“Investigating the Effect of Nano-Silica on Recycled Aggregate Concrete” Colby Mire & Jordan Licciardi Advisor: Mohamed Zeidan ET 493

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).

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.

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

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.

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.

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.

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).

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.

Sieve Analysis (Sand)

Percent Coarse Aggregate (D = B/A x 100) = 0% Percent Fine Aggregate (E = C/A x 100) = 100% A = Mass of total sample B = Mass retained on the.187 in. sieve C = Mass passing.187 in. sieve; C = A-B D = Percent coarse aggregate E = Percent fine aggregate

Sieve Analysis (Natural Aggregate)

Percent Coarse Aggregate (D = B/A x 100) = 89.53% Percent Fine Aggregate (E = C/A x 100) = 10.47% A = Mass of total sample B = Mass retained on the.187 in. sieve C = Mass passing.187 in. sieve; C = A-B D = Percent coarse aggregate E = Percent fine aggregate

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.

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.

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.

Concrete Testing (Concrete Durability)  Abrasion Resistance Test  Evaluates the durability of a concrete specimen in the presence of : 1.Stimulated waterborne abrasives 2.Abrasives under traffic on concrete surfaces  Demonstrates the concretes ability to resist abrasive wear.  ASTM C 148 Standard.

Analysis  Results from the five 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?

Summary of Progress  Up to this point, we have accomplished the following: Research of concrete testing, recycled concrete aggregate, and nano-silica. Ordered compression test machine and sieve apparatus. Modifications of a shelving unit for specific gravity testing. RCA donated and received from Abita Concrete Recycling. Quantity measurements of materials. Sieve analysis for sand and natural aggregate; results calculated.

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

Timeline