Colby Mire & Jordan Licciardi Advisor: Mohamed Zeidan ET 493 “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 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

Drawbacks of RCA Aside from its many benefits, using RCA has a few quality drawbacks as well. 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 Testing will be done to study the fresh concrete properties, hardened concrete properties, and durability properties. 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).

Concrete Testing Fresh Concrete Properties: Air content: using a pressure meter as indicated by ASTM C 231 Slump test: as indicated by ASTM C 143 Hardened Concrete Properties: Compressive strength test: conducted at different curing ages as indicated by ASTM C 39 Tensile splitting strength test: perform at an age of 28 days as indicated by ASTM C 496 Concrete Durability: Abrasion resistance test: as indicated by ASTM C 418 Water absorption rates: measured as indicated by ASTM C 1585

Analysis Results from the six 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?

Timeline