Effect of Polycarboxylate Superplasticizer on Properties of Calcium
2 Aluminate Cement Mortar
3 Neven Ukrainczyk
4 Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg
5 19, 10 000 Zagreb, Croatia (e-mail:
[email protected])
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7 Abstract
8 The effect of polycarboxilate ether (PCE) based superplasticizer onto the fresh and hardened
9 properties of calcium aluminate cement (CAC) based materials was investigated. Cohesion of
10 the fresh mortar was improved by addition of methyl-cellulose, thus avoiding segregation
11 induced by the superplasticiser action. As PCE significantly retarded the setting time, Li2CO3
12 was investigated as an accelerator by calorimetric measurements. Compressive and flexural
13 strengths, porosity and dynamic modulus were tested after 1 day and 9 days cured at 23 °C
14 and after transformation of metastable hydration products to stable ones at 60 °C. The
15 combined usage of PCE with methyl-cellulose and Li2CO3 showed promising
16 superplasticizing properties for CAC that improved properties of the material.
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18 Keywords: Calcium aluminate cement, calorimetry, hydration kinetics, mechanical
19 properties, rheology, setting time, superplasticizer.
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21 1. Introduction
22 Calcium aluminate cement (CAC) is a special cement with many specific applications
23 (Bensted, 2002; Robson, 1962; Fentiman et al., 2008; Scrivener et al., 1998, 1999) mainly
24 attributed to it’s rapid hardening (Ukrainczyk, 2010; Ukrainczyk et al., 2013, 2012; Sipusic et
25 al., 2013; Gosselin et al., 201 0) and excellent resistance to chemical attack, fire, abrasion and
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26 impact (Scrivener et al.,). CACs are favorably used in cryogenic areas, such as the loading
27 docks of liquid-gas plants, because of the excellent thermal shock resistance. Furthermore
28 CAC is an excellent material for encapsulation of toxic wastes (Ukrainczyk et al., 2012;
29 Navarro-Blasco et al., 2013). CAC harden rapidly with high early strengths even under
30 freezing temperatures, if protected from freezing prior to initial set. The hydration process of
31 other types of cements (e.g. Portland cement, PC) is greatly slowed or even stopped at such
32 low temperatures. The rapid hardening characteristic of CAC makes it suitable to put a
33 cement based lining (e.g. floor or highway and bridge deck repair patch (Ukrainczyk and
34 Rogina, 2013; Ukrainczyk et al., 2013; Sipusic et al., 2013; Justnes, 2008)) back in service
35 within a few hours. The ultra-rapid setting CAC based materials, which set within a few
36 minutes, can be readily obtained by a very small addition of Li salts (Ukrainczyk and Rogina,
37 2013; Ukrainczyk et al., 2013; Sipusic et al., 2013; Gosselin et al., 2010). Time for concrete
38 repair and retrofitting may become a critical consideration for a structure where the costs and
39 disruption of its remaining out of service can have a significant impact on the operation.
40 Compared to PC, the general kinetic difference in CAC hydration, is that the hydration
41 products do not form an initial film barrier on the surface of anhydrous cement grains, as in
42 calcium silicate (i.e. PC) hydration, but precipitate in water-filled pores homogenously
43 (Lamour et al, 2001; Ukrainczyk, 2010). This through-solution (homogenised crystallisation)
44 mechanism is responsible for the unhindered hydration process and the resulting rapid
45 hydration evolution after the massive nucleation process. During the hydration of CAC, a
46 large quantity (typically 70–90% (Ukrainczyk, 2010)) of total heat is liberated in a short
47 period (the first 24 h) that could cause a considerable increase in material temperature
48 (Ukrainczyk and Rogina, 2013; Ukrainczyk and Matusinović, 2010).
49 The use of CAC is limited by the high price and adverse effects of concrete properties such as
50 a reduction of strength. The hydration of CAC is highly temperature dependent, yielding
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51 morphologically and structurally different hydration products that continuously alter the
52 material properties (Ukrainczyk and Rogina, 2013; Ukrainczyk and Matusinović, 2010;
53 Gosselin et a., 2010). In contrast, PC hydration has a much less pronounced temperature
54 dependency. Setting and hardening of CAC is primarily due to the hydration of CA (cement
55 notation: C - CaO, A - Al2O3, F - Fe2O3, S - SiO2, H - H2O), but other compounds also
56 participate in the hardening process especially in long-term strength development (Bensted,
57 2002). The hydration of CAC yields CAH10 as main products at temperatures less than 20oC,
58 C2AH8 (Ukrainczyk et al., 2007) and AH3 at about 30oC, and C3AH6 and AH3 at temperatures
59 higher than 55oC. CAH10 and C2AH8 are known to be metastable at ambient temperature and
60 convert to the more stable C3AH6 and AH3 that have higher density thus resulting in increase
61 of material porosity and permeability and a loss of strength (Bensted, 2002; Scrivener and
62 Capmas, 1998; Gares, 1997). The transformation is accelerated by temperature and moisture
63 availability for the dissolution and re-precipitation processes to take place. It has to be taken into
64 account because collapses of CAC concretes in different countries have led to disasters and its
65 use is forbidden for structural applications due to the strength regression and the quick
66 carbonation which leads into premature reinforcement corrosion. The w/c and the amount of
67 the main (active) minerals in CAC are the principal variables governing the porosity and
68 strength development during the transformation reactions (Bensted, 2002). This is because the
69 free water is released by transformation reactions (metastable hydrates contain more water
70 than the stable ones) which contributes to a further hydration of non-hydrated cement that
71 further fills the porosity. Thus, the deleterious effect of the transformation reactions on
72 properties of CAC based materials could be reduced by lowering of the w/c. Earlier
73 construction failures in the history of CAC concrete emphasized that a design must be on the basis
74 of the transformed properties (primarily strength) and the limits on the w/c (