“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 resourcesLower the cost for waste treatmentReduce the overall cost of new infrastructureReduction 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 sampleB = Mass retained on the .187 in. sieveC = Mass passing .187 in. sieve; C = A-BD = Percent coarse aggregateE = 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 sampleB = Mass retained on the .187 in. sieveC = Mass passing .187 in. sieve; C = A-BD = Percent coarse aggregateE = 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 contentDetermines 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 - .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.

Timeline