International Concrete Abstracts Portal

The goal of this study was to implement cost-effective techniques for improving bridge deck service life through the reduction of cracking. Work was performed both in the laboratory and in the field, resulting in the creation of Low-Cracking High-Performance Concrete (LC-HPC) specifications that minimize cracking through the use of low slump, low paste content, moderate compressive strength, concrete temperature control, good consolidation, minimum finishing, and extended curing. This paper documents the performance of 17 decks constructed with LC-HPC specifications and 13 matching control bridge decks based on crack surveys. The LCHPC bridge decks exhibit less cracking than the matching control decks in the vast majority of cases. Only two LCHPC bridge decks have higher overall crack densities than their control decks, which are the two best performing control decks in the program, and the differences are small. The majority of the cracks are transverse and run parallel to the top layer of the deck reinforcement. The results of this study demonstrate the positive effects of reduced cement paste contents, concrete temperature control, limitations on or de-emphasis of maximum concrete compressive strength, limitations on maximum slump, the use of good consolidation, minimizing finishing operations, and application of curing shortly after finishing and for an extended time on minimizing cracking in bridge decks.

The results of an experimental investigation into the mechanical properties and durability of recycled and natural coarse aggregates concrete are reported. A total of thirty-six specimens were tested. The percentages of replacement of coarse aggregates with recycled aggregates in the concrete mixes were 0%, 50%, and 100%. The source of recycled aggregates in this study was the concrete specimens tested in the laboratory. These specimens were crushed and then sieved into medium aggregates (4.75-9.5 mm) [0.19-0.37 in.] and coarse aggregates (9.5-19mm) [0.37-0.75 in.]. The replacement of fine aggregates was not considered in this study. The properties of concrete mixes containing natural aggregates as control mix and those containing Recycled Concrete Aggregates (RCAs) have been studied, including fresh properties, mechanical properties and durability. The influence of saturation state of RCA (dried or saturated) on the properties of concretes of identical compositions has first been studied. The theoretical amount of absorbed water is added at the beginning of mixing. Durability performance of hardened concrete made with recycled aggregates as partial or full replacement of natural coarse aggregates is reported. Resistance to pure water and sulfate attack is investigated. The results show that a replacement ratio of 50% does not have a significant effect on the performance of recycled aggregate concrete mixes. Moreover, the recycled aggregate concrete performs relatively satisfactorily under various conditions and has a comparable durability to natural aggregate concrete if properly designed.

Cement production is one of the largest contributors to CO2 emissions in the U.S. One method of reducing emissions associated with concrete is through usage of alternative cements (ACMs). Some of the more common ACMs include calcium sulfoaluminate cement, calcium aluminate cement, ternary calcium aluminate-calcium sulfate-portland cements, and chemicallyactivated binders, all of which have been shown to have lower carbon footprints than ordinary portland cement (OPC). However, the durability, and more specifically, the shrinkage behavior, of these cements has not been adequately examined, and must be better understood and able to be controlled before ACM concrete can be effectively used in the field. As a first step in increase understanding of shrinkage in ACMs, this paper examines chemical, autogenous, and drying shrinkage in the ACMs listed above. Results show that, despite greater quantities of chemical shrinkage, CSA, CAC, and chemically activated fly ash binder undergo less autogenous and drying shrinkage than OPC.

In this study, we tested compressive strength, rheology, initial setting time and transport properties of mortar samples mixed with green corrosion-inhibiting admixtures were tested. Four types of green corrosion inhibitors were adopted, which were extracted from peony leave, Kentucky blue grass, sugar beet leave and dandelion. All of them affected the compressive strength adversely but improved other properties of mortar samples. Resistance of mortar to chloride induced corrosion was evaluated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. The results indicated that these green corrosion-inhibiting admixtures provided promising inhibiting performance under chloride environment. The results also suggested these green corrosion-inhibitors have the potential to be used as multifunction corrosion inhibitors for concrete, such as serving as water reducer and set retarder. Future work would focus on chemical mechanism of green corrosion inhibitors and the comparative evaluation of these green corrosion inhibitors with other commercially available corrosion inhibitors.

Supplementary cementitious materials (SCMs) in conjunction with pre-wetted fine lightweight aggregate to provide internal curing are being increasingly used to produce high performance, low-shrinking concrete to mitigate bridge deck cracking, providing more sustainable projects with a longer service life. Additionally, the SCMs aid in concrete sustainability by reducing the amount of cement needed in these projects. This study examines the density of cracks in bridge decks in Indiana and Utah that incorporated internal curing with various combinations of portland cement and SCMs, specifically, slag cement, Class C and Class F fly ash, and silica fume, in concrete mixtures with water-cementitious material ratios ranging from 0.39 to 0.44. When compared with crack densities in low-cracking high-performance concrete (LC-HPC) and control bridge decks in Kansas, concrete mixtures with a paste content higher than 27% exhibited more cracking, regardless of the use of internal curing or SCMs. Bridge decks with paste contents below 26% that incorporate internal curing and SCMs exhibited low cracking at early ages, although additional surveys will be needed before conclusions on long term behavior can be made.