AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
TOPIC HIGHLIGHTED HIGH PERFORMANCE CONCRETE DEFINITION CHARACTERISTIC TEST MIX PROPORTION
HIGH STRENGTH CONCRETE DEFINITION CHARACTERISTIC TEST MIX PROPORTION
SELF COMPACTING CONCRETE DEFINITION CHARACTERISTIC TEST MIX PROPORTION
REACTIVE POWDER CONCRETE DEFINITION CHARACTERISTIC TEST MIX PROPORTION APPLICATION IN REAL WORLD
COMPARISON
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
HIGH PERFORMANCE CONCRETE DEFINITION HPC can be defined as a concrete made with appropriate materials (super-plasticizer, retarder, fly ash, blast furnace slag and silica fume) combined to give excellent performance in some properties of concrete, such as high compressive strength, high density, low permeability, and good resistance to certain forms of attack. Any concrete which satisfies certain criteria proposed to overcome limitations of conventional concretes may be called High-Performance concrete (HPC). Therefore it is not possible to provide a unique definition of HPC without considering the performance requirements of the intended use of the concrete.
American Concrete Institute define HPC as concrete which meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing, and curing practices. Concretes possessing many of these characteristics often achieve higher strength. Therefore HPC is often of high strength, but high strength concrete may not necessarily be of High-Performance.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
Category of HPC
Maximum
Minimum
Minimum Compressive
Water/
Frost
Strength
Cement
Durability
Ratio
Factor
Very early strength (VES) Option A (with Type III cement)
14MPa in 6 hours
0.40
80%
Option B (with PBC-XT cement)
17.5MPa in 4 hours
0.29
80%
High early strength (HES) (with
17.5MPa in 24 hours
0.35
80%
Very high strength (VHS)
70 MPa
0.35
80%
(with Type I cement)
in 28 hours
Type III cement)
Definition of HPC according to SHRP C-205 project (Zia, et al. 1993)
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
CHARACTERISTIC Based on the results of SHRP C-103 and SHRP C-205 research, the Federal Highway Administration (FHWA) has proposed criteria for four different performance grades of HPC. The criteria are expressed in terms of eight performance characteristics including
Strength Elasticity Freezing/thawing durability Chloride permeability
Abrasion resistance Scaling resistance Shrinkage Creep
Depending on a specific application, a given HPC may require different grade of performance for each performance characteristics. The Benefits
early stripping of formwork greater stiffness These factors higher axial strength. lead to
smaller columns
high economic efficiency high utility long-term engineering economy.
Barriers o o
Current design criteria may not clearly define the properties and usage of HPC. More research is needed in this area. Compared to normal-strength concrete, the performance of HPC is more brittle in regions with high seismic activity. This is due to the greater stiffness of HPC.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
TEST Performance
Standard Test
Characteristic
Method
Notes AASHTO T 161
1. Test specimen 76.2 x 76.2 x 279.4 mm (3 x 3 x 11 in) cast or cut from
Freeze/Thaw ASTM C 666
152.4 x 304.8 mm (6 x 12 in) cylinder
Durability Proc. A Scaling
2. Acoustically measure dynamic modulus until 300 cycles. 1. Test specimen to have a surface area of 46,451 mm 2 (72 in2).
ASTM C 672 Resistance
2. Perform visual inspection after 50 cycles 1. Concrete shall be tested at 3 different locations. 2. At each location, 98 Newton, for three, 2 minute, abrasion periods
Abrasion
shall be applied for a total of 6 minutes of abrasion time per location. 3. The depth of abrasion shall be determined per ASTM C 799 Procedure B.
Chloride
AASHTO T 277
Permeability
ASTM C 1202
1. Test per standard test method. 1. Molds shall be rigid metal or one time use rigid plastic. 2. Cylinders shall be 100 mm dia. x200 mm long (3.9 x 7.8 in) or 150 mm dia. x300 mm long (5.9 x 11.2 in). 3. Ends shall be capped with high strength capping compound, AASHTO T 22
ground parallel, or placed onto neoprene pads per AASHTO
Strength ASTM C39
specifications for Concretes 4. Use of neoprene pads on early age testing of concrete exceeding 70Mpa at 56 days should use neoprene pads on the 56 day tests 5. The 56 day strength is recommend
Elasticity
ASTM C 469
1. Test per standard test method. 1. Use 76.2 x 76.2 x 285 mm (3 x 3 11 1/4 in) specimens
Shrinkage
ASTM C 157
2. Shrinkage measurements are to start 28 days after moist curing and be taken for a drying period of 180 days. 1. Use 152 x 305 mm (6 x 12 in) specimens 2. Cure specimens at 73° F and 50% RH after 7 days until loading at 28
Creep
ASTM C 512
days. 3. Creep measurements to be taken for a creep loading period of 180 days.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
MIX PROPORTION As different HPC mixtures served different purpose of performances, some of the mix ratio below is being applied
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
HIGH STRENGTH CONCRETE DEFINITION The primary difference between HSC and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. The American Concrete Institute defines HSC as concrete with a compressive strength greater than 40MPa. This value was adopted in 1984, but is not yet hard and fast, because ACI recognizes that the definition of high strength varies on a geographical basis. Prof. J. Francis Young of the University of Illinois at Champaign-Urbana has developed a strength classification system that, though not yet adopted by a recognized authority, is a helpful tool for describing HSC (see below). Strength Classification Of Concrete
Manufacture of HSC involves making optimal use of the basic ingredients that constitute normal-strength concrete. When selecting aggregates for HSC, producers consider the strength of the aggregate, the optimum size of the aggregate, the bond between the cement paste and the aggregate, and the surface characteristics of the aggregate. Any of these properties affects the ultimate strength of HSC.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
CHARACTERISTIC Overview Traditionally, compressive strength high-rise structures now requiring whereby the structural elements in periods of a year or more. Under
tests are made at 28 days, but many HSC employ a construction schedule the lower floors are not fully loaded for these circumstances, it is reasonable to
specify compressive strengths based on either 56 or 90 day results, thereby taking advantage of the strength gain that occurs after 28 days. The upper limit of concrete strength at 90 days and beyond appears to be 172 to 207MPa. A versatile material, HSC possesses desirable properties other than high strength. The most dramatic and memorable applications stem from this aspect, however, as high-rise buildings like 311 South Wacker Drive create striking visual impressions. This structure, at 295m, was the world’s tallest concrete building when completed in 1989, utilizing concrete with compressive strength of up to 83MPa. In high-rise buildings, HSC helps to achieve more efficient floor plans through smaller vertical members and has also often proven to be the most economical alternative by reducing both the total volume of concrete and the amount of steel required for a load-bearing member. Also, formwork is a large portion of the cost of constructing a column and smaller column sizes reduce the amount of formwork needed and result in further cost savings. Why do we need HSC in short? o
To put the concrete into service at much earlier age, for example opening the pavement at 3-days.
o
To build high-rise buildings by reducing column sizes and increasing available space. To build the superstructures of long-span bridges.
o o
To satisfy the specific needs of special applications such as durability, modulus of elasticity, and flexural strength.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
TEST Sample Size The American Concrete Institute has recently published a new Guide to Quality Control and Testing of HSC. The compressive strength is measured on 150 x 300 mm generally at 56 or 90-days, more than normal strength concretes. Concrete tested at an age of 56 or 90 days generally has a higher compressive strength than concrete tested at 28 days. This is more noticeable with concrete containing fly ash and less noticeable with concrete containing silica fume. In addition, it is recommended that at least three specimens be made for each test age. Smaller test cylinders (100 x 200 mm) are acceptable provided the strength is determined in accordance with ASTM C 39 and the same size cylinder is used for both trial mixtures and acceptance testing. Break-off Test Method This method was developed in 1977, by researchers at the Norwegian Technical University (NTH), and the Research Institute for Cement and Concrete in Norway. An ASTM standard test procedure for this method is also under current standardization process. The Break-Off test method measures the flexural strength of the in-place concrete with a rupture plane located at 70 mm from the concrete surface. The test principle involves breaking off a cylindrical test specimen formed in the concrete by applying a force at the top of the test specimen. The test specimen is formed by inserting a tubular sleeve when the concrete is plastic and removing it prior to testing, or by drilling a core, in the hardened concrete, at the time of the break-Off test. The core is drilled with a special diamond-tipped drill bit. The force is applied through a load cell placed at the top of the specimen. Approximately one stroke of the hand-pump per second is applied by the use of a manual hydraulic pump attached to the load cell. The pumping is continued until the break-off specimen fails. The pressure required to break-off the test specimen is measured by a mechanically operated manometer.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
MIX PROPORTION How to Design HSC Mixtures? Some of the basic concepts that need to be understood for HSC are:
Aggregates should be strong and durable. Generally smaller maximum size coarse aggregate is used for higher strength concretes. HSC mixtures will have a high cementitious materials content that increases the heat of hydration. Most mixtures contain one or more supplementary cementitious materials HSC mixtures generally need to have a low water-cementitious ratio (w/cm). W/cm ratios can be in the range of 0.23 to 0.35. The total cementitious material content will be typically around 415 kg/m but not more than about 650 kg/m. The use of air entrainment in HSC will greatly reduce the strength potential.
Water-cementitious materials ratio. The most important variable in achieving HSC is the water-cement ratio. However, most HSC contain binding materials other than cement. Consequently, the water-cementitious materials ratio must be considered instead. In general, as the water-cementitious materials ratio decreases, the concrete compressive strength increases. Portland cement. Proper selection of the type and source of cement is one of the most important steps in the production of HSC. To achieve higher strengths, it is necessary to include other materials such as fly ash, silica fume, GGBFS, or combinations of these materials
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
Coarse aggregate. In general, a smaller size aggregate will result in a higher compressive strength concrete. However, the use of large coarse aggregate size is important to increase the modulus of elasticity or reduce creep and shrinkage. Fine aggregate. Fine aggregates with a fineness modulus in the range of 2.5 to 3.2 are preferable for HSC. Concretes with a fineness modulus less than 2.5 may be sticky and result in poor workability and high water requirement. Chemical admixtures. Water reducers are essential in HSC to ensure adequate workability while achieving a low water-cementitious materials ratio. The water-reducing retarder slows the hydration of the cement and allows workers more time to place the concrete. Low permeability concrete Fly ash and GGBFS generally reduce the permeability of concrete even when the cement content is relatively low, and silica fume is especially effective in this regard. Tests show that the permeability of concrete decreases as the quantity of hydrated cementitious materials increases and the water-cementitious materials ratio decreases. Admixtures Pozzolans (fly ash and silica fume) is the commonly used admixtures in HSC. These materials impart additional strength to the concrete by reacting with Portland cement hydration products to create additional C-S-H gel responsible for concrete strength. It would be difficult to produce HSC mixtures without using chemical admixtures such as super-plasticizer combine with water-reducing retarder. The super-plasticizer gives the concrete adequate workability at low water-cement ratios, leading to concrete with greater strength.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
SELF COMPACTING CONCRETE DEFINITION SCC (SCC) is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. The hardened concrete has the same engineering properties and durability as traditional vibrated concrete. Concrete that requires little vibration or compaction has been used in Europe since the early 1970s but SCC was not developed until the late 1980’s in Japan. In Europe it was probably first used in civil works for transportation networks in Sweden in the mid 1990’s. The EC funded a multi-national, industry lead project SCC 1997-2000 and since then SCC has found increasing use in all European countries. SCC offers a rapid rate of concrete placement, with faster construction times and ease of flow around congested reinforcement. The fluidity and segregation resistance of SCC ensures a high level of homogeneity, minimal concrete voids and uniform concrete strength, providing the potential for a superior level of finish and durability to the structure. SCC is often produced with low water-cement ratio providing the potential for high early strength, earlier demoulding and faster use of elements and structures. The elimination of vibrating equipment reduces the exposure of workers to noise and vibration. The improved construction practice and performance, combined with the health and safety benefits, make SCC a very attractive solution for both precast concrete and civil engineering construction. In 2004, a document “The European Guidelines for Self Compacting Concrete” was published and addresses those issues related to the absence of European specifications, standards and agreed test methods.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
CHARACTERISTICS Compressive strength SCC with a similar water cement or cement binder ratio will usually have a slightly higher strength compared with traditional vibrated concrete, due to the lack of vibration giving an improved interface between the aggregate and hardened paste. Tensile strength The tensile strength may be safely assumed to be the same as normal concrete as the volume of paste (cement + fines + water) has no significant effect on tensile strength. Static modulus of elasticity Aggregate with a high E-value will increase the modulus of elasticity of concrete. However, increasing the paste volume could decrease the E-value. Because SCC often has higher paste content than traditional vibrated concrete, the E-value may be lower. Creep Creep is defined as the gradual increase in deformation with constant applied stress. Creep in compression reduces the pre-stressing forces in pre-stressed concrete elements. Creep in tension can be beneficial as it relieves the stresses induced by other restrained movements. Creep is influenced by its porosity which is related to water/cement ratio. During hydration, the porosity reduces and creep reduces. Cements that hydrate rapidly will have higher strength at the age of loading, a lower stress/strength ratio and a lower creep. As the aggregates restrain the creep of the cement paste, the higher the volume of the aggregate and the higher the E-value of the aggregate, the lower the creep will be. Due to the higher volume of cement paste, the creep coefficient for SCC expected to be higher.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
Shrinkage Autogenous shrinkage is caused by the internal consumption of water during hydration. Drying shrinkage is caused by the loss of water to the atmosphere. The main loss of water is from the aggregate. The aggregate restrains shrinkage of the cement paste and so the higher the volume of the aggregate and the higher the E-value of the aggregate, the lower the drying shrinkage. A decrease in the maximum aggregate size which results in a higher paste volume increases the drying shrinkage. As compressive strength is related to the water/cement ratio, in SCC with a low water/cement ratio drying shrinkage reduces and the autogenous shrinkage can exceed it. Tests performed on creep and shrinkage of different types of SCC show that • the deformation caused by shrinkage is higher • the deformation caused by creep is lower Coefficient of thermal expansion Using an aggregate with a lower coefficient of thermal expansion will reduce the coefficient of thermal expansion of the resulting concrete. While the range of the coefficient of thermal expansion is from 8 to13 microstrains/K, EN 1992-1-1 states that unless more accurate information is available, it may be taken as 10 to 13 microstrains/K. The same is assumed for SCC. Bond to reinforcement, prestressing and wires Reinforced concrete is based on an effective bond between concrete and the reinforcing bars. The effectiveness of bond is affected by the position of the embedded bars and the quality of concrete as cast. Poor bond often results from a failure of the concrete to encapsulate the bar during placing or bleed and segregation of the concrete before hardening. SCC fluidity and cohesion minimize these effects, especially for top bars in deep sections.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
Shear force capacity across pour planes The surface of hardened SCC after casting and hardening may be rather smooth and waterproof. Without any treatment of the surface after placing the first layer, the shear force capacity between the first and second layer may be lower than for vibrated concrete and may therefore be insufficient to carry any shear force. A surface treatment such as surface retarder, brushing or surface roughening should to be sufficient. Fire resistance Concrete is non-combustible and does not support the spread of flames. The fire resistance of SCC is similar to normal concrete. In general a low permeability concrete may be more prone to spalling. SCC can easily achieve the requirements for high strength, low permeability concrete and will perform in a similar way to any normal high strength concrete under fire conditions. Durability The durability of a concrete structure is closely associated to the permeability of the surface layer against ingress of substances and depends on material selection, concrete composition, placing, compaction, finishing and curing. Lack of compaction has been recognized as a key factor of poor durability of reinforced concrete structures exposed to honeycombing, segregation, and bleeding. The comparison of permeability between SCC and normal vibrated concrete will depend on the selection of materials and the effective water cement ratio. SCC with the right properties will be free from those shortcomings hence, better durability.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
TEST A wide range of test methods have been developed to measure and assess the fresh properties of SCC. Table below lists the most common tests grouped according to the property assessed. No single test is capable of assessing all of the key parameters, and a combination of tests is required to fully characterize an SCC mix. Characteristic
Test method
Measured value
Slump-flow
total spread
Kajima box T500
visual filling
V-funnel
flow time
O-funnel
flow time
Orimet
flow time
L-box
passing ratio
U-box
height difference
J-ring
step height, total flow
Kajima box
visual passing ability
penetration
depth
sieve segregation
percent laitance
settlement column
segregation ratio
Flowability/filling ability
Viscosity/ flowability
Passing ability
Segregation resistance
flow time
Test properties and methods for evaluating SCC
Slump-flow and T500 time test Introduction The slump-flow and T500 time is a test to assess the flowability and the flow rate of SCC in the absence of obstructions. It is based on the slump test described in EN 12350-2. The result is an indication of the filling ability of self-compacting concrete. The T500 time is also a measure of the speed of flow and hence the viscosity of the self-compacting concrete. Principle The fresh concrete is poured into a cone as used for the EN 12350-2 slump test. When the cone is withdrawn upwards the time from commencing upward
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
movement of the cone to when the concrete has flowed to a diameter of 500 mm is measured; this is the T500 time. The largest diameter of the flow spread of the concrete and the diameter of the spread at right angles to it are then measured and the mean is the slump-flow.
V-funnel test Introduction The V-funnel test is used to assess the viscosity and filling ability of self-compacting concrete. Principle A V-shaped funnel is filled with fresh concrete and the time taken for the concrete to flow out of the funnel is measured and recorded as the V-funnel flow time.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
L-box test Introduction The L-box test is used to assess the passing ability of self-compacting concrete to flow through tight openings including spaces between reinforcing bars and other obstructions without segregation or blocking. There are two variations; the two bar test and the three bar test. The three bar test simulates more congested reinforcement. Principle A measured volume of fresh concrete is allowed to flow horizontally through the gaps between vertical, smooth reinforcing bars and the height of the concrete beyond the reinforcement is measured.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
MIX PROPORTION There is no standard method for SCC mix design and many academic institutions and companies have developed their own mix proportioning methods. These guidelines are not intended to provide specific advice on mix design but the following table gives an indication of the typical range of constituents in SCC by weight and by volume. These proportions are in no way restrictive and many SCC mixes will fall outside this range for one or more constituents. Constituent
Typical range by mass
Typical range by
3
(kg/m )
volume 3
(liters/m ) Powder
380 - 600
Paste
300 - 380
Water
150 - 210
150 - 210
Coarse aggregate
750 - 1000
270 - 360
Fine aggregate (sand)
Content balances the volume of the other constituents, typically 48 – 55% of total aggregate weight.
Water/Powder ratio by volume
0.85 – 1.10
Typical range of SCC mix composition Mix design approach The mix design is generally based on the approach outlined below: o o o o o o o
evaluate the water demand and optimize the flow and stability of the paste determine the proportion of sand and the dose of admixture to give the required robustness test the sensitivity for small variations in quantities (the robustness) add an appropriate amount of coarse aggregate produce the fresh SCC in the laboratory mixer, perform the required tests test the properties of the SCC in the hardened state produce trial mixes in the plant mixer.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
Select required performance based on purchaser
Select constituent materials (From the bulk supply if possible)
Evaluate alternative materials
Design mix composition
Not Satisfactory Verify or adjust performance by laboratory testing Satisfactory Verify or adjust performance by trials on site or in the plant Sequence of mix design approach
In the event that satisfactory performance is not obtained, the following courses of action might be appropriate: o o o o
adjust the cement/powder ratio and the water/powder ratio and test the flow and other properties of the paste try different types of addition (if available) adjust the proportions of the fine aggregate and the dosage of super-plasticizer adjust the proportion or grading of the coarse aggregate
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
REACTIVE POWDER CONCRETE DEFINITION Overview HDR Engineering Inc.'s former parent corporation, the French firm Bouygues, has used High Performance Concrete (HPC) with characteristic strengths up to 100MPa -- approximately four times the strength of conventional sidewalk concrete. Through this work, new frontiers have been opened in the development of new materials and led to a breakthrough product: Reactive Powder Concrete (RPC). The term Reactive Powder Concrete (RPC) or Ultra High Performance Concrete has been used to describe a fiber-reinforced, super-plasticized, silica fume-cement mixture with very low water-cement ratio (w/c) characterized by the presence of very fine quartz sand (0.15-0.40 mm) instead of ordinary aggregate. In fact, it is not a concrete because there is no coarse aggregate in the cement mixture. The absence of coarse aggregate was considered by the inventors to be a key-aspect for the microstructure and the performance of the RPC in order to reduce the heterogeneity between the cement matrix and the aggregate. The Technology Developed in the 1990s by Bouygues' laboratory in France and was nominated for the 1999 Nova Awards from the Construction Innovation Forum. Its microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. It uses highly refined silica fume and optimization of the Portland cement to produce the highest strength hydrates. RPC represents a new class of Portland cement-based material with compressive strengths exceed 200MPa range. By incorporating with fine steel fibers, RPC can achieve flexural strength up to 50MPa. RPC exhibits high ductility a character previously reserved for metals. RPC will be promisingly able to solve a lot of drawbacks of last concretes, i.e. poor flexural behavior, cracks, shrinkage, and creep. For these reasons, RPC will be suitable in various applications for structures with light and thin components such as roofs of stadiums, long spans of bridges, or structures requiring safe protection such as security enclosures for banks, containment
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
of nuclear waste and so on. The concrete is composed of extremely fine powders, including glass-making sand, cement, quartz and silica fume. Reportedly, its largest particles don't exceed 500 micrometers in diameter! The properties of RPC are achieved by: o o o o o
No coarse aggregates Optimizing the grain size distribution to densify the mixture Post-set heat-treatment to improve the microstructure Addition of steel and synthetic fibers (about 2% by volume) Use of super-plasticizers to decrease the water to cement ratio
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
CHARACTERISTICS Overview However, due to the use of very fine sand instead of ordinary aggregate, the cement factor of the RPC is as high as 900-1000 kg/m3. This unusual cement factor could increase drying shrinkage and creep strain of the RPC with respect to ordinary concrete with cement factor usually in the range of 300-500 kg/m3. The compressive strength of RPC is typically around 200MPa, but can be produced with compressive strengths up to 810MPa. However, the low comparative tensile strength requires prestressing reinforcement in severe structural service. The material's ductility and ability to absorb energy is also improved with typical values 300 times greater than HPC, making it comparable to that of some metals.
Its superior strength combined with higher shear capacity results in significant dead load reduction and limitless structural member shape. RPC provides improved seismic performance by reducing inertia loads with lighter members, allowing larger deflections with reduced cross sections, and providing higher energy absorption. Its low and non-interconnected porosity diminishes mass transfer making penetration of liquid/gas or radioactive elements nearly non-existent.
RPC vs. Steel The RPC concept is based on the principle that a material with minimum defects such as micro-cracks and inside voids. Therefore, it will be able to realize a greater load-carrying capacity and greater durability. RPC can, in
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
some areas, compete with steel. The refinements involved in RPC technology make it possible to create a more homogeneous cement-based material by reducing the differences between the cement and aggregate. This results in a concrete product with properties which, in the past, have been reserved for metals and allows for the design of new products and structures using concrete. If we consider of its performances nearing those of metals and slightly, RPC is truly competitive where steel is predominant. However, RPC will not replace concrete where conventional concrete economically meet the required performance criteria. X-shaped prestressed beams The current structural code used for prestressed beams would not take maximum advantages of the capabilities of RPC. An RPC prestressed beam, with an hourglass cross section (referred to as X-shaped) and without any kind of secondary steel bar reinforcement, was tested to carry equal moment capacity when compared to its steel wide-flange counterpart and to have the same depth and very close weight. By using RPC, the depth of the member can be reduced by 50 percent and its weight by 75 percent compared to conventional prestressed concrete.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
TEST So far, only two methods have been highlighted. One is the conventional way of treating the RPC as normal concrete. Another one which is still under further experiment is ultrasonic testing. Because of the homogeneous, highly packed nature of the RPC microstructure, it is possible to use ultrasonic testing in ways not possible with traditional concrete. Transducer frequencies of 10 to 20 times those used in normal concrete can be used to launch and receive ultrasonic waves over distances on the order of several hundred millimeters.
Test setup for measuring ultrasonic velocities, showing (A) compression spring, (B) transducer jig, (C) ultrasonic transducer, and (D) RPC cube.
Initial research indicates that ultrasonic wave velocities can help determine the elastic properties of the material, and traditional pulse-echo ultrasonic testing can be used to detect cracks in the cement matrix. Ongoing research is exploring how ultrasonic velocity measurements can be used as a quality-control tool during construction and how ultrasonic testing may be used for in-service inspection of bridges constructed of RPC. The outcome of the experiment has confirmed that ultrasonic testing has the potential to be used as guide for RPC testing and further testing is required.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
MIX PROPORTION
Material
Amount (lb/yd3)
Percent by Weight
Portland Cement
1200
28.7
Fine sand
1720
41.1
Silica Fume
390
9.3
Ground Quartz
355
8.5
Super-plasticizer
22
0.5
Steel Fibers
270
6.4
Water
230
5.5
1 lb/yd3 = 0.593 kg/m3
Typical composition of RPC
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
APPLICATION IN REAL WORLD Sherbrooke pedestrian bridge
An international team has been formed to construct a lightweight space-truss pedestrian/bikeway using this RPC in Sherbrooke, Canada. To demonstrate the unique characteristics of RPC and minimize weight, a design concept was chosen which differs significantly from those used for traditional concrete structures. The superstructure of the bridge will be a three-dimensional prestressed space truss spanning 200 feet. The walkway deck, which also serves as the top chord of the truss, is only 1 inch thick. The web members will be a composite design using RPC confined in thin-wall stainless steel tubing. No conventional reinforcing steel is planned for the entire superstructure. The footbridge's thickness is six inches. A comparative study showed that the same structure made of HPC would have required a thickness of 15 inches! RPC technology will allow the footbridge builders to optimize material use, realize economic benefits and build a structure that is environmentally friendly. Applied RPC technology allows the design of more mechanically intelligent structures and a more rational use of construction materials.
AUTHOR: AU YONG THEAN SENG www.madisonvelocity.blogspot.com
COMPARISON
HPC DEFINITION
CHARACTERISTIC
TEST
MIX PROPORTION
HSC
SCC
RPC
Emphasized on certain
Compressive strength
Doesn't required vibration
required performance
> 40MPa
and compaction
Depends on required
Can reach 200MPa in
Fluidity and segregation
- High ductility
characteristic
90 days
resistant
- Homogenous
Same as conventional testing
No large coarse aggregate
-Slump Break-off test
-V-funnel
Ultrasonic
-L Shape Box
Depends on required
Optimizing all related
characteristic
mixture factors
Typical mixture
Typical mixture