Date of Award

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Civil Engineering

Advisor

GADKAR, SHUBHADA A

Committee Member

RANGARAJU , Dr. PRASAD

Committee Member

PUTMAN , Dr. BRADLEY

Committee Member

POURSAEE , Dr. AMIR

Committee Member

SANDERS , Dr. JOHN

Abstract

Ground tire rubber also known as crumb rubber has been widely used in asphalt concrete over the past several years due to its ability to improve temperature susceptibility of asphalt binders and enhance the performance of asphalt pavements. However, its inclusion in portland cement concrete is comparatively recent and more research is needed before adopting it as a regular construction material. Past research has shown that while addition of rubber aggregates in concrete reduces its compressive, tensile and flexural strengths, but is useful in improving durability properties as freeze-thaw resistance due to the ability of crumb rubber to generate an effective air-void system in rubberized concrete. Previous studies have focused on the effect of the addition of the various sizes and replacement levels of crumb rubber on strength and other mechanical properties; however, a comprehensive assessment of these variables on freeze-thaw durability or air void parameters due to the ambient and cryogenic types of crumb rubber has not yet been fully conducted. The results of such investigations would potentially address issues such as instability and the loss of air and its effect on the air-void system in conventionally air-entrained concretes.
To address this need, the main objective of this study was to investigate the freeze-thaw durability of rubberized portland cement concrete through the addition of two types of crumb rubber particles, ambient and cryogenic. In addition, three sizes of crumb rubber aggregates, #8 (2.36 mm), #50 (0.60 mm) and #100 (0.30 mm) at three replacement levels, 8%, 16% and 24%, by volume of fine aggregates were used in the preparation of the concrete specimens. The results of rubberized concrete were compared with both non-air-entrained concrete and air-entrained concrete without the addition of rubber. The effect of the alkalinity of cement, the absence of super-plasticizer, the vibration time and frequency of the consolidation of fresh concrete, and the addition of supplementary cementing materials with high loss-on-ignition (LOI) that affects the air content in concrete, such as rice husk ash, was studied. Also, comparative studies were conducted with latex emulsions to understand if crumb rubber has any similarity with latex on concrete properties.
The investigations on freeze-thaw durability of crumb rubber concrete concluded that the use of finer sized particles i.e. #50 and #100 of both types of crumb rubber at 16% and 24% replacement levels, by volume of sand, displayed improved durability performance in freeze-thaw test without the need for conventional air-entraining admixtures. Concrete mixtures containing finer crumb rubber for higher dosage levels in combination with both low-alkali and high-alkali cements exhibited higher durability factors, of more than 60% at the end of 300 F-T cycles, as compared to the non-air entrained control concrete and coarser rubber concrete specimens. It was observed that the system of air bubbles incorporated in concrete due to the addition of crumb rubber particles was not adversely affected by the high carbon content in the #50 size ambient crumb rubber concrete specimens with rice husk ash (RHA), the different vibration frequency for consolidation of ambient crumb rubber concrete and in the absence of super-plasticizer in combination with the low alkali cement. Also, the vibration time in cryogenic rubber concrete did not affect its F-T performance. The F-T performance of latex modified concrete with the low alkali cement was also comparable to the finer size crumb rubber concrete.
However, the rubber concrete specimens prepared from combinations of RHA with #100 size and both low and high alkali cement along with #50 size crumb rubber concrete specimens with high alkali cement negatively affected the F-T performance. The vibration time in ambient rubberized concrete specimens affected their performance indicating that these factors affect the air entrainment in rubberized concrete similar to the conventionally air entrained concrete mixtures. Also, the latex modified concrete with higher replacement levels and high alkali cement was not effective in providing adequate F-T performance as compared to the crumb concrete with finer size and higher replacement levels.
In summary, the findings from this research indicate that the use of finer rubber sizes and higher rubber replacement levels, improves the freeze-thaw durability performance of concrete, even though the strength of the concrete is decreased. However, a difference in the properties of rubberized concrete with #50 and #100 size fractions was observed in the various parameters studied here which needs to be investigated in further depth. The use of rubberized concrete is recommended in applications where the strength requirements are minimal but high durability requirements need to be satisfied.
The hydrophobic nature of the crumb rubber and increased specific surface area (SSA) of finer size fractions of crumb rubber particles appears to be the principal mechanism leading to the increased air entrainment in the rubberized concrete. Standard petrographic examination methods are adequate to characterize the air content parameters even in rubberized concretes. If the finer crumb rubber particles can be used as a partial replacement to fine aggregates, it can reduce the usage of natural mineral aggregates greatly and minimize their rapid depletion. Crumb rubber particles may prove to be a sustainable option for producing frost resistant concrete and also provide an opportunity for economic and environmental friendly solution for the disposal of high amount of waste tires in the landfills.

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