Comparative Study on performance of concrete with Natural sand and Robo sand

Concrete Utility is increasing day by day in construction works. Generally, river sand is most used as fine aggregate in concrete for construction. River sand is becoming scarce due to the continuous mining of river beds. Also mining of sand from river bed is causing a lot of problems in environment. In this present experimental study natural sand is 100% replaced with manufactured sand or Robo Sand. The 28-days compressive strength and Durability of M30 grade concrete is determined. Acids considered for immersion of concrete cubes are 5% hydrochloric acid(HCL) and 5% Magnesium Sulphate(MgSO4) by weight of water for a period of 28-days. It is observed that compressive strength of Robo Sand is to be higher about 26.48% when compared to natural sand. Further Robo sand concrete resulted higher resistance to chloride attack than Conventional Concrete. Further when it is immersed in Magnesium Sulphate solution no strength loss is observed. From the study it is finally concluded that Robo sand concrete performed better than conventional concrete in durability aspect. KeywordRobo sand concrete, Conventional concrete, Compressive strength, Durability, acid attack, Sulphate attack

increase in strength 10-12% when compared to conventional concrete. Finally the investigation concluded that 100% replacement of fine aggregate with quarry dust is possible. A. Priyanka Jadhava, and K. Dilip   [2] studied the effect of replacement of natural Sand by manufacture sand on the properties of cement mortar. The mortar proportions are 1:2, 1:3 and 1:6 with water cement ratio as 0.5 and 0.55. Therefore, the Robo Sand has a potential to provide alternative to natural sand and helps in maintaining the environment as well as economical balance. R. Vinayak Supekar, and D. Popat Kumbhar's, (2012) [3] studied the properties of concrete by replacement of natural sand with Artificial sand by 60%. This resulted in producing artificial sand concrete of satisfactory workability and strength properties. The replacement of natural sand with artificial sand will help in conserving the natural resources as well as maintain ecological balance.
V. Bhikshma et al. (2010) [4] investigated flexural behaviour of high strength concrete with manufactured sand. In experimental work they casted concrete beams replacing different percentages of fine aggregate with Robo sand (0%, 25%, 50%,75%, 100%) by using super plasticizer. From the results it is reported that compressive strength of concrete increased as the the percentage of Robo sand increased. Similarly their increased flexural strength also. Finally it is concluded that manufacture sand can be used as alternative material to the natural sand. Priyanka, A. Jadhav, and Dilip, K. Kulkarni, (2012) [5] studied on an Experiment investigation on the properties of the concrete containing manufacture sand. In experimental work they casted concrete cubes, beams, cylinders with by replacing of fine aggregate with Robo Sand of varying percentages (0%,20%,40%,60%,80%,100%) and with different water cement ratio 0.4, 0.45, 0.5, 0.55 and conducted compressive strength, flexural strength, split tensile strength to the concrete specimens. It is observed that ideal replacement of fine aggregate with manufacture sand is 60%. Finally it is concluded that concrete with manufactured sand gives better finishing when compared to conventional concrete.
S. Sudhir Kapgate, and S. R. Satone (2013) [6], studied on the effect of quarry dust as partial replacement of sand in concrete. In the experimental work concrete cubes, beams, cylinders are casted by replacing with different replacement levels of quarry dust (0%, 20%,25%,30%,35%) conducted compressive strength, flexural strength, split tensile strength test and compaction factor test to the concrete specimens. In experimental program it is observed that aggregates with higher surface area require more water to wet the surface of particle in order to maintain specific workability. Obviously increase in water content in mixture will adversely affect the quality of concrete. Finally it is concluded that the quarry dust is an alternative material to the sand.
The objectives of the present study is to study the strength and durability characteristics of Robo sand concrete and conventional concrete considering acid attack and Sulphate attack and compare the performance Robo sand concrete and conventional concrete in aggressive environment.
The scope of the study is to assess the use of robo sand in place of natural sand in concrete.

A. Cement
Portland Pozzolana Cement conforming to IS 1489-1991 [7] is used in the present study. The properties of the cement are tabulated in table 1.

B. Fine Aggregate
The fine aggregate used in this study is natural sand and robo sand as per requirements of IS 383-1970 [8]. The Robo sand is manufactured from Vertical Shaft Impactor (V.S.I) using granite aggregate. The properties of fine aggregate are determined based on tests recommended IS 2386-1968 [9]. The results are tabulated in table 2.

C. Coarse Aggregate
In the present investigation crushed stone aggregate of 20mm size is used. The properties of coarse aggregate are tabulated in table 3. The coarse aggregate is used in saturated surface dry condition.

D. Water
In present study, potable water conforming to IS 3025-1986 [10] is used.

E. Mix Design
The mix design of the concrete is done as per IS 10262-2009 [11]. For the present study, final proportions are concluded by casting several trails batch of concrete which is the tabulated in table 4.

III. EXPERIMENTAL STUDY
Concrete of M30 grade is prepared with help of obtained Mix Proportions by using Natural sand and Robo Sand. The Concrete Specimens are 100 x 100 x 100 mm in size.
Initially cement, fine aggregate, coarse aggregate, weighed accurately. These ingredients mixed in Pan mixer for 2 minutes [12]. Cubes are casted with the help of table vibrator. The casted cubes are demoulded and cured for a period of 28 days. Specimens are immersed in HCL solution and MgSo4 to determine acid attack and Sulphate attack on concrete as shown in Fig.1 after weighing. Concentration is 5% for HCL by weight of water with pH about 2 [13] and 5% for MgSo4 by weight of water with pH about 6.4-6.9 [13]. pH is maintained throughout the curing period. After 28 days of immersion, the concrete cubes are taken out of curing and tested for their compressive strength as per IS 516-1959 [14] in compression testing machine as shown in Fig. 2. Specimens are weighed prior to testing.

Plot 1 28-days Compressive strength of Robo sand and Conventional concrete
From Plot 1 it is observed that the compressive strength of robo sand concrete is more when compared to conventional concrete. The improvement in compressive strength is as high as 26.48 %. The increase in compressive strength is due to the sharp edged particles of robo sand providing better bond with the cement than rounded natural aggregate. This contributes to better binding effect with available cement paste improving compressive strength of concrete. Robo sand particles also give better packing due to high fineness modulus and cubic gradation. This leads to densification of paste by reducing pores and increase in strength. From Plot 2 it is observed that the weight loss in conventional concrete is 2.55% where as in robo sand concrete it is 1.15%. Low percentage of weight loss in robo sand concrete may be due to lesser permeability as of lesser voids.

Plot 3 Percentage loss in Compressive Strength of specimens after 28-days acid attack
From Plot 3 it is observed that loss of compressive strength in conventional concrete is 15.18% and slightly lower in robo sand concrete which is 14.34%. This indicates that higher acidic action takes place in conventional concrete. The observed compressive strength of acid attacked Robo Sand concrete is 7.36% higher when compared to natural sand concrete or conventional concrete when immersed in HCL and observations are similar to the findings of Shaikh, M. G. and Daimi, S.A. [15]. Acid attack takes place through porosity of concrete which is related to void ratio. Void ratio is higher in conventional concrete than robo sand concrete. The higher packing efficiency is achieved in robo sand indicating lesser permeability. Hence acid resistance is more in robo sand concrete. From Plot 5 it is observed that there is no loss in compressive strength for robo sand concrete and conventional concrete. It may be due to the reaction between sulphate and cement constituents of concrete results in conversion of calcium hydroxide to calcium sulphate (gypsum) which, in turn may be converted to sulfoaluminate.

V. CONCLUSION
From the experimental study it is concluded that [1] Robo sand concrete resulted 26.48% increase in compressive strength when compared to conventional concrete. [2] Weight loss in HCL solution is 1.150% and 2.55% robo sand concrete and natural sand concrete in respectively. [3] Loss in compressive strength of robo sand concrete is 14.34% and natural sand concrete is 15.18% due to acid attack. [4] Percentage weight loss is negligible in Robo sand concrete and 0.25% in conventional concrete. [5] There is no loss in compressive strength for both concrete after immersion in MgSO4 solution.
Robo Sand concrete is slightly superior to Conventional concrete in durabilities. Hence Robo sand can be alternative to natural sand.