The Impact of Marine Water on Different Types of Coarse Aggregate of Geopolymer Concrete

This research studies the impact of different types of coarse aggregate on the behavior of geopolymer concrete based on both fly ash (FA) and ground granulated blast furnace slag (GGBFS) in different marine environments. Aiming to solve the problems caused by the construction and demolition waste and the depletion of natural aggregates, in the present study coarse recycled aggregates is used to produce new green concrete with a fly ash-slag based geopolymer. By this examination, the research seeks to improve the quality and productivity of concrete used in construction and hydraulic projects. For this research, four mixtures containing different types of coarse aggregate in two different water environments were used. The utilized mixtures contained natural aggregate concrete (NAC) such as basalt and crushed marble. Also, recycled coarse aggregate concrete (RAC), which totally replaced natural aggregate, was presented in this paper such as crushed concrete and crushed ceramic. For this study, in the sieve analysis; specific and unit weights, was recorded. Furthermore, the mechanical properties were determined, using a compressive test that was conducted on the 7th, 28th, 56th and 90th days at different water environments; potable water (PW) and sea water (SW). Durability test was also performed for total absorption measurement. Results indicated that geopolymer concrete exhibits better strength in marine environments than in those of potable water. Results also showed that crushed marble (CMA) exhibits higher compressive strength and durability.


Introduction
Concrete is an essential component in hydraulic construction projects all over the world. It is one of the elements that account for the highest cost in any construction project [1]. Annually, humankind consumes huge amounts of concrete resources and produces vast quantities of waste and pollution as a result of this consumption process [2]. However, for an effective utilization of concrete waste, it is necessary to use the recycled aggregate as concrete aggregate. The practical usage of the recycled aggregate concrete, produced by crushing concrete waste, reduces the consumption of natural aggregate. Using Portland cement in concrete contributes remarkably to greenhouse gas emissions. The total of annual emissions caused by cement production is estimated to be about 1.35 billion tons [3]. Geopolymer concrete is provided as one of the solutions formed by using source materials that contain both reactive silica (SiO 2 ) and alumina (Al 2 O 3 ) activated with alkali solutions. The source of these materials can be derived from low-cost substances or industrial wastes, such as metakaolin, fly ash, rice husk ash, and furnace slag [4] [5] [6] [7]. Geopolymers concrete can be characterized by high compressive strength, low shrinkage, good acid resistance, and good fire resistance [8] [9].
The permeability of geopolymer concrete affects its durability in salt water. This feature is the main factor for determining the durability of concrete in marine environment. Accordingly, denser concrete will lead destructive agents to penetrate and flow through the pores [10]. Yet, in sometimes, the chloride environment can increase the compressive strength of the geopolymer concrete [11]. It is important to mention that some previous studies stated that fly ash-based geopolymer concrete has better durability than Portland-based concrete in aggressive environment such as sulphate, acid, and fire [12] [13].
The current research examines the mechanical properties of hand-mixed based geopolymer concrete. It also studies the effect coarse recycled aggregates has on geopolymer concrete (RAGC) in different marine environment, in comparison to the properties of geopolymer concrete made with natural aggregate concrete (basalt). Furthermore, the research studies their effect on the properties of geopolymer concrete in different water environments; sea and tap water.

Background
In order to formulate a good GPC mix-design, it is essential to know the different factors that will affect the properties of fly ash/slag which are based on GPC.

Aluminosilicate
Fly ash (FA) is considered to be one of the main sources of silica (SiO 2 ) and S. Y. Megahed et al. alumina (Al 2 O 3 ) in GPC. Regarding ASTM C618, FA is classified based on its chemical composition, in which the main difference is the calcium amount [14] [15] [16]. Due to improved mechanical and microstructural properties, ground granulated blast furnace slag (GGBFS) becomes one of the most common components in geopolymer mortar and concrete [15]. However, adding GGBFS causes poor workability as a result to the higher viscosity [17]. A previous study shows that the significant improvement in both setting time and compressive strength can be obtained by adding ground granulated blast furnace slag in the mixtures [18].

Alkaline Solution
Alkaline solution is utilized to activate aluminosilicate base materials in order to obtain geopolymer concrete. For the alkali-activators, several choices are adopted.
Silicate and aluminum silicate enrich the alkaline activator species in a notable way. Theoretically, as mentioned in reference [19], any alkali element can be used in geopolymerisation reactions; however, most of the studies have focused on the effect of sodium (Na + ) and potassium (K + ) ions [19]- [30].
The durability of structure started to decrease since the first year (2005), when research was conducted, and kept on increasing throughout 20 years of investigation. A previous research calculated the safety factor needed to obtain the structure's performance in sea water [31]. It was found that the protection of the structure has been declined gradually year by year. Reference [11] finds that geopolymer concrete that is cured in sea water provides a higher compressive strength than the other curing systems that employ fresh water and room temperature. Reference [32] shows that there is abundance of Na + in the surrounding area in salt water curing. It is probably that Na + as well as other cations (Ca 2+ ) in the sample are less exposed to leaching. These excess cations in the surrounding curing solution and in the sample will help to promote the mechanism's reaction and geopolymer formation.

Coarse Aggregate (C.A)
The used coarse aggregate in this research are:  Natural aggregate (Baslt);  Recycled aggregate (crushed concrete, crushed marble and crushed ceramic).
Well graded coarse aggregate was used with the maximum size of 19 mm.

1) Natural aggregate (NCA)
The researcher used natural coarse aggregate as basalt; supplied from Elminia quarries. This coarse aggregate is characterized by a specific gravity 2.63, Volume Weight 1.61 (t/m 3 ), and Absorption 0.8% as shown in Figure 1.  The used crushed marble is supplied from residues of broken marble. It is of a specific gravity 2.62, Volume Weight 1.62 (t/m 3 ), and Absorption 0.4%. Table 1 shows the results of Sieve Analysis Test for crushed marble. And Table 1 shows the Chemical Composition of crushed marble. b) Crushed concrete The used crushed concrete is supplied from residues of ceramic factories. It is characterized by a specific gravity 2.5, Volume Weight 1.47 (t/m 3 ), and Absorption 6.19%. c) Crushed ceramic The used crushed ceramic in this study is supplied from residues of ceramic factories. The specific gravity of the crushed ceramic is 2.12, Volume Weight is 1.15 (t/m 3 ) and Absorption is 10.62%. Table 2 shows the chemical composition of crushed ceramic. Table 3 shows the results of Sieve Analysis Test for different types of aggregate while Figure 1 shows different types sample of the aggregate.

Fine Aggregate (F.A)
The used fine aggregate in this research was natural sand from 6 October quarries as shown in Figure 2. This fine aggregate's specific gravity is 2.55, Volume weight is 1.52 (t/m 3 ), and Fineness modulus is 2.57.

Fly Ash
Fly ash is a by-product which is the outcome of coal's combustion. Fly ash used in the study was low-calcium (ASTM Class F); dry fly ash brought from a factory in Sadat City-Egypt as shown in Figure 3. The specific gravity of the used fly ash is 1.9. Fly ashes are produced from bituminous and sub bituminous coals. They also contain alumina silicate glasses as active components. Figure 4 shows XRD of fly ash. This fly ash has a pozzolanic nature and contains less than 10% lime (CaO). Table 4 summarizes the chemical structure of fly ash as per the manufacturer.

The Ground Granulated Blast Furnace Slag (GGBS)
GGBFS is an industrial by-product which results from rapid water cooling of molten steel as shown in Figure 5. Ground granulated blast furnace slag materials have been composed of amorphous constituents. Figure 6 shows XRD of the slag. This material has favorable properties for cement industry as they are both relatively inexpensive and highly resistant to chemical attack. Table 5 shows the chemical composition of a slag with a specific gravity 3.2 that is available in Iron and Steel Factory and supplied from Helwan Governate.

Activator Solution
The utilized alkaline activator in this study was made as result of the combination of sodium silicate and sodium hydroxide solution. However, the activator that was made as a combination of the sodium silicate solution (Na 2 O = 12.6%, SiO 2 = 29.39%, water = 57% by mass) and sodium hydroxide (NaOH) in flakes or pellets-shape with 99% purity was prepared according to the reference.

Super Plasticizer
The current research used super plasticizer to reduce the early setting time of the concrete, the matter which in turn improves the mechanical behavior of GPC.
For the work needs, the study used a high Range Water Reducing (HRWR) polymer-based super-plasticizer Naphthalene Sulfonate (BVS) that is supplied from CMB. Also, super plasticizers of 2% weight from binder were added. Table   6 shows the characteristics of the used admixture.

Strengths Measurements
The hardening of concrete was accessed from this test using cube specimens of 100 × 100 × 100 mm size. Figure 7 shows casting and testing of cube specimens ASTM: C109/C109M-13.
The research obtained the splitting tensile strength from the cylindrical specimen of diameter 150 mm and 300 height. Figure 8 shows the casting and testing of cylinder specimens [33]. J. Minerals and Materials Characterization and Engineering     Test Procedure The specimens that were used in the test were oven-dried at 1050˚C for 24 hours. After the oven-drying, the specimens were immersed in water for another 24 hours. Absorption of geopolymer concrete with different aggregate was measured by evaluating the difference in weight of specimen after both the completion of the oven-drying process at 1050˚C, and immersion in water [34].

Permeability of Geopolymer Concrete
The specimens were tested with permeability machine as shown Figure 9. The specimens were placed in the apparatus and a water pressure of (500 ± 50) Kpa was applied for 72 hours. The specimens were exposed to water pressure from one side after 28 days, then permeability factor and high water in side of the cupe were evaluated [35].

X-Ray Diffraction (XRD)
The present study adopted powder method of X-ray diffraction. For this method, a Philips diffractometer PW 1730 with X-ray source of Cu kα radiation (λ = 1.5418 Å) was used. The scan step size was 2θ, the collection time was 1 s, and in the range 2θ from 5˚C to 65˚C. The current and X-ray tube voltage were fixed at 40 KV and 40 mA respectively [36].

SEM Examinations
The paste samples were examined by SEM to show the morphology of these ma-  to 1,000,000 and resolution for Gun.1n, FEI Company, Netherlands. To study the specimen's morphology without any coating, Backscattered electron detector (BSED) imaging was used [37].

Curing Water
Geopolymer concrete treatment was done using curing in potable water and sea water. The treatment lasted for 28 days, then an immersion in different water environments (potable water & sea water from the Qaroun Fayoum Lake) took place. The chemical analysis of Qaroon Lake water is given in Table 7.

Mix properties
S. Y. Megahed et al. of the cementitious material (fly ash), was added. Then the alkaline activator solution and fly ash were added to the wet mixture. For a proper bonding, the mixing lasted for4 to 5 minutes. After the mixing took place, specimens were poured by giving the proper compaction. Four mixes were immersed in sea water (SW) and tab water (PW) for 60 days after curing. It was observed from the past studies that the quantity of the total binder was 450 kg/m 3 (80% fly ash and 20% slag). Table 9 and Figure 10 showed that geopolymer concrete used in crushed marble has a higher compressive strength than other mixes in salt water. Geopolymer concrete with basalt was used as a controlling specimen to compare its compressive strength with recycled aggregate geopolymer concrete. It is proved that salt water influences the strength of geopolymer concrete. Figure  According to the above, it is proved that the geopolymer concrete in sea water is more resistant than in tab water.

Split Tensile Strengths
Split tensile strengths for various mixes were obtained from the cylinder specimens    compressive strength was also noticed in case of the split tensile strength on the 28th day. Figure 11, Table 10 show that the used geopolymer concrete in crushed marble has higher split tensile strength than other mixes. Geopolymer      Figure 13 showed the near-, mid-, and far-infrared (IR) spectra of synthetic,

X-Ray Diffraction XRD
The X-ray diffraction XRD was used to study the transformation in crystalli-

Permeability of Geopolymer Concrete with Different Aggregate
In this examination, to study the permeability of geopolymer concrete with different types of aggregate, four different samples were prepared; basalt, crushed concrete, crushed marble and crushed ceramic respectively. Figure 15 demonstrates the permeability factor of geopolymer concrete with basalt concrete which was 0.605 × 10 −6 , yet decreased by 25.6% and 131.4% for crushed concrete and crushed ceramic; however, it increased by 14.9% for crushed marble as shown in Table 11. Figure 16 shows High of water in all samples, Figure 17 shows permeability sample with different types of aggregate.
To calculate permeability factor let parameter in equation: Figure 15. Permeability of all samples.

Absorption Percentage of Geopolymer Concrete with Different Types of Aggregate
Water absorption of the geopolymer concrete plays an important role for the durability of the structure. Ingress of water deteriorates concrete and in reinforced concrete structure. Table 12 shows Weight before sub-margin, Weight after submerge in water for 24 hours. The result demonstrates that water absorption of geopolymer concrete with basalt aggregate was, 45%, then decreased by 11.1% and 44.4% for crushed concrete and crushed ceramic. It also increased by 21.11 for crushed marble as shown in Table 12, Figure 18.

Conclusions
This experimental study examined the impact of sea water on recycled coarse aggregate, which is obtained from the materials' waste, on both hardness and durability of the geopolymer concrete. Main conclusions derived based on the present study could be summarized as follows: 1) Geopolymer concrete in salt water has higher compressive strength than geopolymer concrete in potable water. This matter proves that geopolymer concrete is durable in marine environment since there is abundance of Na + in sea water. The maximum value of compressive strength at 90 days for geopolymer concrete utilized crushed marble in salt water increased percentage than geopolymer concrete utilized crushed marble in potable water by 14.86%.
2) Geopolymer concrete reaches its strength at higher rate in early stages (7 days age), and reaches a ratio of about 55 to 65 % of the compressive strength at 3) Geopolymer concrete utilized in crushed marble has higher compressive strength than other mixes, increasing percentage by 5%, 23,37% and 17% for basalt, crushed concrete and crushed ceramic .
4) The presence of sodium in crushed ceramic improves compressive strength. 5) Permeability and water absorption for geopolymer concrete with marble have better durability than other mixes. 6) Geopolymer concrete with crushed marble has an excellent quality in hydraulic buildings and buildings under water such as dams, tanks, channels, pier and bridges.