WO2015149176A1

WO2015149176A1 - Geopolymer cement compositions and methods of making and using same

Info

Publication number: WO2015149176A1
Application number: PCT/CA2015/050260
Authority: WO
Inventors: M. Shahria ALAM; Mohammad Shahidul ISLAM; Anantray M. PARGHI; Eric Matthew MARCINIAK; Brendan POGUE
Original assignee: The University Of British Columbia; Polyrap Pavement Systems Ltd.
Priority date: 2014-03-31
Filing date: 2015-03-31
Publication date: 2015-10-08

Abstract

A geopolymer cement composition that utilizes a combination of industrial waste by-products that includes a mixture of mine tailings and recycled glass powder (RGP) along with an alkali activator and optionally an alumina additive for activating the geopolymer cement which can be used to produce geopolymer concrete products.

Description

GEOPOLYMER CEMENT COMPOSITIONS AND METHODS OF MAKING

AND USING SAME

FIELD OF THE INVENTION

[0001] The present invention relates to the field of cement and concrete materials, in particular, a geopolymer cement composed of industrial wastes, which can be used as a binding material in a variety of forms including cement paste, grout, or concrete.

BACKGROUND OF THE INVENTION

[0002] Ordinary Portland cement (OPC) is known as the conventional binder material in the production of concrete. Due to its characteristic ability to take a variety of forms and harden into a strong material, Portland cement is one of the largest commodity products produced worldwide with over 2.5 billion tons annually. However, the use of OPC as a main building material has been questioned extensively over the last few decades primarily because of the environmental impact of clinker production. The production of Portland cement in fact emits the equivalent amount of C0₂, accounting for about 5% of the total man-made C0₂ emissions. Accordingly, the production of Portland cement comes at a high level of environmental cost.

[0003] In addition to OPC, concrete production involves the use of sand and aggregate components. Production of such components requires the quarrying process which is also energy intensive and produces large amounts of waste materials. In many countries shortage of natural resources for construction materials has also led to long distance haulage and hence considerably increased the production cost of construction materials. All of these factors combined present challenges to the development of a sustainable construction industry. [0004] Geopolymers are a class of inorganic polymer formed by combining source materials having high silica and alumina content with strong alkali solution, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), and soluble silicates such as sodium silicate. The dissolved alumina (Al₂Os) and silica (Si0₂) species undergo geopolymerization to form a three-dimensional amorphous aluminosilicate network having strength that is comparable or even higher than that of the OPC concrete. The considerably lower energy requirements for producing geopolymer cement and the range of sources that can potentially be used to provide the aluminosilicate materials have made geopolymer cement an environmentally appealing alternative to conventional Portland cements.

[0005] Various sources of aluminosilicate materials have been utilized, including naturally occurring clays and industrial waste products such as fly ash and bottom ash, ground granulated blast-furnace slags, bauxite processing residues, kaolinitic clays, certain mine wastes, and naturally occurring pozzolans. Utilizing waste products reduces the environmental impact of these waste products while further allowing these waste products to be repurposed into geopolymer cements.

[0006] Given the environmental cost of conventional Portland cement, providing alternative cement compositions, such as geopolymer cement that can be designed to exhibit binding properties similar to Portland cement without the considerable environmental cost is needed.

[0007] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

SUMMARY OF THE INVENTION

[0008] Disclosed herein are exemplary embodiments pertaining to geopolymer cement compositions and methods of making and using same. In accordance with one aspect, there is described a geopolymer cement composition comprising, a combination of waste by-products comprising mine tailings, recycled glass powder (RGP), and fly ash, in reactive combination with an alkali activator, wherein the combination of said waste by-products with said alkali activator result in a geopolymer cement suitable for producing a geopolymer concrete.

[0009] In accordance with another aspect, there is described a geopolymer cement composition comprising, a combination of waste by-products comprising mine tailings, recycled glass powder, and fly ash, in reactive combination with an alkali activator and an alumina additive, wherein the combination of said waste by-products with said alkali activator and alumina additive result in a geopolymer cement suitable for producing a geopolymer concrete.

[0010] In accordance with another aspect, there is described a geopolymer cement composition comprising, a combination of waste by-products comprising about 70% (w/w) mine tailings, about 10% to about 15% (w/w) recycled glass powder, and about 15% to about 20% (w/w) fly ash, in reactive combination with about 10M alkali activator, and about 1M alumina additive, wherein the combination of said waste byproducts with said alkali activator and alumina additive result in a geopolymer cement suitable for producing a geopolymer concrete.

[0011] In accordance with another aspect, there is described a method for producing a geopolymer concrete from waste by-products comprising: providing a combination of waste by-products comprising mine tailings, recycled glass powder, and fly ash; reacting said combination of waste by-products with an alkali activator to form a geopolymeric matrix; and curing said reacted combination to form said geopolymer concrete. According to certain embodiments of the method, the combination of waste by-products is reacted with said alkali activator and an alumina additive.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings.

[0013] Figure 1 is a graphical presentation of the compressive strength of cement mortar cubes at 7, 14, and 28 days after production, comprising 30% fine materials including cement and fine mine tailings (FMT) (<80μηι); [0014] Figure 2 is a graphical presentation of the compressive strength of alkali activated mortar cubes at 3, 7, and 28 days after production, comprising 30% fine materials of different combinations of fly ash (FA) and fine mine tailings (FMT) (<80μιη);

[0015] Figure 3 is a flowchart illustrating the experimental testing conducted;

[0016] Figure 4 is a graphical presentation of the compressive strength development of recycled glass powder modified mortar, (a) Series-A, containing recycled glass powder (b) Series-B, containing RGP and FA (c) Series-C, containing RGP, FA and silica fume (SF);

[0017] Figure 5 is a graphical presentation of the flexural strength development of recycled glass powder modified mortar, (a) Series-A, containing RGP (b) Series-B, containing RGP and FA (c) Series-C, containing RGP, FA and SF;

[0018] Figure 6 is a graphical presentation of the compressive strength activity index of RGP modified mortar, (a) Series-A, containing RGP (b) Series-B, containing RGP and FA (c) Series-C, containing RGP, FA and SF;

[0019] Figure 7 is a graphical presentation of the alkali silica reaction of the mortar bar on RGP modified mortar, (a) Series-A, containing RGP (b) Series-B, containing RGP and FA (c) Series-C, containing RGP, FA;

[0020] Figure 8 is a graphical presentation of the particle size distribution of waste glass powder;

[0021] Figure 9 is a graphical presentation of the preliminary compressive strength test results of waste glass powder based mortar with mine tailings activated with (NaOH+NaA10₂); and

[0022] Figure 10 is a graphical presentation of the comparison of compressive strength of geo-polymer concrete with and without waste glass powder. DETAILED DESCRIPTION OF THE INVENTION

[0023] Geopolymer cements are an environmentally appealing alternative to conventional Portland cements. In addition to having considerably lower energy requirements for production of geopolymer concrete, the geopolymerization process is amenable to the use of industrial waste products for production, thereby further reducing the environmental cost of production.

[0024] Geopolymers are formed by the reaction between an alkali metal hydroxide/silicate solution (often referred to as the chemical activator) and an aluminosilicate fine binder. The process involves forming monomers in solution then thermally triggering them to polymerize to form a solid polymer. The "monomers" that are formed:

- Si - O - Al - O - (poly[silalate]), or

- Si - O - Al - O - Si - O - (poly[silalate-siloxi]) polymerize to form the geopolymeric matrix. Depending on the ratio of Si/Al, the geopolymeric matrix can range from being rigid, suitable as a concrete, cement or waste encapsulating medium, or more flexible, suitable as an adhesive, sealant, or resin.

[0025] The compositions according to embodiments of the present disclosure combine two major waste materials, such as mine tailings and waste recycled glass powder, into a binding material suitable for producing a geopolymer concrete. Mine tailings comprise high concentrations of hazardous waste, and have thus presented adverse environmental effects due to issues of fugitive dust, metal leaching and acid rock drainage. Waste glass has also presented an environmental impact due to the immense volume of this waste by-product and the struggle for recycling programs to effectively keep up. The compositions, according to embodiments of the present disclosure, repurpose these industrial waste by-products to produce the bonding requirements of concrete type construction materials. In this way, significant amounts of the carbon footprint is reduced by the production of such sustainable materials. [0026] According to further embodiments of the present disclosure, waste byproducts are combined and reacted with an alkali activator and in some embodiments an alumina additive to form a geopolymeric matrix that is suitable for producing a geopolymer concrete. The combination of waste glass powder and the addition of an alumina additive, in such embodiments, increases the reactivity of the activators allowing geopolymerization to be activated even in the presence of mine tailings having insignificant silica and alumina content. In this way, the silica and alumina content of the mine tailings does not limit the use of mine tailings in the present compositions, allowing for a wide range of mine tailings to be used in compositions of the present disclosure.

Definitions

[0027] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. [0028] As used herein, the term "about" refers to an approximately +/-10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

[0029] As used herein, the term "cement" refers to a binding system, a substance that sets and hardens and can bind together other materials typically used in construction. Cement forms the base of both mortar and concrete.

[0030] As used herein, the term "mortar" refers to a mixture made with cement for bonding materials together, typically building materials such as brick or stone.

[0031] As used herein, the term "concrete" refers to a mixture made with cement, typically combined with water, sand and course aggregate for forming structural projects including, for example, building foundations and support structures as well as precast concrete products.

[0032] As used herein, the term "glass" encompasses all inorganic products which have cooled to a rigid solid without undergoing crystallization process. Glass comprises several chemical varieties without limitation such as packing glass, alkali silicate glass, boro-silicate glass, lead glass, barium glass, alumino-silicate glass and ternary soda- lime silicate glass. In addition, the glass can be conventional, recyclable waste glass containing mixed colour waste glass, plate glass, glass bottles and other molded glass shapes, and waste glass fibers. The term "glass" is also intended to include other glassy materials including ceramic materials such as porcelain.

Geopolymer Cement Compositions

[0033] Geopolymer cement compositions according to embodiments of the present disclosure comprise, a combination of waste by-products in reactive combination with an alkali activator. Reactive combination of the waste by-products with the alkali activator results in formation of a geopolymeric matrix that exhibits binding properties suitable for producing a geopolymer mortar or concrete, including for example precast concrete products.

Combination of Waste By-Products [0034] According to embodiments of the present disclosure, the geopolymer cement compositions utilize combinations of waste by-products that include mine tailings and glass powder, preferably recycled glass powder. According to further embodiments, the combination of waste by-products include mine tailings, and glass powder, in further combination with other industrial by-products. In such embodiments, the additional industrial by-products may provide a further source of aluminosilicate, for example, fly ash. The addition of fly ash, for example, will generally be a function of activity of the mine tailings and recycled glass powder and the strength requirements for the final product. Fly ash can include any type of combustion residue derived from coal power stations, including but not limited to bottom ash and products of processing such residues including fine grinding. According to embodiments of the present disclosure, the combination of waste by-products includes mine tailings, glass powder, and fly ash.

[0035] A wide variety of mine tailings can be utilized in the compositions of the present disclosure. According to certain embodiments, gold mine tailings are combined with glass powder and/or fly ash to form the combination of waste by-products. According to other embodiments, desulphurized mine tailings are utilized. Depending on the composition of the mine tailings, the mine tailings can provide a source of silica and alumina for the geopolymeric reaction. According to other embodiments, the mine tailings may not contain a significant level of silica and alumina and, according to such embodiments, may make up the aggregate of the composition.

[0036] The relative amount of mine tailings in the combination of waste by-products, according to embodiments of the present disclosure, can range from about 50% to about 70% w/w of the combination. According to other embodiments, the amount of mine tailings can range from about 55% to about 70% (w/w). According to further embodiments, the amount of mine tailings can range from about 60% to about 70% (w/w). According to other embodiments, the amount of mine tailings can range from about 65% to about 70% (w/w).

[0037] The particle size of the mine tailings can vary depending on the end use of the geopolymer cement. For example, according to embodiments of the present disclosure, the mine tailings can have an average particle size of less than about 4.75μηι which is suitable for mortar-type applications. According to other embodiments, the mine tailings can have an average particle size of up to about 10 mm (coarse aggregate), suitable for concrete-type applications.

[0038] Waste glass powder, according to embodiments of the present disclosure, can provide a source of silica for reaction with the alkali activator in forming the geopolymeric matrix. According to embodiments of the present disclosure, the waste glass powder comprises glass particles of relatively uniform size. According to certain embodiments, the average glass particle size is less than about ΙΟΟμηι. According to further embodiments, the average glass particle size is less than about 80μηι. According to other embodiments, the average glass particle size is less than about 75μηι. According to other embodiments, the average glass particle size is less than about 65μηι. According to further embodiments, the glass particles are between about 20μηι and about 1 ΙΟμηι. According to preferred embodiments, the glass particle size of the recycled glass powder is between about 20μηι to about 40μηι. [0039] The relative amount of glass powder in the combination of waste by-products, according to embodiments of the present disclosure, can range from about 5% to about 30%. According to other embodiments, the amount of glass powder can range from about 10% to about 30% w/w of the combination. According to further embodiments, the amount of glass powder can range from about 15% to about 30% (w/w). According to other embodiments, the amount of glass powder can range from about 20% to about 30% (w/w). According to further embodiments, the amount of glass powder can range from about 25% to about 30% (w/w).

[0040] According to certain embodiments of the present disclosure, the combination of waste by-products can include fly ash which can provide an additional source of silica and alumina for the geopolymeric reaction. According to such embodiments, the amount of fly ash in the combination can range from about 15% to about 30% w/w of the combination. According to other embodiments, the amount of fly ash can range from about 20% to about 30% (w/w). According to further embodiments, the amount of fly ash can range from about 25% to about 30% (w/w).

Geopolymeric Reaction - Activators and Additives

[0041] The geopolymer cement compositions of the present disclosure comprise an alkali activator to reactively combine with the combination of waste by-products to form the geopolymeric matrix. Specifically, the alkali activator reacts with the silicon and aluminium ions in the combination to form the matrix. According to embodiments of the present disclosure, the alkali activator is an alkali metal hydroxide. According to such embodiments, the alkali metal hydroxide is sodium hydroxide, potassium hydroxide, or a combination of sodium hydroxide and potassium hydroxide. According to further embodiments, the alkali activator further includes a silicate. According to such embodiments, the silicate is sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate. It is contemplated that other alkali metal systems or mixtures of different alkalis can be used, as can any waste source of concentrated alkali. [0042] According to certain embodiments of the present disclosure, the composition comprises an alumina additive. Particularly in compositions where the combination of waste by-products includes mine tailings with lower silica and alumina content, an alumina additive can be included to improve activation of the geopolymer reaction to form a geopolymer cement suitable for producing a geopolymer concrete. According to embodiments of the present disclosure, the alumina additive can be sodium aluminate, potassium aluminate, or a combination of sodium aluminate and potassium aluminate.

Production of Cement, Mortar, and Concrete Products

[0043] According to another aspect of the present disclosure, the geopolymer cement compositions can be used to produce mortar and concrete products. According to such embodiments, a combination of waste by-products is reacted with an alkali activator and/or additive to form a geopolymeric matrix, as described above. The formed matrix is then allowed to cure to form the geopolymeric mortar or concrete product.

[0044] The curing of the cement composition may be achieved by simply allowing the cement composition to stand, as with conventional cement. Alternatively, or in addition, curing may be assisted by applying heat or steam.

Uses

[0045] The geopolymer cement compositions of the present disclosure can be used for the same purposes as any conventional cement. For example, the composition can be used for the production of geopolymer mortars, concretes, precast concretes, pastes and adhesives.

[0046] To gain a better understanding of the invention described herein, the following examples are set forth. It will be understood that these examples are intended to describe illustrative embodiments of the invention and are not intended to limit the scope of the invention in any way. EXAMPLES

Methods and Materials

Preparation of Mortar

[0047] For the reference mixture, the mixing procedure was carried out in accordance with standard protocols CSA-A3004-C2 (2013), similar to ASTM-C305 (2013). First, the mixing water was placed in a bowl followed by the addition of the cement. Mixing was initiated in a mixer at slow speed (140 ± 5 rpm) for 30 seconds. During this slow speed, the entire quantity of sand was added slowly over a 30 second period while mixing continued at slow speed. Mixing was stopped in order to change to a medium speed (285 ± 10 rpm), and then continued for about 30 seconds. Mixing was then stopped for 1.5 minutes to set the sand and mortar. Mixing was then restarted at a medium speed (285 ± 10 rpm) for 1 minute. During this time, in the first 15 second period, any mortar that was collected on the side of the bowl was quickly scraped down and mixing was then resumed at a medium speed (285 ± 10 rpm).

[0048] For mixtures that include activator, the same procedure was followed with the exception that activator instead of water was placed in the mixing bowl, followed by the addition of fly ash, and then mixed at slow speed.

[0049] Preparations containing mine tailings used gold mine tailings from San Gold's Rice Lake mining complex (Manitoba, Canada).

[0050] The mortar specimens were cast into molds (50 ^χ mm ^χ 50 mm χ 50 mm) in two layers to make cubes. Immediately after casting, the test specimens were covered with plastic film to minimize the water evaporation during curing at an elevated temperature. The test specimens were cured in an oven at 60 °C for 24 hrs. After the curing period, the test specimens were left in the moulds for at least to air-dry condition in the laboratory with the temperature and humidity of 27 °C and 80%, respectively until the day of test. Compressive Strength Test

[0051] Mortar cubes were tested for compressive strength in accordance with the standard test procedure given in the protocol CSA-A3004-C2 (2013) and ASTM-109 (2013). The final compressive strength recorded was the average of the results obtained from three cubes where:

Compressive strength, (f_c) = failure load (P)/ loaded area (A).

Water Absorption Test

[0052] Water absorption may be defined as the percentage of water absorbed by hardened cement mortar or concrete to its dry weight. Specimens were immersed in fresh water at 20 ± 2 °C for 24 hrs. Specimens were then removed from the water and the excess water quickly wiped off using a wet cloth. The specimen was then weighed immediately to give the wet weight of the specimen. The dry weight was measured after drying the specimens in an oven for 24 hrs. Water absorption was calculated from the difference between the two weights (wet and dry) divided by the volume of the specimens. The total water absorption was recorded as an average value of three specimens.

Flexural Strength Test

[0053] In order to study the flexural strength, the beam specimens were prepared using the mold size of 40 ^χ mm ^χ 40 mm χ 160 mm for the center-point flexural strength test according to ASTM C348 (2008) and ASTM C305 (2012) test methods. Three specimens were prepared for each mix. The curing method has been used similar to compressive strength test. The flexural strength test was conducted in accordance with the test procedure given in the protocol ASTM C348 (2008). The flexural strength of mortar cube was determined as the average of three specimens. Pozzolanic Activity

[0054] The pozzolanic effect (Strength Activity Index) of fine RGP, FA and SF mortars were evaluated by studying compressive strength of control and glass mortar cubes in accordance with the standard protocol ASTM C311 (2011). The SAI is the ratio between the average strength of RGP, FA and SF mortar and strength of corresponding control mortar at the same curing period.

Durability Test [0055] In order to evaluate durability property and the effect of glass powder on its ability to mitigate alkali silica reaction (ASR), accelerated mortar bar test as per standard protocol ASTM C1260 (2007) was performed, where two mortar beams (25 ^χ mm x 25 mm ^χ 285 mm) were prepared for each mortar proportion. Prior to testing, all specimens underwent a 28 day curing time. In this test system, higher temperature (80 ± 2°C) for a period of 24 hrs and increased alkalinity (I N NaOH) was found to accelerate the reaction. The ASTM CI 260 (2007) method is not anticipated to capture the influence of increased alkalis from glass powder, however, it is used in these studies to understand the expansion characteristics of plain and modified mortars (Schwarz et al. 2008). This test method was further used to evaluate the effectiveness of SCMs in reducing the expansion due to ASR (Shayan and Xu 2006).

EXAMPLE 1: CEMENT BASED MINE TAILING MORTARS

[0056] The performance characteristics of cement based mine tailing mortars were investigated. Cement based mine tailing mortars having the mix proportions presented in Table 1 were prepared as described above and the performance characteristics tested.

Table 1: Mix proportions of cement based mine tailing mortars

Mix-ID OPC FA FMT CMT Superplasticizer Water

(gm) (gm) (Sin) (gm) (ml) (ml)

C-30/ FMT -0 900 0 1800 9 360

C-20/ FMT -10 600 - 300 1800 9 360

C-15/ FMT -15 450 - 450 1800 10 360

C- 10/ FMT -20 300 - 600 1800 9 360

Note: OPC-Ordinary Portland cement, FA-Fly ash, FMT-Fine mine tailing (<80μηι), CMT- Coarse mine tailing (>80μηι) Compressive Strength Test Results

[0057] The compressive strength test of the cement based mine tailing mortars was conducted using the protocols described above. The compressive strength was determined for each cement mortar cube at 7, 14, and 28 days after production. The cement mortars tested comprised 30% very fine materials, including cement and fine mine tailings (FMT) (<80μηι). As shown in Table 1, the control mixtures comprised 30% cement (OPC), and the various test mixtures comprised different combinations of cement and FMT. In these mixtures the cement contents were reduced to 20%, 15% and 10% and replaced with the FMT to investigate the binding capabilities of FMT.

[0058] The results of the compressive strength test are shown in Figure 1. From the compressive strength test results, it is observed that the compressive strengths decrease with the increase percentage of FMT. Hence, it appears that the FMT does not exhibit the binding capabilities with cement.

EXAMPLE 2: ALKALI ACTIVATED MINE TAILING MORTARS

[0059] Alkali activated mine tailing mortars were prepared using the above described protocols. The water absorption capacity and the compressive strength of these mortars were investigated. The mortar cube specimens were prepared with different fly ash contents. The mix proportions of the fly ash based mortars with mine tailings are presented in Table 2. Table 2: Mix proportions of fly ash based mortar with mine tailings

Activator (ml) Fly ash MT FMT CMT Sand

Mix-ID

NaOH (l5M) Na₂Si0₃ (gm) (gm) (gm) (gm) (gm)

FA-30/MT-70 350 810 1890 - - -

FA-30/FMT-30/CMT-40 425 810 - 810 1080 -

FA-30/MT-50/S-20 310 540 900 - - 360

FA-20/FMT- 10/CMT-70 400 500 - 250 1750 -

FA- 10/FMT-20/CMT-70 400 250 - 500 1750 -

FA-30/MT-70,Si/OH-l 175 175 750 1750 - - -

Note: FA-Fly ash, MT- Mine tailing (without any screening), FMT-Fine mine tailing (<80μηι), CMT- Coarse mine tailing (>80μηι).

Water Absorption Test Results

[0060] Water absorption of each preparation was tested using the protocol described above. The test was carried out on the specimens after 28 days of production. The water absorption results of the alkali activated specimens is shown in Table 3. It can be seen that the average absorption of each type of alkali activated mine tailing mortar preparation that was tested is within the acceptable limits specified in the ASTM-C90 standard for load bearing masonry units of 208 kg/m³. It was also observed that the absorption capacity increased with the reduction of fly ash content and replacement with the fine mine tailings (FMT). It is noted, however, that the absorption capacity of the specimen containing 10% fly ash with 20% FMT (FA- 10/ FMT -20/CMT-70) could not be determined due to disintegration of the matrix.

Table 3: Absorption capacity of the mortar cube

Mix ID Absorption (kg/m³) ASTM C 90

FA-30/MT-70 60.96 Average maximum

FA-20/FMT- 10/CMT-70 109.48 acceptable

absorption is 208

FA-10/FMT-20/CMT-70* - kg/m³ for normal

FA-30/FMT-30/CMT-40 68.08 weight load bearing

FA-30/MT-50/S-20 71.28 masonry unit

FA-30/MT-70,Si/OH-l 69.36

* Absorption test could not perform due to the disintegration of the specimens after 24 hours of submerged condition. Compressive Strength Test Results

[0061] The compressive strength of the alkali activated mortar specimen cubes was also tested as described above. Figure 2 shows the compressive strength test results at 3, 7, and 28 days after mortar production. The alkali activated mortars comprised 30% fine materials, including different combinations of fly ash (FA) and fine mine tailings (<80μηι). In the first mixture, 30% fly ash (FA) was used with the raw mine tailings and NaOH (15M) along with the activator of fly ash for chemical activation. Other mixtures were produced by reducing the fly ash (FA) content to 20%, and 10% and replaced with the fine mine tailings (FMT) in order to investigate the binding capabilities of fine mine tailings (FMT) (i.e., alumina and silicate) in the presence of alkali activators.

[0062] From the compressive strength test results (Figure 2) it is observed that the compressive strengths decreases with the reduction of fly ash content and replacement with FMT. Hence, it appears that the fine mine tailings do not exhibit the binding capabilities to form cementing material like fly ash.

EXAMPLE 3: GLASS POWDER BASED MORTARS

[0063] The performance of recycled glass powder (RGP) as a partial replacement of cement along with fly ash (FA) and silica fume (SF) was investigated.

[0064] The mix proportion of mortar specimens were classified into three series as shown in Table 4. The series of mortar mixes were prepared with different mix proportions of RGP, FA and SF with ordinary Portland cement (OPC).

Table 4: Mix proportions of mortars

Mix-ID OPC RGP FA SF Sand Water w/c

(gm) (gm) (gm) (gm) (gm) (ml) Ratio

Control 450 0 - - 1237.5 180 0.40

A5 405 45 - - 1237.5 180 0.40

A10 383 68 - - 1237.5 180 0.40

A15 360 90 - - 1237.5 180 0.40

A20 338 113 - - 1237.5 180 0.40

A25 315 135 - - 1237.5 180 0.40

Control 405 0 45 - 1237.5 180 0.40

ΓΠ B5 360 45 45 - 1237.5 180 0.40

BIO 338 68 45 - 1237.5 180 0.40

^' C B15 315 90 45 - 1237.5 180 0.40

B20 293 113 45 - 1237.5 180 0.40

B25 270 135 45 - 1237.5 180 0.40

Control 360 0 45 45 1237.5 180 0.40

C5 315 45 45 45 1237.5 180 0.40

CIO 293 68 45 45 1237.5 180 0.40

^' C C15 270 90 45 45 1237.5 180 0.40

C20 248 113 45 45 1237.5 180 0.40

C25 225 135 45 45 1237.5 180 0.40

OPC = Ordinary Portland cement, RGP = recycled glass powder

[0065] The physical, mechanical and durability tests were performed for each type of mortar cube. In physical and mechanical tests, the compressive and flexural strengths were investigated. In addition to these tests, dry bulk density, water absorption, and the rate of water absorption were also conducted. As a part of the durability test, resistance to alkali silica reaction (ASR) was investigated. A detailed procedure of the studies performed is illustrated in the flowchart shown in Figure 3.

Compressive Strength of Recycled Glass Powder (RGP) Mortar

[0066] The compressive strength (fc) of each series at a particular age is an average of three test results. The comparison of mortar specimens containing RGP, RGP + FA, and RGP + FA + SF are presented in Figures 4 (a), (b) and (c), respectively. It can be observed that the fc of all series of mortar increases as the percentage of RGP and the curing age increases from 7 to 90 days compared to the control specimen. In addition, increasing the FA and SF content showed increases in mortar compressive strengths. Evidently, incorporating RGP particles has a positive effect on the fc of the mortar. For example, referring to series-A, the increase in fc at 7, 28, 56 and 90 days can be seen to be in the range of 7% to 25%, 10% to 30%, 11% to 37% and 13% to 40%, respectively compared to the control specimen. The fc increases were probably due to the fine particles of RGP which act as filler within the voids present between cement particles and the fine aggregate-cement interface. The micro-filler effect of RGP, FA and SF particles produced a denser cement paste matrix which is attributable to a marginally higher fc of the RGP mortar as compared to the control mortar. With prolonged curing of 28 days, the higher hydration rate of Portland cement as compared to RGP offset the micro-filler effect of RGP. Thus, resulting in a larger difference between the compressive strength of the control mortar and RGP mortar.

[0067] Similarly, in series-B the increase in the fc at 7, 28, 56 and 90 days was in the range of 13% to 45%, 14% to 47%, 19% to 49% and 14% to 45%, respectively compared to the control specimen. Likewise, in series-C, the increase in fc at 7, 28, 56 and 90 days was in the range of 16% to 62%, 25% to 64%, 27% to 73% and 30% to 74%, respectively compared to the control specimen. These increases demonstrate that the hybrid incorporation of supplementary cementitious materials (SCMs) and fine RGP greatly improves the mechanical properties of the cement mortar matrix.

Flexural Strength Development of RGP Mortar [0068] The flexural strength (Rf) of the RGP mortar specimen behaves similarly to the fc. Figure 5 (a) to (c) shows that the incorporation of RGP improves the Rf compared to the control specimen. The addition of FA and SF introduce further improvement to the Rf of RGP mortar. It can be observed that the increase in the Rf for series-A specimens at 7, 28, 56 and 90 days was in the range of 16% to 33%, 17% to 39%, 22% to 45% and 25% to 47%, respectively compared to the control specimen. Similarly, the increase in Rf for series-B specimens at 7, 28, 56 and 90 days was in the range of 12% to 59%, 27% to 51%, 31% to 52% and 39% to 55%, respectively compared to the control specimen. Likewise, the increase in flexural strength for series- C specimens at 7, 28, 56 and 90 days was in the range of 34% to 72%, 40% to 74%, 41% to 75% and 41% to 76%, respectively compared to those of the control specimen. The mortar specimens containing RGP, FA, and SF revealed the highest Rf, which confirms the similarity between the compressive and flexural strength.

Pozzolanic Activity of RGP Mortar

[0069] The Strength Activity Index (SAI) of series-A (RGP), series-B (RGP + FA), and series-C (RGP + FA + SF) at 7, 28, 56 and 90 days cured specimens are presented in Figure 6 (a) to (c), respectively. The series-A specimens pozzolanic SAI values were around 107% to 140% at 7, 28, 56 and 90 days, which were much higher than the standard (minimum of 75%) specified in ASTM C618 (2012) for pozzolanic materials.

[0070] Similarly, series-B, and C specimen's pozzolanic SAI values were around 113% to 145%, and 116% to 174% respectively at 7, 28, 56 and 90 days. It can be observed that the series- C specimen shows the highest strength and SAI compared to the control specimen. From a strength aspect, it is suggested that RGP is a good pozzolanic material.

[0071] The results here indicate that the pozzolanic SAI of RGP mortar went to around 110% at 28 days, which is much higher than that of the FA mortar (Chen et al. 2006). This SAI result suggests that RGP has a very high pozzolanic reactivity at a replacement of 25% RGP and improves strength when compared to 100% OPC at 28 days. The results here also indicate that RGP, FA, SF and SBR are effective in increasing the strength of cement mortar. Durability Test

[0072] Alkali-silica reaction (ASR) is the process in which certain minerals (typically, glass type silica) in the presence of moisture, crack by the extreme alkaline environment of concrete. This creates a gel that expands and produces tensile forces in the concrete matrix which causes the cracking of concrete (Cement 2012). The potential expansion caused by reaction between the alkali in cement and silica in the RGP modified mortars was investigated using the protocol described above.

[0073] The percentage of expansions of mortar bars of series-A, series-B, and series- C are illustrated in Figures 7 (a) to (c), respectively. It can be observed that in series-A specimen with the increase of RGP content up 20%, there is a clear reduction in the expansion of the mortar bar (equal to 20%) as compared to the control specimens. Whereas, at 25% RGP replacement to OPC the expansions of the mortar bar increase 1% compared to the control mortar specimens. However, the expansions of all specimens were less 0.10% demonstrating that no potential deleterious expansion occurred in the RGP specimens as per ASTM CI 260 (2007). This decrease in the expansion of the specimens is related to the reduction of available alkali due to the consumption of RGP.

EXAMPLE 4: ALUMINO-SILICATE MATRIX FORMATION - GLASS POWDER BASED GEOPOLYMER MORTARS

[0074] The addition of fine crushed glass powder as a source of silica (Si0₂), and potassium or sodium aluminate as a source of alumina (Al₂Os), was investigated to determine the effect on the formation of a strong binding matrix of sodium or potassium alumino silicate, instrumental in geopolymerization: (M_n{-(Si0₂)z-A10₂}n,wH20, where M_n = Na or K).

Waste Glass Powders (RGP)

[0075] Waste glass powder having a particle size ranging from 20μηι to Ι ΙΟμηι was used as a source of silica. 88% of the waste glass powder particles had a particle size of under 80μηι. The particle size distribution of the waste glass powder used is shown in Figure 8.

[0076] Mine tailing mortars comprising RGP in the mix proportions presented in Tables 5 and 6 were prepared as described above and the performance characteristics tested.

Table 5: Mix proportions of recycled glass powder based mortar with mine tailings activating with (NaOH+NaA10₂)

Activator Fly ash MT Glass Powder Sum

Mix ID

( aOH+ NaA10₂) (ml) (gm) (gm) (gm) (gm)

FA-30/MT70/GP0 300 900 2100 0 3000

FA-25/MT70/GP5 250 750 2100 150 3000

FA-20/MT70/GP10 300 600 2100 300 3000

FA-30/MT65/GP5 300 900 1950 150 3000

FA-30/MT60/GP10 300 900 1800 300 3000

FA-20/MT60/GP20 250 600 1800 600 3000

FA-15/MT60/GP25 375 450 1800 750 3000

Note: FA-Fly ash, MT- Mine tailing (without any screening).

Table 6: Mix proportions of recycled glass powder based mortar with mine tailings activating with (KOH+KA10₂)

Activator Fly ash MT Glass Powder Sum

Mix ID

(KOH+ KA10₂) (ml) (gm) (gm) (gm) (gm)

FA-30/MT70/GP0 300 900 2100 0 3000

FA-25/MT70/GP5 250 750 2100 150 3000

FA-20/MT70/GP10 300 600 2100 300 3000

FA-30/MT65/GP5 300 900 1950 150 3000

FA-30/MT60/GP10 300 900 1800 300 3000

FA-20/MT60/GP20 250 600 1800 600 3000

FA-15/MT60/GP25 375 450 1800 750 3000

Note: FA-Fly ash, MT- Mine tailing (without any screening).

[0077] Based on the above mix proportions a preliminary test series was conducted to measure the compressive strength after 3 days and 7 days according to the protocol described above. As presented in Figure 9, it is observed that the compressive strength of mortars having a fly ash content partially replaced with RGP alone does not exhibit the binding capabilities to form cementing material like fly ash. However, for a specific fly ash content (e.g. 20%), addition of RGP improves the binding capabilities to form cementing material as shown in Figure 10. EXAMPLE 5: PERFORMANCE COMPARISON OF RGP BASED MINE TAILING GEOPOLYMER MORTARS

[0078] The addition of additives to mine tailing mortars comprising RGP was investigated. Specifically, the addition of sodium or potassium aluminate as a supplemental source of alumina (AI₂O₃) was investigated. It is contemplated that byproduct wastes of Bauxite industry could be an alternative option as a supplemental source of alumina (AI₂O₃).

[0079] The mix proportions presented in Table 7 were prepared as described above and the performance characteristics tested. Table 7: Glass powder based geopolymer concrete composition

Range Example Mixes

Materials Mix 1 Mix 2 Mix 3 Mix 4 Mix 5

Fly Ash 15% - 30% 20% 20% 15% 30% 20%

Glass Powder 5% - 30% - 5% 15% - 10%

Mine Tailings 50% - 70% 80% 70% 70% 70% 70%

Activator

NaOH/KOH 6M-15M 15M 10M 10M 15M 10M

99.98% by wt.

Na₂Si0₃/ K₂Si0₃ (Ratio used: 1 : 1; - - - 1: 1 - NaOH:Na₂Si0₃)

NaA10₂/ KA10₂ 0.5M - 8M - - 1M - 1M

3 days Compressive Strength (MPa) 6.29 11.42 12.4 21.77 28.2

[0080] The compressive strength of geopolymer concrete with and without waste glass powder and the sodium or potassium aluminate was compared (Figure 10). It was found that at 28 days compressive strength of geopolymer concrete containing glass powder (with 20% fly ash) was 218% higher than that of the geopolymer concrete without glass powder having the same fly ash content. Moreover, 28 days compressive strength of geopolymer concrete containing glass powder (with 15% fly ash) was 90% higher than that of the geopolymer concrete without glass powder having 20% fly ash content. [0081] Accordingly, it would appear that the addition of RGP with sodium or potassium aluminate can improve the geopolymerization of a mine tailing mortar and its binding properties.

[0082] The disclosures of all patents, patent applications, publications and database entries referenced in this specification are hereby specifically incorporated by reference in their entirety to the same extent as if each such individual patent, patent application, publication and database entry were specifically and individually indicated to be incorporated by reference.

[0083] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A geopolymer cement composition comprising, a combination of waste byproducts comprising mine tailings, recycled glass powder, and fly ash, in reactive combination with an alkali activator, wherein the combination of said waste byproducts with said alkali activator result in a geopolymer cement suitable for producing a geopolymer concrete.

2. The geopolymer cement composition according to claim 1, further comprising an alumina additive.

3. The geopolymer cement composition according to claim 1, wherein said alkali activator is an alkali metal hydroxide, or an alkali metal hydroxide and silicate.

4. The geopolymer cement composition according to claim 3, wherein said alkali metal hydroxide is sodium hydroxide, potassium hydroxide, or a combination of sodium hydroxide and potassium hydroxide.

5. The geopolymer cement composition according to claim 3, wherein said silicate is sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate.

6. The geopolymer cement composition according to claim 2, wherein said alumina additive is sodium aluminate, potassium aluminate, or a combination of sodium aluminate and potassium aluminate.

7. The geopolymer cement composition according to claim 1, wherein said combination of waste by-products comprises recycled glass powder having a particle size of under 80 μηι.

8. The geopolymer cement composition according to claim 1, wherein said combination of waste by-products comprises about 50% to about 70% mine tailings, about 5% to about 30% recycled glass powder, and about 15% to about 30% fly ash.

9. A geopolymer cement composition comprising, a combination of waste byproducts comprising mine tailings, recycled glass powder, and fly ash, in reactive combination with an alkali activator and an alumina additive, wherein the combination of said waste by-products with said alkali activator and alumina additive result in a geopolymer cement suitable for producing a geopolymer concrete.

10. The geopolymer cement composition according to claim 9, wherein said alkali activator is an alkali metal hydroxide, or an alkali metal hydroxide and silicate.

11. The geopolymer cement composition according to claim 10, wherein said alkali metal hydroxide is sodium hydroxide, potassium hydroxide, or a combination of sodium hydroxide and potassium hydroxide.

12. The geopolymer cement composition according to claim 10, wherein said silicate is sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate.

13. The geopolymer cement composition according to claim 9, wherein said alumina additive is sodium aluminate, potassium aluminate, or a combination of sodium aluminate and potassium aluminate.

14. The geopolymer cement composition according to claim 9, wherein said combination of waste by-products comprises glass powder having a particle size of under 80μηι.

15. The geopolymer cement composition according to claim 9, wherein said combination of waste by-products comprises about 50% to about 70% mine tailings, about 5% to about 30% glass powder, and about 15% to about 30% fly ash.

16. The geopolymer cement composition according to claim 15, wherein said combination of waste by-products comprises about 70% mine tailings, about 15% glass powder, and about 15% fly ash.

17. The geopolymer cement composition according to claim 15, wherein said combination of waste by-products comprises about 70% mine tailings, about 10% glass powder, and about 20% fly ash.

18. The geopolymer cement composition according to claim 15, wherein said combination of waste by-products is in reactive combination with about 6M to about 15M alkali activator and about 0.5M to about 8M alumina additive.

19. The geopolymer cement composition according to claim 18, wherein said combination of waste by-products is in reactive combination with about 10M alkali activator and about 1M alumina additive.

20. A geopolymer cement composition comprising, a combination of waste byproducts comprising about 70% mine tailings, about 10% to about 15% glass powder, and about 15% to about 20% fly ash, in reactive combination with about 10M alkali activator, and about 1M alumina additive, wherein the combination of said waste byproducts with said alkali activator and alumina additive result in a geopolymer cement suitable for producing a geopolymer concrete.

21. The geopolymer cement composition according to claim 20, wherein alkali activator is sodium hydroxide, potassium hydroxide, or a combination of sodium hydroxide and potassium hydroxide.

22. The geopolymer cement composition according to claim 20, wherein said alumina additive is sodium aluminate, potassium aluminate, or a combination of sodium aluminate and potassium aluminate.

23. The geopolymer cement composition according to claim 20, wherein said combination of waste by-products comprises glass powder having a particle size of under 80 μηι.

24. A method for producing a geopolymer concrete from waste by-products comprising: providing a combination of waste by-products comprising mine tailings, glass powder, and fly ash; reacting said combination of waste by-products with an alkali activator to form a geopolymeric matrix; and curing said reacted combination to form said geopolymer concrete.

25. The method according to claim 24, wherein said combination of waste byproducts is reacted with said alkali activator and an alumina additive.

26. The method according to claim 24, wherein said alkali activator is an alkali metal hydroxide, or an alkali metal hydroxide and silicate.

27. The method according to claim 26, wherein said alkali metal hydroxide is sodium hydroxide, potassium hydroxide, or a combination of sodium hydroxide and potassium hydroxide.

28. The method according to claim 26, wherein said silicate is sodium silicate, potassium silicate, or a combination of sodium silicate and potassium silicate.

29. The method according to claim 25, wherein said alumina additive is sodium aluminate, potassium aluminate, or a combination of sodium aluminate and potassium aluminate.

30. The method according to claim 24, wherein said combination of waste byproducts comprises glass powder having a particle size of under 80 μηι.

31. The method according to claim 24, wherein said combination of waste byproducts comprises about 50% to about 70% mine tailings, about 5% to about 30% glass powder, and about 15% to about 30% fly ash.

32. The method according to claim 31, wherein said combination of waste byproducts comprises about 70% mine tailings, about 15% glass powder, and about 15% fly ash.

33. The method according to claim 31, wherein said combination of waste byproducts comprises about 70% mine tailings, about 10% glass powder, and about 20% fly ash.

34. The method according to claim 31, wherein said combination of waste byproducts is in reactive combination with about 6M to about 15M alkali activator and about 0.5M to about 8M alumina additive.

35. The method according to claim 34, wherein said combination of waste byproducts is in reactive combination with about 10M alkali activator and about 1M alumina additive.