International Concrete Abstracts Portal

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.

In this work, the freeze/thaw resistance and ambient-temperature salt resistance of fly ash geopolymer pervious concrete specimens were investigated separately, to isolate the physical and chemical phenomena underlying their deterioration during “salt scaling”. The laboratory investigation examined four groups of samples, with portland cement or activated fly ash as the sole binder, with or without graphene oxide (GO) modification, respectively. The incorporation of GO significantly improved the resistance of pervious concrete to freeze/ thaw cycles and ambient-temperature salt attack, regardless of the binder type. The specimens were then examined by using X-ray Diffraction (XRD) method, which revealed that the mineralogy and chemical composition of fly ash pastes differed significantly from those of cement pastes. Nuclear magnetic resonance (NMR) was also employed to study the chemical structure and ordering of different hydrates. This work provides an enhanced understanding into the freeze/thaw and salt scaling resistance of fly ash pervious concrete and the role of GO.

In this research, a natural pozzolanic cementitious material known as zeolite is being utilized to investigate the performance of High-Performance Concrete (HPC). Several binary (cement+zeolite) and ternary (cement+zeolite+other supplementary cementitious material) based concrete mixtures including a control mixture of Ordinary Portland Cement (OPC) with water - cementitious (w/cm) ratios of 0.40 and 0.44 are cast by replacing cement with different percentage level of zeolite material. The purpose of this study is to investigate effectiveness of zeolite material by means of long term compressive strength (7 to 91 days), tensile strength, modulus of elasticity and corrosion resistance in several concrete mixtures from 7 to 28 days. The compressometer is utilized for the measurement of the modulus of elasticity and Universal Testing Machine (UTM) is utilized to measure the compressive and tensile strength of concrete. In addition, a 4-point Wenner Probe resistivity meter is tested to determine the surface electrical resistivity of concrete, which provides an indirect indication of permeability and in turn, chloride induced corrosion durability in reinforced concrete structures. Overall, zeolite based concrete mixtures with 0.40 w/cm ratio and ¾ inch aggregate size provide promising results in terms of compressive strength, tensile strength and remarkable improvement on corrosion resistance in terms of achievement of surface resistivity data.

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.