INTERNATIONAL CONCRETE SUSTAINABILITY

CONFERENCE 2015RECYCLED MATERIAL USED AS AGGREGATE IN

CONCRETE MANUFACTURING

DAVID HOLT, MICHAEL MULLEN, MATTHEW SNEAD, REID PIERSON, DR. MICHELLE LONDA, DR. JIONG HU

INTRODUCTION

World population– 2.5 billion in 1950– 9 billion in 2050– World population is growing at an

continuous rate creating a need for more sustainable building practices involving concrete

World demand/year– 11.5 billion tons of concrete– 1.5 billion tons of cement– 1 billion tons of water– 9 billion tons of aggregate

Conservation of resources– Waste products of one industry can be

recycled as a substitute for virgin raw materials of another, reducing the environmental impact of both.

– Currently 140 million tons of concrete is being recycled in the U.S. per year.

– Sand is being consumed at a far greater rate than its renewal, which necessitates the need to find sustainable alternatives.

Recycled Products for Coarse Aggregates– Concrete– Glass– Bricks– Ceramics

Recycled Products for Fine Aggregates– Pulverized plastic– Sheet glass powder– Crushed granite fine– Fly ash

Rubber Tires– 10 billion scrap tires are stockpiled globally– State landfill regulations7

• 38 states ban whole tires from landfills• Leach toxins into the environment• Create harmful fires• Emit significant amounts of CO2 and dioxins

when burned as fuel One man’s trash is another man’s treasure!

WHY ARE WE HERE

Static Variables– Portland Cement (13 lbs..)– Pea Gravel (28.2 lbs..)– Water / Cement Ratio (~0.4)

Dynamic Variables– Sand

• 0.2 wt.% water absorption• Adjusted by % volume

– Recycled Rubber Tires• 2.5 wt.% water absorption • Density of rubber crucial • Adjusted by % volume

– Super Plasticizer

DOE VARIABLES

Pre cure unit weight (lbs.) Post cure unit weight (lbs.) Slump (in) Compressive Strength (psi)

– 9 days– 22 days– 90 days

RESPONSES

RESULTS-WEIGHT

RESULTS-SLUMP

TEST MARK COMPRESSIVE STRENGTH No Super Plasticizer

With Super Plasticizer

TINIUS OLSEN STRESS-STRAIN RESULTS

TINIUS OLSEN STRESS-STRAIN RESULTS The Effect of Rubber Concentration and Super Plasticizer

Level on Compressive Strength (90 days cure)

The Effect of Rubber Concentration and Super Plasticizer Level on Modulus (90 days cure)

TINIUS OLSEN STRESS-STRAIN RESULTS

The Effect of Rubber Concentration on the Compressive Stress / Strain Fracture Behavior of Concrete (90 days cure)

TINIUS OLSEN STRESS-STRAIN RESULTS

ML RubberL Rubber

BRITTLE FRACTURE

DUCTILE FRACTURE

MH RubberM Rubber

ANALYSIS - MODULUS

ANALYSIS – LEVERAGE PLOTS

ANALYSIS – REGRESSION

CONCLUSIONS Highlights

– Baseline concrete samples reached 9,049 psi– Achieved a 3,000 and 4,000 PSI ultimate strength with one of the rubber

formulations – TEST MARK– Toughness enhanced with the addition of rubber– Although the ultimate strength and modulus are decreased, the balance of

stiffness and toughness should be valuable in many applications– To be commercially viable, however, an improvement in the interfacial

adhesion between the rubber and the cement need to be investigated– With rubber added to the concrete mix the overall weight would significantly

reduce fuel cost in transportation.

Where do we go from here?– The evaluation of additives to gain back some of the strength lost upon the

addition of the recycled tire rubber while maintaining the toughness– Long term durability testing will also be required

• Temp Cycle• Thermal Shock• Autoclave

ACKNOWLEDGEMENTS Texas State Professors

– Dr. Michelle Londa– Dr. Jiong Hu– Mr. Jerel Walters– Mr. Steve Zinkgraft

Graduate Assistance [Technology]– Eric Adams

Undergrad Assistants [Technology]– Brian Ledsinger