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Internal curing of high-performance concrete for bridge decksDeboodt, Tyler 09 December 2011 (has links)
High performance concrete (HPC) provides a long lasting, durable concrete that is typically used in bridge decks due to its low permeability, high abrasion resistance, freeze-thaw resistance and strength. However, this type of concrete is highly susceptible to the deleterious effects of both autogenous and drying shrinkage. Both types of shrinkage occur when water leaves small pores , (< 50
nm) in the paste matrix to aid in hydration or is lost to the surrounding environment. Autogenous deformation (self-desiccation) occurs as the internal relative humidity decreases due to hydration of the cementitious material. Drying (and subsequent shrinkage) occurs when water is lost to the environment and continues until the internal relative humidity is equivalent to the ambient relative humidity. Typically, the magnitude of autogenous shrinkage is less than that of drying shrinkage. These two types of shrinkage do not act independently, and the total shrinkage is the aggregation of the two shrinkage mechanisms. It is imperative to minimize the amount of shrinkage in restrained members, such as bridge decks, to reduce the cracking potential. Various methods have been researched to minimize both types of shrinkage. Two methods to that have been reported to reduce shrinkage were selected for further research; internal curing
using pre-soaked lightweight fine aggregate (LWFA) and shrinkage reducing admixtures (SRAs). The purpose of this study was to determine the long-term drying shrinkage performance of these two methods while reducing the external curing duration of 14 days for new bridge deck construction as specified by the Oregon Department of Transportation. In addition to monitoring drying shrinkage, durability testing was performed on concrete specimens to ensure these shrinkage mitigation methods performed at levels similar to concrete with the current mixture design. Freeze-thaw testing, permeability testing and restrained drying shrinkage testing were conducted. It was concluded that the combination of SRAs and pre-soaked LWFA was the most effective method to reduce longterm
drying shrinkage for all curing durations (1, 7, and 14 day). Additionally, for durability testing, it was found that the use of SRAs performed the best in freeze-thaw testing, chloride permeability and restrained shrinkage. / Graduation date: 2012
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Impact of curing methods on the strength of copper slag concreteKyalika, Cynthia Mumeka 10 1900 (has links)
The eco-friendly alternatives use is increasing momentum in a conscious effort
towards sustainability. In this regards, the relevance and the economic value of
using copper slag as a concrete aggregate are explored in this study in order to
contribute towards metallurgical waste recycling. Emphasis is placed on the
evaluation of the concretes strengthening prepared with copper slag contents and
produced under four curing methods: water immersion, water spraying, plastic
sheet covering and air-drying. In each curing case excluding for water immersion,
was duplicated in indoors (i.e. in the laboratory) and outdoor exposure (so was
prone to varying environmental conditions). This was specifically aimed at
capturing the effects of tropical weather conditions typical of the Lualaba province
in the Democratic Republic of Congo.
The control mix was designed to reach 25 MPa of compressive strength. Copper
slag was successively incorporated as sand replacement at the following mass
fractions: 20 %, 40 % and 60 %. Freshly mixed concrete samples were evaluated
for workability. Cube specimens were cast accordingly, cured for 28 days and then
tested for density and compressive strength.
Results indicated an increase in strength up to 20 % of replacement rate for all the
curing methods. Further additions resulted in reduction in the strength, but the rate
of reduction depended on curing conditions. The increase in strength was mainly
credited to the physical properties of copper slag that could have contributed to the
cohesion of the concrete matrix. It has been found that appropriate ways of curing
can still achieve greater results than that of the control mix since 80 % of humidity
is ensure. The two-way ANOVA test performed on the 28-days compressive
strength values confirmed the significant influence of the curing methods, of copper
slag content and the interaction between them. It has been found that considerable
influence is attributed to copper slag content and that warm environmental
conditions further extend the concrete strengthening. / College of Engineering, Science and Technology / M. Tech. (Chemical Engineering)
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