41 CHAPTER 3 CHARACTERIZATION OF MANUFACTURED SAND 3.1 GENERAL The characteristics of concrete mainly depend upon the properties of materials used. Grading, mineralogical composition, shape and texture of the aggregate affects the fresh and hardened properties of concrete. The amount of micro fines present in the fine aggregate affects the strength and durability properties of concrete. So it is necessary to study the characteristics of materials used in concrete to obtain a good quality concrete. The characterization of manufactured sand is explained in this chapter. 3.2 TEST DETAILS To characterize the manufactured sand, the following tests were conducted and compared with the properties with natural sand (NS). 1. Hydrometer analysis 2. Laser particle size analysis 3. Microscopic analysis 4. Sodium sulphate soundness test 5. Energy Dispersive Spectroscopy (EDS) analysis 6. Methylene Blue absorption test 7. Settling method test and 8. Sand equivalent test
42 3.2.1 Hydrometer Analysis (ASTM D 422) A hydrometer analysis is the process by which fine-grained soils, silts and clays are graded. It is performed for the particles of grain sizes being too small. The grain diameter can be calculated from the knowledge of the distance and time of fall. The diameter of the particle was calculated by using the following formula: D 10 F H t 5 e (3.1) The percentage of finer was calculated by the following formula: N' 100GR h M G 1 d (3.2) 3.2.2 Laser Particle Size Analysis (AASHTO T 11) Laser size distribution was more accurate than hydrometer analysis, for determining the particle sizes of microfine aggregates. In this method, a laser was directed through particles dispersed in a gas or liquid. Interpretation of the diffraction pattern from particle shadows gives the information on particle size, Agrawal et al (1991). This technique can be used to grade the particles as small as 0.4 to 3.5 m upto 2mm. This test was conducted at Sastra University, Tanjore, Tamil Nadu. 3.2.3 Microscopic Analysis (ASTM C 457 and C 856) The shape and texture of fine aggregate have an important effect on workability of fresh concrete and have an effect on strength and durability of hardened concrete. In fact, the effects of shape and texture of fine aggregate are much more important than the effects of coarse aggregate. The shape and
43 surface texture of natural sand and manufactured sand were viewed by a high resolution microscope. 3.2.4 Sodium Sulphate Soundness Test AS 1141.24 (1997) The sodium sulphate soundness test was one of the earliest recorded tests for aggregate durability. It is used to find out the percentage loss of the aggregate, when it is exposed to the chemical attack. This test was conducted as per AS 1141.24. The aggregate was separated into size fractions that are: passing 4.75mm retained 2.36mm; passing 2.36mm retained 1.18mm; passing 1.18mm retained 0.6mm; and passing 0.6mm retained 0.3mm as shown in Figure 3.1. The aggregate sample was exposed to a saturated solution of sodium sulphate at 23 C. The aggregate fractions were exposed to five cycles of immersion in the salt solution, each cycle comprising 8 hours of total immersion. Each immersion cycle was followed by a 16 hours drying cycle at 105 C. The loss in weight was calculated from the following formula: The individual fraction loss is given by: Loss in % = (Original mass Final mass) x 100 / Original mass The weight loss is given by: n Weight loss in % = (C n x P n ) / 100 (3.3) 1 where, C n is the individual fraction percentage loss and P n is the percent by mass of each tested fraction in the original sample.
44 Figure 3.1 Aggregate samples for sodium sulphate soundness test 3.2.5 Mineralogy The strength and durability of the concrete depends on the mineral composition of the parent rock. In natural aggregate, the particles passing 75 microns include silt and clay minerals. In many specifications including AS 2758.1, the percentage passing 75 microns is restricted as a control over clay and silt fines that may cause water and cement demand, shrinkage and cracking. Clay is present in aggregate in the form of surface coatings, which interfere in the bond between aggregate and the cement paste. So to identify the minerals present in the aggregate, the following tests were conducted. 3.2.5.1 Energy Dispersive Spectroscopy (EDS) Analysis The minerals present in the natural sand and manufactured sand were identified by Energy Dispersive Spectroscopy (EDS) analysis which was conducted at Sastra University, Tanjore, Tamil Nadu. EDS detects the elements present in the specimen based on the detection of X-Rays emitted by that specimen.
45 3.2.5.2 Methylene Blue Absorption Test (AASHTO TP57-99) Methylene Blue (MB) dye absorption was used for determining and specifying the presence of clay minerals in aggregates. The test followed AASHTO TP57-99 standard test method for Methylene Blue value of clays, mineral fillers, and fines. Methylene Blue (C H N SCl.3H O) solution of 16 18 3 2 1mg/ml was titrated against the slurry of passing 75 micron material. As each aliquot of Methylene Blue (MB) was added, the sample was tested for the end point by removing a small drop of the slurry on a stirring rod and placing the dyed dust and liquid drop onto a filter paper. The filter paper draws off a 'halo' of water around the dust particles. At the end point, when the dust could not absorb any further MB, this 'halo' was permanently stained with a light blue colour. This is shown in Figure 3.2. The MB value of the aggregate was reported as the number of milligrams of dye absorbed per gram of material passing 75 micron. Figure 3.2 Methylene Blue absorption of NS and MS
46 3.2.5.3 Settling Method (AS 1141.33) The settling method (clay and fine silt test) also known as the volumetric silt test is a rapid field procedure for testing of deleterious components in sand. The method given in AS 1141.33 was followed in this thesis. This test measured the volumetric ratio (reported as a percentage) of silt and clay compared with the proportion of sand-sized particles in the test portion. 100ml of sample passing 75 micron size was agitated in a similar volume of 1% NaCl solution and the slurry formed was allowed to settle for 3 hours is shown in Figure 3.3. Sand particles settled rapidly in the liquid column while the silts and clays settled slowly, forming a distinct sediment layer above the sand. After 3 hours, the heights of the silt-and-clay column (F) and of the sand column (S) were read from the graduations on the cylinder. The clay and fine silt result (C) was given as C = F/S*100 (3.4) Figure 3.3 Settling Method
47 3.2.5.4 Sand Equivalent Test (AS 1289.3.7.1 2002) The latest publication of this test that appeared in Australian Standards AS 1289.3.7.1 2002; was used for this research work. The fine aggregate passing 4.75mm was placed in a transparent, graduated cylinder and was agitated in a power operated machine in an aqueous solution containing a flocculent and a preservative. The flocculation solution consists of 2.67g anhydrous calcium chloride, 12.06g (9.53ml) BP glycerine and 0.28g (0.26ml) 40% formaldehyde solution (as a preservative) per litre of solution. Following agitation, the sediment column was allowed to stand for 20 minutes. A plunger was inserted into the cylinder that slightly compressed the sand column. At this time the height of the sand and flocculated column was measured. The sand equivalent value is calculated as Height of sand Sand equivalent value (%) = X 100 (3.5) Height of sand and clay Figure 3.4 Sand equivalent test samples
48 3.3 DISCUSSION OF TEST RESULTS 3.3.1 Hydrometer Analysis Hydrometer analysis test results of natural sand and manufactured sand are represented in Figure 3.5. Figure 3.5 Particle size analysis of NS and MS by hydrometer Figure 3.5 explains that the finer fractions below 75 microns are higher in manufactured sand when compared to the natural sand, which may reduce the workability and strength of the concrete. 3.3.2 Laser Particle Size Analysis Particle sizes of natural sand and manufactured sand less than 75 microns are depicted in Figures 3.6 (a) and (b).
49 (a) Natural sand (b) Manufactured sand Figure 3.6 Laser particle size analysis of NS and MS From Figure 3.6, the diameter of the particles corresponding to 10 percent (d 10 ), 50 percent (d 50 ) and 90 percent (d 90 ) for the natural sand and manufactured sand is found out and given in Table 3.1. Table 3.1 Particle sizes of the NS and MS (< 75 microns) Fine aggregate d 10 (microns) d 50 (microns) d 90 (microns) Manufactured sand 4.47 15.83 43.49 Natural sand 3.05 12.20 32.42 Table 3.1 makes it clear that the diameter of the manufactured sand particles is coarser than the natural sand particles. The coarser particles have less specific surface area, which may require less amount of water. 3.3.3 Microscopic Analysis The microscopic view of the natural sand and manufactured sand is shown in Figures 3.7 (a) and (b).
50 (a)natural sand (b) Manufactured sand Figure 3.7 Microscopic view of NS and MS Figure 3.7 shows that the natural sand has rounded particles and smooth surface texture which may increase the workability of the concrete. The manufactured sand particles are angular in shape and have rough surface texture, which may improve the bond between the particles. 3.3.4 Sodium Sulphate Soundness Test Sodium sulphate soundness test results of natural sand and manufactured sand are given in Figure 3.8. Figure 3.8 Percentage loss of NS and MS
51 From Figure 3.8, it is observed that the percentage loss is less in manufactured sand when compared to the natural sand. This implies that the manufactured sand is a good and durable material. 3.3.5 Mineralogy 3.3.5.1 Energy Dispersive Spectroscopy (EDS) Analysis Figure 3.9 shows the EDS analysis of NS and MS. (a) Natural sand (b) Manufactured sand Figure 3.9 EDS analysis of NS and MS From Figure 3.9, it is noticed that the natural sand contains the minerals of silica and oxides, whereas the manufactured sand contains the minerals of silica, alumina and oxides. This alumina content forms as the gel, when it combines with the water. When it reacts with cement, it sets rapidly thus it may reduce the workability of the concrete. 3.3.5.2 Methylene Blue Absorption (MB) Value Methylene Blue values of various proportions of manufactured sand varying from 0 to 100% designated as A, B, C, D, E, F, G, H, I, J and K respectively, are shown in Figure 3.10.
52 Figure 3.10 Methylene blue value of NS and MS Figure 3.10 implies that the Methylene Blue Value (MBV) represents the clay content which is reduced while increasing the proportions of manufactured sand. It represents less quantity of active clay present in the manufactured sand which may improve the strength and durability properties of concrete. 3.3.5.3 Settling Method Figure 3.11 shows the clay and silt value of various proportions of MS. Figure 3.11 Clay and silt value of NS and MS From Figure 3.11, it is seen that the clay and silt value is reduced while increasing the proportions of manufactured sand. This shows that the silt and clay content is less in manufactured sand when compared to the natural sand. This indicates that the strength and durability properties of concrete may get increased.
53 3.3.5.4 Sand Equivalent Test MS. Figure 3.12 shows the Sand equivalent value of various proportions of Figure 3.12 Sand equivalent value of NS and MS Figure 3.12 indicates that the sand equivalent value is increased with the increasing proportions of manufactured sand. The higher the percentage is represented, the greater is the proportion of sand size material and less proportion of clay size materials. A higher sand equivalent value indicates that the manufactured sand has less clay content and is taken to be a better material. 3.4 CONCLUDING REMARKS The experimental studies on physical and micro structural properties of manufactured sand are presented in this chapter. While comparing the properties of natural sand (spherical particles), the manufactured sand (angular particles) gives better interlocking between the particles and hence enhancement in strength and durability characteristics may be obtained.