Mateusz Radlinski

Effects of Curing Conditions on the Properties of Ternary (Ordinary Portland Cement/Fly Ash/Silica Fume) Concrete

This paper presents the effects of various curing methods that are frequently encountered in the field on several properties of ternary (Ordinary Portland Cement/Fly Ash/Silica Fume) concrete mixtures containing ordinary portland cement (OPC), 20 or 30% of Class C fly ash (FA), and 5 or 7% of silica fume (SF). The curing conditions evaluated in the study included: air drying (absence of wet burlap, plastic sheet, or curing compound), 7-day curing compound application, 3-day curing under wet burlap, and 7-day curing under wet burlap. The properties studied at both early and late ages included compressive strength, salt scaling resistance, resistance to chloride ion penetration (RCP), initial rate of absorption (sorptivity), and free shrinkage. The analysis of variance (ANOVA) analysis was performed to identify statistically significant differences in the test results for the different curing conditions. In addition, the impact of curing conditions on the respective properties was compared in the quantitative manner.

The Practical Application of a Flatbed Scanner for Air-Void Characterization of Hardened Concrete

Over the past 30 years, with the advent of computers and digital imaging, many automated systems have been introduced for the purpose of air-void characterization. The majority of the systems employs a contrast-enhancement procedure where a polished cross-section of concrete is darkened with paint, and white powder is forced into the depressions left by air-voids. The system described here follows the same approach and uses a flatbed scanner to collect a single digital image of the entire sample. For all of the systems based on contrast enhancement, the first step is to select a threshold level. Image pixels brighter than the threshold level represent air and image pixels darker than the threshold level represent non-air (i.e., paste or aggregate). Further digital processing steps may be employed but the initial selection of threshold level exerts a strong influence on whether a pixel in the final data set is classified as air or non-air. A systematic approach for threshold determination has been proposed based on an iterative procedure that compares automatically determined air-void parameters to manually determined air-void parameters from a set of training specimens. The calibration procedure finds a single optimum threshold level for the automated system that is to be used for all subsequent analyses. The approach was tested on a population of 88 specimens with manually determined air-void parameters, with the goal of determining an appropriate value for the number of training specimens.

Development and Application of Maturity Method for Prediction of Concrete's Resistance to Chloride Ion Penetration

The applicability of the maturity method for prediction of the resistance of concrete to chloride ion penetration as measured by the ASTM C1202 Rapid Chloride Permeability Test was examined. Predictive capability of the method was successfully validated for laboratory-made, continuously moist cured ternary concrete containing 20% fly ash and 5% silica fume and was found to be excellent. Applicability of the developed maturity method was also verified for field-made and field-exposed ternary concrete used during a two-phase construction of a pilot high-performance concrete bridge deck in Indiana. Although agreement between the predicted and measured coulomb values was good for Phase 2 (constructed in spring), the rapid chloride permeability (RCP) values for Phase 1 (constructed in late fall) were consistently underestimated. Reasons for these disparities were thoroughly investigated. It was concluded that the measured values were higher than the predicted ones mainly because of the reduced degree of cement hydration and the potential increase in the water-to-cementitious materials ratio of concrete. Finally, two additional applications of the developed maturity method were demonstrated. The first application enables prediction of RCP values of concrete subjected to an accelerated curing procedure. This result may prove particularly useful for quality control, as 56-day RCP values may be obtained in about 13 days if temperature is elevated to 38°C. The second application allows for estimation of RCP values at a predefined age of first exposure to deicing salts as a function of construction date (assuming certain temperature history).

High-Performance Concrete Bridge Decks: A Fast-Track Implementation Study, Volume 2: Materials

The purpose of this research was to examine the applicability of ternary binder systems containing ordinary portland cement (OPC), class C fly ash (FA) and silica fume (SF) for bridge deck concrete. This was accomplished in two parts, the laboratory part and a field application part. During the laboratory studies, four ternary mixtures, each containing either 20% or 30% FA and either 5% or 7% SF were subjected to four different curing regimes (air drying, 7 days curing compound application and 3 or 7 days wet burlap curing). In general, all four ternary mixtures exhibited very good water and chloride solution transport-controlling properties (resistance to chloride-ion penetration, chloride diffusivity and rate of water absorption). However, it was concluded that in order to ensure adequate strength, good freezing and thawing resistance, satisfactory resistance to salt scaling, and adequate shrinkage cracking resistance the FA content should not exceed 20%, SF content should not exceed 5% (by total mass of binder) and paste content should be kept below 24% by volume of concrete. Further, wet burlap curing for a minimum of 3 days was required to achieve satisfactory performance and to obtain a reliable assessment of in-situ compressive strength (up to 28 days) using maturity method. The second part of this research examined the performance of ternary concrete containing 20% FA and 5% SF in the pilot high-performance concrete bridge deck constructed in northern Indiana. Using maturity method developed for the purpose of this study, it was determined that the unexpectedly high rapid chloride permeability (RCP) values of concrete placed late in the construction season were mostly attributed to low ambient temperature. Additional applications of the developed maturity method were also demonstrated. These include assessment of risk of scaling and reduction in time to corrosion initiation as a function of construction date, as well as estimation of long-term RCP values of concrete subjected to accelerated curing.

Investigation of Premature Distress Around Joints in PCC Pavements: Parts I & II

Some of the Indiana concrete pavements that have been constructed within the last 10 years have shown signs of premature deterioration, especially in the areas adjacent to the longitudinal joints. This deterioration typically manifests itself as cracking and spalling of concrete combined with the loss of joint sealant. These processes create a cavity in the joint area that traps water and, as a consequence, accelerates further deterioration of concrete during the freezing and thawing cycles. The objective of this study was to examine in details the microstructural and chemical changes in concrete extracted form the affected areas in an attempt to determine the cause of this premature deterioration. The investigation started with a detailed inventory of selected areas of affected pavements in order to identify and classify the existing types of distresses and select locations for collection of the cores. The cores have been collected from the following four locations: NB lines of I-65 near downtown Indianapolis, SR 933 near South Bend, Intersection of 86th Street and Payne Road in Indianapolis and a ramp from US67 to I-465E, also in Indianapolis. A total of thirty six 6-in. diameter cores were removed from pavements at these locations and transported to the laboratory where they were subjected to eight different tests: air-void system determination, Scanning Electronic Microscopy (SEM) analysis, X-ray diffraction (XRD) analysis, sorptivity test, freeze-thaw & resonance frequency test, resistance to chloride ion penetration (RCP) test and chloride profile (concentration) determination. The test results identified several cases of in-filling of the air voids (especially smaller air bubbles) with secondary deposits. These deposits were most likely the result of the repetitive saturation of air voids with water and substantially reduced the effectiveness of the air voids system with respect to providing an adequate level of freeze-thaw protection. In addition, the affected concrete often developed an extensive network of microcracks, showed higher rates of absorption and reduced ability to resist chloride ions penetration.