A ductal, high compressive construction material
Ultra-High Performance Concrete (UHPC) is a new class of concrete that has been developed in recent decades for its exceptional properties of strength and durability. This high performance concrete can be utilized in structural rehabilitation and accelerated bridge construction in addition to several other applications. Read on to learn more about the history of UHPC, its composition and applications. UHPC is very ductal and certainly has excellent compressive strength. It must contain fiber. Most often metal fiber. It is a very unique material. Cement and other cementitious ingredients are crucial to the binder characteristics required. The aggregate industries can supply the different types of sands often used in UHPC. Most ingredients can be found in the United States. Although higher strength is one of the things that make UHPC different as it relates to other concrete mix design, by itself strength is not enough for without flexural and ductal properties, UHPC is just a brittle high-strength material. This is where the specific fiber types come into play.
Ultra-High Performance Concrete was first used by the U.S. Army Corps of Engineers in the late 1980’s and became available in the US in 2000. The commercial availability of UHPC allowed the Federal Highway Administration (FHWA) to start investigation in order to use UHPC for highway infrastructure. The FHWA investigations led to additional research from universities and demonstration projects. The result was a body of publications on UHPC and a long list of “bridge applications” including:
- Prestressed girders
- Precast waffle panels for bridge decks
- Field-cast closure pours for prefabricated bridge elements (Joint-Fills)
- Precast concrete piles
- Seismic retrofits of bridges
- Thin bonded overlays of bridge decks
- Security and blast mitigation applications
UHPC was first used in bridge construction in North America for a pedestrian bridge in Canada in 1997. Following that, 34 research projects were conducted throughout multiple research institutes for the goal of making UHPC a reliable, commonly available, economically feasible and regularly applied material. Germany also has several bridges using UHPC along with Australia, Austria, Croatia, Italy, Japan, Malaysia, the Netherlands, New Zealand, Slovenia, South Korea, and Switzerland.
- Development of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) CE 443/543 Advanced Concrete Materials Asst. Prof. Dr. İrem Şanal Prepared By ISSA IBRAHIM
- Contents Introduction Definition of UHPFRC Why UHFPRC UHPFRC characteristics Materials and methods Conclusions
- Introduction Increasing requirements for durability, safety and security of concrete structures push its development still further. High rise buildings and other structures of strategic importance such as government buildings and television towers have become a symbol of developed cities worldwide. However, such structures are threatened by possible extreme- load events like earthquakes, gas explosions, car or plane impact and, in recent years, terrorist attacks. New hi-tech materials such as ultra-high performance fiber reinforced concrete (UHPFRC) are ideal for applications where high compressive and tensile strength, small thickness and high energy absorption capacity are required.
- UHPFRC are Advanced Cementitious Materials (ACM) with specifically tailored properties. They are characterized by an ultra-compact matrix with very low permeability and by tensile strain-hardening. Definition of UHPFRC
- Heat treatment after setting very low water-cement ratio small-size steel fibres very high cement content very high superplasticiser dosage
- Why UHFPRC Durable • Outstanding protective properties • Outstanding mechanical properties • Tensile strain hardening • Applicable on site • Adoptable to site conditions • Sustainable repair solution
- UHPFRC characteristics Selfleveling Outstanding protective properties “Selfleveling” Low air permeability
- Materials and methods Materials: The cement used in this study is Ordinary Portland Cement (OPC) CEM I 52.5 R. A polycarboxylic ether based superplasticizer is used to adjust the workability of concrete. The limestone powder is used as a filler to replace cement. A commercially available nano-silica in a slurry is applied as pozzolanic material. Two types of sand are used, one is normal sand in the fraction of 0–2 mm and the other one is a microsand in the 0–1 mm size range.. Additionally, three types of steel fibres are utilized: (1) Long straight fibre (LSF), length = 13 mm, diameter = 0.2 mm; (2) Short straight fibre (SSF), length = 6 mm, fibre diameter = 0.16 mm; (3) Hooked fibre (HF) length = 35 mm, diameter = 0.55 mm. The densities of the used materials are shown in Table.
- Information of materials used. Specific density (kg/m3) TypeMaterials 3150CEM I 52.5 RCement 2710powderFiller Limestone 2720MicrosandFine sand 2640Sand 0–2Coarse sand 1050Polycarboxylate etherSuperplasticizer 2200(nS)Nano-silicaPozzolanic material 7800Long steel fibre (13/0.2)Fibre-1 7800Short steel fibre (6/0.16)Fibre-2 7800Hooked steel fibre (35/0.55)Fibre-3
- Experimental methodology: Mix design of UHPFRC: In the previous investigations of the authors, it was demonstrated how to produce UHPFRC with a relatively low binder amount Hence, also in this study, the modified Andreasen and Andersen model is utilized to design all the concrete mixtures, which is shown as follows: where D is the particle size (lm), P(D) is the fraction of the total solids smaller than size D, Dmax is the maximum particle size (lm), Dmin is the minimum particle size (lm) and q is the distribution modulus.
- Particle size distribution of the involved ingredients, the target curve and the resulting integral grading curve of the mixtures.
- Steel fibers used in this study
- Mixing procedure: In this study, the concrete matrix is well mixed with steel fibers. Before the hybrid fibers are added into the concrete mixture, the fibers are mixed together for 1 min. The mixing is always executed under laboratory conditions with dried and tempered aggregates and powder materials. The room temperature while mixing and testing is constant at around 21 C. Flowability of UHPFRC: The slump flow of the fresh UHPFRC mixtures with only straight. The data illustrates the variation of the slump flow of UHPFRC with different short straight fibre (SSF) and long straight fibre (LSF) amounts. SSF-0, SSF-0.5, SSF-1.0, SSF-1.5 and SSF-2.0 represent the mixtures from Nos. 2 to 6, respectively. It can be clearly seen that the slump flows of the designed UHPFRC are all larger than 25 cm, and fluctuate around 29 cm, which can treated as self-compacting mortar, according to the European Guidelines for Self-Compacting Concrete  and the recommendation presented in . Moreover, it is important to notice that with an increase of the SSF amount in the fresh concrete mixtures, the slump flow ability of UHPFRC firstly increases, and then sharply decreases when only the short straight fibres are present. For example, when there are only long straight fibres (LSFs) in the concrete mixture, the slump flow is 28.8 cm, which slightly increases to around 30.0 cm when 0.5% Vol. LSF and 1.5% Vol. SSF are added.
- Variation of the slump flow (using the Hagerman cone) of the developed UHPFRC with only straight steel fibers (SSF-0, SSF-0.5, SSF-1.0, SSF-1.5 and SSF-2.0
- Mechanical properties of UHPFRC The flexural strengths of the designed UHPFRC with only straight steel fibers. The ‘‘Reference’’ represents the mixture without fibers. It is clear that the addition of fibers significantly improves the mechanical properties of concrete. However, the improvement depends on different fibers hybridization. As can be seen, the flexural strengths of the concrete with LSF (1.5% Vol.) and SSF (0.5% Vol.) at 7 and 28 days are always the highest, which are 24.3 MPa and 30.9 MPa, respectively. When only SSF is utilized (2% Vol.), the flexural strengths at 7 and 28 days reduce to around 18.4 MPa and 21.5 MPa, respectively. This can be explained by the following two reasons: (1) SSF can efficiently bridge micro cracks, while LSF is more efficient in resisting the development of macro cracks. Hence, when the micro cracks are just generated in the concrete specimen, the SSF can effectively bridge them. As the micro cracks grow and merge into larger macro cracks, LSF become more active in crack bridging. In this way, the flexural strength of UHPFRC can be improved; (2) LSF are always well oriented between the two imaginary borders, and these borders may also be the walls of the molds. With such positions, LSF form a kind of a barrier for SSF, and limit their space for rotation. The SSF will therefore be somewhat better oriented when combined together with LSF. Hence, more fibres distribute in the direction perpendicular to the load direction in the flexural test, thus the mechanical properties can be significantly improved
- Flexural (a) and compressive (b) strength of the developed UHPFRC with only straight steel fibres (Reference: UHPFRC without fibres).
- Flexural toughness of UHPFRC It can be noticed that the first crack flexural toughness’s of the tested UHPFRC are very small and similar to each other, and fluctuate around 0.2 N m. After that, with a deflection increase, a difference between the post crack flexural toughness’s of UHPFRC can be observed. Especially at the deflection of 10.5 d, the mixture with ternary fibers has the largest post crack flexural toughness (4.1 N m), which is followed by the HF + SSF (3.3 N m), HF + LSF (3.2 N m) and HF (3.1 N m), respectively. , the flexural toughness of the mixture with ternary fibers is the highest, while the flexural toughness of the mixture with only HF is the smallest. HF > HF + LSF + SSF > HF + LSF > HF + SSF. Hence, it can be summarized that the concrete mixture with only HF has the largest flexural toughness, which is closely followed by the mixture with ternary fibers.
- Calculated flexural toughness of the developed UHPFRC based on ASTM C1018-97 (HF, HF + LSF + SSF, HF + LSF and HF + SSF
- Flexural performance of 100 x 100 x 350 mm beam specimens
- Blast performance 5 T of TNT @ 30 m “standard”concrete UHPFRC
- Conclusions An original concept using Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) for the rehabilitation of concrete structures has been presented and validated by means of four applications. This conceptual idea combines efficiently protection and resistance functions of UHPFRC with conventional structural concrete. The rehabilitated structures have significantly improved structural resistance and durability. The full scale realizations of the concept under realistic site conditions demonstrate the potential of applications and that the technology of UHPFRC is mature for cast insitu and prefabrication using standard equipment for concrete manufacturing.