Investigate and Comparison effect add Amorphous and Crystalline - Nano SiO 2 on properties of Concrete

In this paper, the study included the comparison between amorphous silica and crystalline silica (quartz), and with nano scale size, two types of silica was added to concrete by ratios (5%, 10%, 15%

. In many instances, the serviceability of the deteriorated structures becomes an important issue and therefore the cost-effective solution is often to use patch repair [11]. Nano materials have attracted much scientific interest due to the potentially new performance of the particles in nanometer (10 -9 meter) scale. The nano scale particles can result in dramatically improved or different properties from conventional grain-size materials of the same chemical composition. Hence industries can re-engineer many existing products and design novel products that function at unprecedented levels. Nano particles can make traditional building materials stronger and harder, giving them enhanced ductility and formability. However, the present applications of these materials are mainly limited to produce antiaging, antiseptic, purified air composite paint or other ecological building materials using nano-TiO 2 , nano-SiO 2 or nano-Fe 2 O 3 . There is little research on mixing nano-particles in cement-based materials [1]. In view of the above-mentioned, the aim of the study was to investigate the influences of nano-SiO 2 in cement mortars. Silica fume in micro scale and in powder form with SiO 2 ranging from 85% to 95% has been used either as a partial replacement for cement or as an additive when special properties are desired. Many investigating the use of silica fume as a partial replacement for cement in combination with superplasticizer have shown a significant increase in the strength of concrete.
The development of an ultra-high strength concrete was made possible by the application of DSP (Densified System containing homogeneously arranged ultrafine Particles) with superplasticizer and silica fume content. The amorphous or glassy silica, which is the major component of a pozzolan, reacts with calcium hydroxide formed from the hydration of the calcium silicates. The rate of pozzolanic reaction will be proportional to the amount of surface area available for reaction [2,3].

EXPERIMENTAL WORK MATERIALS:-Cement
Ordinary Portland cement manufactured by (tasluga factory \ Bazian) cement factory was used throughout this investigation. Table (1) and (2) show the physical and chemical properties.    Types of silica: -Amorphous and Crystalline SiO 2 added as ratios (5%, 10%, 15% and 20%) by weight of cement and the physical properties show in table (5), and chemical properties show in table (6). And (fig1) show X.R.D of amorphous and crystalline (quartz) silica. The details of mix proportions are presented in Table (7). All mixes was adding silica as a partial replacement by cement weight content, and cast a specimens as a cylinder mold (100×200) mm to compressive and tensile strength and cubic molds (150×150×150) mm to non-destructive tests.  ‫٭‬W/C : water/Cement ratio Mixing Procedure:-Adopted concrete mix 1:2:3 in the casting process from each mix. a total of 3 cylindrical concrete specimens 100 mm in diameter and 200 mm high [4] and 3 cubic specimens 150×150×150 mm [5]. The molds were oiled properly for easy out specimen and then fill the mold with three layers of the mixture and with each layer instills by tamping rod to ensure out the bubbles and distribution. After casting and finishing, the specimens were demolded after 24 hours of casting and then they were transferred to a curing tank placed at the laboratory temperature of 18 to 20ºC. The specimens were cured in the water tank for 28 days, and then dried in the air to be tested.

RESULTS AND DISCUSSION:-Destructive tests Compressive and Splitting tensile Strength:-
Compressive and Splitting tensile Strength was calculated from examination of the dimensions of the cylinder (100×200 mm) Concrete containing Quartz and amorphous silica, and ratios (5%, 10%, 15% and 20%) and the results are shown in Figure (2,3). The test measured according to ASTM C39 for Compressive strength and ASTM C496 for splitting tensile strength [7 and 8]. &Tech.Journal, Vol. 33,Part (B), No.3,2015

Investigate and Comparison effect add Amorphous and Crystalline -Nano SiO 2 on properties of Concrete
The specimen without additives recorded (20 Mpa) in compression and (2.6 Mpa) in tensile, and from (Figures 2 and 3) observed that the compressive and splitting strength increases with adding two types of silica to the ratio 15%, and also noted that the effect of mechanical properties of amorphous silica was more in the concrete than the crystal silica.

Non-Destructive tests • Reboun d number (Schmidt Hammer):-
The specimen tests non-destructive test by (Schmidt Hammer / Proceq Company). Where the specimen determine by rebound number (R) of hammer on the surfaces of cubic specimens, and the tested take different places from the same specimen and determine the average of rebound number, then knowing the compressive strength from the rebound number by the curve was gives with device. The rebound number of concrete specimen without additives record (24.5), and noted as show curve below in (Fig4), the rebound number of hammer was high in the ratio 15% compared with Investigate and Comparison effect add Amorphous and Crystalline -Nano SiO 2 on properties of Concrete another ratios in amorphous silica, thus the compressive strength was high according to the curve of device, that it is mean the hardness of concrete is good. And also noted that the ratio 15% of crystalline silica (quartz) show (Fig 5) high rebound number of hammer compared with another ratio, so the 15% ratio have high compressive strength. And with compared amorphous silica with crystalline silica, noted the amorphous silica have higher rebound number and thus high compressive strength than the crystalline silica. Investigate and Comparison effect add Amorphous and Crystalline -Nano SiO 2 on properties of Concrete (4.24 Km/sec), and by determine the pulse velocity of concrete that contain amorphous silica show increase the pulse velocity by increase the additives, but noted that the high velocity was in 15% than the other ratio of amorphous silica as show in (Fig 6), also the pulse velocity of concrete have crystalline silica increase by increase the additives, and the high velocity was 15% than other additives (Fig 7). And the highest pulse velocity was in 15% amorphous additives. However, all the specimens was good but the specimen have 15% amorphous was excellent according to Neville, A.M. (Table 8)

Water Absorption%
The specimens contain quartz and amorphous nano-silica show decrease in absorption of water at 28 days comparison with reference specimen (7.780 absorption %), while the table 9 show all specimens. The test measure according to ASTM C642 [9].

CONCLUSIONS
Conclusion from this research, Nano-amorphous silica is active than Nanocrystalline silica in concrete mix, where amorphous silica show high mechanical properties and show high quality in non-distractive test than crystalline silica. Also conclusion is the better added ratio is 15% in both type of silica, but the percentage of ratio15 % in amorphous silica was higher than in crystalline silica.