MXPA01000536A - Additive for controlling flexural bond strength, air entrainement and workability of mortar cement - Google Patents

Abstract

A mortar cement composition is composed of a cement or ground portland cement clinker, ground limestone and/or lime, sand, a sufficient amount of water to render the composition flowable, and at least one water-soluble polymer present in the amount having a lower limit of about 0.001 wt.%and an upper limit of about 0.04 wt.%based on total dry weight of the ingredients, with the proviso that the extent of adsorption of the polymer onto the cement is less than 50%, and wherein the resulting mortar has 8-16%air content and greater than 70 psi flexural bond strength. This mortar cement composition is for use in building structures in all seismic zones.

Description

FLUIDIFYING ADDITIVE WITH LOW AIR CONTENT AND RESISTANCE TO FLEXION FOR CEMENT MORTAR This invention relates to a cement mortar composition with improved properties useful for producing mortar for masonry for laying brick, block and stone in masonry construction. More specifically, this invention relates to the use of a class of polymer additives in which the composition improves the flexural strength or flexural adhesion resistance, under air entrainment, and improves the workability that is approved for use in building structures. in all seismic zones.

BACKGROUND Hydraulic cement is a mixture of fine crushed lime, alumina and silica that makes a hard product by adding water powder adhesion, which is chemically combined with the other ingredients to form a hydrate. Prior to the present invention, there were two main factories producing hydraulic cement products used in masonry construction: the traditional cement for masonry and the cement mortar mixture Portland lime. Currently, the United States market is divided between these two products. Both types of hydraulic cement products contain Portland cement as their main ingredient. Portland cement is a type of hydraulic cement in the form of finely divided gray powder composed of crushed limestone, alumina, silica, and iron oxide such as tetracalcium aluminoferrate (4CaO, A1203, Fe203), tricalcic aluminate (3CaO.Al203), tricalcic silicate (3CaO.Si02) and dicalcic silicate (2CaO.Si02). small amounts of magnesium, sodium, potassium and sulfur are also present. Hardening does not require air, and will occur under water. Masonry cement is a class of special cements that commonly produce more plastic and manageable mortars than Portland / lime cement mixtures. Traditional masonry cement is commonly unsuitable for construction of unsupported load bearing masonry, specifically in areas of high seismic activity due to its low reputation in flexural strength, and poor adhesion capacity. The high air content (for example, 18-20%) and the lack or low level of increased resistance and adhesion agents are generally responsible for the inability to eliminate these deficiencies. A cement for conventional masonry based on mortar for masonry is a mixture of a cement for masonry, sand, functional additives and water. In general, masonry mortar does not provide adequate flexural adhesion strength for use in masonry construction of unreinforced load elements. To meet the need for flexional adhesion strength, two kinds of mortar can be used. One kind of material is a mixture of Portland cement and lime. The other recently introduced class of special cement is cement mortar. Cement mortars are appropriate formulations that have a variety of compositions, all of which include crushed Portland cement clinker, crushed limestone, and functional additives that may include lime. A cement mortar is required to have a minimum flexural strength specification, according to ASTM 1329. Three types of cement mortars, for example, M, N and S, are currently specified for use in the construction industry for masonry. These types of cement mortars are classified based on their strength properties. Generally, the resistance is based on the amount of crushed Portland clinker, crushed limestone, lime, air entraining agent, and other additives. The following Table A describes the physical requirements according to ASTM C-1329 for these type cement mortars.

TABLE A Physical requirements Portland lime cement mixes are used today to produce mortars with high flexural adhesion strength. Nevertheless, these mortars made with Portland cement and lime commonly have poor manageability. Accordingly, there is a need to produce a cement mortar having a good flexural adhesion strength and good workability with relatively low air content as specified in ASTM C-1329. Therefore, at the time of the invention it refers to new classes of polymeric additives for use in cement mortars that meet this need for flexional adhesion strength and good workability with a low air content. This class of polymer additives is characterized by its low adsorption on Portland cement which is a critical component of cement mortar and is a new defined class of construction materials for masonry. No prior art has been found to describe the use of polymer additives at the time for this specific application.

COMPENDIUM OF THE INVENTION. The present invention is directed to a composition of a cement mortar containing: a) crushed Portland cement clinker, b) crushed limestone and / or lime, c) sand, d) sufficient amount of water to make the composition flowable, and e) at least one polymer present soluble in water in the amount having a lower limit of about 0. 001% by weight and an upper limit of approximately 0.04% by weight based on the total dry weight of the ingredients, except that the adsorption area of the polymer on Portland cement is less than 50%, and where the Cement mortar has 8-16% air content and flexural adhesion strength greater than 70 pounds on an inch as defined in ASTM C-1329-96. The present invention also comprises a method of improving the flexural adhesion strength of a cement mortar consisting of adding a cement mortar consisting of cement, sand, water and at least one water soluble polymer in an amount having a lower limit of about 0.001% by weight and an upper limit of about 0.04 % by weight based on the total dry weight of the ingredients, where the cement mortar has 8-16% air content and a flexural adhesion strength greater than 70 pounds on an inch as defined. ne in ASTM C-1329-96.

DETAILED DESCRIPTION OF THE INVENTION It has been surprisingly discovered that certain additives, due to the low concentration, need to increase the flexural adhesion strength (FBS) of the cement mortar without deteriorating the workability, and that it meets other requirements specified in ASTM C 1329. Also, surprisingly it was found that the polymers that produce the flexural adhesion strength and workability, all have low levels of adsorption on Portland cement that is less than 50%, preferably less than 40%, and more preferably less than 30% based on in the total of solid contents. The additive is a polymer family soluble in water, which has good stability and high alkali conditions (for example, pH greater than 10). These are cellulose or synthetic polymers soluble in water, which are engineered to have a high water retention capacity and low adsorption behavior on Portland cement. The amount of hydrophobic and molecular weight polymers were engineered in a way that only minimal amounts of polymers interact with minerals, and most of the polymer is available in the aqueous phase. These generate good manageability with low air content and high flexional adhesion strength. These are compatible with Other commercial cement powder additives for masonry mortar applications. As examples, hydroxyethylcellulose modified with alkylglycidyl (marketed by Hercules Incoporated under the trademarks Nexton® M23W, Nexton® M20W, and Nexton® 3082R), methylhydroxyethylcellulose (MHEC) (marketed by Hercules Incorporated under the trademark Culminal® MHEC 40,000P), and methylhydroxypropyl cellulose (MHPC) (marketed by Hercules Incorporated under the trademark Culminal® MHPC 20000PFR or Dow's product MHPC Methocel® 240S) can be used for this cement mortar application. Other water-soluble polymers, such as modified polyvinyl alcohol and modified starches, may also be engineered to have such an adsorption behavior on Portland cement. A practical way in which this can be completed by mixing different polymers with different adsorption values for cement mortar applications. The present invention is applicable to any cement mortar composition containing Portland cement. The present amount of cement in the composition of the present invention has a lower limit of 20% by weight based on the total of dry ingredients, preferably 23% by weight, more preferably 25% by weight; the upper limit amount of the cement is 40% by weight, preferably % by weight, more preferably 30% by weight. Any type of sand that is commonly used in the construction industry can be used in this invention. Commonly, examples of the sand are ASTM 20/30 silica sands and site sands. The amount of sand in the composition of the present invention has a lower limit of 55% by weight, preferably 60% by weight, and more preferably 65% by weight; the amount of sand present in the upper limit is 80% by weight, preferably 78% by weight, and more preferably 75% by weight. In the present invention, a small amount of water must be present to meet the required flow properties. In other words, a sufficient amount of water must be present to make the composition of the mortar flowable. The amount of water in the mortar is determined by many factors such as humidity, moisture levels in the other components and addition of water to the mixture. By the term "fluid" or "flowable" it means that the mortar contains enough water to produce a mortar of a usable consistency for the promised application. According to the present invention, the water-soluble polymer is selected from the group consisting of hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylcellulose (MHEC) (marketed by Hercules Incorporated under the tradename Culminal®) MHEC 40,000P), and hydrophobically modified hydroxyethylcellulose (HMHEC), as soon as the selected polymer has an adsorption level on Portland cement less than 50%. The HMHEC is a hydrophobically modified HEC, where the hydrophobic part is a straight or branched chain of the alkyl or aryl group having an upper limit of 20 carbons, preferably 8 carbon atoms, and more preferably 4 carbon atoms. The lower limit of the carbons in the hydrophobe for the HMHEC is 2 carbon atoms for straight alkyl chains and 3 for branched alkyl chains. It should be understood that the skeleton of the HMHEC may contain more than one type of hydrophobe. For example, an alkyl group having 2 carbons and an alkyl group having 4 carbons both may be present in the same polymer backbone. Specific examples of HMHEC are ethylhydroxyethylcellulose, butylglycidyletherhydroxyethylcellulose and laurylglycidyletherhydroxyethylcellulose. The degree of hydrophobic molar substitution of the HMHEC has a lower limit of 0.005 and an upper limit of 0.2. The average molecular weight of the weight of the polymers of the present invention has a lower limit of about 50,000, preferably 70,000 and more preferably 100,000 and an upper limit of approximately 1,500,000. In summary, the polymer of the present invention has a viscous solution of at least 100 cps at 4% polymer concentration as measured at 25 ° C on a Brookfield viscometer at 30 rpm. According to the present invention, the water-soluble polymer should be present in the composition with an upper limit of less than 0.049% by weight, preferably 0.04% by weight, more preferably 0.03% by weight, and still more preferably 0.02% by weight with the most preferable amount being 0.01% by weight. In accordance with the present invention, optimally functional additives can be used in the composition. The manufacturer will determine the need and type of functional additive that will be used depending on the end use promised and other conditions that are known in this industry. Examples of these functional additives are air entraining agent, setting retarder, fine ash, or grinding instruments. The amounts of functional additives are adjusted to provide good mortar properties and generally have an amount of upper limit present in the composition of one percent by weight. These functional additives are optional and can not be used to replace the water-soluble polymers of the present invention.

The following examples are merely to declare to further illustrate the invention and are not considered as a limitation of the invention. All parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A series of three polymers of hydroxyethylcellulose modified with alkylglycidyl were mixed with Portland cement and Xe powder marble stone (a crushed limestone form) to produce a cement mortar. The Portland cement / marble dust ratio was 70/30 based on weight. The concentration of the polymer was 0.007% by weight of the solid ingredients of the mortar. The test of the formulation of the common cement mortar that was used is stated in the following Table 1.

Table 1: Formulations of cement mortar * Cement for S-type masonry was a commercial product of Keystone Cement Inc. ** Arena is Ottawa and Silica graduated silica blend /30 (1/1 ratio) according to ASTM C-778, obtained from Union Corp. Le Seur, Minnesota. *** The water content was adjusted based on the flow of mortar, measured 110-130 by a flow chart (ASTMA 1329). a - This is an experimental HMHEC polymer with a 1% Brookfield viscosity of 800-1200 cps at 25 ° C.

The mortar was prepared with a mixing laboratory Hobert. The water content of adjusted to have a flow of 125 ± 5 for measure of flexional adhesion. Some pair of specimens were prepared with the National Concrete Masonry Association (NCMA), Herndon, Virgina, standard cement bricks to measure their flexural adhesion strength (FBS). The pairs were cured 28 days before the FBS measurement with an adhesion key (according to Uniform Building Code (UBC) 21-20). Water retention and air content were measured according to ASTM C91-96. The manageability of mortars was graded as poor, adequate, good and excellent. The adsorption of water-soluble polymer on Portland cement was measured in the supernatant, which was obtained from the mixture of Portland cement, polymer and water (0.05% by weight of polymer) after centrifugation. Portland cement type 1, polymer and water (400 g / 0.2 g / 150 g) were mixed for 10 minutes in a bucket with a mechanical agitator. The solution of cement paste was transferred to a centrifuge tube and centrifuged for one hour at 1300 rpm. The supernatant was separated from the slurry of cement and also centrifuged for 30 minutes. The supernatant was filtered with a 25 mm syringe filter (from Chromacol, Trumbul, CT) before being analyzed by polymer concentration. The polymer concentration in the supernatant was measured using a size exclusion chromatograph (SEC) with a detector of reflective index (ERMA 7512, ERMA CR Inc., Tokyo, Japan) at 30 ° C. The polymer concentration of the supernatant was determined from the weight of the isolated polymer peak on the SEC chromatogram. The SEC is assembled with three HPLA Synchropak columns (two GPC 300-250 x 4.6 mm and a GPC 100-250 x 4.6 mm) as a mobile phase, 70% methanol solution with 0.5 molar lithium nitrate was used. The properties of the mortar columns and polymer adsorption data are summarized below in Table 2. Table 2: Properties of the mortar and adsorption data of the polymer EXAMPLE 2 The mortar was prepared with white cement made with 62% crushed Portland cement clinker, 34% crushed limestone, and 4% gypsum. It was prepared at Construction 'Technology Laboratories (CTL), Skokie, Illinois, with a handy ground ball mill for a fineness of 600 m2 / kg on a specific blaine surface. [sic] Experimental formulations for mortar were prepared with Ottawa sand at a flow rate of 125. The properties of the modified polymer mortar samples Culminal® 20000 PFR MHPC, Nexton® M20 HMHEC, Culminal®4000 PFR MHPC and Natrosol® 250HR HEC are shown in the following Table 3. The mortar data in experiment 9 in Table 3 were obtained from the mixture of two polymers (Nexton® M20W HMHEC and Culminal® 3000P MC, 65% by weight / 35% by weight). The polymer mixture was mixed with cement and sand as for Example 1.

Table 3: Mortar properties data and polymer adsorption * The adsorption property of the polymers in portland cement in water was measured by a size exclusion chromatograph (SEC), the same as in Example 1.

Comparative Example A The mortars were prepared with hydroxypropylcarbonate and carboxymethylcellulose (CMC) and synthetic water-soluble polymers such as alkali-soluble polyacrylate (Alcogum® L-35) and modified polyacrylate (Acrysol® TT-935). Alcogum® L35 is a product of Aleo Chemical Corporation. Acrysol® TT-935 is a product of Rohm and Haas. The mortar formulations were the same as in Experiment 3 in Example 1, except the Nexton® polymer which was replaced by hydroxypropylguar (HPG), carboxymethylcellulose (CMC) and synthetic water-soluble polymers. The polymer concentrations were also the same as in Experiment 3 (0.007% based on solids). The mortar properties are shown in Table 4. Mortars with these polymers have very poor workability and low water retention (<50%) since most of the polymers were adsorbed onto the cement. Samples that had poor manageability and water retention such that they were not useful for preparing pairs of samples acceptable for FBS tests.

Table 4: Mortar properties and polymer adsorption data * The handling of the mortar is very poor and the water retention is very low and its pairs can not be prepared for FBS measurements. ** The air content is not measured because the mortar has poor quality and not acceptable water retention.

EXAMPLE 3 The mortar formulations were prepared with different amounts of hydrophobically modified hydroxyethyl cellulose (Nexton M20 product). The mortar composition was the same as in Table 1, except that the polymer concentrations were changed as indicated in Table 5. This Example in Table 5 verifies the differences of this invention from U.S. Patent 4,938,192. The invention requires much lower water-soluble polymer concentrations (< 0.05% by weight of the total solid) in a composition under construction, specifically for a cement mortar application.

Table 5: Physical properties of mortars with different amounts of Nexton AD202 * The polymer concentration was described in a composition for construction described in Table 6 of USP 4,939,192 by H. E. t'Sas. The concentration in the upper limit in the present invention is significantly lower than the lower limit of concentration of USP 4, 939, 192.

** The FBS was not measured because the mortar has poor handling and is sticky.

While the invention has been described with respect to specific embodiments, it is understood that they are not limited and that many variations and modifications are possible without departing from the scope and spirit of this invention.

Claims (47)

1. A cement mortar composition consisting of a) crushed portland cement clinker, b) crushed limestone and / or lime, c) sand, d) a sufficient amount of water to make the composition flowable, e) at least one polymer soluble in water present in the amount that has a lower limit of approximately

0. 001% by weight and an upper limit of approximately 0.04% by weight based on the total dry weight of the ingredients, with the proviso that the adsorption area of the polymer on the portland cement is less than 50%, and wherein the cement has 8-16% air content and greater than 70 pounds / inch flexural adhesion strength according to ASTM C-1329-96. The composition of claim 1, wherein the cement is present in an amount having a lower limit of 20% by weight based on the total dry weight of the ingredients. The composition of claim 2, wherein the cement is present in an amount having an upper limit of 40% by weight based on the total dry weight of the ingredients.

4. The composition of claim 1, wherein the sand is present in an amount having a lower limit of 55% by weight based on the total dry weight of the ingredients. The composition of claim 4, wherein the sand is present in an amount having an upper limit of 80% by weight based on the total dry weight of the ingredients. The composition of claim 1, wherein the water soluble polymer has a lower limit of 0.003% by weight based on the total dry weight of the ingredients.

7. The composition of claim 1, wherein the water soluble polymer has a lower limit of 0.005% by weight based on the total dry weight of the ingredients. The composition of claim 1, wherein the water soluble polymer has an upper limit of 0.03% by weight based on the total dry weight of the ingredients. The composition of claim 1, wherein the water soluble polymer has an upper limit of 0.02% by weight based on the total dry weight of the ingredients. The composition of claim 1, wherein the water soluble polymer is present in an amount of 0.01% by weight based on the total dry weight of the ingredients. 11. The composition of claim 1, wherein the Water soluble polymer is selected from the group consisting of hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylcellulose (MHEC), hydrophobically modified hydroxyethylcellulose (HMHEC), and mixtures thereof. The composition of claim 11, wherein the water soluble polymer is HMHEC wherein the HMHEC contains at least one hydrophobe wherein the hydrophobe is an alkyl or an aryl portion having a lower limit of 2 carbons and an upper limit of 20 carbons. The composition of claim 12, wherein the water soluble polymer is a mixture of HMHEC and HPMC. 14. The composition of claim 12, wherein the upper limit is 10 carbons. 15. The composition of claim 14, wherein the upper limit is 6 carbons. The composition of claim 1, wherein the viscous solution is at least 100 cps at 4% polymer concentration as measured at 25 ° C on a Brookfield viscometer at 30 rpm. The composition of claim 15, wherein the degree of hydrophobic molar substitution has a lower limit of 0.005 and an upper limit of about 0.2. 18. The composition of claim 1, wherein the weight The average molecular weight of the water soluble polymer has a lower limit of about 50,000 and an upper limit of about 1,500,000. 19. The composition of claim 1, wherein the adsorption area of the polymer in portland cement is less than 40%. The composition of claim 1, wherein the adsorption area of the polymer in portland cement is less than 30%. The composition of claim 1, wherein the adsorption area of the polymer in portland cement is less than 20%. 22. The composition of claim 1, wherein at least one functional additive is present in the composition. The composition of claim 22, wherein at least one functional additive is present in an amount having an upper limit of 1% by weight. The composition of claim 22, wherein the functional additive is selected from a group consisting of an air entraining agent, a setting retarder, fine ashes, and grinding instruments. 25. A method for improving the flexural adhesion strength of a cement mortar comprising the addition for a cement mortar comprising crushed Portland cement clinker, crushed limestone and / or lime, sand and water, at least one water-soluble polymer in the amount having a lower limit of about 0.001% by weight and an upper limit of about 0.04% by weight based on the total dry weight of the ingredients, with the proviso that the area of Adsorption of the polymer on crushed Portland cement clinker is less than 50% by weight, and wherein the resulting mortar has an air content of 8-16% and greater than 70 pounds / inch of flexural adhesion strength. 26. The method of claim 25, wherein the crushed Portland cement clinker is present in an amount having a lower limit of 20% by weight. The method of claim 26, wherein the crushed Portland cement clinker is present in an amount having an upper limit of 40% by weight based on the total dry weight of the ingredients. The method of claim 25, wherein the sand is present in an amount having a lower limit of 55% by weight based on the total dry weight of the ingredients. 29. The method of claim 28, wherein the sand is present in an amount having an upper limit of 80% by weight based on the total dry weight of the ingredients. 30. The method of claim 25, wherein the polymer soluble in water has a lower limit of 0.003% by weight based on the total dry weight of the ingredients. 31. The method of claim 25, wherein the water soluble polymer has a lower limit of 0.005% by weight based on the total dry weight of the ingredients. 32. The method of claim 25, wherein the water soluble polymer has an upper limit of 0.03% by weight based on the total dry weight of the ingredients. 33. The method of claim 25, wherein the water soluble polymer has an upper limit of 0.02% by weight based on the total dry weight of the ingredients. 34. The method of claim 25, wherein the water soluble polymer is present in the amount of 0.01% by weight based on the total dry weight of the ingredients. 35. The method of claim 25, wherein the water-soluble polymer is selected from the group consisting of hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), methylcellulose (MC), methylhydroxypropylcellulose (MHPC), methylhydroxyethylcellulose (MHEC), hydroxyethylcellulose hydrophobically modified (HMHEC), and mixtures thereof. 36. The method of claim 35, wherein the water soluble polymer is HMHEC wherein the hydrophobe is an alkyl or aryl radical having a lower limit of 2 and an upper limit of 16 carbons. 37. The composition of claim 36, wherein the Water soluble polymer is a mixture of HMHEC and HPMC.

38. The method of claim 36, wherein the upper limit is 10 carbons. 39. The method of claim 36, wherein the upper limit is 6 carbons. 40. The method of claim 24, wherein the adsorption area of the crushed Portland cement clinker polymer is less than 40%. 41. The method of claim 38, wherein the adsorption area of the polymer on the shredded portland cement clinker is less than 30%. 42. The method of claim 39, wherein the adsorption area of the polymer on the crushed Portland cement clinker is less than 20%. 43. The method of claim 25, wherein at least one functional additive is added to the cement mortar. 44. The method of claim 43, wherein at least one functional additive is added in an amount having an upper limit of 1% by weight. 45. The method of claim 43, wherein the functional additive is selected from the group consisting of an air entraining agent, a setting retarder, fine ashes and grinding instruments. 46. The method of claim 36, wherein the HMHEC has a hydrophobic molar substitution of lower limit of approximately 0.005 and upper limit of approximately

0.

2. The method of claim 36, wherein the HMHEC has a lower limit molecular weight of about 50,000 and an upper limit of about 1,500,000.