Ultra High Strength Concrete

ULTRA HIGH STRENGTH CONCRETE (UHSC) Prepared by Shihab A. Ibrahim

20131679

Content 

Introduction

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Material properties

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Mixing

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Placing

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Compacting

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Pumping

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Curing

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Heat treatment

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 Application

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Mix design

Introduction 

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Strength is on of the most important characteristic characteristic of hardened concrete. compressive, flexural and tensile are the most common type of concrete strength. When the term “strength” use with concrete it will express its

compression compression strength How ever there is no specific classification limits according to strength but may may be summarized summarized as follow: follow: Normal strength concrete (10 Mpa  – 40 Mpa) High strength concrete (40 Mpa  –100 Mpa) Ultra high strength concrete (100 Mpa  – 800 Mpa)

UHSC (Ultra High Strength Concrete) 

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This type of concrete is developed in the 1990s by Bouygues' laboratory in France. It consists of a special concrete concrete where its microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. UHSC is composed of cement, fine sand, quartz powder, micro silica, HRWRA (High Range Water Reducer Admixture) and steel fibers optional to increase its concrete ductility and tensile strength. w/b ratio of this type of concretes are very low around ~(0.120.15)*  This new family of materials has compressive strengths greater than 150 MPa , Modulus of elasticity up to 70 Gpa, and flexural strength of 30 to 50 MPa, depending on the type of fibers used.  Additionally,  Additionally, it has a tensile strength of between 6 and 13 MPa that is maintained after first cracking.

UHSC (Ultra High Strength Concrete) 

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The absence of coarse aggregate is considered by the inventors to be a key-aspect for the microstructure and the performance of the UHSC in order to reduce the heterogeneity between the cement matrix and the aggregate. However, due to the use of very fine sand instead of ordinary aggregate, the cement content of the UHSC is as high as 600-1000 kg/m3 instead of 300-500 kg/m3 that are usually used for ordinary concrete. Nowadays, UHSC is regarded as a promising material for special pre-stressed and precast concrete members, including including those within industrial and nuclear waste storage facilities.

UHSC (Ultra High Strength Concrete)  Although production production costs of UHSC are generally generally high, some economical advantages also exist in UHSC applications. It is possible to reduce or eliminate passive reinforcement using steel fibers.   And, due to ultra-high ultra-high mechanical mechanical performance of UHSC, UHSC, the thickness of concrete elements can be reduced, which results in materials and cost savings. 

Material properties Cement: 

Ordinary Portland cement type I/II/V can be used. The main

property that the cement must has its low amount of C 3 A and blain properties according to ASTM C150. Some researches indicated that the free C3 A cement gives higher strength than other types, with respect to type of curing.

Material properties Sand:  

fine sand (passing ASTM ASTM No. 30 sieve) are used. Fine sand, generally between 150 and 600 μm, is dimensionally dimensionally the largest granular material that are used in UHSC.

Material properties Micro-silica or Silica fume:

Material properties Super-plasticizer : 

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Third generation of superplasticizer with high dosage (1.2  – 2.5 %) are used for gaining workability in UHSC with w/c ratio lower than 0.22. The new generation of this kind of admixtures is represented by polycarboxlate ether-based superplasticizers (PCEs). With a relatively low dosage (0.15 –0.3% by cement weight) they allow a water reduction up to 40%, due to their chemical structure which enables good particle dispersion.

 Mixing 

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Since UHSC is composed of very fine materials, the conventional mixing method is not appropriate and the mixing method cannot be the same.  According to most researchers this is the common way for mixing: mixing:

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Drying of mixing powders (including cement, quartz sand, crushed quartz and silica fume) for about 1 min at a constant speed of 1800 r/min

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 Addition of half half volume of water water containing containing half amount of SP

Mixing for about 3 min with a speed of about 285 r/min d)  Addition of the remaining water and SP e) Mixing for about 8 min at a constant speed of 1800 r/min. c)

placing 

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UHSC consist of fine material with highly cementitious property and low W/C ratio that make the concrete to be very sticky. sticky.

placing of this type of concrete need skilled person due to the behavior of material and proper technique of placing

Compacting 

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*Due to highly fineness of material and cementieouse cementieouse property the concrete does not fill every parts perfectly. *There is special process for removing air bubles in the concrete that says "Pressure application", before setting and durring setting a pressure will apply to the concrete so as to remove the air voids. *If not, it needs long vibration to make sure of filling any portion of the element. *For precast members recommended to use table t able vibrator to gain better result.

Curing 

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Concrete must be properly cured if its optimum properties are to be developed . An adequate supply of moisture is necessary for ensuring that hydration is sufficient for reducing the porosity to a level such that the desired strength can be attained. There are some type of curing regime that can be made to ensuring the hydration of the material:

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27 °C water.

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60 °C water for 7 days.

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60 °C, 95% RH, mist chamber for 7 days.

Curing 

From Figure, it is found that curing at 60 °C show a remarkable compressive strength at the first 7 days, that is almost equal to the 28-day compressive strength of UHSC under standard water curing at 27 °C. This indicates that curing temperature has a significant effect on the early strength development of UHSC . The increased early strength is due to the rapid hydration of cement at higher curing temperatures of 60 °C compared with that of 27 °C. Moreover, Moreover, the pozzolanic reactions are also accelerated by the higher curing temperatures.

Heat treatment 

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It has been reported that the strength development of ultra-highperformance concrete is strongly temperature dependent. Post setting heat treatment is essential to produce concrete with ultraultra high strength. Type of heat treatments:

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20 °C dry air for 16 h & 48 h

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100 °C oven dry for 16 h & 48 h

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250 °C oven dry for 16 h & 48 h

Effect of temperature and heat-treatment duration on compressive strength of UHSC in 3 days

Heat treatment 

From Figure, it is found that the compressive strength of UHSC increases rapidly with temperature, from 20 °C to t o 250 °C. When the UHSC samples are heattreated at a temperature of about 100 °C for 16 and 48 h, compressive c ompressive strengths of about 120 MPa can be achieved in 3 days. However, However, compressive strengths go up to about 200 MPa when the UHSC samples are heattreated at a temperature of about 250 °C for 16 and 48 h in 3 days, a very high strength value. The increases are much more, when compared with that at room temperature of 20 °C. Increased heattreatment temperature would lead to long C –S –H chains and this phenomenon could be attributed to the progression of cement hydration as well as pozzolanic activity of silica fume and crushed quartz.

 Advantage of UHSC 

UHSC results in smaller sections and significant weight reductions.

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Reduced elements number of structural elements.

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Greater energy absorption during seismic events.

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Dense microstructure of UHSC provides excellent protection against corrosion. Excellent chloride penetration resistance and lower water

Disadvantage of UHSC: 

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*Highly brittleness limited the usage of this concrete, but by adding fiber material the ductility will improve. *high cost, with fiber 1242$ while without fiber 332$ for one cubic meter, meter, (5-10) times expensive than HPC. *Applying pressure to mix and applying heat treatment in the field has got technological difficulties and cost. *Implementation. *There is less research about how it stand in long

Mix design

 Application 

Precast concrete units

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High-pressure pipes

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Blast resistant structures

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Seismic resistant structures

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Security enclosures

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Walkways

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Long span bridges

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Nuclear waste containment structures

 Application 

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First prestressed hybrid pedestrian bridge at Sherbrooke in Canada in 1997. The thickness of the bridge was only 35 mm.

 Application 

Replacement of steel beams of the cooling tower in Cattenom in France in 1997

 Application 

Two heavy traffic bridges built at Bourg-lès-Valence Bourg-lès-Valence in France build in 2001

 Application 

Sunyudo (Peace) footbridge in Seoul, Korea the largest UHSC bridge in the world with a single span of 120m

 Application 

Sakata Mirai Footbridge was planned to replace the old prestressed concrete pedestrian bridge that had been built about 40 years ago in Sakata city, Japan .

 Application 

In addition to the its reputation as the tallest bridge in the world, tollgate of the Millau Viaduct in France, France, is one of the best ever made UHPC roof which was finished in 2003.

 Application 

Hybrid bridge over across the River Fulda in Germany in 2004 was a pedestrian and cycle track bridge with a length of 133.2 m and longest single span of 36 m.

References 

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“Optimal conditions conditions for producing reactive powder concrete” C. M. Tam, V. W. Y. Tam† and K. M. Ng “Ultra-High Strength Concrete Mixtures Using Local Materials” Srinivas Allena and Craig M. Newtson “Fresh and Strength Properties of New Cementitious Composite Material Using Reactive Powder” Masami

UZAWA, Yoshihide SHIMOYAMA and Shigeo KOSHIKAWA. 

“Material Property Characterization of Ultra -High Performance Concrete” PUBLICATION NO. FHWA -HRT-06-

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