Metakaolin can also be found by calcining indigenous red clay. The progress of pozzolanic properties in cooked clays depends primarily on the nature and abundance of the clay minerals in the feedstock, the calcination conditions and the fineness of the final product. The calcination temperature resulting from the reaction state is usually in the range from 600 to 800 °C. After heating, recrystallization and formation of MK (2SiO₂Al₂O₃) or mullite (3Al₂O₃_2SiO₂) occur in the reduction of material reactivity. The following section details the metakaolin production process, the chemical analysis, physical properties of Metakaolin (Table 3), and Chemical requirements of Pozzolan ASTM C618 [8] (Table 4).

Iraqi common citrate cement (I) (Portland cement I) was used in this study. The cement bag is stored in an airtight plastic container to prevent any moisture. Results analysis of chemical and physical properties of the cement are listed in Tables 5 and 6. The test results show that the cement used is in accordance with IOS No. 5 / 1984 [9]. Tests were made in the building research directorate in Baghdad University.

An alkaline liquid mixture of sodium silicate and sodium hydroxide solution was prepared which allowed mixing in the polymerization for a minimum of 24 hours. The sodium silicate solution is commercially available in various grades using a sodium silicate solution (Na₂SiO₃) and sodium hydroxide(NaOH) having a mass of 3.5. Sodium hydroxide of 97-98% purity in the form of granules is commercially available. The solid is dissolved in water to make a solution of the desired concentration. Fourteen molar (14M) solutions were used. Since the molecular weight of sodium hydroxide was 40, a 14-molar solution of 14 x 40 = 560 g of sodium was prepared. The hydroxide was dissolved in 1000 ml of water. The mass of NaOH solids in the solution varies depending on the concentration of the solution.

Recycled concrete is used as a coarse aggregate and fine aggregate in concrete mixes to reduce the environment of gravel and produce inexpensive local concrete. A locally available 12.5 mm pulverized concrete is used as a coarse aggregate, and a 4.75 mm is used as the fine aggregate. Recycled aggregates obtained from the demolished construction are used to produce aggregates in the study beams, cubes, cylinders and prisms. The classification of coarse and fine aggregates is in accordance with Iraqi Standard IQS (No. 45/1984) [10]. At first, the stone was broken with a crusher at the Materials Laboratory of the University of Michigan's School of Engineering (Tables 11-14).

The second waste of steel is iron filings, which is produced locally in large quantities in workshops and steel mills. This product has a negative impact on the environment when it is eliminated, for this reason, the research project started. Most of the previous investigations referred to steel slag, where one of the few referred to the presentation of iron (Tables 15 and 16).

The additional water used in the concrete mix design is the drinking water from the water network system.

This type is used to dissolve sodium hydroxide to make NaOH solution.

A third-generation geopolymer-based super plasticizer type (F) according to ASTM C494-04 [11], designed for the production of UHPC is used (Glenium 51) in Table 17.

Control samples were cast from each mixture to determine the mechanical properties of NC and GPC, including compressive strength (fcu), split tensile strength (fct), modulus of rupture (fr), and modulus of elasticity (Ec). The average of the three samples was considered for each mixture. Table 8 shows the properties of hardened concrete.

The compressive strength test is done with BS. 1881: Part 116: 1989 [14]. Three cubes with dimensions of 100×100×100 in mms for each mix were tested by using a hydraulic compression machine of 2000kN. The test was carried out at age of 28 days. The result of the compressive strength test was shown in Table 20 and Fig. (4).

Fig. (4). Compression failure of NC and GPC cubes after failure.

Table 20 and Fig. (5) show that the increase of iron filings from 0 to 0.5%, 0.75%,and 1.0%, resulted in increasing percentage of the compressive strength (f_cu), with 2%, 5%, and 10% for Geopolymer Concrete with Recycled Concrete Aggregate (GCRA), 2%, 6% and 9% for Geopolymer Concrete with Natural Aggregate (GCNA), 4%, 7% and 10% for normal concrete with natural aggregate (NCNA), and 3%, 14% and 23% for Normal Concrete with Recycled Concrete Aggregate (NCRA). The maximum value of the compressive strength was 28.5 MPa for GNRA, 33.6 MPa for GCNA, 36 MPa for NCNA and 42 MPa for NCRA occurred with iron filings 1%.

Fig. (5). Iron filings effect on compressive strength

The indirect tensile strength is carried out with (ASTM C496-2004) [15] specification and three cylinders of (100×200) mm for each mix is used. The test conducted by using a hydraulic compression machine of 2000 kN. Thin plywood strips are put between the specimen and both the upper and the lower bearing blocks of testing machine. The test involved applying a diametric compressive force along the length of a cylindrical concrete specimen (Fig. 6).

Fig. (6). Splitting failure of NC and GPC cylinders.

Table 20 and Fig. (7) show that an increasing of iron filings from 0 to 0.5%, 0.75%,and 1.0%, resulted increasing percentage of the splitting tensile strength with 20%, 25%, and 32% for GCRA, 26%, 40% and 52% for GCNA, 9%, 12% and 19% for NCNA and 10%, 14% and 19% for NCRA. The maximum value of the splitting tensile strength was 3.51 MPa for GCRA, 4.57 MPa for GCNA, 3.8 MPa for NCNA and 4.63 MPa for NCRA occurred with iron filings 1%.

Fig. (7). Iron filings effect on the splitting tensile strength.

The flexural strength was carried out according to (ASTM C78-2005) [16] with three (100×100×500)mm prisms used for each mix (Fig. 8).

Fig. (8). Modulus of rupture test of NC and GPC prisms.

Table 20 and Fig. (9) show that an increasing of iron filings from 0 to 0.5%, 0.75%,and 1.0%, resulted increasing percentage of the flexural tensile strength with 26%, 32%, and 42% for GCRA, 13%, 26% and 31% for GCNA, 17%, 21% and 26% for NCNA and 20%, 50% and 67% for NCRA. The maximum value of the flexural tensile strength was 3.6 MPa for GCRA, 4.962 MPa for GCNA, 4.5 MPa for NCNA, and 6.85 MPa for NCRA, occurred with iron filings 1%.

Fig. (9). Iron Filings effect on the flexural tensile strength.

Static modulus of elasticity test was performed according to ASTM C469-2002 [17]. This test method provides a stress-strain curve for hardened concrete at whatever age and curing conditions may be designated. The slope of the curve representing the chord modulus is given by the slope of the line from the point representing the longitudinal strain of 50 microstrains to the point corresponding to 40% of the ultimate load for normal concrete and 30% of the ultimate load for geopolymer concrete. The three specimen cylinders (150*300) mm for each mix was tested (Fig. 10).

Fig. (10). Modulus of elasticity (Ec) test for NC and GPC cylinders.

Table 20 and Fig. (11) show that an increase of iron filings from 0 to 0.5%, 0.75%,and 1.0%, resulted in increasing percentage of the modulus of elasticity with 2%, 9%, and 11% for GCRA, 5%, 8% and 17% for GCNA, 1%, 8% and 12% for NCNA and 5%, 10% and 14% for NCRA. The maximum value of the modulus of elasticity was 20.8 MPa GCRA, 24.2 MPa for GCNA, 27.8 MPa for NCNA and 28.5 MPa for NCRA occurred with iron filings 1%.

Fig. (11). Effect of iron filings on modulus of elasticity.

Due to the high softness of iron filings, it improves the value of the concrete. It fills the voids and improves the internal structure of cement and Geopolymer paste. Due to the very low aspect ratio, the phenomenon of baking does not occur, which leads to the spread of the iron filings in the mixture and positively affect the resistance.

The roughness of the surface of the recycled concrete aggregates used and its bonding more strongly with the cement paste than for the sulphate with the smooth surface, therefore, NCRA more resistance of NCNA.

An electron microscope that produces a sample image by scanning the surface specimen with a focused electron beam. The electron interacts with atoms in the sample to produce several signals containing information about the morphology and composition of the sample surface. The electron beam is scanned in a scan pattern of the frame and the position of the beam is combined with the detected signal to produce an image. SEM can achieve resolutions better than 1 nanometer. Samples can be observed in high vacuum in conventional SEM, or in variable pressure or ambient SEM under low-pressure vacuum or humidity conditions, and raised at a wide range of cryogenic temperatures or with specialized instruments [18].

By checking three samples and by types of mixtures, it has been observed from Figs. (12 and 13) that:

Fig. (12). SEM for 20 μm.

Fig. (13). SEM for 10 µm.

1. The use of recycled concrete aggregate in (NCRA) with cement, the processes of clarification increase because the recycled aggregates act as a reservoir for water and help in the continuation of the processes of clarification as well as increase the strength of bonding between the aggregates and cement and increase density and over time consist of crystals form the increase of concrete resistance.
2. (GCRA) The density of the concrete is low and the presence of high gaps due to the presence of cement materials that are not ripe with recycled concrete aggregate, which lead to the absorption of the water of the mixture and hardening of the geopolymer in the first days and the absence of continuous operations of the defect, which leads to the formation of internal gaps and thus decrease density.
3. (GCNA) When replacing the recycled concrete aggregate with natural aggregates, the microscopic structure of the geopolymer improves, the gap ratio decreases and thus the density increases.