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UBLICATION

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DEC 3 0 1970

A111D3 D7M71S

taken 1 i '

BUILDING SCIENCE SERIES

28

U.S.

APARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Exploratory Studies

of Early Strength

Development in

Portland Cement

Pastes and Mortars
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UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

Exploratory Studies of Early Strength Development

In Portland Cement Pastes and Mortars

R. L. Blaine and L. A. Tomes

Building Research Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 28, 14 pages (July 1970) CODEN: BSSNB

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Building Science Series 28

Issued July 1970
NATIONAL BUREAU OF STANUWuo

SEP 1 2 1971 ^1

Contents

Page

1. Introduction 1

2. Apparatus 1

3. Cements 2

4. Methods of Tests 3

5. Results of Tests 4

6. Discussion 7

7. Summary and Conclusions 9

8. References 10

Appendix A 10

Appendix B 11

II
Exploratory Studies of Early Strength Development

In Portland Cement Pastes and Mortars

R. L. Blaine* and L. A. Tomes*

A modified vane-shear apparatus was used to measure the shear resistance of neat cement

pastes of normal consistency and 1:2.75 (cement to sand) mortars of standard consistency, and

to measure the increase in shear resistance with time as the cements hardened. The hardening

process appeared to occur in three stages. The rate of increase of shear resistance as well as the duration of the different phases differed with the different cements. The results were

analyzed in terms of the various theories proposed to explain the hardening of cements. Key words: Cement; cement mortar; cement paste; early strength; false set; hardening of cement; hydration; shear resistance; theory of cement hardening; time of set; vane-shear

apparatus.

1. Introduction

There is extensive literature dealing with the early

hydration reactions of portland cements and the de- velopment of structure which causes stiifening and

hardening [1-6]. The plasticity as well as the rate of stiffening and hardening of cement pastes, mortars,

and concretes are of great importance in the construction industry. The rheology of freshly mixed cementwater pastes, mortars, and concretes have been studied

by various means, using viscometers [7] , shear ap- paratus [8] , penetrometers [9] as well as pull-out pins

[10], soniscope [11], and other devices. A discussion

of the various methods was presented by Kelly [12]

and the reactions involved have been reviewed by

Steinour [13] and more recently by Kondo and

Ueda [6] . The Vicat and Gillmore needles are also used for determining time of set, that is, the time at which the neat cement pastes have attained strength

adequate to prevent a penetration of the Gillmore

needles or a limited penetration of the Vicat needle.

It has been stated [3] that "Published information on the viscosity or consistency of cement pastes during

the early period of hydration is scanty, however, and

somewhat lacking in agreement . . .". One of the problems has been the lack of apparatus sensitive enough to measure small differences in rheological

properties but with a sufficient range to evaluate any

strength from the time of mixing to the time of hardening. The present exploratory studies are reported

at this time to indicate the application of a modified

vane-shear apparatus in obtaining information on

changes of rheological properties and apparent de- velopment of structure of cement pastes and mortars

during the first two to three hours after mixing.

The vane-shear apparatus has been used in measuring the rheological properties of soils and many articles have been published with respect to its use [14-18]

.

These articles also give reference to many other publications in the field. One of the problems associated

with its use has been the fact that the soil sample is disturbed when the vane is inserted. This would

also happen if the vane were inserted in hardening cement paste. It was therefore necessary to modify

the apparatus and techniques for use in studying the early hardening of cement pastes and mortars as indi- cated in the following sections and in the appendix A.

2. Apparatus

The commercially available vane-shear apparatus

as modified is shown in figure 1. The vanes are placed

in the freshly mixed mortar. The torque is applied

by means of a helical spring through a couple of universal joints and a sheet of polytetrafluoroethylene

is used as a base plate to minimize the friction beFicURE 1. Vane-shear apparatus and extra springs.

^ Figures in bracltets refer to the literature references on page Deceased. Both formerly associated with the Building Research

Division, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

1
tween the vane and base. It was also necessary to make a spring with about a tenth the strength of the weakest spring which came with the apparatus in order to make measurements on the plastic mortars. Linkage between the shear apparatus and the vanes

is indicated in figure 2 and described in appendix A.

®

®

SILVER SOLDER

(s)

FLATTEN ONE SIDE FOR SET SCREW

0.5 cm ROUND STEEL

SILVER SOLDER —0.9 cm ROUND STEEL

1.5 cm

SILVER SOLDER

0.5 cm ROUND STEEL

STEEL NUT BRASS 2mm (SQUARE)

BOTTOM VIEW 'B' HOLLOW ^ O.e cm

% 0.4cm SQUARE «0.5em AT MIDDLE

LOOSE FIT B

I cm VANE BOTTOM

VIEW

.5mm, 3mm DEEP

1.6 mm SHEET

STEEL BENT KfL

Lk 45* ALL VANES

SIDES AND BOTTOM 2cm VANE

Figure 2a. Vanes and linkage between shear apparatus and

vanes.

FASTENED TO SPRING LOADING DEVICE

0.5 em. STEEL

••-CORO

CRADLE FROM

BALANCE

-WEIGHTS ^BALANCE PAN

Figure 2b. Calibration of springs in shear apparatus.^

The springs were calibrated using a cord attached | to a horizontal rod 10 cm from the center of the

spring, (see appendix B and Figure 2b) The cord

passed over a' pulley to a balance cradle and pan and

a series of weights were placed on the pan noting

the number of degrees of rotation required to bring

the spring and weights to equilibrium. Plots of the

rotation values versus the weights resulted in straight

lines passing through the origin with each of the

springs. The constants for the springs used in this study were calculated in terms of the grams per de- gree rotation at 1 cm radius. The weakest spring had

a value of 1.91 g/deg rotation, the second spring 21.4

g/deg and the strongest spring 44.9 g/deg.

The vanes were made of 1.6 mm steel sheets bent at right angles and silver soldered together as indicated

in figure 2. They were then machined to size ±0.05

mm and the side edges and bottom edges beveled

(see figure 2a) to relieve any friction between the edges and mortar or paste when the vane was rotated. Vanes were made having a width or diameter of 1, and 2 cm. The 1 cm vanes were made for use in a 2.5 cm-deep mold* and the 2 cm vanes for use in a 4

cm-deep mold.** The lengths of the vanes were about

1 cm greater than the depth of the respective molds.

The equation used to compute the shear values was

as follows:

5= degrees rotation X spring constant n {D H r)

where 5 = shear resistance

7r = pi = 3.1416

D = width of vane or diameter = depth of vane in mortar or paste

r = radius of vane. This does not take into account any end effect. If

effect of the bottom of the vane is included, the

equation would be as follows:

degrees rotation X spring constant

TT (D H r + « 4D)

If the depth in mortar and paste is constant and

only one size vane used, the shear equals a constant times the degrees of rotation. The constants used with

the different springs would be different depending on

their calibration factor.

3. Cements >

Tests were made on six portland cements which

had previously been used in the Cement and Concrete

Reference Laboratory (CCRL) interlaboratory refer- ence sample program. These included two type I (CCRL Nos. 3 & 4), two type lA (CCRL Nos. 5 & 6),

and two type III (CCRL Nos. 9 & 10) cements. The

chemical composition and results of some of the

ASTM Designation C190, Tensile Strength of Hydraulic Cement

Mortars.

•* ASTM Designation C348, Flexural Strength of Hydraulic Cement Mortars.

2
physical tests as determined in Cement and Concrete

Reference Laboratory interlaboratory tests are pre- sented in table 1. These values are the averages of values reported by all laboratories after outlying re- sults from a few laboratories had been eliminated.

There were 85 to 145 laboratories reporting chemical

results and 104 to 162 laboratories reporting physical

results. The estimated standard deviations of the time of set values determined by the different laboratories ranged from 14 to 28 min for Vicat time of

set, from 22 to 36 min for Gillmore initial set and from

44 to 56 min for Gillmore final set.

4. Methods of Tests

A number of preliminary tests were made using the

different sized vanes in different molds before adopting the techniques presented in this report. Further

information about the preliminary tests will be pre- sented in the discussion. Tests were made on neat cement pastes mixed in a mechanical mixer in accordance with specification

ASTM Designation C3()5-65 except that 1400 g of cement were used. The percentage water was that given in table 1. After mixing, a scoop of paste was

placed in each of 3 molds of a 3-gang briquet mold

and this was then vibrated sufficiently to cause the paste to flow to the edges,—about 5 to 10 s. The ex- cess paste was cut off,^—the mold trowelled once and

then cut off with a sharp trowel using a sawing motion. One of the 1 cm vanes was placed in each half of the briquet at about the center of the broadest

dimensions making six vanes for each mold. The

mold with paste and vanes was then given 2 or 3

Table 1. Average values for chemical analyses and physical tests reported for Cement and Concrete Reference Laboratory

interlaboratory tests on six cements

Cement No. 3 4 5 6 9 10 SiO^ % 20.52 21.31 20.21 21.68 20.14 20.09 % 5.05 449 6.12 5.51 4.84 5.42

Fe,03 % 2.96 2.89 2.17 2.34 2.26 2.43 CaO % 62.79 63.11 63.61 63.42 62.89 65.46 MgO % 423 433 2.77 2.35 3.90 1.66

SO3 % 2.42 2.29 2.65 2.81 3.52 3.12

Loss % 1.14 0.83 1.15 1.00 1.76 1.06

Insol % 0.19 0.15 0.15 0.22 0.33 0.13 Na^O % .13 .19 .35 .31 .19 .15 K^O % .82 .64 .96 .79 .57 .63

Normal consistency, H^O % 240 25.62 25.49 25.57 28.53 26.87

Vicat time of set, min 147 207 123 103 155 77

Gillmore initial set, min 177 223 158 145 196 120

Gillmore final set, min 300 335 283 270 316 221

Air content, 1:4 mortar, % 9.6 8.8 18.6 18.3 10.0 10.8

HjO, 1:2.75 mortar, % 46.6 47.0 45.2 45.5 50.0 47.8 Comp str, Id psi 3318 3590

Comp str, 3d psi 3060 3310 2913 2665 5041 5058

Comp str, 7d psi 3990 4320 3615 3504

Fineness (air perm), cm^/g 3379 3537 3358 3782 5784 4857

C3A (3CaO • AI2O3), %* 8 7 13 11 9 10

C3S (3CaO • SiO^), %* 55 54 55 45 57 65

C3S (2CaO • SiO^), %* 18 20 17 28 15 9

C^AF (4CaO • ALfi^ • Fefi^), %* 9 9 7 7 7 7

Potential compound composition calculated from average values

reported.
short "bursts" of vibration (1 to 2 s) to settle the paste back around the vanes. The molds and vanes were then covered with a thin transparent plastic sheet. Four 3-gang molds were filled as rapidly as possible.

This usually required about 6 to 7 min.

In vibrating the molds, a vibrator table with fre- quency of 60 Hz was used with an amplitude of 0.4 mm. The molds were held on the vibrating table by hand—i.e. no clamps were used, hence the amplitude of vibration of the mold was less than that noted on the dial indicator. A minimum of vibration was used in order to avoid as much as possible the bleeding and segregation that may occur with excessive vibration. The shear tests were normally started at 10 min

after making the first specimen. In making the shear

test, the load-transfer device was placed on top of a vane and universal joints and spring section lowered

onto the load-transfer device. Torque was then ap- plied to the spring by means of a worm gear and the number of degrees of rotation required to cause a shear failure (that is the maximum torque developed) was observed and noted. Measurements were made on

the other vanes at various intervals as noted in the

figures until the capacity of the apparatus was ap- proached or no more vanes remained to be tested. Tests were also made of 2 cements using 3 per- centage points more water than that required for normal consistency.

A series of tests was also made on 1:2.75 (cement to graded Ottawa sand) mortars using the standard mixing procedure and the amount of water noted in table

1. The mortar was vibrated only a few seconds, cut

off, trowelled once, sawed off. and the 1 cm vanes

inserted and a "burst" or two of vibration was used

to consolidate the mortar around the vanes. One

test was made with one of the cements which had a moderate amount of premature stiffening. In this case the sand and cement were mixed dry, the water added in 5 s and the mortar mixed for only 30 s at the medium speed.

A third series of tests on these cements was made

using the 2 cm vanes in 4 X 4 X 16-cm molds, placing 3 vanes in each mold.

5. Results of Tests

The results of tests on the neat cement pastes are presented in figures 3, 4 and 5, plotting individual

shear-strength values in g/cm- versus time in minutes on a log-log scale. A series of three straight lines giving the best visual fit were drawn through the values obtained with each of the cements; the values ap- peared reasonably close to the lines drawn. There

were, as may be noted, some values especially in the 10

to 50 min measurements which were erratic. The slopes of the lines for the different phases of the hardening process were different with the dif- ferent cements and were of different duration. Increas- ing the water content by 3 percentage points delayed

by 10 to 20 min the start of the second phase and

about 20 min the start of the third phase with cements

5 and 9. Indicated on these graphs are the values for Vicat

time of set and the times of Gillmore initial and final

set values as obtained in table 1. At the time of the Vicat initial set, the shear resistance ranged from

400 to 1200 g/cm- with four of the cements (Nos

3, 6, 9, and 10) ; this was shortly after the start of the

third phase. With two of the cements, (Nos. 4 and

5) the Vicat time of set came somewhat later. At the time of initial set as determined by means of the Gillmore needle, the six cements had a shear resistance ranging from 1300 to 3200 g/cm- with an average

of about 2100 g/cm-. With the apparatus used to- gether with the size of the vanes and depth of the

paste, it was not possible to obtain the shear resistance

at the time of the Gillmore final set. Extrapolating

the third phase lines to the time of final set would

indicate a shear resistance of 10,000 to 20,000 g/cm^.

The results of tests of the 1:2.75 mortars are pre- sented in figures 6, 7, and 8. The results obtained for cements 4 and 5 were somewhat erratic,—especially

in the first and second phases of the hardening process. The time of inflection in the curves obtained with the mortars are close to those obtained in the curves for

the neat cement. If the lines drawn through the values obtained on the 1:2.75 mortar are superimposed on

the lines drawn through the values obtained with

20,000

10,000 -

Figure 3. Graph indicating shear strength in g/cm^ versus time in minutes for neat pastes of normal consistencies of cements 3 and 4. t/=Time of Vicat time cf set, G/=GilImore initial set, GF=Gillmore final set.

4
Figure 4. Graph indicating shear strength in g/ cnfi versus time in minutes for neat pastes of normal con- sistency of cements 5 and 6. V=:Time of Vicat time of set, G/=Gillmore initial set, GF=Gillmore final set, Af.C.=Normal consistency.N.C. +3=:Normal consistency plus 3.0 percentage points extra water.

Figure 5. Graph indicating shear strength in g/ cm^ versus time in minutes for neat pastes of normal con- sistency of cements 9 and 10. V=Time of Vicat time of set, G/=Gillmore initial set, GF=Gillmore final set, N.C.=Normal consistency,N.C. +3=:Normal consistency plus 3.0 percentage points extra water.

Figure 6. Graph indicating shear strength in g/cm^ versus Figure 7. Graph indicating shear strength in g/cm- versus time in minutes of 1 :2.75 mortars of standard con- time in minutes of 1 :2.75 mortars of standard consistency, cements 3 and 4. sistency, cements 5 and 6.

5
1—I I

I 1 1 11

1

"I I I I I I

I I I

I I I I I 1

1

20 50 100 200

I I I I I I I I I I I 10 20 50 100 300

TIME.min

Figure 8. Graph indicating shear strength in g/arfl versus time in minutes of 1:2.75 mortars of standard consistency, cements 9 and 10.

- 11 1 1 1 1 1 II 1 1 1 1 1 1 III 1 1 1-

neat/ /l:2.75

'3 NEAT/ / / r

/ /h2.75 —

1

1

10 20

1 1 1 1 1 1 1 1 50 1001 1 1 1 1 1 II 200 400

1 1 1 ID 20 50 100 200 400

TIME.min FicuHE 9. Graph superimposing the shear strengths of neat cements and mortars of cements 3 and 4.

10,000

5,000 -

2.000

~£ 500 -

200

100 -

50

20

T I

I II II II

1—I I I 1 1 II

I r

2.75

10 20 50 100 200 400 J I I I I I III \ I 1 I I I III I 1_L_

lO 20 50 100 200 400

TIME.min

Figure 10. Graph superimposing the shear strengths of neat cements and mortars of cements 5 and 6.

50 100 200 400

TIME.min

Figure 11. Graph superimposing the shear strength of neat cements and mortars of cements 9 and 10.

the respective neat cement pastes as indicated in

figures 9, 10, and 11, it may be noted that the curves

cross. Whereas, the mortars had greater shear resist- ance at the start of the test, the shear resistance de- veloped more slowly for the first two phases of the hardening process and with some of the cements the

lines representing the third phase appeared less steep.

A single test was made of the cement having moderate false set. The Shear resistance of the mortar mixed

for 30 s was higher than that occurring when the normal mixing procedure was used as indicated in figure 12. There was no increase in shear resistance

for 50 to 60 min. The slope of the second phase was

6
TIME.min

Figure 12. Graph indicating the effect of time of mixing a 1:275 mortar (cement to graded Ottawa sand) on

the shear strength versus time using a cement hav- ing a moderate amount of false set.

less than that of the mortar mixed for the time

required in specifications. Only one value was obtained in the third phase and this was close to the

line obtained with the mortar mixed according to specification requirements. In figures 13 and 14 the results obtained with the six cements have been traced on the same graphs. The

lines of the first two phases appear to cross to a greater

extent than was the case in the third phase. Most of

the lines in the third phase were fairly parallel on the

log-log plot but were displaced with respect to the time the phase started. Although a log-log plot was used to show the overall picture of the hardening process, the first phase

may well be presented on a linear plot graph as in figure 15. The early stiffening as measured by means

of the vane shear apparatus resulted in straight lines. The slopes of the lines obtained with the different cements differ to some extent and if a shear test is used to measure the plasticity of neat cement paste or

TIME , min

Figure 13. Graph indicating the shtur strength in gl cm^

versus time in minutes of the six neat cements of normal consistency.

mortar, attention must be given to the time after mixing, or placing, that the test is made.

6. Discussion

Many theories have been proposed relating to the mechanism of the early development of structure in hardening cement pastes. These have been reviewed

by Green [3] and more recently by Kondo and Ueda

[6]. Among these theories were those of Segalova

[19] and Rehbinder [20] who proposed, on the

basis of work by a previous Russian research Avorker, A. A. Baikov, that there were three phases in the hardening process which may overlap in time. The

first phase was a colloidization of the cement particles,

especially the C^A (tricalcium aluminate) after which

there is a coagulation of cement particles and reaction

products and finally the development of new hydrated

compounds through crystallization which brings about

the strengthening.

Sivertsev [21] considered that the initial phase of

the setting process was the absorption of water by the
5,000 —

i;2.75

2,000

1,000

500 —

"e

(J

on —

< 200 —

100 —

TIME, min

Figure 14. Graph indicating the shear strength in g/ cm^

versus time in minutes of the six 1 :2.75 (cement

to graded Ottawa sand) mortars of standard consistency.

cement particles, which was followed by formation of micelles which later coagulate into structures. Budnikov

and Strelkov [22] have shown that a fibrous material

is formed within the first few seconds. These fibrous

materials were noted in extracts from cement-water

mixtures. The extracts were dried and observed using

a microscope.

Schwietes, Ludwig and Jager [23] have presented

electron micrographs indicating that ettringite is formed on .the C,A in the form of needles within a few minutes and lance-like foils of Ca(0H)2 had also formed on the CaO.

Even after a few minutes contact with water there is (1) an apparent roughening of the cement particles

(especially the CgA) [23] making it more difficult for

the particles to move past each other in the shear test, (2) a reduction in the amount of free water because

of the approximately 31 molecules of water taken up

per molecule of ettringite, lowering the water/cement

ratio of the paste, and (3) a solution of some of the compounds in cement which may be absorbed on the grains of cement [22] . All or combinations of these

factors may be responsible for the slight increase in

TIME , min

Figure 15. Graph indicating the shear strengths in glcmversus time in minutes of neat cement pastes of normal consistency.

shear resistance in the first phase of the hardening

process. The second phase which coincides approximately

with the time of the start of the second increase in heat

generated by cements may be, as suggested by Sivertsev

[21], the formation of micelles which then filled the space occupied by the free water. Increasing the water/cement ratio with cements 5 and 9 increased

the time at which the second phase started by 10 to 20 min. The 1:2.75 mortars with a higher water/cement ratio had generally a slightly longer first period

than the neat cements with the lower W/C. In some

instances, however, the times of the first inflection of the curves were very close. Early investigators in

this field have indicated that the solutions are super- saturated which may account for the formation of

the micelles. The third phase, starting at 80 to 160 min with dif- ferent cements after mixing with water, may indicate

the start of chemical bonding of the hydration products. Cement pats at this stage will normally have

lost their sheen, indicating the end of the bleeding

period and the continuing uptake of water by the hydration process. It was of interest to note in comparing the curves of the 1:2.75 mortars and those of the neat cements, that the time of the start of this phase

was, with each of the cements, within 10 to 20 min,

irrespective of the differences in water/cement ratios and the presence of sand grains in the mortars.

It was observed in conducting the shear test that the method of failure was not always the same. In the

first phase the paste or mortar built up in front of the vane and a space was noted in back of each vane. There were no visible cracks extending into the rest of

the paste from the edge of the vane. As the paste be- came stiffer, as in phase two, cracks were noted

from the edges of the vanes in the direction the blades were turning. The V-shaped cracks extended half a centimeter in some instances and the paste or mortar at time of failure was not attached to the back of the

8
I vane. This effect in soil tests has previously been

noted by Wilson [16d]. No cracks were noted at the higher shear strengths and the pastes and mortars

appeared attached to both sides of each vane.

I Regardless of the interpretation and/or significance

of the three phases of hardening of neat cement pastes

and mortars observed in these exploratory tests, it appears that the vane shear apparatus offers an exI cellent means for studying this phenomenon. It also

j appears that the apparatus would offer a means for studying the effects of different admixtures on cements,

j The apparatus may also be used to determine the

i consistency of cement pastes and mortars, obtaining

j the values in terms of g/cm^ instead of percent flow on a flow table or penetration of a cylinder or needle

of specified weight and diameter.

As indicated earlier, many papers [14-18] have

i been published on the use of the vane-shear apparatus

for measuring the shear strength of soils. Among the

' variables that have been studied and reviewed by

Brand [18] are the vane geometry (height to diameter

j ratio) and the number of blades, the effect of the rate

! of strain, the mode of failure, the effect of inhomogeneity, anisotropy, and effect of soil disturbance.

! The last three items would possibly not affect the tests on neat pastes or mortars as conducted in the present

studies. More work is necessary and certain refinements in both apparatus and techniques appear desirable. In

correlating these values for rate of hardening with

existing time of set tests it would be desirable to have an apparatus rugged enough to measure a shear

strength of 20,000 to 30,000 g/cm' (about that cor- responding to final set as determined by the Gillmore

apparatus) after which compressive strength measurements could be made to follow further strength

development. It would have been possible to increase

the range of the instrument used by using smaller vanes and a shallower depth of paste or mortar. It appeared desirable to use only the one size vane

(1 cm diameter) in each series of tests, changing

the springs as necessary to make the measurements

of the more mature pastes. With the neat cement

pastes, there was the problem of relatively large oc- cluded air bubbles making some of the measurements

of questionable value when the air bubbles were in the shear plane. The use of larger vanes would give a better ratio of diameter of vane to diameter of bubbles of occluded air, but more air bubbles would

be present in the shear plane and it would not be

possible with the apparatus used to follow the strength

development past the time of initial set. Another problem with the small vanes was their tendency to tilt as

the mortar or paste was vibrated into place. This could

possibly be remedied by using some type of jig for holding them in place until after the mortar or paste

had been vibrated in place around the vanes. For

measurements of consistency of freshly mixed pastes or mortars, the larger vanes (2 or 3 cm) appear desirable because they do not tilt as readily as the 1 cm vanes. In preliminary tests using a 2.5 X 2.5 X 28 cm

mold, the specimen cracked lengthwise instead of shearing out a cylinder. This occurred only at the higher shearing values but prompted the use of briquette molds with more rigid sides in later tests. This also helped to isolate the vanes to a greater

extent.

In calculations of shear resistance the effect at the end of the vane was ignored. This may or may not have had an effect. Brand [18] indicated that with

a vane of height twice the diameter the end effect would account for only 3 to 4 percent of the shear

value. With a 2^2 to 1 ratio for height to diameter, the end effect should be less. Although polytetrafluoroethylene was used as a base, there was some bond be- tween the cement paste and the plastic at the later ages. The effect of method of placement and amount of

vibration used in forming the paste and mortar speci- mens and setting of the vanes requires further study.

Some preliminary tests with lighter gage brass vanes

indicated that they were deformed at high shear values. During the past 20 years, much research has been

conducted relating the shear of soils as measured by

the vane-shear apparatus and shear tests conducted

by other means. There have also been published dis- cussions of the nature of the shear, the stresses in- volved, the effect of pore-water pressure or dilatency

at the edge of the vane, and how the linear stresses are translated to a circular stress to shear out a

cylinder. Very little appears to be known with respect

to the distribution of the stresses on the boundary

between soil and the testing device. The authors are

not aware of any photoelastic studies of the stresses generated by a turning vane of the type used. Al- though the apparatus appears very simple, there are, as indicated by a review of many articles on soil mechanics, still many unknown factors which need

further study and clarification. Although a four-bladed vane was used in these

tests on pastes and mortars, a shear-vane having the configuration of a spline shaft may possibly be better

for use in concrete in order to avoid having large

aggregates in the shear plane. The edges away from

the lead edges of the splines would have to be cut back or beveled to avoid friction with the mortar.

7. Summary and Conclusions

The results of exploratory studies indicated that a modified vane shear apparatus offers a means for determining the early strength development in portland cement pastes and mortars. The shear tests indi- cated what appear to be three distinct phases in the

setting and early hardening process as postulated

earlier by various authors as cited. Three phases were

evident in each of the six cements tested and in both

neat cement pastes and in cement-sand mortars. The

rate of increase of shear resistance with time as well

as the duration of the different phases differed with the

different cements.

9

!
8. References

[1] Bogue, R. H., The Chemistry of Portland Cement, 2nd

edition, p 647-690 (Reinhold Publishing Corp., New York,

1955).

[2] Lea, F. M., and Desch, C. H., The Chemistry of Cement

and Concrete, (Revised edition), p 215-260. (St. Martin's

Press Inc., New York, 1956).

[3] Greene, Kenneth T., Early hydration reactions of port- land cement. Proceedings of the Fourth International Symposium on the Chemistry of Cements, Nat. Bur. Stand.

(U.S.), Monogr. 43, Vol. 1, p 359, Aug. 1962.

[4] Schwiete, H. E., Ludwig, U., and Jager, P. Investigations

in the system 3 CaO • AI2O3 • CaSO, • CaO • H2O,

Symposium on Structure of Portland Cement Paste and

Concrete, Highway Research Board, NRC SP 90 p

353, 1966. [5] Budnikov, P. P., Strelkov, M. I., Some recent concepts on Portland cement hydration and hardening. Symposium

on Structure of Portland Cement Paste and Concrete, Highway Research Board, NRC, SP 90 p 447, 1966.

[6] Kondo, R., and Ueda, S., Kinetics and mechanisms of the hydration of cements. Proceedings of the Fifth Inter- national Symposium on the Chemistry of Cement, Vol. II, p 203, Tokyo, 1968. See also Discussion by Stein, H. N., Proceedings of the Fifth International Symposium on

the Chemistry of Cement, Vol. II, p 248, Tokyo, 1968. [7] Ish-Shalom, Moshe, and Greenberg, S. A., The rheology

of fresh portland cement pastes. Proceedings of the Fourth International Symposium on the Chemistry of Cements, Nat. Bur. Stand. (U.S.), Monogr. 43 Vol 2, p

731, Sept. 1962. [8] Hershel, W. H., and Pissapia, E. A., Factors of workability of Portland cement concrete, Proc. A.C.I. Vol. 32, p

631-658 (1936).

[9] Tuthill, L. H., and Cordon, W. A., Properties and

uses of initially retarded concrete, A.C.I., Proc. Vol. 52, p 273, Nov. 1955, and Discussion, A.C.I., Proc. Vol. 52, p 1187, Dec. 1956. [10] Kelly, T. M. and Bryant, D. E., Measuring the rate of hardening of concrete by bond pullout pins, Proc. ASTM,

Vol. 57, p 1029, 1957. [11] Whitehurst, E. A., Use of the soniscope for measuring

setting time of concrete, Proc. ASTM Vol. 51, p 1166 and p 1176, 1951. [12] Kelly, T. M., Setting Time. Significance of tests and

properties of concrete and concrete-making materials, ASTM STP 169A, p 102, 1966. [13] Steinour, Harold, H., The Setting of Portland Cement, A

Review of Theory, Performance and Control, Bulletin 98, Research and Development Laboratories of the Port- land Cement Association, Research Department, Nov.

1958. [14] ASTM Symposium on Vane Shear Testing of Soils, ASTM STP 193 (1957).

(a) Osterberg, J. 0., Introduction, p. 1. (b) Gibbs, H. J. An apparatus and method of vane

shear testing of soils, p 9. (c) Fenske, C. W., Deep vane tests in Gulf of Mexico,

p. 16. (d) Hill, W. C, Vane in-place shear device developed and applied by Oergon State Highway Department,

p. 26. (e) Eden, W. J., and Hamilton, J. J., The use of a field vane apparatus in sensitive clay, p 41. Discussions by Anderson, A., Kallstenius, Torsten, Cadling, L., and Lindskog, G., Housel, W. S., Burmister, D. M., and Osterberg, J. 0. [15] ASTM Symposium on Soil Exploration, ASTM STP No.

351 (1963).

(a) Liu, T. K., and Thornburn, T. H., Investigation of

surficial soils by field vane test, p 44. (b) Hall, E. B., Shear-strength of soft clayey soil by

field and laboratory methods, p 53. [16] ASTM Symposium on Laboratory Shear Testing of Soils, ASTM, STP 361 (1%5).

(a) Roscoe, K. H., Schofield, A. N., and Thurairjah, A..J An evaluation of test data for selecting a yieldj criterion for soils, p 111.

j (b) Rowe, P. W., Stress Dilatancy Performance of Clays.- p 135.

(c) Schmertmann, J. H., Generalizing and measuringthe Hvorsley effective components of shear resistance, p 147. (d) Wilson, N. E., Laboratory vane shear tests and thd

influence of pore-water stresses, p 377. [17] ASTM Symposium on Vane Shear and Cone Penetrationr! Resistance Testing of In-Situ Soils, ASTM STP 399,;: (1965). j (a) Andresen, A., and SoUie, S., An inspection vane,-' p 3. (b) Eden, W. J., An evaluation of the field vane test in| sensitive clay, p 8.

] (c) Miller, E. A., and Hall, E. B., A comparison of soil; shear strengths as determined with field and labora- j tory vane shear apparatus, p 18. (d) Sibley, E. A., and Yamane, G., A simple shear test 1 for saturated cohesive soils, p 39.

j [18] Brand, E. W., The Vane Shear Test and its use for.1 Strength Measurements of Cohesive Soils, Bulletin, The

International Union of Testing and Research Laboratories

for Materials and Structures (RILEM) Bulletin 36, Sept. 1967. [19] Segalova, E. E., and Solovyeva, E. S., Study of the mechansm of structure formation in cement suspensions and effect of admixtures of hydrophilic plasticizers on

these processes. Reports of Symposium on the Chemistry

of Cements. State Publication of Literature on Structural

Materials, Moscow (1956). Translated from Russian by

Margaret Corbin, Portland Cement Association, Skokie,

111. [20] Rehbinder, P. A., Physico-chemical concepts of the mechanism of setting and hardening of mineral binders, Reports of Symposium on the Chemistry of Cement, State Publication of Literature on Structural Materials, Moscow

(1956). Translated from Russian by Margaret Corbin, Portland Cement Association, Skokie, IlL [21] Sivertsev, G. N., Some experimental preliminaries for the formation of a general theory of cement hardening based on colloid chemistry. Reports on the Chemistry of Ce- ments, State Publication of Literature on Structural

Materials, Moscow, (1956) Translated from Russian by

Margaret Corbin, Portland Cement Association, Skokie,

111. [22] Budnikov, P. P., and Strelkov, M. I., Some recent con- cepts on Portland cement hydration and hardening,

Symposium on Structure of Portland Cement Paste and

Concrete. SP 90, Highway Research Board, Wash., D.C.

(1966).

[23] Schwiete, H. E., Ludwig, U., and Jager, P., Investigations in the systems 3 CaO»Al203»CaSo4»CaO»H20, Symposium on Structure of Portland Cement Paste and Concrete. SP 90, Highway Research Board, NRC, Wash.,

D.C. (1966).

Appendix A

Modifications of the shear apparatus linkage are

indicated in figure 2a. Part "A" of figure 2a is attached to the spring

portion of the apparatus by means of a set screw. Part "B" is hooked over part "A" and acts as a universal joini when torque is applied. Actually the contact is on the sides of the hook when the spring portion and part "A" are lowered onto the load transfer device "C". The upper section of part "C" is square in cross section and somewhat larger in the midsection than at the top or bottom and fits rather

loosely in order to act as a universal joint with the

10
^bottom hollow portion of part "B". The bottom of

part "C" has notches at right angles to fit over and

J engage the vanes, part "D", and transfers the torque

to the vanes. Some details of the 2 cm vane are

5 indicated in part "E".

" The worm-gear for loading the spring in the ap3 paratus used had a 30 to 1 ratio. The gear was turned

at the rate of 1 revolution per second. With diflferent

' strength springs, the rate of loading would then be

' different and no account was taken of this in computations of shear resistance.

1 In making a shear test, the load transfer device "C"

\ was placed on the vane "D" which was previously

j imbedded in cement paste or mortar. The mold with mortar and vane were aligned under part "B" and

the spring (with screw loading device and indicator)

j together with parts "A" and "B" were lowered onto

I the parts "C" and "D" until part "B" lost contact

I with part "A" on the horizontal part of the hook.

Torque was then applied, noting the maximum number

of degrees that the spring was rotated before shear

failure occurred. Appendix B, Calibration

An inverted Tee with arms each approximately

12 cm long as indicated in figure 2b was attached to the shear apparatus in place of the vane. The cord was attached to the inverted Tee at 10 cm from the

center. The cord was horizontal from the Tee to the

pulley and at right angles to the Tee. The balance

cradle and vertical portion of the cord from the pulley

to the cradle were weighed and additional weights

added, noting the combined weights and the number

of degrees of spring rotation necessary to raise the balance pan off its support. The results of spring rota- tion with the different weights were plotted for each of

the springs and the values for grams force at 1 cm

radius per degree rotation calculated for use in ex- pressing experimental shear values.

11

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