Abstract:
The invention relates to compositions of cement and concrete having properties of resistance, modulus and expansion which are significantly improved, using an additive for cement based on thermoplastic styrene-butadiene-styrene (SBS) copolymer in cationic latex, when compared with non-modified cement and concrete references.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention refers to the use of styrene-butadiene-styrene (SBS) latex as an additive in Portland cement or concrete. 
       BACKGROUND OF THE INVENTION 
       [0002]    The pavement systems containing cement-bound layers have been used worldwide for over a century, with great success. Portland cement can be used in virtually every layer in a pavement system. Typical applications include improving the quality of subgrade soils and stabilizing base materials. Integrating multiple cement-based layers into a pavement design may provide a cost-effective method for achieving a stronger, more durable, sustainable pavement. For instance, using a cement-modified soil and cement-treated base as opposed to an unbound granular base placed on an unprepared subgrade can reduce the required thickness of the base material. In addition, a cement treated base may decrease the thickness needed for the concrete or asphalt surface, resulting in less materials and overall reduced cost. In addition to being the key constituent of new concrete pavement and concrete overlay surfaces, other unique surface applications of cement include roller compacted concrete (RCC), precast pavements, and pervious concrete pavements. Cement is also use in numerous pavement repair techniques, as well as an array of pavement recycling and reclamation applications. 
         [0003]    Mixtures for concrete pavements typically incorporate the following constituents: a blend of coarse and fine aggregates, Portland cement, water, and sometimes other cementations materials such as fly ash and slag cement, and/or chemical ad mixtures (see  FIG. 1 ). 
         [0004]    Although cement and concrete systems have adequate properties for many construction applications, there are many properties, like strength or deformation, which are not acceptable. 
         [0005]    Polymer latex modified Portland cement systems develop significant changes in physical properties when compared against unmodified concrete and cement mortar. There are many patents about the use of latex-modified cement systems, specifically from styrene-butadiene polymer latex (SBR random), acrylic latex, EPDM and Ethylene vinyl acetate (EVA) latex to Portland cement having improved strength, flexibility, adhesion, elongation at break and others. However, there are not any patents describing the use of SBS latex. This type of latex is not reported in literature for concrete modification. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    The present invention is directed to cement and concrete compositions having significantly improved strength properties, modulus and elongation, which use a cement additive based on styrene-butadiene-styrene thermoplastic copolymer (SBS) in cationic latex, when compared against unmodified cement and concrete references. Most patent works that describe any other latex different from SBS latex, are addressed to flexibility improvements, but none of them are addressed to the improvement of strength and deformation. 
         [0007]    In addition, these type of SBS lattices improved the elastic modulus of concrete, while most of the other lattices are used for improving the strength in cement. Elastic modulus improvement is an important variable for structural supports such as pillars and columns in bridges. 
         [0008]    There are some applications like well cementing where plasticity is an important variable for concrete, where the concrete once cured can adopt the form of holes, or as stabilization of piping during well perforation. Here, the improvement of strength and deformation are critical variables because they have relation with plasticity. The polymer latex proposed in this invention helps to increase the plasticity in well cementing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  describes the main ingredients and general overview of the concrete composition. 
           [0010]      FIG. 2  describes describes different structural forms of SBS polymers, which can be used to formulate SBS latex. In this work, only linear SBS is included, but the rest can be used as references for future developments and patent works. 
           [0011]      FIG. 3  shows a similar (even better) performance of elastic modulus by stress compression of modified concrete specimens (sample 2 from table 3) versus non-modified concrete. 
           [0012]      FIG. 4  as well as  FIG. 3  shows a better performance of elastic modulus by stress compression of modified concrete specimens (sample 3 from table 3) versus non-modified concrete (conventional concrete). In addition, these results confirm the good improvement of SBS Latex in modified concrete formulation. 
           [0013]      FIG. 5  also shows a better performance of elastic modulus by stress compression of modified concrete specimens (sample 4 from table 3) versus non-modified concrete (conventional concrete) Again, these results confirm the good improvement of SBS Latex in modified concrete formulation. 
           [0014]      FIG. 6  also shows a better performance of elastic modulus by stress compression of modified concrete specimens (sample 5 from table 3) versus non-modified concrete (conventional concrete). In addition, these results confirm the good improvement of SBS Latex in modified concrete formulation. 
           [0015]      FIG. 7  indicates that area percentage below the curve Stress/Strain is higher in modified concrete using SBS latex at 1.5% of SBS polymer than unmodified concrete. This performance defines a better plasticity in modified concrete specimens. 
           [0016]      FIG. 8  as well as  FIG. 7 , indicates that area percentage below the curve Stress/Strain is higher in modified concrete using SBS latex at 3% of SBS polymer than unmodified concrete. This performance defines a better plasticity in modified concrete specimens. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The present invention focuses in the use of styrene-butadiene-styrene thermoplastic copolymer (SBS) latex as an additive in Portland cement or concrete to improve tensile strength, elastic modulus and plastic in cement mortar and final concrete formulations 
         [0018]    The term “Portland cement”, as used herein, refers to the type of product obtained by heating lime-clay mixtures, or natural cement rock, to such temperature that practically the entire product is sintered followed to grinding. The product composition can include a mixture of di-calcium and tri-calcium silicate with some amounts of aluminate. Different additives can be included to obtain different properties and fast curing in accordance with Portland cement manufactures practice guides. For purposes of this invention and for evaluating what we call hydraulic cements, the cement used is known as calcium-aluminate cement. 
         [0019]    In many examples, it may be desirable to combine the cement compositions of this invention with aggregate material to form the hydraulic concrete or concrete. In this regard, the preferred aggregate material is sand: however, any particulate material may be used including stone, gravel, granite, marble chips, mica and the like. 
         [0020]    The term “styrene-butadiene-styrene” latex, as used herein, means any aqueous colloidal dispersion from SBS. This SBS can have different configurations such as linear, radial or multiarm as shown in  FIG. 2 . 
         [0021]    In this SBS latex the styrene content is moving from 10 to 50% weight/weight and the butadiene content is moving from 50 to 90% weight/weight, in polymer based. The total solids content in polymer latex is moving from 20 to 70% weight/weight. This polymer is emulsified in water containing emulsifying agent or agents in a stable system without any sediment with time. The size of micelles is moving from 2 to 60 microns. 
         [0022]    For application examples in this patent, a linear SBS latex is used. In the first example, the SBS-latex is used as a cement modifier without any filler of aggregate into the formulation, wherein compressive strength increases in modified cement versus unmodified cement in specimens prepared under method ASTM C109. This method describes the methodology for testing the compression strength of mortars using cubes of material that are two inches on a side. 
         [0023]    A mechanical testing machine equipped with the appropriate compression platens is used for the test. One of the platens must be spherically seated to allow slight tilt adjustment if the faces of the specimen are not perfectly parallel. The test machine operates in compression at slow test speeds in a load rate range indicated by the specification. Once the appropriate load rate is achieved, a constant rate of movement is maintained through sample break. Accurate speed control is required in order to maintain the rate of motion once the sample begins to yield and ultimately break. Hydraulic compression testers are preferred for these tests due to their high force capacity. 
         [0024]    In a second example of the application, the linear SBS latex was used as a concrete modifier, where an aggregate with controlled granulometry was incorporated into the concrete formulation. Here there is an important increase in elastic modulus in specimens molded with modified concrete versus unmodified concrete. 
         [0025]    Finally in a third example, the linear SBS latex was used as a concrete modifier and said examples shows that plasticity is increased in the modified concrete versus unmodified concrete. In this example, besides the combination of cement and SBS latex, a coarse aggregate and also a fine aggregate portion are included. The area of curve strength-deformation is larger in the case of modified concrete versus unmodified concrete and cure time is critical to obtain the maximum values. 
       EXAMPLE 1 
     Evaluation of SBS Latex in Cement Mortar 
       [0026]    Cement mortar was prepared for strength testing by mixing the ingredients mentioned in table 1, using a Hobart mixer. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Ingredients and recipe or preparing a cement mortar 
               
             
          
           
               
                   
                   
                 COMPOSI- 
                 COMPOSI- 
                 COMPOSI- 
               
               
                   
                 REFERENCE 
                 TION 1 
                 TION 2 
                 TION 3 
               
               
                 INGREDIENT 
                 (grams) 
                 (grams) 
                 (grams) 
                 (grams) 
               
               
                   
               
             
          
           
               
                 Standard Silica 
                 1,950 
                 1,950 
                 1,950 
                 1,950 
               
               
                 Sand 
                   
                   
                   
                   
               
               
                 Portland 
                 450 
                 450 
                 450 
                 450 
               
               
                 Cement 
                   
                   
                   
                   
               
               
                 SBS Latex 
                 0 
                 114 
                 231 
                 285 
               
               
                 Water 
                 459 
                 345 
                 228 
                 174 
               
               
                   
               
             
          
         
       
     
         [0027]    The mortar was molded into 2 inch cubes and tensile briquettes with a 1 inch square cross section in accordance with ASTM methods. The specimens were wet-cured for 24 hours and cured in air at 72° F. and 50% of relative humidity for 30 days. Half of specimens were tested on compressive and tensile strength. The other half was immersed in water for seven days and then tested wet. In this experiment linear SBS latex with 55% weight/weight solids was used in the ratio described in table 1. The results of compressive strength are described in table 2. 
         [0028]    The increase in compressive strength and tensile strength are important variables for applications as adhesive cement paste for glazed tile and ceramics, as well as cement coatings for walls and ceiling (Tyrol). 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Results of compressive strength for cement mortar 
               
             
          
           
               
                   
                 Cement Results 
               
             
          
           
               
                   
                   
                   
                   
                 Modi- 
               
               
                   
                   
                   
                   
                 fied  
               
               
                   
                   
                   
                   
                 Mortar 
               
               
                   
                   
                   
                   
                 cment 
               
               
                   
                   
                   
                   
                 with 
               
               
                 Compressive 
                 Reference 
                 Modified Mor- 
                 Modified Mor- 
                 SBX 
               
               
                 Strength, PSI 
                 of Mortar 
                 tar cement 
                 tar cement 
                 latex 
               
               
                 (according 
                 cement 
                 with SBS latex 
                 with SBS latex 
                 (com- 
               
               
                 with ASTM 
                 without 
                 (composition 
                 (composition 
                 position 
               
               
                 C109) 
                 SBS Latex 
                 1) 
                 2) 
                 3) 
               
               
                   
               
             
          
           
               
                 First Condi- 
                 5467 
                 7277 
                 8344 
                 9941 
               
               
                 tion: 14 days 
                   
                   
                   
                   
               
               
                 and air dried 
                   
                   
                   
                   
               
               
                 Second Condi- 
                 4768 
                 5301 
                 5578 
                 7011 
               
               
                 tion: 14 days 
                   
                   
                   
                   
               
               
                 air dried + 14 
                   
                   
                   
                   
               
               
                 days inmersed 
                   
                   
                   
                   
               
               
                 in water 
                   
                   
                   
                   
               
             
          
           
               
                 Tensile Strength; PSI (ASTM C109) 
               
             
          
           
               
                 14 days air 
                 462 
                 599 
                 698 
                 792 
               
               
                 dried + 14 
                   
                   
                   
                   
               
               
                 days inmersed 
                   
                   
                   
                   
               
               
                 in water 
               
               
                   
               
             
          
         
       
     
       EXAMPLE 2 
     Evaluation of Elastic Modulus Using SBS Latex in Modified Concrete 
       [0029]    Concrete modification studies were done using formulations described in table 3. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Concrete Formulations 
               
             
          
           
               
                   
                 Sam- 
                   
                   
                   
                   
               
               
                   
                 ple 1: 
                   
                   
                 Sam- 
                   
               
               
                   
                 Refer- 
                   
                   
                 ple 4: 
                   
               
               
                   
                 ence 
                   
                   
                 Modi- 
                   
               
               
                   
                 for 
                   
                   
                 fied 
                   
               
               
                   
                 un- 
                 Sample 2: 
                 Sample 3: 
                 Con- 
                 Sample 6: 
               
               
                   
                 modi- 
                 Modified 
                 Modified 
                 crete 
                 Modified 
               
               
                   
                 fied 
                 Concrete 
                 Concrete 
                 using 
                 Concrete 
               
               
                   
                 con- 
                 using SBS 
                 using SBS 
                 SBS 
                 using SBS 
               
               
                 INGREDIENT 
                 crete 
                 latex a   
                 latex b   
                 latex a   
                 latex 
               
               
                   
               
             
          
           
               
                 Cement; % 
                 15 
                 14.25 
                 13.5 
                 14.3 
                 13.5 
               
               
                 weight/weight 
                   
                   
                   
                   
                   
               
               
                 Water, % 
                 5 
                 4.25 
                 3.5 
                 4.2 
                 3.5 
               
               
                 weight/weight 
                   
                   
                   
                   
                   
               
               
                 Latex, % 
                 0 
                 1.5 
                 3 
                 1.5 
                 3.0 
               
               
                 weight/weight 
                   
                   
                   
                   
                   
               
               
                 Fine Aggregate, 
                 35 
                 35 
                 35 
                 20 
                 20 
               
               
                 % weight/weight 
                   
                   
                   
                   
                   
               
               
                 Coarse Aggre- 
                 45 
                 45 
                 45 
                 60 
                 60 
               
               
                 gate, % 
                   
                   
                   
                   
                   
               
               
                 weight/weight 
                   
                   
                   
                   
                   
               
               
                   
               
               
                 NOTE: 
               
               
                   a For having at the end around 0.75% SBS in finished modified concrete. 
               
               
                   b For having at the end around 1.5% SBS in finished modified concrete. 
               
             
          
         
       
     
         [0030]    On the other hand, table 4 describes the particle size curve per each aggregate used in this investigation. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Particle size curves for aggregates used in this work 
               
             
          
           
               
                   
                 Particle Size  
                 Fine Aggregate,  
                 Coarse Aggregate, % 
               
               
                   
                 Sieve 
                 % pass 
                 pass 
               
               
                   
                   
               
             
          
           
               
                   
                 7.62 centimeters 
                   
                 0 
               
               
                   
                 5.08 centimeters 
                   
                 0 
               
               
                   
                 3.81 centimeters 
                   
                 100 
               
               
                   
                   1 centimeter 
                   
                 99.6 
               
               
                   
                 1.90 centimeters 
                   
                 63.6 
               
               
                   
                 1.27 centimeters 
                   
                 15.1 
               
               
                   
                 0.95 centimeter 
                 100 
                 6.7 
               
               
                   
                 No. 4 
                 90.9 
                 2.5 
               
               
                   
                 No. 8 
                 70.6 
                 1.9 
               
               
                   
                 No. 16 
                 53.8 
                   
               
               
                   
                 No. 30 
                 44.3 
                   
               
               
                   
                 No. 50 
                 38.4 
                   
               
               
                   
                 No. 100 
                 30.9 
                   
               
               
                   
                 No. 200 
                 23.3 
               
               
                   
                   
               
             
          
         
       
     
         [0031]    Combination of both aggregates according with the recipes described in table 3, allowed to mold cylindrical specimens for measuring elastic modulus according with ASTM C39. SBS latex was used as an additive in the concrete formulation using 0.75% and 1.5% weight/weight of SBS polymer in the final composition.  FIGS. 3, 4, 5 and 6  show the performance of modified concrete versus unmodified concrete at three levels of concrete set curing. 
         [0032]    The ASTM C39 method covers determination of compressive strength of cylindrical concrete specimens such as molded cylinders and drilled cores. It is limited to concrete having a density in excess of 800 kg/m3 [50 lb/ft3]. 
         [0033]    Cylinders cast and cured in the field are transported to the laboratory within 24 to 48 hours of production. Cylinders are then cured in water (or high-humidity chamber) for the specified curing period (e.g., 7 days, 28 days, etc.). On the date the cylinder has cured for the specified period of time, the cylinder is removed from the water tank and tested in compression with strength and failure mode reported. 
         [0034]    An increase in elastic modulus is important for hydraulic concrete used as structural support of columns and pillar for bridges. 
       EXAMPLE 3 
     Evaluation of Plasticity Using SBS Latex in Modified Concrete 
       [0035]    Using formulations described in table 5 and aggregates from table 4, the stress-strain figure was determined according with ASTM C39, leaving deformation more than 40% until break in test specimen. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Formulations of modified and unmodified 
               
               
                 concrete for plasticity studies. 
               
             
          
           
               
                   
                   
                 Sample 1: 
                 Sample 2: 
                 Sample 3: 
               
               
                   
                   
                 Reference  
                 Modified  
                 Modified 
               
               
                   
                   
                 for 
                 Concrete 
                 Concrete 
               
               
                   
                   
                 unmodified 
                 using 
                 using SBS 
               
               
                   
                 INGREDIENT 
                 concrete 
                 SBS latex 
                 latex 
               
               
                   
                   
               
             
          
           
               
                   
                 Cement; % 
                 15 
                 13.5 
                 12 
               
               
                   
                 weight/weight 
                   
                   
                   
               
               
                   
                 Water, % weight/weight 
                 5 
                 3.5 
                 2 
               
               
                   
                 Latex, % weight/weight 
                 0 
                 3 
                 6 
               
               
                   
                 Fine Aggregate, % 
                 35 
                 35 
                 35 
               
               
                   
                 weight/weight 
                   
                   
                   
               
               
                   
                 Coarse Aggregate, % 
                 45 
                 45 
                 45 
               
               
                   
                 weight/weight 
               
               
                   
                   
               
               
                   
                 NOTE: 
               
               
                   
                 a. For having at the end around 1.5% SBS in finished modified concrete. 
               
               
                   
                 b. For having at the end around 3.0% SBS in finished modified concrete. 
               
             
          
         
       
     
         [0036]      FIGS. 7 and 8  show the stress-strain figures with two different SBS latex concentration in modified concrete. 
         [0037]    An increase of area below the curve of stress-strain defines the plasticity. The higher the area, the higher the plasticity. SBS latex improves plasticity in concrete which can be interesting for well cementing applications where hydraulic concrete needs to be molded into the cavity where oil piping is introduced to get the oil well for pumping. The application can be considered for use in Portland cements standard quality and class H and G (for well cementing).