Kansas Geological Survey, Bulletin 191, pt. 1, originally published in 1968

Cellular Concrete of Kansas Pozzolanic Materials

by Clayton M. Crosier and Ronald G. Hardy

Clayton M. Crosier, Associate Professor of Civil Engineering, University of Kansas; has conducted this research project since 1954.
Ronald G. Hardy, Chief, Mineral Resources Section, Kansas State Geological Survey; initiated this research in 1953.

Originally published in 1968 as part of "Short Papers on Research in 1967," Kansas Geological Survey Bulletin 191, part 1, p. 27-34. This is, in general, the original text as published. The information has not been updated.

Abstract

Nearly 200 batches of cellular concrete, foamed, were made of Kansas pozzolans with portland cement and were autoclaved. Volcanic ashes produced concretes having unusually high strength-density ratios. The desirable conditions of making such concretes were broadly determined. The compressive-strength-versus-dry-density relationships of the concretes that satisfied these conditions were about 1500 psi at 40 pcf to 3000 psi at 55 pcf. The moduli of elasticity agreed closely with those given by the 1963 ACI Code formula.

For a number of years the State Geological Survey of Kansas has sponsored research in the Concrete Laboratory at the University of Kansas on the use of Kansas pozzolans, especially volcanic ashes, in cellular concrete.

Nineteen different Kansas pozzolanic materials have been tried, 10 have shown practical potential. These 10 materials, their chemical analyses, and their geographic sources are shown in Table 1. Nearly 200 (195) batches of cellular concrete have been made. These have involved many variations: in materials, in proportions of the materials, in mixing, in curing, and in drying preparatory to testing. All were the foamed type of cellular concrete, some by the use of preformed foam, most by the mix-foaming method, all using the same commercial foaming agent. Nearly all specimens were autoclaved, usually at about 360°F. The resulting concretes have been tested or measured with respect to density, compressive strength, and modulus of elasticity, the specimens being 3 x 6-inch cylinders, and volumetric stability by standard bars. In some cases flexural strength has been determined, and a few thermal conductivity tests have been made.

Table 1--Properties and sources of pozzolans used.

Analyses of the data show conclusively that the use of Kansas volcanic ash as the pozzolan yields cellular concrete of unusually high strength: 2000 psi at 45 pcf dry density, and 3000 psi at 55 pcf. The modulus of elasticity of this concrete is very nearly that given by the formula in the 1963 American Concrete Institute (ACI) Standard Building Code (1963), which in the notation of the present report is:

E = 33 D^1.5 f'^0.5

in which
E is the modulus of elasticity, psi,
D is the dry density, pcf, and
f' is the compressive strength, psi.

The flexural strength of this high-compressive-strength concrete has not been determined. Its fire-protection value is questionable--exposure to moderately rapid changes in temperature above 150°F, or perhaps to temperatures over 150 to 200°F without changes, usually produced craze-cracking, but quantitative determination of the extent and nature of this weakness will require further research.

The compressive-strength-versus-density relationships of 65 different batches of concrete made in this investigation are presented in Figure 1. The most significant data on these 65 batches are given in Table 2. In all but three of these concretes, the pozzolan used was Kansas volcanic ash. The strength-density relationship is very nearly linear in the density range of Figure 1 and is represented conservatively by the equation:

f' = 115 D - 3100.

At the often-referred-to density of 40 pcf, the mean strength is nearly 1500 psi; at 45 pcf it is over 2100 psi, and at 55 pcf it exceeds 3000 psi.

Figure 1--Strength versus density of foamed cellular concrete made of type III portland cement and Kansas pozzolans.

That these high strengths are attributable primarily, perhaps solely, to the pozzolanic materials used is indicated by the dashed line and the three non-volcanic-ash points in Figure 1. The dashed line represents the linear mean of the highest strength-versus-density values of National Bureau of Standards (NBS) experimental concretes, as reported by Valore (1954, p. 821) in his figures 12 and 14. These NBS concretes were made with either fly ash or expanded shale dust as the pozzolan. The fly ash and expanded shale concretes made in this research at the University of Kansas are in good agreement with NBS concretes. This is indicated by the three non-volcanic-ash points in Figure 1. (The strength of the expanded shale concrete was abnormally high because of the extreme fineness of the shale in that batch.) In all significant respects except for the pozzolan, these three concretes were made and tested like the other 62 in Figure 1.

Table 2--Composition, density, strength, and elasticity of the cellular concrete.

*C in this column indicates that the ash was calcined at 1400°F.
**Median diameter of particle, microns, determined by standard pipette test.
***P-Pre-formed foam used; all other batches were foamed by high-speed mixing; M-Moist cured for x days, all other batches moist cured 1 to 3 days; L-b-Lime, hydrated, was added to the portland cement, b being the ratio of lime to cement-plus-lime, by weight.
^First number is hours heating from 100°F to full heat temperature, second number is hours at full heat ±1/4.
^^Moisture content of the concrete when tested, percent.
Nt = no test.

Figure 2 shows clearly that the modulus of elasticity of this Kansas cellular concrete is in remarkably close agreement with the previously cited formula given in the ACI Building Code (ACI, 1963). This formula was based principally on research on concretes having densities in the range of 90 to 155 pcf (Pauw, 1963). That the modulus of these concretes having densities under 60 pcf, most less than 45, agrees closely with the ACI formula is for this reason doubly significant.

Figure 2--Modulus of elasticity of cellular concrete made with Kansas volcanic ash.

Numerous factors besides the constituent materials and the density affect the strength and other properties of cellular concrete. Many of these have been studied in this investigation. Analysis of the data obtained, although as yet incomplete, shows that when Kansas volcanic ash is the pozzolan, several factors produce effects that are different from those produced by the same factors on fly ash or expanded shale concrete. The selection of the 65 batches of concrete included in this study of strength versus density was made by applying the following limitations to the 15 stated factors:

1. Cement materials used were:
   1. type III portland cement plus;
   2. calcium chloride of weight between 1.5 and 3% of the weight of portland cement; and
   3. either no lime or a weight of lime not greater than that of the cement.
2. The pozzolans were ground to fineness measured by a median diameter less than 17 μ or by the sum of the percentages passing no. 200 and no. 325 screens being not less than 195%.
3. The ratio by weight of portland-cement-plus-lime to pozzolan was 2 to 3, 0.67.
4. All test specimens were cylinders:
   1. that were nominally 3 x 6-inches in size; and
   2. that had height-diameter ratios between 1.9 and 2.0.
5. Specimens were cured by:
   1. moist storage one day in the molds and zero to nine days in the fog room followed immediately by
   2. autoclaving:
      1. the full-heat temperature being 360 ± 5°F
      2. this temperature being maintained for about 8 hours, limits being 7.25 to 8.75 at full heat, or
      3. the heating period--the sum of the hours from 100°F to the end of the full-heat period-being not less than 11.5 hours
      4. the cooling period being about 12 hours, the consequent entire cycle about 24 hours.
6. Specimens were dried to constant weight:
   1. at 130 to 140°F;
   2. with only gradual changes in temperature.
7. The moisture content of specimens at the time of compressive loading was not more than 4%.

Exceptions were made to each of four limitations for the following groups of batches (Table 2), each of which satisfied all but the one limitation indicated by number:

2. RVI, RV2, RVCI--The ROV-1 ash in these batches was at least 50% coarser than the ashes in the other concretes having the same densities--the strengths averaged 25% lower.

5.a. Batches RP2, GVI, and RwVl were stored in the fog room about 150 days, then autoclaved. A specific study indicated that, for Kansas volcanic ash concretes, 90 to 180 days of such storage usually affects the autoclaved strength less than 2%.

5.b. (2&3). Cylinders of GV5, GV6, and GV7 were autoclaved by heating over 100°F for only 9 3/4 hours, at full heat (only 355°F) for only 5 1/4 hours. As Figure 1 shows, strengths were lowered about 15% at 39 pcf to 35% at 47 pcf.

5.b. (2&3). All MG batches were autoclaved at full heat for only about 5 1/2 hours, but the heating period was at least 11 hours in all but one case. The strengths agree well with the linear mean curve of Figure 1. For the ML batches the times at full heat were somewhat less, the strengths were markedly less. Obviously, more data are needed on these higher density cellular concretes.

References

American Concrete Institute, 1963, ACI Standard Building Code Requirements for Reinforced Concrete (ACI 318-63): American Concrete Institute, Detroit, Michigan.

Valore, R. C., Jr., 1954, Cellular concretes: American Concrete Institute, Journal, Proceedings, v. 50, pt. 1, no. 9 (May), p. 773-796; Pt. 2, no. 10 (June), p. 817-836.

Pauw, Adrian, 1960, Static modulus of elasticity as affected by density: American Concrete Institute, Journal, Proceedings, v. 57, no. 6 (Dec.), p. 679-688.

Kansas Geological Survey, Short Papers on Research in 1967
Placed on web Aug. 16, 2011; originally published in April 1968.
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