Comparison of Setting Time Measured Using Ultrasonic Wave Propagation with Saw-Cutting Times on Pavements

At present, there is little fundamental guidance available to assist contractors in choosing when to schedule saw cuts on joints. To conduct pavement finishing and sawing activities effectively, however, contractors need to know when a concrete mixture is going to reach initial set, or when the sawing window will open. Previous research investigated the use of the ultrasonic pulse velocity (UPV) method to predict the saw-cutting window for early entry sawing. The results indicated that the method has the potential to provide effective guidance to contractors as to when to conduct early entry sawing. The aim of this project was to conduct similar work to observe the correlation between initial setting and conventional sawing time. Sixteen construction sites were visited in Minnesota and Missouri over a two-year period. At each site, initial set was determined using a p-wave propagation technique with a commercial device. Calorimetric data were collected using a commercial semi-adiabatic device at a majority of the sites. Concrete samples were collected in front of the paver and tested using both methods with equipment that was set up next to the pavement during paving. The data collected revealed that the UPV method looks promising for early entry and conventional sawing in the field, both early entry and conventional sawing times can be predicted for the range of mixtures tested

Extended Use of Limestone Fines in Various Concretes

Limestone fines are increasingly used in cement and concrete for improved material properties and sustainability. This paper presents recent research at Iowa State University on utilization of limestone fines in concrete. It includes the beneficial uses of limestone fines in: (1) limestone blended Portland cement; (2) SFSCC (semi-flowable self-consolidating concrete); and (3) HPC (high performance concrete). The research results show that using 5%~10% of limestone fines to replace for Type IP cement (with 25% fly ash) increased mortar strength. Well-designed SFSCC with 25% limestone fines (by mass of cementitious materials) displayed desirable rheological and mechanical properties required for slip-forming construction. The newly developed limestone fines-based HPC reached the one-day compressive strength of over 28 MPa

Development of Performance Properties of Ternary Mixtures: Field Demonstrations and Project Summary

Supplementary cementitious materials (SCM) have become common parts of modern concrete practice. The blending of two or three cementitious materials to optimize durability, strength, or economics provides owners, engineers, materials suppliers, and contractors with substantial advantages over mixtures containing only portland cement. However, these advances in concrete technology and engineering have not always been adequately captured in specifications for concrete. Users need specific guidance to assist them in defining the performance requirements for a concrete application and the selection of optimal proportions of the cementitious materials needed to produce the required durable concrete. The fact that blended cements are currently available in many regions increases options for mixtures and thus can complicate the selection process. Both Portland and blended cements have already been optimized by the manufacturer to provide specific properties (such as setting time, shrinkage, and strength gain). The addition of SCMs (as binary, ternary, or even more complex mixtures) can alter these properties, and therefore has the potential to impact the overall performance and applications of concrete. This report is the final of a series of publications describing a project aimed at addressing effective use of ternary systems. The work was conducted in several stages and individual reports have been published at the end of each stage

Pervious Concrete Physical Characteristics and Effectiveness in Stormwater Pollution Reduction

The objective of this research was to investigate the physical/chemical and water flow characteristics of various previous concrete mixes made of different concrete materials and their effectiveness in attenuating water pollution. Four pervious concrete mixes were prepared with Portland cement and with 15% cementitious materials (slag, limestone powder, and fly ash) as a Portland cement replacement. All four pervious concrete mixtures had acceptable workability. The unit weight of the fresh pervious concrete mixtures ranged from 115.9 lb/yd3 to 119.6 lb/yd3 , while the 28 day compressive strength of the pervious concrete mixes ranged from 1858 psi (mix with 15% slag) to 2285 psi (pure cement mix). The compressive strength generally increased with unit weight and decreased with total porosity (air void ratio). The permeability of the four mixes generally decreased with unit weight and increased with total porosity. The permeability coefficients ranged from 340 in./hr for the pure cement mix to 642 in./hr for the mix with 15% slag. The total porosities of the four pervious concrete mixes ranged from 24.00% (mix with 15% slag) to 31.41% (pure cement mix) as measured by the flatbed scanner test method, while the porosities ranged from 18.93% (mix with 15% slag) to 24.15% (pure cement mix) as measured by the RapidAir method. The total porosities of the four pervious concrete mixes measured by the flatbed scanner method were higher than those measured by the Rapid Air method, but the specific surface areas measured by the flatbed scanner method were all lower than those measured by the Rapid Air method. For the pollution abatement experiments, mixes with fly ash and limestone powder removed about 30% of the input naphthalene concentration, while the mix with slag only removed 0.5% of the influent naphthalene concentration. The water volume balance showed that less than 1% of the water added was retained in the experimental column setup

Investigation into Shrinkage of High-Performance Concrete Used for Iowa Bridge Decks and Overlays

High-performance concrete (HPC) overlays have been used increasingly as an effective and economical method for bridge decks in Iowa and other states. However, due to its high cementitious material content, HPC often displays high shrinkage cracking potential. This study investigated the shrinkage behavior and cracking potential of the HPC overlay mixes commonly used in Iowa. In the study, 11 HPC overlay mixes were studied. These mixes consisted of three types of cements (Type I, I/II, and IP) and various supplementary cementitious materials (Class C fly ash, slag and metakaolin). Limestone with two different gradations was used as coarse aggregates in 10 mixes and quartzite was used in one mix. Chemical shrinkage of pastes, free drying shrinkage, autogenous shrinkage of mortar and concrete, and restrained ring shrinkage of concrete were monitored over time. Mechanical properties (such as elastic modulus and compressive and splitting tensile strength) of these concrete mixes were measured at different ages. Creep coefficients of these concrete mixes were estimated using the RILEM B3 and NCHRP Report 496 models. Cracking potential of the concrete mixes was assessed based on both ASTM C 1581 and simple stress-to-strength ratio methods. The results indicate that among the 11 mixes studied, three mixes (4, 5, and 6) cracked at the age of 15, 11, and 17 days, respectively. Autogenous shrinkage of the HPC mixes ranges from 150 to 250 microstrain and free dying shrinkage of the concrete ranges from 700 to 1,200 microstrain at 56 days. Different concrete materials (cementitious type and admixtures) and mix proportions (cementitious material content) affect concrete shrinkage in different ways. Not all mixes having a high shrinkage value cracked first. The stresses in the concrete are associated primarily with the concrete shrinkage, elastic modulus, tensile strength, and creep. However, a good relationship is found between cementitious material content and total (autogenous and free drying) shrinkage of concrete

Improving Variability and Precision of Air-Void Analyzer (AVA) Test Results and Developing Rational Specification Limits

Since air-void analyzer (AVA) was introduced in the 1990s, various studies have been conducted in the United States to apply this technology. Many concerns are raised on (a) the variation of the AVA tests, (b) the relationship between AVA and other standard measurements, and (c) AVA specification limits. The application of AVA tests in concrete practice is therefore very challenging. The goals of the present research project are to reduce variability and improve precision of AVA test results and to develop rational specification limits for controlling concrete freezing and thawing (F-T) damage using the AVA test parameters. This project consists of three phases: (1) Phase 1—Literature search and analysis of existing AVA data (June 2007–August 2008), (2) Phase 2—AVA testing procedure and specification modification, (3) Phase 3—Field study of AVA and specification refinement. In the present research report, the major activities and findings of the Phase 1 study are presented, and the major tasks for the Phase 2 study are recommended. The major activities of the Phase 1 study included the following: performing a literature search, collecting and reviewing available AVA data, completing a statistical analysis on collected AVA data, and carrying out some AVA trial tests in lab. The results indicate that AVA is a time- and cost-effective tool for concrete quality control. However, robustness of the AVA equipment, test procedures, and resulting interoperations need further improvement for a proper implementation of the AVA technology in concrete practice

Experimental Quantum Fingerprinting

Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof of concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity.Comment: 11 pages, 6 Figure