Effect of constituent materials and curing methods on the abrasion resistance and durability of high performance concrete for pre-cast pre-stressed bridge deck slabs

Abstract

This thesis is the consequence of a research effort undertaken by the School of Civil and Construction Engineering at Oregon State University and funded by the Oregon Department of Transportation (ODOT) and the Federal Highway Administration (FHWA). The principal objective of the effort was to reduce the life cycle cost of bridges by developing one or more materials systems for precast and pre-stressed bridge deck components that improve the studded tire wear (abrasion) resistance and durability of bridge decks. Degradation of the concrete bridge decks due to abrasion caused by the studded tires and accelerated corrosion of the reinforcing steel in the concrete often triggers costly, premature rehabilitation or replacement of these bridges. High performance concrete (HPC) can provide improved abrasion resistance, but is more costly than ordinary concrete and can exhibit early age cracking when used for cast-in-place concrete members, which can accelerate corrosion of embedded reinforcing steel. However, several studies have suggested that HPC developed for precast members offers a viable alternative to cast-in-place concrete deck slabs due in part to improved control of the curing process.

The scope of this research was to develop one or more mixture designs for HPC that improve the durability and abrasion resistance of the bridge decks through careful selection and proper proportioning of the constituent materials and improved control of the curing process. The materials investigated in this research included silica fume, slag, and fly ash as partial replacement of Type I and Type III portland cement mixed with crushed aggregate and river gravel. Phase I of the study included development of 15 mixture designs incorporating various combinations of the materials. Mixtures were cast under controlled laboratory conditions and cured using a variety of methods. The results of tests conducted on the cured samples indicated that the mixture with silica fume and slag had greater strength than the mixture with silica fume and fly ash mixture, and that mixtures with crushed rock provided better abrasion resistance than those with river gravel. Results from the chloride ion penetration test for permeability indicated that mixtures cured in saturated lime water for 28 days exhibited reduced permeability in comparison to mixtures which were steam cured followed by ambient curing. Following phase I, a pilot study was undertaken to identify the best curing method to apply during production at precast yards to assist high early strength gain so that the concrete member can be removed from the casting bed in a matter of several hours as well as to facilitate high ultimate strength, improved abrasion resistance, and low permeability. The pilot study indicated the best curing method to be steam curing followed by application of a curing compound. Phase II of the research study included seven mix designs and focused on various levels of supplementary cementitious materials. It adopted the curing method suggested by the pilot study. Results from phase II indicated that slag was better in enhancing durability of the concrete than fly ash. Increasing the proportion of silica fume did not improve the properties of high performance concrete significantly. Some other interesting results indicated that compressive strength was inversely proportional to wear rate and chloride ion penetration. Wear rate was directly proportional to chloride ion penetration. There was no relationship between durability factor (freeze-thaw test) and compressive strength or chloride ion penetration. Two mixtures were identified as having significantly improved abrasion and permeability characteristics over the control mixture (ODOT bridge deck mixture). Both included slag and silica fume as supplementary cementitious materials as a partial replacement of portland cement and one did not contain an air entraining admixture.