Innovative cementitious composites (ICC): high-volume reclaimed asphalt pavement aggregate

Abstract

An ultra-high-performance cement composites comprising cement, a polycarboxylate ether-based superplasticizer, fly ash, silica fume, reclaimed asphalt pavement granules, water and red sand. A very low water-to-binder ratio could be obtained using the polycarboxylate ether-based superplasticizer that overcomes the hydrophobic properties of reclaimed asphalt pavement and yields an ultra-high-performance cement composite.

Claims

1. A cement composite, comprising: cement, a polycarboxylate ether-based superplasticizer, fly ash, silica fume, reclaimed asphalt pavement (RAP) granules, water, and red sand; wherein the cement composite comprises between about 25% to about 40% RAP.

2. The composite of claim 1, comprising between about 30% to about 40% cement by weight.

3. The composite of claim 1, comprising between about 20-30 L/m.sup.3 of the polycarboxylate ether-based superplasticizer.

4. The composite of claim 1, comprising between about 4% to about 9% fly ash.

5. The composite of claim 1, comprising between about 2% to about 5% silica fume.

6. The composite of claim 1, comprising between about 1% to about 4% red sand.

7. The composite of claim 1, further comprising between about 0.5 to about 2% microsteel fibers.

8. A method of making a cement composite, the method comprising: mixing water with a polycarboxylate ether-based superplasticizer dosage for initial flowability; adding fly ash to the water and the polycarboxylate ether-based superplasticizer dosage to create a first mixture; stirring the first mixture; adding cement to the first mixture to obtain a second mixture; stirring the second mixture in a high-shear mixer; gently adding silica fume to the second mixture to obtain a third mixture and stirring the third mixture; gradually adding reclaimed asphalt pavement (RAP) granules and red sand to the third mixture to obtain a fourth mixture; stirring the fourth mixture; optionally adding micro-steel fibers to the fourth mixture to obtain a fifth mixture; optionally measuring an initial flowability of the fifth mixture; and casting the fourth mixture or the fifth mixture, if made, into a target mold to obtain a cement composite.

9. The method of claim 8, wherein the method includes the steps of: adding micro-steel fibers to the fourth mixture to obtain a fifth mixture; measuring an initial flowability of the fifth mixture; and casting the fifth mixture into a target mold to obtain a cement composite.

10. The method of claim 8, wherein the initial flowability is about 200 mm to 240 mm.

11. The method of claim 8, wherein stirring the first mixture lasts for about 1 minute.

12. The method of claim 8, wherein stirring the second mixture in the high shear mixer lasts for about 2 minutes.

13. The method of claim 8, wherein stirring the third mixture in the high shear mixer lasts for about 3 minutes.

14. The method of claim 8, wherein stirring the fourth mixture lasts for about 2 minutes.

15. The method of claim 9, wherein measuring the flowability of the fifth mixture comprising using a modified mini-slump cone.

16. The method of claim 8, wherein the target mold comprises one of a prism shape and a cube shape.

17. The method of claim 8, wherein the fourth mixture comprises between 30% to 40% cement by weight, between 20-30 L/m.sup.3 of the polycarboxylate ether-based superplasticizer by weight, between 4% to 9% fly ash by weight, between 2% to 5% silica fume by weight, between 25% to 40% RAP by weight, and between 1% to 4% red sand by weight.

18. The method of claim 9, wherein a median size of the red sand does not exceed 300 microns.

19. The method of claim 9, wherein a median size of the RAP is less than 3 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic of an embodiment of a concrete composite as described herein.

(2) FIG. 2 is a graph of a sieve analysis of RAP aggregate.

(3) FIGS. 3A, 3B, 3C, 3D, 3E. 3F, and 3G are optical microscope pictures of the RAP in each of the different sizes of the groups in FIG. 2: FIG. 3A=S1=0.1-0.4 mm; FIG. 3B=S2=0.2-0.6 mm; FIG. 3C=S3=0.7-1.1 mm; FIG. 3D=S3=1.1-1.2 mm; FIG. 3E=1.2 mm-2.5 mm; FIG. 3F=S6=1.7-4 mm; FIG. 3G=S7=4-6.3 mm.

(4) FIGS. 4A, 4B, and 4C are embodiments of optimization of the RAP-UHPC mix following the maximum tolerance approach. FIG. 4A shows gradual addition of RAP. FIG. 4B shows maximum content of RAP with target flow. FIG. 4C shows MSF addition until target flow was achieved.

(5) FIG. 5 is a graph showing the development of compressive strength over time for various mixes containing different asphalt aggregate contents.

(6) FIG. 6 shows the fused interstitial transition zone (FITZ) matrix.

(7) FIG. 7 is a graph showing the development of compressive strength over time for different mixes containing different asphalt aggregate contents and micro-steel fiber.

(8) FIG. 8 is a graph showing the flexural properties of the mixes without fibers (MF5 and MF10) at 28 days of curing.

(9) FIG. 9 is a graph of flexural properties of the mixes with fibers at 28 days of curing compared to the mix with 100% natural aggregate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) The following definitions are provided for the purpose of understanding the present subject matter and for construing the appended patent claims.

Definitions

(11) Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, or comprising specific process steps, it is contemplated that compositions of the present teachings can also consist essentially of, or consist of, the recited components, and that the processes of the present teachings can also consist essentially of, or consist of, the recited process steps.

(12) It is noted that, as used in this specification and the appended claims, the singular forms a, an, and the include plural references unless the context clearly dictates otherwise.

(13) In the application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that the element or component can be any one of the recited elements or components, or the element or component can be selected from a group consisting of two or more of the recited elements or components. Further, it should be understood that elements and/or features of a composition or a method described herein can be combined in a variety of ways without departing from the spirit and scope of the present teachings, whether explicit or implicit herein.

(14) The use of the terms include, includes, including, have, has, or having should be generally understood as open-ended and non-limiting unless specifically stated otherwise.

(15) The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term about is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term about refers to a ?10% variation from the nominal value unless otherwise indicated or inferred.

(16) The term optional or optionally means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances in which it does not.

(17) It will be understood by those skilled in the art with respect to any chemical group containing one or more substituents that such groups are not intended to introduce any substitution or substitution patterns that are sterically impractical and/or physically non-feasible.

(18) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently described subject matter pertains.

(19) Where a range of values is provided, for example, concentration ranges, percentage ranges, or ratio ranges, it is understood that each intervening value, to the tenth of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the described subject matter. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and such embodiments are also encompassed within the described subject matter, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the described subject matter.

(20) Throughout the application, descriptions of various embodiments use comprising language. However, it will be understood by one of skill in the art, that in some specific instances, an embodiment can alternatively be described using the language consisting essentially of or consisting of.

(21) For purposes of better understanding the present teachings and in no way limiting the scope of the teachings, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

(22) Asphalt is composed of bitumen, filler, and aggregates. Bitumen is composed of organic compounds from the distillation of petroleum. Asphalt contains two main components: maltenes, which are subdivided into aromatic compounds and resins, and asphaltenes (aromatic compounds based on carbon, nitrogen, and sulfur with a few hydroxyl groups). These aromatic compounds can be chemically integrated with polycarboxylate ether-based compounds and any other similar compounds.

(23) The present subject matter relates to a concrete mixture that includes an integrated cementitious matrix and a superplasticizer that serves as a hydrophilic-hydrophobic dual linker between the cement and the organic portion of the optimized asphalt granules (bitumen) through electronegativity (nitrogen, sulfur, and oxygen) and intermolecular forces (hydrogen bonds), as illustrated in FIG. 1. Therefore, with a very low water-to-cement ratio, a significant amount of polycarboxylate ether-based superplasticizer becomes mandatory for flowable cementitious mixes. At these elevated dosages of superplasticizer, a highly effective fused interstitial transition zone (FITZ) with improved hybrid properties can be formed. Most of the problems associated with the organic portion of asphalt might be resolved using the composition as described herein.

(24) In an embodiment, the present subject matter relates to a concrete composite comprising cement, superplasticizer, fly ash, silica fume, reclaimed asphalt pavement (RAP) granules, water, red sand, and microsteel fibers.

(25) In one embodiment, the superplasticizer may be a polycarboxylate ether-based superplasticizer.

(26) In another embodiment, the concrete composite may include between about 30% to about 40% cement by weight.

(27) In a further embodiment, the concrete composite may include between about 20 to about 30 L/m.sup.3 superplasticizer.

(28) In an embodiment, the concrete composite may include between about 4% to about 9% fly ash.

(29) In another embodiment, the concrete composite may include between about 2% to about 5% silica fume.

(30) In a further embodiment, the concrete composite may include between about 25% to about 40% RAP.

(31) In an embodiment, the concrete composite may include between about 1% to about 4% red sand.

(32) In another embodiment, the concrete composite may include between about 0.5 to about 2% microsteel fibers.

(33) The present subject matter also relates to a method of making a cement composite, the method comprising: mixing water with an optimal superplasticizer dosage for initial flowability; adding fly ash to the water and the optimal superplasticizer dosage to create a first mixture; stirring the first mixture; adding cement to the mixture to obtain a second mixture; stirring the second mixture in a high-shear mixer; gently adding silica fume to the second mixture to obtain a third mixture and stirring the third mixture; gradually adding reclaimed asphalt pavement (RAP) granules to the third mixture to obtain a fourth mixture; stirring the fourth mixture; adding micro-steel fibers to the fourth mixture to obtain a fifth mixture; measuring the initial flowability of the fifth mixture; and casting the fifth mixture into a target mold to obtain a cement composite.

(34) In an embodiment, the initial flowability may be about 200 mm to about 240 mm.

(35) In another embodiment of the present subject matter, stirring the first mixture may last for at least about 1 minute, or about 1 minute.

(36) In a further embodiment, stirring the second mixture in the high shear mixer may last for about 2 minutes.

(37) In a still further embodiment, stirring the third mixture in the high shear mixer may last for about 3 minutes.

(38) In an embodiment, stirring the fourth mixture may last for about 2 minutes.

(39) In another embodiment, measuring the flowability of the fifth mixture may include but is not limited to a modified mini-slump cone.

(40) In a further embodiment, the target mold may include but is not limited to one of a prism shape and a cube shape.

(41) In a still further embodiment, the fourth mixture comprises between about 30% to about 40% cement by weight, between about 20-30 L/m.sup.3 of superplasticizer, between about 4% to about 9% fly ash, between about 2% to about 5% silica fume, between about 25% to about 40% RAP, and between about 1% to about 4% red sand.

(42) In one embodiment, a median size of the red sand may not exceed about 300 microns, or 300 microns.

(43) In another embodiment, a median size of the RAP may be less than about 3 mm, or less than 3 mm.

(44) The following examples illustrate the present teachings.

Example 1

(45) Method of Mixing Concrete Composite

(46) This method relied on two main concepts: reducing mixing water to the lowest possible level and increasing the superplasticizer dosage to deliver two benefits: high flowability and an efficient linker between hydrated cement and the organic part in asphalt granules. The sequence of mixing procedure is summarized below: 1. Pour water into the bowl with the optimum superplasticizer dosage for an initial flowability of about 220?20 mm. 2. Add fly ash first and stir for 1 minute, followed by cement for 2 minutes in a high-shear mixer. 3. Then, gently insert silica fume and mix for another 3 minutes in a high shear mixer, followed by the gradual addition of asphalt granules in two minutes. 4. Adding the optimized micro-steel fibers, if exists, gradually for 1 minute 5. Measuring the followability using the modified mini-slump cone 6. Cast the mix into the target molds.

Example 2

(47) Reclaimed Asphalt Pavement (RAP) Aggregate

(48) The sieve and microscopic analysis of RAP are shown in FIGS. 2 and 3, respectively. The sieve analysis shown in FIG. 2 is divided into seven sizes of zones that are monitored using an optical microscope. The range of particle sizes is visualized in each zone, as in FIG. 3.

Example 3

(49) Mix Composition

(50) The determination of the mix composition was conducted following the concept described herein, which relies on the maximum tolerance of the mix to accept an additional component while maintaining the target flow, as depicted in FIG. 4. The paste was prepared first, followed by the gradual addition of RAP aggregates until apparent followability was achieved, followed by the addition of micro-steel fibers (MSF) if used, as depicted in FIG. 4.

(51) Based on this protocol, the final mix composition could be defined, as presented in Table 1. The binder content varied between 800 and 1200 kg/m.sup.3 with the cement content varying between 600 and 900 kg/m.sup.3. However, limestone dust can replace up to 40% of the cement content. Fly ash (FA) and silica fume (SF) varied between 4-9% and 2-5%, respectively. RAP varied between 25 and 40% of the total weight of the mix, while red sand (RS) varied between 1 and 4%. Superplasticizer dosage varied between 20 and 30 L/m.sup.3. The volume content of microsteel fibers (MSF) varied between 0.5 and 2%.

(52) TABLE-US-00001 TABLE 1 Table 1. An example of the optimized mix composition given in kg/m.sup.3 Cement FA SF RAP RS W SP MSF 885 196 75 877 66 198 24 99

Example 4

(53) Optimization in RAP Content

(54) The variation in the RAP content was monitored in different UHPC mixes (M0-M15) at different curing ages of 1, 7 and 28 days, as presented in Tables 2. The results are shown in FIG. 5.

(55) TABLE-US-00002 TABLE 2 RAP and red sand content in the mixes M0 to M15 Red Sand Mix I.D. RAP (wt %) (wt %) M0 40.64 0 M1 40.12 3 M2 39.07 6 M3 37.13 11 M4 33.78 20 M5 38.12 3 M6 35.02 6 M7 28.82 12 M8 16.44 24 M9 40.63 0 M10 37.63 3 M11 32.79 5.5 M12 29.79 10 M13 29.81 10 M14 32.38 5 M15 29.22 10

(56) The fractured surfaces of concrete were analyzed using an optical microscope. The results confirmed that nearly no interstitial transition zone could be observed, which is identified as fused (FITZ) as demonstrated in FIG. 6.

(57) Fiber Reinforced Mixes

(58) Different mixes with different RAP contents (27.5-37%) and MSF dosages varying from 0 to 4.8% were prepared for compressive strength and flexural properties, as per the values shown in Table 3. The compressive strengths of the mixes are shown in FIG. 7.

(59) Compressive Strength

(60) As illustrated in Table 3 and FIG. 7, a strength over 140 MPa can be obtained with a high volume of RAP aggregates (27.5%).

(61) TABLE-US-00003 TABLE 3 MF1 MF2 MF3 MF4 MF5 MF6 MF7 MF8 MF9 MF10 Asph 36.00 35.71 35.43 34.51 37.21 34.33*** 27.52 30.29 33.06 35.40 Agg4* Asp 0.00 0.00 0.00 0.00 2.79 2.58 9.14 6.39 3.64 0.00 powder** RS 2.70 2.68 2.66 5.18 8.38 7.73 0.00 0.00 0.00 2.87 MSF 3.24 4.02 4.79 4.66 0.00 3.87 4.13 4.13 4.13 0.00 UHPC mixes with RAP and MSF (% wt ) *Asphalt aggregate of maximum size of 6.3 mm. **Fine asphalt aggregate of maximum size of 0.6 mm ***Asphalt aggregate is replaced by natural one (NA)
Flexural Properties

(62) The flexural properties are shown in FIGS. 8 and 9. FIG. 8 confirms that a minimum amount of RS is preferable. Moreover, it is possible to obtain comparable flexural properties in the mix with high-volume RAP aggregates to those in the mix with 100% natural aggregate. This will make the recycling of high-volume reclaimed asphalt pavement aggregates feasible and beneficial.

(63) It is to be understood that the concrete composite and method of making the concrete composite described herein is not limited to the specific embodiments described above but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.