Cement formulation based on aluminium sulphate with a specific proportion of Ye'elimite systems

Abstract

The present invention corresponds to a cement formulation based on sulfoaluminate comprising a specific Ye'elimite crystal proportion having enhanced mechanical resistance, setting and low CO2 emission features. A concrete obtained when mixing said formulation with water and gypsum is further described, having a superior performance at initial ages compared to concrete obtained from Portland cement.

Claims

1. A calcium sulfoaluminate-based cement formulation, comprising: Ye'elimite (C.sub.4A.sub.3S) with a ratio between its orthorhombic crystalline system (o-C.sub.4A.sub.3S) and its cubic crystalline system (c-C.sub.4A.sub.3S) of 1.40 to 2.95, wherein the Ye'elimite is present in an amount between 43 to 66%; Calcium sulfate (CS) with a ratio between its dihydrate and anhydrous forms lower or equal to 10, wherein the calcium sulfate is present between 9 to 25%; and a maximum silica content of 12% (S).

2. The formulation of claim 1, further comprising: Felite, ferrite or Brownmillerite (C.sub.4AF) less or equal to 1%, Belite (C.sub.2S) from 4 to 8%, Alite (C.sub.3S) less or equal to 1%, Calcite (CaO) from 0 to 4%.

3. The formulation of claim 1, further comprising one or more of the following minerals: Gehlenite (C.sub.2AS), tricalcium aluminate (C.sub.3A) and quartz.

4. The formulation of claim 1, mixed with at least water and arids to obtain concrete.

5. The formulation of claim 4, wherein the concrete shows 25 to 30% greater performance at early ages compared to the concrete obtained from Portland cement.

6. The formulation of claim 4, wherein the concrete is characterized by having a mechanical resistance at 1 day of hydration age of between 19 to 47 Mpa, and at 28 days of 25 to 55 Mpa.

7. The formulation of claim 4, showing quick setting compared to the concrete made with Portland cement.

8. The formulation of claim 1, wherein the Ye'elimite is obtained by sintering a mixture of: CaO (39 to 45%), Al.sub.2O.sub.3 (31 to 35%), SO.sub.3 (8 to 13%) and SiO.sub.2 (1 to 12%) at a temperature from 1250 C. to 1300 C.

9. The formulation of claim 8, wherein the sintering shows a reduction of CO.sub.2 emissions of up to 27% compared with those produced with Portland cement.

Description

4. BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a graphic with the setting times for the three invention cements, with different mineralogical compositions.

(2) FIG. 2 illustrates a comparison graph of the resistance to compression of the three different concrete mixes according to the invention and a concretero type Portland cement.

(3) FIG. 3 shows how the minimum resistance obtained by one of the concretes produced with CSA (CSA-1A) cement reaches about 20 Mpa in 1 day, and how the higher resistance is achieved by the CSA-2 cement; about 55 Mpa in 28 days.

5. DETAILED DESCRIPTION OF THE PRESENT INVENTION

(4) In diverse embodiments, the present disclosure describes a sulfoaluminate based cement formulation (CSA) comprising a specific proportion of Ye'elimite crystals. Preferably, the present invention is made with a sulfoaluminate based cement formulation comprising orthorhombic and cubic Ye'elimite crystals in a ratio greater or equal to 1.40. Some other embodiments of the present invention further comprise calcium salts in their dihydrate and anhydrous forms.

(5) Three invention embodiments are exemplified wherein the calcium sulfoaluminate based cement shows different mineralogical compositions corresponding to different embodiments through which the present invention can be materialized, but without constituting a restriction thereof.

(6) In one of the invention embodiments, the calcium salts correspond to dihydrate and anhydrous calcium sulfate in a ratio comprised between 1.0 and 3.0. The other components are related in Table 1. Said composition, describing the preferred invention embodiments, is obtained after sintering at temperatures between 1250 and 1300 C., a mix elaborated by dividing up materials allowing to reach a composition of about 39 to 45% CaO, 31 to 35% Al.sub.2O.sub.3, 8 to 13% SO.sub.3 and 1 to 12% SiO.sub.2.

(7) Sintering a CSA cement at a temperature between a minimum of 1250 C. and a maximum of 1300 C.according to the hereinabove described invention embodiments, wherein the temperature is reduced in about 250 C., in comparison to a Portland cement, generating almost null C.sub.3S contents and obtaining acceptable or superior performances of the CSA cement in comparison to the Portland cement. The sintering process is the most critical phase. Therefore, a stepped slope as a function of temperature should be established. Cooling is another critical phase in polymorph obtainment, reason why it must be controlled properly.

(8) The cements obtained in the invention embodiments are basically composed of orthorhombic and cubic Ye'elimite, gypsum in dihydrate and anhydrous form and gehlenite. The other components are used according to the appropriate amounts, as illustrated in Table 1. The obtained cements are identified as CSA-2, CSA-1B and CSA-1A, whose Ye'elimite content decreases in the herein described order.

(9) However, as an illustrative embodiment form, the detailed description has been exemplified with formulations for concrete. These same formulations can be used in any formulation of an industrial-use conglomerate.

(10) TABLE-US-00001 TABLE 1 Minearologic composition of cements (the analysis were carried out in the Universidad Nacional de Colombia - Medellin) CSA-2 CSA-1B CSA-1A Compound (% weight) (% weight) (% weight) Orthorhombic Ye'elimite 48.9 27.0 25.5 Cubic Ye'elimite 16.7 16.2 18.3 C.sub.3S - Alita, Nishi et al 0.3 0.0 0.8 C.sub.2S - Belite(Mumme) 4.6 7.4 4.9 Gehlenite 0.0 31.2 27.0 C.sub.3A - Cubic Aluminate 2.0 4.5 3.3 Dihydrate calcium Sulfate- 22.7 5.5 10.9 Gypsum Calcium Sulfate - Anhydrous 2.2 4.2 5.9 Calcite 0.4 1.3 1.9 Quartz 1.4 0.8 1.3 Brownmillerite 0.0 0.7 0.0 Calcium Oxide 0.1 0.0 0.3 C.sub.3A 0.6 0.4 0.1

(11) The following assays are described: quick setting time check, high strength check and reduction of CO.sub.2 emissions check.

(12) FIG. 1 is related to the quick setting time check results. The obtained cements were evaluated according to the ASTM C191-01 norm [35] (equivalent to NTC 118). This procedure consists of knowing the initial setting time (IST) indicating the moment when the sample starts loosing plasticity and is shown when a 1 mm diameter needle of Vicat apparatus, Soiltest brand, penetrates 25 mm into the paste, and the final setting time (FST) indicating the moment when the sample begins gaining strength and the final reading is when the needle stops penetrating the paste. In FIG. 1, relatively quick setting time values are observed for the cement produced in this invention. Particularly, CSA-2 has the shortest initial setting time. This differential behavior is based in the particular crystalline composition of the cement proposed in this invention. The setting time is determined as established in norms ASTM C187 and ASTM C191.

(13) The above results vary as to the initial and final setting for the three cements due to their varied mineralogical composition. However, the quick setting times obtained evidence one of the utmost important features of the CSA cement, referring to a quick hardening in contrast to Portland cement.

(14) CSA-2 has lesser setting times, due to a greater orthorhombic Ye'elimite content, its high reactivity, and very low Gehlenite content, a non-hydraulic material. The setting values are described in the following table:

(15) TABLE-US-00002 TABLE 2 Setting times in cements of the present invention Analysis CSA-1A CSA-1B CSA-2 Initial setting 60 68 30 Final setting 180 180 165

(16) As for CSA-1A and CSA-1B, the difference in the Ye'elimite and the dehydrated gypsum polymorph content establishes the difference between these two cements, which is reflected in the initial shortest setting time regarding the CSA-1A cement. The normal consistency, necessary for the setting time measure, was determined using norms ASTM C187 and ASTM C191.

(17) Additionally, a high strength check was carried out on the different cement formulations of the subject invention. The mechanical performance of the compositions was evaluated measuring the compression resistances, where the determination of the concrete mix fluidity is first specified, using ASTM C1437, storage and in-water setting according to ASTM C349, until obtaining different hydration ages of 1, 3, 7 and 28 days.

(18) TABLE-US-00003 TABLE 3 Mechanical resistance to compression of concrete Mechanical resistance CSA-2 CSA-1B CSA-1A 1 d (Mpa) 37.5 21.0 22.7 3 d (Mpa) 39.0 21.8 23.9 7 d (Mpa) 41.0 23.2 26.4 28 d (Mpa) 47.3 26.4 27.6

(19) According to the above table, the concrete obtained with CSA-2 cement generates greater initial resistance to compression and fast development through time. This can be corroborated through the quick setting, which evidences a high reactivity of this particular cement that in turn is due to its previously referred mineralogical composition, as well as its orthorhombic/cubic Ye'elimite ratio and the lower presence of other non-reactive phases (as gehlenite).

(20) The CSA-2 cement composition having a polymorphic ratio of orthorhombic to cubic Ye'elimite of >2.5, exhibits better performance. Compositions with a polymorphic ratio of orthorhombic to cubic Ye'elimite of >2.5, exhibit a greater development of mechanical resistances in concrete, namely, compression resistances at all ages.

(21) Furthermore, the concrete obtained with the CSA-2 mixture, for a mix design of 5000 psi, shows a high development of resistance at early ages, up until 28 days. It was compared against a type III Portland cement or concretero (local description for type III cement), showing superior performance, as illustrated in FIG. 3. This CSA concrete was produced identically as the Portland cement is produced, replacing only the amount of cement in the concrete mix. Like it was noted in the mortar (FIG. 2), the mix made with CSA-2 evidences a better behavior compared to other CSA mixes and to the Portland cement mortar (Concretero), at ages of 1, 3 and 7 days. In the concrete resistance evaluation (FIG. 3), the formulation with CSA-2 cement surpasses all the concretes used regarding compression resistances, including the concrete made with Portland cement. The CSA-2 concrete crystalline matrix allows for improving the compression resistance between 25 and 30% and its quick hardening allows for several alternatives when using CSA-2 cement in concrete.

(22) FIG. 3 shows how the minimum resistance obtained by one of the concretes produced with CSA (CSA-1A) cement reaches about 20 MPa in 1 day, and how the higher resistance is achieved by the CSA-2 cement; about 55 MPa in 28 days.

(23) In addition to the above, an evaluation of the reduction of the CO.sub.2 emissions was carried out. The emission reduction that was evidenced in the production process was seen as high as 27%, and after grinding, it increased about 6% more. The amount of CO.sub.2 emitted during the production of the different cements was measured. The data of the gas measurements and the reduction are shown in Table 3, where the CSA clinkers with a Portland clinker are compared.

(24) TABLE-US-00004 TABLE 3 CO2 emissions Material [%] CO2 CO2 [%] Reduction Portland Clinker 20.45 0% CSA 1Clinker 14.25 27% CSA 2Clinker 15.05 23%

(25) The comparative assay carried out with a composition that does not comply with the orthorhombic/cubic condition of being greater or equal to 1.40 and the CaSO.sub.4.2H.sub.2O/anhydrous ratio between 1.0 and 3.0, exhibited very poor performance.

(26) It must be understood that although the present invention has been specifically disclosed by a preferred embodiment form and some optional features, any modification, improvement and variation of the invention in the present disclosed document is possible by persons skilled in the art. Moreover, such modifications, improvements and variations are considered as being within the scope of the invention. The components, formulations and examples provided herein are representative of preferred embodiments, i.e., they are examples and are not intended as limitations for the invention scope.

(27) All the publications, patent applications, patents, commercially used methods herein mentioned are expressly attached only as reference.