Patent Publication Number: US-2022234951-A1

Title: Concrete mix design and method for realizing dam or other massive structure by using the concrete mix design

Description:
TECHNICAL FIELD 
     The present invention relates to a concrete mix design and placement method for realizing dam or other massive structure by using the concrete mix design approach. 
     In particular, the mix design of the present invention has been optimized for the construction of dams (or other massive structures) to be placed by no-conventional means. 
     BACKGROUND ART 
     For several years, the problem of the durability and cost of construction of concrete structures was a major topic of interest in particular in the construction of dams. 
     A dam is a huge construction that needs massive amount of concrete to build it with and that leads to high cost, so alternative methods should be considered to minimize the cost of constructing the dams with new material methods. 
     One known method is building the dams with Roller Compacted Concrete (RCC), which by definition is a composite construction material with no-slump consistency in its unhardened state and it has achieved its name from the construction method. The definition for a no-slump consistency is a freshly mixed concrete with a slump less than 6 mm. 
     The RCC is placed with the help of paving and earthmoving equipment and then it is compacted by vibrating roller equipment from the surface rather than with immersion type vibrators. The basic ingredients RCC mix designs are the same as for the conventional concrete but it has different ratios in the materials that are blended to produce concrete that yields an entirely different set of fresh properties that normal weigh concrete. It differs when it comes to aggregates because both similar aggregates used in conventional concrete or aggregates that do not fulfill the normal standards can be used in the RCC mixtures, in particular the amount of fines (% passing ASTM E11 Sieve #200, minus 75 micron) and smaller sieve sizes in the sand fraction. 
     The RCC dams are usually built in thin, horizontal lifts, in such a way to reduce the amount of formwork and allow for successful external consolidation by vibratory rollers. 
     RCC addressed two factors to lower the cost and decrease the time of concrete dam construction:
         Reducing the amount of water, and therefore cement, in the mix design. This resulted in a direct savings in material cost, without a decrease in strength. Cement is the second greatest material cost after aggregates;   Reducing the dependency on labor on the construction process to a greater extent, both in the skill level and number of workers. This savings was two-fold:
           Increased mechanization allowed for faster construction periods, i.e. machines can do more work than people;   Decreased dependency on labor lessoned the risk of obtaining skilled workers, as well as number of workers required for a project.   
               

     One of the key concepts in the RCC method of building dams is to place one large lift of concrete, about 300 mm in depth, in a continuous manner for the entire surface of the dam, covering each layer with another layer before the initial set of the previous layer. This results in a chemical bond between the layers and results in a more monolithic structure. 
     Because RCC is dryer than normal mass concrete, dozers can spread the material and double or single drum vibrating rollers compact the RCC (similar to building an asphalt road). This is opposed to immersion type vibrators used in typical mass concrete. 
     The method of one layer of continuous placement is opposed to the method of individual blocks used in conventional mass concrete construction. 
     So, the key steps in RCC Dam  100  construction are ( FIG. 1 a   ):
         Batching of RCC  10 ,   Delivery  1  to the dam  100 ,   Transfer  2  to placing location on the dam,   Spreading  3  the RCC,   Compacting  4  the RCC,   GEVR placement  5 ,   Associated formwork  6 .       

     However, for RCC method it is necessary to use machines for spreading and compacting the lifts.  FIG. 1 a    represents the known prior art relative to the RCC used for a dam construction activity. 
     In particular, this type of construction consumes huge amount of construction material and takes long construction period which increases overhead cost and significantly affect the environment. 
     DISCLOSURE OF THE INVENTION 
     In this context, the technical task underlying the present invention is to propose a concrete mix design and a method of placement for realizing dam or other massive structure by using the concrete mix design that overcomes the drawbacks of the prior art mentioned above. 
     In particular, it is an object of the present invention to provide a structural mix design which could be used for a massive self-compacting concrete (MSCC) method for realizing a dam. 
     In detail, it is an object of the present invention to reduce both the equipment and machines used as well as the number of people in construction process for building dams further still from the RCC method of construction as well as traditional conventionally cast and immersion vibrated concrete. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Additional features and advantages of the present invention will become more evident from the approximate and thus non-limiting description of a preferred but non-exclusive embodiment of a concrete mix design and a method of placement for realizing dam or other massive structure by using the concrete mix design, as illustrated in the appended drawings, in which: 
         FIG. 1 a    illustrates a Roller compacting concrete (RCC) method used for realizing a dam in the known prior art; 
         FIG. 1 b    illustrates a Massive Self compacting concrete (MSCC) method used for realizing a dam according to a first embodiment of the present invention; 
         FIG. 1 c    illustrates a Massive Self compacting concrete (MSCC) method used for realizing a dam according to a second embodiment of the present invention; 
         FIGS. 2 a , 2 b    illustrates a table and a graph of the sieve analysis composing the mix design; 
         FIGS. 3 a , 3 b , 3 c , 3 d    illustrates a table and a graph and a photo of the mix design analysis. 
     
    
    
     With reference to the drawings, they serve solely to illustrate embodiments of the invention with the aim of better clarifying, in combination with the description, the inventive principles of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     The present invention refers to a concrete mix design and method for realizing dam  100  or other massive structure by using Self-compacting/Self-consolidating Concrete  101 , particularly mass structural concrete. 
     In particular, the specific concrete below described for the present invention is a massive self levelling concrete  101  (MSCC) which is different from concrete used for an known SCC. 
     There have been laboratory investigations to determine the feasibility of developing a normal weight, Self-compacting/Self-consolidating, portland cement based concrete mix design. It is envisioned that the mix design of the present invention has highly modified dosages (with respect to conventional Roller Compacted Concrete) of various admixes to enable the ability to flow freely and self-compact and thought to be outside of presently known building codes and practices. 
     The massive self-compacting/self-leveling concrete  101  is being developed for use in mass and conventional concrete structures, both reinforced and unreinforced, to allow for little or no internal or external consolidation effort. Typical applications include, but are not limited to, gravity dams  100 , arch dams  100 , foundation slabs, runways, bridge abutments and other members, loch walls, ballast blocks, and other concrete structures. 
     The concrete mix design provide that:
         Slump and cement content are related, mainly by water/cement ration (w/c), but also with the total amount of cement (and/or fly ash) and other variables.   Slump is also effected by the gradation of the aggregate, the overall gradation as well as the amount of very fine material at the bottom end of the gradation.   At the finer end of the gradation (minus #200 ASTM Sieve, minus 75 micron) the material can start to “act” like cement/fly ash in terms of influencing slump, but can add or subtract, so it gets fairly tricky, fairly quick.   Sometimes the same material (minus 75 micron) can also effect the hardened properties (meaning it sometimes contributes to the strength, although this is again tricky).   The very fine material in the aggregate can also effect the w/c that will influence the hardened properties (Strength, as well as others).   Addition of chemical admixtures.   Cement content, w/c, and other properties also effect the Modulus of Elasticity, an important hardened property.       

     In particular, the mix design depends on a “heavily” influenced mix in terms of chemical admixtures to take advantage of advances in the industry. 
     It is used a lower cement/fly ash content, for many reasons, some of which are heat of hydration (trying to reduce), as well as economy, as well as shrinkage. 
     Further, it is using a “dirty” sand. This means that there is more fine material at the bottom end of the gradation that would be normally used for traditional structural or mass concrete. 
     Below is described an example of realizing the concrete design mix:
         The cementitious (Cement+Fly Ash) would preferably be in the 250 kg minus range, ideally 200 kg minus, per m3 (low cementitious content). This compares to closer to circa 300 (and greater) kg for regular structural concrete.   The fines content (minus 75 micron sieve size) would be significantly more that would be allowed for normal structural concrete.   ASTM C33 sets a limit on passing the 75 micron sieve for fine aggregate to be 0 to 3%, up to 5% in some instances depending on the concrete use, and up to 7% for rock type and concrete use.   For coarse aggregates the limit is basically 0, as there should be no passing the 75 micron in the coarse aggregate, although it is not uncommon to have a %1 or some fraction.   We are looking to use a combined gradation of greater than %10, and possibly up to %15. This puts us in a different category than normal I believe.       

     Water content of the mix design is comprised between 150 l/m 3  and 250 l/m 3  and preferably 200 l/m 3 . 
     Regarding the chemical admixtures, they are showed and indicated in the table represented in  FIG. 3   a.    
     In detail, chemical admixtures comprising one or more components, preferably all these components, selected between the following list:
         an acrylic, formaldehyde-free polymer-based admixture, modified in aqueous solution (Dynamon PW by MAPEI®);   a surfactant admixture configured to entrain micro air bubbles in concrete (Mapeair AE 20 by MAPEI®);   an organic polymer comprising hydrophilic groups for increasing the viscosity of the mixture (Viscofluid SCC/10 by MAPEI®).       

     The acrylic formaldehyde-free polymer-based admixture has a density of 1.07 g/m 3 , a dosage comprised between 3 liter/m 3  and 4 liter/m 3  of cementitious content and a dosage comprised between 2% and 3% liter/m 3  of the volume of the cementitious content. 
     The surfactant admixture has a density of 1,005 g/m 3 , a dosage comprised between 0.7 liter/m 3  and 1 liter/m 3  of cementitious content and a dosage comprised between 0.5% liter/m 3  and 0.7% liter/m 3  of the volume of the cementitious content. 
     The organic polymer admixture has a density of 1,022 g/m 3 , a dosage comprised between 4 liter/m 3  and 5 liter/m 3  of cementitious content and a dosage comprised between 2% liter/m 3  and 5% liter/m 3  of the volume of the cementitious content. 
     Testing Standards: 
     ASTM standards are the main referenced standards, although equivalent internationally recognized standards may be substituted. 
     Initial targets, fresh properties:
         Slump—no lower limit on slump, upper limit to be evaluated against the followability and Self-consolidation, tested by ASTM C143 and ASTM C230.   Initial/Final Set Time—No requirements for initial or final set time will be established in the initial trials, but will be tested in accordance with ASTM C403.   Temperature—No requirements for temperature shall be established in the initial trials, provide the mix is not subject to hot or cold placing temperature conditions as described by ACI, tested by ASTM C1064.   Air content—5%, +/−1%, by ASTM C231. Although lesser % of air contents are also to be considered.       

     Initial Targets, Hardened Properties, Mechanical: 
     
         
         
           
             Unit weight—No target, but will be tested according to ASTM C138 
             Compressive strength—Strength targets will be between 10 and +/−30 Mpa at 365 days, ASTM C39 and ASTM C31 
             Tensile strength—No target, but will be tested, ASTM C496 
             Modulus of Elasticity—No target, but will be tested, ASTM 469 
             Poisson ratio—No target, but will be tested, ASTM 469 
           
         
       
    
     Initial Targets, Hardened Properties, Thermal: 
     (no thermal properties will be tested until satisfactory fresh and hardened mechanical properties are established. However, the following are test envisioned for the thermal properties testing:
         Adiabatic temperature rise   Diffusivity   Coefficient of thermal expansion   Specific heat of concrete       

     Initial Targets, Materials: 
     
         
         
           
             Portland Cement—Type I/II, ASTM C150 
             Fly Ash—Type F and C, ASTM C618 
             Mineral filler, both natural and manufactured, to be evaluated as a fly ash replacement 
             Water—Clean and potable, including: 
             Water Soluble Chloride, ASTM C1218 
             Aggregates—ASTM C33, including: 
             C127 Standard Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate 
             C128 Standard Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate 
             Sand equivalency—ASTM D2419 
             Flakiness and Elongation—BS 812 
             Admixtures—To be determined in first stage of initial trials, generally conforming to the following: 
             ASTM C494 
             ASTM C260 
           
         
       
    
     Initial Targets, Coarse Aggregate Grading 
       
     
       
         
           
               
               
               
            
               
                   
                   
               
               
                   
                 Sieve Size 
                 Percentage passing indicated sieve size 
               
            
           
           
               
               
               
               
               
            
               
                   
                 (mm) 
                 20-40 
                 10-20 
                 4.75-10 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 63 
                 100 
                   
                   
               
               
                   
                 40 
                 85-100 
                 100 
                   
               
               
                   
                 20 
                 0-20 
                 85-100 
                   
               
               
                   
                 12.5 
                   
                   
                 100 
               
               
                   
                 10 
                 0-5  
                 0-20 
                 85-100 
               
               
                   
                 4.75 
                  0 
                 0-5  
                 0-20 
               
               
                   
                 2.36 
                   
                   
                 0-5  
               
               
                   
                   
               
            
           
         
       
     
     Initial Targets, Fine Aggregate Grading 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Sieve Size 
                 Percentage passing indicated sieve size 
               
               
                   
                 (mm) 
                 Sand 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 9.5 
                 100 
               
               
                   
                 4.75 
                 95-100 
               
               
                   
                 2.36 
                 80-95  
               
               
                   
                 1.18 
                 65-90  
               
               
                   
                 0.60 
                 40-70  
               
               
                   
                 0.300 
                 15-35  
               
               
                   
                 0.150 
                 10-25  
               
               
                   
                 0.075 
                 8-18 
               
               
                   
                 FM 
                 3.5-2.3  
               
               
                   
                   
               
            
           
         
       
     
     Initial Targets, Mix Proportions: 
     Mix proportions will be determined after initial review of proposed admixture types and dosages, as well as actual determination of:
         Aggregate specific gravities   Aggregate absorptions   Aggregate moisture contents
 
Initial Additional Testing, where Deemed Required:
   C29/C29M Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate   C31 Standard Practice for Making and Curing Concrete Test Specimens in the Field   C33 Standard Specification for Concrete Aggregates   C39 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens   C40 Test Method for Organic Impurities in Fine Aggregates for Concrete   C87 Test Method for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar   C88 Test Method for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate   C94 Standard Specification for Ready-Mixed Concrete   C117 Test Method for Materials Finer than 75-μm (No. 200) Sieve in Mineral Aggregates by Washing   C123 Test Method for Lightweight Particles in Aggregate   C125 Terminology Relating to Concrete and Concrete Aggregates   C127 Standard Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate   C128 Standard Test Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate   C131 Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine   C136 Test Method for Sieve Analysis of Fine and Coarse Aggregates   C138 Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete   C142 Test Method for Clay Lumps and Friable Particles in Aggregates   C150 Specification for Portland Cement   C157 Standard Test Method for Length Change of Hardened Hydraulic-Cement, Mortar, and Concrete   C227 Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method)   C230 Standard Specification for Flow Table for Use in Tests of Hydraulic Cement   C231 Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method   C289 Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method)   C294 Descriptive Nomenclature for Constituents of Concrete Aggregates   C295 Guide for Petrographic Examination of Aggregates for Concrete   C311 Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland-Cement Concrete   C330 Specification for Lightweight Aggregates for Structural Concrete   C331 Specification for Lightweight Aggregates for Concrete Masonry Units   C332 Specification for Lightweight Aggregates for Insulating Concrete   C342 Test Method for Potential Volume Change of Cement-Aggregate Combinations (Withdrawn 2001)4   C403 Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance   C441 Test Method for Effectiveness of Pozzolans or Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction   C469 Standard Test Method for Static Modulus of Elasticity and Poisson&#39;s Ratio of Concrete in Compression   C496 Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens   C535 Test Method for Resistance to Degradation of Large-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine   C586 Test Method for Potential Alkali Reactivity of Carbonate Rocks as Concrete Aggregates (Rock-Cylinder Method)   C595 Specification for Blended Hydraulic Cements   C618 Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete   C637 Specification for Aggregates for Radiation-Shielding Concrete   C638 Descriptive Nomenclature of Constituents of Aggregates for Radiation-Shielding Concrete   C666/C666M Test Method for Resistance of Concrete to Rapid Freezing and Thawing   C989 Specification for Slag Cement for Use in Concrete and Mortars   C1105 Test Method for Length Change of Concrete Due to Alkali-Carbonate Rock Reaction   C1064 Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete   C1157 Performance Specification for Hydraulic Cement   C1218 Water Soluble Chloride   C1240 Specification for Silica Fume Used in Cementitious Mixtures   C1260 Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method)   C1293 Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction   C1567 Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar Method)   D75 Practice for Sampling Aggregates   D422 Test Method for Particle-Size Analysis of Soils   D2419 Test Method for Sand Equivalent Value of Soils and Fine Aggregate   D3665 Practice for Random Sampling of Construction Materials   E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves   ACI 318       

     Regarding the method for realizing dam  100  or other massive structure by using the concrete mix design, one of the key concepts in the MSCC  101  concept of building dams  100  is to borrow the RCC method of placing concrete for the entire lift surface, but using gravity to accomplish the compaction effort, thus eliminating much of the required equipment. 
     If the concrete can behave more closely to the properties of an ideal fluid, then it will be self-leveling, and no need for compaction effort. 
     Assuming that the construction process would be similar to RCC construction and be placed in one continuous lift across the entire dam  100  surface with a massive self-leveling type of concrete, precast elements  7  could be used for the US and DS facing elements. 
     These would be left in place after construction, and the erection process to be heavily automated. Conventional formwork  6  solutions could also be utilized. 
     The overall placement of the MSCC  101  for the dam  100  construction aims to be similar to 3D printing, where the user directly deposit the material at the point needed for construction, and move forward at a rapid rate until completion with the minimal amount of unit processes involved during construction. 
     So, the key steps in MSCC  101  Dam  100  construction are:
         Batching of MSCC  101 ;   Positioning formworks  6 ;   Delivery  1  of the MSCC  101  to the dam  100 ;   Self levelling and self compacting of the MSCC  101 ;   Removal of the formworks  6 .       

     In particular, with reference to  FIGS. 1 b  and 1 c   , the first phases of MSCC  101  batching and delivery to dam  100  are advantageously performed through pumping means rather than by gravity. In fact the new concrete mix design allows to be pumped while the existing RCC cannot be pumped. 
     This aspect is advantageous because the new concrete could be easily transported and placed at the dam  100  location. 
       FIGS. 1 b  and 1 c    illustrate two embodiments of the method according to the present invention: 
       FIG. 1 b    shows steps of using US and DS formworks  6  (made of plastic or metals or other materials) that contains the area to be poured by fresh MSCC  101 ; 
       FIG. 1 c    shows steps of using US and DS precast  7  formworks that pile on one another, and pouring fresh MSCC  101  into the voids between them and produce a consolidated concrete structure. 
     Further, it has to be noted that the new concrete mix design avoids the external vibrating phase of concrete otherwise provided for the RCC method ( FIG. 1 a   ), as well as the internal vibrating phase with conventional concrete.