/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Special Technical Publication, 691, pp. 455-463, 1980 Freeze-thaw durability of porous building materials Litvan, G. G. ASTM ARWRAt3rWater held in the pates of a solid becomes unstable when caoled to tcrnperatutes below O°C. If the conditions permit, the water leaves the pores and ice accumulates outside the system. In case of high cooling rate, high degree of saturation, and long diffusion path, the water cannot reach the external surface and solidifies in a glassy. amorphous state. Mechanical damage occurs only in the latter case. This mechanism is not indigenous to any single type of solid, thus it is applicable to cement paste, done, and brick, and could be used Tor increasing the durability of porous materials and for impmving test procedures.

/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Society, 55, 1, pp. 38-42, 1972-01 Phase transitions of adsorbates. IV. Mechanism of frost action in hardened cement paste Litvan, G. G. The dimensional changes and the thermograms of cement specimens were determined during temperature cycles (+5O to -60°C, 0.33"C/min). In each case, freezing processes at -8" and -40°C and melting processes at -11' and 0°C were observed. The results could be explained by a theory previously developed for the porous-glass-water system. At the higher temperature, freezing occurs on the outer surface of the specimen; at the lower temperature, it occurs in the pores after redistribution of the water. Because water does not freeze in pores filled on adsorption, it migrates out of these pores when the relative humidity (expressed in terms of the vapor pressure of undercooled water), unavoidably decreases on cooling. Expansion is deleterious when the water content of the paste is significantly greater than the equilibrium value at the prevailing relative humidity. The effects of the water/ cement ratio, degree of saturation, air entrainment, sample dimensions, and cooling rate were consistent with the theory. Journal of the American Ceramic

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Changes in the dimensions and heat content of hydrated cement specimens were determined as a function of temperature and concentration of deicing agent in cooling‐warming cycles between +15° and ‐ 70°C. The concentration of the polar deicer (NaCl) solution varied from 0 to 26% and that of the nonpolar (urea) solution from 0 to 40%. The W/C ratios were 0.4,0.6, and 0.8 plain and 0.5 air‐entrained. Experiments were also conducted to clarify the effect of cooling rate and sample size. The observations can be explained by the mechanism previously proposed for phase transitions of adsorbates. In the presence of salts, freezing and melting of liquid exuded from the pores on cooling proceed according to the bulk phase diagram, producing double peaks in the thermograms except at extreme concentrations. The detrimental effect of deicers is attributed mainly to the high degree of saturation, a consequence of the low vapor pressure of the solutions. A beneficial aspect is the widening of the temperature range in which transitions occur. These opposing effects result in the worst conditions at a low deicer concentration (5% NaCl) and optimum conditions at a moderately high concentration (13% NaCl). Since the effect of deicers is physical, it should be common to all chemicals. Air entrainment, although beneficial in most circumstances, can be detrimental. The best protection against “salt scaling” appears to be reduction of porosity.

ABSTRACT1Ieasurements of the expansion of porous Vqcor glass containing fixed quantities of adsorbed water indicate that in every instance a phase transition starts belo\\ -50" C, with the main change occurring below -160" C. Two other anomalies of the length variation mere observed near -22" C and -7" C when the amount of adsorbed water exceeded the value equivalent to two monolayers. The length of the adsorbent after co~npletion of a temperature cycle was different from the initial length. This is thought to be due to damage suffered by the glass aiid t o the fact that the length of the adsorbent is different for adsorption and desorption although the quantity adsorbed may be the same.The phase transition of adsorbed xenon takes place below the normal triple point and is a function of surface concentration as shown by length variations and equilibrium pressures for fixed quantities adsorbed. All transitions are gradual aiid hysteresis is exhibited by the isosteres. The adsorption isotherms for xenon -I'ycor glass show a decreasing adsorptive capacity and a contraction of the hysteresis loop with lower temperature. The inadequacy of the capillary coildensation theory of adsorption in relation t o these results is discussed.The capillary condensation theory assumes that the free energy of the adsorbate is less than that of bulk material a t the same temperature because it is held under concave menisci in the pores of the adsorbent. The vapor pressure of the condensed substance is calculated by the relationship due to Kelvin. The theory implies that the adsorbent is inert, and only the shape and size of the pores play any role in determining the adsorptive characteristics. I t follo\vs also that the adsorbate has bulk properties except the lowered free energy arising from the presence of the concave meniscus.There is, however, ample experimental evidence to the contrary. The observed dimensional changes of the adsorbents (0.37, in the case of 17ycor glass -water system (1)) during the adsorption process indicate that the solid is perturbed by the presence of the adsorbate. Similarly, the infrared spectra of the adsorbate contain lines caused by forbidden transitions normally observable only in the Raman spectra (2,3) showing that the adsorbed liquid is in a state different from the bulk state. The crystal structure of the frozen adsorbate, too, has been found by X-ray diffraction methods to differ from the one of the bulk crystal (4). Accordingly, solidified adsorbates failed to nucleate undercooled bulk liquid of the same composition (5). These findings are to be expected in view of the fact that adsorption is the result of molecular interaction between adsorbate and adsorbent, and this interaction perturbs both.On applying the equation due to Kelvin the question arises: is it permissible to use the relationship even as an approximation when most of the quantities involved are not only unknown quantitatively but are meaningless on a molecular scale? Surface tension (or even the tern1 surface itself) of a liquid ...

'I'he specific heat and dimensior~al changes of the porous !)6yo silica glass -\\later s).stem n-ere measured simultaneously between -35 "C and +2 'C with coverages of 1.6, 4.0, 5.3, cuid '7.7 molecular layers. 'I'he specific heat of the adsorbate below the transition range was found to be higher than that of ice. Xo phase change was detected with the lowest concentration. At the higher coverages, transition always occurred near -0.5' a~l d was of the anomalous first order type. The values of the specific latent heat of fusion, calculated by assuming that. two monolayers do not freeze, are 40.4, 54.4, and 5S..i cal g-l, deperiding on the concentr;~tion. 'I'he correlation between the results of calorimetric and dimensional change measuretiielits 1v;is considered s;~tisfactory.

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