Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1996-06-28
1998-01-20
Marcantoni, Paul
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106735, 106737, 106785, 106819, C04B 2200
Patent
active
057097437
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new agent for accelerating the setting and hardening of siliceous hydraulic binders, under usual temperature and pressure conditions.
Usual temperature and pressure conditions are understood to mean, in the present description, a temperature not exceeding 90.degree. C. and most often less than 80.degree. C. and a pressure of the order of magnitude of atmospheric pressure.
Shortening the consolidation time of mixtures based on siliceous hydraulic binders is an important condition for certain work, in particular for cold-weather concrete placing, fast demolding or form removal, manufacture of prefabricated units, sealings, waterproofing, sprayed concretes, coatings of facades, and the like.
It is known that the consolidation of mixtures based on hydraulic binders is divided into two stages which more or less overlap: the first is denoted by the name of "setting" and the second by "hardening", the combined process being known as consolidation. Setting is determined using a Vicat setting tester and hardening is determined by the initial mechanical strengths.
Setting of cements results from the incorporation of water in a siliceous hydraulic binder which triggers, by hydration of the anhydrous inorganic oxides, irreversible crystal formation reactions, the intermeshing of the crystals thickening and "solidifying" the paste. This strengthening, which can be very sudden, marks the beginning of setting. Setting is exothermic and it is accelerated by an external heat contribution (for example, steam curing of precast concretes). The time of the beginning of setting is the period of time which has passed between forming the paste by mixing with water and a significant strengthening, corresponding to the moment when the Vicat needle, plunging into the paste, no longer reaches the bottom, in accordance with EN standard 196-3 for pure pastes and with NF standard P15-431 for mortars. The time of the beginning of setting of pure cement pastes is a component of their standardized characteristics. Thus, the time of the beginning of setting of Portland cements, for grades 35 and 45, at 20.degree. C., is greater than 1 h 30 and greater than 1 h for grades 55 and HP (high performance) of Portland cements, under the same conditions. The time of the end of setting corresponds to the moment when the Vicat needle no longer penetrates the pure paste or the mortar.
Hardening follows the phenomenon of setting: the strength, still mediocre at the end of the setting, will increase throughout the hardening, rapidly at the beginning and then increasingly slowly. Cements are regarded as having finished 4/5th of their hardening after 28 days but hardening can still continue for several months.
By virtue of the hardening following on the setting, the binders and the structural components manufactured with them acquire the properties which correspond to the use envisaged and which are a function of the choice of the binder and of the aggregates, as well as of the manufacturing process.
Shortening the consolidation can be obtained by various means, such as a heat treatment, chemical additions or a greater fineness of the hydraulic binder.
Many chemical compounds are known which are capable of accelerating the setting and the hardening of siliceous hydraulic binders.
The most effective and the best known accelerator is calcium chloride. However, the use of this accelerator, in the preparation of grouts, mortars and concretes, is regulated by the D.T.U.* No. 21.4 of October 1977 amended in April 1979, in order to limit: chloride or to the use capable of having an effect on the durability of grouts, mortars or concretes. building art and techniques)
Consequently, the use of CaCl.sub.2 is very restricted in all concretes reinforced with metal reinforcements. However, CaCl.sub.2 remains the most widely used accelerating agent in non-reinforced concretes, whenever economical manufacture is sought for, as is the case in precasting.
Chlorine-free admixtures are, in contrast, intended for certain reinforced items (m
REFERENCES:
patent: Re35194 (1996-04-01), Gerber
patent: 4402922 (1983-09-01), Gaynor et al.
patent: 4504315 (1985-03-01), Allemann et al.
patent: 4650523 (1987-03-01), Kikuchi et al.
Database WPI, Week 8125, AN 81-45758D & SU,A,771 042, Oct. 16, 1980.
Chappuis Jacques
Latrasse Bruno
Leture Philippe
Lafarge
Marcantoni Paul
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