ULTRA-HIGH PERFORMANCE CONCRETE

PREPARED BY:SHAIKH MOHAMMADSOYAB A. GUIDED BY:AANAL SHAH :DHARA SHAH CODE NO: SD-1810

CONTENT:

INTRODUCTION ADVANTAGES of UHPFC APPLICATION OF UHPFC COMPOSITION OF UHPFC MIXING PROCEDURE OF UHPFC TESTING ON UHPFC RESULT AND CONCLUSION CASESTUDY FUTURE SCOPE REFERENCE

INTRODUCTION

ultra-High Performance Concrete (UHPC) is one of the latest advances in concrete technology and it addresses the shortcomings of many concretes today: low strength to weight ratio, low tensile strength, low ductility, and volume instability.

In addition to achieving high compressive strengths in excess of 25,000 psi (sometimes greater than 30,000 psi), UHPC is also nearly impermeable.

This very low permeability allows UHPC to withstand many distresses normally associated with NSC and HPC such as freeze-thaw deterioration, corrosion of embedded steel, and chemical ingress.

DEFINATION OF UHPC:

It is also known as Reactive Powder Concrete (RPC).

It is a high strength, ductile material formulated by combining Portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers.

ADVANTAGES OF UHPC:

Can be sprayed in very dense reinforcement. Fast strength development. Can be finished with a smooth surface. Both wet and dry method are possible. It has very low permeability. Ultra high strength and stiffness. Strengthening individual intact members by local- or

complete filling. Greater capacity to deform and support flexural and

tensile loads, even after initial cracking. Abrasion resistance similar to natural rock.

Applications of UHCP

Scraper paths in treatment plants Bridges Narrow supports Thin or slab-like components Buttresses for high pressures Repair and strengthening of structure

COMPOSITION OF UHPC: While considered a relatively new material, UHPC

consists mostly of the same constituents as normal strength concrete such Portland cement, silica fume, water, and quartz, sand. However, it also includes finely ground quartz, steel fibers ,and superplasticizer.

Table 2.2: Composition of a Typical UHPC

Constituent s Lb/yd3 %byWeight

Premix Portland cement silica fume Ground quartz fine sand

1180-1710

385-5300-3901293-

1770

27-388-90-939-41

Metallic fiber 245-320 5-8

Siperplastisizer 20-30 0.5-1

water 260-350 5-8

Water/cement ratio 0.14-.27 ----

UHPC Mixing Procedure:

In mixing of UHPC premix, fibers, and liquids are used. The liquids that were mixed with the UHPC included

water, accelerator, and a high-range water-reducing admixture (HRWA).

The fibres included in the UHPC were always unreformed cylindrical steel fibres that were 0.5 in. long and had a 0.008-in. diameter. These fibers were included in the mix at a concentration of 2% by volume.

The mix proportions used throughout this study included the following:

Premix 137.0 lb/ft3 of concrete

Water 6.81 lb/ft3 of concrete

HRWA 1.92 lb/ft3 of concrete

Accelerator 1.87 lb/ft3 of concrete

Steel Fibers 9.74 lb/ft3 of concrete

These mix proportions were followed for all except three batches.

In two batches, the accelerator was replaced by an additional 1.80 lb/ft3 of water.

In the remaining batch the fibers were not included in the mix so that compression test behaviour in unreinforced UHPC could be studied.

A 2.0 ft3 capacity pan mixer was used for nearly all of the UHPC mixing.

A 0.3 ft3 mixer was used for the two batches that only required a

small volume of material.

Key points in the mixing procedure are graphically shown in Figure . The mixing procedure for UHPC included the following steps:

Weigh all constituent materials. Add ½ of HRWA to water.

Place premix in mixer pan, and mix for 2 minutes.

Add water (with ½ of HRWA) to premix slowly over the course of 2 minutes.

Wait 1 minute then add remaining HRWA to premix over the course of 30seconds.

Wait 1 minute then add accelerator over the span of 1 minute.

Continue mixing as the UHPC changes from a dry powder to a thick paste.

The time for this process will vary.

Add fibers to the mix slowly over the course of 2 minutes.

After the fibers have been added, continue running mixer for 1 minute to ensure that the fibers are well dispersed.

Figure 3.2-A: Mixing of UHPC including (clockwise from left) water addition, HRWA addition, pre-paste consistency, fiber addition, and finished mix

Casting of UHPC: As soon as mixing was completed, the casting of

specimens and the measurement of the rheological properties of the UHPC commenced.

The rheology of the UHPC was measured via a flow table test.

. In the test that was implemented in this study, the

mini slump cone is filled then removed to allow the concrete to flow outward.

Once the concrete reaches a steady state, the average diameters is determined by measuring the concrete at three locations.

Next, the flow table is dropped 20 times in approximately 20 seconds. Again, the concrete is allowed to settle then its average diameter is recorded.

The casting of all UHPC specimens used in this material characterization study was completed within 20 minutes after the completion of mixing.

All specimens were cast on vibrating table and were allowed to remain on the table for approximately 30 seconds after filling.

The filling of molds was completed via scoops used to move the UHPC from the mixing pan into the mold.

After filling, specimens were removed from the vibrating table and were screeded.

The demolding of the specimens occurred approximately 24 hours after casting.

Curing of UHPC: Four curing regimes were implemented in order to

study UHPC characteristics under different curing conditions.

The standard, manufacturer recommended curing treatment included steaming the UHPC at 90ºC and 95% relative humidity (RH) for 48 hours.

In practice, this procedure included 2 hours of increasing steam and 2 hours of decreasing steam, leaving 44 total hours of constant steaming at 90ºC and 95% RH.

This treatment was initiated within 4 hours after demolding.

This curing condition will henceforth be referred to as Steam treatment. The remaining three regimes include Air treatment, Tempered Steam treatment, and Delayed Steam treatment.

The Air treatment allowed the specimens to remain in a standard laboratory environment from demolding until testing.

The Tempered Steam treatment is very similar to the Steam treatment, except that the temperature inside the steam chamber was limited to 60ºC.

Finally, the Delayed Steam treatment is a curing regime where in the Steam treatment described above is followed, but it is not initiated.

TEST ON UHFC:

COMPRESSION TEST: The compression test carried out for

NSC,HPC,and UHPC for same specimen and same load.

SPECIEMAN:3 inch diameter cylinder

LOAD: 200 ksi

Figure 3.3-A: (a) Grinding and (b) measuring of 3-in. diameter cylinders

Figure 3.3-B: 3-in. diameter cylinders (a) before and (b) after compression testing

PROPERTIES NSC HPC UHPC

Compression Strength, (ksi)

3.0-6.0 6.0-14.0 25.0-33.0

Split Cylinder Tensile Strength, (ksi)

.36-.45 - 1-3.5

Poisson's Ratio .11-.21 - .19-.24

Creep Coefficient, Cu 2.35 1.6-1.9

Porosity 20-25% 10-15% 2-6%

Fracture Energy, (k-in/in2)

0.00057-0.00086

- 0.057-0.228

Young's Modulus, (ksi)

2000-6000

4500-8000

Coefficient of Thermal Expansion

4.1-7.3x10-6

7.5-8.6 x10-6

RESULT

DURABILITY TEST:Durability test carried out for NSC,HPC,UHPC for the

same specimen.

PROPERTIES NSC HPC UHPC

Freeze/Thaw Resistance

10%DURABLE

90%DURABLE

100%DURABLE

Chloride Penetration

>2000 500-2000

<100

Water Absorption 4*10^-3 5*10^-4 7.1*10^-5

Chloride ion diffusion coefficient(by steady state diffusion), (in2/s)

1.55*10^-7

7.55*10^-10

3.1*10^-11

CASE STUDY

UHPC will be used in pretensioned, prestressed concrete beams in a bridge replacement project in southern Wapello County.

The beams will be pretensioned using 0.6-inch diameter low relaxation strands. No mild reinforcing steel, except an amount to provide composite action between the beam and cast-in-place deck, will be used.

To verify shear and flexural capacity of the beam, 10-inch and 12-inch shear beams and a 71-foot–long test beam have been cast.

BRIDGE DESCRIPTIONTest Batch at Materials Laboratory in Ames, Iowa The replacement bridge will be a 110-foot simple span bridge

with a three-beam cross section. The abutments will be integral and an 8-inch cast-in-place deck will be used. Beam spacing will be 9 feet 7 inches with 4-foot overhangs. See Figure 4 for additional details.

For the demonstration, a mixer with a two-cubic ft capacity was used to produce a one-cubic ft batch (see Figure 5). Three-inch by six-inch test cylinders were cast along with four-inch by four-inch by 18-inch beams.

Specimens were cast on a vibrating table using a small plastic

tremie tube. Curing of the specimens took place in sealed metal containers placed in ovens at 140° F for 72 hours. Results of the test cylinder compressive strengths are shown in Table 2.

Description Quantity

Ductile mix 137 lbs

Water 8.03 lbs

super plasticizer

850 g

Steel fibers 9.7 lbs

Test Mix Proportions

Cylinder Compressive strength (psi)

1 15,896

2 16,123

3 20,004

4 15,943

Proposed bridge cross section

Mixing of UHPC

Lower than expected compressive strengths (30,000 psi was expected) were found when the cylinders were tested. The following reasons may have contributed to the reduced strengths:

1. Steam curing was started 24 hours after casting and before initial set had taken place. Without accelerators, initial set can take up to 40 hours.

2. There was difficulty in achieving plane ends of test cylinders for uniform compressive loading. The ends of the cylinders were trimmed with a concrete saw to provide square ends.

3. Visual inspection of a cylinder that was cut lengthwise showed higher than expected air voids.

Because of these problems, Materials Lab produced a second test batch. Three-inch by six-inch test cylinders and two-inch cubes were prepared.

Compressive strengths of the cylinders improved, but were still lower than expected for the cylinders. Difficulty in achieving plane surfaces for uniform compression loading was believed to be the main cause of the lower strength values.

Beam Design and Plan Preparation A modified Iowa 45-inch bulb tee was used. To save

material in the beam section, the web width was reduced by two inches, top flange by one inch, and the bottom flange by two inches (see Figures 6 and 7).

The following additional design data were also used:

1. Release compressive strength: 14,500 psi

2. Release modulus of elasticity: 5,800 psi

3. Final design compressive strength: 24,000 psi

4. Final modulus of elasticity: 8,000 psi

5. Allowable tension stress at service: 600 psi

6. Allowable compression stress at service: 14400 psi

7. LRFD HL-93 loading

8. Grillage analysis for distribution factors

Iowa Standard 45 in. Bulb-T

Preliminary Section

The final beam design section used 49 0.6-inch strands stressed to 72.6% of ultimate. To reduce end beam stresses, five strands were draped along with debonding (see Figure 8 for strand layout). The 71-foot test beam used an identical strand layout to verify release stresses.

OVERVIEW OF TEST BEAMCasting and Release of Strands

Composite Connection between the Beam and Cast-in-Place Deck

The test beam was cast with three options for developing the composite connection between the beam and deck . These options were studied due to the requirement that the top of the beam be covered with plastic immediately after placement of the concrete to prevent shrinkage cracks and the need for the plastic be placed directly on the concrete.

After the casting, the use of the mild steel U-bar option was selected. The selection was based on the simplified detail and ease of installation during casting of the test beam.

Strand Anchorage and Transfer of Prestressing Force “Bond Performance Between Ultra-High Performance Concrete

and Prestressing Strands,” showed improved bond strength using UHPC.

Because of the improved bond and transfer, there was concern that the reduced transfer lengths (possibly less than 12 inches) may cause a concentration of release forces at the interface between the bottom flange and web.

To reduce these forces, both debonding and draping of the strands were provided. Under inspection, no visible cracks were found at the interface after release of the strands for the test beam.

Short-Term and Long-Term Losses To attempt to measure losses in the beam, fiber optic strain

gauges were attached to the bottom row of strands on the test beam before casting. Based on the changes in strain measured at release and the final strains after curing, the release losses and total losses at midspan were calculated. Final losses were calculated to be approximately 27% higher than those estimated in design.

.

Release and Final Compressive Strengths (Percent Difference)

Beam strands were released at initial concrete strengths of 14,500 psi. Final compressive strengths from three-inch x six-inch test cylinders varied from 20,400 psi to 33,700 psi, with an average of 28,976 psi.

Lower values of compressive strengths may have been due to poor end-cylinder preparation.

Flexure Test The initial flexure test was limited to just over

the concrete cracking load. There was concern that flexure testing to failure might adversely effect the ultimate shear test at the beam ends.

Four jacks were placed symmetrically at midspan, spaced 2.6 feet and 4.5 feet from the center line of the span.

The estimated cracking load for the beam was between 240 kips and 280 kips, based on the loss estimates. Actual cracking was noted at 64 kips per jack or 256 kips total. See Figure 11. The maximum load applied was 264 kips with 3¼ inches of deflection.

Flexure test

Measured flexure cracking at midspan

Shear Test

To help develop a better understanding of the shear capacity of the UHPC mix, additional shear testing was included as part of the research. Shear tests will be performed on a series of smaller beam shapes (10-inch deep by 54-inch long and 12-inch deep by 64-inch long) with web widths from 1½ to 2 inches.

.

Ten-inch and 12-inch shear beams at Iowa State University

FUTURESCOPE:

In UHPC a high amount of steel fiber Added .so that it increases the tensile strength,ductility,durability,fatigue behavior of concrete and also reduces the permeability of concrete.

Shrinkage of concrete reduce and compressive strength also increase at some extent.

REFFERANCES:

“CONCRETE JOURNALS” “INTERNATE”

CHARACTERIZATION OF THE BEHAVIOR OF ULTRA-HIGH PERFORMANCE CONCRETE By Benjamin A. Graybeal

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