FEATI UNIVERSITY-CIVIL ENGINEERING DEPARTMENT THESIS AND RESEARCH 2007

ABSTRACT

Title : “USING ABACA TO STRENGTHEN THE QUALITY OF THE

GLUE USED FOR REPAIRING CONCRETE CRACKS”


Researchers : IAN OSBORNE CANEDO and LAURENCE ESTILLORE

Adviser : Dr. Tomas U. Ganiron Jr

School : FEATI University

Date : March 2007

Degree : Bachelor of Science in Civil Engineering


Reinforced concrete slabs have been widely used in modern transportation engineering, such as highway and airport pavements and bridge decks. Cracking in slabs reduces the local capacity and has been linked to fatigue failure in addition; cracks allow water and other chemical agents, such as deicing salt, to go through the cover layer to come into contact with the reinforcements, loading to reinforcement corrosion and rupture. Concrete shrinkage and temperature changes are the principal reasons for the initial crack formation and preparation afterward in slabs. Therefore, in order to prolong the service life of concrete pavements and bridge decks, shrinkage and temperature induced cracks using abaca strips to strengthen the quality of the glue in concrete pavements and bridge decks, cracking in concrete due to shrinkage and temperature changes can be avoided. Moreover, cracks, especially shrinkage and temperature cracks are localized into designated strips, where abaca material with tensile strain-hardening and high strain capacity is used. As a result, while microstructure damage exists in the abaca strip, the concrete remains intact.
Due to the special material properties of the abaca material, the strain energy produced by shrinkage of hardened cement and temperature changes can be released by the high strain ability material so that cracking in plain concrete can be avoided. By replacing standard joints in concrete pavements, common deterioration problems associated with joints will be eliminated. A possible abaca strip is a fiber reinforced engineered cementations composite (ECC).

SUMMARY OF FINDINGS
The tensile specimens were tested at 7 days and 28 days after casting, respectively. The test procedure was the same as that used for the tensile test on plain concrete. From the results, the researchers for the specimen cured only for 7 days, the specimen failed in a brittle manner even though the first crack already occurred in the abaca strip in one of the two specimens. However, the final failure occurred in the concrete section of this specimen. This is expected, since at 7 days curing the first crack strength of abaca strips and the tensile strength of plain concrete are very close;. Therefore, even if the first cracking occurs in the abaca strip, as load increases, the stress in the concrete section may reach the concrete tensile strength, resulting in failure in the concrete section instead of further development of new cracks in the abaca strip. For the specimen cured for 28 days, the situation is totally different
In this case, the concrete tensile strength is much higher than the first crack strength of ECC and even higher than the ultimate tensile strength of ECC. Therefore, as the specimen is loaded in tension, first cracking will occur in the abaca strip and multiple cracking can be developed in it due to sufficient difference between the ultimate tensile strengths of ECC and concrete. Cracking with crack widths less than 0.1 mm was successfully localized into the abaca strip instead of in the concrete section. This is the final goal of the present investigation. Furthermore, in the present dimension of the specimen, the strain attained 1.4% at peak load 3.5 MPa.

CONCLUSION
This research presents an experimental study on the potential applications of abaca engineered cementations composite in continuously steel reinforced concrete slabs, such as concrete bridge decks and pavement, for the purpose of eliminating cracks in concrete. It is found that a composite slab containing both plain concrete and abaca strips, with proper design at the ECC/concrete interfaces and careful selection of material properties to as-sure that the tensile strength of concrete higher than that of ECC material.. It is possible to localize tensile cracks into the abaca strip instead of in the concrete section. The current concrete mix satisfies the above condition after 14 days of water curing. Due to the strain-hardening performance of the ECC material with a high strain capacity up to 5%as well as a high fatigue crack resistance behavior, the overall strain capacity and the integrity as well as the fatigue durability of the composite slab can be significantly improved. In the present study, the overall strain capacity of the test specimen achieves 1.4% at peak load.