1. “Investigating the Effect of Nano-Silica on Recycled Aggregate Concrete” Colby Mire & Jordan Licciardi Advisor: Mohamed Zeidan ET 494

2. Abstract  Nanotechnology has extended the economic and environmental stride of the concrete industry.  Studies prove that nano-silica can be used to strengthen the Interfacial Transition Zone (ITZ) between the paste and aggregates in concrete.  Our study will attempt to discover the possible benefits of using nano-silica to improve the ITZ of concrete made with recycled concrete aggregate (RCA).

3. Background  Concrete is by far the most important building material used in the construction industry.  In the U.S. alone, approximately two hundred to three hundred million tons of concrete waste is generated a year, due to demolition.  Recycling the demolition waste can be a solution to a number of problems faced by civilization.

4. Recycled Concrete Aggregate (RCA)  Using recycled concrete as the aggregate for creating more concrete can be helpful in many ways:  Conserve natural resources  Lower the cost for waste treatment  Reduce the overall cost of new infrastructure  Reduction of CO2 emissions

5. Drawbacks of RCA  Using RCA has a few quality drawbacks:  The ITZ formed between the RCA particles and cement paste is porous and weak.  Due to the fact that the quality of the ITZ of concrete mixtures is directly proportional to the overall strength of the concrete mix, porous ITZ can be very detrimental in using RCA concrete in structural applications.

6. Interfacial Transition Zone (ITZ)  The cement particles in fresh concrete can not pack together as efficiently when they are in close vicinity with aggregates.  Shearing stresses are exerted on the cement paste by aggregate particles during mixing. This causes the water to separate from the cement particles.  The resulting narrow region around the aggregate particles with more water and fewer cement particles is referred to as the ITZ.

7. Purpose  The need to address the issues concerning the ITZ of RCA is very apparent.  The use of nano-silica may be a solution.  The idea is that the introduction of nano-silica, as a cement additive, may be able to create a more dense ITZ between the RCA and cement.  The effects of nano-silica will be evaluated through research and testing, and potentially become a viable option for increasing the strength of RCA concrete.

8. Procedure  Research on the testing method of concrete mix performance has been done.  Through testing, multiple mixes will be created with the purpose of revealing an optimum mix.  All results will be compared to the results of our control mix (natural aggregate concrete without nano-silica).

9. Quantities  The following quantities of materials needed for testing have been collected:  Sand -.309 cubic yards  Cement -.053 cubic yards  Natural Aggregate -.272 cubic yards  Recycled Concrete Aggregate -.272 cubic yards  The Recycled concrete aggregate was generously donated by Abita Concrete Recycling.

10. Mix Designs  A summary of the mix design process includes the following:  Selecting the appropriate water – cementing materials ratio for the durability and strength needed.  Two characteristics of aggregates are to be considered: 1.Grading (particle size and distribution) 2.Nature of particles (shape, porosity, surface texture)  Slump (workability of concrete)  A properly proportioned concrete mix should posses the following qualities: 1.Acceptable workability of freshly mixed concrete. 2.Durability, strength, and uniform appearance of hardened concrete. 3.Economy.

11. Sieve Analysis (Sand) Sieve Analysis on Sand sieve size Sieve Opening (in) Mass of aggregate retained on each sieve (g) % of individual fraction retained cumulative % retained % passing 1/40.2542.202.12 97.88 No. 40.1957.102.864.9895.02 No. 60.1384.304.239.2190.79 No. 120.07141.607.1016.3183.69 No. 200.03169.808.5224.8275.18 No. 300.02176.708.8633.6866.32 No. 400.02544.1027.2860.9739.03 No. 500.01524.7026.3187.2812.72 No. 700.01182.809.1796.453.56 No. 1000.0154.502.7399.180.82 No. 1400.006.700.3499.510.49 No. 2000.006.300.3299.830.17 Pan0.003.400.17100.000.00 total = 1994.20 nominal maximum size0.13 fineness modulus2.51

12. Sieve Analysis (Sand)

13. Sieve Analysis (Natural Aggregate) Sieve Analysis on Natural Aggregate sieve size Sieve Opening (in) Mass of aggregate retained on rach sieve (g) % of individual fraction retained cumulative % retained % passing 1 In1.000.00 100.00 1/2 In0.50472.0028.70 71.30 3/8 In0.38336.0020.5049.2050.80 1/4 In0.25463.0028.2077.4022.60 No. 40.19200.0012.2089.6010.40 No. 60.13118.007.2096.803.20 No. 120.0754.003.30100.000.00 No. 200.030.00 100.000.00 No. 300.020.00 100.000.00 No. 400.020.00 100.000.00 No. 500.010.00 100.000.00 No. 700.010.00 100.000.00 No. 1000.010.00 100.000.00 No. 1400.00 100.000.00 No. 2000.00 100.000.00 No. 2700.00 100.000.00 Pan0.00 100.000.00 total = 1643.00 nominal maximum size0.50

14. Sieve Analysis (Natural Aggregate)

15. Specific Gravity and Absorption Testing  Specific Gravity (Relative Density)  Ratio of the weight of a given volume of aggregate to the weight of an equal volume of water.  Measures aggregate weight under 3 sample conditions: 1.Oven dry 2.Saturated surface dry (SSD) 3.Submerged in water  Absorption (% Abs.)  Increase in weight of aggregate due to water in the pores of materials.

16. Specific Gravity Testing Results (RCA)  Apparent mass of saturated test sample in water = 990g  Mass of saturated-surface-dry test sample in air = 1700g  Mass of oven dry test sample in air = 1590g Values For RCA Relative density (specific gravity) (OD)= A/(B-C)2.24 Relative density (specific gravity) (SSD)= B/(B-C)2.39 Apparent relative density (apparent specific gravity)= A/(A-C)2.65 Density (OD), kg/m^3, = 997.5 A/(B-C)2233.84kg/m^3 Density (SSD), kg/m^3, = 997.5 B/(B-C)2388.38kg/m^3 Apparent density, kg/m^3, = 997.5 A/(A-C)2643.38kg/m^3 Absorption, % = [(B-A)/A]*1006.92%

17. Specific Gravity Testing Results (NA) Values for NA Relative density (specific gravity) (OD)= A/(B-C)2.43 Relative density (specific gravity) (SSD)= B/(B-C)2.51 Apparent relative density (apparent specific gravity)= A/(A-C)2.63 Density (OD), kg/m^3, = 997.5 A/(B-C)2428.70kg/m^3 Density (SSD), kg/m^3, = 997.5 B/(B-C)2500.98kg/m^3 Apparent density, kg/m^3, = 997.5 A/(A-C)2618.44kg/m^3 Absorption, % = [(B-A)/A]*1002.98%  Apparent mass of saturated test sample in water = 1040g  Mass of saturated-surface-dry test sample in air = 1730g  Mass of oven dry test sample in air = 1680g

18.  Mpw,t = Mass of the pycnometer and water at test temperature  Mpws,t = Mass of the pycnometer, water, and soil solids at test temperature  Ms = Mass of the oven dry solids  K = Temperature coefficient Specific Gravity Testing Results (Sand) Values For Sand mass (g) Mpw,t1430 GtGt2.722 Mpws,t1740 G₂₀2.717 MsMs490 Absorption %2.041 k0.99821 SSD500

19. Concrete Testing (Fresh Concrete Properties)  Air content  Determines the air content of freshly mixed concrete exclusive of any air that may exist inside voids within aggregate particles.  ASTM C 231 standard using a Type B pressure meter.  Slump  Used to measure and monitor the consistency of fresh concrete.  ASTM C 143 standard.

20. Concrete Testing (Hardened Concrete Properties)  Compressive Strength Test  Consists of applying a compressive axial load to the molded cylinders until failure occurs.  Compressive Strength = (max load / cross sectional area)  ASTM C 39 Standard.  Tensile Splitting Strength Test  Tensile strength of concrete is derived by applying a compressive force lengthwise along the cylinder, inducing a tensile stress.  ASTM C 496 Standard.

21. Trial Mix  Trial mixes were done in order to create a control batch for the RCA mixes with nano-silica.  Trial mixes consisted of natural aggregate, fine aggregate (sand), cement, and water.  Tests were conducted and results were recorded.

22. Analysis  Results from the mixes and tests previously mentioned will be gathered and evaluated.  A definite claim should be made regarding the specific mixes and proportions.  Does nano-silica strengthen the ITZ of RCA, and if so, at what proportionality is this strength optimal?

23. Summary of Progress (Fall break – Present) Carried out a second sieve analysis on sand. Constructed a specific gravity testing work table. Specific gravity and absorption testing on NA, RCA, and fine aggregate (sand) Ordered and received nano-silica fume. Created concrete mix design spreadsheet. Calibrated air content meter. Moisture content test for NA and sand to prepare for trial mix # 1. Mixed 2 trial batches and recorded results from testing.

24. Timeline