Laboratory Investigation of Workable and Durable Concretes for Bridge Repair

About the report:

Concretes for bridge repair that attained 3,000 psi compressive strength within 10 hours, 1 day, and 7 days and had high workability and durability were investigated in the laboratory.  Supplementary cementitious materials (SCMs) were used in concrete with portland cement to make the mixture resist the penetration of harmful solutions and chemical attack.  These concretes were air entrained for proper resistance to cycles of freezing and thawing.  When high early strength was needed, high amounts of portland cement and low water–cementitious materials ratios were used in these concretes that made them prone to cracking.  However, fibers were investigated to control the cracking.  Mixtures with rapid setting cement were also tested for high early strengths.

Test results indicated that with high amounts of portland cement with an SCM or the use of rapid setting cement, desired strength can be achieved within 10 hours.  To achieve 3,000 psi in 1 day and 7 days, lower amounts of portland cement with an SCM and overall lower paste contents were used, making them less prone to cracking. 

The study recommends that high amounts of portland cements with SCMs be used to achieve 3,000 psi within 10 hours with setting times long enough for mixing and delivery by truck mixers and placement.  These concretes may need to be insulated at the job site to retain heat to ensure early strengths are achieved.  If shorter setting times can be accommodated using on-site mobile mixers,  rapid setting cement can be used to achieve a 3,000 psi compressive strength within a few hours, i.e., much less than 10 hours.  For longer times, more than 1 day, to attain 3,000 psi, portland cements containing SCMs with a low cementitious materials content should be used; they are cost-effective, easier to make, and have less cracking potential than the high early strength mixtures with portland cement with an SCM.  If cracking is anticipated, fibers can be added. In the laboratory, an efficient pan type mixer was used to obtain uniform blending of ingredients and good distribution of fibers.  In future field work, large quantities of material would be mixed and delivered in ready mixed concrete trucks or mobile mixers, which are not as efficient as laboratory mixers.  Use of ready mixed trucks and mobile mixers to provide the recommended mixtures needs to be investigated to identify any issues and to streamline the implementation of the mixtures.

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