Paul J. Tikalsky

PROPERTIES OF CONTROLLED LOW-STRENGTH MATERIAL CONTAINING FOUNDRY SAND

Highway engineers, contractors, and state regulatory officials have been skeptical about using foundry sand in construction because of the lack of engineering data and the perceived risks associated with any nontraditional materials technical and environmental performance. This research study was performed to document and evaluate engineering properties of controlled low-strength material (CLSM) containing byproduct foundry sand. Mixtures containing clay-bonded and chemically bonded sand were compared in the plastic and hardened states to CLSM mixtures containing uniformly graded crushed limestone sand. The data show that byproduct foundry sand can be successfully used in CLSM, and it provides similar or better properties to that of CLSM containing crushed limestone sand. The foundry sand assisted in keeping the strength from exceeding the desired upper limit of 700 kPa. Clay-bonded sand retarded the setting time, and chemically bonded sands required a reduction in water to control bleeding. CLSM containing a combination of fly ash and chemically bonded sands was shown to have excellent characteristics for flowable backfill and excavatable base material.

PERFORMANCE OF SUPPLEMENTARY CEMENTITIOUS MATERIALS IN CONCRETE RESISTIVITY AND CORROSION MONITORING EVALUATIONS

A testing regime was developed to optimize strength and durability characteristics of a wide range of high-performance concrete mixtures. The aim of the selected designs was to offer multiple solutions for creating a highly durable and effective structural material that would be implemented on Pennsylvania bridge decks, with a life expectancy of 75-100 years. A prime method for optimizing the mixtures was to implement supplemental cementitious materials, at their most advantageous levels. Fly ash, slag cement and microsilica all proved effective in creating more durable concrete design mixtures. These materials have also shown success in substantially lowering chloride ingress, thus extending the initiation phase of corrosion. An additional benefit studied in this program is the ability of these materials to extend the propagation phase of corrosion due to the high resistivity they impart to the concrete. Ternary mixtures from these materials were particularly effective, showing much higher resistivity values than the materials used separately.

PROPORTIONING SPENT CASTING SAND IN CONTROLLED LOW-STRENGTH MATERIALS

This research evaluated the potential of spent foundry or casting sand as a constituent controlled low-strength material (CLSM). The physical characteristics of spent casting sand or foundry sand are similar to those of fine aggregate used in high quality CLSM. This study developed different mix proportions for CLSM containing spent casting sand that had strengths between 300 kPa and 800 kPa at 7 days and sufficient flowing characteristics to be self-compacting and self-leveling. Each mix was tested for strength, water demand, rate of strength development, and fluidity. The results show that the spent casting sands provide high-quality material for CLSM. The spent chemically bonded casting sands are excellent replacements for portions of the fine aggregate, while clay-bonded casting sands must be more carefully proportioned and tested to prevent fluidity problems.

Redefining cement characteristics for sulfate-resistant Portland cement

Abstract Experimental research was performed to relate specific cement characteristics to expansion due to sulfate attack. Twenty-one North American cement of statistically diverse chemical composition were used in the study. ASTM 1012 “Standard Test Method for Length Change of Hydraulic Cement Mortars Exposed to a Sulfate Solution” was performed using mortars prepared with each of the cement. First-order and multivariate relationships between cement characteristics and sulfate expansion were correlated at different ages. Analysis revealed that while tricalcium aluminate (C3A) has typically been targeted as the chief contributor to sulfate attack, iron oxide (Fe2O3) or tetracalcium aluminoferrite (C4AF) content, combined with total equivalent alkalis, showed a much stronger negative correlation with expansions at all ages. These results are in agreement with a broad spectrum of sulfate expansion theories and can provide a better means of specifying sulfate-resistant cement.

Statistical Variations in Chloride Diffusion in Concrete Bridges

Designing durability into the civil infrastructure requires advanced knowledge of deterioration mechanisms, material science, properties and methods of production of construction materials, structural design, quality control, and construction methods. In the case of reinforced concrete structural elements, corrosion is initiated and accelerated by, among other things, the presence of chlorides at the depth of the reinforcing steel. This article describes the simulation-based reliability assessment (SBRA) method which can be used for the probabilistic prediction of chloride diffusion. The authors present data from the in-place measurement of chloride penetration and concrete cover from more than 200 samples taken from 40 bridge decks in the northeastern United States. The bridge decks were constructed under identical construction and design specifications over a 13-year period and exposed to deicing salts as well as normal environmental cycles. The results of simulation and analysis show that the initiation of corrosion from the diffusion of chlorides can be delayed for decades by using high-performance concrete with lower diffusion coefficients. The article includes histograms that illustrate the effect of variations in diffusion coefficients and cover depths.

Prediction of Equivalent Steady-State Chloride Diffusion Coefficients

This paper presents an approach for determining the chloride migration rate of hardened concrete by applying fundamental electrochemistry for different cementitious mixtures using the measurements from the chloride-ion penetration test (CIPT) data following ASTM C1202 specifications. The steady-state condition is verified by comparing the numerical values of chloride migration rates during 5, 30, and 360 minutes of testing. Three different theoretical approaches—Nernst-Plank, Nernst-Einstein, and the Zhang-Gjorv method—were applied to obtain the equivalent steady-state diffusion coefficients for different cementitious materials. These results are compared with the diffusion coefficients obtained from Berke’s empirical equation using CIPT data. These methods for the computation of diffusion coefficients include both the joule effect and temperature dependency and eliminate the need for other extended migration tests to obtain the steady-state conditions. Overall, this research presents a reliable method of determining the chloride migration rate for diffusion coefficient prediction.

CONCRETE MATURITY FIELD STUDIES FOR HIGHWAY APPLICATIONS

The Arrhenius maturity function was used to estimate strength evolution in three highway structures: a bridge pier, a bridge deck, and pavement. The research documents field instrumentation and strength estimation. Each structure was constructed with a mixture containing 35% ground granulated blast-furnace slag as a mass replacement of total cementitious materials and approximately a 0.40 water-cementitious materials ratio. The temperature profiles for each application were recorded and discussed. The logarithmic strength-maturity relationship was compared with the hyperbolic strength-maturity relationship for each application. Cylindrical concrete specimens, cast on site during construction, were exposed to a variety of curing conditions. Minor differences in material proportions were also investigated. The quality of cure of the companion specimens significantly affected the strength-maturity relationship. Small deviations in mixture proportions did not appear to affect significantly the strength maturity relationship for the mixtures studied.

CONCRETE MATURITY PROGRESS: SURVEY OF DEPARTMENTS OF TRANSPORTATION

Results are provided from a concrete maturity survey that was distributed to representatives of 50 departments of transportation (DOTs) in the summer of 2000. The purpose was to display the state of national advancements and practices relating to concrete applications for predicting in situ portland cement concrete strength. Information such as DOT project and research details, method of maturity determination, state applications, and general attitudes toward the concept was requested. Representatives from 44 states replied to the 12-question survey. Results revealed that about 73 percent of the states that responded either have conducted or are currently involved in at least minor research with the concept. Furthermore, approximately 30 percent of the represented states have protocol or specifications governing the use of this developing technology. Representatives throughout the United States have reported that maturity is being used to predict critical strengths for such actions as pavement opening to the public; pavement opening to construction traffic; structural acceptance; and formwork removal for bridges, pavements, and other highway structures.

Long-term durability models of concrete in highway bridges, and Practical approaches to durability-based design

The paper will present a model for improving the durability and doubling the life of highway bridges. Data from a detailed characterization of highway bridges and new concrete mixture designs is presented to show the potential for simulation based reliability assessment (SBRA) for predicting chloride intrusion into bridge decks exposed to deicing salts. The paper presents performance based guidelines that can improve the long-term durability of bridges through the design and control of concrete constituents and construction practices.

INFLUENCE OF ALKALINE EARTH SILICATE ADMIXTURE ON DURABILITY OF PENNSYLVANIA TURNPIKE BRIDGES

Chlorides from deicing salts are the primary cause of premature corrosion of reinforcement in concrete bridge decks. An alkaline earth silicate admixture (AESA) can reduce the permeability of concrete, preventing the ingress of chlorides, delaying the onset of rebar corrosion, and therefore increasing the design life of bridges. The performance of an AESA in bridge decks that have been in service for more than 25 years is compared with the performance of identical control bridges of comparable age. Visual inspection reveals serious deterioration in the control specimens. The decks of the control bridges reveal cracks, delaminations, and spalling in many of the precast deck panels. In the bridges with AESA, there is minimal visible deterioration. The goal of this research is to identify and characterize the effect of AESA on inservice bridge decks. Chemical and microscopic techniques are used to determine the nature of AESA in hardened concrete. Water and chloride ion permeability tests are performed to quantitatively determine the relative effects between control concrete and concrete containing the AESA. Testing has shown that AESA has chemical characteristics that enable it to react with portland cement and control the microstructural development in concrete. Quantitative tests for permeability and environmental scanning electron microscopy (ESEM) reveal a microstructure that is more continuous and interlocked than that of the control samples, indicating that the AESA reacts with cement to provide a microstructure that is less permeable.