Study The Impact of Geopolymer Mortar Reinforced by Micro Steel Fibers

I n this research, geopolymer mortar had to be designed with 50% to 50% slag and fly ash with and without 1% micro steel fiber at curing temperature of 240℃. The molarity of alkaline solution adjusted with 12 molar sodium hydroxid to sodium silicate was 2 to 1, reaspectivly. The heat of curing increased the geopolymerization proceses of geoplymer mortar, which led to increasing strength, giving the best result and early curing age. The heat was applied for two days by four hours each day. It was discovered in the impact test that the value first crack of each mix was somewhat similar, but the failure increased 72% for the mixture that did not contain fiber. For the energy observation results it was shown that the mixtures with fiber increased by about 40% compared with the mixtuers without fibers at the first crack and 72% at the failure, respectively.


INTRODUCTION
In 1978, Davidovits developed the word "geopolymer" to refer to a category of mineral binders with chemical properties comparable to zeolites. However, as opposed to conventional Portland/pozzolanic cement, geopolymers employ silica and alumina precursors polycondensation to create the matrix and provide strength (Provis and Deventer, 2009). By adding environmentally friendly materials to civil engineering projects, it is possible to reduce CO2 emissions from cement producers and assist recycling industrial wastes that have a substantial impact on environmental contamination (Muhsin and Fawzi, 2021). In addition to conventional concrete, there are several types of cement composites. GGBFS, fly ash, and silica fume are examples of supplementary cementitious materials (Sicakova et el., 2020). Environmentally friendly materials have been developed in an effort to reduce global warming. There have been attempts to make mortar and concrete using fractional replacement of cement with other materials such "Rice Husk Ash, Fly Ash, Silica Fume, Metakaolin, and Ground Granulated Blast Furnace Slag (GGBFS)". Another attempt was to come up with a cement replacement as a binder (Duxson at el., 2007). If thermal power plant fly ash and slag refuse are not treated and reused, they constitute a significant environmental threat. When thermal power plant fly ash is deposited, it causes longterm environmental damage (contaminating groundwater supplies, destroying farmland, etc.) by polluting groundwater and harming farmland (Phan and Nguyen, 2021). To address these drawbacks, a lot of work has gone into developing "Geopolymers," an environmentally favorable innovative alternative to traditional Portland cement. Using this kind of geopolymer cement to make geopolymer concrete offers environmental and economic benefits for the construction and civil engineering sectors, as well as the potential to reduce CO2 emissions by up to 80% (Davidovits, 1994) and (Hussein and Fawzi, 2021).

LITERATURE REVIEW
(Najeb and Fawzi, 2022) studied the effect of additional steel fibers on the mechanical properties of slurry infiltrated fiber concrete and found the increment compressive strength increased by (1.5%, 6.9%) and flexural strength (23%, 6.5%), respectively, for both sets.
(He. et al., 2020) said that the remaining compressive strength of the micro steel fiber reinforced concrete cubic and prismatic specimens might be as high as 65.3% to 81.6% and as low as 62.6 percent to 77.0 percent of the original loading strength correspondingly. In the same way, Type I micro steel fibre reinforced concrete has more residual strength than Type II micro steel fibre reinforced concrete. Micro steel fibre (cold-drawn wire with a diameter of approximately 0.2mm, typically smooth). (Satpute et al., 2012) explained that all other test variables were kept constant while examining the impact of geopolymer concrete's compressive strength when heated at a higher temperature. Compressive strength rises with increasing heating temperature for the same curing time. After curing for 24 hours, the rate of strength growth increases linearly. The difference between curing for 16 hours and 24 hours is negligible. As a result, after curing at 120℃ for 24 hours, compressive strengths of above 60 MPa can be obtained. (Hussein, 2021) studied different mix compositions of fly ash to slag (75%:25%, 65%:35%, 55%:45%), respectively, and found the increased proportion of Slag to Fly ash leads to increase compressive strength. (Girawale, 2015) made researchers test Geopolymer concrete's compressive strength as well as flexural and split tensile strength as part of the project. They found the strengths mentioned above largely depend on changes in various parameters, such as (Na2SiO3/ NaOH) ratio and molarity of the alkaline solution, while keeping the curing temperature constant at 80°C. Faster construction is possible because geopolymer concrete's compressive strength may improve dramatically in the first 24 hours. (Fawzi, 2006) studied that reinforced concrete mortar hardness is interpreted in the mechanical feature of reinforcement pulling and breaking ductility. The friction resistance of their shared surface is improved by good adhesion between the bonding substance and support, increasing the absorption capacity of reinforcement and helping to improve these qualities in the presence of (feldspar or silica powder). A lot of energy is needed to pull the clamps out of the binder (lightweight cement mortar) without breaking, so the reinforcement (lattices and fibers) acts as interconnected bridges to prevent crack expansion. Short iron fibers with a uniform random distribution are added to the binder to further increase this energy absorption.

Fly ash
The properties composition of the Fly ash used in this study is shown in Table (1). According to the findings, the fly ash used in this research satisfies ASTM C618,2015 standards, as indicated in the table.  1.8 --Na2O 0.8 --

NaOH
Hydroxide sodium is made by melting caustic soda flakes with water. Different molar concentrations can be derived based on a ratio. This experiment's NaOH solution is described in further detail in (ASTM E291-2009). In this investigation, 12 Molar was utilized as the proportion.

Sodium silicate, Na2SiO3
The concentration of Na2SiO3 is determined by the ratio of Na2O to SiO2 and H2O. In addition, the Na2SiO3 used in this formulation was produced in the UAE.

Water
To produce the NaOH solution, distilled water must be used to dissolve flakes of NaOH. To the geopolymer mix, tap water was added. Design as an additional water source to enhance workability, and it conforms to IQS 1703-(2018).

Fine aggregate
The fine aggregate in this study was natural sand from the Al-Ekhadir (Karbala city) region. As indicated in Tables (3) and (4), it was zone two and met the physical and chemical criteria of the Iraqi standard requirements IQS (No.45/1984).

Superplasticizer
A locally sourced product, KUT PLAST SP400, was made accessible. The ASTM C494 Type F standard was followed. It is used to increase workability.

Preparation of alkaline solution
When producing the geopolymer concrete, the alkaline solution must be prepared first. The sodium hydroxide molar proportion was set at 12 molars, and the sodium silicate-to-sodium hydroxide ratio was set at 2:1., thus the solution's weight availability. While dividing the result by 3, we found the weight of sodium hydroxide to get the value, but multiplying by 2 brings us to sodium silicate, which has a mass of sodium hydroxide.

MIXING
Before beginning the mixing procedure, the alkaline liquid was made a day ahead of time and blended with the superplasticizer. GGBFS, fly ash, fiber, and sand were manually mixed for about 2 minutes before adding the alkaline solutions. To achieve homogeneity, mixing takes around 10 to 15 minutes.

CURING
After one day of casting, the specimen was put in the oven at a selection of temperatures (80, 160 and 240)℃ for four hours through two days and then stored in another oven for cooling and retaining temperatures until the date of the test, as shown in Fig. (1).

TESTS
These tests utilized a 6.35 cm (dia.) hardened steel ball, thrown from a meter high over a (500*500*50) mm slab to determine the impact resistance of one percent micro steel fibre for (28) days of curing age, inspired by (ACI 544.2R-10). The equipment used for these tests includes : • A strong steel bracket supports the device throughout the test, and another stand constructed of steel angle plate is used to hold the test specimen in position, so it does not move about during the test. Together, these two stands provide enough support for the device and are impact-resistant . • An inner diameter of 10.5 cm cylindrical tube secured with brackets prevents it from moving throughout the test. This tube includes an aperture of various heights (0.5, 1.5, and 1) m; a 1.5-meter height was chosen for conducting this test. • A 3.07 kg hardened steel ball thrown from a height of one and a half meters onto the specimen many times to measure its resistance to impact is the standard method for determining the mass of a falling object. • To calculate the impact energy, the following equation was used: Impact energy (N.m) = N * m * g * h Where : N = number of steel balls thrown m = mass of steel ball (kg) g = acceleration of gravity ( m/s 2 ) h = hight of thrown balls (m)

RESULT AND DISCUSSIONS
The impact resistance test was carried out after 28 days of curing ages with 240℃ heat of curing for two samples of 1% of fiber and two samples without fibers. Table (7) and Fig. (2) and (3) describe the impact test results. From the table, it is clear that when the fibers are additional, the impact resistance increase (the number of blows increases until the sample crush and failure occur). The raising in impact resistance is due to the interlocking of the fiber network in the mortar, which increased the absorption energy due to additional fibers that complied with (Kiran et al., 2015).  As shown in Table (8) and Fig. (4), the results reveal that adding micro steel fibers to mixes G2 increases energy absorption in the first crack and failure when compared to mixes G1 at 240°C and 28 days of curing time.