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“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
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