Dowel Bar Retrofit Mix Design and Specification

mahyarov · 11-17-2012, 12:08 PM

The focus of this project was on identifying critical properties that control long‐term performance of repair concrete, especially rapid-setting materials extended using pea gravel (maximum size aggregate 9.5 mm). In the first phase of this project, four commercial rapid‐setting materials (CRSMs) were selected and development of mixture proportions in terms of optimum pea gravel content and water content was performed. Optimized mixtures were further evaluated at three different initial temperature conditions. The properties evaluated included workability, setting time, rate of compressive strength developed, slant shear bond strength, freeze‐thaw resistance, air‐void system characteristics of hardened concrete, drying shrinkage and cracking potential. It was observed that some of the CRSMs evaluated did not meet requirements of ASTM C 928. All, except one, CRSMs tested exhibited low resistance to freezing and thawing but all had high resistance to cracking. In the second phase of the project, rapid‐setting self‐consolidating concrete (RSSCC) was developed using ternary blend of cementitious materials, high‐range water reducer (HRWR) and accelerators. Slump flow, visual stability index (VSI), compressive strength at various ages and the power consumption values for the mortar mixer indicated that a five minutes mixing sequence involving a 2‐Step addition of HRWR produces stable RSSCC mixture. The results of various tests carried out indicate that it is possible to develop a small aggregate size‐based self‐consolidating repair concrete that achieves a compressive strength of 19 MPa at the end of 6 hrs, has good bond characteristics and excellent freezing and thawing durability (DF>90%). The sensitivity of RSSCC to aggregate characteristics and production variables was also evaluated. Specifically, the influence of aggregate gradation and aggregate moisture content using different types of mixers and re‐mixing after a period of rest was evaluated. It was observed that variation in aggregate moisture content and aggregate gradation resulted in noticeable changes in fresh concrete properties such as the slump flow, stability and V‐funnel flow values. While changes in moisture content and gradation of aggregates had an impact on the early (6 h) compressive strength, the compressive strength at the end of 24 hours was not significantly affected.

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