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Shrinkage compensating concrete

a concrete and compression technology, applied in the direction of chemistry apparatus and processes, other chemical processes, etc., can solve the problems of constraint characteristics of the present concrete that have not been achieved before, and achieve the effect of reducing the stress

Inactive Publication Date: 2006-09-14
PKL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0011] Shrinkage compensating mortars may similarly be restrai

Problems solved by technology

Although the use of fibers in cement is known (see for example E. K. Rice, G. L. Vondran and H. Kunbargi, Mat. Res. Soc. Symp. Proc., Vol. 114, 1988, 145-150), the restraint characteristics of the present concrete have not been previously achieved.

Method used

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  • Shrinkage compensating concrete
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  • Shrinkage compensating concrete

Examples

Experimental program
Comparison scheme
Effect test

example i

Laboratory Testing

[0041] Specimens were prepared according to ASTM standard C 878. All specimens were poured in C 878 molds so as to contain ninety cubic inches of concrete and have the dimensions 3″×3″×10″.

[0042] The fibers used had the following characteristics, as described by their vendors:

PolypropylenePVADensity (g · cm−3)0.911.3Tensile Strength90-110 ksi160 N / mm2Modulus of elasticity  500 ksi 37 kN / mm2

[0043] One half cubic foot batches of concrete were prepared. Each half cubic foot contained 9.63 pounds (520 pounds per cubic yard [pcy]) Portland cement and 1.67 pounds (90 pcy) of an expansive material (Komponent® manufactured by CTS Cement Company, Cypress, Calif.). Expansive materials are typically added to Portland cements in amount of 5-20% according to requirements of the cement industry. After the Portland cement and expensive material were mixed, 0.041 pounds of fibers were added and incorporated into the mixture, representing 2.2 pcy, 34.26 pounds (1850 pcy) ¾″ sto...

example ii

Field Testing

[0049] In order to confirm the results of laboratory testing on a larger scale, a field test was carried out in which slabs were placed on compacted fill. The slabs were 6 inches thick, 50 feet or 24 feet long and 6 feet wide. The concrete mix was the same as that used for the laboratory testing. One pair of slabs used Portland cement and had #4 rebar 24″ on center each way. One pair of slabs used shrinkage compensating cement and had #4 rebars 24″ on center each way. One pair of slabs simply used polypropylene fibers-reinforced shrinkage compensating concrete and no rebar. The slabs were wet-cured for seven days and allowed to air dry. Dial gauges were placed at both ends of each slab. Readings were taken daily for a week and weekly for a month. FIG. 3 shows the results of this field testing.

[0050] The fiber-reinforced concrete performed comparably or better than the slabs with shrinkage compensating cement and rebars. All slabs with shrinkage compensating cement per...

example iii

Full Scale Field Test

[0053] An additional full scale test was made with the test floor having four 8 inch thick slabs, and two 6 inch thick slabs, constructed with 1725 cubic yards of concrete and fibers as described above. Each slab was about 110 feet by 130 feet. No conventional shrinkage saw cuts or steel reinforcing were used. The concrete was finished with a conventional automated laser screed machine, resulting in an exceptionally flat floor (FF=99.8) at the time of construction. The machine was able to screed the concrete quickly and efficiently because there was no rebar to impede the work.

[0054] Three modified ASTM expansion bars were made on each of the six concrete placement days, for a total of 18 bars, utilizing the fibers in the mix to provide restraint against expansion. At 7 days of moist curing, the average expansion was 0.045% (range 0.031% to 0.052%), after which the bars were removed from the moist cure. After 21 days of air drying, the average expansion was 0....

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Abstract

Synthetic fibers, such as polypropylene fibers, are mixed in a shrinkage compensating concrete to provide restraint in lieu of conventional steel reinforcement used in a shrinkage compensating concrete. While the synthetic fibers have a low elastic modulus and low strength, they act to restrain expansion of the concrete in the same way that conventional steel rebar does. In addition, only a small amount of the synthetic fibers are needed to restrain the expansion. As a result, shrinkage compensating concrete can be used in more varied applications, and can be provided more quickly, easily and inexpensively. Construction time requirements and expenses of concrete structures are correspondingly reduced.

Description

[0001] The field of the invention is shrinkage compensating concrete. [0002] As is well known, concrete tends to shrink as it dries or cures. This shrinkage occurs with loss of water as the concrete dries. When the concrete is restrained from freely shrinking, as it usually is, the drying shrinkage creates tensile stresses in the concrete. Since concrete generally has low tensile strength, stresses from shrinkage often cause cracking. [0003] To better avoid or reduce cracking caused by shrinkage, various expansive concretes have been used. See for example Klein, U.S. Pat. No. 3,251,701, Rice, U.S. Pat. No. 4,419,136, and Rice U.S. Pat. No. 5,846,316, each incorporated herein by reference. These and other shrinkage compensating concretes include an expansive cement. Expansive cement generally is a Portland cement that includes an expansive material. The expansive cement causes the concrete to expand slightly, which helps to offset or compensate for the shrinkage associated with dryin...

Claims

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Application Information

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IPC IPC(8): C04B14/48C04B28/04C04B24/00
CPCC04B28/04C04B2111/34C04B14/06C04B16/0633C04B22/008C04B24/26C04B2103/20C04B2103/32C04B2103/54Y10S264/43
Inventor RICE, EDWARD K.BESCHER, ERICFLAX, DAVIDGOODS, DANIELDE BRUYN, KYLE
Owner PKL CORP