I
HERMAN B. WAGNER Tile Council of America Research Center, Princeton, N.
Methylcellulose in
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Water-Re te ntive Hydraulic Cements
A Methylcellulose prevents portland cement mortar from losing both cohesion and udhesion when placed on absorptive surfaces
These portland cement compositions can bond dry, absorptive surfaces. They are used widely as a lightweight, setting bed f o i ceramic tile e
Effectivr. Concentrations of methylcellulose range from about 0.2 to 3%, based on the weight of cement, and depending on viscosity type of methylcellulose. Some bond to dry porous masorry materials can be obtained using solutions having a viscosity of only about SO cp. However, viscosities i n excess of about 800 cp. give optimum bonding which is 2 to 4 times stronger rhan that obtained with conventional portland cement compositions under optimum curing conditions.
IN
where ceramic materials are involved hydraulic cements are frequentIy used, both as a structural and bonding material. Special precautions are needed to prevent water loss from the cement. Absorptive ceramics require saturation with water prior to installation and air-exposed surfaces have to be covered. Use of thin mortar layers, even as an adhesive, has been impossible. A typical absorptive tile, for example, absorbs water equal to about 13% of its weight or one fourth of its dry volume. Thus the basic problem is to prevent movement of water from the wet cement into the pores of the tile. I n the work described here methylcellulose is added t o the cement t o retard such movement. I t does not flocculate the cement nor is it precipitated by it. CONSTRUCTION
Ex per imenfa I T h e higher molecular weight types of methylcellulose produce a large increase in viscosity a t relatively low polymer concentrations. At a concentration of
1.576, for example, 4000-cp. grade niethylcellulose raises the viscosity of water from 1 to approximately 1500 cp.
Table 1. Methylcellulose Retards Water Transmission from Thin Layers of Cement to the Tile Body
Soh. \risc.,a CP.
Methylcellulose ' Concn., %
22,400 4,250 341 147 38 0.9
3.00 2.00 1.14 0.75
Av. Flow Rate into Tile Bodyb
0.0005 0.0019 0.0071 0.0180 0.0805 2000-3000
0.50
0
Water ImbibedCilfter 4 min. 30 min. 6 hr. 1 20 150
750 1,800 11,500 50,000
0.154 0.060 0.012 0.009 0.000 0.000 0.000
0.170 0.060 0.013 0.020 0.006 0.004 0.005
0.185 0.115 0.085 0.070 0.040 0.018
...
Shear Strength,d P.S.I. 1 48 200 850 2,500 45,000 140,000
For the data on watrr irnbibirior; (Table I ) , absorptive tile having a n area of 117 sq. cm. (12.5% by wcight water absorption) w.is first weighed dr? 1=t0.01 gram), then placed in contact with slurries of r,ethylcellulose and portland ccment, and reweighed. \Vater moves into the tile almosr immediately, and this loss of water from the cement, which results in a noncohesive mortar layer, prevenrs reaction to form a continuous, hardened cement stIuctu:'e. Under these conditions ria adhesion can be developed. For the shear-bond strengths shown ir. Table I , cl '/*-inch laver of cemen: mixed with meihylcellulose was placed between the porous hacks of two absorptive ceramic tiles which were 10.8 cm. square. An edge of one tile extended 0.75 cm. beyond the edge of the other. This provided a shearing action when the staggered edges were presentt:d to the cross-heads of a Tinius Olsen Super L universal tester.
0
31 173 319 394 430 360
Added to 3 times its weight of Type I portland cement for testing shear strength and water imbibed. * Rfl./sq. cm./hr. Av. flow rate over period required for 0.25 to 0.42 ml./sq. em. of solution imbibed. C M1./ sq. em. a t 25" C., values expressed as yo of dry tile weight. Shear bond strength: mean of 4 determinations: 28 days curing time at 22' to 26O C.
Table II. Methylcellulose Increases the Setting Time of Portland Cement
XIethylcellulose, Vise. grade,
%" 0
0.40 0.43 0.83 1.23 1.50 2.70
CP.
...
7000 4000 400
100 50
15
Setting Time,bHr. Initial Final 23/4 53/4 63/a
6l/4 lo'/, 10 10
5 101/4 11 3 / 4 1O'/z
19 19 19
Based on dry cement. ASTM Method C266-58T; Gilmore needles. a
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90
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ICon.~onl rl 54nn dl.. OSPlO. I6 nr
0
so
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TIME ,
I50
zoo
250
300
SECONDS
Movement of methylcellulose solutions into glass capillary tubes decreases as viscosity and tube diameter increases A B.
Varied viscosity Varied tube diameter 0
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20
I M TIME
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, 60
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60
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Discussion Bonding is first effected when viscosity of the aqueous phase is as low as 48 cp. (Table I). T h e effective viscosity, however, may be somewhat higher than this value because the available water is reduced as formation of the cement gel proceeds. With the relatively low shear values, failure occurred a t the tile to mortar interface, with the entire surface of one tile broken cleanly from the mortar. With the higher shear-strength values, (319 p.s.i. and higher) approximately half the area of each tile was separated from the mortar, with cleavage of the mortar layer occurring through its '/*-inch thickness, generally near the midpoint. For absorptive ceramic tile
Table 111. Methylcellulose Affects Physical Properties of Portland Cement (28-day curing time; mean of 4 determinations) Portland Cement/ Portland Methyl Cement Cellulose Compressive 9750 6440 strength,a p.s.i. Tensile strength: 324 298 p.s.i. Shear strength," 255 225 p.s.i. Hardnessd 80 66 Shrinkage," yo 0.08 0.08 a 2-in. cubes, molded according to ASThl Method C109-58. Briquets, molded according to ASTM Method C 190-58. Cylindrical specimens of cross-sectional area equal t o 0.25 sq. in.; damp-cured. The low value may be caused by the small cross-sectional area and a cutting action exerted by the applied stress. Ames hardness; 15-kg. load on '/a-in. steel ball. * Linear contraction of 6 X 1 X 1/4 in. cast bar.
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saturated with water, shear and bond strengths of only 100 to 200 p.s.i. are obtained. For the data in Table 11, approximately the same viscosity (850 cp.) was obtained by using different viscosity grades of methylcellulose. Both initial and final set is retarded by methylcellulose, although [he effect here is related to concentration of the methylcellulose, rather than to viscosity obtained in the aqueous phase. This retardation is typical of water-soluble, hydroxylcontaining organic compounds ( 2 ) . Methylcellulose probably remains dissolved in the fraction of the water that is not consumed in the hydration reaction, and thus does not participate in the crystal structure. Typically, its volume constitutes about 0.5 to 2Yo of the total volume. T h e total water component constitutes about 40% of the total volume, and of this about 15 to 25% ultimately participates in the cement hydration reaction (7). Physical Properties. Hardness and shrinkage were determined on mixes having a 2.0% concentration of 4000cp. grade methylcellulose in the aqueous phase; compressive, tensile, and shear
Table IV. For Materials Bonded with Water-Retentive Cement, Break Usually Occurs within the Material Breaking Surface Strength, Plane of Bonded P.S.I. Rupture Cinder block 243 Through block Cement asbestos 129 At interface board Foamed polystyrene 38 Through polystyrene Gypsum wallboard 79 Through paper Cement block 286 Through block
INDUSTRIAL AND ENGINEERING CHEMISTRY
strengths were determined a t a 3.6y0 concentration (Table 111). The ratio of water to portland cement was held constant at 0.33. Workability of pastes and mortars containing methylcellulose is also affected to some extent. For example, when thew compositions are spread on a vertical surface, sagging is greater than with conventional portland cement compositions. I n practice, this can be eliminated by adding small amounts of fibrous fillers such as asbestos. T h e ceramic surface with its high degree of absorption and relatively fine porosity, provides a n excellent substrate for test purposes. A considerable variety of other absorhent materials have also been effectively bonded with these watei,-retentive compositions-e.g., hardened concrete, cinder block, cement block, brick, asbestos-cement board, foamed polystyrene, and even the paper surface of dry gypsum wallboard. These have been bonded or laminated using dry materials and dry curing conditions throughout and with mortar layers as thin as l/16 inch. The surfaces of these absorbent materials arc of particular interest as backing materials for setting ceramic tile, and specimens prepared by bonding tile to these materials have been evaluated under shear-bond tests. Typical values are given in Table I\'-rupture usually occurs within the material bonded rather than a t the substrate-mortar interface. I t has been noted repeatedly that when relatively nonabsorptive surfaces are bonded with neat cement pastes, bonding strength decreases with time. This effect has been attributed to the higher degree of shrinkage encountered with the neat pastes. Maximum longterm strengths to impervious and vitreous ceramic tile, for example, are obtained a t 1 to 1 or 2 to 1 sand-cement ratios. Acknowledgment This work was supported by the Tile Council of America, Inc., and conducted under the supervision of J. V. Fitzgerald. Credit is given here, also, to Robert Kleinhans, Joseph Spataro, and David Fankhauser for carrying out the physical tests. References (1) Bogue, R. H., Lerch, W., IND.ENG. CHEM.26, 837 (1934). (2) Burchartz, H., Zernent 13, 11; 509
(1924).
( 3 ) Jaenicke, others (to American Lurgi Corp.), U. S. Patent 2,311,233 (1952). , (4) Ritter, H. L., Drake, L. C . , IND.ENG.
CHEM.(ANAL. ED) 17,782 (1945). (5) Wagner, Herman B. (to Tile Council of America, Inc.), U. S. Patent 2,838,411 (1958). (6) Zbid., 2,820,713 (1958). RECEIVED for review July 8, 1959 ACCEPTED December 23, 1959
