Smart-Dynamic Concrete SDC

Written By Vero Pents on August 20, 2012 | 15:50



Smart Dynamic Concrete (SDC) 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 is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete.



smart dynamic concrete The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete.





Smart Dynamic Concrete offers a rapid rate of concrete placement,
with faster construction times and ease of flow around congested reinforcement. The fluidity and segregation resistance of SDC 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. SDC 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 improves the environment on and near construction and precast sites where concrete is being placed, reducing the exposure of workers to noise and vibration.



 The improved construction practice and performance, combined with the health and safety benefits, make SDC a very attractive solution for both precast concrete and civil engineering construction.

Constituent materials
 General
The constituent materials for SDC are the same as those used in traditional vibrated concrete conforming to EN 206-1. In most cases the requirements for constituents are individually covered by specific European standards. However, in order to be sure of uniform and consistent performance for SDC, additional care is needed in initial selection and also in the continual monitoring for uniformity of incoming batches.
To achieve these requirements the control of the constituent materials needs to be increased and the tolerable variations restricted, so that daily production of SDC is within the conformity criteria without the need to test and/or adjust every batch.
 Cement
All cements which conform to EN 197-1 can be used for the production of SDC. The correct choice of cement type is normally dictated by the specific requirements of each application or what is currently being used by the producer rather than the specific requirements of SDC.
 Additions
Due to the fresh property requirements of SDC, inert and pozzolanic/hydraulic additions are commonly used to improve and maintain the cohesion and segregation resistance. The addition will also regulate the cement content in order to reduce the heat of hydration and thermal shrinkage.
The additions are classified according to their reactive capacity with water:


TYPE I
Inert or semi-inert


                • Mineral filler (limestone, dolomite etc)
                • Pigments
TYPE II
Pozzolanic


                • Fly ash conforming to EN 450 S
                • Silica fume conforming to EN 13263
Hydraulic


                • Ground granulated blast furnace slag


(If not combined in an EN 197-1 cement, national standards may apply until the new EN 15167 standard is published)


Additions, other than those combined in an EN 197-1 cement, may not be as well controlled in terms of particle size distribution and composition as some other concrete constituents so increased monitoring of deliveries may be necessary.
Smart Dynamic Concrete is often selected for its high quality finish and good appearance but this may be compromised if the source of the addition does not have good colour consistency.
Mineral fillers
 The particle size distribution, shape and water absorption of mineral fillers may affect the water demand /sensitivity and therefore suitability for use in the manufacture of SDC. Calcium carbonate based mineral fillers are widely used and can give excellent rheological properties and a good finish. The most advantageous fraction is that smaller than 0.125 mm and in general it is desirable for >70% to pass a 0.063mm sieve. Fillers specifically ground for this application offer the advantage of improved batch to batch consistency of particle size distribution, giving improved control over water demand and making them particularly suitable for SDC compared with other available materials.
 Fly Ash
Fly ash has been shown to be an effective addition for SDC providing increased cohesion and reduced sensitivity to changes in water content. However, high levels of fly ash may produce a paste fraction which is so cohesive that it can be resistant to flow.
 Silica fume
The high level of fineness and practically spherical shape of silica fume results in good cohesion and improved resistance to segregation. However, silica fume is also very effective in reducing or eliminating bleed and this can give rise to problems of rapid surface crusting. This can result in cold joints or surface defects if there are any breaks in concrete delivery and also to difficulty in finishing the top surface.
 Ground blast furnace slag
Ground granulated blast furnace slag (ggbs) provides reactive fines with a low heat of hydration. GGBS is already present in some CEM II or CEM III cements but is also available as an addition in some countries and may be added at the mixer. A high proportion of ggbs may affect stability of SDC resulting in reduced robustness with problems of consistence control while slower setting can also increase the risk of segregation.
 Other additions
Super Fine Fly Ash, Metakaolin, natural pozzolana, ground glass, air cooled slag and other fine fillers have also been used or considered as additions for SDC but their effects need to be carefully and individually evaluated for both short and long term effects on the concrete.
 Aggregates
Normal-weight aggregates should conform to EN 12620 and meet the durability requirements of EN 206-1. Lightweight aggregates should conform to EN 13055-1.
NOTE: Aggregate particles smaller than 0,125 mm are deemed to contribute to the powder content of the SDC.
The moisture content, water absorption, grading and variations in fines content of all aggregates should be closely and continuously monitored and must be taken into account in order to produce SDC of constant quality. Using washed aggregates will normally give a more consistent product. Changing the source of supply is likely to make a significant change to the concrete properties and should be carefully and fully evaluated.
The shape and particle size distribution of the aggregate is very important and affects the packing and voids content. Some mix design methods use the voids content of the aggregate in predicting the volumes of paste and of mortar required. Single size aggregates and/or a gap in the grading between coarse and fine aggregates are used in some mix designs.
 Coarse aggregate
Coarse aggregates conforming to EN 12620 are appropriate for the production of SDC.
 The reinforcement spacing is the main factor in determining the maximum aggregate size. Aggregate blocking must be avoided as SDC flows through the reinforcement and the L-box test is indicative of the passing ability of an SDC mix. The maximum aggregate size should generally be limited to 12 – 20 mm, although larger sizes are being used.
The particle size distribution and the shape of coarse aggregate directly influence the flow and passing ability of SDC and its paste demand. The more spherical the aggregate particles the less they are likely to cause blocking and the greater the flow because of reduced internal friction.
 Fine Aggregate / Sands
The influence of fine aggregates on the fresh properties of the SDC is significantly greater than that of coarse aggregate. Particles size fractions of less than 0.125 mm should be include the fines content of the paste and should also be taken into account in calculating the water powder ratio.
The high volume of paste in SDC mixes helps to reduce the internal friction between the sand particles but a good grain size distribution is still very important. Many SDC mix design methods use blended sands to match an optimized aggregate grading curve and this can also help to reduce the paste content. Some producers prefer gap-graded sand.
 Admixtures
HyperPlasticisers or high range water reducing admixtures conforming to EN 934-2 Tables 3.1 and 3.2 are an essential component of SDC. Viscosity modifying admixtures (VMA) must also be used to help reduce segregation and the sensitivity of the mix due to variations in other constituents, especially to moisture content. Other admixtures including air entraining, accelerating and retarding may be used in the same way as in traditional vibrated concrete but advice should be sought from the admixture manufacturer on use and the optimum time for addition and they should conform to EN 934-2.
Choice of admixture for optimum performance may be influenced by the physical and chemical properties of the binder/addition. Factors such as fineness, carbon content, alkalis and C3A may have an effect. It is therefore recommended that compatibility is carefully checked if a change in supply of any of these constituents is to be made.
Admixtures will normally be very consistent from batch to batch but moving to another source or to another type from the same manufacturer is likely to have a significant effect on SDC performance and should be fully checked before any change is made.
Hyper-Plasticizer
The concrete should contain an admixture based on Polycarboxylic ether which has been tailored to specific user requirements and the effects of other mix constituents.
The admixture should bring about the required water reduction and fluidity but should also maintain its dispersing effect during the time required for transport and application. The required consistence retention will depend on the application. The admixture should be based on nano particle distribution which in effect will control the stiffening and/or setting of the concrete.


Viscosity modifying admixtures
Admixtures that modify the cohesion of the SDC without significantly altering its fluidity are called viscosity modifying (VMA). These admixtures are used in SDC to minimise the effect of variations in moisture content, fines in the sands or its grain size distribution, making the SDC more robust and less sensitive to small variations in the proportions and condition of other constituents. However, they should not be regarded as a way of avoiding the need for a good mix design and careful selection of other SDC constituents.
 At present EN 934-2 does not cover VMAs but they should conform to the general requirements in Table 1 of EN 934-2. In addition, evidence of performance should be provided by the supplier. A draft method for establishing suitability of VMAs (based on EN 934-2) is given on the EFCA web site www.efca.info.
Mixing water
Water conforming to EN 1008 should be used in SDC mixes. Where recycled water, recovered from processes in the concrete industry, is used the type/content and in particular any variation in content of suspended particles should be taken into account as this may affect batch to batch uniformity of the mix.
 Mix design approach
Laboratory trials should be used to verify properties of the initial mix composition with respect to the specified characteristics and classes. If necessary, adjustments to the mix composition should then be made. Once all requirements are fulfilled, the mix should be tested at full scale in the concrete plant and if necessary at site to verify both the fresh and hardened properties.
 The mix design is generally based on the approach outlined below:
                      • evaluate the water demand and optimise 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 which should constitute
                • approximately 40% of the total aggregate in the mix design.
                • produce the fresh SDC in the laboratory mixer, perform the required tests
                • test the properties of the SDC in the hardened state
                • produce trial mixes in the plant mixer.
Test methods
 Smart Dynamic Concrete
 Laboratory Tests                   :          Slump-flow by Abrams cone                    600-700    
                                                            T50cm slump flow by Abrams cone          3-5 sec
                                                     V-Funnel                                                       6-12 sec
                                                     V-Funnel at T5 minutes                              + 3 sec
                                                      


Site Tests                               :           Slump-flow by Abrams cone                      600-700 mm
                                                            T50cm slump flow by Abrams cone          3-5 sec
                                                     V-Funnel                                                       6-12 sec


Rerenced standards
 EN 197-1 Cement – Part 1: Composition, specifications and conformity criteria for common cements
EN 206-1 Concrete – Part 1: Specification, performance, production, and conformity
EN 450-1 Fly ash for concrete – Part 1: Definitions, specifications and quality control
EN 450-2 Fly ash for concrete – Part 2: Conformity control
EN 934-2 Admixtures for concrete, mortar and grout – Part 2: Concrete admixtures - Definitions and requirements
EN 1008 Mixing water for concrete – Specification for sampling, testing and assessing the suitability of water, including water recovered from processes in the concrete industry, as mixing water for concrete
EN1992-1 Eurocode 2: Design of concrete structures Part 1-1 – General rules and rules for buildings Part 1-2 – General rules – Structural file design
EN 12350-1 Testing fresh concrete: Part 1: Sampling
EN 12350-2 Testing fresh concrete: Part 2: Slump test
EN 12620 Aggregates for concrete
EN 12878 Pigments for colouring of building materials based on cement and/or lime – Specification and methods of test
EN 13055-1 Lightweight aggregates – Part 1: Lightweight aggregates for concrete, mortar and grout
EN 13263-1 Silica fume for concrete – Part 1: Definitions, requirements and conformity control
EN 13263-2 Silica fume for concrete – Part 2: Conformity evaluation
EN 13369 Common rules for precast concrete products
EN 13670 Execution of concrete structures
EN 14889 Fibres for concrete
EN 15167-1 Ground granulated blastfurnace slag for use in concrete, mortar and grout – Part 1: Definitions, specifications and conformity criterion
EN 15167 -2 Ground granulated blastfurnace slag for use in concrete, mortar and grout – Part 2: Conformity evaluation
EN ISO 5725 Accuracy (trueness and precision) of Measurement Methods and Results
EN ISO 9001 Quality management systems – Requirements
The European Guidelines for Self-Compacting Concrete.
Note: Some of these EN standards are still in preparation; the latest version of undated standards should be referred to.

The specification, performance and conformity requirements for structural concrete are given in EN 206-1. However, in the case of SDC some properties in the fresh state exceed the limits and classes provided in this standard. None of the test methods in the current EN 12350 series ‘Testing fresh concrete’ are suitable for assessment of the key properties of fresh SDC. Appropriate test methods for SDC are given in Annex B of the The European Guidelines for Smart Dynamic Concrete and it is envisaged that the EN 12350 series will be extended to cover these test methods.


The filling ability and stability of Smart Dynamic Concrete in the fresh state can be defined by four key characteristics. Each characteristic can be addressed by one or more test methods:


Characteristic
Preferred test method(s)
Flow ability
Slump-flow test
Viscosity (assessed by rate of flow)
T500 Slump-flow test or V-funnel test
Passing ability
L-box test
Segregation
J Ring
 These test methods for SDC are described in Annex B of the The European Guidelines for Self-Compacting Concrete.
Types of Smart Dynamic Concrete.

SDC can be used in various structures within a construction site and not all these areas have heavily congested steel, therefore different types of SDC can be utilized.
The best way of differentiating the SDC mixes are by volume of steel incorporated within the structure.
 This type of SDC mix is designed to flow around heavily congested steel. Typical areas were this SDC would be utilized is in sections with more than 100Kg of steel reinforcing per m3 and where the reinforcing bars are closer than 200 mm. The most likely elements that could utilize this form of SDC would be Columns and Walls
 Theoretical Concrete Mix Design                                                             Kg/m3 Dry
                                                           
                                                            Total Cementitious Content                       450
                                                            Course Aggregate 20 mm                          400
                                                            Course Aggregate 10 mm                          350
                                                            Fine Aggregate 0-5 mm                              740
                                                            Dune Sand                                                   370
                                                            Admixture –   Glenium HyperPlasticiser  6.0 lts
                                                                                    Rheomatrix                           1.0 lts
                                                            Water                                                              170
                                                            W/C Ratio                                                      0.378
           
The above concrete mix design, although based on previous concrete mixes, are theoretical and supplied as guidance only.  We would strongly recommend that trial mixes are carried out in order to ascertain that the resulting concrete properties are satisfactory for your requirements.
 This type of SDC mix is designed to flow around less heavily congested steel. Typical areas for this type of concrete would be section with less than 100Kg of steel reinforcing per m3 and where the reinforcing bars are further apart than 200 mm. The most likely elements that could utilize Smart Dynamic Concrete would be Piles, Raft Foundations and Floors.
 Theoretical Concrete Mix Design                                                             Kg/m3 Dry
                                                           
                                                            Total Cementitious Content                       400
                                                            Course Aggregate 20 mm                          300
                                                            Course Aggregate 10 mm                          427
                                                            Fine Aggregate 0-5 mm                              540
                                                            Dune Sand                                                   538
                                                            Admixture –   Glenium HyperPlasticiser 3.5 lts
                                                                                    Rheomatrix                           0.75


                                                            Water                                                              180
                                                            W/C Ratio                                                      0.45

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