Production of geoploymer mortar reinforced with sustainable fibers


 Geopolymer has been presented as new evolution in the concrete technology world, where cementitious materials such as ceramic powder and Slag have been replaced by high percentages of cement used in construction. Thus, the activation of such materials was performed by highly alkaline solutions in order to be acted as a binder in the mix. Therefore, the selection of suitable ingredients proportion of geopolymer mortar to achieve desired strength at required workability has been intended in this study. The experimental Program has been implemented for the preparation of geopolymer mortar mixes. The concentration of sodium hydroxide solution was kept constant in the order of 12 M throughout the experiment. The ratio of Water to geopolymer binder ratio was 0.35, alkaline solution-to- cementitiuos materials ratio was 0.30 and sodium silicate-to-sodium hydroxide ratio was 1.85 by mass. Workability of geopolymer mortar was measured by flow table apparatus and cubes of 50 mm side were cast and tested for compressive strength after 28 days of normal water curing. The study concludes that the combination of ceramic powder and Slag up to 40% (by weight), in the total binder material, can be used for developing the geopolymer mortar. Continuously, the use of 1% steel fibers or 1% steel fiber with 0.5% sisal fibers promotes the level of cement replacement by such cementitous materials (slag and ceramic powder) up to 60%.


Introduction
For the last two decades, the increased demand to design and produce green or eco-friendly materials remarkably contributed to develop substitutes for Portland cement, researches on environmentally friendly along with ways of by-products and reusing industrial waste materials. Therefore, geopolymer materials have exhibited a great interest and are still raising their popularity in the field of building and construction industries [1][2][3][4].
And for reducing the pollution which evolves from the constructional activity and by-products generated by manufacturing industries, such pollution is continued to become a big concern to the research fraternity across the world. In most of the construction activities, ordinary Portland cement is employed regularly and the increase in its usage is resulting in large amount of CO 2 emission. As cement industry accounts for 5-7% of global CO 2 emissions, looking for alternatives to cement based binders is the need of the hour. On the other hand, many industrial wastes such as fly ash, red mud, slag, ceramic powder, mine tailings, etc., whose generation only are increasing drastically, but not their utilization levels. Therefore, it is inevitable to minimize or utilize the solid industrial waste, due to their serious negative impact on geo environment. Equally, devising novel methods for beneficial use of different wastes is also challenging because their composition invariably differs from a marginal to a considerable extent from waste to waste. In this regard, geopolymer binders are found to be a promising option and reported to be effective. The various industrial wastes as mentioned above are highly suitable for producing geopolymers because most of them are rich in alumino silicates. The geopolymerization process that are performing of geopolymers of alumina and silica species in the raw material reacting with highly alkaline activator solutions to produce a threedimensional polymeric chain and ring type structure consisting of (Si-O-Al-O) bonds [4]. Significant numbers of researches on geopolymer materials exhibited great performance that such materials can be suitable for the structural applications, with a workable slump, and compa-rable grade of strength to ordinary Portland cement concrete [5][6][7][8][9].
Adding fibers to the mortar or concrete can greatly enhance the mechanical properties of such materials [5]. Many studies [9][10][11][12][13][14] have reported significant advantages due to the use of different fibers in the cement mortar or/ and concrete.

Problem statement
Thousands of tons of the waste materials (that can be recycled and reused) fill our city's landfills. The accumulation of waste materials will affect human's health and the appearance of the city. Thus, we must reduce these waste material in different ways. One of these ways is that we use some of these waste materials in the construction.
Since our planet has a limited supply of natural resources, the increase of the rate of population will increase the demand on the natural resources as well as, the global concrete usage is second only to water. The demand for Portland cement increases due to the great demand for concrete as construction materials. The cement industry is held responsible for some of the CO 2 emissions and the climate change due to global warming and environmental protection has become major concerns. Some of the cement proportion in concrete mixes must be exchanged by using the waste material such as slag or ceramic powder or both of them.
The emission of greenhouse gases to the atmosphere by human activities leads to global warming such as carbon dioxide (CO 2 ). Thus, CO 2 contributes about 65% of global warming. Because the production of one ton of Portland cement emits approximately one ton of CO 2 into the atmosphere, the environment must be protected by preventing dumping of waste/by-product materials in uncontrolled manners [4].

Objectives
1. Design the control concrete mortar mix that is used to product geopolymer concrete. 2. Study the physical and mechanical properties for the control geopolymer concrete mix by the inclusions of different percentages of slag and ceramic powder. 3. Produce the geopolymer concrete using the selected concrete mix that gives the best properties.

Cement
Ordinary Portland cement (OPC) was used in this study was Produced by "Badoush factory", which conforms to ASTM C150 [15] and it is suitable for use in general concrete construction. The chemical, physical and mechanical properties are provided in Tables 1 and 2.

Fine aggregate (sand)
Good quality locally available river sand from (Kanhash Quarry) was used in this study. The specific gravity and fineness modulus of the sand used here are 2.62 and 2.76, respectively.

Superplasticizer
Is the chemical admixture used to reduce (water/cement ratio) in concrete mixes. superplasticizer reduces the amount of required water to make workable mortar and concrete. Hyperplast PC200 (Formerly known as Flocrete PC200) has been used in this study. Hyperplast PC200 complies with ASTM C494, Type A and G, [16] depending on dosage used. It has been manufactured by Don Construction Products. The technical data for this admixture is depicted in Table 3.

Ceramic waste powder
It is a powder of local ceramic (traditional) was used in this study. Powder must be passed from sieve No.325 (0.045 mm). The chemical compositions of the ceramic powder used in this study are shown in Table 4.

Slag
Slag from the iron and steel industries used in this study, slag must be passed from sieve No.325 (0.045 mm). The chemical compositions of the slag used in this study are listed in Table 5.

Mixing water
Ordinary potable water destined for drinking was used in this study and was free of soluble salts and organic materials.

Alkaline liquid
Generally alkaline liquids were prepared by mixing each of the sodium hydroxide solution with sodium silicate at room temperature. Then, the resultant solution have been started to react i.e. (polymerisation takes place). Such reaction liberates large amount of heat so it has been left for about 24 hours, thus the alkaline liquid has been considered ready as binding agent. Sodium-based solutions were utilized as they are cheaper than that of Potassium-based solutions. The sodium hydroxide (NaOH) solution was prepared by dissolving either the flakes or the pellets in water. The NaOH mass solids in a solution may remarkably be varied depending on the concentration of the solution expressed in terms of molar, M. For instance, NaOH solution with a concentration of 12 M consisted of 12×40 = 480 grams of NaOH solids (in flake or pellet form) per liter of the solution, where 40 is the molecular weight of NaOH [4].

Sodium hydroxide
The solid state of sodium hydroxides is widely available whether of pellets and flakes form. Their cost is mainly varied according to the purity of the substance. The geopolymer mortar is a homogenous material and such material is the main process to activate the sodium silicate. It is preferred to use the lowest cost "i.e. up to 94% to 96% purity" [4].
In this investigation, the sodium hydroxide pellets in 12 molar concentrations were used. The technical data related to physical properties are given in Table 6.

Sodium silicate
The compound sodium metasilicate which its common name is sodium silicate is used in this study. Water glass or liquid glass is also referred to Na 2 SiO 3 . Such material is abundant in sold form or aqueous solution. The molten sodium carbonate and silicon dioxide will be reacted. In present investigation aqueous sodium silicate solution was used. Silicates as bonding agent were supplied by the manufacturer to the detergent company and textile industry. Same Sodium silicate was used for the making of geopolymer mortar [4]. The physical properties of Sodium silicate are shown in Table 7.

Sisal fiber
Sisal fibers are fully biodegradable, green composites were fabricated with soy protein resin modified with gelatin.
Sisal fibers, modified soy protein resins, and composites were characterized for their mechanical and thermal properties. The chemical compounds are listed in Table 8.

Steel fibers
Steel fibers are significantly used as a reinforcing material of concrete or mortar, which provides certain advantages compared with traditional reinforcement. Majix round crimped steel fibers were used in this study. The properties of such fibers are shown in Table 9.

Mix design and process
For 12 M NaOH solution preparation, 480 grams of NaOH pellets have been dissolved in distilled water in a one litervolumetric flask obtaining 12 M solution. The NaOH solution was kept for settling down up to 24 hours. After 24 hours, NaOH and Na 2 SiO 3 solutions were mixed. The mixture was left for settling down up to few hours. Hence, for safety factor, hand gloves were used. The slag, ceramic powder, cement and sand were mixed in dry form. Then, alkaline activator has been added to the dry mix and wet mixing is done for about 3 to 4 minutes. Lastly, steel fibers were added to the wet mix.

Compressive strength
The compressive strength test was determined according to (C 109/C 109M) [17]. The specimens were tested using testing machine in the laboratory with capacity of 2000 Kn , using three Cube Specimens for each test.
Determine the compressive strength of concrete specimen as follows: Compressive strength (psi, kg/cm 2 , N/mm 2 ) = P/A where: P = the maximum force required for failure (lb, kg); and A = the cross-sectional area (in 2 , cm 2 , mm 2 ).

Flexural strength
This test was done according to ASTM C 348 [18], by using prisms 40 × 40 × 160 mm. Simply supported prisms with one point loading using compressive strength test machine

Calculations
Calculate the flexural strength of the specimen as follows: Where: R = modulus of rupture in (kg/cm 2 , psi, N/mm 2 ) units. P = maximum total applied load on the beam in (kg, lb). L = span length (clear span) of specimen, (cm, in). b = average width of specimen at the fracture, (cm, in). d = average depth of specimen at the fracture, (cm, in).

Tensile strength
Standard test method for tensile strength of hydraulic cement mortars (CRD-C 260-01) [19]. This test method allows for the determination of tensile strength of a hydraulic cement mortar by casting and testing briquette specimens.

Density and absorption
This test is done according to ASTM C642 [20]. At the age of 28 days Three cubes (100mm) were taken from the tap water tank. After removing the samples, surface dried with a towel and weighed. Finally, the cubes were keeping in oven (105±5 ∘ C) for 24 hrs. After removing from the oven, they were weighed and the following calculation were made: (a) Determine the density of each specimen as follows: Density (g/cm 3

) = M/V
Where: M = the mass of the specimen (g); V = the volume of the specimen (cm 3 ).

Absorption % = [(B − A)/A] × 100
Where: A = mass of oven-dried sample in air, g B = mass of surface-dry sample in air after immersion, g 4 Results and discussions

Compressive strength
Compressive strength test was conducted at the ages of 7 and 28 days after successful curing period. Cube specimens of mortar used in the test. Results of compressive strength tests for the mortar specimens are given in the Tables 10-14 and Figure 1. a) It is possible to conclude that compressive strengths of the specimens with different rate of cementreplacement mixes without Alkali-Activator decreased when the combination of ceramic powder waste and slag contents increased as shown in Table 10. b) Compressive strengths of the specimens that partially replaced the cement with ceramic powder waste were higher than compressive strengths of the specimens that partially replaced the cement with slag due to higher percentage of silica oxide in ceramic waste [21]. c) The using of Alkali-Activator liquid improved the results of compressive strength therefore it can be used in increasing the percentage of cement replacement as shown in Tables 11 & 12. The percentage of increase in compressive strength of geopolymer mortar using 40% of combination from cementitious materials (ceramic powder and slag) is 32.3% compared with traditional or control mortar mix. Besides, the use of 50% from the combination of ceramic powder and slag increases the compressive strength by about 10.87% compared with traditional or control mortar mix. Such results are supported by other researches [21][22][23][24][25][26][27]. Figure 1 shows the relative compressive strength of geopolymer mortar prepared by different percentages of cementitious ma-   Tables 13 and 14. Thus, the use of 1% steel fibers in geopolymer mortar prepared by 40% from the combination of ceramic powder and slag increases the compressive strength of the geopolymer mortar by about 40.4%. Whereas, the use of 1% steel fibers + 0.5% sisal fibers in geopolymer mortar prepared by the same percentage of combination mentioned above gives an increment in the compressive strength of the geopolymer mortar by about 34.9%. Such behavior can be attributed to the ability of fibers to bridging the cracks propagation which rises the ultimate strength of mortar [23][24][25][26][27].

Tensile Test
The total maximum load indicated by the testing machine and the cross-sectional area of a briquet after failure. Three briquettes used for each mix proportion. Direct tensile strength test was conducted at and 28 days after successful curing period. The results for such property are shown in Tables 15-18. However, the results of direct tensile strength for traditional mortar has been achieved as shown in Table 15. Furthermore, the results of tensile strength for geopolymer mortar reinforced by different percentages of combination of ceramic powder and slag are shown in Table 16. It can be seen from this Table that the use of 40% from the combination from cementitious materials (ceramic powder and slag) has increased the direct tensile strength up to 39.2% compared with traditional or control mortar mix. Besides, the use of 60% from the combination of ceramic powder and slag increases the direct tensile strength by about 6% compared with traditional or control mortar mix. Such results are supported by other researches [22][23][24][25][26][27]. The reinforcement of geopolymer mortar by using steel fibers or hybrid fibers from steel and sisal fibers has shown significant results as presented in Tables 17&18. Thus, the use of 1% steel fibers in geopolymer mortar prepared by 40% from the combination of ceramic powder and slag increases the tensile strength of the geopolymer mortar by about 40.8%. Whereas, the use of 1% steel fibers + 0.5% sisal fibers in geopolymer mortar prepared by the same percentage of combination men-

Flexural strength test
The results for flexural strength are shown in Tables 19-22. However, the results for traditional mortar has been achieved as shown in Table 19. Moreover, the results of flexural strength for geopolymer mortar reinforced by different percentages of combination of ceramic powder and slag are shown in Table 20. It can be noticed from this Table that the use of 40% from the combination of cementitious materials (ceramic powder and slag) has developed the flexural strength by about 4.7% compared with traditional or control mortar mix. The reinforcement of geopolymer mortar by using steel fibers or hybrid fibers from steel and sisal fibers has shown sig-nificant results as presented in Tables 21&22. Thus, the use of 1% steel fibers in geopolymer mortar prepared by 40% from the combination of ceramic powder and slag increases the flexural strength of the geopolymer mortar by about 19.6%. Whereas, the use of 1% steel fibers + 0.5% sisal fibers in geopolymer mortar prepared by the same percentage of combination mentioned above gives an increment in the flexural strength of the geopolymer mortar by about 15.7%.

Absorption
Absorption values were tested according to ASTM C642 where the results for the traditional mortar are shown in Table 23. The results for geopolymer mortar mixes with and without fibers are presented in Tables 24-26. However, the geopolymer mortar mixes exhibited higher ranges of absorption compared with the traditional mortar. As the percentage of combination from cementitious materials (ceramic powder and slag) increases, the absorption of geopolymer mortar has also been increased as shown in Table 24. However, the use of fibers reduces slightly the increment in absorption for geopolymer mortar. And the steel fibers exhibited better performance than that of sisal fibers in reducing the porosity of the geopolymer mortar reinforced with fibers [7] as shown in Tables 25 and 26.