Date of Graduation

5-2013

Document Type

Thesis

Degree Name

Bachelor of Science in Civil Engineering

Degree Level

Undergraduate

Department

Civil Engineering

Advisor/Mentor

Hale, W. Micah

Committee Member/Reader

Braham, Andrew

Committee Member/Second Reader

Zhang, Wen

Abstract

Curing refers to the process of maintaining the hydration of the concrete as it hardens, or sets up. Concrete is cured to prevent things such as cracking and shrinkage. Autogenous shrinkage occurs internally in concrete because there isn’t enough water in the concrete for hydration, so the concrete rapidly draws out water to complete the hydration cycle, causing internal drying of concrete. There are two types of curing: external and internal. External curing utilizes water from external sources such as saturated burlap mats, ponding, or fogging. Internal curing supplies water from an internal source inside the concrete, such as saturated fine lightweight aggregate (FLWA). FLWA are very porous and when saturated supply an internal source of water. The use of internal curing in concrete mixes reduces the cracking of concrete due to shrinkage. It has already been proven that the first water lost due to hydration is lost from the aggregates inside the concrete, and there is little information on the right amount of pre-wet LWA to use to hydrate a mix without increasing the water/cement ratio (w/c) of the concrete. If the w/c of a concrete is too high, then it will lose its strength properties, but if it is too low then the concrete will experience premature cracking and shrinkage. Internal curing is a more efficient, and enhanced, method of curing concrete because of the process that the concrete undergoes. Where external curing requires constant maintenance of the concrete to keep it hydrated, internal curing requires no maintenance because the pre-wet FLWA does all the labor and maintenance that would be required. Pre-wet FLWA has not been used in bridge deck pavement mixes, and that’s what this project is aiming to accomplish. The American Society of Civil Engineers puts out a report card for the infrastructure in American each year; in 2009 they gave the United States on a whole a C for bridges. They go on to say that 25%, or one in every four, of Arkansas’ bridges are either structurally deficient or functionally obsolete. Bridge decks carry the vast majority of the loads on bridges, and when they start to shrink or crack, they become a big part of why a bridge becomes “structurally deficient.” Adding internal curing to bridge decks will eliminate the shrinkage and cracking, allowing for more durability and less maintenance, ultimately giving the bridges a longer service life. In this project, two types of fine aggregates, expanded shale and expanded clay, will be used. Batches will be done with mixes containing 100, 200, and 300lb/ft3 of lightweight fine aggregate. The drying shrinkage of the concrete will be done using ASTM C 490. Monitoring for the drying shrinkage of each mix design will go on for up to six months after the concrete has been batched. The other big aspect of bridge deck concrete, compressive strength, will be measured at 1 day, 7 days, 28 days, and 90 days.

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