Conclusions
literature Cited
NO increase of thermal conductivity was observed on aging uncut samples of comparable castor oil-based and polyetherbased fluorocarbon-blowm, rigid urethane foams for 6 to 12 months. T o simulate actual foamed-in-place applications, these foams were undisturbed before testing. Thus, the lowcost, castor oil-based foams (7, 8) appear to be capable of performance comparable to that of polyether-based foams when evaluated under simulated end-use conditions. T h e thermal conductivity of cut samples of the same foams increased on aging because of diffusion of air into the foam cells. Initial diffusion rates were greater for castor-based foam, but both types approached equilibrium thermal conductivities of 0.165 to 0.175. These results suggest that low thermal conductivities can best be maintained in both types of foam by using them in undistiirbed foamed-in-place applications and that more representative 1;-value measurements can be obtained by analyzing undisturbed foam samples.
(1) D’Eustachio, D., Schreiner, R. E., A . S . H . V . E . Trans. 58, 331 (1952). ( 2 ) Doherty, D. J., Hurd, R., Lester, G. R., Chern. Ind. (London)
1962,1340. ( 3 ) Du Pont Co., Freon Products Division, Bull. BA-4 (January
1961). (4) Ehrlich: A., Patton, T. C., M o d . Plastics 41, 154 (1964). (5) Frisch, K. C., Robertson, E. J., Ibid., 40, No. 2, 165 (1962). (6) Hallinan. M. R., Himniler, W. A , , Kaplan, M., 18th .4nnual Conference, SPE, Pittsburgh, Pa., Feb. 2, 1962, Preprint Book 20-4, p. 2. (7) Lyon, C. K., Garrett, V. H., Goldblatt, L. A . , J . A m . Oil Chemists’ SOC. 39, 69 (1962). ( 8 ) Ibid., 41, 23 (1964). (9) Skochdopole, R. E., Chern. Eng. Prog. 57, No. 10, 55 (1961). RECEIVED for review February IO, 1965 ACCEPTED June 30, 1965 Division of Organic Coatings and Plastics Chemistry, 148th Meeting, .4CS, Chicago, Ill.. August-September 1964. Reference to a company or product name does not imply approval or recommendation of the product by the U. S. Department of Agriculture to the exclusion of others that may be suitable.
POLYMER-MODIFIED HYDRAULIC CEMENTS H E R M A N B. W A G N E R Drexel Institute of Technology, Philadelphia 4, Pa.
Certain fundamental characteristics of polymer-modified portland cement compositions were studied. Rate of generation of specific surface area of the cement gel i s retarded b y some latexes and accelerated b y others. After about 28 days, however, the surface areas developed are comparable. The development of polymer coalescence i s found to require from 8 to 72 hours, to occur gradually, and to depend primarily on water content of the composition. Structure of the coalesced polymer within such compositions i s detailed microscopically and related to the inorganic components. A basis i s laid for subsequent studies of the mechanisms whereby polymer modification effectively alters the physical and chemical properties of the conventional compositions.
the last 15 years there has been extensive empirical investigation of polymer-modified hydraulic cement systems. Such modification has a substantial influence on such diverse properties as compressive and tensile strength. elastic modulus: hardness: permeability, and chemical resistance. Commonly, hoivever, data obtained have been related only to such gross variables a s identity of the polymer. level of polymer content, and conditions surrounding the hardening reaction. hlinimal attention has been turned to the development of a more lundamental understanding of the behavior of such systems. ivirh the noteivorthy exception of the lvork of Geist, Amagna. and hfellor ( 3 ) . ‘The objective in the investigation reported here has been a more basic and quantitative understanding of such systems developed against the background of unmodified, or ”conventional,” hydraulic cements. I n this initial paper some more general aspccts of this investigation are given; in subsequent papers it is planned to present a more detailed treatment of the various properties noted above. URING
Hydration Reactions of Portland Cernenl
‘Tricalcium silicate and beta-dicalcium silicate constitute about three quarters of the \\,eight of a typical portland cement po\\-dcr. T h e remaining fraction consists chiefly of tricalcium aluminate and tetracalcium aluminoferrite. Under ordinary temperature conditions, and \vith adequate ivater available, the hydration of the latter t\vo constituents is essentially com-
plete within 7 days ( 7 ) . Hydration of the tricalcium silicate, although well advanced at this time, may require a year or longer for essential completion, while the hydration of dicalcium silicate is appreciable only after several months, approaching completion after several years. T h e “cement gel” that is progressively developed as the product of these hydration reactions comprises chemical species of high specific surface, including within their structures the so-called “gel pores” (2, 4 ) . Typically, the surface area that can ultimately develop is about 1000 times as great as that of the cement powder. IVhile the quantity of Lvater required for complete hydration of the cement compounds varies somewhat for each of these, lvater to the extent of about 0.25 of the weight of the dry portland cement is required for reaction, and a n additional 0.15 for inclusion Ivithin the gel pores. T h e former is often designated as “reacted Lvater,” and the latter as “gel water.” Because reaction, formation of the gel pores, and the water inclusion occur concomitantly in forming the structure of the cement gel, the ratio of the water in either of these forms to that in the other is necessarily the same a t any stage of the hydration process. Effect of Polymer Modification on Strength
Strength development in a conventional composition is intimately associated with formation of the cement gel, and the accompanying increase in surface area. T h e marked effect VOL. 4
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191
upon certain physical properties of the hardened cement composition that polymer modification can superimpose is illustrated by the data in Table I . Here, compositions consisting of Ottawa sand and portland cement were combined with the respective polymer latexes so that the resulting compositions contained polymer and water, in the ratios of 0.15 and 0.32, respectively: to the dry cement weight. Data were obtained following 1 4 days' hardening, under comparable laboratory conditions, and are given only to emphasize the appreciable effects of polymer modification under specific conditions, in either a positive or negative direction.
Table 1.
Variation of Compressive and Tensile Strength Values with Polymer latex Modification CompressiLe Strength, Polymer Latex Type
I I1 I11 IV V VI VI1
None Poly(\inylidene, vinyl chloride) Polyacrylic Poly(styrene, butadiene) Polystyrene Poly(viny1 chloride) Poly(viny1 acetate)
Tensile Strength,
P.s. I. 250 970 565 760 345 405 600
p.s.r. 4930 8800 3665 5610 4275 4800 3040
Table II. Influence of latex on Rate of Generation of Cement Gel
Each composition listed a t the bottom of Table I1 was allowed to hydrate for progressively increased periods, a t 2 1 C., then pulverized and dried to constant \?eight over magnesium perchlorate. This last procedure (P drying) removes essentially all but the reacted \\rater ( 2 ) , leaving the surface of the cement gel formed up to that time accessible for adsorption of a water layer. Adsorption was then determined by equilibrating 2- to 4gram samples, thus prepared. to air and carbon-dioxide free atmospheres, maintained a t fixed and successively increased relative water vapor pressures. From these data the specific surface area of the cement gel existent a t any particular stage of reaction was computed, utilizing the BET equation, and following the procedure of Powers and Brownyard (5). The following form of this equation was employed: -1 w
x
X ~
1-x
+
1 c 1 _-_ - ~x x
vmc
V,C
where w = the quantity of water adsorbed, per gram of cement, a t vapor pressure, p ; x = p / p s , where p s is the saturation vapor pressure; C = a constant (related to the heat of adsorption); and Vm = the quantity of adsorbate water required for a completely condensed layer on the gel surface. For each composition, the value of w corresponding, in turn, to the several values of x was measured (Table 11). For each composition, and a given reaction period, 1 / w X ~ / ( 1- x ) is plotted against x , as in Figure 1 (here, for the 3-day period of hydration). From each plot the constant Cis evaluated as equal to 1 - l/x, when 1/20 X x/(l - x) equals 0, while V , is evaluated as (1 C)/2C X ze~, when x = 0.5. The specific surface area, S,is then calculated from the equation (5):
+
Water-Adsorption Quantities for Various Reaction Periods (Each w value = mean of t\vo determinations) Reaction Compositiona -_ Period I 11 IIr IV V VI
0.32 0.0316 0.0485 0.0496 0.0561
0.0274 0.0380 0.0520 0.0530
0.0339 0.0517 0.0535 0.0595
0.0269 0.0548 0.0511 0.0540
0.42 0.0344 0.0514 0.0540 0.0611
0.0310 0.0419 0.0576 0.0639
0.0369 0.0565 0.0580 0.0606
0.0305 0.0593 0.0566 0.0591
x =
24hours 72 hours 7 days 28 days
0.0270 0.0487 0.0596 0.0627
0.0165 0.0400 0.0433 0.0547
0.0302 0.0526 0.0672 0.0681
0.0187 0.0420 0.0493 0.0590
x =
24hours 72 hours 7days 28 days
0.58 0.0463 0.0617 0.0651 0.081
x =
24 hours 0.0452 72 hours 0,0655 7davs 0.0815 28 days 0.085 I. Water-cement
0.0229 0.0496 0.0553 0.076
0.0376 0.0478 0.0408 0.0528 0.0728 0.0757 0.0695 0.0707 0.0703 0.076 0.074 0.074 at 0.3-1/1.00 ratio. 11. Poly(oinylidrnr, r,inyZ
chloride)-water-cei~ient, 0.7 7 / 0 . 3 J / 1.00. III. Polyacr>lic-reatrrcement, 0.14/0.3-1/1.00. IC/. Poly(styrene-butadirne)-riater-ceinent, 0.17/0.34/ 1.00. V. Polystyren~-ieater-cement, 0. 7 7/0.37/ 1.00. VI. Poly( c~inylidene, Z'i71l.l chloride) 4tBater-cement, 0.17/0.3.i/ 1.00. b ~VonJiim-forming copolymer.
Table 111. Rate of Cement Gel Specific Surface Area (S) Development for Various Polymer-Modified Compositions
(Square centimeters per gram! times 10-5) Composition
24 hr.
I I1 111
6.7 6.9 3.2 5.3 6.7 5.8
1v V VI
Reaction T i m e 72 lir. 7dal.s 8.5 9.0 9.0 11.6 6.7 7.3 7.3 9.7 10.2 9.7 10.6 9.7
28 days
11.6 11.8 11.3 10.3 10.0
10.2
S = (36 X lo6) V, sq. cm. the values thus obtained being shown in Table 111. Among the various polymer latexes, the initial rate of development of cement gel specific surface area varies, some retarding and some accelerating it relative to that of the unmodified composition ( 7 ) . After 28 d a y , however, the surface areas developed are comparable. Other calorimetric data, obtained in following heat evolved by the hydration reactions during the first 48 hours. were consistent with these data, as were also determinations of reacted water for these various compositions. Coalescence of Polymer latexes within Hardened Compositions
Certain of the polymers (compositions 11, 111, and IV) are of the coalescing or film-forming type, under the temperature conditions involved ; others (V, VI) are noncoalescing under these conditions. 192
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
Several methods were employed to determine \\.hen, during the hardening reactions, polymer coalescence in the former occurs. Method A. Acid-Immersion Method. Thin sections of poly(vinylidene, vinyl chloride) (\'e\'c), and polyacrylic (Ac)-modified cement pastes, of varied composition (Table IV) were prepared, hardening being accomplished bet\\.een glass plates. These sections, measuring approximately 10 by 10 by 0.3 cm., were provided progressively increased periods of hardening, a t 21 C., \vithout evaporative \Taler loss. At the end of each selected period the sample \vas removed and completely immersed for 24 hours in 10yc hydrochloric acid, the plane of the sample being in the vertical position. At the end of this time the condition of the sample \vas noted, an intact sample indicating that appreciable coalescence of the polymer had occurred, since the inorganic portion of these compositions is readily disintegrated by the acid. By taking into account the amount of ivater removed in the course of reaction to form cement gel, the remaining ivater
I
9
20
40
X
60 Time (houts)
80
100
Figure 1. 1 / w X x / ( 1 - x ) vs. x , for determination of cement gel surface area at 3 days
Figure 2. Effect of specific conductance on hardening time for Saran-modified cement composition
available for maintaining dispersion of the polymer can be calculated. This average concentration of polymer, in the aqueous phase remaining, a t the approximate time when effective coalescence of the polymer particles has occurred, is shown in Table V, where the initial polymer concentration (on a volume basis) is also shown. The higher the ratio of water to cement, the longer the coalescence of the polymer is delayed. At the lowest watercement ratio, coalescence has occurred within the first 8 hours; with the highest ratio! coalescence appears to occur effectively only after about 72 hours. Table V, holvever, shows that although higher watercement ratios delay coalescence, coalescence in such circurnstances occurs at lower concentrations of polymer in the aqueous phase that remains. Separate experiments have shown, also, that in the absence of cement it is possible to concentrate these two polymer latexes to at least 67% polymer
volume, \\ithout having coalescence occur. It is indicated, accordingly, that in the cement-containing compositions effects additional to rhat of simple water removal contribute to the fusion of the polymer particles.
Table IV. Composition. RelatiLe IVright Parts Cement Polymer TVater
Effect of Acid Immersion Conditiona of Sample Follozting Acid Immersion Hours _ _Hardening _ _ _ _ Period?rior, ~_____ _ 4 8 16 2d 4 ‘ 8
_ 100
O 1 2
S 6 5
1 2
16
3
’IC
_ 17
_
O 4
D 6 j D
D D D D
D I D D
D I I D
D I I D
I I D
D I I I
~ D D I I I I 3 2 7 D D D D D I 3 5 D D D D D D I D , sample disintegated. I , sanifile intact. DI, sample Partially disintegrated.
15 2 15
The third column of Table VI sho\vs the polymer concentrations calculated on the basis of no coalescence, while the second column gives the actual concentrations of polymer found in the centrifugate. T h e first appearance of a marked deviation bet\\ een .‘calculated” and “found” values of polymer concentration indicates this as the approximate time \\hen coalescence occurred. These times are indicated as about 12 hours for the third composition, and between 11 and 17 hours for the fifth composition, in general agreement n i t h the results obtained by Method A.
72
Ve/Vc 100
Method B. Centrifuging Method for Following Coalescence. The third and fifth compositions of Table IV were allowed to harden. without evaporative water loss, for the periods noted in Table VI. Then the composition was centrifuged and the polymer content of the centrifugate determined. It’ith hardening periods of 3l/2 hours, and longer, it was necessary to make a measured addition of water immediately before centrifuging to facilitate separation of any uncoalesced polymer.
Method C. Measurement of Electrolytic Conductance. Data obtained for specific conductance of a cement-VeVcwater composirion, a t 100 : 30: 30 \veight ratios are shown in Figure 2, as a function of hardening time, a t 24” C. The form of the curve is characteristic of unmodified cement, the absence of any abrupt changes in the curve suggesting that there is no sudden development of coalescence, but rather a gradual fusion of polymer particles. A reasonable picture of the formation of coalesced polymer within these compositions appears to involve the follo\ving stages: During the initial 8- to 48-hour period, following combination of the cement powder and the latex, the polymer particles VOL. 4
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Table
V.
Volume Concentrations of Polymer in Starting Latex and in Remaining - Wafer at Coalescence Comporition Prepared, Polymer Concentration Rdotiue Weizht Parts At maCement Polympr Water Initial 18$6ence
Figure 3. Structure of Saran polymer within hordened sand-cement composition (57X)
Figure 4. Structure of Saran polymer within hardened sond-cement composition
diameter from ahout 3 X 10-5 to 3 X lo-' cm. diameter are interpreted as regions of cement gel formcd in thc interstitial space betwcen the cement grains, and about which the polymer coalescence has occurred. 'Thus, the very finest strands af coalesced polymer appear to surround or to interweave the cement gel particles. This hne-structured network of coalesced polymer and cement gel in turn encompasses the cement grains (or the portion of these rcmaining unhydrated)
Figure 5. Structure of Saran polymer within hardened cement composition (6760 X )
..~".-.
-.
..I..I._
, I.'I"* r~',""' hardened sand-cement composition ~
..lllllll
_-__
.. ,.
Figure 6. Structure of Saran polymer within hardened plaster of Paris composition
rigure 0 . arructure of acrylic polymer within hardened sand-cement composition ( 1 3 9 X )
to construct the coarser ne,twork lying between sand particles, as shown in Figure 3. An additional observation of interest in Figure 5 is the nodular structure evident within many of the polymer areas. Each nodule corresponds to a single polymer latex particle, of diameter approximately 1500 A. It is of interest also to contrast the continuous structure of Figure 6 , which shows a plaster of Paris, VeVc latex compasi-
tion (mag-nification 6760X), with the interrupted structure of the polymer areas in Figure 5. In the former composition hydration occurs very rapidly and apparently only about the boundary surface of the grains of the plaster powder, with little or no precipitation of the dihydrate within the body of the latex dispersion. Figure 7 (magnification 5 7 X ) shows the grass structure of the polyacrylate polymer within a sand-cement-polymer-water VOL. 4
NO. 3 S E P T E M B E R 1 9 6 5 195
Figure
9.
Figure 11. Structure of coalesces poiy(styrene, butadiene) polymer within hardened sand-cement composition (57 X )
Structure of polyethylene polymer
within hordened sond-cement composition (57X)
within a sand-cement-palyethylene polymer-water campix i tion, at 300:100:16:32weight proportions. Fiqure 10 is of interest in that the . unlvmer , 1 film-forming, poly(vinylidene, vinyl chloride) t actual coalescence would be expected here. TI however, show the numerous cavities corresponoing 10 m e cement grain sites (compare with Figure 3), and it is evident that some degree of polymer cohesion has becn developed here. O n the othcr hand, a nonfilm-forming polystyrene latex showcd no cohesion developed within the composition, complete removal of the polymer, as well as the inorganic fractions, being eRected by the extraction treatment. Figure 11, in contrast, s h o w the structure of the oofvmer resultant from a poly(styrene, butadiene) latex, coalescence here being well developed. Acknowledgment
T h e assistance of Robert Miller, Frank Jordan, and Thomas McGinley in the laboratory work is gratefully acknowledged, as is that of E. B. Bradford in obtainins t h e electron micrographs Literature Cited (1), ~R o m e .~ R... H..o 1.m-h. Chtr .. ~., W.,~Ind. Eq. ~ , n. 26,837 (1934). (2) Brunauer, S., Copel;ind, E., Bragg, R. H., J . Phy’. Chrrn. j
Figure 10. Structure of noncoalencing poly(vinyl, vinylidene) polymer within hardened sandcement composition (57X)
composition, a t 300:100:16:32 weight proportions. Here again the largest, dark areas correspond to positions occupied by sand grains. Fi9’re shn’Ys the Same, at higher magnification.
196
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N 1
116 (1956). (3) Geist, .IM., . Amagna, S. V., Mellor, B. B., Ind. Erg. Chern. 45, 759 (1953). (4) Powers, T. C., Brownyard, T. L., Proc. Am. Concrete Inst., 43. 469 (1947). (5) fbid., P. 479: R a c ~ i w ofor review March 8, 1965 ACCEPTED July 2, 1965 Research sponsored by the Saran Products Laboratory, Plastics Department, Daw Chemical C-
