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Advantages of the technology
K10 PC Strand is a new stage of evolution in the development of prestressed steel.
Let's consider the distinctive features of various types of steel reinforcement.

Smooth rebar

A240 (240 MPa yield strength class)

Surface: smooth without relief

Bond to the concrete: adhesive and friction

Yield strength (strength class): 240 N/mm2

Maximum possible prestressing: not used

To realize a higher specific strength, especially for prestressing, reinforcement requires higher adhesion to concrete, achieved due to the developed surface relief

Ribbed rebar

with a die-rolled periodic profile A 800

Surface: with 1mm protruding ribs

Bond to the concrete: mechanical (crumpling/cutting) and adhesive

Yield strength (strength class): 800 N/mm2

Maximum possible pre-voltage: 720 N/mm2

For the rod: (154 mm2 х 720 N/mm2) = 110,9 kN = 11,3 ts

The Low Relaxation (stabilized) PC Strands made of high-carbon wire hardened by cold deformation are used to increase the specific strength of the reinforcement, which allows to implement prestressing

7-wire Low Relaxation PC Strands

Surface: rounded, with a periodic profile in the form of dents with a depth of 0.07 — 0.12 mm, in 2, 3 or 4 longitudinal lines, located in relation to the strand randomly

Bond to the concrete: mainly adhesive with a small proportion of mechanical (crumpling)

Yield strength (strength class): 1650 N/mm2

Maximum possible prestress: 80% of the yield strength = 1320 N/mm2

For 15.7 mm 7-wire PC strand: (150 mm2 х 1320 N/mm2) = 198 kN = 20,2 ts

Problem:

Round strands do not have sufficient adhesion to concrete, and it is impossible to put dents of such depth on the wires that would increase the adhesion to a sufficient level.

Therefore, the prestressing force of strands is set in the range of 800-1150 N / mm2, which is 45-75% of the permissible values.

The 15.7 mm 7-wire PC strand is prestressed for an average of 150 kN, i.e. 15.3 ts.

Round strands are not using 4.9 tc,

for which you have to pay

There is a solution:
K10 trihedral 10-wire PC Strand allows you to use all the strength of the high-strength stranded steel in the concrete. Due to the shape, K10 eliminates slipping in concrete both in a straight line and in a spiral, in the direction of lay.

K10 Low Relaxation PC Strand

Surface: with inclined faces and a periodic profile in the form of 0.2-0.3 mm high projections on the outward-facing surface of the wires

Bond to the concrete: mechanical (wedging + crumpling), adhesive

Yield strength (strength class): 1740 N/mm2

Maximum possible prestressing: 80% of the yield strength = 1392 N/mm2

For 13.8 mm K10 PC Strand: (150 mm2 х 1392 N/mm2) = 208,8 kN = 21,3 ts

This is an additional 6.0 tc with the same cross-section and weight of the strand. The economic effect of the transition from K7 to K10 in this example is = 39%. The inclined faces of K-10 provide reliable support on concrete under any deformations.
Comparison of K10 and K7 strands
Bond to the concrete of the K10 Strand is about 2 times higher than that of K7
K10
Pronounced surface relief from protruding side faces
K7
Lack of surface relief

Adhesion to the concrete К10

25% more, than K7

K10
9 wires out of 10 come into contact with concrete
K7
6 wires out of 7 come into contact with concrete
The enveloping contour K10 is larger than K7
K10
PK10
PK10 = LcirK7 + 25%
K7
LcirK7
Armasteel Production Photos
Complete absence of slippage in concrete
K10
- Absence of slippage in C15 concrete
K7
– Defect
Greater strength at the edges of products

Tests on the bearing capacity of the reference zone:

K10
– An inclined crack does not occur from the edge
- An inclined crack does not occur from the edge
K7
– An inclined crack occurs from the edge
- The edges of the slab are under-reinforced
Reduction of cement and aggregate costs

It is not necessary to increase the concrete grade to hold the K10 strands

K10
At least C20
K7
- At least C35 (for retention in concrete) (for retention in concrete)
Gravel aggregate is sufficient for bond to the concrete

to hold the К10 strands, it is not necessary to increase the concrete grade

K10
— Gravel inert fill
K7
— Only crushed stone inert fill

Reduction of cement

and steel consumption

The tension of the К10 PC Strand is 30% more

K10

1320 — 1500 МPа

80%from the conditional yield point to (SP63)

K7

900 — 1050 МPа

60%from the conditional yield point to (SP63)
The aggregate strength of the strand at the same cross-section is 10% higher

SK10= SK7

σK10 + σK7 + 10%

K10
K7
With an equal cross-section of strands, К10 wires are thinner than К7 wires, and the specific strength is higher.
for S = 150mm2:

4,3mm — wire diameter

309kN — aggregate breaking strength

5,2mm — wire diameter

279kN — aggregate breaking strength

The maximum cross-section is 42% larger with the same specific strength
K10
K7
dmax = 5.2mm2

214mm2 maximum cross-section

1860 н/mm2 —specific strength

398 кН —aggregate strength

150мм2 maximum cross-section

1860 н/mm2 —specific strength

279 кН —aggregate strength

Reducing the number of strands and geometric cross-section dimensions in products
K10
K7

Multiple reduction

of transfer area length

2-3 times

depending

on the size of the strand

Comparison of the transfer area length of PC Strands in prestressed hollowcore floor slabs
K10

Prestressing with K10 strands according to TU 259311-001-2019

K7

Prestressing with K7 strands according to GOST R 53772-2010, ASTM A416, BS 5896 etc.

The confirmed economic effect of replacing the 7-wire PC Strands with K10 PC Strands in hollowcore slabs reaches an average of 30-40%. This effect increases with the increase in the geometric dimensions and load capacity of the products.
The percentage of savings of PC Strands in hollowcore slabs with a height of 220 mm due to the use of K10 strands.
Calculation of the economic effect of using 1tn of K10 PC Strand

on the example of the production

of hollowcore slabs PB60.12-8

Specific consumption of materials

per 1 item:

Concrete: C20 = 0.84 m3

M500 Cement: 250kg/m3 = 210kg

K10 strand = 10kg

Concrete: C40 = 0.84 m3

M500 cement: kg/m3 = 420kg

K7 strand = 14kg

The use of K10 PC Strand allows to increase the productivity of plants without expensive reconstructions due to:
– reducing the holding time of products on the lines up to 30%
- exclusion of slippage defects

1tn of K10 PC Strand is spent on 90 items

Economy

Steel: 90pcs x (14-10) = 360kg ≈ $400

Cement: 90pcs x (500-250) = 22.5 t ≈ $1000

The cumulative economic effect of using 1T K10 PC Strand is $1400
+ the effect of end slip exception
+ the effect of reducing the holding time of products before removing strands cutting
Reviews about K10
"We have implemented the world's first test of the TK-10 PC Strand on the formless molding line by manufacturing hollowcore slabs prestressed by TK10 and K7 ropes in a 50/50 ratio and testing the capacity of these slabs. The advantage of TK10 strands in comparison with K7 in adhesion to concrete was striking. With the destructive load and the slip of the K7 strands, the TK10 strands remained in place. The bearing capacity of the slabs increased by 15%, TK10 strands did not slip due to their design features, fully used their strength ...
Ravil Mukhteev
Chief Engineer of Tyumen Reinforced Concrete Plant No. 1
"Together with the specialists of NIIZHB, we conducted tests of prestressed hollowcore floor slabs made by the method of formless molding. The test readings of floor slabs reinforced with TK-10 strands for anchoring in concrete clearly exceed the readings of slabs reinforced with K7 strands. This gives a number of economic advantages for the production of prestressed concrete..."
Alexander Kiselyov
Chief Technologist of JSC "Barricade" (St. Petersburg)
"We have conducted several series of tests of the new TK10 PC Strand in hollowcore slabs of formless molding. We reduced the amount of prestressing steel and the cement, used gravel instead of crushed granite rubble. All produced slabs have successfully passed the tests for rigidity, crack resistance and load capacity..."
Andrey Medvedev
Technical Director of the Kulonstroy reinforced concrete plant (Kazan). Chief Engineer of Tyumen Reinforced Concrete Plant No. 1
Our partners
Armasteel Franchise
Armasteel Industries JSC presents the sale of a license for the industrial production of a product for the first external buyer. The franchise includes a license for the production of TK10 PC Strand and equipment for its production on the basis of its own production.
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