A porosimetric study of calcium sulfoaluminate cement pastes cured at early ages Graziella Bernardo, Antonio Telesca, Gian Lorenzo Valenti ⁎ Dipartimento di Ingegneria e Fisica dell'Ambiente, Facoltà di Ingegneria, Università degli Studi della Basilicata Via dell'Ateneo Lucano, 10, 85100 Potenza, Italy Received 3 December 2004; accepted 21 February 2006 Abstract Calcium sulfoaluminate and Portland cement pastes, both prepared with a water/solid mass ratio equal to 0.5 and cured for time periods comprised between 2 h and 28 days, show completely different pore size distributions by mercury intrusion. Portland cement pastes aged at 12 h and 1 day exhibit a unimodal distribution of pore sizes related to a continuous network of capillary pores with a threshold pore radius decreasing from nearly 650 to 350nm. After 7 and 28days of curing, this parameter shifts to about 150nm and a region having smaller pores appears (with a second threshold pore radius roughly comprised between 10 and 30 nm), made discontinuous by blockages of hydration products which occlude the interconnected pore system and isolate the interior space. For calcium sulfoaluminate cement pastes, a bimodal distribution is rapidly established, in which the regions with a lower porosity (threshold pore radii up to about 25 nm) are dominant, while the decrease of total porosity almost ceases at later ages. The porosimetric behaviour of calcium sulfoaluminate-based cement is related to its very fast hydration rate and to the lack of water needed to continue the hydration reactions. © 2006 Elsevier Ltd. All rights reserved. Keywords: Hydration; Characterization; Mercury porosimetry; Pore size distribution; Sulfoaluminate cement 1. Introduction The most important property of C 4 A 3 S ¯ -based cements has been considered for a long time the ability of their key component, when hydrated in the presence of calcium sulfate and calcium hydroxide, to generate expansive ettringite. Several calcium sulfoaluminate (CS ¯ A) formulations, alone or mixed with Portland cement, are used as shrinkage-compensating or self-stressing binders [1–6]. However CS ¯ A cements show other interesting features such as, for example, the environment- friendly character of their manufacturing process [7–16]. In this regard, compared to Portland clinkers, CS ¯ A clinkers can be synthesized at lower temperatures (about 1250°C) and, due to their higher porosity, are easier to grind. The limestone concentration in the raw mix is reduced and, consequently, kiln thermal requirements and CO 2 generation are decreased per unit mass of clinker. Moreover, a large number of industrial wastes and by-products, whose disposal or reuse is sometimes quite complicated, can be successfully used for the manufacture of CS ¯ A cements [12–16]. During the last decade, the interest of several researchers and engineers has been attracted by rapid-hardening and dimensionally stable CS ¯ A cements, containing also dicalcium silicate and calcium aluminates, developed by the China Building Materials Academy [4,17–20].C 4 A 3 S ¯ reacts with calcium sulfate (normally added but also present in the clinkers) and water to give a non-expansive ettringite which achieves high mechanical strength at early ages. Moreover, well-made matrices have high freeze–thaw and chemical resistance, low values of dry shrinkage, permeability and solution alkalinity (but not such a low alkalinity that embedded steel is depassivated). The remarkable properties of Chinese CS ¯ A formulations are useful for a variety of special applications. New uses have been recently suggested [21,22]. In recent years, papers concerning both the study of the hydration chemistry of CS ¯ A cements and the interpre- tation of their engineering properties have been published [23–26]. Cement and Concrete Research 36 (2006) 1042 – 1047 ⁎ Corresponding author. E-mail address: valenti@unibas.it (G.L. Valenti). 0008-8846/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2006.02.014