TIBM - 37

TECHNICAL INFORMATION. ON .BUILDING ; MATER I ALS •

FOR USE IN THE DESIGN OF LOW-COST HOUSING

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THE NATIONAL BUREAU OF STANDARDS

UNITED STATES DEPARTMENT OF COMMERCE

WASHINGTON, D. C.

November 2, 193 6

COMMERCIAL I :AS0NBY CEMENT INVESTIGATIONS

This is a digest of Research Paper, RP 746, "Investigation of Commercial Masonry Cements” 'December 1934 k, by Jesse S, Rogers and

Raymond L. Blaine, issued by the National Bureau of Standards,,

Forty-one commercial cements as well as mortars made from then

were studied at the National Bureau of Standards. Cements were classified as hydrated or hydraulic lime, natural cement, Portland cement

with or without admixtures, mixtures of portland cement and lime,

Portland and natural cements, portland cement with unidentified materials, blast furnace slag with various additions, and two whose identity could not be established. About half of the cements contained waterrepellent materials. The forty-one cements were. used individually in

four mortars: (X) 1:3 standard Ottawa sand by weight; (X— 1 ) 1:3 mixed

sand (2 parts standard Ottawa and 1 part pit run Ottawa) by weight;

(Y l 1:3 mixed sand (as described in X-l ) by volume; and (Z) 1 volume

neat cement paste to 1.57 volumes of dry-rodded mixed sand (previously

described in X-l).

Fourteen and a half minutes after water had been added to the dry

mix, workability (stirring resistance) was measured. It was observed

that mortars containing cement with water repellent additions generally worked more easily than those without, despite the fact that they

showed a marked resistance to wetting. More water had to be added to

the non-water repellent mortars to produce equal ease of working

resistance values within the same range. ‘The relation between resistance and water content of a few mortars of the ”X” type was observed,

demonstrating two important facts; (l) that to obtain the same resistance values for different cements in mortar ”X”, the water requirement

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Varied over a wide range; (2) *h&t the resistance values of mprt&rs

of some of the cements change more rapidly than others with equal

changes in mixing water,. Increased resistance was noted between mortar

"X" and mortar "Y"; the latter being more resistant because of its

greater proportion of sand and therefore having a lesser amount of

cement -water paste, which latter furnishes the plasticizing or "workreducing" agent in mortar. This same mortar "Y" made from graded sand

and containing considerable "fines" required more water than mortar "X"

containing larger sand particles.

Water retaining capacities of mortars were measured by subjecting

them to a suction equivalent to that produced by a dry process brick

having an absorption of about 6.5 percent in three minutes. Composition of the mortar seemed to be the dominant feature controlling this

property. Natural cements, cements containing considerable hydrated

lime or partially hydrated additions were high in water retention; a Portland cement -hydrated lime mixture being the highest. It was not

possible to say if these materials were effective only because of

their extreme fineness of grind or their nature being such as to hold

tenaciously large amounts of water. The least amount of water was retained by a cement largely Portland; cements containing large

amounts of slag and largely of port land cement lost greater percentages

of mixing water than those of other classes. Cements requiring smaller

amounts of water to produce workability and retaining this when on an absorbent brick usually had other good characteristics. The cements re- taining no less than 0.9 and 0.85 percent of mixing water at normal

flow^ for one and three minutes of suction, respectively, retained a satisfactory workability. Water-repellent additions in cements were

not effective in reducing the withdrawal of water. With but three ex- ceptions no more water was extracted by the three minute suction than

by the one minute.

Volume yields of various mortars were found to be influenced by

the incorporation of air; larger yields were due to larger volumes

of air in the mortar, the increase being nearly proportional to the

amount of air retained. Mortars containing water-repellent cements

retained the greater amount of air* The greatest amount of air con- tained by a non-water-repellent cement mortar was 7 percent; only

two of twenty-three mortars with water-repellent cements contained

less than 8 percent and only six less than 14 percent.

qNormal flow determined with apparatus developed by Committee

C— 1 , Cement, American Society for Testing Materials, for a study of

a method to determine the normal consistency of port land cement

pastes

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Linear change measurements, during and after hardening, were

made with specimens of mortar with three different proportions

of water; that required for normal flow, that with 1 percent more,

and that with 1 percent less. During' the first twenty-four hours,

shrinkage varied from .087 to .585 percent. Little difference was noted between cements with and without water-repellents at twentyfour hours; the length changes during the immediate year following

being small compared to those of the first twenty-four hours. Ho

relation could be found between linear changes and other properties

of mortars, nor were there any data conclusive enough to indicate

the maximum amount of changes permissible.

Compressive tests were made with all four mortars. The masonry

and portland cements acted in much the same manner with increased

amounts of water; such increases producing lesser strengths. Portland cement mortars and those with large proportions of portland

cement gave greater strength than those with smaller proportions,

and such cements as hydraulic lime, while having little strength at

early ages, increased in strength with time pr oport ionately more

than most others. It is evident that a wide variety of compositions

may be used and good strengths obtained. Strength was shown to in- crease with age in the case of all the cements. Increased strengths were also noted in mortar "X-l 7

’ {using mixed sand) as compared with

mortar "X” (using standard sand). Compressive strengths varied over

a wide range, the twenty-eight day strength of mortar "Y” ranging

from 50 to 3,650 pounds per sq. in., and the strengths of the fortyone cements scattered between these extremes. Thirteen were below

300 pounds and twenty-two below 600 pounds per sq. in.

As in the compressive tests, cements richest in portland cement

tended to give mortars with higher transverse strengths, the modulus

of rupture showing an approximate relation to compressive strength,

with twenty-eight day mortars varying from 25 to 590 pounds per sq.

in.

The durability of the mortars when subjected to freezing and

thawing tests could be predicted with reasonable accuracy in the time

required for mortar specimens, each 1x4x6 in. and 28 days old,

to attain 90 percent of their seventy-two hour absorption. The specimens, with one exception, requiring more than one hour to absorb 90

percent of the water that would otherwise be absorbed in seventy-two

hours, were not' disrupted by ten cycles of freezing and thawing.

'There was little difference in the destructive action of freezing

and thawing on the rich mortar ”X” and the leaner mortar ”Y". Comparing the results of these tests with those of compressive and transverse strengths it was noted that mortars of low strength or low

modulus, with one exception, showed poor resistance. Higher resistances

generally resulted in mortars whose cements were rich in portland.

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Water-repellent cements were, as a group, more durable than the 'nonwater-repellent types. Mortar ’hZ” at twenty-eight days had but three

failures .out of twenty-three water-repellent cements in ten freezings

and thawings, whereas, thirteen non-water-repellent cements out of

seventeen failed in ten freezing and thawing cycles.

The linear rise of water in the specimens also gave indication

of their durability. The halves of the broken specimens previously

used for transverse strength tests, were placed on end in water to a depth of one-half inch and the heights to which they became wet were measured over periods of time up to seventy-two hours. Mortars having a two inch rise in one hour or less, all failed in ten or less

cycles of freezing and thawing. In fifty-nine cases, out of seventyone, mortars showing a rise of two inches in three hours or less

failed in ten cycles. The leaner mortar ”Y: ’ shoved a more rapid rise

than mortar :,X”, and with both types the rise at seven days' age was more rapid than at twenty-eight days.

Efflorescence observations were made at the end of a three months

storage period showing generally that the development of efflorescence

depends upon the composition of cement. Efflorescence was observed on specimens with all of the six cements containing natural cement, one

of the two of unidentified composition, three of the eight of portland

cement and lime, two of the six with large- amounts of slag, two of the

ten of portland cement and unidentified material, and one of the seven

classed as largely portland cement.

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