Further study of particulate admixtures for enhanced freeze-thaw resistance of concrete

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Further study of particulate admixtures for enhanced freeze-thaw

resistance of concrete

Litvan, G. G.

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construction

Further Study of Particulate Admixtures

for Enhanced Freeze- Tha

w Resistance

of Concrete

by G.G. Litvan

Reprinted from

ACI Journal

September-October 1985, No. 5

Proceedings V.

82, p. 724-730

(IRC Paper No. 1403)

Price $2.00

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L ' a u t e u r p o u r s u i t l ' e t u d e d ' u n e methode m i s e a u y o l n r p r 5 c 6 d e m n t e t p e r m e t t a n t d ' a c c r o t t r e l a r e s i s t a n c e du b e t o n a u g e l e t a u d e g e l p a r l ' a d d i t i o n d e p a r t i c u l e s p o r e u s e s a y a n t une s t r u c t u r e d e p o r e s d e f i n i e . On a k v a l u e l ' a p t i t u d e de l a v e r m i c u l i t e e t d e deux t y p e s d e p i e r r e ponce e t de p e r l i t e 3 s e r v i r d ' a d d i t i f s , e t compare l e u r performance 3 c e l l e d ' u n e b r i q u e k t u d i e e p l u s t a t . Parmi l e s mineraux t e s t & , l a v e r m i c u l i t e , un t y p e de p i e r r e ponce e t un t y p e de p e r l i t e a s s u r e n t une e x c e l l e n t e r e s i s t a n c e au g e l e t a u d e g e l pour les p a t e s de ciment ( r a p p o r t s e a u l c i m e n t = 0.48 e t 0,42), l e m o r t i e r ( r a p p o r t e a u l c i m e n t = 0,75) e t l e b6ton ( r a p p o r t e a u l c i m e n t = 0.63).

---"

Title no.

82-66

Further Study of Particulate Admixtures for Enhanced

Freeze-Thaw Resistance of Concrete

Title no. 82-66

Further Study of Particulate Admixtures for Enhanced

Freeze-Thaw Resistance of Concrete

by G.

G.

Litvan

Investigation of a previously developed method o f increasirig the re- sistance of concrete to freezing and thawing by the addition of po- rous particulates of specified pore structure is continued. k'ermiculile and two grades of pumice and perlite were tested for suitability as additives, and their perfornzance compared with that of a previously examined brick. Of the mineral tested, vermiculite, one prrrr~ice, and one perlite provide excellent resistance to freezing and tho wrng of ce- ment pastes (water-cement ratios = 0.48 and 0.42), mortar (water- cement ratio = 0.751, and concrele (water-cement ratio == 0.63).

Keywords: admixtures; bricks; cement pastes; compressive strength; concretes; freeze-thaw durability; mortars (material); perlite; porosity; pumice; vermicu- lite.

The resistance of hydrated cement paste and con- crete to freezing and thawing can be improved signifi- cantly by the addition of porous particulates with the pore characteristics of 30 percent total porosity and pore diameters mainly between 0.3 and 2 p.' The po- tential benefits of replacing a conventional air-entrain- ing agent by a particulate admixture are significant. It is extremely difficult t o control air content when mixing and placing concrete under many conditions (Whiting and Stark2 list 23 factors that affect air en- trainment). Using a porous-particulates admixture

Table 1

-

Properties of materials used as additives

would eliminate practically all such problems and per- mit good control of air content. Moreover, the use of particles would enable controlled air entrainment in two areas of growing importance: (1) concrete made with blended cements, particularly with fly ash; and (2) con- crete formed or compacted by extrusion, dry-impac- tion, vacuum dewatering, or other similar techniques. The present inability to control air entrainm 'ilt in fly-

ash concrete is the major impediment t o its use in northern countries.

Particulate admixtures commercially marketed for industrial use must be effective and inexpensive and must not react detrimentally with the constituents of concrete. Waste materials from manufacturing pro- cesses, such as clay or refractory brick wastes, are usu- ally unsuitable because they are not uniform. Effective mixtures may be obtained by crushing and sieving good-quality bricks, but this is an expensive process. Diatomaceous earth must be excluded because certain types have a tendency to react with the alkali in con- crete. A survey of potentially suitable minerals shows that the pore characteristics of perlite, vermiculite, and pumice meet the requirements in terms of both total porosity and pore size distributions (Table l), are often available in the required grain size, and are quite inex- pensive. For these reasons, their effectiveness as ad- mixtures was investigated.

A previous work was concerned mainly with the ef-

fects of crushed brick, diatomaceous earth, and sin- tered fly ash on the freeze-thaw resistance of cement paste.' The present study assesses the performance of vermiculite, perlite, and pumice in protecting cement paste, mortar, and concrete from damage due to freez- ing and thawing. For comparison, a previously investi- gated crushed brick was included in the test program.

Received June 6, 1984, and reviewed under Institute publication policies. Copyright @ 1985, American Concrete Institute. All rights reserved, including

the making of copies unless permission is obtained from the copyright propri- etors. Pertinent discussion will be published in the May-June 1986 ACI JOUR- N A L if received by Apr. 1, 1986.

ACI member G. G. Litvan is Senior Research Officer of the Division of Build- ing Research, National Research Council of Canada. Dr. Lilvan's research deals with surface chemical problems of concrere durability. He IS a corresponding member of ACI Commirtee 201, Durabi1it.v of Concrete, a member of Com- mitlee 362, Parking Struclures, and a member of lechnrcal commitrees of CSA and RILEM. He is Pas1 President of the Easrern Ontario and Quebec 4 C I Chapter.

RESEARCH SIGNIFICANCE

Materials with a particular pore structure when used as admixtures are capable of protecting cement paste, mortar, and concrete from the detrimental effects of freezing and thawing. Certain types of perlite, vermi- culite, and pumice have been found to be well-suited as admixtures and are in good supply and inexpensive. This method of protection against freezing and thaw- ing promises to be more reliable, and thus more etfec- tive, than air entrainment. In addition, fly ash, ex- truded, dry impacted, and vacuum concrete might also be protected, though this is not possible or practical at the present time.

EXPERIMENTAL Materials

Brick - Commercially fired building brick, previ- ously designated A.'

Vermiculite - U.S. origin, expanded, construction grade.

Perlite

-

U.S. origin, expanded in Canada, con- struction grade; the two types are designated HW and LW.

Pumice RH - Icelandic origin, brown.

Pumice LK - Icelandic origin, black.

Cement - Portland cement Type 10.

Aggregate

-

Crushed limestone of 16 mm maximum dimension.

The grain size of all the admixtures was between 1.2 and 0.3 mm (16 to 50 mesh).

Test methods

Porosity and pore size distribution were determined by a mercury intrusion porosimeter (420 M P a maxi- mum pressure) and density by an air compression pyc- nometer using helium gas. Water absorption was mea- sured by a vacuum electrobalance. Freezing and thaw- ing resistance was determined in conformity with the requirements of ASTM Standard C 666-80.3

Mix design

Previous research' established that a 10 percent con- centration of Brick A particles by weight of cement was necessary t o render cement paste frost resistant. A 60 ml bulk volume of brick provides this concentration in 6000 g of cement in mortar or cement mix. This figure was adopted as the standard amount for all admixtures t o achieve similar particle concentrations for all speci- mens.

Because the particle size of all the additives was the same, the number of particles in each mix was approx- imately equal, although deviations from the target ACI JOURNAL I September-October 1985

Table 2

-

Admixture concentration and spacing factor of cement paste and mortar specimens at low (L) and high (H) dosage levels

--

Number of Concen-

particles per trarion, Spacing mlx, weight factor, Particulate percent

--

mm samples L H L H L H Brick A 205 410 10.0 20.0 0.62 _- 0.49 - .

- -

- . Vermiculite 673 1345 1.2 2.5 0.41 0.32 - Pumice RH 247 494

_-

4.9 9.8 0.57 0.45 .- Pumice LK 248 496 4.9 9.8 0.57 0.45 Perlite 233 466 1.2 2.3 0.58 0.46 _-

value could be expected because of differences in par- ticle size distribution and shape. As the primary objec- tive of this work was to establish the effectiveness of the additives in absolute and not necessarily in relative terms, effort was made to maintain only approximately uniform concentration levels. Mixes were prepared with single (high concentration) and double (low concentra- tion) doses.

The number of particles in a single dose and the spacing in the hardened paste can be calculated as fol- lows. As the true density of brick is 2.83 g/ml, the true volume of brick particles having 60 ml bulk volume is V = 60/2.83 = 21.2 ml. The brick particle has 36 per- cent porosity; thus, the apparent volume is V , =

21.210.64 = 33.13 ml. With an average diameter of 0.067 cm, the volume of a single particle is V, = 1.61

x

ml. The number of particles in a standard dose is thus V , / V , = 33.13/1.61

x

10 = 2.06

x

lo5. Similar calculations for the other additives result in the values given with weight concentrations in Table 2.

The maximum distance between particles at any point within the paste, or the spacing factor, can also be cal- culated. The volume of the hardened paste (in cube form) was 367.08 ml, and contained 1.96

x

lo5 brick particles when the single dose was added. If the volume of a cube surrounding the particle is 187

x

cm3, the distance between particles is 1.23 mm, or the spacing factor is 0.62 mm. The values obtained for the other additives at the two concentration levels are also given in Table 2. The calculated spacing factor values could not be verified experimentally because attempts to de- termine them by microscopical examination4 failed due t o insufficient contrast between the particles and the matrix.

Twelve mixes containing each of the six additives, with water-cement ratios of 0.42 and 0.48, were pre- pared in addition t o a plain cement which served as reference. Mortar specimens at water-cement ratio =

0.75 and cement-sand ratio = 2.75 were also fabri- cated.

Because of water adsorption, the addition of porous particles to the cement mix can alter the water-cement ratio. The extent of water gain depends on the adsorp- tive capacity of the porous particle, its water content at the time of mixing, the rates of hydration and adsorp- tion, the water-cement ratio of the mix, and other fac- tors. I t is not possible t o calculate accurately t h e 725

P E R L I T E L W P = 9 7 . 4 % P E R L I T E H W P = 86. 3% P U M I C E LK P = 4 7 . 3 % P U M I C E R H P = 6 9 . 3 % V E R M I C U L I T E P = 9 7 . 1 %

I

I I

B R I C K

I

P O R E D I A M E T E R , p m

Fig. I-Pore size distribution of particulates

1 1 " ' 1 ' 1 ' 1 1

PERLITE HW PERLITE LW PUMICE LK PUMICE RH

-

V) VERMICULITE Z

-

w

-

BRICK

P

PLA l N WIC 0.42 PLAIN WIC 0.38 s9 4 N U M B E R O F C Y C L E S

Fig. 2-Residual expansion as a function of number of freeze-thaw cycles of duplicate cement paste specimens

with (water-cement ratio = 0.42) and without (water-

cement ratios = 0.38, 0.40, and 0.42) particulate ad-

mixture in low concentration

Table 3

-

Water-cement ratio, number, and concentration of particles, spacing factor, and compressive strength of concrete containing low

(L) and high (H) concentration of additives

Concen- Compre- samples Brick A Vermiculite Pumice RH Pumice LK Perlite Plain concrete

amount of water withdrawn from the mix by the parti- cles, and therefore not possible to determine the effec- tive water-cement ratio. To evaluate more realistically the effectiveness of the admixtures relative to plain ce- ment paste, standard mixes containing no admixture were prepared with lower water-cement ratios than the test mixes. For example, in the series with nominal 0.42 water-cement ratio, the standards with 0.40 and 0.38 water-cement ratio are also included.

The cement paste and mortar mixes were prepared according to the provisions of ASTM C 305.5 The par- ticulates were added with the dry cement. Bars 25 x 25 x 300 mm were fabricated and the change in their length measured according to ASTM C 490-77.6

Concrete mixes were prepared by hand mixing, with a cement:sand:aggregate ratio of 1 :2.25:2.75. The wa- ter-cement ratios for the different mixes were chosen to maintain constant slump. The mixes, particle concen- trations, and spacing factors are listed in Table 3. Two bars 75 x 75 x 300 mm were fabricated from each mix.

The specimens were cured in a fog room for 28 days before testing.

RESULTS AND DISCUSSION Porosity

According to values given in Column 3 of Table 1, all six materials meet the previously formulated' require- ment of porosity in excess of 30 percent volume.

Pore size distribution

As shown in Fig. 1, the pore volume in the 0.30 to 2.0 pm range varies substantially in terms of both the apparent volume of the solid (Column 4 of Table 1) and the fraction of the porosity (Column 5 of Table 1). Optimally, the particulate matter should have high po- rosity, all of it in the critical pore sizes (- 0.3

-

2 pm). In such cases durability of the paste can be achieved with the minimum number of particles without intro- ducing excessive porosity, which will decrease strength and may have other detrimental effects.

Brick A is the most efficient additive, with 87 per- cent of its porosity in the required size range, while

PERLITE LW

w

-

6

PUM l CE LK

1

VERMICULITE BRICK

k

PLAIN WIC 0.42

I

N U M B E R O F C Y C L E S

Fig. 3-Residual expansion as a function of number of freeze-thaw cycles of duplicate cement paste specimens with (water-cement ratio = 0.42) and without (water- cement ratios = 0.38, 0.40, and 0.42) particulate ad- mixture in high concentration

Pumice LK has an overall low porosity with only 15 percent in pores of the required size.

Density

As shown in Table 1, Column 2, the true densities of the materials range from 2.83 to 0.81 g/ml. No diffi- culties were experienced in mixing, even with Perlite HW; the particles dispersed satisfactorily and showed no tendency to float to the surface.

Resistance to freezing and thawing

The length changes of hydrated cement paste speci- mens (water-cement ratio 0.42 and 0.48) as a function of a number of freeze-thaw cycles are shown in Fig. 2 through 5. Residual expansion is a reliable and sensi- tive indicator of freeze-thaw durability;' in susceptible solids, residual expansion significantly increases with the number of cycles. Plotted as a function of the

I _{number of cycles, the curve becomes exponential be-}

fore failure.

The present experiments confirm that porous parti- cles do provide protection against frost action. The

I plain, unprotected pastes survived fewer cycles than did

those containing the particulate admixture, even though the reference pastes had lower water-cement ratios. It is possible that the water-cement ratio of the particle-pro-

I

PERLITE

HW

w

PERLITE LW PUMICE LK PUMICE RH a a X W

'

~ ~ ~ c u L I T E PLAIN WIC 0.48 d

oCI

1 I I 1 I I I I

I

0 100 200 300 400 500 N U M B E R O F C Y C L E S

Fig. 4-Residual expansion as a function of the num- ber of freeze-thaw cycles of duplicate cement paste specimens (water-cement ratio = 0.48) with and with- out particulate admixture in low concentration

I

PERLITE HW

I

brk

PLAIN WIC 0.48

d

N U M B E R O F C Y C L E S

Fig. 5-Residual expansion as a function of the num- ber of freeze-thaw cycles of duplicate cement paste specimens (water-cement ratio = 0.48) with an without particulate admixture in high concentration

tected paste was less than the nominal value. Based on the water adsorption values of the additives, it is esti- mated that due to the presence of the particles, the wa- ter-cement ratio of the mixes could have been lowered ACI JOURNAL I September-October 1985

1 1 1 1 1 1 ( PERLITE HW 1 1 ' 1 PERLITE LW

d

PUMICE LK

c

P L A I N WIC 0.70

0

1

z 0

-

V) z a 0- X I & ! -

-

PLA I N WIC 0.65

I

PUMICE

RM

-

_{VERM ICULlfE}

7

BRICK

P

N U M B E R OF C Y C L E S

Fig. 6-Residual expansion as a function of number of freeze-thaw cycles of duplicate mortar specimens with (water-cement ratio = 0.75) and without (water-ce- ment ratios = 0.70 and 0.65) particulate admixture in low concentration

to between 0.395 and 0.380 from the nominal 0.42 de- sign value. Pick-up of a large quantity of water by the admixture is not probable; however, if substantial amounts of water had accumulated in the pores of the particles, this would have made them ineffective and susceptible to frost.

While the uncertainty of the true water-cement ratio water makes comparative evaluation somewhat diffi- cult, whether due to the protective action of the parti- cles or to the water-reducing effect, from a practical point of view only the de facto resistance to freezing and thawing matters. For example, sprinkling addi- tional particles on surfaces where the water-cement ra- tio is usually increased by the finishing operation could be a n effective method of providing extra protection for the top surface of sidewalks and roadways.

Of the six materials studied, vermiculite, Pumice RH, and Perlite LW showed consistently good results. Sur- prisingly, the specimens made of the high water-cement ratio paste containing brick in low concentration failed after 100 and 160 cycles (Fig. 4), a finding in need of further investigation. In every other instance (Fig. 2, 3, and 5) brick appeared to give excellent protection (in- dicated by the very low slope of the curves). The paste containing Pumice LK, o n the other hand, showed

I

PERLITE HW

I

I

PUMICE LK

1

PUMICE RH

I

w VERMICULITE BRICK

1

PLAIN WIC 0.70

0

i

0 PLA l N WIC 0.65 1 1 I I I I I I 1 N U M B E R O F C Y C L E S I

Fig. 7-Residual expansion as a function of number of freeze-thaw cycles of duplicate mortar specimens with (water-cement ratio = 0.75) and without (water-ce- ment ratios = 0.70 and 0.65) particulate admixture in

high concentration I

consistently poor durability; thus this additive must be judged unsuitable.

The mortar specimens protected with any of the par- ticulate admixtures showed good resistance to freezing and thawing (Fig. 6 and 7). No indication of suscepti- bility can be detected even with Pumice LK at low con- centration. According to the residual expansion and relative dynamic modulus of elasticity results [Fig. 8(a) and (b)], concrete specimens containing particulate ad- mixtures in high concentration showed no freeze-thaw susceptibility, except for Pumice LK. At low additive concentration, Pumice LK and Perlite LW proved to be nondurable [Fig. 9 (a) and (b)]. The plain reference concrete failed after 60 cycles despite its lower water- cement ratio (0.60 versus 0.65), and even at water ce- ment ratio = 0.56 unprotected concrete was destroyed after 300 cycles. Vermiculite, Pumice RH, and brick and perlite additives provided very good protection against freezing and thawing.

Compressive strength

In general, the addition of particles (with the excep- tion of brick) lowered compressive strength. Values for concrete cylinders cured for 28 days are given in the last column of Table 3. At the lower particle concentra- tions the reduction in compressive strength is 7.7 per- cent for vermiculite, 6.1 percent for Pumice R H , and ACI JOURNAL I September-October 1985

N U M B E R O F C Y C L E S 0 L PUMICE RH VERMICULITE n Y 2 C

-

BRICK d

t

h

~

~

~

~

d WlC 0.56 P l A I N WIC 0.60 0 100 200 300 400 500 N U M B E R O F C Y C L E S

Fig. 8-Concrete without (water-cement ratios = 0.60 and 0.56) and with (water- cement ratio = 0.63) particulate admixture in high concentration:

(a)

residual ex- pansion (duplicate specimens except for Pumices LK and RH), and (b) relative dy- namic modulus of elasticity as a function of the number of freeze-thaw cycles

Y 2

-

BRICK

-

I 5 Y PI PLAIN WIC 0.60 I I I I I L I I N U M B E R O F C Y C L E S N U M B E R O F C Y C L E S

Fig. 9-Concrete without (water-cement ratios = 0.60 and 0.56) and with (water- cement ratio = 0.63) particulate admixture in low concentration: (a) residual ex- pansion (duplicate specimens except for Pumice RH), and (b) relative dynamic modulus of elasticity as a function of the number of freeze-thaw cycles

19.5 percent for Perlite LW. Though undesirable, such pensation of better durability, which is a major con- a decrease is probably acceptable for many applica- cern, appears to be worthwhile. In applications for tions. For sidewalks, roadways, and other horizontal which high strength is essential brick particles can be surfaces, strength is usually not critical and the com- used.

CONCLUSIONS

1. The general effectiveness of porous particulate admixtures in providing resistance t o freezing and thawing is confirmed; specifically, the effectiveness of Brick A as an admixture designed to increase resistance to freezing and thawing of cement paste, mortar, and concrete is confirmed.

2. Vermiculite, Pumice RH, and Perlite LW admix- tures, in the proper amounts, provide good frost resis- tance to cement, mortar, and concrete.

3. Pumice LK and, to a lesser degree, Perlite LW ap- pear to be the least effective additives of those studied to provide resistance to freezing and thawing.

ACKNOWLEDGMENT

The author is indebted to Paul Benoit and Herman Schultz for carrying out the experimental work very competently. This paper is a contribution from the Division of Building Research, National Re- search Council of Canada, and is published with the approval of the Director of the Division.

REFERENCES

1. Litvan, G. G., and Sereda, P. J., "Particulate Admixture for Enhanced Freeze-Thaw Resistance of Concrete," Cement and Con-

crete Research, V. 8, No. 1, Jan. 1978, pp. 53-60.

2. Whiting, D., and Stark, D., "Control of Air Content in Con- crete," NCHRP Report No. 258, Transportation Research Board, Washington, D.C., May 1983, 84 pp.

3. "Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing" (ASTM C 666-SO), 1981 Annual Book of ASTM Standards, Part 14, ASTM, Philadelphia, pp. 396-402.

4. "Standard Practice for Microscopical Determination of Air- Void Content and Parameters of the Air-Void System in Hardened Concrete" (ASTM C 457-SO), 1981 Annual Book of ASTM Stan- dards. Part 14, ASTM, Philadelphia, pp. 279-294.

5. "Standard Method for Mechanical Mixing of Hydrodynamic Cement Pastes and Mortars of Plastic Consistency" (ASTM C 305-

SO), I981 Annual Book of ASTM Standards, Part 13, ASTM, Phila-

delphia, pp. 246-249.

6. "Standard Specification for Apparatus for Use in Measurement of Length Change of Hardened Cement Paste, Mortar, and Con- crete" (ASTM C 490-77), I981 Annual Book of ASTM Standards.

Part 14, ASTM, Philadelphia, pp. 306-312.

7. Litvan, G. G., "Frost Action in Cement Paste," Materials and

Structures, Research and Testing (RILEM, Paris), V. 6, No. 34, July- A u ~ . 1973, pp. 293-298.

T h i s p a p e r

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