Expansive additives

In a work-producing expansion, the temperature of the process fluid is always reduced hence, coohng does not depend on being below the inversion temperature prior to expansion. Additionally, the work-producing expansion results in a larger amount of coohng than in an isenthalpic expansion over the same pressure difference. 

To evaluate the averages like those in Eq. (4.78), it is very convenient to pass from cosines ((en)k) to the set of corresponding Legendre polynomials for which a spherical harmonics expansion (addition theorem)... 

Treatment of cyclohexane oxime sulphonates with a methyl Grignard reagent results in a ring-expansion addition of another... 

Figure 4.38 Fifty-six-day length change of latex-modified mortars with expansive additives.

Type M expansive cement is a combination of ordinary Portland cement, calcium aluminate cement, and additional gypsum or calcium hemihydrate, typically in the ratio 66 20 14 (Mikhailov, 1960 Budnikov and Kravchenko, 1968). It may be produced by mixing these constituents in a plant. Alternatively, an expansive additive consisting of high-alumina cement, gypsum or henuhydrate, and hydrated lime may be added to the fresh concrete mix during mixing. By this approach the extent of expansion may be controlled by the amount of additive added to the mix. 

In type M, just as in type K cement, the matrix of the hardened paste is produced by the hydration of the existing Portland cement. Ettringite, the phase responsible for expansion, is formed in a reaction of calcium monoaluminate (CA), the main constituent of high-alitmina cemerrt, with calcium sulfate and calcium hydroxide, formed in the hydration of Portland cement and also added to the system as a constituent of the expansive additive ... 

Expansive cements based on calcium oxide are rarely used because of difficulties in controlling the extent and the kinetics of expansion. It has been suggested that expansive additives based on free CaO should be used to prevent early age thermal cracking in hardening concrete (Ebensperger and Springenschmidt, 1992). 

Unlike MgO-based binders, expansive cements (or expansive additives) based on ettringite formation or Ca(OH)2 formation from CaO are of little benefit for controlling cooling shrinkage in mass concrete, because they would undergo complete hydration before the maximum temperamre in the hardening concrete mix was reached. Consequently, the compressive stresses produced by these expansive reactions relax too soon to prevent crack formation in the concrete body in the course of cooling. 

Ishida et al. (1997) developed an expansive agent containing free lime in combination with anhydrite and hauyne. Calcium lydroxide, ettringite, and in later stages also monosulfate, are formed in its Itydration, causing expansion when added to a non-expansive cement. The additive is particularly effective in slag cements in which the performance of conventional expansive additives is rather limited. 

Degenkolb, M., and Knoefel, D. (1996) Expansive additives in Ume- and slag-based mortars, va. Proceedings 18th International Conference on Cement Microscopy, pp. 304-316. 

Ebensperger, L.E., and Springenschmidt, R. (1992) Effectiveness of expansive additives avoiding early age thermal cracking, in Proceedings 9th ICCC, New Delhi, Vol. 5, pp. 578-584. 

Fu, Y. et al. (1995a) Effect of chemical admixtirres on the expansion of shrinkage-compensating cement containing a prehydrated alttmina cemerrt-based expansive additive. Cement and Concrete Research 25,29-38. 

Fu, Y., Ding, J., and Beaudoin, J.J. (1995b) Expansion characteristics of a compoimded expansive additive and pre-hydrated high-alirmina cement based expansive additive. Cement and Concrete Research 25,1295-1304. 

Ishida, A. et al. (1997) Expansive behaviour of slag cement with expansive additive, in Proceedings 10th ICCC, Goteborg, paper 3iii017. 

Q f and P f are similar to Qf and Pf. Now, expanding the terms of (7,18) into power series in e and equating coefficients of like powers of e separately for the regular functions and for each type of boundary function, we obtain equations for the terms of the asymptotic expansion. Additional conditions are obtained by substituting (7.17) into (7.14) and (7.15). This gives... 

Also, the creep strain and creep coefficient are significantly smaller than for unmodified concretes, and special expansive additives are used to reduce drying shrinkage (Ohama and Demura 1991). The bonding of PMC to ordinary concretes is excellent over long periods of time, if not destroyed... 

Ohama, Y., Demura, K. (1991) Properties of polymer-modified mortars with expansive additives, Int. Symp. Concrete Polymer Composites, H. Schom and M. Middel, eds, Bochum, Germany pp. 19-26. 

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