al.
Alkali binding in cement pastes. Part I. The C–S–H phase
Cem. Concr. Res.
(1999) - et al.
Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement
Cem. Concr. Res.
(2008) - et al.
Thermodynamic properties of Portland cement hydrates in the system CaO–Al2O3–SiO2–CaSO4–CaCO3–H2O
Cem. Concr. Res.
(2007) - et al.
The role of calcium carbonate in cement hydration
Cem. Concr. Res.
(2007) - et al.
Influence of finely ground limestone on cement hydration
Cem. Conc. Comp.
(1999) - et al.
The AFm phase in Portland cement
Cem. Concr. Res.
(2007) - et al.
A new aluminium-hydrate species in hydrated Portland cements characterized by 27Al and 29Si MAS NMR spectroscopy
Cem. Concr. Res.
(2006) - et al.
Solubility behavior of Ca-, S-, Al-, and Si-bearing solid phases in Portland cement pore solutions as a function of hydration time
Cem. Concr. Res.
(2002) About the hydration theory and the composition of th eliquid phase of Portland cement
Cem. Concr. Res.
(1982)
A thermodynamic approach to the hydration of sulphate-resisting Portland cement
Waste Manage.
Solubility of ettringite (Ca6[Al(OH)6]2(SO4)3 ·26H2O) at 5–75 °C
Geochim. Cosmochim. Acta
Early hydration of a Portland cement in water and sodium hydroxide solutions: composition of solutions and nature of solid phases
Cem. Concr. Res.
Evolution at early hydration times of the chemical composition of liquid phase of oil-well cement pastes with and without additives. Part I. Additive free cement pastes
Cem. Concr. Res.
Solubility of Ca(OH)2 and CaSO4·2H2O in the liquid paste from hardened cement paste
Cem. Concr. Res.
Hydration of C3A in the presence of Ca(OH)2, CaSO4·2H2O and CaCO3
Cem. Concr. Res.
Comparative study of the kinetics and mechanisms of dissolution of carbonate minerals
Chem. Geol.
An evaluation of rate equations for calcite precipitation kinetics at pCO2 less than 0.01atm and pH greater than 8
Geochim. Cosmochim. Acta
Dissolution–precipitation behavior of ettringite, monosulfate, and calcium silicate hydrate
Cem. Concr. Res.
Studies on the carboaluminate formation in limestone filler-blended cements
Cem. Concr. Res.
A thermodynamic and experimental study of the conditions of thaumasite formation
Cem. Concr. Res.
The permeability of Portland limestone cement concrete
Cem. Concr. Res.
An analysis of the properties of Portland limestone cements and concrete
Cem. Concr. Compos.
The effects of limestone addition, clinker type and fineness on properties of Portland cement
Cem. Concr. Res.
The Use of Limestone in Portland Cement: a State-of-the-Art Review
The early hydration of limestone-filled cements
Carboaluminate reactions as influenced by limestone additions
An investigation of the formation of carboaluminates
Cited by (1123)
A comprehensive analysis of hydration kinetics and compressive strength development of fly ash-Portland cement binders
2024, Journal of Building EngineeringEffect of SAP on the properties and microstructure of cement-based materials in the low humidity environment
2024, Case Studies in Construction MaterialsDistribution of sulphate and aluminium in hydrated cement pastes
2024, Cement and Concrete ResearchUnified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates
2024, Cement and Concrete ResearchThermodynamic study on the mutual influence of CaSO<inf>4</inf>·2H<inf>2</inf>O and CaCO<inf>3</inf> in the reactions with C<inf>3</inf>A
2024, Journal of Building Engineering