# Development and Evaluation of Nano-Silica Sustainable Concrete
## 2 Materials and Methods
### Test Methods  
The following tests were carried out to determine the fresh properties, mechanical properties, and morphological characteristics of the six nano-silica concrete mixtures in this study. a. The slump and flow tests of concrete were carried out in the lab according to ASTM C143/C143M-15a and BS 1881: Part 105: 1984, respectively. The slump and flow tests were indicators of the concrete's workability. b. The density (unit weight) of freshly mixed concrete was carried out according to ASTM C138/C138M-17a. This test is a great tool in controlling the quality of the newly mixed concrete. A high or low unit weight gave different indications such as that the concrete suffered from high or low air content, high or low water content, or change of the ingredients' proportions had taken place. c. The compressive strength test was performed according to BS 1881: Part 116: 1983. Compressive strength is one of the main structural design requirements to ensure that the structure will be able to carry the intended load [24]. The test was performed on cubical specimens by applying axial compressive load with a specified loading rate until failure took place after 1, 3, 7, and 28 days of curing. Three cubical (100 \(\times\) 100 \(\times\) 100 mm) specimens were tested at each day and the results were reported as an average of the three tests' results. Figure 1: Concrete pieces inside the solid resins. d. The modulus of elasticity of concrete cylinders was carried out according to ASTM C 469-02. For a homogeneous isotropic and linear elastic material, the proportional constant between normal stress and normal strain of an axially loaded member is the modulus of elasticity or Young's modulus [24]. A slowly increasing longitudinal compressive strength was applied to a cylindrical specimen. Longitudinal strains are determined using either a bonded or unbonded sensing device that measures the average deformation of two diametrically opposite locations to the nearest 5 millionths of strain [25]. The applied load and longitudinal strain are recorded when the longitudinal strain is 50 millionths and when the applied load is equal to 40% of the cylinder compressive strength [25]. Three cylindrical (150 \(\times\) 300 mm) specimens were tested after 28 days of curing for each mixture, and the results were reported as an average of three tests' results. e. The modulus of rupture of concrete beams was performed according to ASTM C293/C293M-16. Three (500 \(\times\) 100 \(\times\) 100 mm) beams were tested in the three-point loading apparatus after 28 days of curing for each mixture and the results were reported as an average of the three tests' results. The load was continuously applied at a specified rate until rupture [24]. The modulus of rupture was calculated when the fracture initiates in the tension surface within the middle third of the span length by using the following equation [24]. \[R=\frac{3 PL}{2 bd^{2}} \tag{1}\]  
where  
\(R\) = Flexure strength, MPa  
\(P\) = Maximum applied load, N  
\(L\) = Span length, mm  
\(b\) = Average width of the specimen, mm  
\(d\) = Average depth of the specimen, mm  
f. The rapid chloride permeability test was carried out according to ASTM C1202. Originally developed in the early 1980s, and standardized as ASTM in 1991, the rapid chloride permeability test is now being used extensively in specifications, quality control, and concrete durability research [26]. The RCPT is performed by monitoring the amount of electrical current that passes through a sample 50 mm thick by 100 mm in diameter in 6 h [27]. Throughout the test, a 60V DC voltage was maintained across the ends of the specimen. One lead is immersed in a 3.0% salt (NaCl) solution and the other in a 0.3 M sodium hydroxide (NaOH) solution [27].